OK, this has been bugging me for years. I've tried Googling but not come up
with anything, and ayway I quite like discussing things here sometimes, you
never know what else may turn up.

I have always understood that the lowest frequency that can be generated in
a room is determined by the dimensions of that room. (Governed by V = F
Lambda). eg to produce 100 Hz, there must be a minimum distance between
corners of about 3.4 metres.

Anyway, quite clearly, a pair of headphones with ears attatched is nowhere
near 3.4 metres in size yet can produce vey low frequencies with ease. Why?


Thanks,


Gareth.

Gareth Magennis wrote:
I have always understood that the lowest frequency that can be generated in
a room is determined by the dimensions of that room.

Wrong. Dimensions of the room affect the resonance of the room, not the
frequencies that can propigate through it.

"Joe Kesselman" wrote in message
...
Gareth Magennis wrote:
I have always understood that the lowest frequency that can be generated
in a room is determined by the dimensions of that room.

Wrong. Dimensions of the room affect the resonance of the room, not the
frequencies that can propigate through it.


Oh, I was under the impression that for a wave to exist in a room, there had
to be enough distance between walls to support one complete wavelength.
Maybe I should go back to school for a bit.


Thanks,

Gareth.

On Sat, 10 Dec 2005 16:23:06 +0000 (UTC), "Gareth Magennis"
wrote:


"Joe Kesselman" wrote in message
...
Gareth Magennis wrote:
I have always understood that the lowest frequency that can be generated
in a room is determined by the dimensions of that room.

Wrong. Dimensions of the room affect the resonance of the room, not the
frequencies that can propigate through it.


Oh, I was under the impression that for a wave to exist in a room, there had
to be enough distance between walls to support one complete wavelength.
Maybe I should go back to school for a bit.


Thanks,

Gareth.

Here is an e-book that might have more than you want to know.

http://www.motionmountain.net/



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place

Gareth Magennis wrote:
"Joe Kesselman" wrote in message
...
Gareth Magennis wrote:
I have always understood that the lowest frequency that can be generated
in a room is determined by the dimensions of that room.

Wrong. Dimensions of the room affect the resonance of the room, not the
frequencies that can propigate through it.

Oh, I was under the impression that for a wave to exist in a room, there had
to be enough distance between walls to support one complete wavelength.

For a WAVE to exist in a room, yes, the room has to have sufficient
dimensions.

But to PRODUCE a tone of any given frequency, all you have to
do is change the pressure at that frequency. Imagine a very small
room, say, 10 cm by 10 cm by 10 cm, that's very well sealed and
filled with air at STP. Hook a small hose to the room and alternately
blow in and suck air out, say 5-6 times per minute. Obviously, the
pressure in the room will change at a frquency of 5-6/minute (about
1/10 Hz!). You've produced a 1/10 Hz sound in this little room, a room
which is MUCH smaller than a 1/10 Hz wave (which is about a mile
long!).

Maybe I should go back to school for a bit.

No, just don't go to THAT one any more! :-)

wrote:
You've produced a 1/10 Hz sound in this little room, a room
which is MUCH smaller than a 1/10 Hz wave (which is about a mile
long!).

Sorry, that's about two miles long.

"Gareth Magennis" wrote in message
...

OK, this has been bugging me for years. I've tried Googling but not come
up with anything, and ayway I quite like discussing things here sometimes,
you never know what else may turn up.

I have always understood that the lowest frequency that can be generated
in a room is determined by the dimensions of that room. (Governed by V =
F Lambda). eg to produce 100 Hz, there must be a minimum distance between
corners of about 3.4 metres.

That would be completely and totally wrong.

In fact it is easier to generate low bass in a smaller room. '

There's a 12 dB up slope (as frequency decreases) in response that commences
at a frequency that is inversely proportional to room size. The smaller the
room the higher the frequency that the upslope commences. The higher the
frequency that the upslope commences, the greater the bass boost at low
frequencies. The smaller the room, the stronger the bass at low frequencies.

This is one reason why speakers with lots of deep bass sound tubby in small
rooms.

Arny,

This is one reason why speakers with lots of deep bass sound tubby in
small rooms.

Another reason is that small room bass resonances start higher up in
frequency. I see this all the time in audio groups and forums, where people
indict Mackie HR-824 loudspeakers as boomy and tubby, with a low end that's
"out of control" or some such. In fact 824s have a very full and very clean
low end, and the real culprit is the room's resonances coupled with a lack
of bass trapping.

--Ethan

wrote in message
oups.com...

Gareth Magennis wrote:
"Joe Kesselman" wrote in message
...
Gareth Magennis wrote:
I have always understood that the lowest frequency that can be
generated
in a room is determined by the dimensions of that room.

Wrong. Dimensions of the room affect the resonance of the room, not the
frequencies that can propigate through it.

