Why you need a subwoofer for music

If you are aiming for the best bass you can get, you need at least one subwoofer, even in a two channel system. When this is suggested, a common response is "my mains have enough bass!" The reasons for using a sub aren't quite so obvious.

What is required to achieve exceptional bass:

• adequate extension to reproduce bass as low as your source material demands
• adequate output to achieve the highest level you expect in your listening position with headroom
• independent level adjustment
• adequate headroom to allow for a room target curve and some EQ
• ability to place the bass speakers where they perform best 
• multiple placements - from one to five units

Obviously the bass drivers included in your existing speakers can't meet all of those requirements. In-built bass drivers on your mains are far too limited to achieve the best that is possible. In most cases, sub will work best in locations that could not be used for a full range speaker.

I use the term "subwoofer" broadly here. An active woofer not intended for home theatre use can also be used.

The main reason for using subwoofers is that they can be placed to get the best out of the room. Once properly integrated, one can achieve a much smoother response that is free from peaks and dips that plague all rooms. It isn't difficult to remove peaks with EQ, but the unique benefit to a multi-sub arrangement is the elimination of dips.

Bass integration guide

In this article, I cover how to best set up the bass in your room. It has occurred to me that many audio enthusiasts pay careful attention to every aspect of their system while accepting mediocre performance in the bass. In response I've put together a process aimed at pursuing the best possible performance. It isn't for those willing to stop at good performance. I'm writing this for those who are passionate about bass. 

The first of this three part series is now online at Hifi Zine:

Bass integration - part 1

(June issue 2011)

The first part focuses on measuring the current level of performance in your room. Some performance targets are also introduced so that you can see the areas that need improvement.

Bass integration - part 2
(September issue 2011)

Part 2 covers acoustic treatment. How to modify your room for improved performance and how to choose bass traps.

Bass integration - part 3
(June issue 2012)

Part 3 covers speaker placement and system calibration.Of particular interest to many will be EQ.

Room measurement service

A new room measurement service in Melbourne

Following numerous requests, I'm now offering a room measurement service to Melbourne suburbs.

Update: I also provide a remote service that enables you to take your own measurements, and I will provide support and interpretation services.

More about the remote service >

When done right and correctly understood, measurements will show you exactly how you can achieve great bass in your room. If you want to learn how to take your own measurements, I can also show you how to do it effectively.

You can find out:

• how your speakers and room are performing
• how you can benefit from acoustic treatment
• how you can benefit from EQ
• how best to integrate your system with the room

I will explain the charts and what they mean.

How the process works

1. Define the goals

You explain what you would like to get out of the process. You might want to see how your system is performing. Or you may be after help with integrating your sub, which is more involved. If your expectations are a bit higher, you might want to go through a complete bass integration process.

2. Measurements

I will take measurements in your room to suit your goals.

3. Analysis

I will explain the charts and what they are indicating, along with pointing out areas for improvement.

4. Suggestions for improvement

Depending on what you are open to considering, I will discuss options to improve.

The process can become more involved than this, depending on your requirements. A complete bass integration may require more than one visit. 

What kind of measurements are involved?

I will take measurements that show the response of of the speakers independent of the room as well as in-room measurements. Frequency response is a start, but there is a lot of important information about a room contained in time domain measurements. Even if you have used EQ to get a flat response, it's more than likely there are substantial further improvements possible when you consider also the time domain.

What happens next?

What you do with the results is entirely up to you. You might satisfy your curiosity or you might want to do everything you possibly can to get great bass. Bass traps, multiple subs, active woofers, EQ, placement changes, phase alignment - those are all options I can help you with.

Room measurement case study >

Enquiries

Contact me to enquire further regarding this service

(Link will launch external contact form)

Cat: "I'm a person in a cat's body!"

Introducing Otis. He thinks he is human. A person in a cat's body! When I saw him sitting in my seat expecting a first class breakfast, I couldn't resist the Kodak moment ... even thought I had to put him up there three times to recreate it!

Unity horns + Acoustic Elegance TD18H + Maelstrom 18

This afternoon I had a chance to take some measurements of some speakers of great interest. One of very few Unity horns, along with some Acoustic Elegance TD18H woofers and a Maelstrom sub.

You can also see a pair of 6th order bandpass subs with 12" drivers. 

 

Nearfield measurement of the Maelstrom. It was converted to Aperiodic since the vents were tuned too high. 

 

Acoustic Elegance TD18H - nearfield measurement. 

