John Sayers' Recording Studio Design Forum Archive

Hello from Croatia! Thanks to everyone here for putting in so much effort, it has been really helpful for me to read all these awesome threads full of invaluable info!

I am in the process of renovating an old studio - mostly focusing on acoustics. No HVAC, soundproofing, etc. I will list the room dimensions, REW measurements and describe my plans, then I will post a couple questions -> any comments or help would be greatly appreciated. The project is fully DIY, and I'll be spending around 2k EUR.

Room dimensions are approximately: H=4m, W=8m, D=5.3m. Pictures are attached - It would be useful to check them out before reading further, as the actual dimensions are not that easy to describe in words only.

As observable from the pictures, the front wall is slanted on both L & R ends - it is "pulled inwards" a bit. The back half of the ceiling is lowered (using wooden planks) to the depth of the ceiling beam (the beam is ferroconcrete), which is around 40 cm deep. (How the beam looks like can be seen from the "hallway" picture - the ceiling is not lowered there). Between these planks and the original ceiling is nothing, just air. The front half of the ceiling is also lowered using planks, but these are sloped a lot (as can be seen from the "left wall and ceiling" picture).

All walls are concrete, except the front wall, which is -> 5cm fiberglass - a layer of porous concrete - air - porous concrete - 5cm fiberglass. On the other side is the live room.

Everything you see in the pictures will be removed - all new equipment goes in after the renovation. Except a couple of the left wall "Isolation boxes". Don't ask why Speaker orientation should (ideally) remain as is.

I've been researching different absorption approaches for weeks non stop, and after almost going crazy ( ) have decided to go for all porous, and then add other types of absorption later if necessary. I figure that all other methods of absorption require a lot more experience to implement properly, and are more hit/miss - although they can be a bit more effective.

I made a quick REW measurement, the files are attached. Not sure how useful this is, as I'll be looking for a better "microlocation" for the desk/speakers after I've tackled the absorption part of the job.

The plan (for now) is:
1. Two 4m high superchunks in both rear wall corners ("fluffy" 5 Pa.s/m2 fiberglass). Base will be 1m x 1m x 1,4m. Yes, It will cover half of the one window
2. The entire back wall will be covered by: 20 cm "fluffy", and 10 cm rigid mineral wool (around 15 Pa.s/m2). Total 30 cm. I would prefer not to go deeper if it won't be extremely beneficial to do so.
3. I plan on filling as much as possible of the air in between the planks and the ceiling with fluffy fiberglass.
4. The front wall fiberglass will be removed, and covered with a new 10 cm layer.
5. Diffusion will be achieved by using planks / slats covering the fiberglass and a big QRD or Skyline diffuser directly behind the desk.

My questions:
1. Do you think this will provide enough absorption for low frequencies? Any suggestions to optimize my idea?
2. Any help regarding diffusion would be really appreciated as my brain is totally worn out from exploring absorption already I'm looking for the optimal slat spacing. I usually prefer "deader" rooms, and mix rather quietly.
3. Is it smart to sacrifice the area directly behind the speakers for the skyline/QRD diffuser? Or is it better to use it for more porous absorption + slats?
4. Do you think I can get away with not doing much in terms of absorption to the L & R walls? The windows are not insulated that much, which is OK because they function as a bass trap (no neighbors). Maybe just some basic early reflection absorption? Which I guess won't be that early considering the walls are 8m apart

Thanks!!!!

Reserved for studio build progress pictures and measurements.

HI there " ReDRuM", and Welcome! Sorry about the delay in response, but there's a lot of activity on the forum right now, and not many folks helping out...

the actual dimensions are not that easy to describe in words only. ... As observable from the pictures, the front wall is slanted on both L & R ends - it is "pulled inwards" a bit.

OK, but the length of the studio is still the distance between the front wall and the back wall, at the longest point.

Between these planks and the original ceiling is nothing, just air.

Not so good. That's a resonant cavity. If you can, at least try to fill that with insulation.

Speaker orientation should (ideally) remain as is.

With that room shape, you don't really have any option! It's not good to have your speakers firing on the shorter axis of the room, but it's also not good to have a room that is not symmetric....

I've been researching different absorption approaches for weeks non stop, and after almost going crazy

Excellent! Then you are now a qualified studio builder! "Weeks of research on one single topic" and "crazy" are symptoms of this disease... and there is no cure...

have decided to go for all porous, and then add other types of absorption later if necessary. I figure that all other methods of absorption require a lot more experience to implement properly, and are more hit/miss - although they can be a bit more effective.

