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Old 2nd February 2009, 02:37 PM   #1
cuibono is offline cuibono  United States
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Default Linkwitz's Xmax calculator question

I've been playing with a little spreadsheet I pulled off linkwitzlab.com - it takes some driver parameters, then calculated a driver's cone displacement based on whatever SPL you give it. I've been using it to explore the limits of some of the drivers I'm planning on using for an upcoming project. I've attached it below, in a zip file.

At the bottom of the spreadsheet, it also calculates the power dissipation for a given SPL and driver - but, it looks like it calculated it for a very large bandwidth - which makes it not really applicable to figuring out how much power a driver will be asked to dissipate at a given SPL...

I tried then to use MJK's mathcad worksheets to do the calculation, because they allow you to define a bandpass, but that didn't work either - the spreadsheet only calculated data under 1kHz.

Does anyone have a spreadsheet that will calculate driver dissipation and displacement for a given SPL?
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Old 2nd February 2009, 05:09 PM   #2
HK26147 is offline HK26147  United States
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Old 2nd February 2009, 07:01 PM   #3
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Default Re: Linkwitz's Xmax calculator question

Quote:
Originally posted by cuibono
I've been playing with a little spreadsheet I pulled off linkwitzlab.com - it takes some driver parameters, then calculated a driver's cone displacement based on whatever SPL you give it. I've been using it to explore the limits of some of the drivers I'm planning on using for an upcoming project. I've attached it below, in a zip file.
Siegfried's closed-box1.xls displays amplifier voltage * current in 1/7 octave increments. It's a good upper bound on power dissipation. Speakers are horribly inefficient, so nearly all of the power used is being lost as heat. The piece missing would be the power factor where the actual dissipation is less than indicated by the peak voltage and current.

Since you have the resistive (column C) and reactive (D) components you could figure power factor

Put some other starting value in B35 on the first page to cover different frequencies.
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Old 3rd February 2009, 03:58 AM   #4
cuibono is offline cuibono  United States
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Thank you both!

Linkwitz has so many spreadsheets hidden here and there - and they are so useful! I haven't gone in depth into the closed-box1 worksheet, but it may do. Hopefully, it will work for dipole mids, and mono/dipole tweeters...

I realize there are a lot of limitations to these sort of calculations (particularly thermal and power compression, which set in well before one reaches maximum displacement and power handling), but I think they give an idea of which driver might fail first. They at least allow for some interesting driver comparisons.
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Old 3rd February 2009, 08:14 PM   #5
cuibono is offline cuibono  United States
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The 'closed-box1' spreadsheet is really floating my boat.

The spreadsheet allows you to import driver parameters, and if you specify D and set a box volume much larger than Vas, you can simulate dipoles. I want to know the spl I can expect for a given power input, at specific frequencies, and it does that, but it calculates for 2.83v, 10v, and the amplifiers max V, all very useful. But I want to limit the drive power to the maximum the driver is specified for - so, lets say my driver has impedance and Re of about 4 ohms, and the long term max power handling is 70W. If I go to "Power Amplifier Specs", and enter 70W and 4ohms, and look at the "max SPL at Vpeak" tab, I get a pretty SPL graph. Does this represent what SPL I can expect, given the drivers power handling limits?

Can someone check my logic?



Heres another mind bender:

If I put in "amplifier power" of 1W across 4 ohms, I get a dipole SPL of 97dB (from the "max SPL at Vpeak" tab)(and a Vpeak of 2.83v).

If I look at the "SPL @ 2.83v" tab, I get 81dB. I add 6db to this (for 2pi radiation on an infinite baffle, I assume), for a total of 87dB. The rated sensitivity of this driver is about 87dB, with 2.83V, on an 'infine' baffle, so those two correspond nicely.

I'm interested in why the "dipole 97dB SPL" would be different than the assumed/rated "infinite baffle 87dB"?
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