I bought some JBL Arena 120,s, they are neat wall mountable speakers, supposedly capable of decent volume and power handling, perfect either side of the TV. They generally sound good but the occasional odd sound comes through, it seems more frequent with female voices and Latin pop of all things, a kind of gravelly harshness.
Curiously, I opened them up and the previous owner had wired the tweeter direct to the speaker post and left the woofer to the crossover. It was obvious because the new wires were just wound on, not soldered or with spades. I contacted previous owner and he just said he sold them for a friend, knew nothing about the wiring.
I removed these wires, connected the proper tweeter spades which were left wrapped up, it sounded better, I think, but I have always had my doubts they were right, the female Google Voice for example and sci-fi slidy doors (think Star trek) sound awful. I plug in head phones and it sounds OK.
Why would someone do this, are tweeters likely to be ruined permanently after bypassing the crossover. Are there any tests other than listening to see if tweeters are duff. I like the speakers and would be hard to replace them, so I am considering sourcing replacement tweeters.
Curiously, I opened them up and the previous owner had wired the tweeter direct to the speaker post and left the woofer to the crossover. It was obvious because the new wires were just wound on, not soldered or with spades. I contacted previous owner and he just said he sold them for a friend, knew nothing about the wiring.
I removed these wires, connected the proper tweeter spades which were left wrapped up, it sounded better, I think, but I have always had my doubts they were right, the female Google Voice for example and sci-fi slidy doors (think Star trek) sound awful. I plug in head phones and it sounds OK.
Why would someone do this, are tweeters likely to be ruined permanently after bypassing the crossover. Are there any tests other than listening to see if tweeters are duff. I like the speakers and would be hard to replace them, so I am considering sourcing replacement tweeters.
Someone would do that because they didn't know what they were doing.
A tweeter must be HP filtered. If they were used this way, damage would result.
It is possible that the crossover capacitors or resistors are bad (open circuit),
and the guy hooked them up direct to bypass the bad parts. But this would
damage the tweeters. If you still have problems with new tweeters, replace
the 4.7uF 50V capacitors. Also check the series resistor to the tweeter for value.
JBL ARENA 120 Service Manual - FREE DOWNLOAD
A tweeter must be HP filtered. If they were used this way, damage would result.
It is possible that the crossover capacitors or resistors are bad (open circuit),
and the guy hooked them up direct to bypass the bad parts. But this would
damage the tweeters. If you still have problems with new tweeters, replace
the 4.7uF 50V capacitors. Also check the series resistor to the tweeter for value.
JBL ARENA 120 Service Manual - FREE DOWNLOAD
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Is it the original tweeter?
Earlier user might have killed the original ones and replaced them with Piezos.
In that case, direct wiring to terminals coould be fine.
If original voice-coil-and-magnet type ones, check they still work, I´d expect a very dead and very open voice coil there.
That said, a few aftermarket general purpose tweeters already have a built-in series capacitor, you might also have one of those.
Earlier user might have killed the original ones and replaced them with Piezos.
In that case, direct wiring to terminals coould be fine.
If original voice-coil-and-magnet type ones, check they still work, I´d expect a very dead and very open voice coil there.
That said, a few aftermarket general purpose tweeters already have a built-in series capacitor, you might also have one of those.
All useful info thanks but I now feel a bit stupid, dug out the photos I took and it was the woofer that was wired direct, the tweeter was to the crossover. Still a bit odd and I have never been totally happy with the sound, is wiring direct to the woofer a similarly bad or damaging?
I did already run the tweeters reverse polarity but it gave it a fake surround/wide stereo effect.
99% certain they are the original tweeters and woofers, there are times when I think maybe it is a characteristic of the quite 'in your face' nature of them, so considered some replacements but how would I go about selecting some?
I did already run the tweeters reverse polarity but it gave it a fake surround/wide stereo effect.
99% certain they are the original tweeters and woofers, there are times when I think maybe it is a characteristic of the quite 'in your face' nature of them, so considered some replacements but how would I go about selecting some?
An externally hosted image should be here but it was not working when we last tested it.
It's usually a sign of cutting corners. It can be a reason for bad sound.
That is probably the most common description when it is wired backward (or other similar blending issue).
This is your picture for those who cannot see it..
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The woofer needs to be hooked up to the crossover. I'm not surprised they sound bad with it wired direct.
You're "lucky" it turned out to be the woofer. Now you can simply rewire as it's supposed to be and should get the original sound back in place.
Possibly the reason for the funny sound is - without the woofer part of the xover in circuit - there was overlap between woofer and tweeter; some audio frequencies being output by both. Perhaps right where female vocals lie too.
Possibly the reason for the funny sound is - without the woofer part of the xover in circuit - there was overlap between woofer and tweeter; some audio frequencies being output by both. Perhaps right where female vocals lie too.
My guess as to why they did it, was to try and get more bass. Have a look at the crossover schematic, there is a 300uF cap in series with the woofer. Not sure what the rollof would be with that without doing some calcs...
Likely the bad sound was woofer breakup that was no longer being suppressed by the crossover.
Tony.
Likely the bad sound was woofer breakup that was no longer being suppressed by the crossover.
Tony.
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Good find Tony, this would appear to explain the uncertainty.
That cap would be there to increase bass, but it's certainly counterintuitive. It's an old technique that wasn't used much.
Either bypass it or not, but definitely reinstate the rest of the woofer crossover 🙂
That cap would be there to increase bass, but it's certainly counterintuitive. It's an old technique that wasn't used much.
Either bypass it or not, but definitely reinstate the rest of the woofer crossover 🙂
What Allen said, a big cap in series with the woofer, in a sealed enclosure, actually provides a bass boost. A trick to provide reasonable bass extension in a small sealed enclosure. I bet that in order to provide the same extension without the cap the enclosure needs to be much bigger and vented.
Ralf
There have been plenty of "audiophile" speakers eg Epos, with a simple direct woofer and single capacitor to the tweeter. The woofer cone breakup adds a bit of character
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How does a component that conducts minimally at low frequencies provide a bass boost?
Capacitors conduct more as frequency increases.
Inductors conduct less as frequency increases.
It does so in cunjunction with the speaker's impedance. It causes a narrow-band lift at the cost of a little more current drawn from the amp over an also narrow frequency band. The other price to pay is a steeper rolloff than that of an ordinary closed box (3rd order instead of 2nd order). The trick can also be done with vented aliognments.
A.N. Thiele once published a paper in JAES on that subject.
Regards
Charles
Edit: The steeper rolloff is not only a disadvantage since it can also act as mild subsonic filter of course.
A.N. Thiele once published a paper in JAES on that subject.
Regards
Charles
Edit: The steeper rolloff is not only a disadvantage since it can also act as mild subsonic filter of course.
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I can say they don't produce masses of bass as most people would expect, previous owner obviously did some experimenting. They are actually a nice amount of bass for an all day every day TV speaker.
Capacitors and inductors is a bit too in depth for me, got some learning to do.
My plan is to get the matching centre speaker, if it sounds the same maybe it's a 'charcteristic' of this speaker range, if it sounds better I will investigate fixing/replacing them.
Capacitors and inductors is a bit too in depth for me, got some learning to do.
My plan is to get the matching centre speaker, if it sounds the same maybe it's a 'charcteristic' of this speaker range, if it sounds better I will investigate fixing/replacing them.