Acoustics question

[Xen Ochren]

Hi all, thanks again for the great forum!

So, I have been trying for a few years now to acquire the perfect rental space for a studio to compose and mix dance music in.

I managed to to find one 4 months ago, all was going ahead, until the owners backflipped on me.

Its been about 3 years of trying and failing, and 1 main problem is my limited cashflow. I have however recently scored a grant, so thats $5000 towards to acoustic treatment of a space, and I can afford to spend another 15.
The other main problem is the nature of renting, where a landlord can change their mind and kick you out with a few months notice, wasting that $20,000 investment.

so I have been thinking about all the mobile ways of doing a studio. Back of a truck, shipping container, mobile granny flat etc
But these are generally only 2.4 metres wide to avoid being a wide load.

I have PMC TB2's, which do like a bit more distance between them and the listening position, at least 1.5-2 metres is recommended.
I also aspire to installing the TLE1 sub if I can afford it one day.

SO here's Question 1.
What specifically are the direct problems which come from a thin studio?

From my current understanding it will reduce the ability to get a good stereo image, (I don't know if this is true, and if it is, I do not understand why)
It will also create peaks and nulls in the same way any of the other dimensions would if they were 2.4m.

so,
would larger volume in other ways help, ie height and length?
and
can larger amounts of absorption on the reflection points have the same potential for great stereo image than wide walls? ie 8 inches thick instead of 2.

And question 2,
would it be worth driving out to somewhere quiet, (I have a place) and mixing in the outdoors? perhaps creating a setup that slides out of the back of a van... I haven't found any mention on this forum or gearslutz, of anyone doing this. Well, nothing where the thread starter reported back on the results anyway.

thanks all for your time!
Xen

[Soundman2020]

Hi Xen, and welcome to the forum!

You bring up a number of interesting points, most of which have no simple black-and-white answer.

But just to get you in the right frame of mind, to answer your question about it being possible to build a quality studio in a container:

http://johnlsayers.com/Pages/Spark_1.htm



Another option that you might not have considered is to build a "modular" studio that consists of sections that can be bolted together and taken apart if a flaky landlord suddenly decides to kick you out. Each section of wall/ceiling would bolt to the next to create your inner-leaf, and teh treatment could also be modular (soffits, cloud, superchunks, etc.), so everything could be loaded onto a truck and taken elsewhere. It would not be meant for frequent assembly/dis-assembly, but doing it 3 or 4 times over a few years would probably be reasonable. It could be done.

But these are generally only 2.4 metres wide to avoid being a wide load

Still wide enough! Not ideal of course, but of you look around the forum you'll find more than just a few studios around 2.4 m wide.

I have PMC TB2's, which do like a bit more distance between them and the listening position, at least 1.5-2 metres is recommended.

That's the recommended distance for all speakers, to be honest! If you take a look at the specifications and guidelines put out by places like IEC, EBU, ITU, Dolby, and others on studio design, you'll find the basic criteria are for speaker separation of around 2m. That said, it is quite possible to get very decent sound with smaller spacing. Room design, layout and treatment play a very large part in that, so just because your speakers sound best at 1.7m does not mean they can't sound pretty good at 1.2m, for example.

What specifically are the direct problems which come from a thin studio?

"Thin" implies "small volume", and sound needs as much volume as possible to "sound" good. But once again, "small" does not have to equate to "bad". It can mean simply "not optimal, but still pretty darn good".

From my current understanding it will reduce the ability to get a good stereo image, (I don't know if this is true, and if it is, I do not understand why)

Your intuition is right! Stereo image does not have to suffer. Of course, if you get really small dimensions, where your head is too close to the speaker to allow the sound fields from the various drivers to merge fully, then that would be an issue for another reason, but stereo imaging can still be good. On the other end of the scale, if you are so far away from the speakers that you are beyond the critical distance for the room, then you won't be able to get a good stereo image anyway, but for a well designed studio the critical distance is probably out near the walls, or even beyond them.

Stereo image is more a function of speaker geometry and room treatment, not just distance between speaker and ear.

It will also create peaks and nulls in the same way any of the other dimensions would if they were 2.4m.

Weeelllllll..., yes and no. It's not so much one specific dimension of the room that matters, but rather the

ratio

between the dimensions. Any time a sound wave fits exactly between two parallel walls, then the room will resonant naturally at the frequency. For walls 2.4m apart, there will be a "mode" at 71.8 Hz, and another at 143.6 Hz, and another at 215.4 Hz., etc. If your walls were 3m apart (instead of 2.5) the those frequencies would be 57,4 Hz., 114.8 Hz., and 172.2 Hz. Nothing changed: you still have modes, except that they are now at different frequencies. So if you room were 2.4m wide (or 3m wide), then those would be your modes for the room width dimension. There would also be another set of modes for the length dimension, and a third set for the height dimension. Those are your "axial" modes, because they occur along the principal axes of the room. However, it is also possible for sound waves to find other paths around the room that get them back to the same starting point in phase with themselves. So there will also be modes that bounce off four surfaces before they do that, and those are called "tangential" modes, as well as modes that bounce off all six surfaces, which are called "oblique" modes. Plot them all in a table or on a graph, and you come up with a picture of the "modal response" of your room.

