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Worth investing in Helmholtz resonator to fix deep nulls at 41 and 82Hz?

polmuaddib

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I already read a similar post here where a member has very similar nulls. Like his, mine are modal in nature (i think) or combined. At first i tried calculating room modes using online calculators, but they probably can't be used for my room, since it is irregular. My front wall is 500 cm wide (16.4 ft), left side wall is 450cm (14.76ft), back wall is 490 cm (16ft) and right side wall is 480 cm (15.75ft). It comes very close to square, which i know is the worst possible shape. And my ceiling is around 320cm (10.5ft).
My main listening position is in the center of the room, and that is where I have my nulls. I found them using online tone generator and it worked much better then calculator. I walked around the room and found bass at those frequencies very loud in the corners and almost non existent in the middle of the room where i want it the most.
I opened a new post, because the similar post was about what could be done about the nulls in general, but i am more specific. I can't change my MLP much, speaker positions don't help significantly (actually, toeing them in helps a bit and putting them closer to the wall) and i don't want to cover my room with huge bass traps, don't like foam and all that studio looking acoustic treatment. Esthetics is important to me, not just because i want to please my wife (although i find nothing wrong in that either), but because i enjoy a nice looking room.
I have one subwoofer, i could buy another or two more and if that is the last option, i will probably do that. But i would much rather do without subs for 2 channel music. I have no problem with my MCH setup.
So, i was thinking of investing in Helmholtz resonators, because they can look very nice and even elegant. I could put some in the corners. I don't need perfection in room response. I don't need absolutely flat response, just to reduce those nulls.
I saw some youtube videos, didn't like the looks those HRs, read some papers and they focus a lot on math for those holes and strips for perfect frequency...
If it is not too hard to build them, i would do that, because it is very hard to buy them in my country since we are not part of the EU and our hifi market is limited. Poor country. But, i would buy them if that would be a much better solution then building them.
I was loooking at Vicoustic products and like all of their Bass trap solutions: Super bass extreme or Victotem ultra. I think, though, that Super bass extreme ultra is better because i can fit them in the corners easily.
Of course, if you think it wouldn't help much, i don't want to waste my money and time. I wish i believed in cables, because that would be easier and i could convince myself i have a tighter, stronger bass, but that's life.
Thanks
 

raindance

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I don't see how absorbers will fill in the nulls. How wide are they and can you actually hear notes disappear at those frequencies?
 

hege

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Invest in UMIK-1 microphone first, using tone generators is horrible and slow.

Helmholz resonators are very hard to tune and place correctly, and you need LOTS of volume. You can't just throw random boxes in corners and hope they work. I made 8 x 100L boxes (~60x50x35cm) myself and the effect in nulls and frequency was miniscule no matter where I tried them (it's so room dependent). Of course they reduced LF decay, but you can achieve that with normal broadband absorbers too, which I now use.

Moving speakers and LP is far more easy, as is using subs (you really need a microphone to properly integrate them).
 

pozz

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You can see a well-documented DIY project here: http://projects.briancofer.com/2015/04/building-helmholtz-resonator.html?m=1

It's largely not worth it especially when considering aesthetics. You can get a another sub instead and EQ at the listening position.

Also reserve the word bass trap for panel-type and Helmholtz type absorbers. Foam or insulation absorbers do not work at bass frequencies.
 

Absolute

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No, definitely not worth it. Better option to use multiple subs with bass-management.
You can use a minidsp with multi-sub optimizer software for automated integration with subs, if that's desirable. Read about it on minidsp.com.
 

patate91

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Corner bass traps will do better. They'll have an effect on all bass frequencies.
 

Hipper

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Do you notice a problem when playing music?

Nulls need to be not only less loud (lower dB) but also quite wide (centred on 41Hz but spreading to for example to 30Hz and 50Hz) for you to hear a problem. Very narrow nulls are unlikely to be noticed. The best way to see how wide and deep they are is to look at a frequency response graph. See my post #60 here, especially the last graph:

https://www.audiosciencereview.com/...in-room-measurements.13540/page-3#post-411614

For this reason I suggest you try an equaliser or DSP. It may not work of course but it might! If you are worried that 10dB will risk damage to your speakers then use some sort of global gain control to reduce the overall volume by 10dB.

I've never used subs but if I had my time again I would look at this as a solution. The beauty of using subs is you have probably got much more choice of where to place them in your room.
 