All up, 3 subs and two active woofers. Quite a lot that can go wrong! There were some challenges in setting up EQ and integrating them. The Maelstrom sub near the couch was used for the bottom end. The bandpass subs were actually reducing the bottom end output due to interference. Compared to integrating a sealed sub with mains, there is a great deal more complexity.

The importance of room damping

Room damping or more specifically bass damping, is an essential part of accurate bass reproduction. All charts shown here are based on a REW simulation of a single subwoofer in the left corner in a small room 4.65m wide x 3.9m deep x 2.85m high. You quickly and easily generate similar results. They will differ based on the chosen listening position. Here we are focusing on the room itself, without any acoustic treatment.

What is bass damping?

Bass damping is simply absorption in the bass range. I refer to it as bass damping as we are dealing with room resonances that need to be damped. You can achieve it with room construction or added treatment. Here we will focus on the former. Plasterboard/drywall light framed walls work well as bass traps. Sound waves cause the boards to flex and in the process, energy is absorbed. The effectiveness is based on the depth of the air gap behind, the presence of insulation in the cavity and the mass and stiffness of the membrane.

Here you can see the impact of damping on the frequency response.

 

The top navy blue line is a room with minimal damping. That means a very low absorption coefficient of 0.1. You can see this is a poorly performing room with the worst peaks and dips. The tell tale sign is that they are all narrow Q (sharp and narrow). The best room has an enclosure with very high absorption coefficients (0.9). Each chart increases the absorption coefficient in increments of 0.1. A coefficient of 0.1 will absorb 10% of a sound wave. The black line represents the kind of damping you might see in an anechoic chamber. Obviously it isn't practical as a listening room due to likely cost and pragmatic issues. This level of damping would only be achieved with a great deal of added acoustic treatment.

Here are three selected rooms.

The navy blue line again shows the worst case scenario. The magenta line shows a room that is quite good and may represent many lightly constructed rooms with plasterboard/drywall and a timber floor. The green line shows a room that is very highly damped. It would probably require added bass traps, or special construction. 

Understanding waterfall plots

 

In this waterfall, you can see just how bad this room is. Not only are the peaks very sharp, but they also decay at a very slow rate. After 300 ms they have only decayed by 10 dB. While this is a problem in the bass range, it is even worse above 100 Hz where the ear is more sensitive to time domain effects. The result would be a cavernous sound. Fortunately few rooms would be this bad.

In this waterfall, you can see much better performance. Here one of the limits of the simulation becomes clear. In a real room, the bass region below 80 Hz would be worse, but above it would probably be better. Still, it isn't too difficult to see how this is a big improvement.

 

With very high damping in this room you can see that the response is much flatter and any peaks and dips are much broader. The decay is very even and rapid. If a room were built to perform this well (not likely), very little extra effort would be required for exceptional performance. Unfortunately this level of damping requires a very well designed room and extensive added bass traps.

Bass traps vs room modification

It is important to combine acoustic treatment with a room that also provides damping within its envelope. The room damping tends to be restricted in bandwidth and is not likely to do all that is required. If it is left out, the additional space required for larger bass traps may not be practical. The best and most sensible approach is to combine the two different types of damping. With this approach in mind, the bass traps used should be of the porous broadband type. Membrane-based traps are not likely to have the required bandwidth.

What are room modes?

Room modes are a collection of resonances that are unique to each room. The are based primarily on the size and shape of the enclosing boundaries seen by sound waves. They present the greatest obstacle to accurate bass reproduction, and they cause problems in even the best sounding rooms. 

Types of modes

There are three types of modes - axial, tangential and oblique.

Axial modes

Axial modes tend to dominate the modal response. They are formed between opposite wall surfaces.

Tangential modes

Oblique modes

Oblique modes are less significant due to their longer path which causes their energy to dissipate.

Getting back to basics

To understand modes, it helps to consider a simpler situation than a normal room. First, let's consider a sine  wave in a free field environment with no boundaries (not even the ground).

At that one frequency, you have peaks (nodes) and dips (anti-nodes). If you were to move towards the source, you would notice the tone gets louder and softer. For simplicity the modes in the first three diagrams are shown as lines, but each line represents a sound wave with peaks and sips along its length as shown above.

Now let's consider what happens when we add a boundary. We'll add in the ground.

