Hi all,
I'm currently trying to see if I can target some low frequency bandwidth.
I don't care about things under 20hz, where I can't hear it anyways. But I am curious if it's possible to try to treat the 20~30hz range here. This is a rectangle room, one sub is on the side wall in the middle (takes care of harmonic first order stuff like a champ). The front two subs are not fully corner loaded but they are near corners and pulled out from the wall behind them. I could potentially put some tall treatment stacks behind these front two subs and stuff the corners maybe. The question is... with what, and from the floor to the roof, or any other idea, like rockwool blocks stacked up, or a frame of it, or another material?
Very best,
I'm currently trying to see if I can target some low frequency bandwidth.
I don't care about things under 20hz, where I can't hear it anyways. But I am curious if it's possible to try to treat the 20~30hz range here. This is a rectangle room, one sub is on the side wall in the middle (takes care of harmonic first order stuff like a champ). The front two subs are not fully corner loaded but they are near corners and pulled out from the wall behind them. I could potentially put some tall treatment stacks behind these front two subs and stuff the corners maybe. The question is... with what, and from the floor to the roof, or any other idea, like rockwool blocks stacked up, or a frame of it, or another material?
Very best,
Since passive absorbers require space proportional to wavelength you want ot absorb. ame with dipersion/diffraction based treatment.
Probably the easiest way todeal with LF modes is actively — use 4+ subwoofers.
dave
Probably the easiest way todeal with LF modes is actively — use 4+ subwoofers.
dave
Ok, figured it was going to be that direction, but wanted to ask to confirm. So rockwool is out of the question and won't help at all then.
Actively, I would have to run more subs in reverse phase, right?
Very best,
Actively, I would have to run more subs in reverse phase, right?
Very best,
yea im pretty sure they are referring to a dual sub array, probably the most effective solution as you "suck" the whole bass frequency range out of the room
another option that helped in my room .... using a cabinet/wardrobe with sliding doors as helmholtzresonator, usually cabinets with closed doors are tuned to sub 20Hz, imo one of the few option that do "something" tho compared to size helmholtzresontors are less effective than rockwool (but they can go more easly down in frequency)
another option that helped in my room .... using a cabinet/wardrobe with sliding doors as helmholtzresonator, usually cabinets with closed doors are tuned to sub 20Hz, imo one of the few option that do "something" tho compared to size helmholtzresontors are less effective than rockwool (but they can go more easly down in frequency)
rockwool will get you to about 80Hz at best. What happens if you reduce the amplitude of your subs?
Please apologize being pedantic but Rockwool won't get you to 80hz at most, it can be used to tame way lower.
The issue is about volume required/strategy to achieve it.
T.Hidley used what he call 'hangers' to do that in Non-Environnement control room principle. Those are semi rigid structure ( kind ofperforated cardboard, named isorel in France) covered both side with Rockwool, hanging from ceiling to floor and covering the entire perimeter of room, closely located next to each others and angled like sawtooth on side and back wall. Ceilind is also covered with them.
Being located on boundary where most mode highest pressure are too they offer some kind of acoustic resistance to sound wave travelling in them and tame down to 20hz.
The thing is they eat a large volume on already very large room. You could not attempt such treatments in a domestic room.
A kind of membranne resonator can have the same kind of effect: VPR.
It's a thin metal sheet covered with foam on one side and located on a frame close to boundary ( less than 15cm for the commercial one i've seen).
Reminds me of a plate reverb working backward... 🙂
Can be diy, some people got great results ( one Indian member in here (Audiothings) achieved same results as Hidley's room and is now commercially offer such design in way smaller rooms using VPR instead of hangers).
If interested check Gearspace there is thread about those VPR.
The issue is about volume required/strategy to achieve it.
T.Hidley used what he call 'hangers' to do that in Non-Environnement control room principle. Those are semi rigid structure ( kind ofperforated cardboard, named isorel in France) covered both side with Rockwool, hanging from ceiling to floor and covering the entire perimeter of room, closely located next to each others and angled like sawtooth on side and back wall. Ceilind is also covered with them.
Being located on boundary where most mode highest pressure are too they offer some kind of acoustic resistance to sound wave travelling in them and tame down to 20hz.
The thing is they eat a large volume on already very large room. You could not attempt such treatments in a domestic room.
A kind of membranne resonator can have the same kind of effect: VPR.
It's a thin metal sheet covered with foam on one side and located on a frame close to boundary ( less than 15cm for the commercial one i've seen).
Reminds me of a plate reverb working backward... 🙂
Can be diy, some people got great results ( one Indian member in here (Audiothings) achieved same results as Hidley's room and is now commercially offer such design in way smaller rooms using VPR instead of hangers).
If interested check Gearspace there is thread about those VPR.
It's all about dissipating acoustic waves in order to avoid standing waves, which creates the nulls and the peaks.
Using simple wideband absorbers, like rockwool you need at least 1/4 wave length of thickness.
For 30Hz, wave length is 343/30=11.4m and 1/4 is 2.8m.
This is not practical in a residential standard rooms unlesse you build the house to have all this space around the room.
The other option mentioned is to dissipate through resonators which are tuned to the frequency range you want to absorb and can be much smaller.
Quick mitigation is through precise equalization, although not perfect.
@krivium - Let me know what you think about the following understanding I have:
Standing waves are formed by the original wave and the reflected wave we have in closed rooms.
It will form peaks and nulls that don't move, thus standing waves.
This creates a horrible non flat low frequency response indoor.
In the peak listening positions (constructive standwaves), normally closed to the walls, where pressure is maximum and velocity is zero, it's possible to reduce the excitation power by precisely identifying the frequencies and attenuating them using an parametric eq (analog or DSP).