Duke

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No, definitely not worth it. Better option to use multiple subs with bass-management.
You can use a minidsp with multi-sub optimizer software for automated integration with subs, if that's desirable. Read about it on minidsp.com.

I Absolutely agree.

And three or four small subs will take up MUCH less space than effective low-frequency room treatments.

In this video clip acoustician Matt Poes compares bass traps with multiple subs. Note that he makes money off of room treatment installations, NOT off of subwoofer sales. He gets his point across in 32 seconds, from 37:37 (should be cued up) to 38:09:


https://youtu.be/shHY7EHY4MA?t=2257



My preference is for asymmetrical scattering of the subs, with no two in acoustically similar locations, such that each will interact with the room modes differently. So for example, I suggest that you don't place subs in two corners, because corners are acoustically similar locations. What you want is de-correlation in the bass region; correlation of the in-room bass energy is what results in major in-room peaks and dips. You may find it beneficial to set one of the subs 180 degrees out-of-phase with the others.

There are other placement strategies which call for symmetrical placement. Nothing against them, but they can be less practical to implement.

Ime bass management or DSP or an optimizing processor is not essential. The main thing is to get multiple bass sources intelligently distributed around the room. You can even dial them in by ear:

First adjust the gain of the sub(s). This makes the most difference.

Then adjust the low-pass filter frequency. This makes less difference.

Then adjust the phase (if available). This makes the least difference.

Cycle back through this sequence several times.

Setting the gain by ear may take a while. This is because a small difference in SPL makes a disproportionate difference in perceived loudness at low frequencies. This is predicted by equal-loudness curves, which bunch up south of 100 Hz. However this also implies that an improvement in in-room bass smoothness will make a disproportionate subjective improvement in bass quality.

For subs which end up closer to the listening position than the main speakers, you want either a steep high-pass filter or a low high-pass filter frequency or both. These subs run the risk of revealing their locations if they pass audible upper bass energy.

The subs do not have to be all the same. If you already have one big sub that goes deep, you can add two or three small ones which do not go as deep. But if you are trying to deal with an 82 Hz issue, then steep (4th order) highpass filters are imo a good idea.

If the subs are overlapping with the main speakers, reversing the polarity of one or more subs can help prevent too much energy in the overlap region.

Maybe just start with the one sub you have, position it far from the mains and asymmetrical relative to them, and see if you can make an improvement. Multiple subs will do a better job, and the location of any one will be much less critical than if you only have one sub.

Disclaimer: Unlike Matt, I am commercially involved with a multi-sub system.
 
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patate91

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I Absolutely agree.

And three or four small subs will take up MUCH less space than effective low-frequency room treatments.

In this video clip acoustician Matt Poes compares bass traps with multiple subs. Note that he makes money off of room treatment installations, NOT off of subwoofer sales. He gets his point across in 32 seconds, from 37:37 (should be cued up) to 38:09:


https://youtu.be/shHY7EHY4MA?t=2257



My preference is for asymmetrical scattering of the subs, with no two in acoustically similar locations, such that each will interact with the room modes differently. So for example, I suggest that you don't place subs in two corners, because corners are acoustically similar locations. What you want is de-correlation in the bass region; correlation of the in-room bass energy is what results in major in-room peaks and dips. You may find it beneficial to set one of the subs 180 degrees out-of-phase with the others.

There are other placement strategies which call for symmetrical placement. Nothing against them, but they can be less practical to implement.

Ime bass management or DSP or an optimizing processor is not essential. The main thing is to get multiple bass sources intelligently distributed around the room. You can even dial them in by ear:

First adjust the gain of the sub(s). This makes the most difference.

Then adjust the low-pass filter frequency. This makes less difference.

Then adjust the phase (if available). This makes the least difference.

Cycle back through this sequence several times.

Setting the gain by ear may take a while. This is because a small difference in SPL makes a disproportionate difference in perceived loudness at low frequencies. This is predicted by equal-loudness curves, which bunch up south of 100 Hz. However this also implies that an improvement in in-room bass smoothness will make a disproportionate subjective improvement in bass quality.

For subs which end up closer to the listening position than the main speakers, you want either a steep high-pass filter or a low high-pass filter frequency or both. These subs run the risk of revealing their locations if they pass audible upper bass energy.

