I need to replace some 10 OHM speakers. Will 8 OHM work OK?

Power (W) = E*E (E squared) / Z (Impeadance)

For 8 Ohms - assuming 10 volts of audio

10*10 / 8 = 12.5 watts

For 10 Ohms -

10*10 / 10 = 10 watts

You’re moving further from a short circuit, so it’s good.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission

“The Aluminum and Fiberglass Mistress"

>
> Bob Dunahugh
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On a partially related note... does anyone know what the watts per channel are on the original GM stereo?

-Dave
1978 Transmode near Pittsburgh

>
> Bob,
> Short answer, You will have no issues running 8 ohm speakers in place of original 10 ohm.
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
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Dave,
The OEM GM radios at the time used a Class A audio amplifier along with
an auto-transformer for impedance matching to the speaker. I don't know
what their actual power output rating was, but judging by the heat
coming off the output transistor, I'm guessing about 8-10 watts max /per
channel.

Bruce Hislop
Perth Communications is now merged with MRC Wireless.
Office and phone numbers remain the same.
519-273-3307 800-565-9983

> On a partially related note... does anyone know what the watts per channel are on the original GM stereo?
>
> -Dave
> 1978 Transmode near Pittsburgh
>

>>
>> Bob,
>> Short answer, You will have no issues running 8 ohm speakers in place of original 10 ohm.
>> --
>> Bruce Hislop
>> ON Canada
>> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
>> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
>> My Staff says I never listen to them, or something like that
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Likely about 4 watts into a 6 ohm load.

The limiting factor has always been that you had 12 volt “rails” to swing the signal against, and if your design was 90% efficient, you would swing 10 volts (which is why I used the number in the earlier example).

Those second generation solid state units were limited (GM didn’t want warranty recalls).

Remember, that for a 1973 coach, it was only one decade before that your new car shipped with a vacuum tube AM radio.

Final note - the 1970’s were tumultuous for car audio. Power standards were not really in place, and loudspeaker impedance could be measured at either 800 hz or 1000 hz, and an awful lot of the specifications came from the marketing department, and tended to be overly optimistic.

I’ve seen three different magnet systems come out of OE coaches. Alnico (early ones), Barium Ferrite and then Strontium ferrite.

I spent the first 15 years of my career with Electro-Voice, Atlas Sound and Altec Lansing. Making loud.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission

“The Aluminum and Fiberglass Mistress"

>
> On a partially related note... does anyone know what the watts per channel are on the original GM stereo?
>
> -Dave
> 1978 Transmode near Pittsburgh
>

>>
>> Bob,
>> Short answer, You will have no issues running 8 ohm speakers in place of original 10 ohm.
>> --
>> Bruce Hislop
>> ON Canada
>> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
>> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
>> My Staff says I never listen to them, or something like that
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Dolph’s the expert, but lowering the speaker impedance increases the
current drawn at a given amplified voltage. But the impedance of the
speaker is merely nominal—a speaker is a reactive load and its impedance
will vary with frequency. A “10-ohm” speaker might vary from 6 to 30 ohms
over the frequency range, and the 8-ohm speaker might be 6 to 18. Give or
take quite a bit depending on the speaker. So 8 and 10-ohm speaker
impedance robably overlap quite a bit.

Rick “surprised they ever biased them to class A operation, which would
reduce the power output quite a bit” Denney

On Fri, Apr 12, 2019 at 12:33 AM Bob Dunahugh via Gmclist <

> Bob Dunahugh
> _______________________________________________
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> Unsubscribe or Change List Options:
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>
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
 
Rick,
They ran them Class A which is why the heatsink got so toasty warm irregardless of the volume setting. It gave a nice "Thud" when the radio powered
ON too.
They ran the power output transistor through an auto-transformer to get a higher voltage (volume) on a 6-10 ohm speaker.

I was working at a car radio / CB shop during the early 70's. Guy's would hang lots of additional speakers in parallel to get more volume. Usually
took out the emitter resistor if I recall. Not too often the power transistor. They were mostly AM radios. Good times!