In the null listening positions (destructive standwaves), normally far from walls, there is nothing you can actively do, since the signal is lost (zero).
Standing waves are formed by addition and subtraction of acoustic waves.
Active filters can only multiply (amplify) and divide (attenuate).
Division (attenuation) is not the inverse function of addition, although you can reverse any number created by addition using the division function.
E.g.: 5+5=10 (sum). If I want to go back to the original 5, you can divide 10 by 2 = 5 (attenuate).
Using same thinking, multiplication (amplification) is not the inverse of subtraction but in this case, you cannot reverse a subtraction using multiplication in case the result is zero or close to zero.
E.g.: 5-5=0 (subtraction). There is no number that can multiply (amplify) 0 to go back to 5.
Using simple wideband absorbers, like rockwool you need at least 1/4 wave length of thickness.
For 30Hz, wave length is 343/30=11.4m and 1/4 is 2.8m.
This is not practical in a residential standard rooms unlesse you build the house to have all this space around the room.
The other option mentioned is to dissipate through resonators which are tuned to the frequency range you want to absorb and can be much smaller.
Quick mitigation is through precise equalization, although not perfect.
@krivium - Let me know what you think about the following understanding I have:
Standing waves are formed by the original wave and the reflected wave we have in closed rooms.
It will form peaks and nulls that don't move, thus standing waves.
This creates a horrible non flat low frequency response indoor.
In the peak listening positions (constructive standwaves), normally closed to the walls, where pressure is maximum and velocity is zero, it's possible to reduce the excitation power by precisely identifying the frequencies and attenuating them using an parametric eq (analog or DSP).
In the null listening positions (destructive standwaves), normally far from walls, there is nothing you can actively do, since the signal is lost (zero).
Standing waves are formed by addition and subtraction of acoustic waves.
Active filters can only multiply (amplify) and divide (attenuate).
Division (attenuation) is not the inverse function of addition, although you can reverse any number created by addition using the division function.
E.g.: 5+5=10 (sum). If I want to go back to the original 5, you can divide 10 by 2 = 5 (attenuate).
Using same thinking, multiplication (amplification) is not the inverse of subtraction but in this case, you cannot reverse a subtraction using multiplication in case the result is zero or close to zero.
E.g.: 5-5=0 (subtraction). There is no number that can multiply (amplify) 0 to go back to 5.
I think you got it but there is not only one spot where nulls/boost occurs, there is many located throughout the whole volume of room.
If the room is a perfect shoebox and walls are infinetly rigide then it's simple to model. In practice it's not that easy and can deviate from model as rooms have rarely a perfect shape and walls/building techniques can be effective membrane absorbers ( it's commonly used by acousticians to offer a degree of low freq absorbtion as well as sound isolation: dual leaf technique with plasterboard/limp membrane/plasterboard 'sandwich' and decoupling from other walls, floor and ceilling... a mouthfull isn't it 😉 ).
In fact rather than spot those are area where modes occurs.
Eq is futile imho. At best it will work on one defined point in space...
I will point you to some video by pm if you are interested on how we decide to locate passive treatment for low end in already existing room. Let me find it, can take a little time...
If the room is a perfect shoebox and walls are infinetly rigide then it's simple to model. In practice it's not that easy and can deviate from model as rooms have rarely a perfect shape and walls/building techniques can be effective membrane absorbers ( it's commonly used by acousticians to offer a degree of low freq absorbtion as well as sound isolation: dual leaf technique with plasterboard/limp membrane/plasterboard 'sandwich' and decoupling from other walls, floor and ceilling... a mouthfull isn't it 😉 ).
In fact rather than spot those are area where modes occurs.
Eq is futile imho. At best it will work on one defined point in space...
I will point you to some video by pm if you are interested on how we decide to locate passive treatment for low end in already existing room. Let me find it, can take a little time...
Yes, works only at a single listening point if that point is not in a null for a specific frequency.
No. It works at a single point bar none. 😉
If you use shelf it can work on wider area ( or people wouldn't complains amplifier missing eq) but specific notch or boost are only useful at the point where mic is located.
It's not a vid but gaves an idea of distribution in space of modes: there is 4 family of them, longitudinal, tangential, in height and oblique in a room. It makes for a bunch of them to take care... 16 iirc.
Another with animation ( great site to grasp the basics in a visual manner imho):
https://blog.soton.ac.uk/soundwaves/standing-waves/5-room-modes/
If you use shelf it can work on wider area ( or people wouldn't complains amplifier missing eq) but specific notch or boost are only useful at the point where mic is located.
It's not a vid but gaves an idea of distribution in space of modes: there is 4 family of them, longitudinal, tangential, in height and oblique in a room. It makes for a bunch of them to take care... 16 iirc.
Another with animation ( great site to grasp the basics in a visual manner imho):
https://blog.soton.ac.uk/soundwaves/standing-waves/5-room-modes/
Attachments
Last edited:
As I modeled some low frequency absorbers myself for future use with a SBA single bass array, it appeared to me that simply using any rockwool will not give you predictable results. You will need "lossy" rockwool with a reasonably low flow resistance, or hemp wool (more healthy and environmentally friendly) with a flow resistance of 3000-5000 Pa.s/m2. I came up with a plan that involves 20cm (8") of rockwool of 5000 Pa.s/m2 at 1.25 meters (50") from back wall, combined with the same 20 cm rockwool, but at 60cm from back wall. So two layers with two spaces between them, and total thickness 40 cm. This thickness is optimal when using 5000 Pa.s/m2 rockwool. Higher flow resistances are not neccesarily better. I used the acousticmodelling.com website.
Last edited: