Reversing polarity in crossovers, JBL 4311 and others

[rhollingsworth]

How the 4311 fits in to this comes a little later in the story.

I have a question about crossovers and driver polarity. I’m no engineer, just curious.

A friend gave me a pair of Technics SB-L50 speakers. Maybe not classic, but old. They were called a “linear phase speaker system.” The three drivers are all mounted on the same plane; i.e., the voice coils are not aligned like some “linear phase” speakers did, so I don’t know what “linear phase” means with respect to this speaker.

I happened to disconnect the LF drivers while playing around and did not mark the wires, mea culpa. I didn’t know how to re-connect them, so I took all the drivers and wiring out (making pictures) to see if I could make an educated guess.

The crossover circuit is one 4.7 mfd cap and one inductor whose value I can’t determine. The terminal marked (+) is wired through the cap to the (–) terminals on both the mid and HF drivers, which are effectively paralleled. So, these two drivers seem to be getting the same signal. There is also a wire from the (+) terminal that goes through the inductor to the LF driver – but to which terminal there, the (+) or the (–)? Trying to keep things alike, I connected this wire to the (–) post on the LF driver. The sound was OK but kind of muddy. Then, I saw some crossover designs where the polarity of the mid and HF drivers are opposite that of the LF driver. So, I reversed the polarity on the LF drivers. The midrange seemed to pop out a bit more on listening. I plan to leave them like this, after replacing the caps.

I was wondering if any of you can say if it makes sense ever to reverse polarity on the mid and HF drivers from that of the LF driver in a crossover circuit.

Now the JBL 4311. Some of the enhanced 4311 crossovers I have seen do this polarity reversing, too. My friend has asked for the Technics speakers back and says he will give me (give me!) a pair of 4311’s which he inherited. Yes, I have explained to him how lopsided this exchange is.

Thanks for any comments you might have.

[JKent]

I'll let a crossover expert answer but I just had to reply. We share the same last name (and it's not that common).

Welcome!

Kent

[Carlspeak]

Polarity reversals are needed when the phase angle of the drivers is 180 deg. out of phase at the crossover point; such as in a 2nd order crossover.

However, the sketch you gave shows a simple 1st order arrangement on all 3 drivers. As such, they should all be connected with the same polarity.

Not know all the details of the speaker's design, there may be a reason why the sound was more pleasing when the OP reversed the woofer's polarity. He said the mid was more evident when polarity was reversed on the woofer. This may be the result of an attenuation of the woofer's output that occured with the reversal. Without acoustic testing, I can't say with absolute certainty, but that's my opinion.

JBL used polarity reversal on woofers because of the phase issues resulting from the design of the crossover.

It's okay to play around a bit with polarity reversals until the sound becomes balanced across the freq. spectrum. Just be sure that both speakers have the same + - connections on all drivers.

[rhollingsworth]

Thanks for the replies.

If reversing polarity on the woofer is wrong, I'll make sure both speakers are wrong the same way. It does sound better.

And, Kent, we had some exchanges in these pages a couple of years back when I was restoring my KLH Seventeens. You gave me some very good guidance on crossover caps and cabinet finishing.

I'll let you know how the JBL 4311's come out. I may decide to spring for some new caps better than the Carlis. The original 4311 crossover is disarmingly simple, accoring to the literature I have seen. I'm just hoping the drivers are in good shape.

Regards,

Roy

[JKent]

Sorry I forgot, Roy. I was thrown by your "newbie" status (and my faulty memory).

Not familiar with the 4311's but found this thread: http://audiokarma.or...ad.php?t=106180

Looks like you just need one 8uF and one 3uF per speaker so even though I like Carli, better caps won't break the bank. I like Clarity Caps from Madisound

In the PX line you can get 2.7 for $4.25 and 8.2 for $6.75, Prices for the SA versions are $8.15 and $15.60.

For a little less, Erse makes some real nice caps. This Pulse-X http://www.erseaudio...l/MPX40-03-3-00 and this one http://www.erseaudio...MPX40-03-8-20_2 are well made and inexpensive.

Kent