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Bass resonances in large room

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Anonymous
November 17, 2004 5:33:04 PM

Archived from groups: rec.audio.pro (More info?)

Recorded in a new school gym that sounded pretty good except for the bass
drum, which created about a 30 Hz rumble that carried for a couple of
seconds.

Roughly 40 x 60 x 24. Concrete block wall, wood floor, nondescript
ceiling. Looks like a band of 703 roughly 6' high running around the room
about 6' below the ceiling.

Other than that rumble of thunder, this was a fairly pleasant room--at
least with a floor full of performers and parents. Don't know how it would
sound empty.

Astonishing note: My local middle school (6th - 8th grades) has nearly 80%
participation in the performing arts. Over 400 students play string
instruments, another 400 in the six (!) bands, and like numbers in the
choruses. Phenomenal!

Is there a portable way to contain that noise if I ever wanted to record
anything important in there?
Anonymous
November 17, 2004 5:33:05 PM

Archived from groups: rec.audio.pro (More info?)

Carey Carlan <gulfjoe@hotmail.com> wrote:
>
>Is there a portable way to contain that noise if I ever wanted to record
>anything important in there?

No, but there is probably a place in the room where you can go (or where you
can put the drum) where it will be less of a problem. It's a standing wave
issue, in all likelyhood.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
November 17, 2004 5:33:05 PM

Archived from groups: rec.audio.pro (More info?)

Carey,

> Recorded in a new school gym that sounded pretty good except for the bass
drum, which created about a 30 Hz rumble that carried for a couple of
seconds. <

In large rooms the low frequency problems are mainly excessive reverb, which
is the case here. With smaller rooms the walls are close together so you get
peaks and deep nulls caused by standing waves, but not reverb. In a large
room you're far enough away from the walls to avoid that. But just like with
small rooms, absorption is the solution - the thicker the better, and lots
of it.

--Ethan
Related resources
Anonymous
November 17, 2004 7:47:40 PM

Archived from groups: rec.audio.pro (More info?)

"Ethan Winer" <ethanw at ethanwiner dot com> wrote in
news:xeqdnb-WzdAP7gbcRVn-sQ@giganews.com:

> In large rooms the low frequency problems are mainly excessive reverb,
> which is the case here. With smaller rooms the walls are close
> together so you get peaks and deep nulls caused by standing waves, but
> not reverb. In a large room you're far enough away from the walls to
> avoid that. But just like with small rooms, absorption is the solution
> - the thicker the better, and lots of it.

"Lots of it' seems to be the keyword.

Assuming about 40 x 60 x 24, what percentage of the walls would need
covering to damp the resonances?
Anonymous
November 17, 2004 10:02:15 PM

Archived from groups: rec.audio.pro (More info?)

>"Ethan Winer" <ethanw at ethanwiner dot com> wrote in
>news:xeqdnb-WzdAP7gbcRVn-sQ@giganews.com:
>
>> In large rooms the low frequency problems are mainly excessive reverb,
>> which is the case here. With smaller rooms the walls are close
>> together so you get peaks and deep nulls caused by standing waves, but
>> not reverb. In a large room you're far enough away from the walls to
>> avoid that. But just like with small rooms, absorption is the solution
>> - the thicker the better, and lots of it.

Call the principal. Tell him the school is in for a giat liability
suit if some kid runs into one of the walls, and that they should get
real thick padding all around. That will cover 1/4 of the walls. Then
you might be able to afford enought for the top of the walls.

On Wed, 17 Nov 2004 16:47:40 GMT, Carey Carlan <gulfjoe@hotmail.com>
wrote:


>
>"Lots of it' seems to be the keyword.
>
>Assuming about 40 x 60 x 24, what percentage of the walls would need
>covering to damp the resonances?

Willie K. Yee, M.D. http://users.bestweb.net/~wkyee
Developer of Problem Knowledge Couplers for Psychiatry http://www.pkc.com
Webmaster and Guitarist for the Big Blue Big Band http://www.bigbluebigband.org
Anonymous
November 18, 2004 12:14:43 AM

Archived from groups: rec.audio.pro (More info?)

