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steverb 20th May 2003 08:16 AM

LR xover question
 
With a Linkwitz Riley 2nd order xover do you reverse yhe
tweeter polarity??
Is a LR just a bessel or butterworth with the xover at the 6 db point (rather than the 3db)? If so would the phases at xover be different than a normal 2nd order xover?

SDF 23rd May 2003 01:42 PM

All 2nd and 3rd order analog filter give more linear response (phase and level response) with inverted tweeter terminals.

pinkmouse 23rd May 2003 03:06 PM

Re: LR xover question
 
Quote:

Originally posted by steverb
With a Linkwitz Riley 2nd order xover do you reverse yhe
tweeter polarity??

In general, yes, but it depends on the configuration and positioning of the drivers in the box. The even order filters actually give a 3db rise at crossover point with polarity inversion, but this is offset by the fact that the polarity inversion gives more control over the polar tilt response of the drivers.

Quote:

Is a LR just a bessel or butterworth with the xover at the 6 db point (rather than the 3db)?
If you mean the -6db point, yes;)

Quote:

If so would the phases at xover be different than a normal 2nd order xover?
The phase response of a LR is similar to that of a standard Butterworth, and all other 2nd orders. However you can tweek the crossover points to sum more acurately if you have driver offset problems by adjusting the relative crossover frequencies of the HP and LP filters, and this will affect phase, ( obvious, as that is what you have to do to achieve flat response)

Sorry if this isn't too clear an explanation, but it is a very deep subject;)

Ken L 15th April 2004 05:48 AM

Re: Re: LR xover question
 
Quote:

Originally posted by pinkmouse


However you can tweek the crossover points to sum more acurately if you have driver offset problems by adjusting the relative crossover frequencies of the HP and LP filters, and this will affect phase.....

Am I correct in understanding you to be saying that if you adjust the relative frequencies of the HP and LP filters by raising or lowering them from the standard L-R design that you will change phase? from what it would be normally using the textbook crossover config?

What I'm thinking about is -

crossing over at 1200, my compression driver is about 6DB higher in efficiency than the Azura/DX4 beneath it.

So what I thought about doing is trying a 1st order slope but trying the high pass cap an octave higher in order to offset the mismatch - on paper this looks pretty good because of the falling response of the driver -

However, will changing the cap value from the textbook values while leaving the inductor value the same - will that situation cause additional phase shift above and beyond the normal 90 degree shift for a 1st order crossover?

thanks

Ken L

sreten 15th April 2004 06:16 AM

Th phase shift of a first order crossover at crossover is 45 degrees eventually becoming 90 degrees, so you will have
more phase shift than 45 degrees at the acoustic croosover
point.

If it looks good on paper try it.

But I've never heard of a 1st order c/o suiting a compression driver.

You will have another 90 degrees of phase shift by the Fs of the driver.

:) sreten.

Ken L 15th April 2004 01:49 PM

My plan is to time align the drivers at crossover point by reversing polarity, generating a sine wave at crossover point, then moving the smaller horn backwards and forwards to the point of greatest null - then reversing the polarity back for regular use and mounting the driver permanently at the position that gave greatest null.

Soooo, although it is obvious that I am not very technical oriented here in terms of crossove phase - etc.

If I do the above procedure to time align - then won't phase be taken care of as well?

Regards

Ken L

Ken L 16th April 2004 12:48 PM

Just bumping this back up _grin_
 
Quote:

Originally posted by Ken L


If I do the above procedure to time align - then won't phase be taken care of as well?

Regards

Ken L


Any thoughtful responses appreciated _grin_

thanks

Ken L

sreten 16th April 2004 12:58 PM

Re: Just bumping this back up _grin_
 
Quote:

Originally posted by Ken L

Any thoughtful responses appreciated _grin_
Ken L


Your procedure is effectively phase aligning the
drivers at crossover not time aligning them.

So phase worries are not an issue ;) .

:) sreten.

RHosch 16th April 2004 01:14 PM

Manually moving one driver with 180 degree phase offsets in signal is a way of finding one position where the drivers are in phase for that frequency. Depending on the frequency used, and the distances you move the driver through, you could well pass through several such points that give a deep null. Obviously you want the null point closest to aligning the acoustic centers... I'd probably run through some calculations (see Linkwitz's website for some assistance) to approximate the offset expected for the XO frequency used to help you find the correct position.

Ken L 16th April 2004 05:50 PM

Re: Re: Just bumping this back up _grin_
 
Quote:

Originally posted by sreten



Your procedure is effectively phase aligning the
drivers at crossover not time aligning them.

So phase worries are not an issue ;) .

:) sreten.

Understood - I figured I would try to come close with time alignment via physical measurement and then figured greatest null would probably be aligned, but I do understand that it would only be in phase.

Thanks for your response


Quote:

Originally posted by RHosch
website for some assistance) to approximate the offset expected for the XO frequency used to help you find the correct position.
Thanks for the input Bob,

I must admit that SL site makes my head hurt. I just don't do well with the calculations _grin_

If I get obsessive about it, I'll probably buy a mic for the Behringer - hook it up active, let it determine the correct delay ( it will do an automatic setting of delay) and then convert the delay setting to distance -

Hopefully, that would get it done -

Thanks for your input.

Hoping Fed Ex will drop off the Radians today.

Regards

Ken L


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