2 8ohm speakers Plus 2 16ohm speakers and one fender deville

mistermikev · Post by **mistermikev** » 21 Jan 2011, 02:44

hello all,

hoping I can get a confirm/deny on a question...
ok, so I have a hot rod deville 4x10. the manual has it able to run 8ohm or 4ohm.

one of my voice coils is rubbing... so I bought two 16ohm replacements (got a deal)

so, I figure I wire 1 * 16ohm + 1 * 8ohm in parallel and get 5.33333 ohm
then wire both sets in series and get 10.66666ohm

as I understand this will actually lighten the load on my amp and not cause any problems... correct?

I think the only problem would be going below 4ohm because less resistance would allow the transformers to run 'hotter' than normal and potentially damage them... do I understand correctly (give it's an over simplification).

thanks in advance for your advice!

or am I "better off"/ok wiring with two 16 ohm in parallel = 8ohms, two 8 ohm in series (16ohm) then the two sets wired in parallel for 5.33333ohm?

bajaman · Post by **bajaman** » 21 Jan 2011, 05:10

get the CORRECT replacement speaker

blackbunny · Post by **blackbunny** » 21 Jan 2011, 08:12

bajaman wrote:get the CORRECT replacement speaker

+1

Never mix 8 and 16 ohm speakers in the same circuit. Neither speaker will be happy and it will sound like s**t.

mistermikev · Post by **mistermikev** » 21 Jan 2011, 11:36

roger that. I couldn't go wrong with $25 for two brand new celestion g10s... guess I'll have to trade em off and get 'the right ones'.
thanks for the responses.

trevize · Post by **trevize** » 21 Jan 2011, 11:38

Get the correct replacement speaker, in the meantime you could use just use the 8ohm speakers wired in parallel (should be 4 ohm) and make it a detuned closed back cabinet (just need to cut a new piece of wood for the back).

check this cabs for example

http://www.yellowcabamplification.com/210S.htm

mistermikev · Post by **mistermikev** » 21 Jan 2011, 11:50

well, as it were I have a lot of options... I have a 70's blue label 15" 16ohm, I could wire up two of the orig 8ohm in series and wire the three in parallel...
as I understand the bulk of the load would be carried by the two 8ohm then... and they are 30watt so I don't see much of a prob there.

I could go with just two like you mentioned...

I think I'll just snag some jensen mod tones as replacements and take the former advice.

I would have bought these either way as for $25 I can always do something with them, and if not I'm certain I can get my money back out.

thanks again for the responses folks.

blackbunny · Post by **blackbunny** » 21 Jan 2011, 13:29

mistermikev wrote:well, as it were I have a lot of options... I have a 70's blue label 15" 16ohm, I could wire up two of the orig 8ohm in series and wire the three in parallel...
as I understand the bulk of the load would be carried by the two 8ohm then... and they are 30watt so I don't see much of a prob there.

This would work; I did exactly this (15" + 2 x 10") mod to an Ampeg VT40 to get more bottom end and it worked fine.
I cut a new baffle and kept the original one... just in case.

As for power sharing, I think the 15" would dissipate the same power as the two 10" speakers together, so at 60 watts output from the amp 30w would be handled by the 15" and 15w by each 10" speaker - 30w for the pair.

The easiest option will be the 4 x compatible 10" speakers though.

JiM · Post by **JiM** » 21 Jan 2011, 21:55

More than the impedance mismatch, i think that other speaker parameters mismatch could be a problem.
I've heard that most tube amps tolerate quite well between half and double of nominal impedance, the latter being more safe. It's open or short circuit that really does damage quickly. Anyway, the real impedance of a speaker varies quite a lot across its frequency range, the rated impedance is just a mean value. http://www.churchsoundcheck.com/imp1.html

blackbunny wrote:As for power sharing, I think the 15" would dissipate the same power as the two 10" speakers together, so at 60 watts output from the amp 30w would be handled by the 15" and 15w by each 10" speaker - 30w for the pair.

Maybe for DC power ... but as a complex reactive load, responding to an harmonic-rich AC signal, things get a lot more complicated. The most relevant part is the "efficiency" or "sensitivity" of the speaker (quoted in dB for 1W at 1m, usually in the 80-110 range). For example, a 10" Greenback is rated at 95dB, compared to 98dB for a G10 Gold. The latter will need half the power to move as much air !

mistermikev · Post by **mistermikev** » 22 Jan 2011, 01:24

thanks everyone for the overwhelming responses.

I know I can trust advice I get on this forum like gold(esp you bajaman-I'm a big fan) and it's a really nice thing to have access to that - thanks again to each and every one who responded! I've learned some things and I appreciate.

I do def want to incorporate that 15" somehow, at some point, cause running into it direct added all that warmth back in...

but as a direct result of former advices I ordered two more celestions that match the two I bought...

BTW FOLKS - 2 * 10" CELESTIONS FOR $50 SHIPPED! AT 'AVATAR SPEAKERS . COM'

so I'm going to wire each set of two in parallel (8ohm), wire those two sets in series (16ohm) and wire in a jack so I can connect that set to the 15" in parallel and get 8ohm total... and 4x10 + 1x15 = STACK!!!!!!!

k1rkyd · Post by **k1rkyd** » 03 Mar 2011, 00:06

I was fixing someones amp (a deville) and he had ordered 4 x 4 ohm speakers!!!
The output of this amp is 8 ohms with an 8 ohm extension cab socket, switching the output transformer into 4 ohms.
I was looking and thinking; "this aint gunna happen" and then i figured that because i can't wire the speakers in series parallel giving me
rt=1/(1/4+1/4)=2ohms output where as in series i get, rt=4+4=8 ohms output.
When you put the two 8 ohm sets in parallel it then gives you your 4 ohm load! I didnt want that so, i wired two of the speakers in series with a jack on the end into one socket from the output transformer and the other two in series giving me the other 8 ohms acting as cab extension. This worked just fine and the customer was very satisfied! The amp sounds louder too.

If you ever get this situation then thats just something to consider.

K1RKYD

blackbunny · Post by **blackbunny** » 04 Mar 2011, 00:34

k1rkyd wrote:When you put the two 8 ohm sets in parallel it then gives you your 4 ohm load! I didnt want that so, i wired two of the speakers in series with a jack on the end into one socket from the output transformer and the other two in series giving me the other 8 ohms acting as cab extension. This worked just fine and the customer was very satisfied! The amp sounds louder too.

If you ever get this situation then thats just something to consider.

.

You found a nice solution to this problem, thinking outside the square!

Another option: the Deville output transformer has a 2 ohm tap which is not used in the 4 x 10 models.

They can be converted to 4 ohm outputs as shown in this diagram, which is how the 2 x 12 models are wired.

Duckman · Post by **Duckman** » 04 Mar 2011, 01:00

Duncan amps provides this wonderful tool to easy calculate various impedance and power configuration.
Hope it helps somebody didn't have yet.

DrNomis · Post by **DrNomis** » 04 Mar 2011, 01:59

Tube/Valve Amplifiers are more finicky when it comes to connecting speakers, for a proper impedance match, you MUST make sure that the speakers present the correct impedance load to the amplifier, otherwise you will do one of these things to the Amplifier:

1, You will cook the Output Transformer....Expensive to replace...

2, You will cook the Output Power Tubes/Valves... Expensive to replace....

3, You will cook the Power Transformer.... Expensive to replace...

4, You will reduce the power output of the Amplifier, and thus cause your amp to sound bad, you're a giging muso and you don't want bad sound,right?...

The best way of avoiding any of the above happening is to always replace the faulty speaker/s with the correct type, I know it is a bit expensive getting the correct speaker, but so is having the above fixed by an amp tech, probably more so....

Solid state amps are a bit more forgiving to impedance mismatches.....

ironman28 · Post by **ironman28** » 14 Mar 2011, 21:03

DrNomis wrote:Tube/Valve Amplifiers are more finicky when it comes to connecting speakers, for a proper impedance match, you MUST make sure that the speakers present the correct impedance load to the amplifier, otherwise you will do one of these things to the Amplifier:

1, You will cook the Output Transformer....Expensive to replace...

2, You will cook the Output Power Tubes/Valves... Expensive to replace....

3, You will cook the Power Transformer.... Expensive to replace...

4, You will reduce the power output of the Amplifier, and thus cause your amp to sound bad, you're a giging muso and you don't want bad sound,right?...

The best way of avoiding any of the above happening is to always replace the faulty speaker/s with the correct type, I know it is a bit expensive getting the correct speaker, but so is having the above fixed by an amp tech, probably more so....

Solid state amps are a bit more forgiving to impedance mismatches.....

wow

I cant believe this kind of mis-information is being propagated still. Impedance mismatches on tube amplifiers will not destroy your amp. It may change the tone or power output but it will not "cook". The effect of impedance mismatch on bandwidth and power in tube power amps is well known. Some manfacturers actually recommend impedance mismatch for different tones: http://support.fender.com/manuals/guita ... manual.pdf

Power distribution between mismatched speakers is another discussion.