>>> In large rooms the low frequency problems are mainly excessive reverb,
>>> which is the case here

In large rooms the high frequency problems are mainly erverb..as you go lower
it's a whole different game.


John A. Chiara
SOS Recording Studio
Live Sound Inc.
Albany, NY
www.sosrecording.net
518-449-1637
Anonymous
November 18, 2004 1:04:36 PM

Archived from groups: rec.audio.pro (More info?)

Carey,

> Assuming about 40 x 60 x 24, what percentage of the walls would need
covering to damp the resonances? <

How much absorption you need to obtain a particular RT60 (reverb decay time)
depends on what's in the room now - what's on all the surfaces, how many
windows, cinder block or sheetrock walls, etc.

I'll guess that 20% of the total area of all six surfaces is a good start.
Since boominess is the main problem and you want the space to sound good for
music, not just speech, a permanent treatment solution would use rigid
fiberglass that's four inches thick. Thicker materials don't absorb "more"
than thin ones, but they do absorb to a lower frequency. If the fiberglass
panels are suspended away from the walls/ceiling by a few inches they'll
absorb to an even lower frequency.

I noticed you asked about a portable solution, and that's what my company
RealTraps makes. But understand that for a space that size you're looking at
a fair number of panels.

--Ethan
Anonymous
November 19, 2004 5:16:05 AM

Archived from groups: rec.audio.pro (More info?)

"Ethan Winer" <ethanw at ethanwiner dot com> wrote in
news:u7-dnSz-n8yKJwHcRVn-3w@giganews.com:

> I noticed you asked about a portable solution, and that's what my
> company RealTraps makes. But understand that for a space that size
> you're looking at a fair number of panels.

Thanks, Ethan. That's what I needed to know. IOW, it isn't an option.
November 19, 2004 12:47:45 PM

Archived from groups: rec.audio.pro (More info?)

Carey Carlan <gulfjoe@hotmail.com> wrote in message news:<Xns95A5D86586A66gulfjoehotmailcom@207.69.189.191>...
> "Ethan Winer" <ethanw at ethanwiner dot com> wrote in
> news:u7-dnSz-n8yKJwHcRVn-3w@giganews.com:
>
> > I noticed you asked about a portable solution, and that's what my
> > company RealTraps makes. But understand that for a space that size
> > you're looking at a fair number of panels.
>
> Thanks, Ethan. That's what I needed to know. IOW, it isn't an option.

Well if you don't care what the live show sounds like but you want to
make the RECORDING sound better, and your problem is really at 30 Hz,
a graphic EQ will be a big help. Just notch out the 30 Hz.



Mark
Anonymous
November 20, 2004 6:00:00 AM

Archived from groups: rec.audio.pro (More info?)

makolber@yahoo.com (Mark) wrote in
news:3367f36e.0411190947.241e3705@posting.google.com:

> Well if you don't care what the live show sounds like but you want to
> make the RECORDING sound better, and your problem is really at 30 Hz,
> a graphic EQ will be a big help. Just notch out the 30 Hz.

At best a second-rate solution. I still need the fundamental of that big
bass drum and some of the resonance. It just needs to fade about three
times as fast.

Does anyone make an anti-reverb? <g>

My best substitute is to run extra-heavy noise reduction band limited to
the resonant range. It pulls down the levels of quiet sounds. I guess an
expander with a very low knee and band pass would also do the job.
Anonymous
November 20, 2004 6:00:01 AM

Archived from groups: rec.audio.pro (More info?)

Carey Carlan <gulfjoe@hotmail.com> wrote:
>makolber@yahoo.com (Mark) wrote in
>news:3367f36e.0411190947.241e3705@posting.google.com:
>
>> Well if you don't care what the live show sounds like but you want to
>> make the RECORDING sound better, and your problem is really at 30 Hz,
>> a graphic EQ will be a big help. Just notch out the 30 Hz.
>
>At best a second-rate solution. I still need the fundamental of that big
>bass drum and some of the resonance. It just needs to fade about three
>times as fast.
>
>Does anyone make an anti-reverb? <g>

