Cheap Bass Traps

MrBoogie

MrBoogie

New member
I came across these on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3278&item=7320958395&rd=1

They're so cheap, I think it might be worth trying them out. I'm wondering something though. Assuming they actually work, would I be able to tell a difference if I only get 2 of them and place them properly? Maybe this depends on the room? Or is there a simple test I could do with them to see if they are really absorbing bass as well as the description says?

Is anyone familar with those?

MrBoogie
 
Those look nice, but they're not really bass traps because they don't go low enough. Bass traps that size have are airtight and have a diaphragm and absorptive material. The absorber doesn't touch the memebrane. See Ethan's stuff:

www.ethanwiner.com/acoustics.htm

www.realtraps.com

The cheapest bass traps are rolls of pink insulation stacked up in the corners.
 
Ah yes, another acoustical product with Absorption Coefficients greater than 1.0 across the entire LISTED spectrum(almost), AND they are advertised as "PANEL/BASS TRAPS. On top of that, they say
1). The frame is on the "back" which is totally confusing..ie..on the back of WHAT? The panel? if so, then why do I see it? And if so, how would it make a MEMBRANE(Panel absorber) NOT to mention :
2)4" of absorption material(mineral), which is WHERE? If the frame is on the back, which I see in the picture as ON THE SIDES, :rolleyes: would imply that the 4" depth is contained within the frame, which MEANS, if this 4" thickness is BEHIND a membane, then it does NOT perform RESISTANCE ABSORPTION (to wavefronts within the room), so the high frequency coefficients are totally confusing.
:confused: :rolleyes: I wonder under what STANDARD these numbers were obtained or at what lab they were tested hmmmmm? Ask them to show you the Lab test results and what standard was used and I'll bet $100 they won't show you. :rolleyes:
To quote a well known and respected acoustician about absorption coeffiecients....
"in regard to what's provided in a lab report, capitalism sometimes rears it's ugly head there, too. "
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Personally, I refer to what my Dad always said.. I LIAR in any form is still a LIAR. AND I'm calling this manufacturer EXACTLY THAT!!! :mad:
apl wrote:
Those look nice, but they're not really bass traps because they don't go low enough. Bass traps that size have are airtight and have a diaphragm and absorptive material. The absorber doesn't touch the memebrane.
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Hmmm, you have me confused with this statement also. IF the specs actually reflected REALITY, their LISTED coefficient at 125hz is more than 1.0(which is highly doubtful), which is what I consider BASS frequencies. So what would NOT make this a bass trap? Moreover, MEMBRANE absorbers are NOT broadband, which their specs suggest they are. With membrane absorbers, the absorption occurs via the flexing of the membrane(energy to heat), they have a narrow absorption band, AND they can send other frequencies back into the room. I believe the absorption material within is to smooth out the resonant peak within the cavity, no? So how would they absorb at the frequencies listed??????Hmmm, can you please explain?

arrrrrggggggggggrrrrrrrrrr!!!!!
fitZ
 
apl said:
Those look nice, but they're not really bass traps because they don't go low enough. Bass traps that size have are airtight and have a diaphragm and absorptive material. The absorber doesn't touch the memebrane. See Ethan's stuff:

www.ethanwiner.com/acoustics.htm

www.realtraps.com

The cheapest bass traps are rolls of pink insulation stacked up in the corners.
Click to expand...

what type of insulation is used for the cheap bass traps in the corners?
 
notbradsohner said:
r-13 is probably fine for rolls in the corners
Click to expand...

Thanks. Anyone have any idea approximately what diameter these rolls come in? (I have a Home Depot 5 minutes away, but I'm lazy.) :)
 
I know I still have a lot to learn, but.......

What makes the Mondo traps so much better? They look similar....similar dimensions, both have a frame, with stuff in the middle, and stuff on the outside. I can't compare the actual designs since neither company is telling us exactly how their traps are built.

I realize the posted data could be completely bogus. As far as getting them to show me the lab results, I'm sure they could print up some nice "reports" that look like real lab test data, so that wouldn't do much good, even if they did show me.

I'm not trying to be argumentative. I'm trying to clarify. After reading just about everything at Ethan's site (and watching his demonstration videos), I still don't understand why Ethan's traps would be so much better....other than they cost more. Is the specific design/build of the Mondo traps posted so I can actually see what it is that makes them better? Is it because they are sealed? I can't find on the site where it says they are sealed.

What about the absorber touching the membrane? I can't find any information about either product that says anything about whether the absorber is touching the membrane or not.

One thing I did learn after reading Ethan's site, is that that buying a couple of those panels wouldn't do much good - I mean just to see if they actually work. He suggests on his site that it'd be better to fill your room with several of the smaller traps rather than only getting a couple of the bigger traps.....so I guess i'd have to get several traps to know if they're really working.
 
Even without a membrane, 4 inches of rigid fiberglass a couple inches off the wall is certainly going to absorb some lower frequencies. That said, whether or not this is technically a "bass trap" is probably debatable.
 
Well, given the fact that they more than likely should be called broadband traps than bass traps, and the numbers are almost certainly exaggerated, even if they are nothing but a frame filled with four inches of 703 fiberglass the price is not bad and they will do the job of four inches of 703 just like a DIY trap would.
 
filled with four inches of 703 fiberglass
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But HOW do you know. It could simply be batt type insulation, and completely bogus numbers. :rolleyes: THAT is the point. With shipping thats $56 for...maybe nothing.
fitZ
 
I've been doing some more research, and I think I might try building those "panels" out of 703, from ceiling to floor. Someone in another thread mentioned doing a 1'x4' panel instead of the usual 2'x4', and that sorta helps with my space issues. I know it won't be a membrane type absorber, which is why I assume(from reading several faqs) it's best to go ceiling to floor.

