JV60 upgrades

One of the most popular speaker kits in Australia was the Jaycar JV60. I upgraded one of these in the past with very good results.

If you are looking for an upgrade, I now recommend LSK TL6.

Are sealed subs faster than vented?

A common opinion expressed is that sealed subs are "faster" than vented, and it's often argued that this is related to their transient response. I'm going to argue a case for vented subs when used in a particular way and it won't suit everyone. There are some important facts that are typically overlooked in the often overly simplified arguments that are frequently made on internet audio forums.

Sealed vs vented subs outdoors

When measured outdoors or in an anechoic chamber, sealed subs tend to have better time domain performance. A vented sub will have some ringing, as seen here:



You can see the port causes a much slower decay when compared to the same driver in a sealed box as shown below:



To put these into perspective, a 20db drop in level means only 1% of the output remains. So in this context we can compare the time taken for a 20 db drop, denoted T20

What happens in a real room?

When placed in a room, the room itself will start to interact as well. Room modes will cause their own ringing, and this will generally be much worse than either sealed or vented subs.

In a typical room it will take around 250ms to achieve T20. Both of the charts above only show down to 200 ms and in both cases, it's off the chart. So even the vented version which has some ringing is actually not the bottleneck - the room is. It should also be noted that this ringing occurs down low where sounds reproduced are most likely to be artificial LFE content and not critical. In the range that deals with instruments, there is no real difference.

So why do they sound different?

Usually there are numerous differences going on simultaneuously and that makes it difficult to pin anything down. A common mistake is to pick just one thing and pin it down as the cause - often something like transient response or group delay which are real and measurable but often more than likely not the audible cause of difference.

The first suspect is frequency response and room transfer function. A sealed sub will have more roll off and this will tend to sound a bit tighter, and when combined with room modes can often yield a better raw response. But if both are equalised flat in room the main differences are likely to quickly disappear.

There are other issues involved here, but I think we can rule out transient response in most rooms.

A dynamic solution

My reason for making this point is that I often see sealed subs chosen for their perceived improvement where a vented design could be made to work better. To do the same job with a sealed driver requires more power and excursion due to the loss of efficiency. More power means more power compression which can be a backward step for dynamics. More excursion also has it's downsides and will also tend to further reduce efficiency. So there is a performance and financial cost involved.

Efficiency and dynamics go hand in hand. A solution I suggest for music applications is a vented active woofer. Aim for a driver with a fs around 40 Hz, decent excursion and high efficiency. Tune around 40 Hz then use EQ to get the in-room response right. Many pro woofers with about 9mm xmax are ideal choices, with about 95 db efficiency. With about 200w you will see about 118 db before compression. Try to get the same result with a sealed woofer and you will lose 12db of efficiency. The typical solution is a HT sub driver, but you will need a lot more power, a very expensive high excursion driver at many times the cost. An equivalent result is possible only with a major cost blowout. A better choice would be a higher quality driver.

Don't dismiss vented alignments

Avoid this mistake. A sealed woofer can be more of a plug and play solution, but also consider the cost in terms of efficiency.

Sub amp options

Budget

In general, I suggest if you can't afford the options discussed here right now, wait and save. You give up a lot by saving a little, and you gain very little in spending any more.

Amp location

Do you want your amp built in? Choose a plate amp.
Do you mind another amp in your rack? In some cases, an amp can be installed out of sight.

Power requirement

This depends on your driver and the design as well as your listening habits, although keep in mind a sub will often change things for many. You might get excited and turn it up more than you expect. Simulations are a good tool for making this choice.

Typical plate amps range from 240 - 500w and they are economical in this range. Higher powered versions increase the cost a great deal and if you need more power, it's often better to use a pro amp.

Plate amp vs stand alone amp

This is the main choice. If you want a simple out of the way solution with decent power, no rack space taken up and decent power, a plate amp is the attractive option. Where more power is desired, a pro power amp is the way to go as they are the most economical option. The downside is this usually means replacing the fan with a quieter version, but instructions online are available for this. Warranty is an issue here but the procedure is quite simple. With a pro amp, an external sub pre/crossover is required. These can be purchased at a kit from places like Jaycar or Altronics in Australia, or you could also consider a MiniDSP active board.

Two recommendations

For a well rounded good value plate amp, I recommend O Audio >

The filtering options are better than most and they are generally cheaper than comparable options. Cheaper options tend to fall short.

For a good bang for buck pro amp with very high power, I recommend Behringer EP4000 >

Instructions online are available for the fan mod. This is a popular choice. You can spend more without any real benefit.

One more suggestions ...

You might also consider Rythmik audio. If you are DIY inclined, then you can buy driver and plate amp designed to go together. All of their products feature servo control, and if you aren't DIY inclined then you can buy them ready made. I have two Rythmik subs > I recommend them highly, they are very accurate subs.

Review: Behringer Ultracurve DEQ2496 EQ processor

Coming soon

Review: Behringer Ultradrive DCX2496 Active crossover

Behringer Ultradrive pro DCX2496 is a relatively powerful digital active crossover.

Elsewhere in this blog, I've compared various active crossovers and also reported on my findings from subjective comparisons over two separate days with a small group:

Subjective listening tests
Active crossover options

My experience with this product

I have used DCX for some time in various DIY speaker projects and as previously mentioned, carefully compared it to other competitive units. I believe it to be a relatively transparent device with decent noise floor performance and a good mix of features.