Porous absorption is, indeed, the best treatment for small rooms. And usually the only treatment it needs. Just LOTS of it.

1. Two 4m high superchunks in both rear wall corners ("fluffy" 5 Pa.s/m2 fiberglass).

You could go a bit higher with the gas flow resistivity.

2. The entire back wall will be covered by: 20 cm "fluffy", and 10 cm rigid mineral wool (around 15 Pa.s/m2). Total 30 cm.

3. I plan on filling as much as possible of the air in between the planks and the ceiling with fluffy fiberglass.

4. The front wall fiberglass will be removed, and covered with a new 10 cm layer.

You also need to get your speaker geometry fixed. The way it is right now is not good. There must be a large SBIR dip in the frequency response at the mix position.

5. Diffusion will be achieved by using planks / slats covering the fiberglass and a big QRD or Skyline diffuser directly behind the desk.

The room is not really big enough for diffusion. It would be if it was oriented along the long axis, as you'd have 8m length to work with, but the wya it is set up right now, there's not enough space between your head and where the diffuser would have to go.

2. Any help regarding diffusion would be really appreciated as my brain is totally worn out from exploring absorption already I'm looking for the optimal slat spacing. I usually prefer "deader" rooms, and mix rather quietly.

The correct acosutic response for a control room is neither "dead" nor "live", but rather plain old "neutral". It's very logical, and sort of obvious when you think about it, but way too many people never really consider the logic at all! Specs such as ITU BS.1116-3 and EBU Tech-3276 specify exactly what "neutral" means, in terms of frequency response and time domain response. Take a look at them.

3. Is it smart to sacrifice the area directly behind the speakers for the skyline/QRD diffuser? Or is it better to use it for more porous absorption + slats?

Not sure what you mean by "behind the speakers" here. IF you are talking about the space between the speakers and the front wall (the wall you are looking at while mixing), then there is no space! There's no gap there at all. Your room is way too small to be able to keep the speakers away from the front wall, so the only possible solution is to put them tight up against the front wall, with just a 10cm gap into which you put 10cm of porous absorption, in order to control the SBIR artifacts as well as possible. If you have your speakers away form the front wall, then you will be pushing the SBIR dip down into the low end, where it is far more noticeable and practically impossible to treat. With the speakers as close as you can get them to the front wall, that dip moves up into the lower mid range, where it is less noticeable, and easier to treat. So there's no "gap" behind the speakers.

4. Do you think I can get away with not doing much in terms of absorption to the L & R walls?

Have you checked with a mirror to be sure that you have no first reflection points there? If you do, then you need absorption in those.

The windows are not insulated that much, which is OK because they function as a bass trap

Why? Do you open them? Glass is not much of a bass trap, by itself. In fact, it is rather reflective. If you have a pane of glass, an air gap, then another pane of glass (which is what it looks like from the photos) then you have a resonant system, that might of might not be tuned to a useful bass frequency. But hopefully it is not tuned anywhere in the audible spectrum. It should be tuned at least an octave lower, where it won't cause issues.

- Stuart -

Hello!!

Thank you for the answer I've done a lot since the original post, but I would still appreciate some help, as I have a couple of things I would like to improve.

I'll describe what I've done until now first.

The top view of the outer shell can be seen in this wonderful drawing - OUTER SHELL LINK

1. FLUFF PARTY - The walls are all fluffed out, described in this PIC - TREATMENT

2. RIGHT WALL - Not visible in the picture -> Windows as original, with the area beneath them filled with 30 cm fluffy.

3. CEILING - To clarify what I've done with the ceiling - I removed some boards, and filled the ENTIRE center section of the ceiling area wth Fluff ->
PIC - CEILING FLUFF - The openings will be covered with some fabric only.

4. CURRENT SETUP - After a lot of experimenting / repositioning, I settled with the speakers (Adam S3A) close to the FW, vertical, on top of the console desk. Adam Sub10 in the center, almost touching the wall. The console desk is more/less empty for now (no equipment in - just a shell basically). PIC - CURRENT SETUP . Sorry for the crappy picture, my phone camera is broken.

5. THE RESULTS are these:

FR BEFORE / AFTER

DECAY BEFORE

DECAY AFTER

I think the results are quite good, except for the obviously longer decay below 50 Hz. I can live with that for now.

I'll post my questions in the next message.

My main issue is a "FRAGILE" SWEET SPOT, and the main culprit is the RIGHT SPEAKER.

