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Electronic/Stereo Gurus- what does this gizmo do?

Hello-

Meet part #911.645.575.00. A parts search from our host shows this as a Stereo Crossover/Diplexer, and a forum search for this 'diplexer' shows the same.

This came out of the door panels of a '88 Carrera, and evidently was used only in the '88s and '89s. I didn't do very well that quarter of college phisics- oops, physics, dealing with electrical stuff. I am helping my son add soundproofing mats inside the doors, plus chasing a rattle, when I discovered these.

My guess is that this device allows the tweeter and the larger speaker to run at the same time with the impedence of only one speaker? or are the signals separated to the larger and smaller speakers? This 911 had the optional factory amp under the pax seat, which was removed before we acquired this Carrera. The factory stereo receiver- I assume a Blaupunkt, was also removed, and replaced with an older Alpine radio/CD unit.

The mounted tweeters also double as the access point to manually crank the electric windows up/down. You are supposed to unscrew the grill, remove the 3 mounting screws, then insert the allen wrench and crank merrily away......

Is this diplexer needed with modern receiver units? I would like to run the tweeters- they are disconnected now. The large door speakers are now 2-way Clarions that someone installed. I know there are impedence issues (which I forget) when you start to add speakers together- too little impedence hurts the receiver somehow.....

Also- he wants to add some boxed speakers in the back- this is a Cabriolet, so they will need to be able to be removed via a plug when the top is down. Will they need a separate amp inside the box to run 2 6x9 Blaupunkts that I have sitting around?

thanks for all the help- as usual

Tim




Old 07-30-2012, 11:17 AM
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No guru here but I think that is a cross over that sends high frequency to the small speaker and low frequecy to the big speaker. Wouldn't need an amp just for the rear, but would help play louder with less distortion if an amp was used for all speakers.
Old 07-30-2012, 11:49 AM
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that is a crossover, which does separate the frequencies that each speaker sees. it should stay with the speakers if you use them or not.

it's true that running too low of an impedence, usually anything under 4, to a headunit is a problem waiting to happen. when you connect 2 speakers in parallel the impedence is halved, in series it is doubled. this page should explain everything in detail, and the website itself is very handy when it comes to car audio.

Series Parallel Speaker Impedance

as far as the rears, there really is no need for them in a 911. your son would be much better off using that money to upgrade the front speakers and get an amp for them. think about when you are at a concert - how many speakers are behind you? if you are dead set on using them i would suggest connecting them to the headunit alone to start and see how you like it, but don't expect any earthshaking bass from them. you can amplify them, but if you are going that route i would suggest getting a 4 channel amplifier so all speakers are amp'd. i know for a fact the alpine pdx line of amps fits quite nicely under the front seats.

when you have some free time you and your son should look over this thread. it should help out.

new audio install
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He is.... nineball. I don't always drive sports cars, but when I do I drive a 1983 911SC Targa. Stay fast my friends.
Old 07-30-2012, 12:02 PM
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Thanks Guys-

Will read these threads tonight......

Tim
Old 07-30-2012, 06:26 PM
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9Ball

Well, I enjoyed reading the first 2 pages of 6 of your 'new audio install thread'-- wow- nice job Sir. I used a similar butyl rubber and a foam product similar to your overkill. Check out RAAMaudio - Automotive sound deadening products for Rick's products- great stuff, and the spray adhesive he sells has no overspray at all- very controlled, so you can spray it inside the car w/o a problem. Rick is a former Navy electronic warfare guy/sub hunter, so he knows a lot about sound attenuation. I have a '77 930 that I gutted like a race car. I took out all the factory fiber/thatched roof/crapola, and installed 2 layers of the aluminum/butyl rubber, then 2 layers of the ensolite foam, then put back in the molded factory 'rubber' piece that covers most of the rear, including the jump seats, then installed the carpeting and rear seats. I did the side panels as well.

Next, I took out the main seats and scraped out all of the factory sound mats on the floor, using a hair dryer and a putty knife. down went 2 layers of the butyl, then two of the foam. In the doors, I put two layers of the butyl over the factory sound deadening mats, and then used the ensolite foam as a vapor barrier. BTW, with all the cracked factory stuff off the floors, this is an excellant opportunity to judiciously use a 'percussion persuader'- a ball peen hammer, to lightly pound out floor dents from misplaced floorlift jacks, rocks, etc..... On my son's '88 Cab, we have done just the floors and doors, with remarkable results. The floors of a car are like a drum skin.