Features

DCX is a well featured unit. While primarily intended for active crossovers, it has enough EQ functions to tame room modes as well with parametric EQ. In the past I had used Ultracurve for this, however, if you run out of EQ options with DCX, you're probably trying to overdo it.

One appealing feature is auto align. This feature, with input from a microphone, applies digital delay so that a speaker is time aligned. Contrary to popular belief, physically aligning driver voice coils doesn't generally time align a speaker correctly. In my system, the tweeter and mid are delayed by 8 metres to align them with the subs.

Dynamic limiting and EQ features are available, however I don't use these as I've found they can easily do more harm than good. Using dynamic EQ can easily reduce bass dynamics.

Convenience and ease of use

DCX is very easy to use once you have spent some time working out how the user interface works. It's very easy to adjust the bass level quickly, if you find that one particular album is bass shy.

Adjustments are all done in real time so you can hear their impact right away.

Time alignment can be done very quickly compared to other manual methods.

Overall it's one of the easiest active crossover units to use.

Build quality and aesthetics

The build quality of this unit is fair, but the aesthetics are one of it's main weaknesses in a home system. Behringer is imprinted on the top of the box in big bold white letters, the front face is very utilitarian with bright flashing lights all over. The rack mount ears give it a PA look so that it doesn't look at home in an audio rack.

I have not had a problem with my unit, however, the experiences of others suggest that the reliability could be better.

Sound Quality

I consider the sonics of this unit to be decent and it held up relatively well to critical comparison. In our comparison we compared the stock unit to a heavily modified unit. Although the mods cost twice the price of the unit itself, we could not pick a difference. We did find that MiniDSP did appear to have a very slight edge, with a lower noise floor and a little more treble detail, however not everyone was able to hear it.

Digital input quirks

Using a digital input is not as straightforward as you might like. You can input both SPDIF and AES EBU digital inputs, but the former can cause the input clip lights to run into the red. I have been told by one who has tested it, that this does not necessarily mean it is actually clipping, and the outputs should be also observed. I have not tested this after hearing it, but if you plan to run digital inputs, this is worth investigating.

Should you buy this unit?

I generally recommend that people first consider MiniDSP as it will often work out cheaper and more flexible. However, DCX does come with 6 channels and digital inputs as well as a warranty as a plug and play unit.  The ability to assign long delays is handy to time align a 3 way system which includes subs. For many, DCX remains an attractive active crossover option.

MiniDSP vs DCX

Review: Behringer Europower EP2500

This amp has become well known in DIY audio circles as the best bang for buck high powered amp available, although it has since been superseded by the EP4000.*

This is a standard 2RU rack mount professional amp intended for high powered applications, although in this review I will be covering it's use in a domestic system.

Mixing domestic and professional audio

To many this will seem like a questionable amplifier choice, especially those who have been immersed into the mythology of high end hifi. The biggest reason to use a pro amplifier in a domestic system is value. In the hifi market it's possible to profit from products which lack real performance to back up marketing claims, but in the no-nonsense pro market this doesn't fly. The pro market is generally much better grounded in engineering and products that don't offer value and performance aren't likely to survive.

Aesthetics and build quality

I'll start with the obvious - this thing is aesthetically challenged. The impact is reduced by making it black - in a room with low light it will disappear as just another black box. In the brightly lit living room, it would look out of place.

The build quality is decent and the steel case is very heavy.

On the front you find a red power LED and yellow signal level lights that flash with the input level in time with the music. Each channel has a passive attenuator which feels very cheap. Normally such a knob would have a pot behind it which offers some resistance to movement, but these feel cheap and nasty. Fortunately they are the one exception - everything else about the build quality of this amp is decent.

Inputs and outputs

XLR and jack inputs are provided. Adaptors can be used to connection with RCA cables. The option to use balanced inputs is handy and may suit some installing this amp out of the room. In that situation you would have very long cables, in which case balanced cables should be considered.

Outputs include screw on binding posts for bare cable or spades. This is an easy option, but with a high power amp like this care should be taken. Speakon outputs are a better choice for their safety and simplicity. They are a fool proof option which prevents incorrect polarity and shorting out cables.

Features

A power amp is a simple device, but a number of features are provided. On the back panel you can see dip switches which allow various options to be selected, including:

• clip limiters
• low cut filters (30/50 Hz)
• 2 channel, bridged or parallel mode

Cooling system

A rear fan runs continuously and sucks air through an internal heatsink and has a filter on the front. The fan noise will be an issue in any domestic system where this amp is placed in the room. For this reason, many users opt to swap the fan with a quieter unit. It will void the warranty, but many have reported good results and have found the amp still runs cool. The amp is designed to run in the most demanding applications, which could include being pushed to it's limit all night in a hot environment. Anyone contemplating opening up the case for any reason should consider if they are qualified to do so. It is possible to electrocute yourself even when it is disconnected from the mains. 

An alternative solution is to install the amp in a rack located outside the room.

Powering up and down

One lesser known issue with using this amp at home is it's behaviour when powering up and down. Consumer amplifiers typically use output protection relays. When powering up there is a delay before any signal gets through, typically about 5 seconds followed by a click. If music were going to the amp when switched on, you would not hear it until the relays switch on. When powering down, the relays disconnect the outputs of the amp. The result is that there are no thumps in either instance.

The Europower does not include output protection relays. When powering up from a cold start, the power supply appears to take some time to charge up, so any upstream thumps don't get through. When powering down, any thumps from upstream can get through, although I have found that some level of protection is provided as their level is reduced.

