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Old 12th February 2008, 07:09 AM   #1
ttan98 is online now ttan98  Australia
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Default Calling X-over designer

This should be easy to all of you.

I am designing a 2-way speakers. I am thinking of implementing either one of these 2 types of x-over, option A - LR12 or LR24 say at 2Khz, option B - Butterworth filter, BW18 at same freq.

Tell me whether I am right if I am wrong please explain.

Option A

No reversal of polarity of the tweeter is required.

Option B

Reversal of tweeter's polarity is required. Please explain why reversal is required. Is this type of x-over recommended?
This site seems to like 3rd order Butterworth,
http://home.wanadoo.nl/dezaire/R&D.htm

Thanks in advance
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Old 12th February 2008, 07:15 AM   #2
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Option A should be better.
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Old 12th February 2008, 07:21 AM   #3
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Without seeing the measured FR/phase of the drivers in your enclosure the question is meaningless.
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Old 12th February 2008, 07:29 AM   #4
ttan98 is online now ttan98  Australia
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Quote:
Originally posted by pinkmouse
Without seeing the measured FR/phase of the drivers in your enclosure the question is meaningless.
I know when I need to reverse the tweeter by looking at the FR graph.

Why sometimes reversal is required what is actual technical explanation?
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Old 12th February 2008, 07:38 AM   #5
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Quote:
Why sometimes reversal is required what is actual technical explanation?
Phase difference of speaker units at crossover frequency.
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Old 12th February 2008, 07:39 AM   #6
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Reversal or not reversal is given by the actual phase relationships between the drivers around the crossover frequency. This includes:

- the phase difference introduced by (any) filter: 180 deg LR2, 360 deg LR4, etc.
- the phase response of the driver themselves (usually significant phase shift is present in the roll-off regions)
- the phase difference (actually time delay) due to the physical misalignment of the drivers voice coils

ALL these should be considered when connecting the tweeter - failure to do so is the reason why "generic" filters don't work well. In practice, one needs to get phase relationships right for a good speaker.
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Old 12th February 2008, 08:07 AM   #7
ttan98 is online now ttan98  Australia
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Quote:
Originally posted by bzfcocon
Reversal or not reversal is given by the actual phase relationships between the drivers around the crossover frequency. This includes:

- the phase difference introduced by (any) filter: 180 deg LR2, 360 deg LR4, etc.
- the phase response of the driver themselves (usually significant phase shift is present in the roll-off regions)
- the phase difference (actually time delay) due to the physical misalignment of the drivers voice coils

ALL these should be considered when connecting the tweeter - failure to do so is the reason why "generic" filters don't work well. In practice, one needs to get phase relationships right for a good speaker.
If the woofer is LR2 and tweeter is LR2 there is STILL a possibility a phase reversal will occur at x-over point due to time allignment, etc.

A very good explanation that is all I need, thanks.
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Old 12th February 2008, 11:07 AM   #8
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Here's a LR2 3-way.

The top graph is with the mid polarity reversed +ve to -ve connection (in phase). The lower graph is with the mid polarity normal, +ve to +ve connection, (out of phase).

LR2 normally has 180 phase difference in the xo which means the tweeter or mid have to be connected in reverse but it doesn't happen all the time with some required normal connection.

What the graph shows that with out of phase there should be deep nulls indicating good phase relationship between the drivers at the xo point. Always a good check when designing an xo.

Pictures worth a 1000 words or something like that.
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Old 12th February 2008, 11:26 AM   #9
ttan98 is online now ttan98  Australia
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Quote:
Originally posted by rabbitz
Here's a LR2 3-way.

The top graph is with the mid polarity reversed +ve to -ve connection (in phase). The lower graph is with the mid polarity normal, +ve to +ve connection, (out of phase).

LR2 normally has 180 phase difference in the xo which means the tweeter or mid have to be connected in reverse but it doesn't happen all the time with some required normal connection.

What the graph shows that with out of phase there should be deep nulls indicating good phase relationship between the drivers at the xo point. Always a good check when designing an xo.

Pictures worth a 1000 words or something like that.

I have seen similar FR graphs before, I just want and explanation.

Thanks for your effort.
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Old 13th February 2008, 12:40 AM   #10
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For 3rd order Butterworth, the frequency response is the same for either polarity, but the group delay is better with the reversed polarity.
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