DIY Broadband Absorber - pictures posted
 

hello,

on the weekend i finally finished my latest DIY room acoustics project.
due to the absolutely great improvement the absorbers have - and the fact it was pretty easy to build them - i decided to share pics and further information.
moreover all that stuff wasn't too pricey.

for the housings i took standard book shelves by the swedish manufacturer ikea. they are pretty damn cheap (35 euro each) and easy to assemble.
the absorbing material is made of hemp fibres - due to possible health issues i wanted to use an organic material instead of fiberglass. it was quite a bit more expensive, but it think it was worth the extra dough. this particular hemp mats are 40mm thick, porous, and they have a gross density of 40 kg/cubic meter. pretty good...
in each shelf there are six sheets of the hemp, so the actual absorber is 24 cm thick.
i covered the front with wooden frames and linen fabric.

it took about 20 hours to build the four modules you can see on the photos.
for all the material i paid about 500 euro. it could have been roughly half of the amount if i had used fiber glass, since the hemp was so expensive (i know what you're thinking now... heh ).
although it took me some more time for research and getting the parts together.

the sonic results are outstanding. i didn't make any measurements yet, though.
the reason for me to build them was, that i had issues in the midrange caused by reflections from the wall behind the monitors. for what it looks like at the moment, this issue has completely been solved.

i'd be happy to answer any questions!

snip

snap

snup

Looks nice. But i got a whole lot more impressed when i scrolled to the second picture. Nice place.

Where did you get the hemp fiber from though?
And does anyone, Ethan maybe, have any thoughts on how that compares sound-wise as compared to fiberglass?

snipp

snapp

snupp

thanks for your comment!

i got the hemp fiber mats from a manufacturer in bavaria/germany.
they provide all necessary information in english - here is a pdf file:

http://www.thermo-hanf.de/upload/pdf...t_2004_ENG.pdf

from what i've read the fibre glass that is being recommended in most DIY forums has a gross density of about 48 kg/cubic meter. so this hemp fiber (40 kg/cubic meter) is in the same ballpark regarding all parameters like structure, gross density...

Cool. One more question, just out of curiosity... what are your speakers standing on? not the stools or whatever underneath, but what are those pads they're sitting on?

they're concrete flagstones. the same kind as are being used for a pavement.
each speaker stands on two flagstones, and each flagstone is about 30 kg. so it's about 60 kg below each speaker.

Coole Sache Hannes kfhkh

I've been waiting for you doing that. I can imagine how much your acoustics improved now.

PS: My girlfriend and I, we'll be in Berlin from 25.5. -29.5. Let's meet and have a beer together.

How much did you spend for all this job, and how much time, if I may ask? Thanks kfhkh

this is great news! i'm looking forward to meeting both of you - let's rather have a couple of drinks than just a single beer... cooge

as i've already written above: without counting the time for research/planning/getting the parts together it took about 20 hours to build them. i didn't do it alone but with the help of someone. it'll take a little longer if you want to do it all alone. and sometimes it's cool to have a couple of helping hands - for instance for covering the wooden frames with the fabric.
i paid roughly 500 euro with the hemp being the most expensive part. if you use fiber glass instead of the hemp and perhaps a cheaper fabric, this job could be done for about 250 euro. not too much at all... cellfone

I'd say I'll cellfone



Your hemp-absorbers: Have you put them only on one side?

you mean only on one side of the room? yes, i didn't want it to become sounding too dead.
moreover i did it following the "live end - dead end" principle. behind the speakers are the broadband absorbers, and on the opposite wall (behind me when i'm sitting in front of the speakers) i have a huge shelf with vinyl records serving as a diffusor.

What about bass frequencies? Have you already an idea for a cheap hemp trap heh

WOW, those panels look tremendous my friend. I applaud your creative genius!
IKEA of all places. Too right!

