I asked for some help in finding what speakers were safe to use in a Fiero. I had tried to Google Rodney Dickmans site but must have gotten an old listing. The listing didn't show any speakers other than the sub-woofer. In a later reply I got a link to the correct site. Rodney has the correct speakers.
The Fiero uses 4 ohm speakers in the back, 10 ohm speakers in the dash and a 10 ohm sub-woofer (if so equiped). Why does it matter? The 10 ohm speakers are put in places the sound travels from best. The increased resistance of a 10 ohm speaker gets less power than a 4 ohm speaker. Why does it matter? The output transister is balanced for the resistance of the speakers. If you use a lot of volume the output transisters of the radio and amplifier will be damaged if you don't use the recommended ohm speakers. Rodneys 8 ohm will balance the circuit just fine.
If you want to use common 4 ohm speakers, here is a way to balance them for the Fiero. Add a resister (3.9 ohm to 5.6 ohm) 10 watt resister or equivalent made up of a series of series or parallel resisters in series with a 4 ohm speaker. It will be seen by the radio as an 8 ohm speaker.
Here are some links for more info:
www.fierosails.com/Speakers.html
www.turnswitch.com/speakers.html
www.reconingspeakers.com/pr...standard-recone-kit/
I'm going to order from Rodney Dickmans.

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woodys 427

ALL the info you need has been posted many, many times. Just use the SEARCH here instead of Google ...

quote Originally posted by woodyhere: I asked for some help in finding what speakers were safe to use in a Fiero. I had tried to Google Rodney Dickmans site but must have gotten an old listing. The listing didn't show any speakers other than the sub-woofer. In a later reply I got a link to the correct site. Rodney has the correct speakers. The Fiero uses 4 ohm speakers in the back, 10 ohm speakers in the dash and a 10 ohm sub-woofer (if so equiped). Why does it matter? The 10 ohm speakers are put in places the sound travels from best. The increased resistance of a 10 ohm speaker gets less power than a 4 ohm speaker. Why does it matter? The output transister is balanced for the resistance of the speakers. If you use a lot of volume the output transisters of the radio and amplifier will be damaged if you don't use the recommended ohm speakers. Rodneys 8 ohm will balance the circuit just fine. If you want to use common 4 ohm speakers, here is a way to balance them for the Fiero. Add a resister (3.9 ohm to 5.6 ohm) 10 watt resister or equivalent made up of a series of series or parallel resisters in series with a 4 ohm speaker. It will be seen by the radio as an 8 ohm speaker. Here are some links for more info: www.fierosails.com/Speakers.html www.turnswitch.com/speakers.html www.reconingspeakers.com/pr...standard-recone-kit/ I'm going to order from Rodney Dickmans.

Interesting about "WHY" the ohms are set the way they are, I wasn't aware of that. Thanks for posting.

Perhaps I didn't do the search of the hundreds of pages I read in the forum correctly. Perhaps You can tell me how I should have searched. Perhaps it all needed to be in one place. I was glad to post what I found - all in one place. Sorry it seems to bother some people so much. Nice way to make a fellow feel welcome!

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woodys 427

Welcome to the Forum! Let us know what you think of it when installed.

Woody,
Great write up, research and links. Thanks for posting your findings. I frequently use info from more than one thread to make comparisons. More info is better than less.

quote Originally posted by woodyhere: Why does it matter? The output transister is balanced for the resistance of the speakers. If you use a lot of volume the output transisters of the radio and amplifier will be damaged if you don't use the recommended ohm speakers.

Curious, did you crossreference the ICamp chip in the stock radio to see what it was rated to deliver and at what ohms it was stable for operation? Reason I ask is because stability issues would only arise from the stock stereo if it wasn't capable of 4 ohm loads. Anyone who's installed a aftermarket unit shouldn't have to worry about that as most of them are 4 ohm stable.

quote Why does it matter? The 10 ohm speakers are put in places the sound travels from best. The increased resistance of a 10 ohm speaker gets less power than a 4 ohm speaker.