Now we have a secondary source with a longer path length. That path difference means that the reflected sound wave will interfere with the direct one. We can expect a dip caused by the difference in phase of the two sound waves. The higher the level of the reflected wave, the greater the impact on the response. This effect is referred to as SBIR (Speaker Boundary Interference Response). The first three reflections are covered there - those off the side and rear wall and the floor.

In a rectangular room there are 6 enclosing boundaries. Now consider the first three diagrams. In the midrange, those nodes and anti-nodes become closely spaced together so that they are reasonably smooth. It is in the lower midrange that there is a transition point where nodes and anti-nodes are spaced far enough apart that they no longer can offer a smooth response. This transition point is called the Shroeder frequency, and it will often be around 200 - 300 Hz. Below that point we see major peaks and dips in the response until we reach the lowest mode. As wavelengths approach and exceed the largest room dimension, we no longer encounter modes and the room becomes uniformly pressurised. The room provides acoustic boost below that point depending on the extent to which bass is either absorbed or transmitted through the envelope.

The importance of position

Room modes create a complex pattern of peaks and dips in a room. The existence of modes is determined by the room shape and its acoustic properties. The way in which those modes are excited depends on the location of the speaker and listening position. As a result, shifting the location of the speakers and listening position will change the response. Placing a subwoofer in the corner will tend to excite the most room modes and achieve the maximum output. This may or may not be a good thing. If you then sit against the back wall you are likely to experience strong peaks and a boomy sound. Shift your seat forward and the bass level and boom will be tamed. This is the simplest form of adjustment to suit the room, but you can certainly improve on that with more advanced techniques.

Here is a section through a room with a depth of 3.9m and a sub in the corner. Position 1 is with a couch against the wall, 2 is moving out and 3 is in the middle of the room. So you can see that if you sit against the wall in position 1, you will see a strong peak at 44 Hz and also one at 88 Hz. Moving out from the wall, both will decrease but in position 2 there will be a dip at the second order resonance. In the middle of the room (position 3), there will be a null at the first order resonance and a peak at the second. All this assumes a sub in the corner as shown to excite all these modes. This is in fact my current listening room. The first order axial mode for this wall pair is at 44 Hz. This can be calculated by this formula:

Frequency = 0.5 x 344 / Distance between walls in metres

The second order mode is a multiple as is the third and so on. In this particular room, in position 1 the 44 Hz mode is dominant with most sub and speaker positions. The result is a 15 dB peak which causes the room to boom.

A decay plot can show up the presence of modes in both frequency and time domain.

The top of the red plot shows the response of a full range speaker, while the purple plot shows the response after 150 ms. Where the gap between the two plots is small, that indicates modal ringing.

1. 44 Hz - first order depth mode
2. 61 Hz - first order height mode
3. 84 Hz - second order depth mode
4. 130 Hz - third order depth mode

Note that two of the four easiest to pick modes are depth modes. The position is against the wall (position 1 on the previous diagram). So this is not surprising. Harman Audio has a useful tool for quickly working out the modes that could possibly be excited in a room.

Download the Harman Audio Room Mode Calculator

It is a handy tool to use in making sense of measurements. 

So what does all this mean? 

Room modes do two things. Firstly, they introduce peaks and dips to the response. Secondly, they cause ringing in the time domain so some frequencies stay in the room longer. This is a serious impediment to accurate bass reproduction. Understanding room modes is just the beginning. Dealing with them ideally involves a mix of acoustic treatment, placement, multiple bass sources and EQ. 

Quickstart guide to bass measurements in REW

This is a quick guide to taking measurements with REW.

You will need:

• Calibrated measurement mic
• Mic phantom power/preamp
• Mic stand
• Cables and adaptors

More about measurement tools

SPL calibration

Initially you will be prompted to perform SPL level calibration. This may be considered optional. You need an SPL meter and this calibration must be done each time you adjust anything that will affect the signal level. This includes your sound card volume control, the gain on your mic preamp, the volume control on your sound system, sub volume. If you change the level at any point, then the SPL calibration must be repeated. Chances are you will change the volume more than once in a measurement session. I normally skip this step and simply ensure that the level is reasonable. A high level may cause room rattles that interfere with the results. A low level may not be much louder than your noise floor and cause inaccurate results. 

Initial setup

1. Go into Preferences under the Preferences Tab.

2. Sound card tab - select input and output devices (start with default). 

3. In the middle of the window, you will see the following:

Click on calibrate and follow the instructions. This will calibrate your sound card. 

