Questions about John's diy absorbers

knightfly · Post by **knightfly** » Thu Aug 19, 2004 4:33 pm

Not a problem - general rule for corners is, "as much as you can do" - if you can't quite do the entire corner, it will only reduce absorption by the percentage of space you missed. Might even be better, no matter how much you calculate your EARS should be the final authority here - although analyzers can sometimes help you see what you're hearing.

Bottom line - do all the corner space you can, do any "first reflection" points, do a "cloud" over the mix area if it's a CR, then listen and test - that's the only REAL way to know when you're done... Steve

Ptownkid · Post by **Ptownkid** » Fri Sep 24, 2004 12:03 pm

So, as i near being able to build these things, i need to know if I can alter one bass trap.

The diagram shows the back corner of the mix/live room. The opening is where there'll be a closet door. What i was going to do was build the bass trap as per John's design and pot it on casters to be moveable.

Can i build it like it's shown in the second picture? Or will it not do it's job properly at that point?

knightfly · Post by **knightfly** » Fri Sep 24, 2004 2:40 pm

It won't be quite as effective with a shallower depth, but since it's behind you it won't affect stereo imaging enough to be able to tell the difference - mainly, it might just make the room so it needs more trapping, like between wall and ceiling joints for example... Steve

Ptownkid · Post by **Ptownkid** » Fri Oct 08, 2004 10:26 am

Should I just follow John's plans, or do I need to take room dimensions into consideration before building these things. I keep reading and reading and the more I do, the more confused I get.

The room in question looks like this

what do i need to take into consideration?

The entire ceiling is RHF covererd with fabric and the walls are painted drywall. The ceiling is 7'-2" high.

knightfly · Post by **knightfly** » Sat Oct 09, 2004 12:23 am

What is RHF??

Ptownkid · Post by **Ptownkid** » Sat Oct 09, 2004 2:07 am

http://www.roxul.com/sw18199.asp

It's rigid insulation, the basic point is that the ceiling is dead.

knightfly · Post by **knightfly** » Sat Oct 09, 2004 9:55 am

OK, got it - looks like a good product, and there's a chart of absorption coefficients in the PDF that's linked on that page too - you can use that and everything else you know about your room to figure out approximate RT-60 in this Reverb Calculator -

http://www.saecollege.de/reference_mate ... m#verbcalc

IF the room sounds pretty good to you right now, then all the calculator will do is let you even out reverb times at different frequency bands - this is what makes a room sound "natural", is getting reverb times pretty even across the frequency range.

Actual RT60's in rooms vary with size of room and type of music - for more contemporary stuff, shorter RT's work better (around 1 to mayb 3 seconds, depending on room size; larger room, longer time) - For control rooms, you want shorter RT's so you know you're NOT listening to the CR's reverb when making mix decisions.

Hope this helps... Steve

knightfly · Post by **knightfly** » Sat Oct 09, 2004 9:59 am

Oh, you didn't specify what thickness the Roxul on the ceiling is, or if it's spaced away from the ceiling - I noticed that the LF performance of that product isn't as good as some, this will make a difference in how much bass trapping you need in the room... Steve

Ptownkid · Post by **Ptownkid** » Sat Oct 09, 2004 12:35 pm

the thickness is 3 inch, screwed directly to the ceiling joists, then 3 inches of air, then some normal insulation up tight against the upstairs sheathing.

Ptownkid · Post by **Ptownkid** » Sat Oct 09, 2004 12:36 pm

the thickness is 3 inch, screwed directly to the ceiling joists, then 3 inches of air, then some normal insulation up tight against the upstairs sheathing.

This room is technically the live room, but i'm gonna be mixing out there too so it needs to be fairly reverbless.

knightfly · Post by **knightfly** » Sat Oct 09, 2004 7:07 pm

OK, this gets kind of iffy to calculate when you have air space behind the material - if you have more than the thickness of the material as an air gap behind the absorber, you could sort of "guesstimate" the absorption by just using the absorption values for the next higher frequency band at each frequency where it starts to fall off - IOW, if your spec is over 1.0 at all frequencies except 125, you could "kind of" assume that it would extend to 1.0 at 125, and maybe .6 at 60 hZ.

A better way, if you can afford it, is to get ETF software and a Behringer ECM-8000 omni mic and MEASURE what's really there - The software runs $150 and the mic can be had for around $50-60 - that way, there's no guessing.

If you're going to be mixing there also, you should probably try to keep your RT down to around 1/2 second or a bit less, and then add electronic 'verb to the parts you want wetter... Steve