The Official Magnepan Owners Thread - Page 138 - AVS | Home Theater Discussions And Reviews
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post #4111 of 4122 Old Yesterday, 05:20 AM
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FWIW, GIK has a special running at the moment for their freestanding bass traps and their thinner freestand acoustic panel. For the bass trap, it will come under $300 after shipping for a pair of absorbers that seem to be a perfect fit for the MMG to 1.7 range of panel sizes. I've been using the freestand bass traps behind my MMGs for a few weeks now and it really is worth it. Of course, one could make a DIY one significantly cheaper (been there with Jon Risch's design a dozen and a half years ago) but the freestands are finished on both sides and the steel feet are a nice touch. Pic enclosed to give an idea of their size.

http://www.gikacoustics.com/product/...and-bass-trap/
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post #4112 of 4122 Old Yesterday, 07:49 AM
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Once you've heard what ASC Tube Traps (or DIY bass traps built with the same observance of acoustic theory) are capable of doing in a sealed room, traps built otherwise (flat panels, which are great for non-bass frequencies) seem like 98 lb. weaklings in comparison, in their ability to absorb very low frequencies. Of course, that ability comes at a substantially higher cost than flat panels.

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post #4113 of 4122 Old Yesterday, 11:33 AM
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My corner traps have about 12" of regular OC-703 or whatever and seem to help somewhat.

Damping the back wave, at least in the midrange and up (preferably lower but that's harder), can make a substantial difference in sound in most rooms. Not everyone likes it, to each his own.

IME/IMO - Don

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post #4114 of 4122 Old Yesterday, 12:14 PM
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Quote:
Originally Posted by DonH50 View Post
My corner traps have about 12" of regular OC-703 or whatever and seem to help somewhat.

Damping the back wave, at least in the midrange and up (preferably lower but that's harder), can make a substantial difference in sound in most rooms. Not everyone likes it, to each his own.

IME/IMO - Don
Whether or not to absorb, or diffuse, the rear wave of a dipole speaker is one thing. Employing bass traps to absorb the build up of bass standing waves in a sealed room is a different thing entirely. There isn't any room or system, no matter what the desired sound characteristic of it may be, that does not benefit from being fitted with bass traps, whether the speakers are dipole, bipole, or monopole; ESL, magnetic-planar, ribbon, horn, dynamic, or any other type of speaker. As far as an enclosed space with any set of speakers in it, a room is a room, and bass is bass. And few of us have one with dimensions optimum for the minimization of bass frequency modes. Too few systems have the cost of bass traps included in their budget, IMO. The room---the single most important component in a system, and the one usually considered only as an afterthought, and with far too little funds earmarked for. In this case, your mileage will NOT vary!

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post #4115 of 4122 Old Yesterday, 12:18 PM
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Right, GIK's naming the panel as a bass absorber is only true in a sense if it's straddling a corner. Otherwise it is just cutting down the reflection of the lower mids on up.

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post #4116 of 4122 Old Yesterday, 12:30 PM
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The "trap" in bass trap is quite literal. Bass frequencies check in, but they don't check out! The only way to achieve that is with a sealed absorber. If it's not sealed, it's not a bass trap. Placing a flat panel across a corner does not make it a bass trap.
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post #4117 of 4122 Old Yesterday, 12:56 PM
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I used two paragraphs for a reason, to indicate they were not the same thing.

My corner absorber is broad-band and is not actually flat but is most certainly not "sealed". It is off the corner a bit since OC-703 etc. absorbers work better a bit off the wall (need some wave velocity to provide better absorption). I am not sure what a "sealed absorber" is nor how broadband; what comes to mind is a resonator (a.la. Helmholtz) or just a cavity (tube) filled with absorbing material. If it is completely sealed I am not sure how it works (but have not tried to think about it). You can go to the NRC or any one of a number of sites to see the absorption curves for various materials. Most fall off at LF, natch, leaving you to make up with thickness. Or switch technologies... Diffusors get too large to be practical in most rooms at very low frequencies (but can be great for higher frequencies). Resonator structures, membrane structures, active systems, etc. etc. etc. Beyond the scope of this thread.