4. Mic/mater tab - enter mic calibration file.

If using a calibrated mic from Cross Spectrum Labs, choose the calibartion at 90 degrees as you will be measuring with the mic pointing down.

What type of measurement?

There are a few different basic measurement techniques you might use for bass integration:

• Nearfield
• Farfield (listening position)
• Ground plane outdoors

You may like to start with nearfield measurements. These are useful to isolate a sub or woofer from the room response. The mic is placed about 1" from the cone, and also close to any ports. You get a measurement free from room effects and it is good firstly to see the response of the speakers without the room. This measurement technique is most suitable for subwoofers, but it does tend to exclude baffle effects and is generally considered a technique for low frequency measurements below 100 Hz. 

Ground plane measurements are a more suitable technique but tend to require a quiet outdoor space such as a vacant parking area. It's an inconvenient technique. The speaker in question is placed so that it sits on the ground to avoid "floor bounce." The mic is placed on the ground. A floorstander measured this way would ideally be placed on its side to avoid floor bounce. 

The measurement of primary interest is the farfield taken from the listening position. The mic is placed where your ears would go. If you are taking a lot of measurements, you may speed up the process by putting the speaker close to that position and moving the mic to the various speaker positions. The result is similar and it's more convenient than moving the speakers. 

Your first measurement

1. Click the measure icon and this dialogue box will appear:

Click on check levels to make sure the level is right. Choose a sensible volume firstly for the signal - one that you might call "moderately loud." Then adjust the volume of the mic preamp so that you have adequate headroom. 

2. Choose the frequency range for the measurement. I choose a range from 15 Hz (start freq) to 400 Hz (end freq). 

Click start measuring. 

A measurement signal will run and you will see a response plot.

This plot is a subwoofer and it is a far field measurement. You can see a dominant peak based on a room mode at 44 Hz. 

Now adjust the limits:

It is important to set these so that you can read the chart easily and not be misled. You should limit the frequency range so you can see the data clearly. You might set the upper limit as low as 200 Hz and as high as 400 Hz. The SPL range will also affect how the chart is perceived. Set the range too large and everything will look too flat. Set it to a narrow range and you will make everything look worse. 

After you have taken a number of plots with different positions, you might like to view "all SPL." Select this tab above the measurement window and you can select which plots to overlay.

Here you can start to appreciate consistent trends. In particular you can see that the peak at 44 Hz is present in many of the other measurements. 

Waterfall plots

Waterfall plots are one of the most useful for analysing bass performance. They show the frequency response over time. 

You can see how over time, the 44 Hz peak decays at a slower rate. 

To generate a waterfall, first select the appropriate measurement in the left column. Then choose the waterfall tab. The chart area will be empty, with a "generate" button in the bottom left hand corner. Click on generate and you will see a waterfall plot. 

You can generate a decay plot in the same way. It shows the same data in 2D form. 

The waterfall tends to show the overall trend in a more intuitive way, but a decay plot such as this is easier to read if you want to see the decay at certain time intervals. Both plots are useful for assessing bass trap effectiveness as well as testing your EQ settings. You can see if your EQ filters are causing problems. 

This guide covers the basics. There are other charts in REW, but these are the ones you will find the most useful. 

More information

Download REW >

REW homepage >
REW online help files >

If you need help with how to setup and use REW, visit the REW forum
REW forum >

REW: Understanding decay and waterfall plots

In order to get the most out of REW, you need to understand how to read decay and waterfall plots. They are the most useful to consider in using REW for bass integration.

Here is a nearfield subwoofer measurement which excludes the impact of the room.

You can see in both plots the kind of result you would see in an anechoic chamber, a nice smooth response with very even and quick decay. You might say this is an ideal waterfall plot. You can also see some mains hum that comes from connecting the PC to the sound system. It it easy to pick because it occurs at 50 Hz and it is continuous, showing no sign of decay.

They decay plot shows a 2D version where the response is plotted at time intervals, in this case out to 150 ms.  Now let's look at a waterfall measured with the room response included. Unlike the previous measurements, this includes subs and mains together.

We can now see the influence of room modes, most of the peaks marked with the red dots. One in particular is marked. You can see it starts as a tiny peak that would hardly be noticed in a response plot. Over time it decays at a slower rate - this is referred to as modal ringing. Now look at all the points at the bottom of the chart where these peaks stand out. This is the main thing we are looking for in decay and waterfall plots. 