No, but they do make an anticompressor. A multiband compressor that will
also do expansion can be a big help for fixing this sort of thing. Make
a band centered around the problem area and expand it while leaving the
rest of the bandwidth unchanged.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
November 20, 2004 11:53:11 AM

Archived from groups: rec.audio.pro (More info?)

kludge@panix.com (Scott Dorsey) wrote in message news:<cnmert$l4q$1@panix3.panix.com>...
> Carey Carlan <gulfjoe@hotmail.com> wrote:
> >makolber@yahoo.com (Mark) wrote in
> >news:3367f36e.0411190947.241e3705@posting.google.com:
> >
> >> Well if you don't care what the live show sounds like but you want to
> >> make the RECORDING sound better, and your problem is really at 30 Hz,
> >> a graphic EQ will be a big help. Just notch out the 30 Hz.
> >
> >At best a second-rate solution. I still need the fundamental of that big
> >bass drum and some of the resonance. It just needs to fade about three
> >times as fast.
> >
> >Does anyone make an anti-reverb? <g>
>
> No, but they do make an anticompressor. A multiband compressor that will
> also do expansion can be a big help for fixing this sort of thing. Make
> a band centered around the problem area and expand it while leaving the
> rest of the bandwidth unchanged.
> --scott

Well that does rasise an interesting question. If a room resonates at
30 Hz and creates a freq response peak and ringing at 30 Hz, if you
create an EQ curve that matches the inverse of the room so it just
flattens the peak, it should also take out the ringing. No? Cascaded
linear systems?

Mark
Anonymous
November 20, 2004 2:31:53 PM

Archived from groups: rec.audio.pro (More info?)

Mark wrote:

> Well that does rasise an interesting question. If a room resonates at
> 30 Hz and creates a freq response peak and ringing at 30 Hz, if you
> create an EQ curve that matches the inverse of the room so it just
> flattens the peak, it should also take out the ringing. No? Cascaded
> linear systems?

If the equalization is not out of phase with the resonance
as measured at the speaker (which is very hard to do) it can
add to it. Inversion means both magnitude and phase correction.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
November 20, 2004 4:26:34 PM

Archived from groups: rec.audio.pro (More info?)

Mark <makolber@yahoo.com> wrote:
>
>Well that does rasise an interesting question. If a room resonates at
>30 Hz and creates a freq response peak and ringing at 30 Hz, if you
>create an EQ curve that matches the inverse of the room so it just
>flattens the peak, it should also take out the ringing. No? Cascaded
>linear systems?

It does. But Carey wants to take the ringing out without removing the
peak, probably because the peak is not evident in the direct sound.

This is not a very common problem, and it's really a sign of just
catastrophically bad acoustics. But considering that I have a gig
in a high school multipurpose room myself in five hours...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
November 20, 2004 8:39:40 PM

Archived from groups: rec.audio.pro (More info?)

>Does anyone make an anti-reverb? <g>

Transient Designer type units can do this on recordings.


John A. Chiara
SOS Recording Studio
Live Sound Inc.
Albany, NY
www.sosrecording.net
518-449-1637
Anonymous
November 20, 2004 8:41:58 PM

Archived from groups: rec.audio.pro (More info?)

>
>Well that does rasise an interesting question. If a room resonates at
>30 Hz and creates a freq response peak and ringing at 30 Hz, if you
>create an EQ curve that matches the inverse of the room so it just
>flattens the peak, it should also take out the ringing. No?

The best solution is to treat the room..but cutting down the amount of
offending frequency produced can help. It won't "take out" the ringing but will
not excite it as much..though you can only control the system response..not the
live source.




John A. Chiara
SOS Recording Studio
Live Sound Inc.
Albany, NY
www.sosrecording.net
518-449-1637
Anonymous
November 20, 2004 8:43:13 PM

Archived from groups: rec.audio.pro (More info?)

>Well that does rasise an interesting question. If a room resonates at
>30 Hz and creates a freq response peak and ringing at 30 Hz, if you
>create an EQ curve that matches the inverse of the room so it just
>flattens the peak, it should also take out the ringing. No?

PLUS...what system do you have that is actually producing substantial energy at
30HZ? It is probably producing harmonics of that.


