Unusual LF in long & narrow rooms

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

Unusual LF in long & narrow rooms

Postby Ido » Fri Sep 10, 2010 5:20 pm

I'm having thoughts on possible influence of room dimensions & ratios on LF in long narrow rooms.
First, 2 examples which emphasized this issue for me, 2 different studios, yet with similarities:
2 drummers who record, both had to have the studio in residential dwellings, so beside obvious TL issues, the inner acoustic room dimensions are a given compromise to be lived with.
In both cases, the drumming-recording space is smallish and squarish, yet came out fine, and the control is long and narrow, and came out ok and as expected, yet less good than the adjoining smaller recording rooms.
In one case, recording and control rooms were "cut out" from a given long space, so that they share the same width. Speaking from memory, width is ~ 3.10 m, height ~ 2.6 m.
the dividing wall is a diagonal wall, and the drumming room average length was ~ 2.2-2.5 m. the control prolly had at least a 4.5 m length.
both rooms had inner drywall envelope, with decent broadband absorption.
After build, the recording drum room feels nice, good and clean, no LF pressure, and the recordings are fine.
The control on the other hand has a LF pressure feel, getting speaker-listener placement was long and not wonderous, still bit compromised, though workable as to be expected.
In the second scenario, the drum room was similar to the above in build, dimensions and end result.
The control however was different, didn't share same width, no drywall, all concrete, and was about 2.8 m high, 3.1 meter wide, and 5 meter long.
This room got massive BB treatment to smooth out LF as much as possible, and the end result was that on the one hand I still felt a bit of LF pressure, which was as to be expected, yet to my surprise I also felt a lack of LF in a different range.
This lack of LF was not major at all, just a wee bit. nothing influenced this (speaker/listener positions), and going to the corners there was less LF than I'm used to (the speaker type has nice LF, the only thing I woulda wanted to check was taking speaks and amp out to another room and check)
I could think of no explanation for lack of LF, no drywall, no cavitys, no absorbing wood etc.
Now to clarify, I don't do measurements, even though we have TEF.
All the above is based on personal subjective evaluation, which y'all can readily dismiss.
when I say "LF pressure", I mean by sense, and even by just being in such a room, before playing music (be it live or amped).
I once wrote about this here, years back, and to this day I don't know if you all sense this LF, if you think I need a vacation, or if several of you do share this experience.
In any case, I'm not getting mystical, I'd love to put this to the test, and I do need a vacation.
I have long felt LF pressure in narrow rooms, and I usually thought it was less of a ratio thing, rather that one should simply try and secure a minimum width-length dimension to let a room "breathe" properly (minimum ~3 m, preferably more).
I am still with this as a general guideline.
I've never been big on room ratios, mostly cause here space is almost non-existent and preplanning ratios is a luxury, and I always figured a bigger volume is usually better than a smaller one, even with less good dimensions-ratios, cause you can always do massive BB absorption (and there is significance on the placement in regard to the ratios) and still end up with bigger volume and an overall better room.
Now, I'm just not sure, and am having thoughts on the possible impact of room ratios in rooms that are long, narrow, and with somewhat similar width & height dimensions.
last time I talked with our friend Jonathan-Jonessy, he told me about his current research into LF, modes and small rooms, and also about the possibility of the significance of psycho-acoustics on all this.
Jonathan, hope I got it right, and would be koel if you'd care to step in.
Even koeler If you'd like to come see and measure them rooms.
I for one find the psycho-acoustic part fascinating, and the way Jonathan brought it up at the time, it felt like this might all be related to some extent.
Also maybe of relevance, I feel that in regard to axial modes, we are less sensitive to the first order ones, regardless of freq and system output, so maybe that’s also related.
Bottom line, I'm sharing thoughts and questions.
I am though fairly convinced of the LF "pressure" thing being emphasized in long & narrow rooms with ratio impact.
I threw in the "lack of LF" just for interest, not sure of it's relevance at all, and Flaviou's case just made me think it might have relevance.
Would be glad to hear thoughts and experiences,
Ido
signature
Ido
 
Posts: 2201
Joined: Mon Feb 09, 2004 7:47 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby jonessy » Wed Sep 15, 2010 3:31 pm

I admit this is a little vague to me; especially the term 'pressure', which naturally makes me think about acoustic pressure and not some subjective metric.
Could you try to explain this perceptual attribute you are referring to a little more in depth?

Also, what is it that you are hypothesising?

In order to deduce that the long-narrow architecture contributes to the lack of bass, we first need to make sure that nothing else is the cause.

Have you encountered this in more than one occasion? If yes, then let's try to find a common denominator, except the fact the rooms were long and narrow.

Cheers, :)

Jon.
__________________________
Bert is still my hero.
What d'ya know.
jonessy
 
Posts: 580
Joined: Wed Jan 04, 2006 3:39 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby Ido » Thu Sep 16, 2010 1:34 pm

jonessy wrote:I admit this is a little vague to me; ....


yea, to me as well :D :bang ,
I talked to friend Jonathan, cleared things up, thanks Jonathan.
Regarding what I experience as "LF pressure", Jonathan mentioned the possibility of the relevance of the 0,0,0 mode, a "pressure" mode, which would explain why I sense this pressure consistently throughout the room.
Jon mentioned how his current academic tutor investigated psychoacoustics sensation in relation to room modes, though not this specific mode.
What is interesting and not clear is how volume versus room ratios affect this basic pressure mode.
For the record, I am aware that talking of "sensing" such a low and "obscure" mode might sound a bit shady… ..Terry M. and I once compared our over-sensitivities :| .
Anyways, I"ll try and measure these specific rooms some time if possible.