Now, in terms of density, we can easily see the and read how this is compared to other acoustic mediums, however, I am incredibly curious about the acoustical coefficients. Does the manufacturer make this data available for the raw materials? If so, can you either List it, or point us to it?

Wonderful, and I am sure your room sounds a SITE bit better than pre-treatment.
Though the frames you are using will reflect a lot of sound, I imagine the trade off between magnificent aesthetics and MASS absorption, is very good.


I'd also love to read about results using ETF software. That would really bring this full circle in my opinion.

Great job!

powerjoe, many thanks for your kind comments! heh
somewhere above in this thread i've posted a link to pdf file from the hemp manufacturer's website. though we're talking about a bavarian company, it's in english.

the paper says the valued degree of noise of this material is (as per ISO 11654 at 160 mm) α = 1,00.
the bulk density is specified like this: 40 kg / cubic meter.

this is all i could find.

i've seen your signature - looks like you are pretty experienced regarding room acoustics.
from what i've heard in room before (and what i hear now) and in comparison to listening tests in rooms that have been professionally treated these absorbers really seem to be a HUGE improvement.
nevertheless i don't have any experience with proper measurements. can you guide me a bit? is there any software/technique/additional equipment you would recommend?

Indeed, I bet that is HUGE difference and a marked in provement!

I recommend download the free ETF acoustic software trial here:

http://www.etfacoustic.com/

It's an impressive and powerfull tool to measure your room acoustics. Of course, we will not know just WHAT the improvement is over your pre-treatment, but it will tell us a good deal about what you are working with now.

I am very interested in your findings!


Good luck!

Joel

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

Airmate:

ETF

Sample Champion

WinMLS

EASERA

Just for general info... here's a list of acoustic testing demo downloads... if no joy on the mac thingy, maybe borrow a PC for a couple of days?

Related query... Anyone ever tried ETF on a Mac with a windoze emulator?

http://www.lismoresystems.com/en/

PS: Nice looking traps! I love the use of the shelving for frames - clever man.

PPS: Hemp? Ya damned hippy! jkthtyrt What did that cost? BTW fiberglass is not a health risk... dat's an urban myth. Just cover it with fabric and you are golden.. Of course you did the upholtery thing with your DIY "Dope Traps" anyway - so I don't see a difference. But what the hell - hemp is always cool right? I think I'll recover the seats in my '57 caddy with it... my $0.02 anyway.

EDIT: FOR THE MAC

http://www.supermegaultragroovy.com/...s/FuzzMeasure/

Looks great Airmate, and the second pic is Definitely impressive! Excuse my ignorance everyone, but I was just wondering Why these units don't count as Bass Traps?? is it just the fact that they are covered in Linen instead of a stiff membrane? they seem big and deep enough to act as bass traps.. confoosed

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.

i paid 235 euro - quite cheap for that much weed, isn't it? cooge

btw: "dope traps" is a great designation...truly funny... jkthtyrt

Smokin'! jkthtyrt

Really, though, what's the flame spread / smoke density specs on hemp compared to fiberglass? wworried

here's the specs - in english:

http://www.thermo-hanf.de/upload/pdf...t_2004_ENG.pdf

peachh

Well its clearly absorptive

http://www.thermo-hanf.de/upload/pdf...sche_Daten.pdf

There is no break down per frequency band... but it did get a 1.00 coefficent on a "Klasse A" curve so that looks good. Look here for a general description

http://www.rockfon.co.uk/sw1165.asp?PID=116

This info is not broken down per frequency - but even absent assurance of how well does low in the band - keeping in mind that these Dope Traps are about a foot thick - I'd bet they are excellent broadband absorbers all the way down to the bottom.

Look at the performance of some other natural fiber products... at 4" / 100mm thick:

http://www.bobgolds.com/Absorber/home.htm

So at a guess, I'd reckon these 240mm thick panels are truly broadband... no need to conseder "upgrading" them with a membrane. That would just introduce peaks and dips in the absorption curve. Why would you want that?

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