RIGHT SPEAKER FR COMPARISON

The left speaker is much more stable. LEFT SPEAKER - SAME MIC POSITIONS AS ABOVE

The reason why I would really like to fix this RS problem is because things "fall apart" quite easily if I change some parameters. The most irritating dip is the one around 100 Hz. Reminder - the measurements were done with only the "shell" of the desk. If I put the wooden TOP SURFACE on the desk itself, everything goes crazy in terms of the FR. This is because the sub helps, and I guess this positive effect is lessened when the sub is "closed off". I concluded this because the same issues are observable if the sub is off. I have measurements of all of this, but I don't want to bombard you with 100 graphs I'd be happy to post anything you request, though. Also, this dip does change a bit if I move the speaker, so I guess it's at least in part SBIR.

So even though my current results are quite good, this setup would require of me to close the desk with some "sound transparent" board, take care not to close it off with equipment etc... Also, any other speakers (not connected to the sub) exhibit these SBIRs even more, my sweet spot is fairly narrow, etc...

The source of the 100 Hz issue is really hard for me to figure out. Maybe I'm going crazy, but it seems to me that adding absorption makes it worse, not better . I know that the discrepancy between the two speakers are most probably caused by the L R wall asymmetry. But, considering the offending frequency is fairly high (100 Hz), I'm hoping there is a way to find it and kill it


So, I would REALLY appreciate help with the following:

1. Maybe someone more knowledgeable and with more experience than me could recognize this pattern, and pinpoint the possible "culprit"?

2. If the above is impossible, could you please advise me how to approach the testing? I guess walking around with a FG panel doesn't make much sense for 100 Hz.

I know that "make the R and L walls symmetrical" is the best advice here, but this cannot be done so easily now. Also, the ISO boxes on the LW HAVE to stay - ISO BOXES PIC. At one point I tried removing the ISO box doors and filling the empty area with 50 cm fluff, but surprisingly there wasn't much change. I would have to be a lot more certain that the treatment I propose will help, before I suggest anything else to my "partners".

Thank you very much!!!

Firstly: If your time and energy is limited (as I believe it is), please ignore everything I ask in this message My main concern is the point addressed in the previous message.

Soundman2020 wrote:HI there " ReDRuM", and Welcome! Sorry about the delay in response, but there's a lot of activity on the forum right now, and not many folks helping out...

Understandable, no problem, I'm thankful for any help I can get

Soundman2020 wrote:Not so good. That's a resonant cavity. If you can, at least try to fill that with insulation.

Done, at least for the center part of the ceiling. Described above.

Soundman2020 wrote: "Weeks of research on one single topic" and "crazy" are symptoms of this disease... and there is no cure...

This is definitely one of the more mentally taxing periods of my life, I'm not exaggerating

Soundman2020 wrote:Porous absorption is, indeed, the best treatment for small rooms. And usually the only treatment it needs. Just LOTS of it.

You're the first acoustics person that described my room as small, I'm offended

Soundman2020 wrote:

1. Two 4m high superchunks in both rear wall corners ("fluffy" 5 Pa.s/m2 fiberglass).

You could go a bit higher with the gas flow resistivity.

I followed the advice that for thicker traps lower GFR is advisable... MY SCs are 1,5 meters at their thickest. This is what the online calcs say -
PIC LINK I know these calcs are not a substitute for experience, but experience I don't have

Soundman2020 wrote:The room is not really big enough for diffusion. It would be if it was oriented along the long axis, as you'd have 8m length to work with, but the wya it is set up right now, there's not enough space between your head and where the diffuser would have to go.

Same as above, I'm a bit puzzled as you're the first person with this opinion. If my listening position is at around 1,5 from the FW, this puts me around 3,4 m from the diffuser. There and back, 6,8m => around 20 ms. I was under the impression this was OK. What's worrying me more is that the diffuser on the BW will reflect low frequencies => more SBIR.

Soundman2020 wrote:The correct acosutic response for a control room is neither "dead" nor "live", but rather plain old "neutral". It's very logical, and sort of obvious when you think about it, but way too many people never really consider the logic at all! Specs such as ITU BS.1116-3 and EBU Tech-3276 specify exactly what "neutral" means, in terms of frequency response and time domain response. Take a look at them.

I will definitely explore these documents, thanks!!

Soundman2020 wrote:

3. Is it smart to sacrifice the area directly behind the speakers for the skyline/QRD diffuser? Or is it better to use it for more porous absorption + slats?

