John Sayers’ Recording Studio Design ForumAn archive of johnlsayers.com, 2003–2022

Need help with vocal booth/ room dimensions

Started by flyguyz on 23 April 2018. 139 replies, 2018–2019. In the Library under Build diaries. Key posts in this thread.

Originally posted at johnlsayers.com, topic 21547.

Soundman2020
The super chunks are triangles of roxul safe n sound about 18” x 18”
OK, that would explain why they aren't doing as much as I expected: they aren't as big as I thought they were. For superchunks, I usually go with 36" sides, or 24" minimum. 18" is not very deep. What you could do to improve the effectiveness of those traps at low frequency is to add a 4" layer of very light density insulation, such as Pink Fluffy, or even polyester (around 20 kg/m3) in front of them, with a 4" empty air gap in between. That would increase the absorption at low frequencies. Also, it seems you only have those two traps in the front corners? Nothing in the back of the room? I'd suggest doing two similar traps in the rear corners, and also covering the rest of the rear wall with something like 6" of insulation, or if you really want good bass low-end acoustics, then put hangers across the rear wall. In the meantime, to double-check the flutter echo thing, use the panels that you have behind the speakers right now on the side walls, exactly in line with the location of the mic, and do a REW test like that. That will confirm that the issue I'm seeing really is flutter from the side walls.
Do you think the side panels will help the dip around 114 Hz or is that a result of something else?
That's probably the typical studio "floor-bounce", coming from reflections off the floor mid way between the speakers and the mic. It's actually not such a big deal as some people imagine, since it has a positive psycho-acoustic effect: your brain uses that to help interpret the acoustics of the room. Not worth worrying about at present. The desk and chair will change that, and probably some of the other treatment too... Also, from that latest photo I noticed that you have a drop ceiling! :shock: What's above that? That is not the hard boundary of the room: the hard boundary is above that. You need to know how far above, and what is in the cavity up there... EDITED TO ADD: You really do need to get those longer cables for your speakers! The desk needs to go into its final position, and it can't right now, due to the short cables. - Stuart -
flyguyz
Soundman2020 wrote:
The super chunks are triangles of roxul safe n sound about 18” x 18”
OK, that would explain why they aren't doing as much as I expected: they aren't as big as I thought they were. For superchunks, I usually go with 36" sides, or 24" minimum. 18" is not very deep. What you could do to improve the effectiveness of those traps at low frequency is to add a 4" layer of very light density insulation, such as Pink Fluffy, or even polyester (around 20 kg/m3) in front of them, with a 4" empty air gap in between. That would increase the absorption at low frequencies. I actually have 6” roxul from floor to ceilin. In the rear of the room. That has been there since my baseline test. I used hen remaining roxul I had leftover for the super chunks and they are in the front and rear corners of the room. Also, it seems you only have those two traps in the front corners? Nothing in the back of the room? I'd suggest doing two similar traps in the rear corners, and also covering the rest of the rear wall with something like 6" of insulation, or if you really want good bass low-end acoustics, then put hangers across the rear wall. In the meantime, to double-check the flutter echo thing, use the panels that you have behind the speakers right now on the side walls, exactly in line with the location of the mic, and do a REW test like that. That will confirm that the issue I'm seeing really is flutter from the side walls. just to clarify, should I place the panels at the reflection points on the side walls (using mirror) or are you saying to put it in line with the microphone (horizontal axis)?
Do you think the side panels will help the dip around 114 Hz or is that a result of something else?
That's probably the typical studio "floor-bounce", coming from reflections off the floor mid way between the speakers and the mic. It's actually not such a big deal as some people imagine, since it has a positive psycho-acoustic effect: your brain uses that to help interpret the acoustics of the room. Not worth worrying about at present. The desk and chair will change that, and probably some of the other treatment too... Also, from that latest photo I noticed that you have a drop ceiling! :shock: What's above that? That is not the hard boundary of the room: the hard boundary is above that. You need to know how far above, and what is in the cavity up there... I explained this earlier in the thread, There are I beams and conduit etc above the drop ceiling and then a weird square wave type ceiling, I believe I attached a picture somewhere in This thread EDITED TO ADD: You really do need to get those longer cables for your speakers! The desk needs to go into its final position, and it can't right now, due to the short cables. cables are arriving Wednesday. I will definitely redo the test once that is situated Also thinking about moving the mic up closer to 38% length and running test to see if anything improves - Stuart -
Soundman2020
just to clarify, should I place tre panels at the reflection point on the sidebar wall (using mirror) or are you saying to put it in line with the microphone (horizontal axis)?
