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-   -   Thoughts......? (http://www.diyaudio.com/forums/subwoofers/190316-thoughts.html)

Brian Steele 6th June 2011 12:04 AM

Thoughts......?
 
Consider this:

DIY Sound Group

In something like this:

Slot-loaded sealed subwoofer (magnet facing into slot)
Vr=57 litres
Vf=22.5 litres
Slot area = 860 cm^2

HornResp predicts 95dB/2.83V/1M, and 90dB/2.83V/1M @40 Hz, in a 2.8 cu.ft. (net) box. with about 117dB peak before Xmax is exceeded.

Here's the thing - the driver is only $77, so you could buy FOUR and series-parallel them to get 101dB/2.83V/1M in a 11.3 cu.ft. (net) box and over 130dB into 2PI space with about 2.5kW of power.

jbell 6th June 2011 12:30 AM

The mfw is a great buy -- if you want, get them quick before they are gone.

lilmike has a big box (f20) on avs that uses this driver.

Last post I saw, there were about 70 or so left -- get 'em while you can.

Djim 6th June 2011 01:05 AM

Quote:

Originally Posted by Brian Steele (Post 2596056)
Here's the thing - the driver is only $77, so you could buy FOUR and series-parallel them to get 101dB/2.83V/1M in a 11.3 cu.ft. (net) box and over 130dB into 2PI space with about 2.5kW of power.

Is there any information about its power compression figures?

littlemike 7th June 2011 02:32 AM

In the F-20 design/build thread, I measured the completed project at 1 watt, then added 5 dB and re-swept until I ran out of amp at +25 dB (~315 watts).

Here is the chart I presented.
https://lh4.googleusercontent.com/-2...2520sweeps.jpg

We saw a bit of compression in the last sweep, which was at the limit of the amplifier and at close to 90 watts over the drivers' thermal rating. I'm not sure which contributed more. I was also driving the coil out of the gap - that may be part of what we saw too.

Sweeps were approximately a minute apart, just enough time to process the FFTs and increase the signal level.

I'm pretty sure that 300 to 500 watts is a fair limit. 625 (2500/4) is probably too much power for the coil to handle.

Djim 7th June 2011 02:50 AM

Hi Littlemike, I think with sine wave sweeps you are only able to measure dynamic compression.

littlemike 7th June 2011 03:11 PM

Not exactly sure what you mean.

It is my understanding that power compression is usually measured and calculated similarly. Illka has provided many tests with similar sweeps, as have many others. My presentation is simply SPL sweeps, I have not "done the math" to calculate power compression numbers.

Really, all I wanted to show is a measurement of this driver in a cabinet (admittedly completely unrelated to the OP's interesting design) that shows additional power in does not equal a proportionate increase in SPL out once the driver's limits are reached.

Djim 7th June 2011 04:42 PM

Quote:

Originally Posted by littlemike (Post 2597638)
Really, all I wanted to show is a measurement of this driver in a cabinet (admittedly completely unrelated to the OP's interesting design) that shows additional power in does not equal a proportionate increase in SPL out once the driver's limits are reached.

Ever measurement is appreciated :up: and yes every driver will have a point where power doesn’t translate in the same SPL rise any longer (lower than 50% of the BL)

Quote:

Originally Posted by littlemike (Post 2597638)
Not exactly sure what you mean.
It is my understanding that power compression is usually measured and calculated similarly. Illka has provided many tests with similar sweeps, as have many others. My presentation is simply SPL sweeps, I have not "done the math" to calculate power compression numbers.

Measuring with sine-waves (non-complex-signal) wont deliver the whole story. You need long time noise signal measurements for power compression. A Noise signal because it is a complex signal like music and long time (>20minutes) because it will create heat like under working conditions.
You can divide power compression in two basic processes;
1.) Dynamic Compression, which is the result of mechanical forces created by suspension. The further the excursion the more force is needed.
2.) Thermal Compression, which is the result of heat development in and around the voice coil trough electric resistance and mechanical resistance.


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