As for my system, I have (in today's dollars) about $12k in speakers and about $3k in room treatment (couple of dozen 2'x4' panels, 4" and 6", plus those thick corner thingies (<since you don't like the word "traps">, mostly kits, a cost-saving compromise between full DIY and commercial). Normally I would not spend (nor require) so much on treatment, but my wonderful big primed room dimensions got thrown all out of whack when we added a bedroom in the basement and I gave up about a third of my area to that and associated hallway. With both asymmetric walls and doubled-up dimensions I had to use a lot more than I had planned, and there is still a 30 Hz fundamental mode that dictates where I sit (at least until and unless I decide to add more subs, but the room is such that even that would be difficult).

It would be a very rare set of speakers in a very special room that would not benefit from some acoustic treatment.

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post #4118 of 4122 Old Yesterday, 12:56 PM
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@BDP24 You don't think you're getting a little hyperbolic?

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post #4119 of 4122 Old Yesterday, 02:37 PM
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Yeah Don, Helmholtz resonator is exactly correct. The term sealed means the sound that goes in does not come back out. It's really a lymph mass, I think it's called. The larger in diameter the trap, the lower in frequency it's effective. They've been built into the walls of recording studios for a long time. What Art Noxon at ASC did was make them free standing and independent of the room's structure, and in different sizes. Then RPG came along, and introduced audiophiles to diffraction---the random scattering of reflections, rather than their absorption. With those two devices, a good sounding room can be had. For a price, of course! There is a new high-performance Hi-Fi dealer in S. California, Brian Berdan, son of Brooks (R.I.P.) at Audio Elements, who did it right, building his main listening room 10' H X 16' W X 26' L. Those dimensions make for the most even, mild room modes possible.

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post #4120 of 4122 Old Yesterday, 08:40 PM
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Hmmm... A resonator is good at a fundamental and at multiples of that. I am guessing the trap is filled to provide deep nulls at a series of frequencies and still offer decent broadband absorption. Been a long time since my grad acoustics classes and my career took a different path... There are resonator structures that provide multiple resonant frequencies to provide a range of control.

Diffusion has been around a long, long time; pretty sure it predates RPG though they have made some popular products. For laymen Everest has a decent presentation. I'd love to add some diffusors but unless you DIY they are much more expensive than just velocity-based absorbers (and harder to make if you DIY). Arguably a better choice sonically.

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post #4121 of 4122 Old Yesterday, 09:17 PM
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Don, there is a lot of technical info on the ASC website about their Tube Traps, way more than I could remember. Art Noxon is an expert in the field, and was doing recording studios for years before he addressed the audiophile consumer market. I give RPG credit for targeting the audiophile market with their diffusors, not for inventing them! I found the RPG products unacceptably over-priced when I looked into them. Diffusors are pretty easy to make, and the formulas to do so are available on the www.
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I should read the ASC white papers again before saying more. read them years ago but it's been a while and I've forgotten most of it (I keep going back to basics; the math was so hideous in those grad acoustics classes that basic principles have -- mostly -- stuck with me). In case it is not obvious, I in no way shape or form consider myself an acoustics expert, just played with it a bit (theoretical and practical, college and work counts for something).

As for easy to make, diffusors are harder to make than throwing sheets over panels, but yah not that hard to make. There are some gorgeous examples in various DIY threads. I'm just lazy. Or maybe too many 60 - 80 workweeks. There are also a number of different schemes (equations) for implementing diffusors, each with their proponents and detractors. Sonically probably little difference to the average listener if it's QRD, PRD, MLS, or whatever. The biggest drawback is they need to be big (and deep) for lower frequencies, making them difficult to recommend behind panels for reducing the back wave. (I have in the primordial past worked in studios that had 4' to 8' deep or so diffusors.) They are my first choice sonically for most wall and ceiling treatments, but I didn't have the funds to buy nor time and resources to build back when I was putting together my new media room.

Note Maggies and most panels act like line sources from lower midrange up and so do not radiate much off the sides or top and bottom. That reduces the need for sidewall and ceiling treatment in most rooms (not mine, alas) and improves their relative efficiency/sensitivity compared to conventional speakers (the sound falls off a little less rapidly with distance).

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