Adventures in auto audio

Shackman

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

arun1963

hi john,

welcome to cp. If I understand correctly, you've swapped your stock tweeter for a ribbon tweeter which is wired in parallel to your stock mid. This is running off your kenwood HU. You're hearing distortion in your sound and you have tried reversing the polarity on your crossover and removing the crossovers. There are no external amps, subs in the chain.

1. By wiring your mids and tweets in parallel you are presenting a 2ohm load to your hu's amp. The head units amp is not stable at 2ohms and you're hearing the clipping of the amp as distortion. You'll blow one or both, the amp or the speakers.

2. Are you telling me the components in your cross over are held together with black shrink wrap? Or is the shrink wrap just covering the housing? If its the later then pls remove the shrink wrap. You're supposed to remove it before installing them. By removing the xovers you have run the ribbon tweet full range i.e. The ribbons may already be blown.

Use the passive xover and don't run the mids and tweets in parallel.

BTW, which upmarket car is this setup in? Just curious as to which manufacturer would recommend a 2 ohm load for a stock hu?

Shackman

Hi arun, thanks for your response.

Sorry if I haven't spelt out properly the details of my install so far. These are:

Car is a '98 Mitsubishi Magna, a medium size 4 door sedan. I'm in Australia where these were manufactured. In the U.S. they were known as the Diamente.

Like almost all modern sedans at the time they come with a stock sound system usually consisting of an entry level AM/FM/cassette stereo head unit, and pretty ordainary 6 inch 2 way front door speakers, plus a couple of 6 by 9 speakers in the parcel shelf. Standard sound system is Eurovox throughout, 4 Ohm, and each speaker is rated at about 5 watts. Sound is passable, but very improvable.

I replaced the HU with the new unit above (I had a tech do that install).
I personally replaced all the stock speakers with new Kenwood units of the same size as stock. The door speakers became 6 inch 3 way 4 Ohm units with a peak rating of ~150 watts, so probably ~30-50 watts RMS. The rear speakers became Kenwood 6 by 9 inch 3 way units with a peak rating of 300 watts, probably ~75 watts RMS. As you see, all the speakers are well within the power rating of the HU which of course incorporates a 4 channel amp to power them.

There are no external amps or subs in this chain, but I do have a self built subwoofer in the trunk, constructed around a Polk 8 inch dual voice coil driver. This is powered by a left over stereo power amp from a previous installation, an old Aiwa MA-3000 unit of 35/35 watts RMS. I also had a pro installer to connect the sub to the HU; too challenging for me. There is no independent connection between the sub or it's amp to the tweeters, other than the HU.

The new system so far has been outstanding- great sound at about a $1100 total cost, including a power aerial.

Time to address your Q's.

1. Re wiring in parallel. Doesn't impedence drop if you wire in series rather than parallel? Ie. Consider two 4 ohm speakers, wired so amp current enters the + terminal of the 1st speaker, leaves via the - terminal and then is wired back to enter the + terminal of the second speaker, and leaves via the - terminal and back to the amp. Isn't that wiring in series, which drops total impedence to half the rated impedence of each speaker in this cofig., or 2 Ohms total? Because that's exactly what I am trying to avoid! Are you suggesting I try to connect like this? Doesn't wiring in parallel maintain impedence? By wiring in parallel, I mean taking the incoming + wire carrying current from the amp and connecting both the exisiting speaker and the new ribbon tweeter at their + terminals from it.

Note that the distortion is local to the one speaker I am trying a test connection with to the ribbon tweeter. I checked a similar test connection to one of the rear speakers- same distortion, same characteristics at that speaker only.

2. The shrink wrap. It appears to shroud the crossover components to provide a bit of environmental protection, moisture/vibration etc. It is definitely not packing material, or black Glad Wrap etc. Too thick and tough for that. There is no housing as such. I can feel what might be a couple of small electronic components on a small PCB within the wrap.

Re the possibility of the ribbons having failed already- I was careful to do my test connections at low volume. I've seen a ribbon fail before and am confident these are still OK.

BTW, I went to a auto aftermarket parts store today. The sound specialist there states that if my exisiting (Kenwood) speakers have a tweeter built in, I will have problems connecting an additional tweeter via them. He described correctly how it will upset the function of the woofer in that speaker group. Perhaps there is already some kind of crossover these 6 inch door speakers incorporate which prevents further on connection of additional tweeters?

Look forward to your response.

Cheers,

John

arun1963

I have to ask here, are you satisfied with the quality of sound in your car and just want to be rid of the distortion issue? Or, do you want to improve the sound quality as well?

If it's the former here's what I would do.

1. Disconnect the ribbons and put them away for the time being. A driver whose crossover is held together by shrink wrap, can be safely bagged for the time being.

2. There's got to be a reason you tried to run them in the first place. If I'm not mistaken, its because you felt the higher frequencies were sort of missing from the sound. So let's eliminate the root cause.

3. I would not run the sub for now. I'd take that 2x35watt aiwa amp and put it on my front triax'es. Your 3way fronts are prob good for 60 rms so 2x35 would be good. You always want to power the front speakers.

4. Head units are very poor sources of clean power. A hu rated at 20rms and 50peak, is only good for about 10 clean watts. Or about 40-45% of max volume at you hu. Beyond that, the distortion levels rise drastically. If you're going for good sound and want a sub, a 4ch amp with two channels running the fronts and two bridged to play the sub is a good setup. You don't really need rears. If you must have them, I would just run them off the hu.

5. You're running a sub without amping the other speakers. So the sub is getting like 120watts and the four speakers between them are getting 40watts. If you split the sound into lows mids and highs, which part is dominating? Now you know, why you felt the need for the additional tweets.

6. Get a 4ch amp hook up your fronts and bring the sub back into your chain.

http://www.bcae1.com/ Here's a link to a good site to understand the basic parts of your sound chain.