Some line level components can have thump issues. One especially obnoxious example is Behringer Feedback Destroyer, which was a popular choice for bass EQ. Many users actually leave this unit powered on all the time to avoid the problem, but I have always considered this an unacceptable solution. Lifespan is shortened and power is wasted. In the past I have used Behringer Ultracurve for EQ purposes and despite using output protection relays, it sends out thumps on powering up and down. Surprisingly Behringer DCX proved to be an answer to the problem since it's relays do a better job and almost completely eliminate thumps.

Here is where I had a problem. I had my system configured so that everything powers up at once. First time was not a problem and powering down was not a problem. However, if I decided to immediately power up the system again, things got ugly. Europower has a big power supply and it takes some time for the caps to discharge. If powered up right away, they are ready to send any thumps through the system. So in that scenario, I'd get a loud thud through the system immediately on powering up.

Performance and sound quality

In independent tests, this amp holds up quite well in comparison to other pro amps, even those which are much more expensive. It would seem that Behringer can be trusted as much as any of the big names in this regard. Although many different ratings are provided, the most interesting are 650w and 450w into 4 and 8 ohms respectively, with both channels driven from 20 - 20k with 0.1% THD. This is a more conservative rating than is often shown, but they also provide a higher rating based on 1k. When bridged into 4 ohms with 1% THD at 1k the rating is 2.4 kW. This would seem to be a more optimistic rating.

I have used this amp for extended periods both for subwoofers and to drive main speakers. My initial purchase was aimed at powering some DIY subs. I auditioned a number of amps, the others being second hand at about the same price point but with a lower power rating of 450w. I tried an Alesis and QSC. Both had similar performance to this amp, but it wasn't too difficult to find their limits and get the amp to clip.

By contrast, I found that the Behringer only reached clipping on two occasions in years of use. The extra headroom was useful for power hungry subs.

For subwoofer use, this amp comes highly recommended. Bass has great control and authority. This amp will keep going where many plate amps will run into clipping and then thermal overload. The difference is not only related to reliability but also brute force and authority. These are the aspects that matter in relation to subwoofer use.

I have also used this amp to drive my TL speakers in the past. It was a surprise at first that the result was quite good. There was no sense that the amp was lacking in any way. Familiar jazz tracks that I often use to judge the finesse and subtlety of a system surrendered none of their quality. Hence I would not overlook this amp as an option for driving full range speakers where high output is desired.

Where not to use this amp

If you don't have a plan to address the fan noise issue, this amp is not for you. If you also don't have a plan to avoid the thumps, I suggest considering your strategy first. I don't recommend manual power sequencing because this allows too much room for user error and is not user friendly. You can purchase a power sequencer as a work around, and some of them are quite affordable.

If you are looking for a relatively powerful amplifier for full range speakers, consider the Behringer A500 at about half the price without fan issues.

Conclusion

This amp is an excellent choice for subwoofer and high powered full range applications. Before buying, you should consider the power up/down issues and fan noise issues. Resolving them does involve some challenge and expense and this should be considered prior to purchasing this amp.

Safety warnings


For safety reasons I cannot recommend modifying this amp in any way or even opening up the box. Electrocution may result, even when the amp is not connected to the mains.

_______________________________________________________
* EP4000 is believed by many to simply be a rebadged version with more optimistic ratings

Review: Behringer A500 power amp

Update (March 2013): I posted previously that this amp had failed. However, it turns out that it was in fact the IEC power cord that failed, a rare problem and fortunately one that is easily solved. However, I do still hesitate to recommend this amp due to problems with one of the inputs. Since this is a popular page, I'm leaving it here but I'd suggest people consider Emotiva power amps.

Behringer A500 is one of the best value power amps on the market. I have used this amp in my active system for a number of years and find it's performance to be quite respectable.

Aesthetics and build quality

For many the looks will be a stumbling block to uncovering a bargain. The attenuators and face plate are plastic and do appear a little cheap. The lights on the front show the output level are a little more bright than many would like. With the lights down low for a movie they are over-bright and can't be dimmed.

The case seems sturdy enough and for the price there is nothing to complain about regarding it's quality.

Looking inside the box, you can see the power supply certainly does appear decent.

Features

Both balanced and unbalanced inputs are provided, along with a choice between two different speaker cable outputs. Bridging is included for 8 ohm loads, but conventionally it is stable into 4 ohm loads and provides 230w into 4 ohms or 160w into 8 ohm loads, or 500w when bridged into 8. Clip indicators warn of over driving.

No muting relays

Unfortunately this amp does not provide muting relays. A conventional hifi amp provides relays which prevent thumps when the system is powered up or down. After switching on such an amp, there is a delay of about 5 seconds followed by a click. In those 5 seconds, the amp remains switched off. Other components up the chain might have thumps that could get through at this point and they can be irritating or even destructive. When powering down, muting relays disconnect the outputs before any thumps get through.

This is one corner I wish Behringer did not cut. Suitable relays cost about $10 each and while this might sound trivial, electronics at this price point eliminate everything they can.

Sound quality

In my blind test results post, I mentioned one test in which this amp was found comparable with much a more pricey amp. In keeping with that result, I have found it to be quite decent. Others have reported less than flattering results, but I always take these kinds of reviews with a pinch of salt. I use this amp in an active system driving only the midrange, so I can't comment too much on the top end or bass performance.

You won't find a long subjective description here with words like liquid midrange, shimmering highs and you definitely won't hear words like rhythm, pace and timing! But I will simply comment that the sound quality differences between this amp and one many times the price are far smaller than many audiophiles would have you believe.