John A. Chiara
SOS Recording Studio
Live Sound Inc.
Albany, NY
www.sosrecording.net
518-449-1637
Anonymous
November 20, 2004 8:43:14 PM

Archived from groups: rec.audio.pro (More info?)

Blind Joni <blindjoni@aol.com> wrote:
>>Well that does rasise an interesting question. If a room resonates at
>>30 Hz and creates a freq response peak and ringing at 30 Hz, if you
>>create an EQ curve that matches the inverse of the room so it just
>>flattens the peak, it should also take out the ringing. No?
>
>PLUS...what system do you have that is actually producing substantial energy at
>30HZ? It is probably producing harmonics of that.

Live tympani. In a gymnasium.
This is the kind of gig that it is best to turn down altogether.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
November 20, 2004 10:16:55 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:

> It does. But Carey wants to take the ringing out without removing the
> peak, probably because the peak is not evident in the direct sound.
>
> This is not a very common problem, and it's really a sign of just
> catastrophically bad acoustics. But considering that I have a gig
> in a high school multipurpose room myself in five hours...

Which makes for a great opportunity for some of us to get educated. So,
are you going to print your multiband expansion to tape (or DAT or DISK)
live? Or is this something you can do later?
Anonymous
November 20, 2004 11:46:19 PM

Archived from groups: rec.audio.pro (More info?)

>Live tympani. In a gymnasium.
>This is the kind of gig that it is best to turn down altogether.
>--scott
>

Absolutely..I played Tympani in high school..we always rehearsed in the
auditorium..but the competitions were in large gyms..very distracting. Once at
All State I had 128 measures of rest and miscounted..ended with my big tympani
flurry with great conviction and style..too bad I was one measure ahead of the
rest of the group.



John A. Chiara
SOS Recording Studio
Live Sound Inc.
Albany, NY
www.sosrecording.net
518-449-1637
Anonymous
November 21, 2004 2:44:47 AM

Archived from groups: rec.audio.pro (More info?)

makolber@yahoo.com (Mark) wrote in
news:3367f36e.0411200853.283eb628@posting.google.com:

> Well that does rasise an interesting question. If a room resonates at
> 30 Hz and creates a freq response peak and ringing at 30 Hz, if you
> create an EQ curve that matches the inverse of the room so it just
> flattens the peak, it should also take out the ringing. No? Cascaded
> linear systems?

You're assuming that the sound comes from a speaker, an electrical signal.
Mine comes from a 6' concert bass drum. (The fundamental of which I really
want in the recording).
Anonymous
November 21, 2004 3:02:00 AM

Archived from groups: rec.audio.pro (More info?)

> You're assuming that the sound comes from a speaker, an electrical
> signal. Mine comes from a 6' concert bass drum. (The fundamental of
> which I really want in the recording).

Make that a FIVE foot concert bass drum. Measuring the drum against the
drummer, I forgot the percussionist was only a 7th-grader.
Anonymous
November 21, 2004 1:25:46 PM

Archived from groups: rec.audio.pro (More info?)

agent86 <jakethedog@backyard.net> wrote:
>Scott Dorsey wrote:
>
>> It does. But Carey wants to take the ringing out without removing the
>> peak, probably because the peak is not evident in the direct sound.
>>
>> This is not a very common problem, and it's really a sign of just
>> catastrophically bad acoustics. But considering that I have a gig
>> in a high school multipurpose room myself in five hours...
>
>Which makes for a great opportunity for some of us to get educated. So,
>are you going to print your multiband expansion to tape (or DAT or DISK)
>live?

Absolutely not. I wouldn't even try and do eq live to tape on remote
gigs. For one thing, I can't trust my monitors all that far on them.
A lot of these problems you don't even notice until you get the thing
back home and listen to it on the big monitors.

It would be sure nice just to fix the acoustics in the room, though.
But sometimes you can't.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
November 21, 2004 6:24:02 PM

Archived from groups: rec.audio.pro (More info?)