Regarding narrow-long rooms, what I am getting at is that I think there is more to long and narrow rooms than just playing with the known ratios.
That something happens with the acoustic energy along these longer-narrow spaces, and that this can be separate of just volume and of the perpendicular walls.
Might not be relevant, but I wonder if this might be also relevant in flutter echoes (large areas with less height).
If there is something to this, I also wonder if it's just ratios or if there is also an absolute (related to air and it's behavior?), so that over a mimimal dimension, different story.
I should learn more on the science behine room ratios :oops: .

question:
Have any of you felt-heard "good" acoustic ambience in a long and narrow room?
Remember dimensions?
Think of a memorable good ambient acoustic room "feel", what type of shape-ratio was it?

2 other things:
I also mentioned to Jon how I sometimes feel that we are less sensitive to the first order axial modes, regardless of freq and system output.
Jon said he don't think so and that it prolly is a freq and system output thing.
I'm talking 60-80 Hz range, and I saw that standard 2 way 6" speaks supposedly do have a decent response down to 60 Hz, so I wonder if any of you have a response to this from personal experience?
When people show these nice measurement graphs of their rooms with those formidable first axials, do they sense them similarly to the second ones? Just on a pure power scale?

Regarding what I mentioned of lack of bass, that was a minor sideline, so forget it for now.

I wish Eric were here to put me in my place :mrgreen: .

Ido
signature
Ido
 
Posts: 2201
Joined: Mon Feb 09, 2004 7:47 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby Ido » Mon Sep 20, 2010 11:38 am

thinking aloud..
wondering if the room ratio studies are only about distribution-spacing,
or if there is also an approach to wave interactions.
that maybe in long-narrow spaces the superposition or whatever would lead to something additional.
which leads me to think of the standing waves in pipes and musical wind instruments,
and of the significance of non-axial modes in long-narrow rooms.
yea, well, maybe sometime..
anyways, y'all watch out for them long-and narrow ones.
signature
Ido
 
Posts: 2201
Joined: Mon Feb 09, 2004 7:47 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby jonessy » Mon Sep 20, 2010 12:23 pm

So ask the ladies what's better; long and narrow, or short and wide. :)

The so called frequency distribution is in fact due to the different modes coinciding in phase or anti-phase.
Room-ratio theory is mainly based on this - it all comes down to dimensions.

But... I feel that the effects of damping are often overlooked.
Damping not only increases the decay rate of modal energy, but also has an apparent effect on the resonant frequencies, as the with a considerable amount of damping the wavelengths effectively become a little 'longer'.
This, in turn, has an effect on the phase response, which may definitely be perceivable.

Size optimization began as a method to figure out how to build reverberation chambers that would be as transparent as possible in the LF region, therefore allowing for smaller chambers to be constructed.

Reverb chambers are highly reflective, therefore particle velocity on the walls can assumed to be zero, and the commonly used room-mode equation (rayleigh solution) can be safely used.
Critical listening rooms are somewhat absorptive in the LF.

Trying to apply the conclusions drawn from reverb chambers to listening rooms is wrong from an objective point of view.

This is not to say that the methodology itself is wrong, but that the 'good ratios' that were calculated for highly reflective rooms may not be applicable.

I have never been a big fan of room ratios, partially because of these reasons.

:)
Jon
__________________________
Bert is still my hero.
What d'ya know.
jonessy
 
Posts: 580
Joined: Wed Jan 04, 2006 3:39 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby Ido » Wed Sep 22, 2010 8:20 am

jonessy wrote:So ask the ladies what's better; long and narrow, or short and wide. :)


short & narrow :D


But... I feel that the effects of damping are often overlooked.
Damping not only increases the decay rate of modal energy, but also has an apparent effect on the resonant frequencies, as the with a considerable amount of damping the wavelengths effectively become a little 'longer'.
This, in turn, has an effect on the phase response, which may definitely be perceivable.


Jon, I think Eric was on to this a long while ago, could look for his sayings.

Size optimization began as a method to figure out how to build reverberation chambers that would be as transparent as possible in the LF region, therefore allowing for smaller chambers to be constructed.


didn't know that, interesting.

I have never been a big fan of room ratios, partially because of these reasons.


I was unclear as usual, in the cases I was talking about, the ratio thing was too correct..
a small room with 2 of it's dimension under 3 m (!) yet "good" ratios felt good, same room with one dimension extended to 4-5 m and "not good" ratios sounded less good, even though was well treated for LF, and obviously had much bigger volume.
next time we meet I'd like to go over it with you in depth.

btw, what's the correlation between that basic 0 pressure mode and the other modes?

see you Jon, thanks for the insights.

could be interesting if the folks here posted there impressions and experiences from rooms, especially the wacky ones.
signature
Ido
 
Posts: 2201
Joined: Mon Feb 09, 2004 7:47 pm
Location: Israel

Re: Unusual LF in long & narrow rooms

Postby Ido » Wed Sep 22, 2010 3:02 pm

yo Jonathan, Sukkot <> acoustics..
no Lf probs, mostly standard ratios, no? might be annoysome reflection in the high-med though...
at least better than a mamad-security room.
signature
Ido
 
Posts: 2201
Joined: Mon Feb 09, 2004 7:47 pm
Location: Israel


Return to Discussion

Who is online

Users browsing this forum: No registered users and 6 guests

cron