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Author Topic: Cant hear the bottom  (Read 5927 times)

blastula

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Cant hear the bottom
« on: December 15, 2010, 04:13:25 pm »

I'm monitoring on proac 100's with an adcom 555 amp. also on self-powered dynaudio bm15a's. the audio passes from a UA2192 (d/a) thru a coleman TB4 (volume control/monitor switcher box).

for some reason my room just soaks up bass. i cant gauge it for shit when mixing. i just blew out the left speaker in my minivan while testing a mix that had ridiculous bottom that i just couldnt hear in my room...

i posted in the "whatever works" forum...leaning toward adding a subwoofer and asking how to do it...but it was suggested there that subwoofers won't help the problem in the room. and one brother suggested i post here.....

i know the problem is the room...i thought that's why subwoofers are used...no??? i dont think i can get into construction right now, but any other ideas would be much appreciated

thanks,
rob laufer
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Dominick

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Re: Cant hear the bottom
« Reply #1 on: December 15, 2010, 05:14:36 pm »

Subwoofers are not to compensate for a bass sucking room.
They are to extend LF bandwidth and power handling of the monitor system.
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Dominick Costanzo

compasspnt

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Re: Cant hear the bottom
« Reply #2 on: December 15, 2010, 05:39:21 pm »

You probably don't need to do any construction, most likely you need some bass trapping acoustic treatment, perhaps in the corners, etc. Every room is different though.

What are the dimensions and wall/floor/ceiling coverings now?

Where in the room are your monitors/desk/etc., relative to the walls?
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KB_S1

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Re: Cant hear the bottom
« Reply #3 on: December 15, 2010, 06:37:19 pm »

It is quite often a back to front approach in basic rooms.
If you can't hear the bass you probably need to add bass trapping.

I had success in a friends place using large rolls of loft insulation.
I simply kept them in their packaging, stood them upright in the corners of the room and placed simple fabric covered frames in front to disguise.
I think I stacked 2 rolls in each corner and got a couple hidden behind furniture too.

Be aware this was a minimum budget approach to help get the room more usable. It did work reasonably well and after I moved a few things around it actually got to be a decent room.

Have you checked your measurements (dimensions)? In the room i am referring to I found that the distance between speakers, listening position and boundaries shared many matches or multiples. Moving the speakers a little helped a lot too.
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Bogic Petrovic

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Re: Cant hear the bottom
« Reply #4 on: December 15, 2010, 07:18:18 pm »

compasspnt wrote on Wed, 15 December 2010 23:39

You probably don't need to do any construction, most likely you need some bass trapping acoustic treatment, perhaps in the corners, etc.....



Right!
Blastula, if you buy a couple of packages of rockwool and simply put it on the floor in your room, and listen your music again, you will easily notice that (some of) low end frequencies "are back" and you can hear it again.

That does the trick!

Classic bass trapping is only more effective, aesthetic and practical method to bring back low end sound in any room.

Waves with large wavelength (you called it "bottom"), cancel each other because reflections from walls... if you absorb it on the walls/corners (dissipate it)... there will be much smaller amount of reflected waves to cancel your direct main wave.

Subwoofers can't resolve this because nature of (phase) cancellation problem. If you put more acoustical energy in room, more will be reflected then more will be cancelled, and this way we can't have any benefit.

Hope this helps

regards

Boggy

blastula

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Re: Cant hear the bottom
« Reply #5 on: December 16, 2010, 01:55:21 pm »

Here's a crude drawing of my room...
(Hope the upload shows up)
The ceiling is 8'hi.
The back wall has a 5'x5' double glass window that is always covered by a rice paper curtain...the wall space on the sides of the window is mostly covered with some kinda soundboard, covered with fabric. all the walls behind the speakers are covered similarly.
index.php/fa/16008/0/
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Geoff Emerick de Fake

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Re: Cant hear the bottom
« Reply #6 on: December 16, 2010, 05:56:15 pm »

Is there enough bass when you stand in the back of the room?
And just a silly question: are you sure your speakers are in-phase?
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KB_S1

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Re: Cant hear the bottom
« Reply #7 on: December 16, 2010, 07:13:58 pm »

That is a pretty decent sized room.
What is the wall construction/materials?
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blastula

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Re: Cant hear the bottom
« Reply #8 on: December 17, 2010, 07:50:21 pm »

the speakers are in phase Smile

the walls are woodframe and drywall...the back wall is double framed, insulation inside, sheetrock and soundboard on top. the walls behind the speakers are single framed with a few layers of soundboard..cloth fabric covers most of the front and back walls...

the perception of bottom doesnt change much in the back of the room, a teeny bit maybe...and the thing is: it's not that i don't hear bottom. it's just that it always sounds okay, i can never hear when there's too much. i think the room is maybe very discriminating in which frequencies it eats. i think it likes around 90hz. thats the one that usually gets the mastering engineers rolling in the aisles....
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Geoff Emerick de Fake

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Re: Cant hear the bottom
« Reply #9 on: December 18, 2010, 03:59:50 am »

Yes, it looks very much like one of the walls is absorbing too much. Basically, all your walls are bass absorbers.
It's not very easy to determine which one, but an RTA would help. Moving the microphone till yoy see asignificant notch in the response. Once you've found it, you must change its resonant parameters. You can rigidify it, dampen it or make it more reflective. The absence of bass build-up at the back of the room seems to point at the back wall.
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DanDan

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Re: Cant hear the bottom
« Reply #10 on: January 05, 2011, 03:30:33 pm »

Rob, the cheapest quickest and very powerful tweak is position.
Try moving your speakers and/or your listening position. And don't forget height.
Unless you have a photographic sonic memory Wink
you will need to measure the response at each position.
An RTA is OK, but software like FuzzMeasure, REW, Smaart, ARTA, ETF, etc. excel at this type of iterative tweaking.