Carey Carlan <gulfjoe@hotmail.com> wrote in message news:<Xns95A7BEBA55507gulfjoehotmailcom@207.69.189.191>...
> makolber@yahoo.com (Mark) wrote in
> news:3367f36e.0411200853.283eb628@posting.google.com:
>
> > Well that does rasise an interesting question. If a room resonates at
> > 30 Hz and creates a freq response peak and ringing at 30 Hz, if you
> > create an EQ curve that matches the inverse of the room so it just
> > flattens the peak, it should also take out the ringing. No? Cascaded
> > linear systems?
>
> You're assuming that the sound comes from a speaker, an electrical signal.
> Mine comes from a 6' concert bass drum. (The fundamental of which I really
> want in the recording).

No..actually I was assuming the signal is being picked up by a mic to
be recorded and therefore can be electrically EQd. Actually it would
be best for you to record it flat (dry) and then you can experiment
with various settings of EQ or whatever when you transfer the
recording i.e. in post.

If the room resonance is accentuating (amplifying) a particular
frequency (30 Hz in your example), then an EQ can bring it back to the
correct level on the recording.

(I know, I wish this web tool has spell checker)

Mark
Anonymous
November 22, 2004 2:51:09 AM

Archived from groups: rec.audio.pro (More info?)

makolber@yahoo.com (Mark) wrote in
news:3367f36e.0411211524.3f15fbb1@posting.google.com:

> If the room resonance is accentuating (amplifying) a particular
> frequency (30 Hz in your example), then an EQ can bring it back to the
> correct level on the recording.

EQ'ing the signal will indeed reduce the volume of the peak, but that fails
to solve my problem.

I want to keep the fundamental at full impact and merely reduce the time it
resonates. Room resonances lengthen the reverb.
November 22, 2004 9:43:05 AM

Archived from groups: rec.audio.pro (More info?)

Carey Carlan <gulfjoe@hotmail.com> wrote in message news:<Xns95A8BFCF2D479gulfjoehotmailcom@207.69.189.191>...
> makolber@yahoo.com (Mark) wrote in
> news:3367f36e.0411211524.3f15fbb1@posting.google.com:
>
> > If the room resonance is accentuating (amplifying) a particular
> > frequency (30 Hz in your example), then an EQ can bring it back to the
> > correct level on the recording.
>
> EQ'ing the signal will indeed reduce the volume of the peak, but that fails
> to solve my problem.
>
> I want to keep the fundamental at full impact and merely reduce the time it
> resonates. Room resonances lengthen the reverb.



How about close mic'ing the drum?

Who is the intended audience that has a playback system that is going
to handle 30Hz?
Anonymous
November 23, 2004 4:02:02 PM

Archived from groups: rec.audio.pro (More info?)

makolber@yahoo.com (Mark) wrote in
news:3367f36e.0411220643.2f0e200@posting.google.com:

>> I want to keep the fundamental at full impact and merely reduce the
>> time it resonates. Room resonances lengthen the reverb.
>
> How about close mic'ing the drum?

This is a 140 piece band. I don't want a mic back in the percussion
section. It would mess up the balance. Also, the close sound of the drum
is not pleasant. I don't want the sound of mallet on head.

> Who is the intended audience that has a playback system that is going
> to handle 30Hz?

In reality, no one. But I'm still going to capture the true sound.
Anonymous
November 24, 2004 3:00:44 AM

Archived from groups: rec.audio.pro (More info?)

On Thu, 18 Nov 2004 16:04:36 +0100, Ethan Winer wrote:

> Carey,
>
>> Assuming about 40 x 60 x 24, what percentage of the walls would need
> covering to damp the resonances? <
.....
> I'll guess that 20% of the total area of all six surfaces is a good
> start. Since boominess is the main problem and you want the space to
> sound good for music, not just speech, a permanent treatment solution
> would use rigid fiberglass that's four inches thick. Thicker materials
> don't absorb "more" than thin ones, but they do absorb to a lower
> frequency. If the fiberglass panels are suspended away from the
> walls/ceiling by a few inches they'll absorb to an even lower frequency.

I think you need more than a few inches for the problem frequencies in
this room: 30 hz. Think you need about 15-30 inches behind the panels to
get a usable absorbtion.

--
Chel van Gennip
Visit Serg van Gennip's site http://www.serg.vangennip.com
!