In line with the mic, horizontally. That's where the flutter will be strongest. This isn't about reflections from the speakers on the side walls and back to the mix position, but rather reflections that are happening between the side walls themselves, rushing back and forth across the room. This is just a test with those panels, to confirm the diagnosis. I might be wrong about it, but it looks very much like side-to-side flutter echo. In fact, if you stand in the middle of the room and clap your hands sharply, you should be able to hear that as a sort of hollow "ziiiinnng" sound. It probably occurs all along the side walls, wherever you go in the room, so this test with the panels in line with the mic should show if that's what it is that I'm seeing. It's not the final location of where you need panels: just to check if that's the issue or not. - Stuart -
flyguyz
Thanks Stuart. I will run that test later today!
Soundman2020
For better effect, you could "offset" the panels a bit, so that the one on the left is a bit more forward than the one on the right. In other words, set them up so that the BACK edge of the panel on the left lines up with the mic, and the FRONT edge of the panel on the left lines up with the mic. That covers twice as much wall area, so it should have a more noticeable effect on flutter. - Stuart -
flyguyz
Soundman2020 wrote:
For better effect, you could "offset" the panels a bit, so that the one on the left is a bit more forward than the one on the right. In other words, set them up so that the BACK edge of the panel on the left lines up with the mic, and the FRONT edge of the panel on the left lines up with the mic. That covers twice as much wall area, so it should have a more noticeable effect on flutter. - Stuart -
I used the offset method and ended up with the following results... https://www.dropbox.com/sh/1j1b8m354qwh ... 1DFMa?dl=0 I don't think these are the results we were looking for... test results look very similar from the last test ran. Im going to move my desk position and run another test. What do you suggest next?
Image not preserved: panels on side wall in line with mic.png
Soundman2020
I don't think these are the results we were looking for... test results look very similar from the last test ran.
Please don't get so hung up on frequency response graphs! I really wish that REW would NOT show that one by default: it isn't even the most important parameter of the room acoustic response... - Stuart -
Soundman2020
test results look very similar from the last test ran.
Here's you REAL results... the ones you SHOULD have been looking for. You wont find flutter echo in frequency response, because it doesn't have anything to do with frequency response! It's a time domain issue, not a frequency domain issue. Here's the difference in decay times. Green curve is before you put the panels on the side walls, blue curve is after:
Image not preserved: FLYGUYZ--REW--RT--flutter-before-green--after-blue.png
I'd say that looks rather different! It's a HUGE improvement, in fact. It's even more clear in the "before" and "after" spectrogram plots, looking at the region between 80 Hz and 3 kHz. BEFORE:
Image not preserved: FLYGUYZ--REW--SP-80--3k--flutter-before.png
AFTER:
Image not preserved: FLYGUYZ--REW--SP-80--3k--flutter-after.png
Major difference, clearly visible. Same on the impulse response graphs, looking up to 180 ms BEFORE:
Image not preserved: FLYGUYZ--REW--FIR-180ms--flutter-before.png
AFTER:
Image not preserved: FLYGUYZ--REW--FIR-180ms--flutter-after.png
Your decay time improved by nearly 30 %!!! That's pretty major, considering all you did was put a couple of small panels on the side wall... And the most obvious of all: waterfall plots, 70 Hz to 5 kHz. BEFORE:
Image not preserved: FLYGUYZ--REW--WF-70--5k--flutter-before.png
AFTER:
Image not preserved: FLYGUYZ--REW--WF-70--5k--flutter-after.png
Glaringly obvious improvement!
I don't think these are the results we were looking for...
