Off-axis SPL vs THD in a two-way system

Bazukaz · 7th January 2012, 09:44 PM

Hello everyone,

After some research I have came up to a conclusion to use the following drivers for the next project : visaton's aluminium cone woofer AL170 & ceramic tweeter KE25SC.
It is a bit difficult to blend them because the woofer shows resonances at ~6 kHz and tweeter's distortion rises below ~2kHz.
I have considered a 24db/oct crossover at ~1.6 kHz with a notch filter for the woofer.
If tweeter and woofer is wired out of phase in simulations I get good FR and -5 db spl for both at crossover point. However off-axis response(mainly > 40 degress to top) shows large(~15 db) dips at ~1.6 kHz.
I can wire both drivers in phase. Then after adjustment of components I get quite good frequency response from 0 to ~60 degress off axis, but both drivers must produce something like 5 db more at crossover point, so I expect distortion of both will be higher.
My question is what is more important : better power response(i.e off-axis SPL) or few db less THD? Maybe someone has real-world experience with it ?

Flaesh · 10:27 PM

i'm avoiding woofers with hf peaks.
and my speakers with exessive headroom allow me to not think about such trifle as spl and distortion..
stupid way. but working goood.

sreten · 7th January 2012, 10:25 PM

Hi,

Theoretical responses with the drivers out of phase is a very bad idea.
A consistent out of phase dip = a consistent in phase response off axis.
Stupid cancellation at the c/o point never works well, ever.

rgds, sreten.

AllenB · 7th January 2012, 11:25 PM

I think the improved power response looks best, although I don't do it that way myself. At the least, why don't you try to get the phase just so on axis, that the notches will be pointing at the floor and ceiling.

strawberry · 7th January 2012, 11:45 PM

Put a zobel circuit on the woofer, 8-10 ohm and 20 uF. Say goodbye to the 6 kHz peak.

AllenB · 8th January 2012, 12:51 AM

On re-reading my post, I'd like to clarify a point. Having the drivers in phase on-axis will centre the main lobe. The way you've done it with the flatter looking power response probably has a deep notch just slightly below axis. Try running top to bottom.

7th January 2012, 10:22 PM	#2
Flaesh diyAudio Member Join Date: Dec 2009 Location: Eburg	i'm avoiding woofers with hf peaks. and my speakers with exessive headroom allow me to not think about such trifle as spl and distortion.. stupid way. but working goood. __________________ flesh flash flush Last edited by Flaesh; 7th January 2012 at 10:27 PM.

7th January 2012, 10:25 PM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Theoretical responses with the drivers out of phase is a very bad idea. A consistent out of phase dip = a consistent in phase response off axis. Stupid cancellation at the c/o point never works well, ever. rgds, sreten. __________________ 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

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7th January 2012, 11:25 PM	#4
AllenB diyAudio Member Join Date: Oct 2008	I think the improved power response looks best, although I don't do it that way myself. At the least, why don't you try to get the phase just so on axis, that the notches will be pointing at the floor and ceiling.

7th January 2012, 11:45 PM	#5
strawberry diyAudio Member Join Date: Dec 2011	Put a zobel circuit on the woofer, 8-10 ohm and 20 uF. Say goodbye to the 6 kHz peak.

8th January 2012, 12:51 AM	#6
AllenB diyAudio Member Join Date: Oct 2008	On re-reading my post, I'd like to clarify a point. Having the drivers in phase on-axis will centre the main lobe. The way you've done it with the flatter looking power response probably has a deep notch just slightly below axis. Try running top to bottom.

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