The room shown above might be considered a good room. It has light construction with plasterboard/drywall and a timber floor. Moderate EQ has been used to tame some of the peaks. Many rooms will in fact be worse than this, however this room really does need acoustic treatment as well to control the modal ringing. 

This is a far better measurement and it includes 3 large bass traps. The decay is now more even and modal ringing has been damped. There is still some room for improvement on paper, but this level of performance would be considered excellent. Subjectively the result is very tight and fast. 

Tips

• When generating the measurement signal, limit the bandwidth to 15 - 400 Hz. This will result in a smaller file size (REW files are large). 
• Set the time window to 300 ms
• Pay attention to the chart limits as they can affect how the chart is perceived. Aim to compare plots with the same limits.
• Waterfalls can be misleading. Notice how the lighter green waterfall appears to have worse ringing below 25 Hz. In reality the improvement is minor, but the dark green waterfall has early roll-off. This makes it appear as if the decay were better. This is where the decay plot proves useful as you can more easily see the relative decay of each. 

Estimating maximum SPL for your subs

Predicting the maximum SPL of your subs in your room is not an exact science. Here I will provide a guide that will enable you to come up with a reasonable estimate. There are two parts to this estimation. The first is the output of your sub in a half space environment. This is what you would get if your sub was set up outdoors. The second is the output you would measure from the listening position in your room. For this exercise we will ignore room modes and simply consider room gain and attenuation due to distance. This should provide some kind of reasonable estimate that is valid up to about 40 Hz. Above that point the output will be dominated by room modes and estimates can be as much as 40 dB out.

Part 1 - Half space estimates


The half space output at 1m is based on the alignment and the total swept volume (VD). The swept volume is limited by power compression, driver excursion, and piston area. If you know the maximum swept volume, then you know the theoretical maximum output. However, real world concerns such as power compression, amplifier power handling and driver power handling may cause that maximum not to be reached.


A simulation program such as WinISD is a good starting point. You may find that a sub can output 120 dB in theory, considering a particular alignment and assuming 2kw of power and 32mm of one way excursion. In practice, we may only have 1kw of amplifier power, output is reduced by 3 dB to 117 dB. We may also find that the driver has 5 dB of power compression due to the heating up of the voice coil. The real output is 112 dB, not nearly as impressive. Any of these issues can be limiting factors.


For some real world measured examples are available:


Home Theatre Shack subwoofer measurements
AV Talk subwoofer measurements

Even if a sub of interest is not in either list, you can no doubt find something similar.

As these measurements are performed at 2 metres, 6 dB should be added to the output. This will yield a result that is comparable to simulations in a half space environment, except that compression is included. Ground plane measurements such as these, measure at 2 metres to counteract the 6 dB gain from the ground to closer approximate an anechoic result. Here, we want a half space figure.

SPL estimate

The table above suggests some typical half space maximum output figures at 20 Hz, and assume that adequate power is available and that no power compression is involved. If you have a small box, less power than required or port compression, you will get lower figures.

You may like to simulate your particular sub in WinISD. If you aren't familiar with this program, I've written a quick start tutorial. If you need to enter in a new driver, I suggest you also look at the post about how to do it.

1. Simulate the driver in the appropriate box size

2. Enter the maximum amplifier power under the signal tab

3. Check the cone excursion and reduce the signal until within xmax

4. You might like to add a High Pass (Rumble filter), especially if it's a vented box

5. View SPL

Part 2 - allowing for the room transfer function

Now the difficult part. If you have a speaker with some kind of output down to 20 Hz, you can work this out with some accuracy. Firstly, I'll cover the estimate where you have the option to take measurements.

1. Place the sub or speaker in the intended position and measure with the mic in your listening position with REW. View REW Quickstart guide if needed.

2. Take a ground plane measurement outdoors. Place the sub on the ground and the mic also on the ground at a distance of one metre.

Ideally you would keep the same level of gain in each case. If you adjust the gain for either measurement, the result becomes invalid.

You can now analyse the results. You will have to ignore peaks and dips in the response and look for changes in the bottom end which suggest gain. You may see greater extension in room which suggests gain. You may also notice that the level drops due to distance. If the sub was running with the same input power both times, you can then create a transfer function from say 20 Hz to the region before the first mode takes over.

Otherwise you can use an estimate.

One example

Let's take a Rythmik 12" sealed servo sub as an example. In the tests, this sub produces 95 dB @ 20 Hz. We will add 6 dB to get a true half space value, 101 dB. Looking at the table above, you can see the estimate is 99 dB at that point. Evidently it is slightly conservative.

