DIY Broadband Absorber - pictures posted

[muttondraw]

Originally Posted by airmate

thanks again, but it seems like it's windows pc only. i'll see what i can do. my place is mac only...

There is a great little app written in java that works on the Mac called Room EQ Wizard and it is free!

http://homepage.ntlworld.com/john.mulcahy/roomeq/

It only works at 44.1k on the Mac because of the limited support for the core JaveSound classes, it is also a little bit rough around the edges but it works very well. A slicker but more limited solution is Fuzzmeaure:

http://www.supermegaultragroovy.com/FuzzMeasure

they have a demo version you can download

[airmate]

Originally Posted by muttondraw

A slicker but more limited solution is Fuzzmeaure

now i made a measurement with fuzzmeasure.

i've recorded a sinus sweep through this chain:
brauner phantom c -> mogami 2791 -> chandler tg channel mk2 (eq not engaged) -> rme multiface @ 96 khz

the microphone was put in my listening position between the speakers.

i'll see if i can organize more accurate equipment for further measurements soon.

and this is it:

[djbrough]

@ airmate
How deep are the bookshelves from IKEA?

[airmate]

Originally Posted by djbrough

@ airmate
How deep are the bookshelves from IKEA?

outside 280 mm. inside a little less than that.

[axtrak]

Originally Posted by airmate

qubi,
they have a membrane on the rear, and there is a gap between them and the wall.
i considered a membrane on the front, but my initial aim was to do something against mid frequencies between 300 and 700 cycles. so i didn't put a membrane on the front, since i didn't want the surface to be reflective at all.

in case i get the feeling that i have to do something in the bass frequencies as well, i know someone who can construct helmholtz resonators for me. but in the moment it looks like i don't need them.

Hi,

i build myself some helmholtz resonators, it´s really easy, just a box with a hole and some absorbing material inside.

The formula is here (german site):
http://www.lautsprechershop.de/tools..._helmholtz.htm

If you make the hole as deep as the material is from which you are building the box it´s really easy.

I´ve been building some of them for my new studio, and they work perfect.

Alex

[Scott R. Foster]

"I´ve been building some of them for my new studio, and they work perfect."

There are some pitfalls to a tuned absorber approach... for example a HH bottle will re-emit the resonate frequency - you can end up extending the problem in time [longer ring].

Not to say they can't work - but it takes a lot more brains and work to get a room right that way versus a broadband approach - at least that's my view.

[Scott R. Foster]

Originally Posted by deft_bonz

Scott

Do I understand this right?

If this hemp has absorption coefficient a=1 for class a measurement after ISO 11654, does it mean that it has a real coefficient of a=0.7 at 250Hz as described in figure 6 here (the link you'd posted): http://www.rockfon.co.uk/sw1165.asp?PID=116

DB:

I haven't studied the spec [I'm sure you can find more detail on the web] but I gather that figure 6 is a series of thresholds that a material must meet to get the rating at that line. In other words, you can get a Class A rating with .7 at 250 Hz, but that doesn't mean the material must roll off at that rate as it aproaches the low end of the spectrum.

Also, the reference curve may not be an absolute criteria - the material might still get class A rating if it exceeded the reference curve at points x y and z even if does not at a b or c... also there may be a weighting giving more credit for adherance to the class refernce line for some parts of the band versus others. So you might be able to get class A even if don't achieve .7 at 250 Hz.

I just told you more than I know about this spec, but I know of other single numbers specs that do this - so I'm always suspiscious of such things. I always look for absorption data broken down per frequency - so you can get your mind around a trend line without any fancy footwork going on where you can't see it. This is real imortant when working with musical noise - as music generally has a much greater low frequency content than something like office noise [office environments being the situation most of these sorts of specs are written around] and therefore the rule set for generating these ratings is often misleading for musical applications.

Nonetheless the customer is happy - and making a WAG from the look of the stuff, the class A rating and the overall depth of material achieved by the installation as described... I bet it really does work well - even low in the band.

[Ol' Betsey]

Hi Scott,

It's great to see you here.

I've huddled around your Acoustics Forum quite a bit when I've got some DIY stuff to do and always recommend it as essential reading when others start heading down that road.

I wonder if Bob Gold will add Airmate's 'Dope Trap' (great 'tag' by the way...) to his list?

Oh and Airmate? Great looking traps. I did something a little similar in my last studio. The previous owner was a DJ and had these huge record shelves with sliding doors stretching across one wall so I just pulled off the doors and pulled out all the shelving, filled in with about 6" of Rockwool and covered it in Burlap/Hessian. I also added two 'Mega Traps' (see Bob Gold's page) in the opposite corners and it sounded great.

Hemp 'Dope Traps'... I love it.

R.

[Anonyme]

nice...

[thinman]

Originally Posted by Ol' Betsey

Airmate's 'Dope Trap' (great 'tag' by the way...)

Airmate Dope Trap®

Sounds like a great little desk top product to be marketed to college dorm dwellers.

Way more classy and contemporary than Towel Under the Door®, used in my college days.