Bogic Petrovic

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Re: Cant hear the bottom
« Reply #11 on: January 06, 2011, 01:43:16 am »

Geoff Emerick de Fake wrote on Sat, 18 December 2010 09:59

Yes, it looks very much like one of the walls is absorbing too much. Basically, all your walls are bass absorbers.
.....

Room modes appears because reflections, and if walls are  absolutely absorptive there wouldn't be a notches because room behavior, in other words, this will be a good thing... and lack of bass response may be because loudspeakers and not the room.

I agree with DanDan, with notches in room bass response, careful loudspeaker placement is valid approach (one of..) to minimize it.

Geoff Emerick de Fake

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Re: Cant hear the bottom
« Reply #12 on: January 06, 2011, 06:19:32 am »

Bogic Petrovic wrote on Thu, 06 January 2011 00:43

Geoff Emerick de Fake wrote on Sat, 18 December 2010 09:59

Yes, it looks very much like one of the walls is absorbing too much. Basically, all your walls are bass absorbers.
.....

Room modes appears because reflections, and if walls are  absolutely absorptive there wouldn't be a notches because room behavior, in other words, this will be a good thing...
I haven't said absolutely absortive. What I mean is due to the flexible nature of the construction, the walls may act as selective absorbers. The desription of the problem rules out room modes as the principal culprit since some frequencies would be dominant, which does not seem to be the case. Room modes produce peaks and dips. Tuned absorbers produce dips only.
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Thomas Jouanjean

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Re: Cant hear the bottom
« Reply #13 on: January 06, 2011, 10:46:14 am »

Geoff Emerick de Fake wrote on Thu, 06 January 2011 05:19

Bogic Petrovic wrote on Thu, 06 January 2011 00:43

Geoff Emerick de Fake wrote on Sat, 18 December 2010 09:59

Yes, it looks very much like one of the walls is absorbing too much. Basically, all your walls are bass absorbers.
.....

Room modes appears because reflections, and if walls are  absolutely absorptive there wouldn't be a notches because room behavior, in other words, this will be a good thing...
I haven't said absolutely absorptive. What I mean is due to the flexible nature of the construction, the walls may act as selective absorbers. The description of the problem rules out room modes as the principal culprit since some frequencies would be dominant, which does not seem to be the case. Room modes produce peaks and dips. Tuned absorbers produce dips only.


I have been in a studio last year that had similar issues, a sharp loss of energy starting gradually under 500Hz and then a sharp tilt down from ~250Hz. A good -4dB trend all over the lower spectrum.

It was a badly semi-treated room with a not so easy geometry we were asked to upgrade.

The problem for the drop in LF was mainly 2 folds:

- side and back walls construction was such that they became rather transparent in the LF (light but very rigid structure). They hence caused a good level of "absorption by transmission" to the adjacent rooms, while the higher frequencies were diffracted back in the room which had little if any treatment at the listening position, creating a clear shift.

- Modal behvaviour was hence weird (not very pro-eminent) and pretty complex (the room had a special shape) and from calculations we discovered that they were spaced in such a way that they likely increased the perception of that shift.

The solution came from adding a certain amount density to the walls, and basically reverse engineer the structure's behaviour in the LF so we would have a good knowledge of the estimated lower coincident frequency behaviour of the walls, which is a good indicator of LF "transparency" roll-in point of a wall, and then treating the room accordingly, knowing the modal response would evolve a certain way in the process.

Doing so allowed to eliminate the shift and raised the room's response to a much higher standard.
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DanDan

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Re: Cant hear the bottom
« Reply #14 on: January 07, 2011, 09:35:08 am »

Just to amplify that loudspeaker point from Bogic.
I have found over and over that mixing translates better with a sloped frequency response. Unfortunately the opposite slope to the one here.
This is described fairly simply at Understanding RTA at studiotips.com
Intriguingly what appears to be the very same curve was used by Bruel and Kjaer on a test record way back. http://www.bksv.com/doc/17-197.pdf

If you have controls on the speakers turn down those tweeters and up the bass.

A couple of sheets of MDF simply placed there might beef up the speaker sides of those closets creating a bit of a bass horn. ( a la Thomas's post)

I am kinda assuming you have HF reflection treatment in place already.
A cloud and side reflection killing panels. Overall sometimes called a Reflection Free Zone. If not, then you could re-read my stsop ni esrever....

DD

franman

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Re: Cant hear the bottom
« Reply #15 on: February 03, 2011, 08:31:21 pm »

Dandan.. right on!! I agree with our advice...

DanDan wrote on Wed, 05 January 2011 15:30

Rob, the cheapest quickest and very powerful tweak is position.
Try moving your speakers and/or your listening position. And don't forget height.
Unless you have a photographic sonic memory Wink
you will need to measure the response at each position.
An RTA is OK, but software like FuzzMeasure, REW, Smaart, ARTA, ETF, etc. excel at this type of iterative tweaking.




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