Not sure what you mean by "behind the speakers" here. IF you are talking about the space between the speakers and the front wall (the wall you are looking at while mixing), then there is no space! There's no gap there at all. Your room is way too small to be able to keep the speakers away from the front wall, so the only possible solution is to put them tight up against the front wall, with just a 10cm gap into which you put 10cm of porous absorption, in order to control the SBIR artifacts as well as possible. If you have your speakers away form the front wall, then you will be pushing the SBIR dip down into the low end, where it is far more noticeable and practically impossible to treat. With the speakers as close as you can get them to the front wall, that dip moves up into the lower mid range, where it is less noticeable, and easier to treat. So there's no "gap" behind the speakers.

Sorry, I explained poorly! By "behind" I meant "back wall". All clear now.

Soundman2020 wrote:

4. Do you think I can get away with not doing much in terms of absorption to the L & R walls?

Have you checked with a mirror to be sure that you have no first reflection points there? If you do, then you need absorption in those.

The "mirror trick" makes sense for high frequencies, right? For the lows this absorption is not really an obstacle. It will help, but lows will still bend around it. Is this correct? I'm thinking about my wonderful 100 Hz problem.

Soundman2020 wrote:

The windows are not insulated that much, which is OK because they function as a bass trap

Why? Do you open them? Glass is not much of a bass trap, by itself. In fact, it is rather reflective. If you have a pane of glass, an air gap, then another pane of glass (which is what it looks like from the photos) then you have a resonant system, that might of might not be tuned to a useful bass frequency. But hopefully it is not tuned anywhere in the audible spectrum. It should be tuned at least an octave lower, where it won't cause issues.

Heh, it seems to me that, in my magical room - opening windows, doors and adding absorption just makes the FR worse But whatever, I JUST WANT TO FIX THE DAMN RIGHT SPEAKER RESPONSE.

After I fix that, I will most probably work from home, as I cannot look at that damn room anymore

Thank you

P.S.: I have two bonus questions

1. Why are resonant cavities bad (in my example - double windows and the ceiling), and then we go and make Helmholtz resonators and panel traps, which are basically resonant cavities / panels. Is the dampening the crucial factor here? Critical dampening vs. underdampening etc...

2. Can an "underdamped" oscillator make the resonant frequency LOUDER in a room, or just prolong its decay?

Please ignore these questions if you don't feel extremely altruistic

Cheers!!!

Wow! Talk about LOTS of questions!

The top view of the outer shell can be seen in this wonderful drawing

First things first: Please post all your photos to the forum itself, instead of linking to off-site photos. It's one of the forum rules, actually... The reason is simply that off-site linked photos normally disappear after a while, because the linked site dies, gets move, goes away, changes structure, expires, etc. So people trying to follow your thread in the future won't be able to see what we are talking about, and it won't be any use to them.

4. CURRENT SETUP - After a lot of experimenting / repositioning, I settled with the speakers (Adam S3A) close to the FW, vertical, on top of the console desk. Adam Sub10 in the center, almost touching the wall.

There's some things right about that setup, and some wrong. One of the "wrong" parts is: " on top of the console desk". That will cause comb filtering and "roughness" in the mid range, artifacts in the lows and low-mids, as well as early reflections from the desk surface, plus possible vibration and early-early sound arriving at our ears before the direct sound from the speakers themselves. Another issue us the "Adam Sub10 in the center". It is usually better to have the sub offset to the left or right, not on the center line, for many reasons. Also, the mix position seems to be too close to the front wall.

5. THE RESULTS are these:

I can't tell much from just those graphs. You are only showing a very small part of the spectrum there, seemingly with too much smoothing, and only for one single speaker, or for only both speakers at once (not clear from the graphs or the explanations). I would need to see the actual MDAT file,

You are also doing your tests way too loud (over 110 dB ? ).... either that, or you did not calibrate REW correctly.

I would suggest that you should first calibrate REW properly, using a hand-held sound level meter, at a level of 76 dBC on each of your three speakers separately, so that you will automatically get 86 dBC with all of them (in the low end). Do a full set of measurements like that, as follows

Left alone
Right alone
Sub alone
Left + sub
Right + sub
Left + Right
Left + Right + Sub

Each of those tests should be run full-spectrum, starting at 15 Hz and up to 22 kHz.

Upload the resulting MDAT file to Dropbox, and post the link (the file will be pretty big)

I think the results are quite good, except for the obviously longer decay below 50 Hz. I can live with that for now.

So you never plan to mix bass guitar in your room? No keyboards either? No large kicks tuned low? No EFX?

My main issue is a "FRAGILE" SWEET SPOT, and the main culprit is the RIGHT SPEAKER. ----- The left speaker is much more stable.

I have no idea what those graphs show. The graphs don't even line up! They use different scales. There's no indication of how anything was set up there at all. No use, I'm afraid.

things "fall apart" quite easily if I change some parameters

What "parameters"?

