Hi there "79_Limited", and Welcome!
I am not looking for complete isolation and will not be doing a room within a room build like my last studio.
Just curious, but why are you thinking about doing it that way? Do you live in an area where there are no neighbors with several hundred feet? And no outside noises that could wreck your recording sessions, such as thunder, wind, rain, hail, aircraft, vehicles, etc? Those are about the only reasons that make sense for not isolating a studio.
Does anyone have experience using cinder block filled with sand vs reinforced Sheetrock with green glue/stick construction?
That's a little confusing! You say that you don't need to isolate your studio, but then you are asking about methods for isolating your studio!
Since you say you do not want isolation, then an ordinary single timber frame with some type of siding on the outside and a single sheet of drywall on the inside should be all that you need. That's the way houses are typically built anyway, so it will be the least expensive option of all, and will give the same amount of isolation as a typical house wall gives you: around 30 dB, maximum.
Concrete block, on the other hand, will give you a little more, especially if it is sand filled, but the amount of isolation you get depends on many factors, such as the type of blocks you use, how you build the wall, and how you finish the surfaces inside and out.
I am considering block construction for the first floor. I hear the block may be more expensive and difficult to work with.
To a certain extent, yes, but there's not a huge difference either way. Your contractor will be able to do either, so just ask him for the relevant quotes, then you can decide which way to go. But why do you only want to do block for the ground floor? Why not also do it for the first floor?
Also, you mention walls a lot, but isolation does not depend only on walls: the ceiling, roof, windows, doors, HVAC system, electrical system, and overall hermetic sealing are also critical factors.
I read the Gervais book but I could not find any STC reduction comparing block vs stick construction
well, you shouldn't be thinking about STC. It's a lousy system for measuring studio isolation, and was never intended for that purpose at all. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio.
It is quite possible to have a wall rated at STC-40 that does not provide even 30 decibels of actual isolation, and I can build you another wall rated at STC-30 that provides much better than 40 dB of isolation. There simply is no relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that. It was designed to measure typical office, school, shop, hotel, and similar isolation, which is basically in the speech range of the spectrum, not the music range.
Here's what the actual STC specification document says about itself: "
4.1 These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television, and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling allies, power transformers, musical instruments, many music systems, and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands."
So forget STC as a useful indicator, and stick to TL graphs.
All the book mentions is that for heavy isolation you want a proper 2 leaf system even when using block.
Correct. There's a reason Rod wrote that and nothing more: If you have only a single leaf wall (concrete block, or drywall, or anything else) then that is subject to law of physics know as "Mass Law", which basically says that you will get lousy isolation unless you build a really thick wall with a huge amount of mass in it (EG, a 16" thick solid reinforced concrete wall). Whereas, if you build a two-leaf wall (using any materials: brick, block, drywall, etc.), you can get much more isolation at much lower cost and much simpler construction. Since Rod is talking mostly about how home studio builders can get the same level of isolation as is typically found in professional studios, at low cost and with simple construction techniques, there's no reason for him to go into the much more expensive and complex techniques that you'd need for a single leaf wall to get the same levels of isolation. That would involve much beefier foundations and slabs, to support the huge weight, as well as placing a lot of expensive form-work and rebar, then getting the large amount of concrete pumped in, having a team of experience concrete workers to make it all happen, etc. That's not the purpose of his book; he wants to show the average home builder how to get pro-level studios using average level building skills, typical building materials, and reasonable costs.
By the way, I noticed that you have your control room set up on the second floor, but you have it facing the wrong way if you want to have usable acoustics: it will not be much use with the mix position facing the stairwell. Turn it around so the mix position faces the wall on the left of your image (where the other desk is), and that would certainly be workable. You also need to get the speakers off the desk and on top of stands, if you want to avoid the typical artifacts created by the "cheap" setup shown in your diagram. Just doing that will greatly improve the acoustics at the mix position. The stands should be very heavy: some people use hollow metal stands filled with sand, others use bricks or blocks.
There are several other things you could do to improve both rooms, acoustically, if you are interested.
- Stuart -
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