John Sayers' Recording Studio Design Forum

Hi

I am trying to decide which of my 2 bedrooms would be better for a studio in a house i have just moved into. I do know a fair bit about acoustics having written my dissertation on small room studio acoustic when i completed my BA Honours degree, for which i got a first... But i am no expert!

The front bedroom has the following dimensions:

L: 4.18m
W: 2.35m
H: 2.26m

This gives me Axial modes 41hz, 73hz, 76hz with the second Axial mode for the length of the room being 82hz.
This was initially my first choice because it is the bigger of the 2 rooms and the one with the lower cut-off frequency, reducing the risk of air loading (my speakers are A7's which have a low frequency responce of 40hz. The problem with this room is obviously the ratio which is dangerously close to being 2 cubes side by side, which is almost as bad as having a cubic room isn't it? Or do you think there is enough distance between the axial modes for it to be ok? There is also an alcove in one corner of this room which is a meter wide and a meter deep... which basically adds an extra meter to the length of almost half of the room. I have put some shelves up here though and it houses books, records etc

The back bedroom has the following dimensions:

L: 3.00m
W: 2.64m
H: 2.26m

Axial modes 57hz, 65hz, 76hz. The ratio of this room is better but now i have the problem of air loading as the room is not big enough to support my speakers...

Whichever room i decide to use i plan to use absorption to deal with any RT60 issues and will probably build some tuned basstraps to try and minimise any issues in the lower frequencies...

Its going to be a lot more convenient for me to use the front bedroom but thinking it is less suitable?

What do you guys think is my best plan of attack? (on a lowish budget)

If anyone can offer me any advice i would appreciate it.

Thanks

John

Ouch! That fails two of the three critical tests that the BBC uses for determining if a room is usable, and the Bonello diagram looks like a cross section of the Himalayas! According to Eric Desart's analysis of the best ratios, yours is classified as "A worst case scenario".

Other interesting numbers:
Cutoff: 41 Hz.
Schroeder Frequency: 156 Hz.
Critical Distance: 3.20m

Well, that means it is not a rectangular room, so simple room mode calculations do not apply, except for the two axial modes and any tangentials that do not involve the wall with the "kink". Those will still be valid, but the others won't. The only way to predict the modal response of such a room is with FEM/FEA. Or you could just measure the actual response!


Now that looks far more reasonable. It almost nails Sepmeyer's best ratio, and the Bonello diagram is nice and smooth. Of course, it is 5 cubic meters less volume, with all that that implies, but if ratios and modal spread is what you are concerned about most, then this is a much better option.

Interesting numbers for this room:
Cutoff: 57 Hz.
Schroeder Frequency: 166 Hz.
Critical Distance: 3.20m

So basically your choice is: Does an increase of 10 Hz in the Schroeder frequency, and 15 in the cutoff frequency, matter to your type of work? Considering the two, I'd say to go with the second option. The first option is actually worse than it looks at first glance: Yes, the cutoff is 41 Hz, but in reality there is just one single mode down there! The REAL modal response of the room doesn't start until the second mode, at 73 Hz, whereas with room #2 you have smooth modal spread, with something close to every single note from 55 Hz upwards.

I'd go with #2, despite the smaller volume.

IMHO.

Weeeellllll.... yes and no. With room #1, tou have one single mode in the low end, at 41 Hz, then NOTHING at all until 73 Hz. With room 2, you have modes close to every note from A1 upwards. Pure numbers can be deceiving, until you look at the relationship between those numbers. Besides, A7's don't suddenly stop producing sound at 46 Hz (the published figure is 46 Hz, not 40): they still produce sound all the way down to 20 Hz, and even lower. It's just that the power rolls off below that. At 46 Hz they are -3 dB down, and one octave lower they are only down by -15dB roughly, so still plenty of energy going on down there to excite modes (if there are any). In fact, if you soffit-mount your A7s, you would be tightening the bass considerably and extending the coverage somewhat, depending on soffit design

The room is too small to have a statistical reverberant field in the low end, so all of your time-domain problems below about 500 Hz will be modes, reflections, flutter echo and such like, not reverberation.



I wouldn't do that. Tuning bass traps looks easy on paper, but is not that easy at all to get right in reality. Just go with broadband absorption for your bass trapping. Lots of it. No, more than that. No, that's STILL not enough! Even MORE!!! (It's a small room, and therefore needs lots of bass trapping. Theory says 223 sabins for that room...


- Stuart -

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