So, if the fader is set in the middle front to rear, the front speakers will not be as loud as the rear because of the increased ohm load present. This is of course very poor sound staging and is most commonly resolved by adjusting the fader by turning it more to the front, reducing the power to the rear speakers while increasing the power to the front to overcome the natural rear bias presented by the mismatched ohm ratings. Again I'm curious, if the front are lower than 10 ohm, you would not need to adjust the fader as far tot he front to overcome the rear bias. So, if the IC amp can handle the lower ohm loads (I've never looked at the specs for it), what damage do you think will occur?

Does anyone happen to have the part number from the IC amp from a stock radio they could post so I could look it up?

[This message has been edited by Khw (edited 04-01-2013).]

Interstingly enough, on your first link we have this.

quote The original Fiero speakers are 10 ohm impedance. For optimum life on the factory radio/amplifier you should use 10 ohm replacements. Use of 8 ohm speakers or worse, 4 ohm speakers, will cause the amplifier to run hotter for the equivalent sound level as a 10 ohm speaker. If you do not run your radio/stereo at full volume, use of speakers which are not 10 ohm impedance should not make much difference. There are many good quality aftermarket speakers such as Kenwood KFC-451C, Pioneer TSA-4103/4105 and AutoBahn AS41Q at about $100 a pair. The "Eclipse" brand is also reputed to be a good choice as are the Polk MOMO line, although the Polk units were discontinued in 2007 and may only be found on places like eBay. The Pyle PLG41.3 4"x10" Triaxial Speaker Pair is reportedly a very good replacement at around $33/pair plus shipping. Speakers are available at most audio shops and via the Internet at sites such as crutchfield.com and cardiscountstereos.com. Some speakers will come with plugs requiring an adapter or will need the wiring soldered or mechanically spliced. See the heading "Speaker Connections" below in this regard.

Oddly enough, they say "If you do not run your radio/stereo at full volume, use of speakers which are not 10 ohm impedance should not make much difference.". So, how many out there turn their volume control to the max setting? Then to top that off, all the speakers they list by part number are, are you ready for this?, yup you guessed it 4 ohms.

The second link is a 404 dead link.

And the third link gives you a recone kit for 1 speaker at $25.00. You'd need 2 kits to do both front speakers, so that's $50.00 for the same crappy speakers the stock unit came with. $50.00 would be a pretty good chunk of change to go towards a new pair of speakers of better quality.

I'm still curious if anyone maybe has a old Delco radio they can get me the number for the IC amp chip from?

[This message has been edited by Khw (edited 04-02-2013).]

I didn't get a 404 on the second link. I got a company that makes speakers in the correct size and ohm rating for lots of older GM stuff including the Fiero. I thought Rodneys looked better. I have ordered other stuff from Rodney and have been very pleased with the price and quality. His cross shaft kit for the shifter took all the play out of mine. Solid as a rock and a perfect fit. Brass bushings instead of plastic.If he says his speakers are better than stock - then they are.
www.fieros.de/en/articles/sub.html has an articlle on the Fiero sub-woofer system. It's by Oliver Scholz. He also has a link for the schematic of the amp. It might be what you are looking for. I think it will explain why speakers are of a set ohm rating and not just controlled by the bias setting. The output transisters will run warmer than designed, even at a normal volume level. I did give an easy way to balance out the common 4 ohm speakers to work just dandy in an 8 ohm application.