My 930 has a few engine mods = louder, plus tire noise, so all the sound deadening has been a remarkable improvement in the cockpit. Stereo wise, I just have an Alpine unit (CDE124-SXM) that is Xm Radio ready, plus 4 new Blaupunkt speakers: 2 x 5-6?inch 2 ways in the doors, and 2 x 5x7 3 ways on the rear shelf- no further amp or such.

I wasn't so concerned with the quality of the music, truth be told, but just basic noise itself. Having flown jet aircraft for 30+ years, I have lost much of the hearing out of my right ear. To make up for that loss, I now have a fairly rare audio/medical condition called "sound recruitment" where loud noises come thru the bone, where somehow it is amplified. So for me, quieter is better, and I don't play the music that loud anyway.....

So, for anyone reading this thread, and you want some good stuff- check out raamaudio. Nineball, you might post where you get your 'overkill' stuff as well....

What a great Forum!! Thanks again, Wayne.

Tim
Old 07-30-2012, 11:29 PM
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i used all second skin products ( Sound Deadening Materials for Noise Reduction | Second Skin Audio ) in mine. i've heard of raammat many times just never used it.

i know it's too late now but using 2 layers of a cld is a big waste of money and effort. it's job is to control vibrations, not stop noise, so anything more than 25-40% coverage is excess and hardly offers any return. cld controls vibrations and lowers the resonant frequency of a large flat metal panel, ccf (closed cell foam) over that acts as a decoupler for the real noise blocker, mlv (mass loaded vinyl). when you get some time read over this site:

Sound Deadener Showdown - Your Source for Sound Deadening Products and Information

don used to host a review of all the major brands and has started making his own now, which is very nice stuff. i used it in my new 2012 fusion dd and i am really amazed at the results. even my sister, who laughs at my audio/car addition, asked me to treat her car like mine after riding in it. it's alomst like riding in a tomb
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- He gave his father "the talk"
- Once while sailing around the world he found a shortcut
- He taught a german shepard how to bark in spanish
He is.... nineball. I don't always drive sports cars, but when I do I drive a 1983 911SC Targa. Stay fast my friends.
Old 07-31-2012, 05:47 AM
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hey tim,. i work for the FAA as an electronic tech.
i have lost most of my hearing in my left ear from playing music. now i dont really listen to much at all. the stereo on the 911 does not work. with it being a targa, the wind noise is too much already.
my BMW one does not work either, but i have no plans on fixing it unless i can find a radio that has that 80's look to it to go with the car. (88 325is). i hate the new radios with all the lights and "fancy" crap that goes with them.
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Old 07-31-2012, 09:24 AM
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Quote:
Originally Posted by T77911S View Post
hey tim,. i work for the FAA as an electronic tech.
i have lost most of my hearing in my left ear from playing music. now i don't really listen to much at all. the stereo on the 911 does not work. with it being a targa, the wind noise is too much already.
my BMW one does not work either, but i have no plans on fixing it unless i can find a radio that has that 80's look to it to go with the car. (88 325is). i hate the new radios with all the lights and "fancy" crap that goes with them.
+1, with the top down and the lovely sound of the 2in/2out @ 6000 Rpm, the blaupunkt is there for the look only
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Old 07-31-2012, 03:11 PM
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Nineball-

Thanks for the input and for more reading material...... Maybe you should post your sound deadening/audio tech expertise in a Tech Section article on the Pelican site. I know, as if you didn't have enough stuff to do..... maybe something short and sweet to give folks something to think about as they start to dive into their interiors and start ripping stuff out... add all your links to interesting articles, and you're done.....

If the two layers of butyl rubber/2 foam was over kill- that's ok in retrospect. I have a 5
speed 915 gearbox in my 930 with pretty short gears, making the 930 a lot more drivable and responsive( versus the stock 930 box..), with a little variable boost tossed in as well. A buddy of mine rebuilt my gearbox since then- I had vibration/noise problems caused by 2 issues: out of balance clutch train- flywheel/ pressure plate, etc, and a loose cast bearing race holder- a known 915 gearbox issue where the casting elongates and allows the bearing race to move. The doubled everything helped cut down on those vibrations, and noise- even better now that the 915 has been redone...

T77911S- I had a '77S Targa as well, now still owned by a buddy I sold it to about 25 years ago..... I'd look on ebay or in the Beamer Forums for a correct period Blaupunkt radio to fit your '88. I agree, I don't like all the fancy doo-waaas of the modern stuff either- I want it fairly plain and simple- turn it on-turn it off. I bought this particular Alpine unit because it was XM ready- I mostly listen to talk radio when on the road now, anyway.........

Tim
Old 07-31-2012, 04:40 PM
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Old 07-31-2012, 04:40 PM
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