John Sayers' Recording Studio Design Forum

Hi All,

I am moving over from the Construction forum to the Acoustics forum to finish my room with some more excellent advice from all on this board.

So as you can see from the pics I am about to hang my panels.

A little info first...

The room is 16'10" x 14'9" with a ceiling height of 8'4". I will be using a sub from time to time to check the bottom end.

At the moment as can be expected the room has a great "ring" to it. There is a real ring at 77.620Hz, 128.80Hz, 199.4Hz, 218Hz. These numbers are what I came up with when I manually swept from 20Hz to 20Khz with a sine wave so they are rough but those freq's really ring loud.

As you can see I have put large bales of R-13 in the 4 corners JUST TILL FRIDAY when my bass traps arrive. I need to work this week so I used the R-13 as a quick fix bass trap extravaganza. The bass traps I ordered are 8' thick for the front corners bottom resting on the ground, then 4' thick on top of those to the ceiling. I also have another 2 4" thick bass traps for the back top corners.

My panels are 2' x 4' and 2" thick. I have eight of them. I also have 8 Auralex MetroFusors Diffusers which are 2' x2' and I plan to use them on the back wall.

So now that you have an idea of my materials and my space what do you suggest I do?

I am thinking...

1. 3 x panels on the front wall behind the speakers.
2. 2 x panels on each side wall starting from the first ER point.
3. 1 x panel on the ceiling above the listening position. Not sure whether to angle them 12 degrees or not.

Problems I foresee are the piano and the AC unit. I can move the piano further towards the back of the room for starters. Not much I can do about the AC unit.

These panels were made to order so I can order some custom sizes for between the piano and the AC I suppose.

What advice please before I start hanging.

Thanks in advance.

-A

i think your layout plan will suffice. the piano probably won't be an issue where it is as much as the desk reflections. consider leveling the monitors even if the acoustic centers end up slightly above your head. if you still find reflections are a problem, consider using REW to measure them and determine where the imbalance exists.

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Glenn

Thanks Glenn.

I went with my original plan and it is working out great. The piano is really not a problem at all so far and the ringing is gone (flutter echo). I am looking forward to getting the bass traps on Friday.

What's not to love about the look of R-13 in the corners though right?

Will post some more pics in the a.m.

-A

Ok......so.....here's what I've done.

3 x 2inch panels behind the speakers one panel of 2inch at first early reflections and one more panel of 2" on the right hand side.

Bass traps are 8inches deep for both front bottom corner with a 4 inch deep ones on top of those. The back corners are 4inch traps on the bottom and 2 inch panels on top. I am getting anther 2 x 4inc deep panels for the back corners to replace the 2inch panels.

The bass is pretty good in here now but there is a hollowness to some bass notes and the room is still a little "live". Not particularly pleasant I must say especially when mixing acoustic instruments.

Questions...

1. Should I put up my diffusion on the back wall? I have 8 x 2feet by 2 feet Auralex MetroFusors. I was going to put two of them between the panels on the right hand side of the room and match that on the left but now I'm not sure.
2. Should I just get some more 2 inch panels for the back of the room, the door and next to the piano?
3. I think I need a cloud. Should I put panels flat against the ceiling above me or angle them 12 degrees and if I angle them do I need to get enough panels to angle all the way down to the front wall?
4. I was told to hang the top bass traps as high as I could to the top of the ceiling. Well....after MUCH trouble I could not get them high enough so there is a small space above the top bass trap in the corner and it's resting on the bottom one. Is this a problem? Should I get some spacers to put between the bottom and top traps to close the gap at the top?

I have posted some pics of the space and also some readings from Fuzzmeasure. I can't make head or tail of the readings. Sometimes it looks like the room sounded flatter with no panels and the Owens Corning bales stuffed in the corners!. All readings are taken with a acoustical measurement mic and from the listening position only.

Any comments greatly appreciated. I have spent a fortune building the place now I need to get it sounding right otherwise I have wasted my money.

Thanks!

-A

OK push has come to shove and I need to really get moving with these acoustics.

I FINALLY got REW working but had to set it up on the laptop and not the studio computer where it just wouldn't work. I need to know what measurements to take. I read all the posts about how to upload the graphs and what smoothing to use. This is what I am thinking now in terms of testing....

