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#55817 01/13/10 10:21 PM
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Hi all.
I have a Q. re a proposed car audio install I'm in the middle of. I bought a set of ribbon tweeters some months ago to complete my revamping of the sound system in my car. I am encountering some distortion on test use, not in the tweeters but in the parent speaker I am piggy backing them off (ie. I am wiring the tweeters in parallel with the door speaker, as the car manufacturers service manual electrical digram specifies for the upmarket model of my car, which had satellite tweeters).

Characteristics of the distortion are as follows:

1. Only in parent speaker, not tweeter.
2. Seems load related- sounds like clipping on musical peaks like drumbeats, bass notes at lower volumes, distortion worsens with volume and becomes more constant.
3. Occurs when crossover in place and correctly oriented. When crossover reversed, no distortion heard but tweeter non functional.
4. When crossover excluded from circuit, no distortion occurs and tweeter functions normally.

Here is the link to the current version of the kit I bought.

http://www.jaycar.com.au/productView.asp?URL=index&ID=CS2339&CATID=15&SUBCATID=459

I have the same as these tweeters, branded "Response Precision CS 2339 ribbon tweeter", but the crossovers supplied with my kit differ. They are a small mystery circuit enclosed in black shrink wrap with sheilded wires at each end. 2 of, one per tweeter obviously. All made in China, of course. No Ohmage quoted on the box but on my multi meter they show 3.5 Ohms, and most car audio including my cars sound system is 4 Ohms. Specs quoted on the box are a freq. response of 3kHz - 40 kHz, and crossover slope of 12dB/octave. No expanded spec sheet inside (or instructions FWIW).

The car head unit is a Kenwood KDC - MP5039U of ~ 22 watts RMS per corner, ~50W peak per corner.

I am contemplating installing the tweeters without the crossover per 4. above. I realise it's a risk but am guessing the worst that can happen is popping the ribbons. I don't routinely listen at deafening volumes, or to very dynamic "doof doof" music, too old.

Does this august company have any advice/comments?

Cheers, John

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Well I'm no engineer, but Bill Cosby did some good comedy on cars. His borgenriffers were causing problems.

I'm going to have to chaw over the options for the sound system for the RV though. And I sure hope that is soon. I've started the home renos (well I hire a guy and supervise he and the wife arguing over the hue in the flooring and such.) Once I get close I'm selling my junk, my Archie Bunker chair (couldn't you guess?) and parking the RV in the driveway while we sand the floors, stage the house and flog it for what I hope is top dollar. As I don't have that mortgage thing anymore I'm buying something small, so none of my kids think of moving in. In fact maybe I'll renovate it so the main bathroom is an outhouse and the other is beside my bed.

Car audio drives me nuts. The only time I like it is if it's classical music and I have the piece sort of memorized, then I can fill in the parts killed by the passing semi hauling beer or garbage to Michigan.

I'm sure you are going to get lots of advice. I know just enough to be dangerous.


John Conley
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Quote:

No Ohmage quoted on the box but on my multi meter they show 3.5 Ohms, and most car audio including my cars sound system is 4 Ohms. Specs quoted on the box are a freq. response of 3kHz - 40 kHz, and crossover slope of 12dB/octave. No expanded spec sheet inside (or instructions FWIW).




While the DC ohmmeter check can tell you something about the impedance of a driver of any kind that has voice coils, it won't tell you that much about a Ribbon Tweeter. And, of course, can tell you nothing about the crossover. This is because of capacitance in both, which does not "pass" DC. Your audio, of course, is AC of varying frequency.

Quote:

The car head unit is a Kenwood KDC - MP5039U of ~ 22 watts RMS per corner, ~50W peak per corner.

I am contemplating installing the tweeters without the crossover per 4. above. I realise it's a risk but am guessing the worst that can happen is popping the ribbons. I don't routinely listen at deafening volumes, or to very dynamic "doof doof" music, too old.




Do NOT do that. The tweeters cannot take fullrange at ANY volume level. Without a crossover, those tweeters will not last long. Ribbon design will die even faster without a crossover, although its a moot point. The low frequencies must be blocked from reaching the tiny diaphragms of any tweeter.

John, I noticed one thing you said-- that the crossovers are using Shielded wiring. I suspect that Capacitance is rearing its ugly head here, and throwing your wideband power amplifier into distortion. This is a rather common phenomenon with Ribbon and Electrostatic tweeter systems. Quite often, the actual AC Impedance of them will drop down below 1 ohm! You can't measure that with the simple DC ohmmeter. It would take an Audio Impedance Bridge to do that. But you are in luck, for I have used the Impedance Bridges and Distortion Analyzers on the test bench many times to prove this rather commonly found situation happening with Electrostatic and Ribbon speaker systems. Sometimes the workaround is to use cheap 20 AWG gauge parallel (NOT shielded) speaker wire, about 20 feet of it for each side, coiled up. This can iron out the problem, but in a vehicle, where to put all that wire? Since your crossover already has shielded cable as part of its design, I don't think I'd even want to try that stunt, though. Shielded cable also is capacitance in and of itself, by the foot.