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woodys 427

Yes, but if the stock IC amp is 4 ohm stable, the fact that it will run hotter in a 4 ohm load is not relevant as it is rated to be stable pushing that load. Also, the sub amp schematic will do me no good as I'm interested in the IC amp used in the headunit itself for the front and rear speakers. The fact that someone posted on a web page somewhere out there that using a 4 ohm speaker will damage the headunit because of increased heat generation doesn't make it true. Oh wait, I read it on the internet so it must be true right? Reality is, unless the stock headunit IC amp is not 4 ohm stable then using 4 ohm speakers versus 10 ohm speakers will not make any difference except in where you set your front to rear fader knob at. Also, using a resistor in series with the speaker, while it may give you a closer to stock ohm rating, decreases the power your speaker will get as some of that power the speaker would normally get will be lost to heat from the resistor. Meaning you will have to turn the knob up higher to get the same volume, which in turn will cause more heat generation from the IC amp. Anyways, I am simply not swayed by some article someone published on the internet which offers no concrete proof that their assertion is true. Especially when they go on to list 4 ohm speakers as good options for replacement.

[This message has been edited by Khw (edited 04-02-2013).]

The someone I listened to was my brother. He is a retired electrical engineer. Graduated top of his class and eventually became a vis pres of the 10 largest companies in CA. The artical I refered you too was just for the schematic I thought you wanted. You are wrong about the resister. Look back at basic transister function.

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woodys 427

quote Originally posted by woodyhere: The artical I refered you too was just for the schematic I thought you wanted. You are wrong about the resister. Look back at basic transister function.

What does a resistor have to do with a transistor? One provides resistance to voltage going through it the other is basically a electronic relay.

quote Originally posted by woodyhere: The someone I listened to was my brother. He is a retired electrical engineer. Graduated top of his class and eventually became a vis pres of the 10 largest companies in CA. The artical I refered you too was just for the schematic I thought you wanted. You are wrong about the resister. Look back at basic transister function.

With those qualifications how often does he find himself wiring up speakers in a Fiero? Sorry for the sarcasm, but you sound like every customer I've ever had. Somehow they always seems to know a guy with amazing qualifications working on the most simple of tasks. This is meant to be a lighthearted jab, please don't take this as an insult.

[This message has been edited by thedude557 (edited 04-02-2013).]

quote Originally posted by thedude557: With those qualifications how often does he find himself wiring up speakers in a Fiero? Sorry for the sarcasm, but you sound like every customer I've ever had. Somehow they always seems to know a guy with amazing qualifications working on the most simple of tasks. This is meant to be a lighthearted jab, please don't take this as an insult.

Yeah no doubt. I could have included that my Father is also a Electrical Engineer and has worked in machinery automation for most of his life. I also worked in machinery automation for awhile and have completed a electronic certification course. Not to mention the many years I was into car audio installation. But that stuff isn't important, we are talking basic electronic principles and parts specifications. It's all good and well that his brother has knowledge, but I doubt he checked the specifications of the headunits IC amp.

Oh and BTW,

quote A resistor is a device that resists, or limits, the flow of electric charge through itself, in the same way that a narrow or partially blocked pipe resists the flow of water through friction. The power source driving the current through the circuit generates electrical energy, and the resistor converts that electrical energy into heat energy.

http://wiki.answers.com/Q/W...and_how_does_it_work

It's how a dummy load on a CB transmitter (or any other transmitter) works as they are just resistors or resistor arrays. It consumes the transmitting power produced by the transmitter and converts it into heat.

I mean look at a multitap resistor.



The reason for the various taps is to get different voltages from one unit. Where does the voltage decreased go? Does it just magically disappear? No, it is turned into heat.

quote Adding Resistance Using a resistor to change, for example, a 4-ohm speaker into an 8-ohm circuit for use with an amp that requires an 8-ohm load will work well, as far as amp loading goes. The speaker, however, will receive only a fraction of the output of the amp, as the resistor will take part of the current and convert it to heat. The voice coil of the speaker moves in a magnetic field while a static resistor does not. A speaker and resistor combination totaling 8 ohms will not be as loud or as responsive as a speaker rated at 8 ohms, connected to the same amp.

http://www.ehow.com/info_12...-small-resistor.html

But those are internet sources so you can dismiss them if you want. If you'd like I can go out to the garage and search for my electronics and car audio installation course books, then scan and post scans of the pages. I think I might know where one of the books is.

