20 Hz Alpine horn sub

This is a custom horn sub designed for 20 Hz extension. It is designed to be installed, hence the dual opposed mounting to avoid vibration transfer to the rest of the house. 

First comment. Hornresp makes things look worse than reality. The peaks don't turn out quite so bad, and the vertical scale makes them look worse. For these two reasons, measured results will usually tend to look better. This one could be used to about 60 Hz. Subs such as these aren't ideal where you might need to cross higher. The first peak around 90 Hz must be avoided. I think these are best to use in a system where you have something else running the upper bass. In this system there are dedicated active woofers.

Here you can see that the design loads the cone down to 20 Hz and below that a high pass filter is required or the output will be severly limited. If one were you use a sealed box to avoid the need for this, the amount of air the drivers must move is increased by a factor of four.

In terms of getting the maximum output for the least total spend, this kind of design can be a good value for money option. In terms of sound quality, it will depend on implementation more than anything.

Sonus Faber Cremona Auditor stand mount

It's a tough job, but someone has to do it!

A client of mine has asked me to evaluate a speaker that he isn't completely satisfied with. Is he expecting something it won't provide? Can it be modified to suit better?

The speaker in question is the Sonus Faber Cremona Auditor - a stand mount featuring the Scan Speak revelator woofer and what appears to be an OEM variant of the Vifa ring radiator. There is no question this is a beautiful speaker and very well made.

First, how does it measure?

The sonogram and waterfall plots reveal good design attention to off axis response, within the limitations of a passive two way direct radiator.

The waterfall is probably the most intuitive for most:

Basically this is showing frequency response at all angles out to 90 degrees with a twist - the on axis measurement is normalised so that it's perfectly flat. As a result, this shows the response off axis that you would get if it were perfectly flat on axis. This particular speaker is quite flat on axis, so it's not far from the truth.

At the bottom of the chart, we start with omni lower midrange - seee how off axis there is very little drop in level? At 1k things are still very wide. By the time we reach 2.8k, a little above the crossover point as specified on one website, you can see a little dip, but nothing major. Once we reach about 7k the off axis response drops off rapidly and the tweeter is now beaming. In a typical untreated room this is unfortunate because the tweeter is beaming where the reverb time will usually drop down. As a result, treble energy is lost more rapidly. This speaker would probably suit a treated room much better.

The sonogram below shows the same information, but think of it as an aerial view of the mountain range, with elevation shown via colours. You can see constant directivity from 2 - 7k which is an important region. Then we reach 40 degrees from 10 - 15k.

My initial impression of this speaker is similar to comments from the owner. At moderately loud levels, cymbals become harsh. Well before it reaches its limits, this becomes an issue. It's clear from the beginning that this speaker has been designed for moderate listening.

Not willing to give up quite so soon, I integrated it with a bass bin to alleviate bass below 200 Hz:

I then applied some EQ to voice the speaker in a way more suitable to higher listening levels. I know what some of you are thinking - this is pure sacrilege!  I'm inclined to agree somewhat, but I wanted to see if modification could allow it to extend it's useful output further. The short answer is yes - it does work. I was then able to enjoy it at a louder level, with a bass curve added and the treble response voiced to be a little more laid back, with a lowered shelf. Treble detail was not give up, but instead it became more listenable as the level climbs up. I'm not talking about extreme SPL, but levels of around 90 dB in the listening position. 

The imaging is very good. 

These are my preliminary thoughts, but I'll be spending more time with them to confirm.

Prior to listening to these I was running S3 to evaluate. I think it would be a great surprise to many to find that S3 is inherently more listenable as the volume goes up. Who would have thought this could be true of a compression driver horn loaded? Yes, I'm certainly biased here considering that S3 is my design, but I would be very interested to hear the impressions of others.

HE2 dispersion

HE2 has now been measured for dispersion:

The woofer has fairly wide dispersion which then narrows above 1k. The waveguide and compression driver combination narrow their pattern gradually towards higher frequencies. A robust compression driver which can run below 1k has been chosen, to allow freedom with the crossover. This makes the smooth handover shown here possible. Some beaming is shown around 15k, meaning there will be some loss of high frequencies radiated to the room. This is not a big issue.

Overall, this is a good result.

S3 prototype dispersion measurements

S3 measurements confirm very good dispersion control. Constant directivity has been achieved and pattern control has been maintained down to the Shroeder frequency of typical listening rooms. The - 6 dB line shows the nominal coverage angle - in this case 80 degrees nominal (or 40 degrees from the central axis as shown on the sonogram). The results have been gated and normalised. The floor reflection has been gated out and normalisation adjusts the axial measurement to a flat response. As a result, the sonogram shows dispersion rather than frequency response. One could achieve a similar result by using EQ to get the axial response flat, but this method is much quicker.

Horizontal: 

Vertical:

The vertical coverage is a little narrower than anticipated and this is a matter for further investigation. My initial supicion is that the dip around 5.5k may skew the result.

What is particularly pleasing with this result is that the beaming often seen before pattern control is lost on the bottom end, has been eliminated.

6 driver mid version

6 driver mid version:

Both versions, with 4 mids and 6 mids, are viable options. Currently working on variations and assessing the merits of both versions.

You get a little hint from the photos that there was some challenge in getting the side mids in place. It's not easy to get the mids this close for a high crossover point, and have 6 of them!

S3 prototype - continued

This is the second horn:

I used polyurethane glue instead of PVA this time for its superior strength and expanding characteristic, so the bond is more forgiving with imprefections.

This is a quick 'n dirty test prototype to test and refine the design. I will be testing some variations before finalising the design. 

Please do not take this as an indication of the build quality of the S3 kit!

The kit will be machined in a factory, rather than using the manual methods you can see here.

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