Woofers gone mad

In 2010 I witnessed a system that used this amp to power some dipole sub drivers. I was watching the lights get very close to clipping as I was concerned the amp was running hard. Then something strange and disturbing happened that sent onlookers into a mad rush to shut down the system, including myself. The drivers were moving wildly at very high excursion, yet the music did not seem to demand this. They were moving as if playing sine waves or test tones. We shut the system down to avoid failure, then started scratching our heads about the cause. After some digging around and discussing the issues with two suitably qualified experts, I came across an answer that makes sense.

It was clear that the driver and amp got caught in a feedback loop, very similar to what occurs in PA setups. We all know the scenario - if the mic is in the direct line with the speakers, the mic picks up the sound from the speakers and tries to amplify it further, resulting in a loud high pitched noise. In this case, the drivers were acting as the microphone. Why doesn't that happen all the time? Normally the amplifier has a damping factor, which prevents this from happening. The situation is made worse by the use of high levels of global negative feedback, which is used to give a lower distortion figure.

Now there is one missing piece in the puzzle - why didn't the damping factor prevent the feedback loop, as would normally be the case? Some amps have their damping factor drop to zero when clipping occurs. It would appear that this is such an amp. Once a certain clipping threshold is passed, the damping factor protection is removed leaving the drivers vulnerable. Had the system been left on, say to break in the woofers, it's possible they could be fried.

Where not to use this amp

This amp should not be used for dipole woofers as it has been found to be unreliable as described above. It should also not be used with drivers that may be sensitive to damage resulting from power on/off transients. In particular it should not be used in an active system for the tweeters. I also don't recommend it for demanding high power applications or subwoofers. I would hesitate to use this amp for demanding speakers such as electrostatic speakers.

Suitable uses 

This amp would make an idea upgrade to the main channels of a home theatre system. Where you have pre outs on your AV receiver, you could use this for the mains. It's an ideal amp for most conventional stand mount or floorstanders. It's a good amp for a studio system, and for domestic 2 channel and multi channel systems.

Others have had apparently good results in using this amp to drive subs, so your experience may vary. I would not use this amp in that way - the Europower amps are in my view a much better choice.

Verdict?

Is it a giant killer? I can't say that it is comparable in all respects to many of the amps it will be compared to. No doubt many will consider it alongside more expensive options like Emotiva, NAD and Rotel. All of these products have advantages beyond the sound that make them still worth considering. However, at the price there are few other options and overall I'd call this amp a very attractive option for those who appreciate bang for buck.

Futher reading

The Audio Critic have a very good review of this amp which includes measurements.

Audio Critic Review 

Which active option is right for me?

Previously I discussed the varios active crossover options. But which one is right for you?

Budget

MiniDSP is easily the cheapest option where US $125 covers a simple 2 way stereo configuration. DCX is the next step up and as this unit often can be purchased second hand, it can be very affordable. Thuneau Allocator will typically cost most, although this is highly variable depending on sound card choices, so you have some control there. DEQX is the most expensive option.

How many channels?

MiniDSP allows 2 inputs and 4 outputs, but multiple cards can be used to cater for surround systems of more complex designs. One master volume pot can control a number of boards. Given the low cost, MiniDSP boards can also be used to extend the number of channels for any of the other options. DCX has 3 inputs and 6 outputs and that will cater to most projects. 1 x 6 way, 2 x 3 way, 3 x 2 way are covered. Allocator both allow 4 channel, although if multiple sound cards are used it's possible to obtain more channels in running multiple instances of Allocator Lite. DEQX provides 8 channels.

Phase correction?

Only DEQX and Thuneau provide phase correction.

Dynamic options

DCX has a number of dynamic options that are not supported in the other options. Dynamic EQ allows the EQ settings to change with level. This means you can compensate for the insensitivity of the ears to bass at lower levels, a very handy feature. It also has limiters so you can make the system "teenager proof." You can also effectively dynamic driver protection so that bass is limited at higher output - effectively a rumble filter that only comes on at a certain level.

Ability to make quick changes

DCX wins here. It's quick and easy to tweak settings. Suppose you wanted to adjust the bass level as a particular CD or movie was bass heavy or bass shy. It's quick and easy with DCX. MiniDSP requires a PC to make any changes. I can't comment on DEQX or Thuneau.

Aesthetics

DCX is a bit like a circus and it will annoy some. DEQX looks more hifi and with the other options you are in control.

Sound Quality

MiniDSP is a new option and I haven't tried it yet. I'm not making any assumptions here as price isn't always a good indicator of sound quality.

The sound quality of DCX is a matter for debate. It certainly won't be more transparent than DEQX, but will you actually notice a difference? There is no shortage of people who claim DCX damaged the sound quality of their system, but that could easily be explained as bias against a pro crossover which many assume to be "mid fi at best." I suggest that those who have concerns make up their own mind, ideally with some sort of blind comparison. There mere suggestion of poor sound quality is enough to sway many away from a potentially great value crossover. Don't be too easily put off. Allocator will be as good as the sound card you choose.

Balanced or unbalanced?

In most home audio systems it would be best to run unbalanced lines. Where noise rejection isn't required, balancing actually adds noise. This is acceptable in a pro application where noise pickup over 200m of cabling would be a disaster, but for home use it's rarely a requirement. In the rare situations where long runs are needed, DCX is handy. You might put a concealed audio rack some distance away where it's convenient. Otherwise, this is a black mark for DCX.

Do you want a PC in your sound system?

