If you haven't heard bass traps in your room ...

... then you need to try it!

For a long time I believed that bass traps were the ideal for the bass perfectionist, if you had the space for it or if your room is a doozy. As my room was small and quite good for bass, I wasn't sure I really needed them. My argument went like this: "My room is one big bass trap, how much will a few corner traps add? They will take up too much space and probably not make much of a difference."

Then I realised I had all the bits to throw them together. It took all of 15 minutes to put up some mattresses and couch cushions in the corners with louvre doors in front to avoid making the room dead.

The result? Wow. The best bass I've heard in my room by far. It sounds a lot more like outdoors bass, yet with the increased output and extension you get from a room.

I took a lot of measurements and did it step by step. Opening door/windows, progressively adding treatment. At this point I could measure but not hear a difference. Then I rigged up the 3 big traps and it was a big step up. This measurement captures it best:



Turns out the time domain does make a difference for bass. I say this because it's not hard to get the bass flat. I've done that before.

So I'm sharing this to inspire people to try it. My suspicion is that if everyone knew how good these things are, there would be two new groups among audio enthusiasts - those who have bass traps and those who wish they did!

Instructions here:
Take the free bass trap test!

And here is my result when I tried it:
My free bass trap test

Photos are in the blog posts but they aren't pretty!

I haven't made pretty versions yet.

4.65 x 3.9 x 2.85

I'm out of time ... Christmas shopping to do!

I see no reason why bass horns should be any different. They are monopole subs and I would expect them all to respond in the same way. The only issue I can see is that most horn subs like to fire into corners. Bass traps also like the corners. That might introduce a challenge in how you fit them both in.


I don't know the context of Bill's statement so it may be unfair to him to challenge it here in a thread he is probably not following. But I'll respond to the idea that bass traps don't work below 80 Hz.

You can see from the waterfall that I posted that clearly there is a difference below 80 Hz. In fact you can see an improvement down to about 20 Hz. I would not have been surprised had the traps only worked down to 100 Hz, I was intending to target 100 - 300 Hz and do the rest below that with EQ. I figured EQ can work below there well enough but above it would just require too many filters and not work well.

BTW, one comment about reading waterfalls.


I've shown it here. See how the modes ring out? I've highlighted on in particular. It's a good one to illustrate because there is only a slight peak, and yet in time it rings out much longer. If you were to EQ down the peak, the mode would still ring out in the same way because it's an acoustic issue can can only be fixed acoustically.

It's a visual trick, but you can be fooled into thinking that EQ fixes the time domain. EQ out a peak and it passes through the Z axis floor quicker, but in reality the decay rate has not changed. After EQ the bass decays at the same rate.

But if you look at the waterfall after the bass trap, the rate of decay is much faster. The decay is more even, because there is much less difference with the modal decay. This is the biggest tell tale sign of a measurement of a trapped vs untrapped room.

No doubt there are plenty of traps you can buy that are simply too small or not the best material.

If you are in doubt about if bass traps do work, then all you need to do is repeat the test I tried. You don't even need to measure or build anything. Just throw it together. Then come back and share what you find. I think for most that quick test will seal the deal.

Has anyone reading this used bass traps and measured them? If so please share! I'm always on the lookout for some good examples to show what they can do. In fact, I went ahead with testing my own because I wasn't very satisfied with what I could find. The measurements mostly didn't really confirm that they were doing much. Although, I should add that in doing it myself, I now know a bit more about what to look for. I was looking at the frequency response, but it appears the time domain is what best shows the improvement.

Thanks Ethan, I've seen that video and I'm glad you've put up still shots. I was pretty impressed with that result and was wanting to see stills. It's a great result although I wonder if the ringing around 40 Hz could be improved more. So I get the impression that the traps you use in there work mainly due to sheer volume. I wonder if some broadband corner traps in the 4 vertical corners would in fact reduce the 40 Hz ringing further. I also wonder if it's less critical down at that point. The response before treatment is just plain nasty.

Thanks Rader, I did my own test because I generally didn't find too many results. Doing my own test also showed me that the time domain is important, so listening is a important part of knowing how to interpret measurements. I can now look at waterfalls and have some idea of what the bass would sound like.

Placing your 2" panels out from the wall means they will work to lower frequencies.

IMO people make the mistake with HTs in making them too much like commercial cinemas. The two situations are very different. The surface to volume ratio is different. A large cinema needs a lot of absorption to avoid excessive reverb and echo, but treating all the walls does not make the space dead. A small room with all the walls covered will be very dead. So I prefer a less is more approach (except with bass traps) that balances concerns like imaging while retaining some energy and life in the room. So I think a mix of diffusion and selective absorption seems like a good choice.

I also think it's time to rethink speakers - to aim for constant directivity. Geddes speakers and the Econowave are getting people to start thinking differently here. Traditionally we've seen people simply putting in floorstanders - speakers which were designed for 2 channel audiophile music! With HT you see the same speakers, just more channels.

Tony, you added membrane traps?

Tony a membrane trap is basically a sealed box placed against a boundary. It has a thin front membrane and damping inside. It has a narrow bandwidth like a Helmholz resonator. Most bass traps are porous broadband.

I can't say too much because I haven't used or measured them. The idea is to use different ones with varying depths to spread out the effect. There is a BBC paper on a modular design for a membrane trap. They tried Helmholz versions as well but found they were a bit finicky. If you search for BBC modular bass trap it should turn up a link from Gearslutz. Interesting read. These membrane traps are also shown in Ethan Winer's early studio on his website

5kw fans? Is that for movies with a hurricane?! :P

Looks pretty good.

Ooops ... the different time scale is a mistake. At the time when I did those, I wasn't thinking about posting the results and I'm not sure why I changed the scale. Here's the corrected version.

Ethan, can you explain a bit about those last two charts?

So that last chart is a farfield response plot?

Mike, I can't see any measurements in that thread!