Take multiple readings at the mix position by moving the mic all around a 2' x 2' area where my head will be. I will then average out all the readings and see what I come up with. I have paid attention to the 38% general rule and the triangle rule. I have treated most of the ER in the front of the room but nothing on the ceiling yet. I know I need treatment above the mix position but I would like to know whether to angle the panels 12% or put them flat up on the ceiling? I plan to use the 2" thick 2' x 4' panels that I have on the wall although I can have custom sizes made if I need to.

At the front of the room the ER sound good. No slapback or ringing. However as I move to the back there is lots of flutter echo. I plan to add panels on the door and the other side of the piano. I am not sure what to do with the wall space between the piano and the AC. Also, do I need panels on the ceiling behind the mix position?

I have no idea what to do with the back wall. It is about 10' away from me at the mix position. The diffusors you see in the pics are available. They are just up there now to look at...that's not the final position. I'm not sure whether diffusion or absorption is the way to go on the back wall.

My biggest problem is the standing wave when I play a C or other notes on the C scale. After plugging my room numbers into Bob Gold's mode calc I can see clearly the modes involved and they all fall on the note C. Using REW is there a way to test and figure out what to do about it?

Thanks for any help. I don't want to spend a ton of $$ only to realize I bought the wrong things.

-A

UPDATE

I spoke to Steven Klein of http://www.soundcontrolroom.com/index.html

He informed me that just by looking at my room dimensions he can see that I have a pretty bad ratio going on with the length and ceiling dimensions. Before getting involved in the construction of a membrane absorber he suggested I first experiment with the placement of the sub. He said he has had a lot of success with using subs to treat modal problems, sometimes even using up to 4 of them. So I'll be doing some experimentation and will post results here.

So that leaves the question of my cloud and whether to angle the panels 12 degrees or just mount them flat on the ceiling.

Any thoughts?

Thanks everyone!

-A

It looks to me like you have an issue with the vertical axial modes (floor-ceiling), and you have no treatment on the ceiling, so that's where I'd start. Not only that, but you have an issue with your 2,0,0 and 0,0,1 axial modes lining up practically on top of each other at 67 Hz., and yes, that's a C.

I'd get that cloud up there before you do anything else. Make it thick absorption, and hard-backed, then angle it at least 12° (maybe more, as needed), and spaced away from the ceiling. That should help with both your modal response, and your flutter echo, hopefully.

Moving the sub might help with the 0,0,1 mode, but probably won't help the vertical mode much, since the sub pretty much has to stay on the floor anyway, and most likely in or close to a corner, so it's going to excite that 2,0,0 mode (plus all the harmonics) very easily, no matter where you put it. You can't make the mode go away by moving the sub: the mode will still be there. All you can hope to do is to move the speaker to a location that doesn't excite it. That said, moving the sub around is a good idea anyway, so go ahead and try that for sure, but you shouldn't expect that the mode will disappear: it wont.

I'd also put more bass trapping in that room: you don't have enough. Try putting bass traps in some of the other corners (there are 12 corners in a room: do as many as you can

And that back wall! It needs thick, deep absorption.

Absorption. Most types of diffuser are not appropriate for small rooms, despite what you might read on the internet. Skyline and QRD types especially create lobing, and it takes a lot of space for that to even out. Your 1D skylines probably aren't doing much for you, and that area could be better used for absorption. Plus, in a small room your problems are mostly going to be in the low end, but in practice you can't build devices big enough to diffuse low frequencies, so it doesn't make a lot of sense to use diffusers in small rooms. Go with absorption on the rear.

Most of your existing absorption seems to be flat against the wall: it would be better to put it on spacers, so that you get a few inches of air behind it.

That would be my approach. Maybe others have different ideas.


- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.

Ok thanks Stuart, that makes sense.

Is 4"thick enough for the cloud? And then 2' x 4' in size?

I have 8 corners done, not sure where the other 4 are...

Is 4" thick enough? Do I need to go floor to ceiling or would 2' x 4' panels at 4" thick work there?

Will that help with Low frequency absorption in those 2" thick panels I have now or is it full frequency that will be improved?

Once again Stuart, thank you so much for your time and excellent advice.

