Harper's Wood studio design questions

[harperswood]

Hi folks,

I have spent the last several days reading the forum. What an incredible resource! I hope I haven't asked too many stupid questions.

I am in the process of gutting the room which we have been using as a control room. There was a lot of water damage after last years ice dams on the roof. I want to improve the acoustics and also have a recording booth.

Harperswood.skp

Room specs (I'm in the States so dimensions are in inches except for the sketch):
Interior wall: inside is 1/2" gypsum over 2"x4" studs, other side is 1/2" oak boards
Exterior walls: inside is 1/2" gypsum over 2"x6" studs; paper-faced fiberglass insulation; outside is 1" pine boards/house wrap/ white cedar shakes
The small windows on the ends are fixed double pane glass. The two windows on the long wall are double hung, double pane glass.

The ceiling is 1/2" gypsum screwed to 3/4" spruce strapping 16" OC which in turn are nailed to hemlock 2"x12" 24"OC. There is about 10" of paper-faced fiberglass insulation.

The way I want to use the room is to have the high wall be the back and the short wall the front.

The floor is 1" hemlock boards on 2"x10" hemlock joists 24" OC. On top of that will be 5/8" underlayment, 1/4" carpet felt and some kind of carpet.

Environment:
There are no neighbors withing earshot. Neither are there any other occupants of the building, so noise suppression is not an issue here. We are in an area that gets a bit of low frequency airplane noise from commercial jets starting their approach to Boston from Europe, there is some intermittent traffic noise on our country road. In the sprng the birds can be loud.

What's it for?:
We record acoustic guitar, Celtic harp, fiddles, flutes and vocals. There is not a lot of low frequency in what we do, at least not at a high level. The harp has a wide dynamic range and has always been a challenge to record.
I am currently using a Roland VS2480 CD hard disc desk with Roland digital modeling speakers (the cabs are front port design

Proposed design

I am thinking I will build a couple of speaker enclosures and have them on either side of the window in the control room. I will probably have to change the included angle from the standard 60° to 75-80° to pull the listening station a little further from the back wall. I intend to build clouds for both rooms with some absorbing panels or slat diffusers on the back wall of the control room and the outside walls of both rooms.

What is the practical difference between an unfaced absorber unit and a slat diffuser? Intuitively it seems that there would be some high frequency bounce with the slats, but I haven't found an explicit dicussion - they do look cool!

Budget
I have quite a bit of material on hand. The stuff I need to purchase will run about $500 (unless there I have made a massive miscalculation in design)
My Questions:
I will be building the oblique wall between the control room and the booth. Would it make sense to put gypsum on the booth side and cover it with a diffusing surface and have the other side covered with cloth or a slat diffuser?
I have a modicum of fake log cabin siding that I can use. It is 8" wide with an arched surface. I would insulate the wall with recycled denim insulation. I checked the specks and it is a pretty good absorber across the frequency range where we are working.

The reason I would use the wall itself as the absorber instead of building a separate unit is to save space. I realize, from reading the forum, that low frequencies will not be as effectively mitigated as when the panel are spaced out from the wall. Does this make sense?

[harperswood]

Hello again,

I spent some more time nosing around in the forum and reread John's site for acoustic theory, Helmholtz calculator and all that. So I guess the question about slot resonators is answered but it leads to another: what frequency range should I be worried about? I assume that room dimensions play a big part in that.

[Soundman2020]

what frequency range should I be worried about?

The entire low end, from around 300 Hz. on down.

I assume that room dimensions play a big part in that.

Among other things, yes. Your basic room modes depend on your room dimensions. That's why it is important to stay away form really bad room ratios, and a good idea to try to get close to one of the known "good" ratios, spacing out your modes evenly and not multiply your problems by stacking several modes at the same frequency. There are numerous calculators and spreadsheets around that will tell you exactly what your problem frequencies are predicted to be, based on the dimensions of your room.

But that will only give you theoretical nu,bers, and the acutal numbers in your finished room will most likely be different.

So rather than trying to identify the dozens of specific frequencies in advance that will be problematic for your specif room and designing treat for each of those, it is much smarter to go some type of broad band approach. If you try to tune your resonators to specific narrow frequencies, chances are you wont get the exact right frequency anyway, so you'll end up NOT absorbing the one you really need to, while you DO absorb something that didn't need it!

