Understanding the relationship between Xmax, SPL and LF response

greenhorn

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I was till recently under the impression that a speakers frequency response was the same no matter what power level you were driving it at.

I was looking at matching an ahuja sub driver to a philips hiq woofer for open baffle. the philips is 93db @ 1W, and the ahuja is 98@1W, but still manages around 90db @ 40hz, and 80dB at 20.
http://www.ahujaradios.co.in/Document/0-d2-L12-MB200_SP.pdf

I assumed that i since the ahuja driver could handle 200W RMS of input, that with a 200W amp, = +23db compared to 1W, the amp would easily be able to manage 90db till 20hz.

but while designing the system using the linkwitz site material, i found that the SPL at lower frequencies is limited due to xmax (the driver claims 2.5mm)
and after pluggin in the TS parameters of the woofer the attatched worksheet http://www.linkwitzlab.com/spl_max1.xls
claimed that the woofer would be able to manage 90db till only 50hz or so because of the xmax limitation.


so back to my question.

Does the xmax apply an overall envelope to the LF (just like the heat sink capacity puts an envelope on power handling, and that with higher levels, you get lesser LF response (like an op amp's LF reduces at higher gains)

Or do you get the same frequency response at all power levels, in which case how do i interpret the xcel sheet model?
 
I was till recently under the impression that a speakers frequency response was the same no matter what power level you were driving it at.

I was looking at matching an ahuja sub driver to a philips hiq woofer for open baffle. the philips is 93db @ 1W, and the ahuja is 98@1W, but still manages around 90db @ 40hz, and 80dB at 20.
http://www.ahujaradios.co.in/Document/0-d2-L12-MB200_SP.pdf

I assumed that i since the ahuja driver could handle 200W RMS of input, that with a 200W amp, = +23db compared to 1W, the amp would easily be able to manage 90db till 20hz.

but while designing the system using the linkwitz site material, i found that the SPL at lower frequencies is limited due to xmax (the driver claims 2.5mm)
and after pluggin in the TS parameters of the woofer the attatched worksheet http://www.linkwitzlab.com/spl_max1.xls
claimed that the woofer would be able to manage 90db till only 50hz or so because of the xmax limitation.


so back to my question.

Does the xmax apply an overall envelope to the LF (just like the heat sink capacity puts an envelope on power handling, and that with higher levels, you get lesser LF response (like an op amp's LF reduces at higher gains)

Or do you get the same frequency response at all power levels, in which case how do i interpret the xcel sheet model?
The Xmax applies a limit to the LF alone. You can plot it in a graph. If the X axis of your graph is log scale of frequency and the Y axis is power in dB (which means it is log s scale), then the Xmax limitation appears as a straight line with a slope. This straight line cuts the X axis at a certain SPL.

I do box modelling using Unibox. I have been using Unibox even when I used to use other software for the other jobs of speaker design. (There's usually no connection between LF performance analysis and xo design anyway, so you can use separate software stacks.) In Unibox, I get this straight line in one of its graphs. Very convenient. Why don't you try Unibox and see for yourself? It needs MS Excel, is free (not open source) and works well.
 
I was till recently under the impression that a speakers frequency response was the same no matter what power level you were driving it at.

I was looking at matching an ahuja sub driver to a philips hiq woofer for open baffle. the philips is 93db @ 1W, and the ahuja is 98@1W, but still manages around 90db @ 40hz, and 80dB at 20.
http://www.ahujaradios.co.in/Document/0-d2-L12-MB200_SP.pdf

I assumed that i since the ahuja driver could handle 200W RMS of input, that with a 200W amp, = +23db compared to 1W, the amp would easily be able to manage 90db till 20hz.
?

A driver performs best under its thermal limits (power rating) and excursion limits. For a high sensitivity pro audio driver, at lower freq, the driver will exceed excursion limits sooner than thermal limit, and at higher frequencies the excursion needed is less so the higher sensitivity is really beneficial up there actually.

For frequencies like 20hz, the 2.5mm xmax is too low even for sealed application, so open baffle is out of question. Open baffle application is excursion intesive not power intensive as pointed in one FAQ of guru Linkwitz.

In sealed alignment 2.5 mm xmax of 11.5" cone produces around 82 dB@1M before hitting xmax, as per piston excursion calculator.
For open baffle atleast, 15" driver with atleast 5mm xmax is recomended. Fortunately, there are so many pro audio drivers available to choose from.

As Tarun pointed out Unibox is good, it shows both, xmax limited spl across frequencies and one can set power level into the driver.
HTH
 
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Yes, I agree that 2.5mm Xmax is diametrically opposite of what is needed for OB. OB woofers suck up all your Xmax and then some.
 
ah ok, I should have known that the woofer was too good to be true.

but then a bunch of folks had reported success building OB's with the ahuja FRX (that's a mid bass with far less LF extension that this one)

anyway , one good outcome is that i don't need to invest in a hefty power amp which i would have needed to get 93db @ 20hz.
This way it will run out of xmax at 70Hz, I'll eq it only till there, and then let it go flat - for which my current amp will do.

Thank you tcpip & goldyrathore. You learn something new every day.
Did a bit more research and found this spreadsheet useful in understanding the story
http://www.musicanddesign.com/codes/Voltage_for_Xmax_worksheet.zip
Thankfully I bought only one such driver. Still need to take a call on if i should buy another one of those for stereo, or buy a car sub with more xmax (which needs more $$$$)
Let me try build this one, If it goes flat till 60hz, it should be able to do as well as a decent bookshelf
 
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ah ok, I should have known that the woofer was too good to be true.

but then a bunch of folks had reported success building OB's with the ahuja FRX (that's a mid bass with far less LF extension that this one)

anyway , one good outcome is that i don't need to invest in a hefty power amp which i would have needed to get 93db @ 20hz.
This way it will run out of xmax at 70Hz, I'll eq it only till there, and then let it go flat - for which my current amp will do.

Thank you tcpip & goldyrathore. You learn something new every day.

Thankfully I bought only one such driver. Still need to take a call on if i should buy another one of those for stereo, or buy a car sub with more xmax (which needs more $$$$)
Let me try build this one, If it goes flat till 60hz, it should be able to do as well as a decent bookshelf
Hey, if you're designing your own OB, then just use what driver you can find, and be prepared to change things later. The OB hardware is cheap (enclosure costs, I mean), and OB requires experimentation, so you should just buy another driver and try building, I feel.
 
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