Need help with vocal booth/ room dimensions

[flyguyz]

I was planning on making a 4" thick panel of OC 703, 24" x 48".

Do you think that will be sufficient?

[Gregwor]

I was planning on making a 4" thick panel of OC 703, 24" x 48".

Do you think that will be sufficient?

Yep.

[flyguyz]

Here is the mdat file for the test run with 4" panels of 703 behind the monitors. I had to jack them up on 2x4's for now until I complete them with fabric and hanging wire.

https://www.dropbox.com/sh/zv577lct2po3 ... PnPla?dl=0

It appears to not have made a real impact on anything in the SPL graph, compared to the last test I ran after adding super chunks.

IM sure its helping tame reflections and echo in the room, but I still have some dips in the SPL id like to figure out how to attack.

Let me know what you think of the results, and what my next step forward should be.

Thanks

[Soundman2020]

It appears to not have made a real impact on anything in the SPL graph, compared to the last test I ran after adding super chunks.

Not so sure about that! Here's a comparison of your original baseline results, to where you are now:

FLYGUYZ--REW--FR-20..500-baseline-plus-4inch.png

That's quite a difference, I'd say! Your SBIR is gone, and your remaining issues are more typical of normal small rooms.

However, the superchunks are not as effective as they should have been. How did you build those? What size? What materials? Photos of the construction?

You also seem to have a flutter-echo issue, between your side walls (at least, the repeat period seems to correspond to the room width), so I'd be thinking about putting some panels on your side walls. You also have a couple of strong modal issues that might need more aggressive treatment, but first I'd like to see how you did those superchunks, and also get some side-wall panels in place, to deal with the flutter.

- Stuart -

[flyguyz]

Hey Stuart, Yes You are correct, in comparison from the first baseline test I ran I have come a long way! I was referring more to the difference between the last two tests I ran (one adding the superchunks, and the last one adding the 2 4” panels behind the monitors). Those two seem to be almost identical in the low end.

The super chunks are triangles of roxul safe n sound about 18” x 18” stacked up on each other from floor to the drop ceiling. There is one 3” panel of roxul standing vertically and then 15” x 15” triangles in front of that to make it 18 x 18

I attached a picture of the panels temporarily in place. I’ll be hanging them higher once wrapped and mounted

Do you think the side panels will help the dip around 114 Hz or is that a result of something else?

I’ll work on side panels next, should these be 4” also, same 703 material? Or should I use a 3” or 6” panel of roxul safe n sound instead?

[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! 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]

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! 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]

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?

[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:

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:

FLYGUYZ--REW--SP-80--3k--flutter-before.png

AFTER:

FLYGUYZ--REW--SP-80--3k--flutter-after.png

Major difference, clearly visible.

Same on the impulse response graphs, looking up to 180 ms
BEFORE:

FLYGUYZ--REW--FIR-180ms--flutter-before.png

AFTER:

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:

FLYGUYZ--REW--WF-70--5k--flutter-before.png

AFTER:

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]

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 test with my desk in position and the side panels still in line with the mic...

https://www.dropbox.com/sh/w5nbpc3jhia0 ... zh6_a?dl=0