Reminder - the measurements were done with only the "shell" of the desk. If I put the wooden TOP SURFACE on the desk itself, everything goes crazy in terms of the FR. T

Not surprising. That's exactly what I would expect from such a setup. You should first of all set up your speaker / mix position geometry correctly, then run the full set of REW tests, as above. Only then can you start thinking about what type of desk to use, how big to make it, what angles to use, what type of treatment / were to put it, etc. Right now you are doing things backwards: Starting with a desk and trying to make the speakers work with it. That ain't gonna work!

This is because the sub helps, and I guess this positive effect is lessened when the sub is "closed off".

Or more likely because the sub is in the wrong place....

I have measurements of all of this, but I don't want to bombard you with 100 graphs

I don't need 1 hundred! Just the set of seven, as above. And I don't need the graphs, either! I need the actual MDAT file.

Also, this dip does change a bit if I move the speaker, so I guess it's at least in part SBIR.

Not necessarily. The dip might not be "changing" at all: you might merely be looking at a different modal situation. There's no way to tell from a couple of FR graphs...

Also, any other speakers (not connected to the sub) exhibit these SBIRs even more, my sweet spot is fairly narrow, etc...

A sure sign that there is a problem with the geometry! First, set up the geometry correctly, and let's see how the response looks for that. Then we can worry about fine tuning that geometry. And only THEN can you think about what type of desk to build, and how to treat the room. See above.

The source of the 100 Hz issue is really hard for me to figure out

Probably floor bounce,or ceiling bounce. Typical of most small studios, or studios with geometry setup issues, or incorrect initial treatment. It might be SBIR, but there's no way to tell from a couple of FR graphs at the wrong resolution, with unknown calibration.

Maybe I'm going crazy, but it seems to me that adding absorption makes it worse, not better

Adding absorption WHERE makes WHAT worse? That's a big clue....

the discrepancy between the two speakers are most probably caused by the L R wall asymmetry.

Whoa!!!! Your WALLS are not symmetric???? Then you have MUCH bigger problems that speaker layout! You will need to take a few stpes back in construction here, and get your room symmetrical first. You cannot fix serious room asymmetry by fiddling with speaker positions. That's like trying to stop a speeding freight train by putting flower petals on the track...

But, considering the offending frequency is fairly high (100 Hz), I'm hoping there is a way to find it and kill it

You have a rather strange definition of "fairly high"! In reality, 100 Hz, is right in the middle of the LOW frequency end of the spectrum. Its somewhere between where kicks drums / floor toms live and where snares / high rack toms live. It's right in the middle of the bass guitar range, and the low end of the keyboard. It's way below most female vocals, and the majority of male vocals: you can apply a low shelving filter below 100 Hz to most vocal tracks without noticing ane real difference at all. So yeah, it's low, for sure. Definitely not "fairly high"! And DEFINITLEY not easy to treat: the wavelength is around 3.5 meters...

1. Maybe someone more knowledgeable and with more experience than me could recognize this pattern, and pinpoint the possible "culprit"?

Yup. Geometry. Start with the room geometry: the front half of your room MUST by symmetrical. You have no choice. If it is not symmetrical, the you can't get a clean, accurate sound stage, You can't get a properly centered, correctly balanced stereo image. There will be no "phantom center". So first of all, get your room geometry right, what ever it takes. Then when that is right, set up your speakers and mix position in the theoretically optimum positions (which is NOT the usual-but-totally-wrong "equilateral triangle" you see all over the internet....), and measure like that. Then adjust / tweak the position, to perfection (using REW, NOT your ears). The start thinking about how to fit furniture around that arrangement, without interfering with it.

2. If the above is impossible, could you please advise me how to approach the testing?

See above: Fix the room geometry, set up the speaker/mix position geometry, calibrate REW correctly, then do the set of seven tests.

I know that "make the R and L walls symmetrical" is the best advice here, but this cannot be done so easily now.

Then I have some really bad news for you....: Your studio also cannot be made usable so easily....

You're the first acoustics person that described my room as small, I'm offended

It's only 5 m long. The wavelength for a 20 Hz tone is 17.2m. So yeah, as far as sound waves are concerned, it is small... (Even worse, the height is only 4m! ... )

I followed the advice that for thicker traps lower GFR is advisable...

Not sure where you got that advice from ! Lower GFR is good for deep bass traps, but thickness isn't relate to GFR (well, it is for impedance, but that's a different story): The point is, you don't need to chose a lower GFR just because you want to make your trap thick. Rather, chose the GFR that is needed for the application, then make it thick enough to do the job.