All rooms have modes: they are a fact of life, and contrary to the garbage found on some "acoustic" web sites, there is NOTHING you can do to eliminate them. What you CAN do is to treat them, so they are not too much of a problem, but almost as important as that is to choose dimensions for your room that are in harmonious relationships, such that the modes do not all occur at the exact same frequency. The idea is simple: find a set of dimensions such that the modes associated with the width of the room are at different frequencies from those associated with the length, and also those associated with the height, and also the tangential modes, and also the oblique modes. Get the, spread out as evenly as possible, with smooth spacing, so that there are no "bunches" of modes around the same frequency, and also so that there are no big gaps between adjacent modes.

It sounds complex, but actually isn't. A lot of scientists and acoustic researchers have already done that for you, and today there are lists and charts and programs for coming up with "good" ratios and warning you about "bad" ratios. So all you really need to do is to plug in the dimensions of your room in a spreadsheet or on-line calculator, and it will tell you how good or bad that is. Then you can play around with those numbers until you come up with something better.

So "width of 2.4m" is only part of the issue: you also need length and height. Of course, if your width is 2.4m, then your height should definitely NOT be 2.4 m...! Maybe 2.2 or 2.6, for example, but the length is also needed.

And contrary to popular myth, changing the angles of the walls so that they are no longer parallel does not "get rid of the modes". It simply moves them to a different frequency, which now becomes impossible to predict with simple room mode calculators. You can still predict it, but you have to use very much more complicated methods to do so.

so,
would larger volume in other ways help, ie height and length?

Yes! General recommendation is for a minimum floor area of 20 m^2, and minimum room volume of about 43 m^3. However, that does NOT mean that you can't get a good studio in much smaller spaces: those are just optimum numbers for world-class studios.

can larger amounts of absorption on the reflection points have the same potential for great stereo image than wide walls? ie 8 inches thick instead of 2.

Yes, no, maybe! That depends on the basic design criteria for the room. The major impact of thicker absorption is that it works down to lower frequencies, which might or might not be needed in your room. Yes, thicker also implies increased effectiveness at higher frequencies too, but once again, that might or might not be needed. In fact, stereo image is not really related to how much absorption you have on your walls: that is a totally different problem, related to the Haas effect. Stereo image is much more about having perfect room symmetry, and correct geometry for the relationship between the speakers, your head, and the walls. If your room is not symmetrical, then you will not ever get good stereo imaging, no matter how much you treat the first reflection points. And at the other extreme, a superbly designed RFZ style room can get away with NO absorption at all on first reflection points, simply because there aren't any first reflection points!

Room design is all about setting you basic goals based regarding what you want to achieve, based realistically on what you have an on your budget. It is all about optimizing the space to be as good as it possibly can be, and seeing if that is "good enough" for what YOU want.

would it be worth driving out to somewhere quiet, (I have a place) and mixing in the outdoors? perhaps creating a setup that slides out of the back of a van... I haven't found any mention on this forum or gearslutz, of anyone doing this.

You COULD do that. but then you are totally at the mercy of the weather, and overflying aircraft, and nearby roads, and animals, and whatever else might make unacceptable noises... If you happen to live close to a place where it never rains, the wind never blows, there are never any planes flying around, nobody else ever comes with 10 miles of, there are never any animals or any other sources of noise, and there is also a clean electrical power supply, then I guess that might be possible...

But then, you'd have the opposite issue: your "room" would be totally dead, acoustically, with perfect absorption on every side: no reflections at all, no reverberation or resonance, no character at all. That's an unrealistic model for how most people will listen to your mixes, so you might find it hard to get mixes that translate well.

Then there's the issue of travel time, set-up time, calibration time, tear-down time, etc. Do you really want to spend half of every day driving out to your magical spot in the country and setting up your gear, then the other half packing it up again and driving home?

It might be worth trying out one day, just to get a feel for it, and see if it would work, but my guess is that it isn't a feasible / realistic scenario.

I would suggest taking a closer look at the container idea, or at the "modular build" idea, and see if you can't come up with something that meets your needs. And that leads to the most important point of all: you really should start out by defining those needs, setting them down on paper, and creating realistic goals.

- Stuart -