Any description and pictures of your amp/crossover/equalizer installations in a C4 would be greatly appreciated. I'm looking for ideas as I plan to replace my Delco/Bose system in my '87 coupe.

While not planning on spending a great deal, I'm willing to invest the time in design. I've been looking at Madisound and have selected a Vifa midrange and a LPG tweeter that should work well together. Now I just have to design the crossover network between my Pioneer 1.5 DIN head unit and an Alpine amp so I can biamp the speakers. I'm considering getting an equalizer, as well. TIA.

 

This is why I tell people to get a Din and not a Din 1.5 unit. Most of the lower end ones don't have double or triple RCA outputs and you need to add splitters, loose the ability to fade, etc. and you pay more. You could just get a new pioneer unit that has front rear sub RCA outputs for $200 and skip the external crossover opting for the internal of the deck and the ability to change the levels of the speakers at the unit. If this is not what you want, you can do a few things: Get a crossover that splits the signal. Problem is this puts the highs one way and lows the other. You need all 4 channels to be regular output, not high or low. The second alternative is to get RCA 1 to 2 splitters. This will split an RCA into 2 wires from one. Again, no fading from the deck and the signal is now not as strong and clear. You will need to do the fading by adjusting the gains of the amps ensurning either the front or rear is not running at full power.
What Alpine amp do you have?

 

Here's what I'm planning. The Pioneer CD/Receiver has speaker outputs for front & rear and one pair of pre-amp outs. I'm designing a crossover that would go into the front speaker outputs of the receiver before entering the inputs of the Alpine 3527S amp (purchased on eBay recently). The amp will take speaker level input so this setup should work. Each channel of this four channel amp would then be used to drive the 4 component drivers I have in front. I get the benefits of an biamping without having to worry about designing a power supply for a true active crossover.

Later on, I can use the rear speaker outputs into a similar setup if I want rear fill or for subs. And I still have the preamp outputs left. Of course, this means an additional amp or two. I'm worried about having enough space for all the boxes and that's why I'm asking for advice. Also, from reading "The Loudspeaker Design Cookbook" by Vance Dickason, it sounds like the automobile environment can produce some interesting peaks and valleys in the frequency response so that's why Delco/Bose and other high end OEM systems have specific equalization curves on their system--so I'm also considering an equalizer at this time.

I've been into high end home audio for a long time and know my way around a little bit. I don't know much but am learning about car audio. Thanks for your advice--and any pictures of how you mounted your equipment.

 

http://forums.corvetteforum.com/zerothread?id=193712
Here's a link to the rear box. I would be concerned with one thing right now with your plan: Engine noise.
Using an amp with an high power in as you have stated was always a noise problem. We always had some noise in steel cars let alone fiberglass ones with bad grounds. Also, the speakers you are looking at are just drivers..You will need to cross them over at the proper frequencies. Since they aren't even made by the same maker, this will be difficult to do and still retain a flat sound curve. Most people buy a set with the manufacturers crossovers as these are tuned to optimal crossover points. Next, if you add an eq or scratchbuilt crossover, you are opening the door to more whine still. It can be done but it is definitely the hard highway you are embarking on.

 

92TripleBlack, I hear you regarding the difficulty of the path I'm on. FWIW, i do have an electrical engineering background but it's been a long time since I've used that knowledge. Thanks for the advice, and I'll let you all know how well things proceed (or not).

 

Good luck. :flag

 

I think you're kind of defeating the purpose of bi-amping by driving the amp from a speaker output w/ passive X-over. You may as well put the X-over after the amp and drive it with the pre-amp outs; you'll have much less noise and be happier with the results.

Then later use the other 2 amp channels for rears; or bridged for a subwoofer. You can buy those cheap inline high-pass / low-pass filters; or design your own. Best solution would be a nice electronic X-over; feed it from your pre-amp outs and it'll give you tweet / mid / subwoofer outputs or front / rear / subwoofer, etc, depending on configuration.

Also one more suggestion- those LPG tweets are hard domes and can be a bit bright (harsh?) in the confines of a car. I also used Vifa 6.5" mid-bass but with Vifa's soft dome neodynium auto tweeter. With a LEAP designed passive X-over from Madisound it's just awesome!

 

gcrouse, thanks for the advice. I'm also a little concerned about the LPG tweeters. The on-axis response does look a little peaky at the higher frequencies--but the off-axis frequency response looks very flat. That's why I'm considering them. I figure that I would mount them on the doors pointing towards the opposing seat. I've downloaded the Madisound catalog and will take a look at the Vifa tweeters. Did you go with one of their Autosound tweeters or one of their 8 ohm ones? Which one?