Not being able to put your crossovers and tweeters on the test bench (and very likely removing that shrink tubing and finding out what's really underneath...) I can't give you a reliable answer to this one that wouldn't involve trying to do things that are obviously outside your scope of reference on the subject.

You might just send these back, or write them off and find a simple set of dynamic tweeters with crossover instead.

Or -- you could purchase another smaller power amp and an electronic crossover to place between the two power amps and safely send the lows to the original amp and woofers and the highs to the new tweeter amp and ribbons.

If it was me, I'd likely go with the first choice, standard dynamic tweeters with a simple capacitive crossover. Less $$, less complexity, for about the same performance, considering it is a vehicle.

Bottom line -- This product is not performing satisfactorily for you and you should send it back.





--Mac

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I think you're playing in a gas pond with matches here. I would suggest you take your car and system to a reputable radio installer and see what needs to be done.

A red flag to me is your door speakers. If these are the original speakers then you have a mis-match. If you bought all new speakers for your system then, are you sure the speakers match the freq and output of the radio's amp? Kenwood systems are great, if installed correctly.


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Thanks Russ, John and especially Mac.

The door and parcel shelf are indeed new Kenwood items, 6 inch 3 way in the front doors and 6 by 9 in the parcel shelf. All 4 Ohm. Head unit as stated. I am confident that the head unit and new speakers are fine for compatibilty with each other. I also constructed a subwoofer for the trunk around a Polk 8' bass driver (and powered it seperately with a dedicated power amp). No complaints with the result so far until the tweeter install of yesterday.

I did call the shop where I bought the tweeters for advice (an electronics type store, like Radio Shack) but the counter jockey was even less au fait with electronics than me. I may actually go in today and enquire further. Maybe an alternative crossover is an option.

Thanks again.

J.

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The adventure continues.

I went to the auto parts store where I had bought my Polk subwoofer and spoke to Mr. Car Audio Expert. His spot diagnosis was just about spot on. He asked if the existing front door speaker that I am piggybacking signal off (in fact, wiring the ribbon tweeter parallel with) had a tweeter itself. It does- it is a Kenwood KFC - M1632A, a current model.His comment was that if it did, adding another tweeter would upset the woofer in that speaker assembly. He described the symptoms well.

On paging thru a very helpful car audio site ( http://www.bcae1.com/) and examining the section on Series-Parallel Basics, it seems that although I wired in parallel to avoid halving the impedence and thus putting the head unit amp at risk, I was wrong about this principle. It looks like the connection I had made was resulting in a total 2 Ohm load. Seems I should wire in series instead. Thus the negative side of the door speaker should be connected to the positive side of the ribbon tweeter, and the negative sisde of the ribbon then sent back to the head unit. Total impedence should then be 8 Ohms as each unit is 4 Ohms.

Is this correct and a safe option for extended use?

Thanks,

J.

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Series would be safer than parallel, which indeed would lower the impedance of the two, likely to a point below that which the amplifier is designed to operate.

Sounds like that tech has "been there, done that" -- and is speaking from experience. What he told you sounds right to me.

Just be sure that you wire the series in phase properly.

Amplifier(+) -> Main Speaker(.)+

Main SPKR(-) -->Tweeter(+)

Tweeter(-) -->Amplifier(-)

Note that in the middle there is one wire going from a minus (-) terminal to a plus (+) terminal here. Series.

If each device in this series wiring is 4 ohms as stated, then the total load would become 8 ohms at the amplifier terminals because series is addition, just add all the impedances in the series string up to arrive at the total.

It should work, but be advised that it is not what I'd call a clean arrangement in the sense that the tweeter circuit may (or may not, depending on how it's crossover is derived) affect what the woofer is getting. Hook it up and give it a listen. If it sounds good, it IS good.

--Mac

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Thanks, Mac. I found the HU's manual which states it will accept a load of b/n 4-8 Ohms. The ribbon is so small a unit that can't believe it will draw much current to work. Will give this a shot today and give you a sitrep.

John

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Mac/others. I have wired (in series) and fired, and it sounds great so far. Adds just a sniff of crispness to the top end range which defines snare and hi hats sounds and also outlines vocal sibilants remarkably- "s" and "t" consanants particularly. No added pathlogical sounds in this configuration. Thanks all for your generous assist.

John

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