Hangers???

danaudio · Post by **danaudio** » Sun Jun 29, 2003 2:41 am

I am constantly seeing hangers everywhere. I understand their purpose, and I understand where they should typically be placed (thanks to john`s manual), but I do not understand exactly what they are.

Do you make them ? they just like cloth taped together or something...or are they actually something you would by from an acoustics supplier?

Any and all info on the subject would be very appreciated.

danaudio · Post by **danaudio** » Sun Jun 29, 2003 4:16 am

nevermind...i found it in the manual....i should have known...but i still have some questions....

Is there a way to determine what size the absorber needs to be to attenuate certain frequencies.

For example...If i wanted to make a hanger that will attenuate 250 HZ...what size should it be? And how would you determine the size?

Sen · Post by **Sen** » Sun Jun 29, 2003 1:00 pm

For example...If i wanted to make a hanger that will attenuate 250 HZ...what size should it be? And how would you determine the size?

Acoustic Hangers. This is a system of fibre board panels that are wrapped with insulation and are hung freely using wire or rope. The large hangers 1.8m x 500mm work in the low frequency range whilst the panels 1.2m x 300mm effect the low mid frequencies. It is common to have up to a 1.2m space at the rear of the control room with the large hangers whilst the smaller hangers are effective if suspended in the ceiling cavity created by a false ceiling.

copy/pasted from sae site

danaudio · Post by **danaudio** » Sun Jun 29, 2003 6:52 pm

right...i read that too....but it does not say anything about dealing with specific areas...what is low? 20-50? 100-250? I mean there must be a way to dtermine size/frequency...does nayone know?

Post by **John Sayers** » Mon Jun 30, 2003 9:36 am

Dan - as far as I know there is no math associated with hangers.

cheers
John

c.bochek · Post by **c.bochek** » Sun Feb 22, 2004 11:11 pm

Hi guys!

First post here, really cool site! Loads of knowledge accrued after a few hours! Awesome!

But, how can there be no math associated with hangers!?!?! Math rules everything (except women)! I first came across hangers while looking at Steve Albini's studio Electrical Audio ( www.electricalaudio.com ) he uses them in his super dead room. They seem to be very cost effective, easy to build, and, from what it seems as per this site, very effective. So I am highly intrigued by them. It was kind of shocking in such a math oriented field that there are no equations for these hangers, or are there? Is it pure guess work as to what frequencies they absorb?

Just a bit of info from Electrical Audio's site... they joined sheets of oriented strand board together to lower their absorption. They have illustrations on the site. No one has mentioned this yet, or is it overkill? So then, how small is too small, 1'x 4'? just some newbie questions. later.

carl

AVare · Post by **AVare** » Mon Feb 23, 2004 2:06 am

was kind of shocking in such a math oriented field that there are no equations for these hangers, or are there? Is it pure guess work as to what frequencies they absorb?

It's not so much that there are no equations for their performance as that what they are used for doesn't require that much math. A couple of equations if you desire.

The absorbers work on the velocity of the air molecules. For 100 % absorption theoretically the trap has to be half a wavelength long. At 45° the velocity is 70% of maximum so 1/4 wavelength is considered acceptable for calculation purposes. If a trap is 1 metre deep that implies effective absorption down to 75Hz. This does not take into account the absorption from an acoustic impedance point.

As a practical example this have a look at the BBC R&D report 1992-11. Among other things it details the theoretical VS, actual absorption of rockwool at various thicknesses. The measured results show a low frequency roll off an octave lower than what theory indicated! The material that the report focuses on is 180mm thick. Test results showed absorption coefficients of 0.98@125Hz! At that frequency, the wavelength is almost 3m!

Another significant factor reported was the negative effect on low frequency absorption of dividing the absorbent material with dividers.

The report is on the web, but the access to it is through a PDF file and I don't know how to pull the URL out.

You put those together and probably a bass absorber of 1m deep will have effective at least down 37HZ, and probably much lower.

Hope this helps you a bit.