How do you cool a speaker?

[B]

I am doing an experiment where I have to send a 20K- 25K tone constantly
through a speaker. This has to continue for 24 hours. The magnet or coil
becomes too hot to touch. Right now I'm using a full range speaker. If I
use a specific tweeter for high frequencies will it stay cooler?

Thanks,
Bruce

[Kalman Rubinson]

On Wed, 23 Jul 2003 22:25:58 GMT, B > wrote:

>I am doing an experiment where I have to send a 20K- 25K tone constantly
>through a speaker. This has to continue for 24 hours. The magnet or coil
>becomes too hot to touch. Right now I'm using a full range speaker. If I
>use a specific tweeter for high frequencies will it stay cooler?

Why not an active cooler using a fluid or Peltier device?

Kal

[Richard D Pierce]

In article >, B > wrote:
>I am doing an experiment where I have to send a 20K- 25K tone constantly
>through a speaker. This has to continue for 24 hours. The magnet or coil
>becomes too hot to touch. Right now I'm using a full range speaker. If I
>use a specific tweeter for high frequencies will it stay cooler?

Probably not, in fact, it might get hotter because the voice
coil and magnet assembly are smaller, have a higher thermal
reistance and thuse, for the same electrical dissipation, will
suffer from a greater temperature rise.

There are a variety of ways of lower the heat dissipation:

1. Pick a more efficient speaker. Typical electroacoustic
efficiencies for driver hover around 1% and less, That
means if the speaker is dissipating 100 watts, only 1
watt is converted to sound, the remaining 99 gets converted
directly to heat.

2. Provide better dissipation for the heat. Consider forced or
active cooling, or increase the passive thermal resistance.
One way to do that, if you have the room, is firmly attach
a large aluminum heatsink to the magnet assembly.

3. Use a driver purpose-designed for the application. A full-
range driver ain't gonna cut it, just from the standpoint
of producing 20k-25kHz. They are really bad at that. A
tweeter might be better in the sense that it's probably
a lot more efficient at 20 kHz than the full-range driver
is, but something more prupose designed could work even
better. For example, a piezo-electric transducer mechanical
tuned to resonant at the required frequency could be VERY
efficient, producing almost no heat.

The problem is that there is important information missing from
your request. FOr example, how much acoustic power over what
sort of area do you need to produce at 20kHz-25kHz? If the area
is very small, on the order of an inch or so, then you could
use an acoustically tuned resonator, increasing the efficiency
that way. If it's over a broad area, you have some fundamental
physical problems to begin with (you simply can't uniformly
distribute something of such short wavelengths over such a wide
area), but the way might be to use mutliple transducers.

Give some idea of the total acoustical power needed, and such.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

[Kevin McMurtrie]

In article >, B >
wrote:

>I am doing an experiment where I have to send a 20K- 25K tone constantly
>through a speaker. This has to continue for 24 hours. The magnet or coil
>becomes too hot to touch. Right now I'm using a full range speaker. If I
>use a specific tweeter for high frequencies will it stay cooler?
>
>Thanks,
>Bruce

Try a piezo horn tweeter from Radio Shack. It will produce 20KHz at
migraine inducing levels with no problem. Cheap piezo tweeters have a
whacky frequency response so you might need to adjust your tone a tiny
bit to avoid dead spots.

[Richard Crowley]

"B" wrote ...
> I am doing an experiment where I have to send a 20K- 25K tone constantly
> through a speaker. This has to continue for 24 hours. The magnet or coil
> becomes too hot to touch. Right now I'm using a full range speaker. If I
> use a specific tweeter for high frequencies will it stay cooler?

Investigate using driver(s) that use magnetic fluid in the gap. One of the
benefits of the fluid is that it sinks the heat from the voice-coil to the
magnet assembly where it can be dissipated.

[flint]

"Kevin McMurtrie" > wrote in message
...
> In article >, B >
> wrote:
>
> >I am doing an experiment where I have to send a 20K- 25K tone constantly
> >through a speaker. This has to continue for 24 hours. The magnet or coil
> >becomes too hot to touch. Right now I'm using a full range speaker. If I
> >use a specific tweeter for high frequencies will it stay cooler?
> >
> >Thanks,
> >Bruce
>
> Try a piezo horn tweeter from Radio Shack. It will produce 20KHz at
> migraine inducing levels with no problem. Cheap piezo tweeters have a
> whacky frequency response so you might need to adjust your tone a tiny
> bit to avoid dead spots.

I double the suggestion to use a piezo horn. I have done hundreds of tests
that required acoustic energy at ultra-sonic frequencies and I was able to
create that energy very easily with a piezo horn and a small amplifier. I
suggest running a 4 or 8 ohm power resistor in series with the horn,
however, to reduce ringing that can blow the amp or the horn.

- FLINT

[Richard D Pierce]

In article >,
Richard Crowley > wrote:
>"B" wrote ...
>> I am doing an experiment where I have to send a 20K- 25K tone constantly
>> through a speaker. This has to continue for 24 hours. The magnet or coil
>> becomes too hot to touch. Right now I'm using a full range speaker. If I
>> use a specific tweeter for high frequencies will it stay cooler?
>
>Investigate using driver(s) that use magnetic fluid in the gap. One of the
>benefits of the fluid is that it sinks the heat from the voice-coil to the
>magnet assembly where it can be dissipated.

Well, we already know from his description that the magnet gets
too hot that this is not the primary issue. The problem is
getting the heat out of the unit as a whole.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |