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|19th November 2012, 07:50 AM||#1|
Join Date: Nov 2012
6" and below that moves the most air regardless of quality
So this is probably a bit of an usual setup, as it's not meant for sound quality. I'm trying to make a model that sinusoidally sucks/blows out of a slot for an experiment.
Basically what I'm after is a 6" (or below, smaller the model is, the less air I need to displace..) subwoofer that has a large excursion (and capable of low freq, below 20Hz). I'll just be putting a sinusoidal voltage through the woofer at various (manually controlled with a signal generator) frequencies and amplitudes to get a desired (sinusoidal) velocity output. So i'm not concerned about how the woofer will react to rapidly changing frequency inputs etc.
Does anyone have any suggestions as to what woofers would be up to the task? The best woofer that I've found so far with the largest excursion is this ScanSpeak (here). It's got a max mechanical excursion of +-13mm - so theoretically capable of displacing 240cm^3 of air (Effective piston area of 92 cm^2).
Am I correct to assume that I could make any woofer beat at a low frequency provided I input a high enough voltage (without the whole thing burning out of course) at the low frequency?
Any help would be greatly appreciated!
|19th November 2012, 09:19 AM||#2|
Join Date: Feb 2008
I am not sure what you are trying to accomplish but I had cooked one of my 8" subs on a free air excursion test.
The Optimus PRO-CSW800 has very similar specs,
I was able to observe its actions at 10hz or so for a very short time, only a few seconds and I burned the voice coil before I could get to the volume control to turn it down and let it cool off!!!
I think I was using my Ashley FTX-2000 if there is any question of how much power I was driving it with.
That is a very expensive driver to be pushing like that.
I do not know how much voltage I was applying as I didn't have my scope hooked up at the time.
But it was doing every bit of its possible excursion and was making very little mechanical noise.
Sadly there was just not enough air movement to keep the voice coil cool enough and too keep it from burning up.
Luckily I was only out about $15 only they can't be found any more.
I had 8 of them and now I have 7.
This driver from MCM is similar to the 8's that I have,
MCM Audio Select 8'' High Excursion Woofer - 120W RMS 4ohm | 55-2421 (552421) | MCM Audio Select
MTX had a driver with the exact specs of my Optimus driver but I don't remember the model number at the moment,But sadly it has been discontinued as well.
I am sure there are many other cheaper drivers that you could use for such an abusive tests.
Unfortunately subs with those types of specs are very expensive in the 5" to 6" diameter range.
I know as I have been doing some searching myself for one that size.
I would hope that the Scanspeak has an extremely low THD for that kind of money.
Even if it did I still couldn't justify the cost for a small driver like that.
When it comes to SPL's and low frequency's, Displacement is the main thing that rules.
For the same SPL's at an octave lower the drivers excursion must increase by a factor of four.
Here is an online calculator that I hope you will find useful,
Last edited by geraldfryjr; 19th November 2012 at 09:43 AM.
|19th November 2012, 03:03 PM||#4|
Join Date: Jan 2008
One thing to factor in is the AES figures used for most speaker rating now use a compressed pink noise source with -6dB crest factor.
Sine waves have a -3dB crest factor, so if you plan on long term usage, you need to use at most -3 dB (half) the AES power figure.
Depending on power compression and cooling (a back vented coil cools more at low frequency, longer "fan") you may be able to increase level over half the AES figure, but the only way to find out how much is too much is to slowly increase level until the coil burns.
Usually, the adhesives start to stink badly before the coil goes...
|19th November 2012, 07:09 PM||#5|
Join Date: Nov 2003
Location: Brighton UK
Why is the size of the model related to the slot size ?
Have you modelled turbulence to see if your air flows are realistic ?
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
|20th November 2012, 04:41 PM||#7|
Join Date: Jun 2012
Location: Appalachia, in the middle of nowhere.
If you do this, you should use a momentary push button switch to connect the speaker.
That way you will be aware of how long you have the speaker on the verge of frying.
It only takes a short time at low frequencies to burn the voice coil.
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