MY SCs are 1,5 meters at their thickest. This is what the online calcs say

What "online calculators"? Did you check the impedance, or only the normal coefficient absorption?

If my listening position is at around 1,5 from the FW

... then it would be too close to the front wall! That would put it roughly in the quarter wave peak for all first order modes, and the null for all second order modes...

Like I said, FIRST get your room geometry correct THEN worry about furniture and treatment.

Same as above, I'm a bit puzzled as you're the first person with this opinion. If my listening position is at around 1,5 from the FW, this puts me around 3,4 m from the diffuser. There and back, 6,8m => around 20 ms. I was under the impression this was OK.

Ask D'Antonio and Cox what they think about that! If you really could get your head 3.4m from the diffuser, that would meet the first condition yes (minimum 3m), but firstly you can't, and secondly you'd then be limited to tuning your diffuser to a range where the wavelength of the lowest scattering frequency (which is one octave lower than the actual diffusion cut-off frequency) allows for at least three full wavelength before the wave reaches your head, or better still, 7 full wavelengths. ....

But that's all about the mix position: what about the couch at the back of the room? How far away will that be form the diffuser? Cna you get that one 3m way from the diffuser as well?

What's worrying me more is that the diffuser on the BW will reflect low frequencies => more SBIR.

Not if you build it right / locate it right...

The "mirror trick" makes sense for high frequencies, right?

Nope. All frequencies. They will all "bounce" off the wall when they hit it. Higher frequencies are more ray-like, and lower frequencies more "sphere-like", true, but there's no hard dividing line.

For the lows this absorption is not really an obstacle.

Really? Why?

It will help, but lows will still bend around it. Is this correct?

Nope! As long as the panels are reasonably large, and reasonable thick, with reasonably good, suitable absorption, then even there's pretty decent absorption down to low frequencies, especially for non-normally incident sound.

I'm thinking about my wonderful 100 Hz problem.

But I though you said that was "fairly high"?

But no, you won't be fixing that with absorption on your first reflection points. Because that's not what it is!

1. Why are resonant cavities bad (in my example - double windows and the ceiling), and then we go and make Helmholtz resonators and panel traps, which are basically resonant cavities / panels. Is the dampening the crucial factor here? Critical dampening vs. underdampening etc...

I'm not sure who "we" are in your example, but don't include me in that! I very seldom do Helmholtz resonators or panel traps... For several reasons.

Bu anyway, to answer your question: For those of "we" who do use them, Helmholtz resonators and panel traps are carefully designed, carefully tuned, and carefully located in the room to provide optimal treatment for a specific, well-identified issues, and they are correctly damped to absorb the problem optimally. Your windows and ceiling are randomly tuned, randomly located, not designed at all, and not damped... who knows WHAT they might be doing! For all you know, they could be amplifying a particular frequency that isn't even a problem, while NOT treating the frequencies that really are problems...

2. Can an "underdamped" oscillator make the resonant frequency LOUDER in a room, or just prolong its decay?

Both! very definitely. Have you ever played up and down the scale on a bass guitar, in an untreated room? Notice how some of the notes really BOOOOOM out, and ring long, while others don't? Those are notes that coincide with resonant frequencies in the room (likely modes). The exact same thing happens on a smaller scale with with any undamped resonant device. That's why many acoustical instruments have resonant cavities inside them, with ports to the outside world. If you take the rear shell of an acoustic guitar, it goes real quiet.... because there undamped resonant cavity that was amplifying the sound, is gone. The same happens if you stuff the cavity with fiberglass insulation.

Please ignore these questions if you don't feel extremely altruistic

Tonight, you got lucky! Now go out and buy a lottery ticket, before that luck runs out (and if you win, half is mine! )

- Stuart -

Soundman2020 wrote:Wow! Talk about LOTS of questions!

Thank you so much for taking the time!!

I'm on a trip so I can't address everything, just a couple important notes. I will provide the measurements you requested tomorrow.

1. I used Dropbox for pics because I couldn't figure out how to attach them in the text body. I'll explore some more. I'll at least add the used pictures later in a separate message - for posterity

2. There is no smoothing in any of the graphs I posted.

3. The "sweet spot" mix position is set like so that the triangle apex is cca 30-40 cm behind the mic, L and R speakers cca 2m apart.

4. The 110 dB "before" measurement was indeed done with an uncalibrated REW setup. Other measurements are OK.

5. I said I can accept the longer decay below 50 Hz simply because I don't know how to fix it now. Also, It seems to me from my measurements that when the sub is engaged the decay is disproportionately longer + I would like to focus on the 100 Hz issues first. If they can be separated

6. Different scales etc.... Right now I have the mdats for the L and R speakers with the mic in the above described position. MDAT L and R in sweet spot

7.

