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blue lander 11th February 2010 12:00 AM

Purpose of "stuffing" an Austin a166?
Me and my wife built a pair of these a few months ago, and because everybody seems to recommend it, I cut up one of those foam pool toys and put it in the back of the compression chamber. I liked the speakers, but I always felt they were a little thin in the upper mids, and were lacking "realness" in the upper frequencies. It got even worse when I removed the dust caps and put phase plugs in. This suprised me as the phase plugs are held to be an improvement by everyone who tries them. I assumed I needed a supertweeter to reinforce the high mids.

On a whim, I took all the foam out and found myself liking the sound much better. The bass was less pronounced, but the upper mids were much sharper and more "there". I did some very unscientific frequency response tests with my laptop and it showed a 3db boost in the frequencies between 3k and 10k. I did lose some bass, though, so I wanted to keep experimenting.

I cut the foam toy into 1/4th and put it back in, and this seemed like the worst of both worlds. The highs sounded dampened again (sort of like the different between running traditional speakers with the grill cloth on rather than off), and I didn't really get much back in the bass.

I want to start experimenting with other stuffing materials, but I'd like to know a little more about the theory behind its purpose. I assume it's supposed to keep soundwaves from the back of the cc from bouncing right back at the drivers. I already dampened the driver with felt and ductseal, so is it still necessary to block these reflective waves?

It also, of course, changes the volume of the compression chamber. Mathematically speaking, is the compression chamber for the A166 too large? Do I need to decrease the volume for the numbers to "add up", so to speak? I'm using the standard fe166e drivers. Some posts I've read say you only need to decrease the volume if you're using a different driver. Does the bass increase as I decrease the volume?

Assuming the volume of the cc is okay, I was thinking of just putting a felt strip in the back of the chamber to tame the sharpness a bit. I was also thinking of putting ductseal back there and notching it up with a knife so it refracts the soundwaves in all directions rather than absorb them like foam. Has anybody experimented with other materials?

rjbond3rd 11th February 2010 04:56 PM

Hi blue lander, I thought the "pool noodle" purpose was merely to reduce the chamber volume for the FE166ES-R driver. Since you're using the FE166E, presumably you shouldn't need it.

Are your FE166E's broken in yet? That could be a factor. There are lots of basket mods, each of which can help a bit. I heard Mssr. Serenechaos do the 99-cent mod which had a subtle but definitely audible effect (putting a tiny amount of damping material in the space between the whizzer and the cone, thus giving a bit of support to the whizzer, making it behave it bit better).

planet10 13th February 2010 07:15 AM

Decreaing the volume of the air cavity moves the acoustic crossover to the horn up in frequency (more mids out the horn mouth). Enlarging gives the opposite.

I would try lining the cavity walls (wool or cotton felt) and playiny with well fluffed polyfluff.


planet10 13th February 2010 07:22 AM

Blue lander,

Other important questions are what amp are you using and wher ein the room do you have them? Pictures?

How well are they executed and what are they made of?

LostForWords 16th February 2010 01:11 PM

""Decreaing the volume of the air cavity moves the acoustic crossover to the horn up in frequency (more mids out the horn mouth)."

It is exactly this issue that concerns me and I must confess to absolute confusion. I started building the excellent Austin cabinets ages ago, but intend to use the FE166ES-R drivers. I've seen reference to a changes in the compression chamber volume to 2.74 litres, but do not know whether this still includes the 'pool noodle' or whether it will further diminuish the cc and raise colouration back through the cone. I know that this combination has been attempted, but do not know what to do. Can anybody please advise?

planet10 16th February 2010 04:51 PM

One of the builds around has an externally variable compression chamber. Our approach is to build large and then fill until it is right with small "blocks".


blue lander 16th February 2010 05:47 PM


Originally Posted by planet10 (
Blue lander,

Other important questions are what amp are you using and wher ein the room do you have them? Pictures?

How well are they executed and what are they made of?

They're rather... utilitarianly (is that a word?) executed. It's the first woodworking project I've done since high school. I built everything as close to the specifications as I could (resorting to wood filler here and there when I had to), but they're by no means professional grade. I wasn't able to find baltic birch to make them out of, so I used the best wood I could find at Home Depot. To be honest, this pair was meant to be a test run before we tried building them again with better wood, but I was so pleased with how they turned out that I'll probably just keep them.

I've been running them for 6 months so I think the drivers are pretty worn in by now. I just Mod Podge'd the speakers a few days ago (one coat, 25% water), though, so I'm going to let them wear in for another week or two before I start messing with the stuffing again. The Mod Podge definitely made them less efficient, but I think it's also flattened out the frequency response a little. At first I thought the Mod Podge dampened the midrange detail out of the speakers. But when I listen closely the detail is still there, it's just crowded by the rest of the frequency range. I'll reserve judgment until they've run in for another week or so.

I'll try felt lining the cc next. I'm happy overall with how they sound since I removed the stuffing, however there's a little "scratchiness" to the vocals that wasn't there before that I'd like to tame. I'm also going to put them on spikes to see if that helps. They might be rattling around a little on the hardwood floor, especially if I play them loud. I think those pool noodles absorbed a lot of kinetic energy.

LostForWords 17th February 2010 10:32 AM

Thanks folks - Does the 'pool noodle' impact on the overall volume or is it part of the design (as it seems to be the focus for acoustic energy in the compression chamber and may have a critical role)? If used, should the volume be adjusted for the space it takes up when changing the compression chamber to 2.74 litres?

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