If a room is small , we can't hear low frequency accuratel..

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It is said that at least 28.5 feet length room is required for the
control room cuz I thought the wave length of 20hz is 56.6 feet

then, I am using Mackie Hr824 monitor speaker in my room
but my room is really small. most long length is just 12feet

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bj <bluesjeon@hotmail.com> wrote:
>It is said that at least 28.5 feet length room is required for the
>control room cuz I thought the wave length of 20hz is 56.6 feet
>
>then, I am using Mackie Hr824 monitor speaker in my room
>but my room is really small. most long length is just 12feet

I'm not sure what you're asking.

But if you play a sweep tone that goes from 20 to 100 Hz, you'll hear
all kinds of things wrong with your room. Play the tone and see.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Scott Dorsey wrote:
> But if you play a sweep tone that goes from 20 to 100 Hz, you'll hear
> all kinds of things wrong with your room. Play the tone and see.

I think the OP was asking if a sound wave can be accurately reproduced
in a room whose longest dimension is *shorter* than half the wavelength
of the frequency in question. (I assume here that "accurate" means
without any form of distortion).

You will still be able to perceive sounds at these low frequencies,
however, it is physically impossible for any resonance to occur in this
frequency range. The sound wave literally "does not fit" into the
geometry of the room. However, the frequency of this sound will not be
altered, therefore, you can still hear it "accurately".

The longest dimension of a room X 2 defines the low frequency below
which resonance simply *cannot* occur. This is known as the room's
cut-off frequency.

1) Measure the longest dimension of your room
2a) If you measured in feet and inches then divide 1125 f/s by that
value
2b) If you measured in metres then divide 343.4 m/s by that value
3) Divide by two again (because resonance occurs at half wavelength
intervals).
4) Now you have the lowest frequency at which resonance can occur
within that room.

This does not mean that all sounds below this cut-off frequency simply
disappear, they are still present, but are contained within a space too
small to permit resonance - therefore, they die away very quickly.

If you do as Scott suggested, then you will hear the volume of various
pitches rise and fall as the sweep passes through the room's resonant
frequencies. Below the cut-off frequency, the sound will appear very
quiet for two reasons:

Firstly, the room is not allowing *any* resonance to occur, therefore,
the sound field that exists at that frequency lasts only for as longs as
the sound wave's journey across the room (only a few milliseconds...)

Secondly, the human ear is poorer at perceiving very low frequency sound
(See the Fletcher-Munson curve of equal perceived volumes)

HTH

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

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"Chris Whealy" <chris.whealy.NO@SPAMsap.com> wrote in message
news02059$hrs$1@news.sap-ag.de
> Scott Dorsey wrote:
>> But if you play a sweep tone that goes from 20 to 100 Hz, you'll hear
>> all kinds of things wrong with your room. Play the tone and see.
>
> I think the OP was asking if a sound wave can be accurately reproduced
> in a room whose longest dimension is *shorter* than half the
> wavelength of the frequency in question. (I assume here that
> "accurate" means without any form of distortion).
>
> You will still be able to perceive sounds at these low frequencies,
> however, it is physically impossible for any resonance to occur in
> this frequency range.

Some rooms can be modelled as a Helmholtz resonator where the resonant
frequency depends on the volume of the room and the size of its vent.

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Arny Krueger wrote:
> Some rooms can be modelled as a Helmholtz resonator where the resonant
> frequency depends on the volume of the room and the size of its vent.
>

?? I'm afraid you lost me on that analogy Arny...

A Helmholtz resonator is the acoustic analogue of a mass-spring system;
it exhibits a single natural resonant frequency. Rooms on the other
hand, exhibit multiple resonant frequencies due to the room have
non-equal dimensions. (I assume your room is not a cube!)

I think you would have to have a very particular shape of room before
modelling it as a Helmholtz resonator would be appropriate.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

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In article <61d1.4224a7fc.52f15@mail.cambridgetechgroup.com>,
"John Hall" <john-news2@cambridgetechgroup.com> wrote:

> "Laurence Payne" <l@laurenceDELETEpayne.freeserve.co.uk> wrote in message
> news:lk79211nvondrvfeght66t34rqh8v0qubt@4ax.com...
>
> > Can you hear booming bass in a car? A lot of youths have wasted a
> > lot of money if you can't :-)
>
> And generally have even if you can.
>
> john
>
>

Is it really wasted if you can annoy the neighbors?

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x

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bj wrote:
> It is said that at least 28.5 feet length room is required for the
> control room. IMO the reason is derived form which the wave length of
> 20hz is 56.6 feet

As I and others have said, it is complete nonsense that you have to
build a control room 28.5 feet long. A 20Hz sound wave will be heard
fine in a small room.

If you did build a control room 28.5 feet long, all you would be doing
is creating a room in which bass resonance extends down to 20Hz!

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

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bluesjeon <bluesjeon@gmail.com> wrote:
>
>It is said that at least 28.5 feet length room is required for the
>control room. in my opinion it is derived from which the wave length
>of 20hz is 56.6 feet

There are a lot of reasons why you want a large control room. First of
all, in a small room it IS difficult to get good and even low end, but
it's possible to do. It doesn't require a room that is longer than a
half wave in all directions, but having a larger room makes it easier.
If you get the F. Alton Everest book, there is a nice introduction to
room mode calculation in there.

But also, in a larger room it's possible to get the speakers farther back
and have a larger sweet spot. And it gives you a lot more options for
placement if you need to worry aboout reflections off the console surface,
or if you want to use planars. If you need to move the speakers around to
get the low end evened out, it helps to have enough room to move them
into a good position without them being on your lap.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On Tue, 01 Mar 2005 17:18:10 +0000, Chris Whealy
<chris.whealy.NO@SPAMsap.com> wrote:

>Arny Krueger wrote:
>> Some rooms can be modelled as a Helmholtz resonator where the resonant
>> frequency depends on the volume of the room and the size of its vent.
>>
>
>?? I'm afraid you lost me on that analogy Arny...

You forgot Arny is moron.