That should be good to start with. But you should make it hard backed if you want it to help with breaking up the vertical modal issue.

2 verticals on the front wall, 2 verticals on the back wall, two horizontals across the front wall, two horizontals across the back wall, two horizontals along the left wall, two horizontals along the right wall. The horizontals are often overlooked: these are the corners at the top, between the wall and the ceiling, and at the bottom, between the wall and the floor...

For the rear wall, I'd start with 4" thick spaced at least 4" away from the wall, and make it as large as you can. If it doesn't give enough effect, then you can either make it larger, or deeper. Or both. But try with a sing 4" 2' x 4', spaced 4" or so, and see how that goes.

Spacing the absorption away from the wall helps it to be more effective down to lower frequencies. Basically, absorption acts on the velocity component of the sound waves, not the pressure component. For any wave hitting the wall, exactly at the wall boundary, pressure is maximum and velocity is zero: The further it gets away from the wall, the pressure goes down and the velocity goes up. You get maximum velocity and minimum pressure at 1/4 wavelength from the wall, so that's where the absorption should be: But you can't just choose a frequency and set up absorption at the 1/4 wave distance, hoping to absorb only that frequency! It would be nice if it worked that simply, but it doesn't, since sound does not approach the wall only at 90°. It approaches at all angles, as it bounces around the room...

But on the back wall especially, since it faces the speakers almost head-on (only 30°) off, a lot of the sound is hitting that wall close to head on, so that's the wall where spaced absorption acts mote like the theoretical predictions.

Of course, you can't set up the spacing for a 63 Hz problem like this! You'd have to use absorption many inches thick, spaced 52 inches away from the wall.... But don't sweat the theory too much: sound in small rooms is not simple single waves traveling direct straight-ray trajectories head into walls. The sound field in a small room is rather more complex, and much of the stuff going on is at grazing angles, where even thin absorption close to wall is very effective, even down to quite low frequencies.

But anyway, to answer your question: basically, yes. Spacing absorption away from the wall improves the low frequency effectiveness. It won't make much difference to high frequencies, where the 1/4 wavelengths are comparable to thickness of absorption: 1/4 wave for 1kHz is roughly 3", so even your 2" panels are having some effect there, and above 2 kHz they are very effective, with or without spacing. The big difference in spacing is in the lower end of the spectrum.

- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.

Hey Stuart or anyone else reading this...

What do you think of these? They are not hard backed per se but are made of rigid fiberglass.

http://www.primacoustic.com/stratus.htm

It would b e easier for me to get these than have my guy build them for me.

I did a search on the forum to see if anyone else has them but found nothing.

Thanks!

http://www.primacoustic.com/pdf/StratusCloud-EDS.pdf

They would probably be OK, but 4" would be better.

The 2" only absorbs full down to 500hz and then rolls off. 4" gets you down to 125hz. Why spend to have someone build them, it is a very simple design. I didn't see what they cost though.

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"It don't get no better than this"

Thanks Eric,

The reason someone else builds them is that I have neither the time, tools or know how to do it properly.

I'll source some 4" panels and go from there. These Primacoustics seem to be $200 per panel!

Thanks for the help!

-A

You could probably make them yourself for less than $50!

All you need is a couple of bits if wood (Home Depot) a hammer (Home Depot) and a hand full of nails (Home Depot). (If you wanted to make them look better, you could cover them in any breathable cloth that you happen to like, and use a simple staple gun to hold it in place (Home Depot).

Did I mention that you can get most of the stuff you need from your local Home Depot or other hardware store? Even with the price of the tools included, you'd still be well under $100: IT would take you a couple of hours, maybe...

Or, you could spend 3 or 4 times more than you need to, then add shipping costs, then wait several days while they arrive... Your call!

- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.

Yes, probably, but the time involved I think would be a LOT more than 2 hours!

My guy can make me custom sizes and charges about $7.50 per sq foot. He's about 25 minutes away from me so i just go and pick em up.

I just asked and he says he can make me the cloud hard backed. Is this the best thing to do?

The cloud will be 6' x 6', 4" deep. It will hang at a 12º angle over the mix position.

Thanks!

Dont make it hard backed.

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"It don't get no better than this"