[This message has been edited by Khw (edited 04-02-2013).]

Sorry about that. My typing is pitiful.

[This message has been edited by cmechmann (edited 04-02-2013).]

quote Originally posted by cmechmann: If you want to read some good articles on amp ratings relative to speaker ohms and amp watt ratings go to. www.audiokarma.org They have stickies in the vintage solid state sections. The one thing I haven't seen mentioned is speaker efficiencey (db at 1 watt rating). That makes a huge difference. A 10 ohm speaker at 96db is going to ask a lot less of the amp as opposed to a speaker at 10 ohms at 86db. The lesser will have to be pushed harder to do the same job. This is even more critical of mid/full range speakers. Speaker efficiencey is going to have a big effect on how they sound from different distances.

Let's see, 10 ohms 86 db at 1 watt would mean 89 db at 2 watts, 92 db at 4 watts and 95 db at 8 watts. So yeah it will take over 8 watts to give the same db versus the other speaker that did it at 1 watt.

It's one reason why I prefer subwoofers that aren't made to work in tiny boxes. They usually have a lower db 1w/1m rating versus a sub designed for a larger enclosure due to the tighter suspension and denser cone material. Like my Boston Acoustics 10.4LF subs from 1995 that use a 1 cubic foot enclosure and has a 96db rating versus the current Boston Acoustic G110-4 subs that use a .5 cubic foot enclosure and has a 87 db rating. I mean, I like trunk space as much as the next guy but even 2 of the new Boston Acoustics will have less db at 1w/1m than the old did (2 of the same type subs gives a 3 db boost if I remember correctly over a single of the same type).

Car makers are going to make what sells. Earlier in car audio, it was originally about what sounded decent for the amount of space.
You have to remember, then it was FM or cassettes. Your source wasn't getting any better. Then you had people that were not satisfied until they threw enough watts to make the sunroof bounce. Then makers started selling higher wattage systems. Then you had higher wattage systems with better digital sources. Most of which was overkill.
You only need so many watts in that small of area if you don't want to drown out what you really want to hear.
My son in law has a 1998 Delta 88. Plenty of room. So he installed an amp and subwoofer in the back. I was able to convince him he would be better off getting decent speakers for the front. Now that he hears more of what he wants clearly, he only uses the added wattage when he is outside with the trunk open. He has stated he enjoys the music better now that he has a better idea of what better sounding is. We have gotten too used to buying for the WOW factor. We spend too much for what is in a car, instead of what makes it work.
Gm did a decent job of matching the speakers for what sources there were. The sources have changed, so matching your sound system is also changing. We don't have the team of engineers to work with us to find out what is the most cost effective decent sounding option, other than looking at specs and trying them out. Each person is also going to have their own perspective on that outcome.
There are too many variables to make an exact choice.
I just say stay close to what to the specs that work for the car and system, but ultimately, it is going to be what YOU like.

I have two Delco manuals in front of me.
The first one is for MY 1987. "2000 Series V.F. Electronically Tuned Receivers".
The second covers MY 1987. "2000 Series V.F.* Full Feature ETR AM ST/FM ST/CASS/IGE. Hi-Tech & Remote CD Player"
*VF = Vacuum Flourescent. (i.e., our blue clock display.)

They cover all car lines. Cadillac, Olds, Chevy, Buick, Pontiac (including the "P" - Fiero.) as well as S-trucks and minivans.

They all use the DM-165 IC. (Dual bridge audio amp.)
They all appear to use the same (value/part #) resistors and capacitors surrounding the ICs, so there are no accommodations made to balance the amplifiers for different output impedences.
(There ARE different parts available depending upon which vehicle the radio was installed in, but they have to do with buttons, lamps and trim plates.
In other words, all differences are cosmetic.)