Whoa!!!! Your WALLS are not symmetric???? Then you have MUCH bigger problems that speaker layout! You will need to take a few stpes back in construction here, and get your room symmetrical first. You cannot fix serious room asymmetry by fiddling with speaker positions. That's like trying to stop a speeding freight train by putting flower petals on the track...

Sorry, again my poor explaining skills... Walls after treatment are as explained in my post after your first post. They are asymmetrical from the center in the sense that there are windows on the right wall, and ISO boxes at the base of the left wall... Otherwise they would be the same. My point was that the incoming audio waves definitely don't see them as being equal, I guess Hope it's clear what I meant now. Also, I don't see how I can make them 100% symmetrical unless I do some magic with the windows and remove the ISO boxes...

8. 100 Hz "fairly high" - What I meant is that its high enough for it to be easier to treat than say 35 Hz - using only porous treatment

9. My comment regarding "the mirror trick" and treating first reflection spots for low frequencies: What I meant was this -> My understanding is that for very high frequencies it is easy to treat the first reflection point - small patch of porous material does the job. For doing the same for low freqs - one needs to cover a much larger surface area, and has to use much thicker materials - the first reflection "spot" is not a "spot" anymore, but 3 m2 Probably related to diffraction and what not... I would like to be able to quantify these "more" and "larger" terms, but it's not so crucial for me right now. If you have some literature you can recommend from the top of your head, please do

10. Anyway... To get back on track -> I will do the measurements you requested tomorrow, and post them here. Hopefully I can at least fix my right speaker low frequency response

THANK YOU!!!!

Soundman2020 wrote:Tonight, you got lucky! Now go out and buy a lottery ticket, before that luck runs out (and if you win, half is mine! )

- Stuart -

Deal!!

I will do the measurements you requested tomorrow, and post them here. Hopefully I can at least fix my right speaker low frequency response

Let's add a couple more tests to the list:

After you complete the above, then physically swap your two speakers around, so the L ends up where the R is, and vice versa. Then repeat the following tests like that:

L alone
R alone
L + sub
R + sub
L + R
L + R + sub

The reason being: I'm wondering of there's a problem with the speaker itself. Maybe not, but this is the way to eliminate that as a possibility.


- Stuart -

Soundman2020 wrote:
...The reason being: I'm wondering of there's a problem with the speaker itself. Maybe not, but this is the way to eliminate that as a possibility.

No problem, I can do that. But I tested this already, it's not the speaker. Also, the problem remains similar with entirely different speakers.

Soundman2020 wrote:
Left alone
Right alone
Sub alone
Left + sub
Right + sub
Left + Right
Left + Right + Sub

Each of those tests should be run full-spectrum, starting at 15 Hz and up to 22 kHz.

Upload the resulting MDAT file to Dropbox, and post the link (the file will be pretty big)

Hi Stuart, I did the tests you suggested. The setup is as described previously. I also tried swapping the speakers, but zero difference in FR, it is not the speaker - no point in wasting your time with those MDATs I think...

Here is the MDAT file -> MDAT LINK

I know that the mic position is not perfect, so there's some weirdness happening in the highs when both speakers are measured together, but it shouldn't matter for figuring out my right speaker LF problems, I guess..

I have a bunch more measurements with only the R speaker - mic moved around, I can post those if you'd like.

Looking forward to your analysis! THANK YOU!

EDIT:

I'll post the MDAT with the different mic positions for R speaker only (no sub) anyway, download them if you think they can help - RIGHT SPEAKER MDAT . The descriptions are clear I think... "Mic 45cm L" means - 45cm left from sweet spot. So these basically are different mic locations from the left side to the right side along the horizontal axis - but only for the right speaker.

Great! The data looks good, and the measurements seem to have been done correctly.

so there's some weirdness happening in the highs when both speakers are measured together,

That's normal. Don't worry: it isn't really there! Or rather, it is but you'll never hear that. It is due to interference at the tip of the mic location, but your ears are spaced many cm to the left and right of that point, so don't worry about that.

What puzzles me is that the room is way too dead for that size space, yet there's still a lot of modal stuff going on! You should have an overall decay time of around 300ms for that size room, but yours is around 130. Less than half. It needs to be "lived up" quote a bit, but evenly across the entire spectrum.