If so then Allocator is probably your choice. This is a good time to consider other benefits of having a PC in your sound system as a media server for audio and video playback and storage. You can save some money here and gain a lot of new features, but it all comes down to whether you like the idea of a PC in the sound system. Personal preference comes into play.

Budget Blu-ray Review - Soniq QBP301B

How good can a cheap Blu-ray player be? The answer might surprise you. In this case, very good.

Soniq is JB Hifi's "home brand." They are low cost value-oriented electronics products. I purchased this to replace a much more expensive Sony DVD player which cost about five times a much. I have a John Mayer music DVD that displayed as black and white on the Sony, but with the Soniq it actually has colour! I've also noticed less problems with scratched DVDs.

Picture and sound quality

No complaints here. I won't say too much in this area since I haven't performed any critical comparisons to other units, but I'll say this much - it's very capable in both areas.

Remote control

This is nearly always the weak point. The remote is obviously cheap. The layout isn't too bad, but there are a few annoying aspects. The response is a little sluggish - often resulting in pressing a button more than once. Also the volume control is very tedious to use. You can't hold it down but each press reduces the volume by 1%. So if the volume isn't close to correct, you often have to press the volume button 50 times.

Multi region

It's very handy to have a multi region player, both for Blu-ray and DVD. This means you can buy cheap discs from overseas, and often it's simple to convert a player to multiregion. At the time of writing (August 2010), no such hacks are available. This unit will only play local DVDs and Blu-ray discs. This may change, but there's a good chance this player will never support multi region. If that's an issue for you, keep looking.

Inputs and outputs

You will find everything you expect here except perhaps multi channel outputs. Those who want to set up a budget HT surround system without a receiver should keep looking. Optical and coax digital outputs are provided.

There is also support for a memory stick in a USB slot. That means you can view photos, captured video (TV etc). Compatibility isn't guaranteed, and external hard drivers may or may not work. This is unfortunate as one could use a PC digital TV tuner to record TV then play it back via the Blu-ray player. This works out as a very cheap PVR system.

Basic use

With Blu-ray discs, the unit starts up quite quickly, but one source of irritation is ejecting discs. After powering up, it takes quite a while to eject, and often starts playing the disc even after the eject button has been pressed. Another gripe is that it lacks memory. With the Sony, I could watch part of a movie, eject the disc and watch another then in a few days put the first disc back in. It would resume from where it last played. The Soniq remembers the position for a very short period. If you have an "intermission" in the middle of a movie, chances are the spot has already been lost. You end up having to pause rather than stop.

Conclusion

Overall it's a capable player. It looks decent and has no major issues or problems. While there are a few minor complaints, at the price it does all that you can expect.

What's wrong with HDMI?

Have you been told that HDMI is the ants pants and bees knees? That it's the modern solution for the digital revolution and therefore always better than analogue? If so it might come as a shock to hear that it's not actually perfect, but a flawed format that's been enthusiastically adopted without really thinking things through.

HDMI was designed to benefit content providers first and foremost. It's all about copy protection - making it difficult if not impossible to pirate HD content. Of course, in order to gain popularity, something new had to be offered, so the appeal comes from using one cable for both audio and video. Sadly, it's a poor format that falls short in a number of areas.

Problems with HDMI

The biggest problem with HDMI is that it is not suitable for the kind of runs that will often be required in a home theatre. About 5 - 7m is the limit and beyond that you can expect problems with reliability. HDMI uses twisted pairs rather than coax which is the much more sensible choice. Coax cable can be run over much longer lenghts without any problems and is much easier to install.

Blue Jeans Cable explain the problems in more detail >

The future is HDbaseT - read about this new format that is far more promising more >

Bi-amp modules

Recently I purchased some bi-amp modules from the SNA classifieds:



This is one module and includes 2 channels:

50w class AB
350w class D
Switch mode power supply.

Since I have two of these modules, they are enough for active 2 way speakers.



With a few inputs and outputs I have 4 channels of power amps.

Coming soon: active surrounds

Soon here is a stretchy term, meaning hopefully some time this year. I bought these to power some active surrounds. The 50w channels will be more than enough for the tweeters and they are class AB. This is a good thing as I don't believe Class D is suitable for treble. I do have some hesitations even for midrange use, although they will probably be good enough.

The design I have in mind will involve compression drivers in waveguides for the treble, and efficient 10" mids in a low profile wall hugging design.

Why active? It might seem like overkill, but when these modules came up at a very attractive price, they were hard to pass up. Active are easier to design and it was a good excuse to get a MiniDSP board which I intend to use - the cost is similar to that of a passive crossover and it could easily work out cheaper considering I can try different options without buying more parts.

So the plan is to obtain a box from a non-working amp and include the MiniDSP crossover along with the amp modules all in one.

The surrounds are shown here:

Active vs passive crossovers

I'll say it up front. All things considered, I think active crossovers are better. This is a big topic and it's quite complex, so for now I will cover what I consider some of the stand out issues. First, I'll start with an opposing view.

Why passive crossovers might be better

Some argue that passive crossover components are in general more sonically transparent in mid and high frequencies and that active crossovers should only be used for bi-amping so that large inductors on bass drivers can be avoided. This is a point of view that can't be easily proven as in comparing active vs passive, there will always be many variables. I don't see any way that you could isolate "sonic transparency." So this will remain an opinion untested.

An obvious advantage to passive crossovers is that only one amplifier is required. This allows spending to focus on just one amp and this might be seen as a cost saving.