Thanks for all the input everyone. It seems like acoustic treatment is like everything else - you can't skimp on spending $$; but also the effectiveness is directly related to the amount of space the traps or other treatments use up.
 
Just a couple of comments on some of the other comments here.

1. The eBay item mentions that the panels are made from 4" thick mineral wool (actually the ad says "4" thick 8 lbs per cubic square foot acoustic mineral treatment"; what the heck is a cubic square foot?). There are spec sheets for 4" mineral wool that depict ratings higher than 1.00 (check out the Roxul spec at http://www.roxul.com/graphics/rx-na/canada/products/afb/afb_product_info.pdf). I can see a panel with a couple of inches of airspace behind it providing the kind of numbers depicted in the ad.

2. Mineral wool is typically much cheaper than 703. I've seen 2'x4'x2" pieces as low as $5-6 apiece, so to make your own panels that have 4" thick internal insulation would cost maybe $12 for the insulation, a few $ for 1x6 wood framing, and some attractive fabric, coming to a grand total of maybe $20-25 for a 2'x4' panel, same as that advertised.

Anyway, fwiw, I think the eBay ad is legit except for the bit about the back membrane piece which should actually lower the absorption rating rather than increase it if it covers the entire back of the panel.

Darryl.....
 
Boogs,

> What makes the Mondo traps so much better? <

We add a membrane to the front surface that 1) increases low frequency absorption over plain rigid fiberglass, and 2) reduces (intentionally) the absorption at mid and high frequencies. A few months ago we switched to an even better limp mass membrane material. This is not to say that plain rigid fiberglass is not effective. It surely is. But a lot of people prefer to buy bass traps from us because they want the best trap possible, and many are professionals who are too busy to waste their time cutting fiberglass and fabric and building frames.

--Ethan
 
DDev said:
Just a couple of comments on some of the other comments here.

1. The eBay item mentions that the panels are made from 4" thick mineral wool (actually the ad says "4" thick 8 lbs per cubic square foot acoustic mineral treatment"; what the heck is a cubic square foot?). There are spec sheets for 4" mineral wool that depict ratings higher than 1.00 (check out the Roxul spec at http://www.roxul.com/graphics/rx-na/canada/products/afb/afb_product_info.pdf). I can see a panel with a couple of inches of airspace behind it providing the kind of numbers depicted in the ad.

2. Mineral wool is typically much cheaper than 703. I've seen 2'x4'x2" pieces as low as $5-6 apiece, so to make your own panels that have 4" thick internal insulation would cost maybe $12 for the insulation, a few $ for 1x6 wood framing, and some attractive fabric, coming to a grand total of maybe $20-25 for a 2'x4' panel, same as that advertised.

Anyway, fwiw, I think the eBay ad is legit except for the bit about the back membrane piece which should actually lower the absorption rating rather than increase it if it covers the entire back of the panel.

Darryl.....
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Mineral wool prices vary regionally. Some places it is way cheaper than 703, others not.

You will note that the specs for accoustic tests specify a typical mounting type. Usually the tests for mineral wool or fiberglass specify a mounting that is a couple of inches off of the wall. Thus the numbers already reflect that. So the numbers do look exaggerated.

Still if it is really filled with four inches of 8pcf rock wool then it is a pretty good price, but once you count in the shipping you can likely do just as well if not better yourself.
 
We add a membrane to the front surface that 1) increases low frequency absorption over plain rigid fiberglass
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Hello Ethan. Are you saying the mondo's are membrane absorbers? If so, isn't the fiberglass for smoothing the frequency peak? If not, I don't understand what the membrane is for exactly.
fitZ
 
A membrane has a natural frequency that it wants to resonate at. Typically this has a high Q. Think of your parametric eq with a really sharp peak. The fiberglass in the trap adds damping. This reduces the height of the peak, but broadens it. Similarly, a bass reflex speaker cabinet acts as Helmholtz resonator. The port would have a very peaky frequency response at its resonance. The fiberglass adds damping to broaden the response.
 
Thanks apl. I understand the principles, but I am still trying to determine if INDEED the Mondo's are MEMBRANE ABSORBERS. IF not, then what is the membrane for. IF so, then mid and high frequencies are automatically kept from being absorbed, as they can't reach the fiberglass, no?
Intentional means by design, which Membrane absorbers by their very nature already do NOT absorb mid and High frequencies. Thats like the old PINK TUNA advertizing gimick :rolleyes: At the turn of the 19th century. to get people to start eating Tuna instead of Salmon, the Tuna industry bought thousands of dollars in full page advertizements in newspapers. They stated:

EAT TUNA!! Its better than Salmon because its "GUARANTEED NEVER TO TURN PINK!!!" :rolleyes:

Sorry Ethan, I know you better than that. Thats why I asked what these are, and what is the membrane for if they are NOT membrane absorbers. If they are, well....your learning the ad mans game. :(

fitZ
 
At the turn of the 19th century. to get people to start eating Tuna instead of Salmon, the Tuna industry bought thousands of dollars in full page advertizements in newspapers. They stated:

EAT TUNA!! Its better than Salmon because its "GUARANTEED NEVER TO TURN PINK!!!"
Click to expand...

I don't get it. ????
 
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