Acoustic Treatment For Sale, Part 2


Well-Known Member
Dec 24, 2016
Low-Frequency Bass Traps - I had a pretty bad bass overhang problem in my listening room, with a pretty big peak shown on Room EQ Wizard in the 25hz – 40hz range. This muddied not only the low bass, but smeared the entire presentation. I tried DSP (which helped moderately, but really not enough for the cost and fact that everything had to go through digital) and lots of the big ASC Tube Traps (again, the improvement was not sufficient and the cost was high). I stumbled upon Acoustic Fields and looked at their bass traps and spoke with Dennis Foley at the company. They make some very big claims about the effectiveness of their bass traps and I was a bit skeptical about what I would hear from them. The bass traps are diaphragmatic bass traps, which are designed to help absorb the lower frequency range. From my reading of Acoustic Absorbers and Diffusers by Trevor Cox and The Master Handbook of Acoustics by F. Alton Everest, I knew that good diaphragmatic absorbers had the potential to help in the lower bass region. Dennis Foley also makes the claim on his website that using activated charcoal in the absorption section of the trap instead of OC fiberglass panels lowers the range of absorption and increases the amount of absorption. I thought this was wacky, but then I went back to the books and there it was in the Trevor Cox book. So I decided to build a limited number and give it a try and test the results. I bought the plans for the traps and the activated charcoal (I did not purchase the charcoal from Acoustic Fields. Dennis Foley says that the activated charcoal he uses is specially manufactured for him. I cannot say whether their charcoal is more effective than the commercial charcoal I used). The units I built were sized to fit in the bottom corners of the front and side walls, so the dimensions are [ ]. I confirmed with Denis Foley that the height and width of the boxes didn’t matter re the effectiveness, as long as the depth and internal dimensions were the same as the design, which they are. From the acoustics books and discussions with Folely, it also became clear that to be really effective, the traps needed to be very rigid (with no flexing) and absolutely sealed. So, for the construction of these traps, I used 2 layers of 1” Ranger Board (which is MDF this uses finer dust and is denser and more rigid) for the top, bottom and sides. For the back, I used 3 layers of the Ranger board. The layers of the Ranger Board are glued together using Green Glue, which is a polymer that really dampens vibration. The unit is also sealed with the green glue. The components are put together with pocket-hole screws, Festool Dominoes and many Spax # 12 screws. This mother is solid and sealed – you could drive a tank over it. It is also quite heavy – my guess is around 300lbs. Inside, it has about 30lbs of the activated charcoal. So, how do they sound? People that know me know that I am not one for using hyperbole, but I have to say that just 5 of these units did a phenomenal job at cleaning up the bass overhang. This resulted in clearer, quicker, more articulate and more impactful bass, but it also cleaned up the entire presentation. Mids and highs were clearer and more open (much more air) and the soundstage widened and deepened. I really wasn’t prepared for what I heard. They were so effective, that I didn’t feel the need to build any more for my room. I have the materials to build more of them, so if anyone is interested, once I get settled in Florida, I can build you whatever sizes you need. I am selling all five and would strongly prefer to sell all of them to one person. I am selling them for $650 each, but will sell all 5 for $3,000. This will include the acoustic/fire retardant fabric to cover the whole unit (I never got the chance to pull them out and cover them). You can certainly buy the plans from Acoustic Fields, the wood and the charcoal and build them yourself, but trust me, these things are a bitch to build properly. The materials alone are close to the cost of the units (the Ranger Board and the charcoal are quite expensive).


GIK Acoustics Q7d Diffusers. - I have two of these. They are 19” x 46” x 6”. You need to have two of them (a period) for them to diffuse properly, so I will only sell them as a pair. These were the first diffusers I tried and they immediately convinced me of the power of diffusion. I placed them on the wall behind my speakers in the center. Everything, particularly voices became much clearer, articulate and denser. I have lent these to a number of friends, who found the exact same thing and wound up buying them. They are small enough and nice enough to have in your living room (and they are light enough to remove as needed), but they do have their limits. The GIK site says that they are designed to go from 350hz – 3khz. That sounds about right (maybe not as low as 350hz). They can be overwhelmed when playing the music loudly and to me, tenor voices can sound a bit congested (this is why I decided to build diffusers designed to handle the lower frequencies). These units are marred a bit (nothing significant), so I would sell them for $275 for the pair. GIK sells them for $520 for the pair.

GIK Acoustics Gotham N23 Two-Dimensional Quadratic Diffusers - These are two-dimensional diffusers – i.e. they diffuse the sound not sideways, but up and down. (GIK says they diffuse from 1250hz to 9,500hz) I found that these skyline type diffusers were best for places where I wanted to preserve the air/reverb in the music I used these on the back wall and the ceiling at the first reflection points and a bit behind the listening location. They did a very good job and are very easy to mount (and look kind of cool when you have a bunch of them together). I have about 20 of these. GIK sells them for $179 a piece (plus pretty high shipping cost). I would sell these for $100 a piece and $85 a piece if you buy 10 or more.

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