[tonymite]

Where does one implement the broadband absorber vs the helmholtz vs the tube-trap ??? where do they cross over ?? or is it " THAT" room dependant ???

[Alexi]

Originally Posted by airmate

outside 280 mm. inside a little less than that.

would you mind sharing the "ikea name" of the bookshelf......?



cheers

[k2m]

Nice Absorber there, mate.

Say where can I get that fabric in .de ? I got most things sorted out but still need info on that fabric.

I guess it is "Leinen" ? How much is it and where do I get that?

Thanks for your help.

[Alexi]

let me guess the names of the shelves either: "Billy" or "Flärke" ?



cheers

[airmate]

guys, i really appreciate this discussion and your comments!

does anyone have a link to bob gold's site? i did a search on google, but i couldn't find anything.

alexi: the name of the shelf is "billy". i assume it's their cheapest model, by the way...

k2m: the fabric is also from ikea. it wasn't the cheapest option, but i really like its look, and since i have to stare at it day in day out...
i think it was about 8 euro per meter which is quite much. but: whatever may suit your taste and budget will work - just make sure it's not too thin!

thinman: yeah, i'm still enjoying that "AIRMATE DOPE TRAP" thing...

[muttondraw]

There you go:
http://www.bobgolds.com/

[k2m]

thanx for the info dude

ps: never thought of looking for fabric in ikea, but it looks damn cool

[airmate]

Originally Posted by k2m

ps: never thought of looking for fabric in ikea, but it looks damn cool

i never thought of it either, but when i was there to purchase the shelves, i occasionally went into the fabric section and found something that looked kinda cool indeed...

[Scott R. Foster]

Originally Posted by tonymite

Where does one implement the broadband absorber vs the helmholtz vs the tube-trap ??? where do they cross over ?? or is it " THAT" room dependant ???

I reccomend a broadband approach... avoid tuned or peaky materials or devices of any sort as much as you can.

My $0.02 here:

http://forum.studiotips.com/viewtopic.php?t=48

[Scott R. Foster]

Originally Posted by Ol' Betsey

Hi Scott,

It's great to see you here.

Thanks OB... always nice to run into a satisfied StudioTips customer.

[not_so_new]

Hey guys.

Maybe this is off subject (sorry if it is ) but which is better...

THIS

....or......

THIS (the corner trap at the bottom). I have some huge nodes around 60 and 120 in my place.

Thanks.....

[Ethan Winer]

Michael,

> which is better <

The solid filled corner is better.

--Ethan

[not_so_new]

Originally Posted by Ethan Winer

Michael,

> which is better <

The solid filled corner is better.

--Ethan

Thanks Ethan.

thumbsup

So the reason most people don't do this because of the price involved?

[djbrough]

This thread has inspired me to make a trip to IKEA with a few bills to spend. This is a nice weekend project. I'd probably use 703 instead of hemp though.

@ airmate
I'll tell my wife that the mess I'm making at home putting these things together is all your fault!

[Ethan Winer]

Michael,

> So the reason most people don't do this because of the price involved? <

Exactly. The cost of materials is much higher, but the performance is only a little better. So unless cost is not an issue, it makes more sense to cover more total corners with a 4-inch panel than treat fewer corners filled solid.

--Ethan

[not_so_new]

Originally Posted by Ethan Winer

Michael,

> So the reason most people don't do this because of the price involved? <

Exactly. The cost of materials is much higher, but the performance is only a little better. So unless cost is not an issue, it makes more sense to cover more total corners with a 4-inch panel than treat fewer corners filled solid.

--Ethan

Thanks again Ethan, very cool.

Okay while I have your attention (still sorry for the thread hijack airmate). Most of the people I see making panel absorbers for corner traps look like they are sealing the sides, top and bottom of the traps so no air can leak around them.

This is a pressure type of panel I would assume that is causing the sound waves to have to fight to work through the 703 or what have you then the air space then some back absorption. Not sure what this type of trap is called but is a sealed trap like this better than just mounting 703 a few inches off the corner wall?


Thanks again man.

[not_so_new]

Bump....

[Scott R. Foster]

Originally Posted by not_so_new

Not sure what this type of trap is called but is a sealed trap like this better than just mounting 703 a few inches off the corner wall?.

No.

Bang for the buck this is the best corner panel you can get... anything you do to surround it with non-acoustically transparent material is a diminution.

[not_so_new]

Originally Posted by Scott R. Foster

No.

Bang for the buck this is the best corner panel you can get... anything you do to surround it with non-acoustically transparent material is a diminution.

Thanks Scott.

So you are saying that the best of all would be to take some 703 and cut it into wedges, lay it flat and stack it one on the other then cover that with a little bit of cloth to dress it up a bit but don't seal the sides or top? Kind of like THIS then?

After that it is best to get some 703 etc and put it in the corner with something behind it like some loose insulation etc. and some sort of fastener to hold it in place. A little bit of cloth to cover it and you are done?

[Scott R. Foster]

Yeah Buddy.. that's a good un. Here is the crux of the biscuit... and again adding non acoustically transparent elements is a diminution.

The Auralex MegaLENRD is also stellar... but not cheap.