I disagree; :) this is DEFINITELY the results we were looking for! A classic text-book case of flutter echo, with a classic simple solution. Crystal clear. So the diagnosis is confirmed: I was correct.... you have a flutter echo problem. This should be very audible in the room, of you do the test I suggested. Clap your hands sharply at the mic position, where the panels are on the side walls, then take a few steps back, away from where those panels are, until you have bare walls on both sides, and clap your hands again. You can certainly hear the difference. - Stuart -
flyguyz
:shock: :oops: Wow thanks for breaking that down for me! I was misunderstanding what we were trying to correct! I thought you were giving me a solution to help resolve the dips in the frequency response! And yes, you can hear the ringing noise if you clap your hands in the room as you suggested. With the ear test, before and after, it definitely sounds better in the room. I am not doubting that the panels will help with taming the echo in the room, I was just focused on the dips in the frequency response graph and searching for ways to improve them. I planned on placing additional panels on the side walls at the reflection points (using mirror trick), and these results definitely prove that they will help a ton! However, I am still wondering if anything else can be done to resolve the dips in the frequency response graph, or should I just not focus on that anymore and work on taming the rest of the flutter in the room? Thanks again Stuart, I appreciate the help, advice, and acoustical knowledge you have been sharing with me along this journey. I truly would not be where I am today with this build if it weren't for this forum, specifically you and gregwor's help! I have enough material left to make 4 more panels, I was going to keep 2 behind the monitors, and then place 2 on each sidewall at the reflection points. I'll post results once I build and run the test. What would you suggest the next step be?
flyguyz
Here is an updated mdat file with the 1st reflection panels added to the side walls. The panels are 2' x 4' x 4" and are placed on the wall with a 4" air gap. I put 2 panels side by side on each wall to catch reflection from L & R monitor. https://www.dropbox.com/sh/abql3urgdhx9 ... YtmOa?dl=0 Please review and provide some feedback. Curious to see what you think of the results and what my next step should be. Thanks!
Gregwor
Can you please post pictures of the treatment each time so that we can see exactly what you did. Strangely, the low mids improved in the mdat, but the upper mids seemed to get worse. There was a slight improvement on the impulse response when I was expecting more. You seem to have a strong reflection ~2.855ms later than the initial transient hits your microphone. So, do the string trick and add this amount to the distance from your speaker to your microphone:
Image not preserved: Distance.png
Let us know where that reflection is coming from. Also, is there anything you have changed other than ADDING panels? I'm wondering if since you said you added two panels on each side, maybe the frames around the insulation are causing other reflections. Without pictures, it's hard to say. Greg
flyguyz
Hey, what do you mean by the string trick? You lost me on that last request of adding distance from speaker to mic. Here are pictures of the panels... they are setup the same on the other wall. Do you think I should remove one of the panels and only worry about catching reflection from the monitor from the opposite side of the room? For example, on the left wall, only have a panel in place where the right monitor woofer/tweeter reflection is seen?
Image not preserved: IMG_1349.JPG
Gregwor
Hey, what do you mean by the string trick? You lost me on that last request of adding distance from speaker to mic.
A few helping hands will make this go really fast: - measure the distance from the acoustic axis of your speaker to the tip of your measurement mic (write this down). - add the distance I gave you to that measurement. - now, mark on a string that total length. That is the distance that first reflection is traveling. - tape, or have your helping hands hold the string so that one end is at the acoustic axis of the speaker and the other is at the tip of the measurement mic. - take the string slack and find out what possible locations the sound would have bounced off of to travel that distance. It's obviously places like the ceiling, floor, walls, desk/other furniture. The goal is to stop that reflection from hitting your mic so loudly, or at all!
Here are pictures of the panels... they are setup the same on the other wall. Do you think I should remove one of the panels and only worry about catching reflection from the monitor from the opposite side of the room? For example, on the left wall, only have a panel in place where the right monitor woofer/tweeter reflection is seen?
When you did the "mirror trick" to determine where your speakers would be bouncing off the side walls, did you happen to put the absorption panels in a place that might allow the vertical framing of the panels to reflect the sound at your head instead of hitting the insulation? Greg
flyguyz
I don't believe so, but Ill double check. Thanks for the string explanation also.