Tuned membrane traps

[RichardT]

I’ve got a big resonant peak in my studio at 70Hz and moving things around (including speakers and bass traps) doesn’t seem to help much, so I’ve just ordered a couple of Scopus T70 tuned membrane traps from GIK.

https://gikacoustics.co.uk/product/gik ... -trap-t70/

They seem to be just the job, with strongly peaked absorption at 70Hz, less than one octave wide. A couple of good reviews give me encouragement too - but also told me that ordering just one is not enough. Actual the ideal is 4 to 6 but that’s just too much for me at the moment.

These are pressure-driven traps so they need to be placed directly next to walls.

It’s a piece of luck that the peak of the resonance is at exactly 70 Hz, so one of the standard traps will work, and I don’t need to order a custom-made one with a user-specified resonant frequency.

I’ll let you know how I get on when they arrive. I’m hoping they will help with some quite significant smearing I get currently get in the bass at 70Hz or so.

[Martin Walker]

Good luck with those Rich, and do let us know how you get on.

I did investigate some adjustable tuned traps many years ago, but ended up getting a refund as they seemed less effective in my then room than straight forward wideband absorbers. However, if your problem is at exactly the same frequency as this design, they may hopefully prove more focused and useful.

Fingers crossed!

Martin

[Hugh Robjohns]

They seem to be just the job, with strongly peaked absorption at 70Hz, less than one octave wide. A couple of good reviews give me encouragement too - but also told me that ordering just one is not enough. Actual the ideal is 4 to 6 but that’s just too much for me at the moment.

It obviously depends on your room dimensions, and which kind of resonance mode is creating this 70Hz leak, but it is likely that there are several axes involved, and all will need treating, hence the 4-6 trap recommendation

These are pressure-driven traps so they need to be placed directly next to walls.

More than that! They will need to be placed in the right positions of the right walls to resolve the right modes. Placement is critical to their effectiveness -- but tuned traps can be extremely good solutions to well defined room resonances.

[RichardT]

They seem to be just the job, with strongly peaked absorption at 70Hz, less than one octave wide. A couple of good reviews give me encouragement too - but also told me that ordering just one is not enough. Actual the ideal is 4 to 6 but that’s just too much for me at the moment.

It obviously depends on your room dimensions, and which kind of resonance mode is creating this 70Hz leak, but it is likely that there are several axes involved, and all will need treating, hence the 4-6 trap recommendation

These are pressure-driven traps so they need to be placed directly next to walls.

More than that! They will need to be placed in the right positions of the right walls to resolve the right modes. Placement is critical to their effectiveness -- but tuned traps can be extremely good solutions to well defined room resonances.

Ah - thanks Hugh, that makes perfect sense.

Yes, placement is critical for these traps to work! I’m planning to do that just by listening to test tones at various locations to see where the resonance is strongest. Is there a better way?

[Martin Walker]

At 70Hz it ought to be fairly easy just to play a test tone and walk around your room to find where its energy is greatest, and then place the tuned trap there.

[DanDan]

Broadly tuned, like VPR are safe. But a highly tuned trap will have a different resonant frequency in different spaces. Even within the one room, proximity to corners, walls, will change it's fc. +1 Sine Waves are very useful for all sorts so acoustic investigation. Note that many plug ins have fairly lumpy frequency adjustment. SignalSuite by FaberAcoustical is smooth. REW has a Frequency Follows Cursor tick box option on the Gennie. When this is engaged sliding the cursor over say the Waterfall will generate exactly the same frequency as the issue on the graph. Plus is is a very smooth sweeper.

[RichardT]

Thanks Dan, by how much can the frequency shift?

I’ve tested out the Cubase test tone generator and it seems to work very well, so I’m planning to use that. I can manually enter frequencies and it responds well. The peak is between 69 and 72 Hz - and falls off more quickly at low rather than high frequencies, which luckily corresponds to the frequency response of the GIK trap.

