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Speaker positioning in a case

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djnik1362

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hi

I was wondering if a standard or rules exists for putting a speaker in a case.

I have a metal case with dimensions of : 710mm x 280mm x 40mm .

I need to put two 3W speakers inside this case as a stereo configuration.
These speakers are departed from each other in a about 55 cm.
Mounting would be in bottom of the case with some 30mm spacers.

Being together in a same volume could be a problem ?
Is speaker's resonance have any relation to this ?
 

Hi,

I´d divide both speaker´s voulmes. So they can´t influence each other.

***
Placement: not critical in a closed case.

But if you use bass reflex system you need an exact distance between reflex opening and speaker. There should be software available to calculate this with the use of Thiele-Small-parameters.


Klaus
 

I believe you should avoid mounting a speaker on a large metal panel of the enclosure. It might vibrate in resonance to certain speaker frequencies.

According to an instruction manual I read, the best stereo effect has the speakers positioned in an equilateral triangle with the listener.
 

BradtheRad said:
I believe you should avoid mounting a speaker on a large metal panel of the enclosure. It might vibrate in resonance to certain speaker frequencies.

According to an instruction manual I read, the best stereo effect has the speakers positioned in an equilateral triangle with the listener.
Click to expand...

Thanks very helpful.

As I said speakers supposed to mount on the case with 4 spacers with 30 mm height.
How about I fasten speakers with some "FIBRE flat washers" to these spacers?
These washers absorb mechanical vibrates .

- - - Updated - - -

KlausST said:
Hi,

I´d divide both speaker´s voulmes. So they can´t influence each other.

***
Placement: not critical in a closed case.

But if you use bass reflex system you need an exact distance between reflex opening and speaker. There should be software available to calculate this with the use of Thiele-Small-parameters.


Klaus
Click to expand...

Thanks for your response.
Do you have any suggestion for separating each speakers volume in the case ?
 

djnik1362 said:
Thanks very helpful.

As I said speakers supposed to mount on the case with 4 spacers with 30 mm height.
How about I fasten speakers with some "FIBRE flat washers" to these spacers?
These washers absorb mechanical vibrates .
Click to expand...

A speaker frame needs to be mounted firmly. If the speaker frame can move (vibrate), then it defeats cone movements. Volume is reduced. Efficiency is lost.

Are your fibre standoffs made of cloth-like or felt-like material? These do not provide a firm mounting. I think a better substance is hard rubber or bakelite or wood.

- - - Updated - - -

It is also important to mount the speaker so that sound waves from the front side cannot meet sound waves from the rear side. Otherwise volume is lost, because sound waves from the two sides are 180 deg out of phase, therefore they cancel.

This means the speaker should be mounted snug against a flat surface.
 

This means the speaker should be mounted snug against a flat surface.
Click to expand...
Yes, I don't understand the "spacers" thing at all. Perhaps we can see a drawing for clarification?
 

BradtheRad said:
A speaker frame needs to be mounted firmly. If the speaker frame can move (vibrate), then it defeats cone movements. Volume is reduced. Efficiency is lost.

Are your fibre standoffs made of cloth-like or felt-like material? These do not provide a firm mounting. I think a better substance is hard rubber or bakelite or wood.

- - - Updated - - -

It is also important to mount the speaker so that sound waves from the front side cannot meet sound waves from the rear side. Otherwise volume is lost, because sound waves from the two sides are 180 deg out of phase, therefore they cancel.

This means the speaker should be mounted snug against a flat surface.
Click to expand...

I have a part number for one of these washers : 3368 - Keystone Electronics
I can say these washers are like ordinary metal washers except they are lighter , cheaper and can absorb mechanical vibrates.
Front side of speaker will be pointed to the opening which is located on case Top part .
My case has two parts : Top & Bottom which will be fit together and tight with screws.

- - - Updated - - -

FvM said:
Yes, I don't understand the "spacers" thing at all. Perhaps we can see a drawing for clarification?
Click to expand...

As i said my case has two parts : Top & Bottom .
Speaker opening located on case Top part.
I can fasten speakers to the top part but because of bad look of mounting screws on top part
I decided to mount speakers on bottom part.
So I have to mount speakers on some spacers and then mount spacers to the bottom part.
A spacer is a standard mechanical part that make physical spacing between two surfaces.
 

I still think the speaker should make solid contact with the enclosure. Then the enclosure becomes a 'sounding board'. The increase in volume should be obvious as you tighten down the screws which fasten the speaker frame.

For further improvement, post #2 mentions bass reflex. This involves putting a hole in the enclosure, creating a certain distance for sound waves to travel, so that bass frequencies are accentuated. It's a clever concept commonly used to improve the listening experience from small speakers.
 