That's the idea with John's design of slot resonators ("slot walls"): they are not tuned to specific narrow frequencies, but rather they are meant to be broadband devices, tuned across a broad range of frequencies in the lows and mids part of the spectrum, which is where most modal problems will be in small rooms. It's a "shotgun" approach that attacks all likely candidates at once, rather than a "sniper" approach that tires to hit them individually

Personally, I think it's far better to pay attention to things like speaker placement and geometry, room geometry, room symmetry, first reflection points, reflection free zone, bass trapping, dimensions, ratios, isolation, and things like that, than it is to try to hit specific problem frequencies in the design stage. It seems to me that it is far better to worry about specific issues only AFTER the room is finished, if there happen to be some nasty ones left over that you didn't hit with the broadband approach. If you do it that way, you can measure the actual room response accurately, figure out exactly what your real-world problems are, and THEN go after them if they are bad enough to warrant it. Theoretical mode models can give you a rough idea about how your room might turn out, but they can never beats actually measuring it once it is built.


- Stuart -

[harperswood]

Thanks Stuart,

It's back to the drawing board to rethink the overall control room dimensions. It's looking like 9'1"x 8'6" will be the maximum I can go (2.77m X 2.59m) That will give room for a booth 9'1" x about 6'. I can move the wall between to avoid compounding the standing waves on either side. I know I don't want the booth to be half as wide as it is deep.

When I get a handle on the floor plan I'll post an update. Likely to be a few days.

Cheers!

Fred

[harperswood]

A lot has happened since my last post. In addition to the studio itself I redid all the ceilings in the second floor, moved some walls, built a new stairway to the attic - in other words I've been busy.

I did get the control/mixing booth done. It's about as small as it can be. It's hard to get a photo but I'll try and post something. Between the angled walls, the slot resonators and the cloud It's a MUCH better listening environment than I ever had before. I also built several movable sound baffles using 6" denim insullation. When I'm mixing they are at the back of the control room, when I'm recording I can move them into a small booth for vocals/flute/guitar or I can deploy them in the next room, which is a bit bigger, for the harp. I'm still trying to find a better situation for recording the violin, which depends almost as much on the acoustics of the room as the instrument.

So far the mixing experience is much improved. I don't know if the finished product is hugely better, but getting there is a lot less stressful.

Remaining to be done is a small cloud in the recording booth. The ceiling is quite high and half cathedral. I am of a divided mind on a dispersion wall. I have a pile of log cabin siding I could use, either horizontally or a vertically. Right now it's 1/2 inch sheetrock all around with one small built-in absorber panel in a corner as an attempt at bass trap. The room is still too lively for controlled recording (i.e. a lot of natural reverb gets recorded and it's not always pleasant.

As soon as I finish relocating the kitchen (October) and get back from the November tour I'll have a window of opportunity to finish the recording booth and get some music down before out winter tour in February.

The forum was invaluable in getting me started down the right path. I could have cobbled something together that looked impressive but didn't work particularly well (I have recorded in such studios) Gaining an understanding of how the acoustics, geometry, and materials interact allowed me to put together something that works for the music we do. If I ever had to do something with drums or acoustic bass or at a high sound level it probably wouldn't do but our loudest, lowest sounds are harp and vocals, so it works for us.

Cheers!

Fred

[gullfo]

if your overhead space is high enough, put some absorption clouds hanging down 1-2'. on the walls, small absorbers scattered across the walls will reduce the liveliness and add diffusion. in the corners (vertical and horizontal) add some "super chunk" absorption for bass trapping.

[harperswood]

Thanks, Glenn.

That's just the sort of overhead treatment I'm looking at doing. I'm going to use the portable sound absorbers for now in lieu of permanent installations primarily for space concerns.

Here's a photo of the control room. You can get an idea of the pitch of the ceiling. The low side is about six feet (~190cm)

IMG_8557.jpg

This room (which is bigger than the booth) is so small I had to build a custom deck to fit the space. I'm left-handed and built it for myself, so it's a challange for my right-handed partner to listen and take notes!