As far as using the pre-amp input on the amplifier, I only have one set of pre-amp outputs on my CD player/receiver. That's why I'm inclined to use the speaker level outputs.

Why do you think the noise levels would be higher using the speaker level outputs? After all, induced noise is a function of the environment and tends to be a constant voltage level (from a RMS perspective). The voltage level of speaker level outputs would be higher than from the pre-amp outputs so I should have lower noise, right? What am I missing? I was planning on actually putting a load on the speaker level outputs of the CD/receiver. Those outputs would drive a crossover. I could tap into the crossover in such a way that I can use the pre-amp inputs on the amp (just a matter of finding the right ratio of resistor values to properly attenuate the input voltage). Having the passive crossover before the input of the amp is advantageous in two respects--better linearity from the perspective that you don't have to worry about how speaker impedance varies with frequency and the fact that you can use much tighter tolerance parts because both inductor and capacitor values are lower, and the ability to bi-amp so the amplifier damping ability can handle the back EMF of the individual drivers rather than being compromised by a passive speaker crossover network.

Glad to hear that Madisound did a good job for you. I may end up doing the same, but am interested in experimenting right now. Here's are two good links if you're interested: http://www.t-linespeakers.org/tech/f...ssiveHLxo.html and http://www.snippets.org/filters/index.php3

Thanks again.

 

I used the Vifa autosound tweeter D26NC05 soft-dome; and the M18WO09 6.5" woofer. I did notice Vifa now makes a hard dome too; you might compare it to the LPG. I just never liked any alum dome tweeter- too obnoxious when it's only 2-3 ft from your ear!

I guess the big problem with using the speaker outs is you're relying on the inferior quality of amplifier in your deck. I suppose with a reasonable voltage and constant resistive load it's freq response / group delay variations would be minimal; it's just never going to be as clean as using the preamp outs. A CD has 96db S/N and in a good deck the preamp should be close to that- but the power amp sure isn't! And then compare THD of the pre-amp vs. power-amp stage (although that could be tough because they quote it under full load). Fact is the cheapo IC amp in that deck is going to add noise and distortion all by itself.

IMHO I've yet to believe bi-amping is worth the trouble- unless you're doing something really esoteric. And I though I worry about backEMF and damping factors on subs, I can't imagine a 3/4" dome tweeter posing much problem. I'd think that 6.5" would use 99% of what's available.

As far as the single pre-out, you could Y it to different amps, although you couldn't control F/R fade from the deck. What I've always done is run it to some form of EQ with fader control and sub x-over. One pre-out goes in; front, rear, sub pre-outs come out. Maybe you could design one of these- just a few op-amps and pots...

 

Oh, and since your original post asked for desriptions and pics, here's my Eclipse head unit plus Eclipse ParamEQ / sub X-over...



Which goes to a pair of tiny Sony amps (55W each bridged mono) under the seats...



Which each drive a 2way Vifa 6.5" component set with PASSIVE crossover at 2.2kHz ...



And of course some bottom end: Precision Power 150W mono amp driving a 10" JL Audio sub. Mounted flush with rear floor using the storage compartments...




[Modified by gcrouse, 3:15 AM 6/23/2002]

 

Very nice installation! Thanks for the pics and advice. It's great to get insight from someone who's knowledgeable. Good point regarding the specs of the output stage. I'll have to look into that.

Hope my installation turns out as well as yours. I'm doing both design and installation myself. As I said, I'm into experimenting right now (even considering building a regulated +/- 12V power supply so that I can run an active 4th order crossover). Will let you know how things turn out as I'll be tackling this project after I get my A/C fixed this month.

BTW, I've solved my lack of pre-amps out and forgot to mention it in my last post. I bought a Rockford Fosgate RFX8350 preamp/CD unit (last year's model) on uBid for about $110, and found that RF is closing out the CD changers, as well. I purchased the 8 CD changer from onlinecarstereo.com for about $100. Couldn't believe it--and now praying that this is one of those exceptions to "If it's too good to be true..."

 

Yeah I did everything myself too. If you have the patience you can make sure everything is done right; plus it saves lots of money which can be better spent on equipment! My only issue was I never found grills to fit my Vifa woofers; they're an oversize 6.5" model so you might check on the ones you're looking at. Got some perforated metal so one of these days I'll make some. After the wheel bearings...

Glad you found a decent deck with more pre-outs; that's a much better way to do it. So you've got a lot of work ahead experimenting and installing all that stuff. Keep us informed and post some photos during the install.