Recall that a bass reflex involves not only an opening, but also a pipe or cavity communicating the main case with the opening.
The case is decribed as having two parts (top and bottom). I'm wondering if the case is designed for a bass reflex and the smaller part is that cavity (even if 40 mm seems too slim to me).
An image or a drawing could help to understand and give a better advice. Can you upload it?

Z
 

zorro said:
Recall that a bass reflex involves not only an opening, but also a pipe or cavity communicating the main case with the opening.
The case is decribed as having two parts (top and bottom). I'm wondering if the case is designed for a bass reflex and the smaller part is that cavity (even if 40 mm seems too slim to me).
An image or a drawing could help to understand and give a better advice. Can you upload it?

Z
Click to expand...

Thanks for your support.
It was not supposed to be a bass reflex opening at all . One of guys just mentioned it .
 

These are only 3w speakers and probably quite small.
While resonance of the large area metal panels "might" be a concern at high audio power levels, in something not much larger than a computer case, I cannot see that happening.

The danger is that the speaker may shake the metal panel producing a tinny sound, but if the panel is reasonably stiff and heavy, that is unlikely to occur.

For best efficiency mount the speakers rigidly over a hole cut into a flat panel.
Ideally the speakers should seal directly against the panel.

No real problem having stereo speakers in a common air volume. When you select the speakers, try to find some with the lowest natural cone resonant frequency.
Some are pretty good in that respect, and some are awful.

Choosing good speakers will be the key to getting good results.
 

Warpspeed said:
Ideally the speakers should seal directly against the panel.
... ... ...
Choosing good speakers will be the key to getting good results.
Click to expand...

There is a rubber ring around the cone and that must make a airtight seal with the mounting plane. The mounting plane should not be recessed too much inward (loss of high frequency).

Consider the speakers as antennas. They are like microphones in reverse and have their own 'lobes'....

As the cone moves, the air inside the enclosure also vibrates 180 deg out of phase. That must be quenched (or damped)- use some sponge or felt mat as inside lining for the cabinet.

As speaker is as good as it cabinet it is mounted in but even a good cabinet can never compensate for a pair of bad speakers. But even excellent speakers cannot compensate for a poor recording with poor stereo separation.

Low power speakers are generally poor in reproducing low frequencies and you can get impressive results with a simple independent bass speaker (in addition).
 

Warpspeed said:
These are only 3w speakers and probably quite small.
While resonance of the large area metal panels "might" be a concern at high audio power levels, in something not much larger than a computer case, I cannot see that happening.

The danger is that the speaker may shake the metal panel producing a tinny sound, but if the panel is reasonably stiff and heavy, that is unlikely to occur.

For best efficiency mount the speakers rigidly over a hole cut into a flat panel.
Ideally the speakers should seal directly against the panel.

No real problem having stereo speakers in a common air volume. When you select the speakers, try to find some with the lowest natural cone resonant frequency.
Some are pretty good in that respect, and some are awful.

Choosing good speakers will be the key to getting good results.
Click to expand...

Thanks for your response.
In my situation speakers have 250 Hz plus-minus 70% resonant frequency. What this means ?
About choosing good speakers , do you know any web site related ? I search in Digikey and Mouser and could'nt find proper speaker.

- - - Updated - - -

c_mitra said:
There is a rubber ring around the cone and that must make a airtight seal with the mounting plane. The mounting plane should not be recessed too much inward (loss of high frequency).

Consider the speakers as antennas. They are like microphones in reverse and have their own 'lobes'....

As the cone moves, the air inside the enclosure also vibrates 180 deg out of phase. That must be quenched (or damped)- use some sponge or felt mat as inside lining for the cabinet.

As speaker is as good as it cabinet it is mounted in but even a good cabinet can never compensate for a pair of bad speakers. But even excellent speakers cannot compensate for a poor recording with poor stereo separation.

Low power speakers are generally poor in reproducing low frequencies and you can get impressive results with a simple independent bass speaker (in addition).
Click to expand...

So you say if i don't seal speaker against flat panel it may be compromise efficiency ? But i decided to mount speakers on bottom part of case so there is a little spacing (about 8mm) from speaker to flat panel. What will be happened in this configuration ?
 

So you say if i don't seal speaker against flat panel it may be compromise efficiency ? But i decided to mount speakers on bottom part of case so there is a little spacing (about 8mm) from speaker to flat panel. What will be happened in this configuration ?
Click to expand...

The air pressure (the acoustic wave) produced by the movement of the speaker cone *must* not leak to the inside of the cabinet; it will compromise the power as well as the frequency response. The rubber seal around the paper cone is precisely meant for this purpose. The speaker (and the mount plane) must not vibrate as a whole.

It does not matter is the speaker is located close to the bottom part (the vibrating cone does not see the inside) of the box; but the mounting (cut out plane) must be secure (air tight seal).
 

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