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Post by ngallio on May 25, 2018 17:54:23 GMT
Hi all, first post here I was reading an interesting FB post from Mr. Winer about absorbing walls and their role in the acoustics of a room ( ) I have a related question: The room I use for mixing has been partitioned from a main room with all solid brick walls. The partition is with a drywall made of two 15mm gypsum boards with an air gap of 70mm. I'm attaching a very rough plan for it.  As expected the main modes that I have measured all pertain to the brick walls and not much to the space enclosed by the drywall. Since the drywall is quite transparent to low frequencies my question is: If I'm building an absorption device that works on the principle of pressure (such as a membrane absorber) would its effect be still useful if it is placed outside the listening position and on the brick wall in pos. B? The other question I have is this: If I was to use a velocity absorber (fiberglass or rockwool panel) would placing it in pos. A be effective regards the length mode of the main brick wall room? Could it be considered as a porous absorber with a large air ago behind it? (possibly ending up in the 1/4 wavelength area for the length mode of the brick room..) Thank you very much n. Attachments:
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Post by rock on May 25, 2018 22:15:08 GMT
I just read Ethan's post on FB and the idea I took away is leaky or less stiff walls reflect less since they pass sound through thereby reducing modal peaks in, let's call it the "primary" room. OK, so now you are thinking since the "secondary" room is receiving some sound from the primary room (through the wall), it might be a good idea to absorb some sound in there and that will influence the "primary" room. Well, I guess that might happen... but without testing or knowing for a fact, I would guess that treating inside the "primary" room to be significantly more effective. So I say no for the "B" question.
For if the space behind the wall counts for space behind a porous absorber like you have as "A", I also say no.
In general, your partition wall is a WALL, it's primarily a boundary that reflects sound even though it may pass some through. My 2 cents.
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Post by ngallio on May 26, 2018 6:55:38 GMT
I just read Ethan's post on FB and the idea I took away is leaky or less stiff walls reflect less since they pass sound through thereby reducing modal peaks in, let's call it the "primary" room. OK, so now you are thinking since the "secondary" room is receiving some sound from the primary room (through the wall), it might be a good idea to absorb some sound in there and that will influence the "primary" room. Well, I guess that might happen... but without testing or knowing for a fact, I would guess that treating inside the "primary" room to be significantly more effective. So I say no for the "B" question. For if the space behind the wall counts for space behind a porous absorber like you have as "A", I also say no. In general, your partition wall is a WALL, it's primarily a boundary that reflects sound even though it may pass some through. My 2 cents. Thank you, the second answer is obviously what I didn't want to hear but it makes sense..   I was in fact hoping I could use the small space for Helmholtz resonator or some other pressure device. The upper room is quite full and I need to tame some resonance/null around the 54Hz area where my porous absorbers seems to have very little effect |
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Post by Ethan Winer on May 27, 2018 17:52:18 GMT
I've actually seen a situation where a room with thin walls has two modes for one dimension: One for higher bass frequencies that the wall reflects, and another for very low frequencies that pass through the wall to a concrete foundation behind. But mostly you treat the room you have, not the next room over.
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Post by Hexspa on May 27, 2018 23:47:34 GMT
I just read Ethan's post on FB and the idea I took away is leaky or less stiff walls reflect less since they pass sound through thereby reducing modal peaks in, let's call it the "primary" room. OK, so now you are thinking since the "secondary" room is receiving some sound from the primary room (through the wall), it might be a good idea to absorb some sound in there and that will influence the "primary" room. Well, I guess that might happen... but without testing or knowing for a fact, I would guess that treating inside the "primary" room to be significantly more effective. So I say no for the "B" question. For if the space behind the wall counts for space behind a porous absorber like you have as "A", I also say no. In general, your partition wall is a WALL, it's primarily a boundary that reflects sound even though it may pass some through. My 2 cents. Thank you, the second answer is obviously what I didn't want to hear but it makes sense.. I was in fact hoping I could use the small space for Helmholtz resonator or some other pressure device. The upper room is quite full and I need to tame some resonance/null around the 54Hz area where my porous absorbers seems to have very little effect I've got some relatively poor decay time around 42Hz. It's not that bad, in practice. You should be fine so long as your other frequencies are tight.
If you're mixing, you still have spectrum analyzers. Regardless of use case you also can apply EQ below your Schroeder frequency. Also, using multiple subwoofers, and adjusting your speaker's relative responses, can help even your SPL.
I know this doesn't solve your decay problem but it's better to burn one tree than totally freeze and keep two.
Can't you mount the resonant absorber on the ceiling? Sorry, I know nothing about them. I'm just asking since you lack floor space. Again, speaking from ignorance, you can always try both locations, take measurements, and weigh your options.
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Post by ngallio on May 28, 2018 6:46:21 GMT
I've actually seen a situation where a room with thin walls has two modes for one dimension: One for higher bass frequencies that the wall reflects, and another for very low frequencies that pass through the wall to a concrete foundation behind. But mostly you treat the room you have, not the next room over. Thanks Ethan, It may be that I'm in the same situation... I'll post some measurements later. |
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Post by ngallio on May 28, 2018 6:49:29 GMT
Thank you, the second answer is obviously what I didn't want to hear but it makes sense.. I was in fact hoping I could use the small space for Helmholtz resonator or some other pressure device. The upper room is quite full and I need to tame some resonance/null around the 54Hz area where my porous absorbers seems to have very little effect I've got some relatively poor decay time around 42Hz. It's not that bad, in practice. You should be fine so long as your other frequencies are tight.
If you're mixing, you still have spectrum analyzers. Regardless of use case you also can apply EQ below your Schroeder frequency. Also, using multiple subwoofers, and adjusting your speaker's relative responses, can help even your SPL.
I know this doesn't solve your decay problem but it's better to burn one tree than totally freeze and keep two.
Can't you mount the resonant absorber on the ceiling? Sorry, I know nothing about them. I'm just asking since you lack floor space. Again, speaking from ignorance, you can always try both locations, take measurements, and weigh your options.
Thanks for chiming in, your advice is sound (no pun intended!) Unfortunately the ceiling is an old drop ceiling and I have no idea of the weight it can support before a visit from a carpenter. I really don't want it to collapse! |
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Post by Hexspa on May 28, 2018 17:50:50 GMT
I've got some relatively poor decay time around 42Hz. It's not that bad, in practice. You should be fine so long as your other frequencies are tight.
If you're mixing, you still have spectrum analyzers. Regardless of use case you also can apply EQ below your Schroeder frequency. Also, using multiple subwoofers, and adjusting your speaker's relative responses, can help even your SPL.
I know this doesn't solve your decay problem but it's better to burn one tree than totally freeze and keep two.
Can't you mount the resonant absorber on the ceiling? Sorry, I know nothing about them. I'm just asking since you lack floor space. Again, speaking from ignorance, you can always try both locations, take measurements, and weigh your options.
Thanks for chiming in, your advice is sound (no pun intended!) Unfortunately the ceiling is an old drop ceiling and I have no idea of the weight it can support before a visit from a carpenter. I really don't want it to collapse! That sounds reasonable |
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Post by rock on May 28, 2018 21:58:18 GMT
I agree, being cautious and getting the advice of a trusted expert is never a bad idea. From what I know about drop ceilings, the grid is usually installed fairly soundly. It's usually the panels that deteriorate over time and start to look bad, often from water leaks that leave a stain and a sag in the panel.
Since you do have a drop ceiling grid, it's a perfect opportunity to retro fit the grid with absorber panels; broadband for RFZ and bass trap style around the perimeter, and/or fill the space above with fluffy.
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