I'm trying to be objective here, but I see this as the extent of the "passive is better" argument.

Why active crossovers are probably better

Control and flexibility
One of the most significant advantages is that an active crossover has much greater power and flexibility. We can easily use steep slopes and a range of EQ and DSP options to gain precise control over the result. We can get tweeters to cross lower and we have far more power to get the most out of the drivers. Cone breakup is far easier to control. Dipole roll-off can be compensated for. Bass drivers can be matched to their box with precise control. All of this means clearly audible improvements and much less compromise.

Active systems have far better dynamics. A passive system will often see clipping caused by power hungry bass drivers, resulting in distortion and a harsh sound coming through the tweeters. An active system avoids this as the tweeter will have it's own amp. Clipping caused by the bass drivers will probably not be audible where with the passive system it causes the system to sound strained and harsh.

Specialist amplifiers
Each amp becomes a specialist and can be chosen for a narrower bandwidth. No need to compromise. You might combine a powerful pro amp for the bass, with your favourite amp in the midrange, and a low powered tube for the tweeter.

Tube amps
Many make the mistake of compromising their speakers simply to use a valve amp that they prefer. With an active system this is not necessary. Drivers can be chosen for ultimate performance in their bandwidth and efficiency becomes less critical. Many efficient drivers have a lot of coloration and problems - that's a high price to pay to use the amp that you prefer. A 7w valve amp will drive any tweeter to very high output levels.

This post is scratching the surface, but some of the best articles I've seen on active are here:

http://sound.westhost.com/bi-amp.htm
http://sound.westhost.com/biamp-vs-passive.htm

How to get started in active

First, have a look at your options. Starting out on a budget, I suggest MiniDSP which involves some light duty DIY. With a few more features and no DIY electronics, many choose Behringer Ultradrive. A step up in performance and a big step up in price is DEQX.

More about active options in detail >

You will need a basic measurement setup >

This will include a mic and mic preamp.

You will then need to obtain software and measure driver acoustic response and work apply filters until you can measure a nice flat response, but your journey won't end there.

Golden ratio rooms for bass

Do golden ratios work for bass? I must admit I'm more than a little skeptical. Talk of golden ratios has always sounded like nonsense to me, the kind of thing that often turns out to be silly when you actually start measuring. I'll investigate this here with some simulations with the FRDC room simulator.

Here is a golden ratio room - 4.8 wide x 7.8m deep x 3m ceiling.


Image courtesy of Cardas Audio
This is just one implementation of Golden Ratios, but could be applied to rooms of different sizes.

Listening is in an equilateral triangle spaced 2.1m from the front wall and 1.3m from side walls. Speakers are 2.1m apart and listening position is the same distance direct from each speaker.




The result is suprisingly good. The bold line shows the bass transfer function of the mains. It is very good! If you actually got that out of a normal room, it would be something to dance around the room about like a nutter. It is flat +/- 5db! 15 - 20 db is more typical.

The purple line is a corner sub combined with the mains. On it's own, the sub is flatter, except for a nasty dip at 60 Hz. Using this setup as a starting point, an excellent result could be achieved easily with a little tuning.

Is it a fluke?

Let's find out what happens when we start breaking the golden rules ...

If we move the listening position back further away, the reponse gets progressively worse, until we see a broad dip centred at 50 Hz at 2m further away.



If we move sideways half a metre, the midbass imrpoves slightly but we see a nasty dip around 120 Hz.

If we move the speakers back but keep the same listening position, so that the speakers are 1m clear of the front wall, we get a narrow dip at 60 Hz.

If we make the room much wider, as if it were now a living room adjacent to a meals and kitchen area (10m), it's not so bad. Finally a change that we don't get punished for!

If you can't beat 'em, join 'em!

I'm surprised to admit that there appears to be something in these golden ratios!

Actual results will vary. The room simulated has a lot of damping and reflects either a lossy room, or one that is well treated for bass absorption.

So if you are building a room you plan to use for audio, and you were going to build a typical 5 x 7m room with 2.7m ceiling, consider this option. Change the dimensions a little, and set up the room a little differently than you might have. Try to stick to it as close as you can. It seems you can get away with changing some things and not others. The beauty of this option is that you can get to a good result very simply. In fact, most will be happy with a simple plug and play setup. A pair of stereo speakers placed as per the ratios with no EQ or special room treatment. All this assumes a lightly constructed room with no concrete or bricks in the enclosing space.

If this doesn't work for you then you will need to work a lot harder for good bass.

More reading

Cardas Audio - Golden Cuboid Listening Room Diagram
Cardas audio - Setting Up Speakers In A Rectangular Room>

Audio myth series

In the audio community, there are a lot of myths that are very persistent. In this series, I'm going to explore many of them. Not everything covered in this series will necessarily turn out to be a myth.

Why are there so many audio myths?

People believe what they want to believe. Once they have formed a belief, many reject any new information that contradicts their established opinion. This is human nature.

To overcome this, an open mind and some education is needed as well as a more scientific approach. Science changes it's opinion based on new information. It sounds simple enough, but this approach while very sensible and based on common sense, isn't so common.

The audio myth series

Myth 1 - small speakers are faster
Myth 2 - fast bass
Myth 3 - cube rooms have bad bass

Cube rooms have bad bass

Do cube shaped rooms have bad bass? The idea is that a room having all the same dimensions will have very bad room modes as they will be the same between opposing wall pairs, thus reinforcing each other. Let's see if it's true, using the FRDC room simulator. This won't prove anything for every single room, but it will show one example.

Here are the results of all the rooms:



The red line is a 3m cube room - you might think it's the worst, but actually it gives the best result! Even better than a typical room of 5 x 7 x 2.7m, shown in black.

The rooms simulated are:

1. 3 x 3 x 3m with speakers 0.6m clear of walls and the listening position centred on the back wall.
2. 4 x 4 x 4m with the speakers 1m clear, listening in the same spot
3. 5 x 5 x 5m as above
4. As above but with the listening chair 1m into the room
5. 6 x 6 x 6 with the listening chair 1m in from the rear wall and speakers 1m clear of walls.



All of these results are good except the standard room! It has a large wide dip that is not easily fixed. It is far too big to EQ and acoustic room treatement will most likely do little to solve it. This room will make a beastly sub sound wimpy compared to it's potential. It will be lacking punch.



The 5m cube looks good until we start moving away from the rear wall. We start to see a dip in the upper bass range. Generally it is better to sit away from walls for imaging, so this arrangement suggests multi subs.

Conclusion

Cube rooms are not necessarily bad for bass. Bass in a room is more complicated than that. This is just a snapshot. Things will look different in a real.

There are a few different factors here:

• size of the room (very small and very large rooms are very different to most)
• where you sit makes a big difference
• where you place bass sources changes everything
• room construction varies

The main point is this: cube rooms aren't necessarily bad for bass. They may in fact be better than a room you expect to be good. Don't assume anything.

Basic measurement setup

Why measure?

Every system can potentially benefit from using measurements. If you are designing or modifying your own speakers, or setting up a subwoofer, measurements are essential. Even if you have a simple 2 channel system there is still some benefit. Measurements won't replace critical listening skills, but they will help you make better choices, including many that simply can't be made by ear. It is a learning process, where you take measurements as well as listen carefully. In this process, you learn what to look for in the measurements since better looking measurements don't always sound better. Expectations often need to change.

Isn't it better to everything by ear, since it is the ear that is the final judge?

Find the answer here:
Measurements vs doing it by ear >

The best $150 you've ever spent on audio?

It's affordable and not exceptionally difficult. In the past, the cost was much greater where a measurement setup would most likely cost more than $1k. Now low cost tools will do the job.




Essential:
Behringer ECM8000 measurement mic >
Behringer XENYX 502 mixer >
Sound card which supports full duplex operation
Mic tripod (you can use a camera tripod but it's inconvenient)

Highly Recommended:

Cross spectrum calibrated mics >
(slightly more expensive than a stock ECM mic, but far more reliable results)
Boom mic stand

You'll find it much easier with a proper stand and if you plan to measure on a fairly regular basis, the extra expense is certainly worth it.

Why can't I just plug the mic into the PC?

The signal will be too low and you will not get a measurement at all.




Software

Fortunately, this part is free.

For bass measurements, download the free program REW from the HT shack here >

 

For full range measurements, Holm Impulse is both free and very easy to use:
Download Holm Impulse here >


Do you need a calibrated mic?

This depends on what you will measure. For fullrange measurements - definitely. For bass optimisation, you be the judge. Here is a chart that shows a number of the Behringer Mic unit to unit variation:


Image courtesy of Cross Spectrum Labs who offer a calibration service, and supply calibrated mics (including the Behringer mic shown here) at a very attractive price.
View Cross Spectrum Labs website >

As you can see, you get about +/- 2db at 40 Hz, worse at 20 Hz but not as bad higher up. The most you are likely to see is 2db out above this point, but if you are lucky you may get 1db or less. In truth that is probably enough, but then when you consider that it doesn't cost much more to be sure I think most would simply pay the extra.

If you already have a mic, you are probably best to sell it and simply buy a new one direct from the lab that has already been calibrated:

Cross spectrum calibrated mics >

The cost shipped to Australia is little more than the stock ECM mic.

There is a thread on the HT shack about this service, with some very useful info:

More info on the service >

Cables and connections

You will need balanced mic cable to connect the mic to the mixer and it's a good idea to pick up a good length like 10m, with XLR connectors on each end. Connect to a PC with jacks on "main out." The simple way is to connect jack > RCA adaptors then just run an RCA cable to PC. You can get a cable with RCA on one end and mini jack on the other, or again use an adaptor.

What kind of results will I see?

The most common use will be to get the bass right in your room. The best bass can't be bought - it must be tuned to your room.

Here is an example of in-room bass measurements >

In that example you will see examples of the mains and subs, how they are combined and a final result with EQ applied.

In the most basic system, it will show you which sub and speaker placements work best. In a more sophisticated system, it will help with placing multiple subwoofers and with using EQ without killing headroom.

How do I measure?

There are various methods to measure covered here:


Measurement techniques - an introduction

Tutorial: Hornresp - getting a small horn to go deeper

Previously we looked at the impact of the rear chamber >

Now we'll take that one step further and see how that impacts extension. Here is our 40 Hz horn with Peerless XLS.



This trick relies on some room gain. Here is a measurement of the in-room bass in my room:



Green: left sub
Red: right sub
Black: both combined
Horizontal divisions are 8db

You can see there is a lot of gain here. So if we use this gain, we can make a small horn get down a bit lower. Many would design a horn flat down to 40 or 50 Hz. That gives better results in the simulation, but in the room you get a big peak in the midbass that requires EQ to remove.