On the other hand, there's a lot of what clearly seems to be modal activity going on, some of it quite powerful, despite the over-damping. You appear to have modal issues at the following frequencies:

25
34 ***
40 ***
49
57
61
63
80
84
91 ***
110 ***
128 ***
156 ***
176
204 ***
242
260
280
310
324
357
371
429
467
514
550

The ones I marked with asterisks are more significant.

It's unusual to be able to see modal stuff at such high frequencies, especially with a big room like that that is dead, and therefor should have a low Schroeder frequency! So this is puzzling.... Perhaps some of it isn't modal at all, and just looks that way... It might well be resonant "things" in the room. I would suggest emptying out hte room of everythgin except the speakers and mic, and doing a couple of tests like that, to see if that's what it is. I'm also suspecting that your L/R issue might be related to furniture, so it would be a good opportunity to test that issue as well.

Regarding that, here's a graph of the difference in frequency response between your two speakers:
So yeah, there's definitely a difference there! It's probably not the speakers themselves, as you already figured out, so I would suspect the following:

- Speaker geometry (location)
- Speaker mounting
- Furniture
Other objects in the room
- The asymmetrical design of the room itself (unbalance between window on right front wall, door on left front, plus windows on right wall / iso cabs on left, etc. To test this, fill the spaces where the windows were with absorption temporarily, and see if you get a change.
- Hidden asymmetric issues (things you can't see, hidden behind wall panels, ceiling panels, etc.) Have you checked that the insulation on the front wall behind each speaker is the same type/thickness? With the same backing behind it?
- Resonance in parts of the room itself (maybe some of those planks have resonant issues?)
- Treatment.
- The position of Venus with respect to Mars at sunrise on the vernal equinox in the year 1984....

So, I would try to get the room down to totally bare: Strip out all of the gear, furniture, and whatever else, leaving only the speakers on suitable heavy, massive stands, and the mic. Nothing else. Test like that, to see if some of the issues have disappeared. Also run continuous sweeps across the low end of the spectrum (15Hz-500Hz) at high volume, while you walk around the room (with ear protection) gently touching all bare surfaces with your fingertips, to see if anything is vibrating obviously.

OK, initial treatment: It's clear that you don't have enough bass trapping in there, so you need plenty of that, but you need to take care that it does not also suck out the highs and mids. I'd suggest superchunks in the rear vertical corners, with plastic of suitable thickness across the front face to keep the highs and mids in place. Make those BIG! At least 90cm wide/deep, if you can. Floor to ceiling, of course. And get rid of that paneling in the middle of the rear wall, behind the couch: replace it with thick absorption, not too heavy density. 6" of OC-703 would be great, if you can get it.

There's lots more going in in there, but let's get the low end under control first, and the issue with the L/R imbalance solved, then move on from there.

I have to say that overall the room is not too bad, and you have reasonably good response, but it can be better. Your room is probably a good candidate for digital tuning, but not yet. That's the final tweak...


- Stuart -

Soundman2020 wrote: I'd suggest superchunks in the rear vertical corners, with plastic of suitable thickness across the front face to keep the highs and mids in place. Make those BIG! At least 90cm wide/deep, if you can. Floor to ceiling, of course. And get rid of that paneling in the middle of the rear wall, behind the couch: replace it with thick absorption, not too heavy density. 6" of OC-703 would be great, if you can get it.

Hello! Thank you for you detailed analysis.

I'm on my phone right now, so I would just point out one thing -> You are suggesting superchunks and removing the paneling at the back... Have you perhaps missed my post where I posted a pic of current treatment? THIS POST

My back wall IS covered with 40 cm of fiberglass (panels removed), both corners with superchunks 4 meters high, 1,5 meters across.

Thank you!

This was the room after I removed the original "treatment" -> back wall panels + original (thin) superchunks.

BARE ROOM MDAT

and with original treatment

ORIGINAL TREATMENT MDAT

ReDRuM wrote:

Soundman2020 wrote: I'd suggest superchunks in the rear vertical corners, with plastic of suitable thickness across the front face to keep the highs and mids in place. Make those BIG! At least 90cm wide/deep, if you can. Floor to ceiling, of course. And get rid of that paneling in the middle of the rear wall, behind the couch: replace it with thick absorption, not too heavy density. 6" of OC-703 would be great, if you can get it.

Hello! Thank you for you detailed analysis.

I'm on my phone right now, so I would just point out one thing -> You are suggesting superchunks and removing the paneling at the back... Have you perhaps missed my post where I posted a pic of current treatment? THIS POST

My back wall IS covered with 40 cm of fiberglass (panels removed), both corners with superchunks 4 meters high, 1,5 meters across.

Thank you!

Bump