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building a small iso cab for my Swart 6v6se
Old 4 weeks ago
Gear Maniac

building a small iso cab for my Swart 6v6se

I live in an NYC apartment and have been recording my Swart 6v6se amp. It's a 5w Class A amp with an 8" speaker.

I had been toying with the idea of making small "iso cab" to put it in for recording, mostly so I avoid annoying the neighbors. I would be removing the chassis of the amp and putting it on top of the isocab, so this enclosure would only need to hold the cabinet of the amp and the speaker (no heat concerns)

I don't need crazy isolation. I just want as much sound reduction as I can get, and want to avoid transferring sound to the walls / floor.

As a cheap DIY-ish solution, I was considering the following:

1. get a plywood box -- I was thinking of the below, which is a plywood carpeted rack case with snug doors / panels for the front and back, and a cable pass through on one.

2. i was then going to load up the inside with something like mass loaded vinyl, though I'm not certain what material would be best

3. i would also try and add some sort of sound-proof gasket to the door panels, and drill some latches on the outside so that they fit snuggly. Not sure what this gasket would be made of exactly

Any suggestions on material, or other solutions entirely, would be much appreciated!
Old 4 weeks ago
Gear Maniac

giving this a little bump
Old 4 weeks ago
Lives for gear

You should probably start by defining how much you need your cabinet to isolate, in terms of decibels. For example, do you need to reduce the level by 5 dB? 10 dB? 20 dB? 30 dB? Something else? Also, what is the lowest frequency that you need to attenuate?

You are planning to build a box with a single-leaf wall, it seems, so the amount of isolation you get is governed by an equation from the world of physics, often referred to as the "mass law" equation. It goes like this:

TL(dB)= 20log(M) + 20log(f) -47.2

M is the surface density of the panel (mass per unit area (kg/m²) ), and
F is the center frequency of any one-third-octave measurement band

It's very simple. All you need to know is the surface density of the materials you are planning to use, and you can figure out how much isolation that will provide for any given frequency. As a point of reference, the absolute density of plywood is somewhere around 560 kg/m3 (depends on many factors, but that's a rough average), so if you used 10mm plywood the surface density would be 5.6 kg/m2, or if you used 19mm plywood then the surface density would be 10.6 kg/m2. MLV has a much higher absolute density, around 1500 kg/m3, so a piece of MLV just 6mm thick would have a surface density of 6 kg/m2, which is already higher than that of the 10mm plywood.

So, once you determine how much isolation you need, you can then just stack up enough layers of the suitable materials to get to the total surface density you need, based on the equation. EG, if you decided that you need a surface density of about 17 kg/m2, you could have two layers of 10mm plywood with a layer of 6mm MLV sandwiched in between, or one layer of 19mm plywood plus 1 layer of 10mm plywood. They are both close to 17 kg/m2, so either would work.

Now, when you do the math to figure out the isolation, don't forget to take into account the equal loudness curves! Let's say you decide you need 20 dB isolation in total: that does NOT mean that you need 20 dB isolation at every frequency! Human hearing is far less sensitive to low frequencies than it is to mids, so you can have maybe just 10 dB isolation at 50 Hz, but you'd need maybe 25 dB isolation at 1 kHz. Those are just examples numbers that I pulled out of thin air! I didn't do the math, and I don't know what sound level you are dealing with, so I have no idea if that's actually what you would need: You have to do the math and check the graphs yourself.

There's another equation that you might find useful as well, which is the empirical mass law equation, which goes like this:

TL = 14.5 log (M * 0.205) + 23 dB

Where: M = Surface density in kg/m2

That estimates the total isolation of the box, across the full audio spectrum, rather than for individual frequencies. So, if you made a box from 10mm plywood, you could expect total overall isolation of about 24 dB, but only about 7 dB at 100 Hz, and nothing at all at 40 Hz. So it's important to figure out what you need first, then do the math!

To prevent the cabinet from transmitting vibration into the floor, buy some Sorbothane pads to rest it on. Once again, you need to do some math to get the right SIZE and RATING of Sorbothane: You will need to know the weight of the entire finished cabinet, with the speaker and mic inside it. Just put it on your bathroom scale, see how much it weighs, then buy the right "Sorbothane hemispheres" for that weight, and stick them to the bottom of the cabinet.

Bingo! Isolated speaker!

- Stuart -
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