Which makes sense. GM designed these things to accommodate a wide variety of environments.
They may not have the best sound quality, but they're designed to be acceptable to probably 85% of consumers, and to be bulletproof while doing it.

Having said that, I've got a 2001 S10 headunit (accommodates an iPod controller) in my Fiero.
The front speakers are Pioneer TSA-4103s and the rear speakers are original.
Sounds just fine. Sounds as good as the 1.5 DIN Pioneer headunit that I also own.

Edit - As for certifications, I posess a General class FCC license. While not a EE, I know my way around electronic stuff.
I've also got 30+ years of industry experience. (I know plenty of EEs. They know how stuff is supposed to work - on paper. Techs know how stuff works in the real world.)

Something that an audiophile friend of mine told me a long time ago that has proven useful - and true:
"It doesn't matter what kind of amp or speakers you have, or their power ratings. Turn it up as loud as you want, as long as you don't hear distortion. If there is no distortion, it's very likely that everything is 'happy'. If there is distortion anywhere, something is operating outside of its design parameters, and youi're asking for trouble."
In many years of cobbling stuff together, it has never failed me.

[This message has been edited by Raydar (edited 04-04-2013).]

quote Originally posted by Raydar: DM-165 GM P/N 16017928 Dual Bridge Audio Edit - Good luck finding a datasheet.

I'll see what I can turn up. I imagine NTE or some other semiconductor manufacturer makes replacements.

quote Originally posted by Khw: I'll see what I can turn up. I imagine NTE or some other semiconductor manufacturer makes replacements.

http://www.datasheetdir.com/TDA7374+Automatic perhaps? Closest thing I could find.

That DM-165 doesn't match the numbers shown on http://www.fieros.de/gif/sub_amp.gif though.

quote Originally posted by dobey: http://www.datasheetdir.com/TDA7374+Automatic perhaps? Closest thing I could find. That DM-165 doesn't match the numbers shown on http://www.fieros.de/gif/sub_amp.gif though.

I'm not wanting the one from the sub amp, I'm looking for the headunit IC amp itself. I just got home and haven't had time to start searching, but the IC amp you linked, if it can be used as a replacement for the stock part, is as I suspected rated at 4 Ohms. That's basically what I'm getting at. If the stock IC amp is a 4 ohm capable unit (which I suspect it is), then using 4 ohm speakers with the stock headunit isn't going to harm it as sugested by the OP.

quote Originally posted by dobey: http://www.datasheetdir.com/TDA7374+Automatic perhaps? Closest thing I could find.

It won't be a drop-in replacement. The pinouts are completely different.
The DM-165 is also a 16 pin DIP package.

quote Originally posted by Raydar: It won't be a drop-in replacement. The pinouts are completely different. The DM-165 is also a 16 pin DIP package.

Yeah, I found a picture of one and several sources to purchase one, but haven't been able to locate a datasheet on one yet .

I couldn't find a actual datasheet on the DM-165. I did find a few write ups on it, but they didn't really include any specific technical information about the IC amp chip, just general information about stereo hook up for units using it and most common causes of problems with them. Problems usually result from shorts betwen the speaker leads and from a couple of capacitors near the heat sink that after 20 some years of heat exposure tend to fail. However, from what I could find there was a common indication that stock 4 ohm speakers were used with the headunits using the DM-165 in some vehicles. In the Fieros with headrest speakers, they used 10 ohm 3.5" speakers. Each channel had two of them wired in parralel, so those presented the headunit with a 5 ohm load. Anyways, what I was able to find indicates to me that the DM-165 is 4 ohm stable but I can't say for sure (still I think it's a pretty safe bet).

[This message has been edited by Khw (edited 04-05-2013).]

NTE are normally rebrands.
Most likely GM was using a National Semiconductor IC or GM only National built IC.
Most were 8-20 watt 4 ohm stable.
At least till the Bose Series came out, early 90s