honeycomb port absorber

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honeycomb port absorber

Postby archive » Mon Apr 12, 2004 3:57 am

From: Dan Nelson <dprimary@e...>
Date: Wed Jan 19, 2000 8:01 am
Subject: honeycomb port absorber

I have the info from Brendan, I just haven't had the time to post it yet.
I wanted to work it into a new article. Do any of you guy's want to write about

resonators that I could edit into the section on bass absorbers?

Dan Nelson

SRF7@a... wrote:

>
> Stuffing broadens the Q (effective range) of the absorber .. if you are
> trying to address a single peak, a unstuffed resonator would be better. I
> wish someone would supply formulae for a "honeycomb" box as alluded to by a
> prior poster to the list ... as I recall he described a unit much like a
> speaker box with throated ports which could be tuned by port size and depth
> for very narrow Q's. An intriguing idea ... interesting to consider however
> that with a tight Q you will actually increase the reverb time of the target
> frequency (the box will store then reemit the captured frequency). This
> would be reduced by a stuffed box, but that would broaden the Q ... I guess
> you really can't buy a free lunch.
>
> >
> > 3) What are the pros/cons to using a fiberglas (loose or ridgid)
> > product with a paper or foil backing ?
>
> The backing acts as an absorptive diaphragm which can be helpful if the
> resonant freq. of the backing is a target frequency ... if the resonant freq.
> of the backing is a hi-Q target freq. then turn the backing toward the room,
> if not then turn the backing away (or even better save money by buying
> un-backed batts and use the savings to buy thicker batts, or beer.
>
> > 4) Should the backing be installed adjacent to the wall or the
> > baffle ?
>
> depends ... see above ... the resonant frequency of paper backed R-11 was
> quoted in this list several weeks ago, but I'm not sure if I recall ... seems
> it was about 250 Hz, but don't rely on my memory.
>
> Scott R. Foster
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Postby archive » Mon Apr 12, 2004 3:58 am

From: SRF7@a...
Date: Wed Jan 19, 2000 3:35 pm
Subject: Re: honeycomb port absorber

In a message dated 1/19/00 3:02:03 AM Eastern Standard Time,
dprimary@e... writes:

> I have the info from Brendan, I just haven't had the time to post it yet.
> I wanted to work it into a new article. Do any of you guy's want to write
> about
>
> resonators that I could edit into the section on bass absorbers?
>
> Dan Nelson
>
> SRF7@a... wrote:
>

Send me the stuff Brendan sent and I'll try and translate to some simple
assembly instructions and a spreadsheet calculator that can be incorporated
in the article.

If that works out I'll take a stab at the pegboard wall.

Scott R. Foster
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Postby archive » Mon Apr 12, 2004 4:00 am

From: Dan Nelson <dprimary@e...>
Date: Thu Jan 20, 2000 12:12 pm
Subject: Re: honeycomb port absorber

I have posted Brendan Minish's spreadsheet for honeycomb port absorbers in the
files along with pictures of the the one that Brendan built.
This is a short explanation that Brendan sent me with the files. The
spreadsheet
is metric. So for US measurement you will have to convert.

Dan Nelson

a honeycomb port absorber is just another kind of Slat absorber or
Helmholtz resonator Except that it uses tuned ports (rather like in
loudspeaker design) instead of narrow slits.

Basically you build a box (or more than one, as needed) and you line it
with rockwool or fiberglass, this provides the absorption.

the front of the box will consist of a sheet of Plywood (I used 18mm
Shuttering ply as here at least, shuttering ply has one side with a
reasonable finish.) with holes drilled into it in a honeycomb pattern with
pipes stuck into them (I used 44mm waste pipe) secured with builders glue.

We can tune the chambers by varying the number of holes or the length on
the pipe.

The basic formula is the Helm-Holtz one

f = c*sqrt(s/LV)/(2*PI)

f = frequency
c = speed of sound
s = surface area of opening
L = length of pipe
V = volume of chamber
PI = 3.14159

Units irrelevant if all the same.
the length of the pipe = physical length of the pipe+2/3 diameter of pipe.
The volume is divided up according to the number of pipes.
So if your box has volume of 1m3 and you have 50 pipes then volume for the
purposes of the equation is 1/50 m3
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Postby archive » Mon Apr 12, 2004 4:00 am

From: Brendan Minish <bminish@o...>
Date: Thu Jan 20, 2000 12:41 pm
Subject: Re: honeycomb port absorber

At 05:12 20/01/2000 -0700, you wrote:
>From: Dan Nelson <dprimary@e...>
>
>I have posted Brendan Minish's spreadsheet for honeycomb port absorbers in the
>files along with pictures of the the one that Brendan built.
> This is a short explanation that Brendan sent me with the files. The
> spreadsheet
>is metric. So for US measurement you will have to convert.

Please note to convert to imperial all you have to do is use your chosen
imperial units for the speed of sound.
--

Brendan Minish
bminish@o...
PGP key available from key servers wwwkeys.pgp.net
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