I have measured this sub at around 36mm peak to peak excursion and the output at 3 metres was 95 dB. So in this case, in my small room it turns out that the ground plane measurement matches the maximum output in my room, which is small and lightly constructed, hence modest room gain is expected. Larger rooms and greater listening distances would see lower output. Concrete floors and masonry walls would increase the output.

Multiple subwoofers

Add a second subwoofer of matching output and you can get up to 6 dB increase in output. This increase can easily be achieved below 40 Hz even when the subs are spaced apart. At higher frequencies the interaction with the room tends to dominate and additional subs will tend to smooth the response without increasing the level.

How accurate are the estimates?

In reality there is no substitute for testing the sub in the actual room. However, if you are choosing a new sub with targets in mind or the room in question has not yet been built, an estimate is needed.

If you want a quick and easy estimate, you may like to start with the links to real measurements and find a sub which is close to what you have in mind. In a small lightly built room the maximum output measured will probably be close to what you will get at 20 Hz at 3m in-room. In a large room with similar construction, you may need to double up. Aim for around 6 dB extra to compensate. A more solid large room may end up with more output than a small lightly constructed room.

So how accurate are these estimates? Probably about as accurate as you need. Consider also that once placed in a real room, you introduce up to +/- 20 dB based on modal fluctuation. With that in mind, it is very difficult to know exactly what you will end up with. 

Estimating maximum SPL for your mains

There are two figures of interest. One is the theoretical maximum that is easy to determine with a WinISD simulation. Of greater interest is the real world useful output, which will normally be substantially lower.

Let's consider a typical hifi floorstander. In a typical room with a listening distance of three metres with about 100 watts of power we can expect around 90 dB of clean output. We might hit 95 dB if we are lucky. How does that compare to a maximum theoretical figure?

Let's assume we have a pair of 6.5" midbass drivers and a vented alignment. Running full range we can expect around 107 dB @ 1m. Input power 40w and at this point, excursion is the limit. Now if we run it actively, set to small with a high pass at 80 Hz, we can apply more power and get 111 dB of excursion and power limited output. Allowing for distance we subtract about 5 dB and we get either 102 or 106 dB depending on whether we are running full range or with a high pass and more power.

So here we have a discrepancy of 7 - 16 dB between the theoretical maximum and the level that subjectively sounds clean. With this in mind, you might like to consider a realistic estimate to be the output at around 10% power level.

1. Estimate the output based on the maximum power of your amplifier

2. Reduce the output if needed to ensure excursion limits are not exceeded

3. Allow for any high pass filtering

4. Allow for attenuation due to distance - around 3 dB per doubling of distance (this figure is 6 dB in a free field but a useful figure in a real room is closer to half that)

5. Reduce the figure by 10 dB

What is cone breakup?

Cone breakup refers to way in which piston drivers bend at the top end of their bandwidth. At lower frequencies the piston moves as a unit, but at a certain point based on the mass, stiffness and geometry bending modes cause sharp peaks in response and resonant ringing. At this point the driver will most likely become unuseable. Stiff cones tend to have sharper breakup with a high Q peak that is easily seen in the response. Soft cones provide damping of cone breakup so that it may in some cases not be visible in the response. As a result, metal cone drivers will tend to have lower distortion prior to breakup and will often need a notch filter, steeper low pass filtering and a lower crossover point. Soft cone drivers may not require any special treatment in the crossover. 

DIY nearfield diffuser panel

Here is a diffuser panel in prototype form that I'm currently testing. I prefer to build prototypes first before coming up with a design that I will build properly.

 

 The process can help with the design. In this case I want to make sure I like the result, and these light easy to make panels can be easily moved to try different placements.

As you can see, it is made with fins of ply and polystyrene wells stuck on with masking tape. They are all parts I had on hand. The panel is around 350 x 400mm and 55mm deep. It is effective to 2k with reduced effectiveness down to 1k.

This particular panel is designed for nearfield placement, around 300 - 500 mm. They will be placed on the rear wall against which my couch sits. In my initial tests I've compared to a bare wall and absorption. I prefer the sound of a bare wall over absorption, as the latter sounds artificially dead. I also prefer the panel over a bare wall as there is an added sense of ambience without adding anything unnatural. The effect with a small area is subtle.

I also have plans for a panel that is 110mm deep which will be effective to1k.

My plans are to add a very large panel to the ceiling and behind the listening couch, with smaller panels distributed around the room.