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Turnswitch seems a good source for purists. Thanks for posting. Bob the short story is a modern 8 Ohm will be slightly louder at the same knob
setting (there are other factors with speaker efficiency, but just discussing impedance here) but as you turn up the radio it will clip at less "knob
rotation" as the output section won't be able to swing as much voltage before clip as load is greater. All in all it will be fine and by using a
modern multi element speaker it should have better freq response. The hard part is finding speakers with small enough magnet structures to fit. I used
Pioneer 4x10 3 ways in the rear and by trimming excess spray foam got them to fit with no hacking. Very good fidelity for a 4 x 10 especially at lower
levels. I'm using a Delco AM FM cass radio that I sent to a company in Fla that installed modern electronics and line in option.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
If you are using the original radio, the speakers are the loads for the output transistors. Other than a ten Ohm impedance will reduce power output,
and to a degree unbalance the output amp resulting in a bit more distortion, and more heat dissipated in the output transistors. Amazon and
Crutchfield have the proper speakers available in the correct sizes. These will give the best results if you are determined to keep the OEM radio
(which I consider substantially less than the best). The opening in the dash is correct fo0r the height of a one DIN replacement. You can then
either bend the control tabs to hold the sides of a one DIN case or cut them off anf make a mask for it and screw it to the existing dash plate. Once
you have a one DIN case, there are myriads of aftermarket radios/CD/Bluray/USB players in every price range. You will have to pull another wire for
each speaker however. Many also have GPS included. Let your pocket be your guide. If you go for a unit with GPD, ensure that the maker will supply
map upgrades for the life of the radio.
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
Johnny,
I have an aftermarket radio but the speaker over the passenger side has ceased to work. When I tried to sus out the problem I was confronted with a box that I assume the PO installed which “adapted" his aftermarket radio. I could make no sense of the output side of this mystery box and have been assuming that my one dead speaker is the result of a failure in the mystery box.
At the end of your post below is the comment that “you will have to pull another wire for each speaker.” Is that the solution to my problem or are there wires in place that would work without the mystery box?
Thanks.
Doug

Douglas & Virginia Smith
dsmithy18 at gmail
Lincoln Nebraska
’73 “Canyonlands” since ‘95: “Wanabizo”, Anishinabe Indian for “He gets lost driving” Yes, really.
Quadrabag/6 wheel disks/3;70 final/Paterson QuadraJet/Sundry other
P&W PT6, no wait, that's the wish list...

>
> If you are using the original radio, the speakers are the loads for the output transistors. Other than a ten Ohm impedance will reduce power output,
> and to a degree unbalance the output amp resulting in a bit more distortion, and more heat dissipated in the output transistors. Amazon and
> Crutchfield have the proper speakers available in the correct sizes. These will give the best results if you are determined to keep the OEM radio
> (which I consider substantially less than the best). The opening in the dash is correct fo0r the height of a one DIN replacement. You can then
> either bend the control tabs to hold the sides of a one DIN case or cut them off anf make a mask for it and screw it to the existing dash plate. Once
> you have a one DIN case, there are myriads of aftermarket radios/CD/Bluray/USB players in every price range. You will have to pull another wire for
> each speaker however. Many also have GPS included. Let your pocket be your guide. If you go for a unit with GPD, ensure that the maker will supply
> map upgrades for the life of the radio.
> --
> Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Doug - the GM radios of the time coupled the output directly to the speaker, and grounded the other side of the speaker. This saves one wire per
speaker and a couple of components in the radio, perhaps being a half dollar saving per car. In that GM built probably twenty million cars using this
design, half a buck was a hell of a saving. At the expense of needing a ten ohm speaker and some other niggling little things. Modern radios
normally have the speaker leads at some potential other than chassis ground, requiring two wires instead of one, but giving better results to the
listener. Crutchfield and others provide transformers to allow connection using one wire and chassis ground to the speakers. It's a 'get - by' to
save pulling wires. They work to a degree, the degree being the quality of the transformers, which come in every quality.
To do it right, pull a pair of wires to each speaker.

--johnny

--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
Yes, depends which radio was fitted, early (one wire) or late, two wires.

And realize if you use the get - by depending the radio design, you may see some weird artifacts in the background. 'Tis simple to draw the wires or
buy the proper speakers. Best and cheapest source for the rear speakers is a trailer harness.. buy a good one with 14ga or 12 ga wire.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
Depending on which year you are putting in a new radio the 73 thru 76 versions used a common ground and one hot lead to the speaker. The 77 & 78 Coaches had a 2 wire system, new radios which are a floating ground do not like the common ground system and you must new wiring to prevent damage to the radio output transistors. There is an adapter that allows a floating ground radio to work with a common ground system. You can check with Crutchfield or other radio installers like Best Buy. GMC Motorhomes Intl newsletter issue page 2 and issue #60 page 3 for information. Both those can be downloaded from the GMCMI site.

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 30’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

>
> Yes, depends which radio was fitted, early (one wire) or late, two wires.
>
> And realize if you use the get - by depending the radio design, you may see some weird artifacts in the background. 'Tis simple to draw the wires or
> buy the proper speakers. Best and cheapest source for the rear speakers is a trailer harness.. buy a good one with 14ga or 12 ga wire.
>
> --johnny
> --
> Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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