Just normal PVB! I didnt know there was such a thing as acoustic laminated...
There's different types of acoustic laminate, with different properties, but they all do add a bit to the cost! I paid about 12% more for acoustic laminate in some windows and sliders last year (as compared to normal PVB laminate), but there were other options too... with rather higher percentage ratings! So your 5k would have been more like 6k, or 7k, or... probably not justifiable, for the small improvement you might get!
The benefit from acoustic PVB (or other acoustic interlayers), happens around the "coincidence dip", which likely isn't going to be much of an issue for you anyway. Coincidence is kind of hard to describe, but it basically means a reduction in isolation for a small range of frequencies where the wavelength of the sound in the air happens to match the wavelength of a bending wave in the glass, at certain angles of incidence. It's usually in the upper mid frequencies, or the low end of the "highs", depending on the characteristics of the panel (glass, in this case).
I've been meaning to write a bit out this for a while, so I'll just do it here, on your thread, then later post links to it.
This whole "coincidence dip" and "bending wave" things probably doesn't mean much to anyone, so let me explain a bit more:
Low frequencies sounds hitting a wall, ceiling, floor, or window, cause the entire panel to "wobble" in and out (as though you were pressing on the panel with your hand, then releasing it, repeatedly), but higher frequencies cause "ripples" that travel along the surface of the panel, sort of like the ripples you seen in a calm pond or lake, if you drop a stone in. There's another difference here: the speed of sound for normal compression waves (the ones that cause the "wobbling" at low frequency) is constant, regardless of the frequency, but for the "ripples" (bending waves), the speed of sound is different for each frequency. Or said another way: each bending wave-length (=frequency) causes waves that travel at a specific speed, so different frequencies cause "ripples" that travel at different speeds. And as a result, it turns out that, for every single frequency above the point where this effect starts happening, there will be one specific angle of incidence (the angle that the sound wave hits the wall) where one specific bending wave in the wall matches the wavelength of the incoming sound. So the panel will resonate at that frequency, and thus it does not isolate well for that frequency. That "lowest frequency where the effect can occur" happens when the incoming sound wave in the air is grazing along the panel, almost parallel to it (going in the same direction as the panel surface), and then for every angle of incidence above that, resonance will happen at a slightly higher frequency, until you get the highest frequency where the waves are arriving "head on" to the panel (perpendicular to the surface). That region, where the frequencies in air can line up with the various frequencies in the panel, is called the "coincidence dip", and is a somewhat broad region.
For most materials commonly used in building studios, the dip will occur somewhere between maybe 1 kHz to maybe 5 Hz, and will be a few hundred Hz wide. This region is usually well isolated anyway.
If you are interested, the equation for calculating this effect is:
Fc = c² / (1.8 * t * Vl * sin²(a))
where:
c = the speed of sound in air (m/s),
t = the panel thickness (m),
Vl = the longitudinal velocity of sound in the panel (m/s)
a = the angle of incidence.
The "longitudinal velocity" is different for different materials (wood, glass, drywall, etc.): you can find tables on-line that tell you what it is for each type of material.
Coincidence generally isn't too much of an issue for typical home studios if they are designed and built well, but it is something to be aware of of you need high isolation.
One interesting point here: If you make a floor (or wall, or ceiling, or whatever) from several layers of material, and you glue them all together, then that brings the coincidence dip DOWN in frequency, which could indeed create a problem for you (it reduces isolation)! Which is why you should not glue together layers of drywall in your wall! If you just leave the layers on top of each other (such as by using only nails or screws to attach them to the studs), then they are free to "slide" past each other when they vibrate, and that can create frictional losses, which improves isolation at the coincidence dip: the dip doesn't go so deep. If you then also add a resilient damping material in between those layers, then you can improve those losses even more (higher losses = better isolation), and if it happens to be a visco-elastic compound, then you can improve them more still, practically eliminating the dip entirely.
The PVB interlayer used in laminated glass, is, in fact, a resilient damping material, which helps to reduce the "coincidence dip". Normal PVB has a pretty decent effect in reducing the dip, but there are more expensive (and sometimes rather exotic!) interlayers that can do a better job at damping that resonance. As I said, it's usually not too much of an issue for home studios, since it is in a part of the spectrum that is already well isolated, usually. It only becomes significant for studios that are aiming for very high isolation, where each small improvement matters. Even them, there are things you can do to improve the situation, if you do have a coincidence dip problem.
Probably more than you needed to know! But interesting, nevertheless.
- Stuart -