[Wonks]

...The peak is between 69 and 72 Hz - and falls off more quickly at low rather than high frequencies..

I don't know anything your monitor setup, but are you sure that's not (at least in part) down to the monitors' output also falling off at lower frequencies rather than the room response?

When I went through a period of testing mic responses, the bass end of my Genelec M040s definitely added its own LF roll-off curve to the measured response from about 100Hz downwards, with a 10dB drop-off between 70Hz and 50Hz.

If you know yours are pretty flat to a much lower frequency than that then fine, but if not, just consider the monitor's response when looking at the room response figures.

[RichardT]

...The peak is between 69 and 72 Hz - and falls off more quickly at low rather than high frequencies..

I don't know anything your monitor setup, but are you sure that's not (at least in part) down to the monitors' output also falling off at lower frequencies rather than the room response?

When I went through a period of testing mic responses, the bass end of my Genelec M040s definitely added its own LF roll-off curve to the measured response from about 100Hz downwards, with a 10dB drop-off between 70Hz and 50Hz.

If you know yours are pretty flat to a much lower frequency than that then fine, but if not, just consider the monitor's response when looking at the room response figures.

Good point, Wonks. My speakers are quoted as -3dB at 45Hz so I think this is more likely a genuine room response.

[Wonks]

Good point, Wonks. My speakers are quoted as -3dB at 45Hz so I think this is more likely a genuine room response.

[DanDan]

I don't know how much the frequency of resonant traps changes with position. It is something I noticed when investigating drum tuning. DAW Gennies are OK, but the one in REW coupled with Frequency Follows Cursor is completely glitch free and has sub Hz resolution. Signalsuite by Faberacoustical is nice too. Have you got an Acoustic Measurement of this space. They can help find the mode(s) and locations.

[RichardT]

Well, they’ve arrived. I did some measurements with a sound meter and a test tone and identified some spots in an alcove where the volume was about 10dB louder than at the listening position. That was where the sound was loudest.

So I’ve put them both there. The first thing I did was to see how much acoustic energy they were picking up - it was a lot, judged by the amount they were vibrating.

Listening has been a revelation. The first impression was of something missing in the sound and of a drier sound than before, that’s normal when I get extra treatment. As I got used the new sound, I could hear a really significant difference in clarity right across the frequency spectrum. Plus instruments seem to go further down in the frequency range than they did before.

I’ve yet to redo my Sonarworks settings, but so far it’s already clear the new traps have been an a real success. I wasn’t expecting such a difference.

Highly recommended!

[Hugh Robjohns]

[mjfe2]

Well, they’ve arrived. I did some measurements with a sound meter and a test tone and identified some spots in an alcove where the volume was about 10dB louder than at the listening position. That was where the sound was loudest.

So I’ve put them both there. The first thing I did was to see how much acoustic energy they were picking up - it was a lot, judged by the amount they were vibrating.

Listening has been a revelation. The first impression was of something missing in the sound and of a drier sound than before, that’s normal when I get extra treatment. As I got used the new sound, I could hear a really significant difference in clarity right across the frequency spectrum. Plus instruments seem to go further down in the frequency range than they did before.

I’ve yet to redo my Sonarworks settings, but so far it’s already clear the new traps have been an a real success. I wasn’t expecting such a difference.

Highly recommended!

Thanks for the update! Do you have any more info about your room eg dimensions, materials, other acoustic treatment etc?

Are there any points in your room where 70hz nulls and is fixed by the traps?

I'm considering some of the T40 traps and am enthused to hear that as few as two are effective in your space!

[RichardT]

I don’t have the measurements (I’m away at the mo) but it’s a very long thin room! It will never be perfect acoustically, but it’s not too bad.

In terms of other treatment, I have some monster traps and corner traps from GIK and some auralex acoustic foam on the ceiling reflection points. Generally I’ve found that more treatment is better.

I don’t know if the tuned traps have affected any nulls, sorry - I concentrated on the listening position.

Good luck!