10" for rock? - Page 5 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-19-09, 09:19 PM
Shackster
MarkN

Join Date: Jan 2009
Location: Brisbane, Australia
Posts: 46
Re: 10" for rock?

Hi, I'm just writing this out as I find this a bit topical and I'd like to know if I'm right about this or not.

My understanding is that WinISD is a bit ambiguous with the way it treats input power when modeling boost circuits.

Each 3dB of boost requires double the power. So a boost of 6dB requires 400% more power than if no boost was used. WinISD doesn't seem to take this into consideration. It appears it applies all filters, boost circuits, etc after the given level of power is applied.

So if you model an Amp that is rated at 350w maximum, and you plug in 350w into WinISD as input power, and then add a boost circuit with 6dB boost, WinISD assumes your amp is capable of providing 350w x 400% = 1400w. You'll only achieve what you see on the SPL plots if your amp can supply 1400w. WinISD doesn't appear to treat the 350w as "maximum" input power.

So what I've always done is:
Work out the maximum boost applied across the frequency curve.
Convert that into the required extra power need to obtain that boost. (eg. 6dB needs 4x the power.)
Divide that figure into your amps maximum power rating. (eg. 350w / 4 = 87.5w)
Plug that number into the WinISD input power field.
Check out excursion, SPL graphs, etc.

It would be nice if WinISD did all this for you as it gets tedious modeling different amounts of boost.
So if people are modeling that with 6dB boost providing WinISD with 70w input power, excursion limits are reached, that means the amp is really delivering 280w to achieve this.

Boost circuits are incredibly useful but not a free lunch. I hope this all makes sense and I've explained this well enough. This has all been deduced based on my observations with WinISD, so please do confirm this or point out if I'm wrong here!

Cheers,
Mark
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