The subs do not have to be all the same. If you already have one big sub that goes deep, you can add two or three small ones which do not go as deep. But if you are trying to deal with an 82 Hz issue, then steep (4th order) highpass filters are imo a good idea.

If the subs are overlapping with the main speakers, reversing the polarity of one or more subs can help prevent too much energy in the overlap region.

Maybe just start with the one sub you have, position it far from the mains and asymmetrical relative to them, and see if you can make an improvement. Multiple subs will do a better job, and the location of any one will be much less critical than if you only have one sub.

Disclaimer: Unlike Matt, I am commercially involved with a multi-sub system.

Strange that they both agree that bass traps are removing energy and that it is less efficient.

Runing 4 more amps is pretty ineficient in terms of energy
 

NTK

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Strange that they both agree that bass traps are removing energy and that it is less efficient.

Runing 4 more amps is pretty ineficient in terms of energy
Not when the 4 sub setup is optimized. Here is a link to a post in AVS Forum by Dr. Toole on the sound level benefits of using 4 smaller subs over 1 big sub in a sound field managed setup.
https://www.avsforum.com/forum/89-s...evel-home-theater-thread-56.html#post53711257

Below is a figure showing his room. In a two sub setup in his room, power demand is 200%. The SFM optimized 4 sub setup only need 137.6% power.

multi-sub.JPG
 

Duke

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Strange that they both agree that bass traps are removing energy and that it is less efficient.

Runing 4 more amps is pretty ineficient in terms of energy

If acoustic efficiency is the priority, a single large sub in a corner will be the most efficient... and will probably have the most lumpy bass response. As for amplifier electrical efficiency, that depends on the type of amp and how much power it draws in use, as well as on the number. (For the record, I use a single Class A/B amplifier for the four-sub system I make, with adding a second amp being optional.)

I don't see bass traps removing energy as being an issue; imo increased damping in the bass region is generally desirable. But bass traps may not be the most efficient use of resources in pursuit of high quality bass.

Notice this about the graphs that NTK posted in Post #11 above: Not only is the bass significantly smoother with four bass sources, but the variation from one seat to another is SIGNIFICANTLY reduced. So if you DO still need to apply some EQ, chances are you will be solving a problem at multiple listening locations, instead of making the bass better at one but worse at others.

Referring again to NTK's graphs, imo there might even be further improvement available from positioning the two subs front asymmetrically, like scooting one of them a foot or two closer to the center of the room. Then each of them would be a different distance from the nearest corner.

Earl Geddes (an original proponent of distributed multisub systems) has stated that the in-room bass smoothness goes up as the number of independent bass sources goes up. "Independent" in this context means "in acoustically dissimilar locations". So two subs can be roughly twice as smooth as one, and four subs can be roughly twice as smooth as two. Earl goes so far as to have one of his subs closer to the ceiling than to the floor, so that his bass sources are distributed in all three planes.
 
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patate91

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Not when the 4 sub setup is optimized. Here is a link to a post in AVS Forum by Dr. Toole on the sound level benefits of using 4 smaller subs over 1 big sub in a sound field managed setup.
https://www.avsforum.com/forum/89-s...evel-home-theater-thread-56.html#post53711257

Below is a figure showing his room. In a two sub setup in his room, power demand is 200%. The SFM optimized 4 sub setup only need 137.6% power.

View attachment 72558

Great read thanks.

But what I wanted to say is acoustic treaments consume 0 energy and produce way less heat.

I'm not against multiple subs. But I think, and I'm not an expert, that acoustic treaments brings a lot of benefits, cost less (diy route, and pretty easy). Once it's done correcting remaining issues is "easier" and more "focused".
 

patate91

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If acoustic efficiency is the priority, a single large sub in a corner will be the most efficient... and will probably have the most lumpy bass response. As for amplifier electrical efficiency, that depends on the type of amp and how much power it draws in use, as well as on the number. (For the record, I use a single Class A/B amplifier for the four-sub system I make, with adding a second amp being optional.)

I don't see bass traps removing energy as being an issue; imo increased damping in the bass region is generally desirable. But bass traps may not be the most efficient use of resources in pursuit of high quality bass.

Notice this about the graphs that NTK posted in Post #11 above: Not only is the bass significantly smoother with four bass sources, but the variation from one seat to another is SIGNIFICANTLY reduced. So if you DO still need to apply some EQ, chances are you will be solving a problem at multiple listening locations, instead of making the bass better at one but worse at others.