Oh, I was under the impression that for a wave to exist in a room, there
had
to be enough distance between walls to support one complete wavelength.

For a WAVE to exist in a room, yes, the room has to have sufficient
dimensions.

But to PRODUCE a tone of any given frequency, all you have to
do is change the pressure at that frequency. Imagine a very small
room, say, 10 cm by 10 cm by 10 cm, that's very well sealed and
filled with air at STP. Hook a small hose to the room and alternately
blow in and suck air out, say 5-6 times per minute. Obviously, the
pressure in the room will change at a frquency of 5-6/minute (about
1/10 Hz!). You've produced a 1/10 Hz sound in this little room, a room
which is MUCH smaller than a 1/10 Hz wave (which is about a mile
long!).

Maybe I should go back to school for a bit.

No, just don't go to THAT one any more! :-)



Makes perfect sense, of course. It's funny how you get locked into an
assumption sometimes about something so fundamental. At some point in the
past I have obviously taken the theory of standing waves and applied it to
propagation. So this is how Homer Simpson feels.



Thanks,

Gareth.

In article , "Arny Krueger" wrote:

"Gareth Magennis" wrote in message
...

OK, this has been bugging me for years. I've tried Googling but not come
up with anything, and ayway I quite like discussing things here sometimes,
you never know what else may turn up.

I have always understood that the lowest frequency that can be generated
in a room is determined by the dimensions of that room. (Governed by V =
F Lambda). eg to produce 100 Hz, there must be a minimum distance between
corners of about 3.4 metres.

That would be completely and totally wrong.

In fact it is easier to generate low bass in a smaller room. '

There's a 12 dB up slope (as frequency decreases) in response that commences
at a frequency that is inversely proportional to room size. The smaller the
room the higher the frequency that the upslope commences. The higher the
frequency that the upslope commences, the greater the bass boost at low
frequencies. The smaller the room, the stronger the bass at low frequencies.

This is one reason why speakers with lots of deep bass sound tubby in small
rooms.


On the other hand, in a really big room, at some far points, the bass can seem very loud compared to
the treble.

greg

On the other hand, in a really big room, at some far points, the bass can
seem very loud compared to
the treble.

greg

I noticed something interesting the other night with regard to bass in large
rooms. The wife and I went to a new Best Buy that opened in the area and I
heard this relatively deep and loud bass coming from the car stereo display.
The bass carried nicely with the 20' high ceilings and the several hundred
feet lenght & width of the store. When I got up close to the bass driver, a
single 12" cone in a small vented box that was doing about 1/2" p-p
excursion, the sound pressure level could not have been above 82dB. I could
not even feel anything. It was audible, but no feely. (In fact the port had
a severe problem with mach noise--it was buzzing and fuzzing like mad, but
that's another story).
From 70' away, the bass was being reinforced nicely by the building. It
sounded like a MUCH bigger and louder system. But there it was, this puny
little el-cheapo boom box that goes in the kids' "ricers".
I've noted how large spaces always reinforce the deeper bass notes nicely.
Gymnasiums do amazing things. I walked into the YMCA one morning to use the
overhead track and I hear this disco music with rather good thumpin' bass. I
look down from the track and there's an arobics class in session and the
stereo is one of those really cheap K-Mart specials from the late 1970s--the
kind with the particle board speakers with Masonite back and baffle panels
and the $2.00 8" drivers with whizzer cones. In a house, they have no bass
at all, but in a large gym, the building reinforces the minutest amount of
low bass with amazing efficiency.
Small rooms' standing waves tend to kill low bass. It takes brute force to
achieve low bass in a small room.
So started the "Bass Pig" Project, more than 20 years ago. I have this 1,000
sq ft studio that, no matter what commercial speakers I put in there, made
all the bass somehow disappear. Speakers that sounded good in the store, had
nothing happening below 125Hz in this room. If I stood 32' away, I could
hear some low bass, but in the middle of the room, forget it. That's when I
custom-built an array that would have more than enough low bass, so I
wouldn't have to stand 32' away to hear and feel a 16Hz organ pedal tone,
for example. In fact, I can't crank it up that much because the ceiling
seems as if it will fall and I can hear sounds like wood cracking up there
and in the walls. But the bass is good now. I can't imagine how it would
sound in a large venue, like a gym.


--
Best Regards,

Mark A. Weiss, P.E. & Resident "Bass Pig"
www.mwcomms.com
-

Gareth Magennis wrote:
wrote

[...the usual lucid explanation...]

Maybe I should go back to school for a bit.

No, just don't go to THAT one any more! :-)

Makes perfect sense, of course. It's funny how you get locked into an
assumption sometimes about something so fundamental. At some point in the
past I have obviously taken the theory of standing waves and applied it to
propagation. So this is how Homer Simpson feels.

No need to feel foolish - some of the high end press perpetuates
misconceptions about smaller spaces "not giving bass room to develop".


Francois.