So instead of a horn that will go flat down to 40 Hz, we might instead try extending it lower with low tuning. We'll need a fairly small rear chamber with a sharp knee and we will see a less appealing response with midbass dip, but this will be deliberate. The room will fill in this dip. The ideal response would be close to the inverse of the room transfer function, but we won't get that. We are now making a design that will work best for one room.

Now let's combine the two:



The grey line shows combined room response of corner subs that are flat from 20 - 80 Hz. The red line is simulated response of a 30 Hz undersized horn. It isn't really big enough to get down that low (more like 40 Hz) but it's intended to work with room gain. You can see the midbass response dips down where room gain will bring it back up and there is a knee in the bottom end. In-room response should get down to about 28 Hz. Unfortunately the 70 Hz dip will be present and so we need another bass source there to fill it in.

Don't make the box too big. It will smooth the knee and it won't get down quite as low, and excursion won't be as well controlled.



They grey version is what you would do if you didn't know room response. The black version has a smaller chamber and lower tuning.

No guess work

You need to measure your room to benefit from this. Otherwise it's a game of pin the tail on the donkey - you have no idea what you are dealing with.

Tutorial: Hornresp tweaking

Want to know how to get better results with Hornresp? Read on.

Here is our front loaded horn with the Peerless XLS driver. It's designed to extend to 40 Hz and has some compromise to make it smaller.



Changing the compression chamber



Press F4 and you will see in light grey the previous plot for all charts. In grey you can see a rear chamber of 10L, but in black 15L. You can see how it smoothes out the knee, and also shows up in the excursion plot:



You can see greater volume means higher excursion. In this case, the bigger volume means xmax is exceeded with 500w. You might think this would not be an issue as the output would not be needed, but in reality these levels would not be reached as they are based on a perfectly solid room with corner loading.

The 15L version has the maximum volume that should be used. If the chamber were made larger, the excursion would increase further. As it stands, this design is fairly robust and the 10L version is even more robust.

Let's see what happens if we make the volume bigger or smaller. Too big: 100L and too small: 5L.



The undersized chamber causes a sharp knee and loss of midbass as well as early roll-off. The oversized chamber isn't too bad, although it doesn't help if we are trying to extend the response a bit lower.



The excursion chart tells us more. 5L leads to very low excursion and this is why we see the midbass dip, but the 100L version loses it's grip on excursion to the point that we need a rumble filter to protect it! The obvious solution is to use a sensible rear chamber volume so that a rumble filter is not needed. In this horn, 10 - 15L should be used. The smaller volume will suit high power use.

Next: How to get a small horn to play deeper >

Tutorial: Hornresp bass horn - basic version

Here's a crash course in knocking up a quick simulation of a bass horn in hornresp.


First, download it here:

Hornresp download >

We'll design a front loaded horn.

1. Choose your driver and enter in it's parameters:



I've entered TS parameters for the Peerless XLS driver. Use mms for mmd. If you don't have either Rms or Cms, they can be calculated. Select Tools/Calculate parameter.

2. Enter Ang and Eg



Ang: double click until it cycles through to 2pi. This means it will correspond to simulations you would get in programs like WinISD. Otherwise you get an exaggerated output figure.

Eg: double click then enter the nominal impedance of the driver. You will now see the efficiency with 1w of input with simulations.

3. Auto generate horn

Select Tools/System design/with driver

In this case, let's choose 40 - 150 Hz. Now you weill notice that fields are filled in:



Press calculate and view the results:



This is a very good result with very high efficiency of around 106 db 1w1m. Normally this driver would have an efficiency around 87 db so we have gained around 19 db. Make sure you use the correct values of Ang and Eg or the efficiency will not be correct.

The schematic shows that the horn is over 2000L in volume! This is too big to be practical and the compression ratio is too high. Compression ratio is SD : S1 and should be 2 for a conventional driver. Now we need to modify the horn to get it down to a practical and workable solution.

4. First attempt at changing some numbers

Remove the throat chamber - enter zero for both Vtc and Atc.

Increase the size of the rear chamber to 15L

Set S1 to half the value of SD

Double click on hyp and a box will open up:

Choose a value for S2 that isn't crazy. This is the mouth area. Use a calculator and work it out in cm. I'll choose 50 cm wide x 120 cm high which gives 6000 cm2.

Now click on L12 - this is the length. We'll let hornresp calculate this based on F12 which is the number we'll input for our cut off - 40 Hz. We hope to get the horn to extend to this point. Select calculate and it works out the length. Now click save and the new numbers are entered:



Now click calculate to see the new results.



Not quite as impressive as before but we have maintained the extension and efficiency except for a midbass dip and the volume is now around 500L.

Let's simulate for corner loading. Change Ang to 0.5 and for Eg double click again and input 0.0625w. This compensates for 12 db of acoustic gain that inflates the efficiency.



Now we have decent performance and it's smooth enough. There isn't much need to try to get it flatter as room response will do much worse. Efficiency has dropped off a little but it's still very high.

Further tweaking

You might like to experiment with different sizes for the rear compression chamber. You will see a change in the excursion chart - a smaller size will cause a sharper peak and lower excursion. A larger size will see a plateau rather than a sharp peak. You will also see a change in the response where a smaller chamber gives a small peak in the bottom end and a larger chamber sees a rounded knee and often slightly less efficiency.

If you've measured the transfer function of your room, then you have some useful info. Suppose you had a 10 db peak at 30 Hz. You could lower the cut off and it would probably work with the gain better, extending the in-room result down to 30 Hz. If you are designing for a particular room, it's very helpful to have this information and incorporate it into the design.

Next: see how you can get better results >