Referring again to NTK's graphs, imo there might even be further improvement available from positioning the two subs front asymmetrically, like scooting one of them a foot or two closer to the center of the room. Then each of them would be a different distance from the nearest corner.

Earl Geddes (an original proponent of distributed multisub systems) has stated that the in-room bass smoothness goes up as the number of independent bass sources goes up. "Independent" in this context means "in acoustically dissimilar locations". So two subs can be roughly twice as smooth as one, and four subs can be roughly twice as smooth as two. Earl goes so far as to have one of his subs closer to the ceiling than to the floor, so that his bass sources are distributed in all three planes.

About one sub usage does it holds for large speakers that, in the end, already have 2 subs.

I agree that bookself and less bass speakers one sub won't give the best result.
 
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polmuaddib

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Thank you all for replying and giving opinions and help. I appreciate. I have read Mr. Winer's post about bass trap myths several times. If i understood right, absorption helps at LF and i can use my corners for that. What i don't like is how large those bass traps are of his and, forgive me, but way too ugly.
It seems that more subwoofers is the way to go. But then i have to use AVR exclusively for music. But the biggest problem i have is integration of subs with my front speakers. Right now i have a cheap Mission m3as sub (paper bass) and my front speakers have Accuton (Ceramic) drivers. I tried integrating them several times, changing phase, volume and crossover and didn't like it. Somehow it sounds off. It, of course, could mean that i am biased or snobish or whatever, it is just in my head....
But then what's the point of all the acoustic treatment, anyway if not for the bass? Because, as i am reading and hopefully learning, above the Shroedinger's (cat) frequency, the loudspeaker dominates. I have no acoustic treatment but our furniture and when i clap my hands, there is no echo, in short i am extremely happy with 100hz to 20hz response.
Anyway, i found a distributor for Vicoustic in my country who is very polite and will bring his Vari bass product to my house to try. He will also bring a measurement mic to test. If we find the product useless i will not buy, we agreed. If i find 6db of improvement i am happy to invest.
 
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polmuaddib

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Invest in UMIK-1 microphone first, using tone generators is horrible and slow.

Helmholz resonators are very hard to tune and place correctly, and you need LOTS of volume. You can't just throw random boxes in corners and hope they work. I made 8 x 100L boxes (~60x50x35cm) myself and the effect in nulls and frequency was miniscule no matter where I tried them (it's so room dependent). Of course they reduced LF decay, but you can achieve that with normal broadband absorbers too, which I now use.

Moving speakers and LP is far more easy, as is using subs (you really need a microphone to properly integrate them).
I ordered a measurement mic with calibration file and still waiting. But it is so obvious a null that i don't need to measure it, it is more then 10db for sure. maybe 20db even. I tried moving speakers for a month now, believe me. But there are so few options that i can try and the result is similar. I changed three pairs of loudspeakers until i realised that my room is sucking LF.
 

patate91

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I ordered a measurement mic with calibration file and still waiting. But it is so obvious a null that i don't need to measure it, it is more then 10db for sure. maybe 20db even. I tried moving speakers for a month now, believe me. But there are so few options that i can try and the result is similar. I changed three pairs of loudspeakers until i realised that my room is sucking LF.

Yes REW + a mic will greatly help to find and correct room issues.
 
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polmuaddib

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I agree. This is only with regular mic and you can see that there is no bass below 100 hz.
 

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sarumbear

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I agree. This is only with regular mic and you can see that there is no bass below 100 hz.
I’m late to the thread but what are your speakers and have you calibrated subwoofer level? It’s very strange that you have such a slope. I can’t imagine any acoustical reason for such an almost smooth downwards slope. Something doesn’t add up.
 
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polmuaddib

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Hello, this is an old thread and I have since solved most of my problems.
That slope was probably not real, because I used a non measurement microphone.
I have now Soundworks XREF 20 mic, moved my speakers and MLP quite a bit, put some mini bass traps (small foam corner shaped) and while my FR is not perfect, I am happy.
This measurements is pure speaker, no sub. There are still some nulls, but most are narrow and maybe a more wide one around 30hz. I have two subs now, but use them with AVR only and Audyssey calibrated. I did not measure FR of speakers and subs through AVR.
Thanks for checking in.
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