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> Replacement Speaker
stevi6
post Oct 8 2007, 02:27 AM
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Hi,
I've got a Mesa Boogie DC5 with a broken speaker. Speaker output are 8 Ohm or 4 Ohm on the amp. Someone gave me a Black Shadow 16 Ohm speaker. What would happen if I connect this one to the 8 ohm output?
Steve
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Saoirse O'Shea
post Oct 8 2007, 02:58 AM
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As I understand it Stevi you will not be pulling the correct load that your DC was designed for. As the new speaker has a higher impedance rating you'll probably end up with a far poorer tone and lowered frequency range then the amp was designed for and is capable of. However, and more importantly, there may also be a potential of damaging the amp (and this would occur if you used a speaker with a lower then specced impedance).

Personally I'd replace like with like and use a speaker set up with either 8 or 4 ohm impedance - if you want a second 16 ohm wired in parallel will give you an 8 ohm 2x12.

Cheers,
Tony


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MickeM
post Oct 8 2007, 03:12 AM
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Well... that would probably work but with a bad sound, at least for a while.

To be on the safe side, always connect the output to the corresponding speaker.
Now I never recall what's worse but I think a 16 Ohm output into a 8 Ohm speaker will cause a nuclear explosion, sort of. The other way around, 8 Ohm output into a 16 Ohm speaker is safer, but likely to blow at some point.

If I remember well you can go sligtly upwards in Ohm (amp to speaker) since that happens when connecting cabinets/speakers of different impedance... I think this is difficult stuff to remember laugh.gif


EDIT: Ok, tonymiro replied already. Anyway, one extra post to warn about impedance cant hurt so i will leave mine aswell tongue.gif

This post has been edited by MickeM: Oct 8 2007, 03:15 AM


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Andrew Cockburn
post Oct 8 2007, 03:27 AM
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QUOTE (MickeM @ Oct 7 2007, 10:12 PM) *
Well... that would probably work but with a bad sound, at least for a while.

To be on the safe side, always connect the output to the corresponding speaker.
Now I never recall what's worse but I think a 16 Ohm output into a 8 Ohm speaker will cause a nuclear explosion, sort of. The other way around, 8 Ohm output into a 16 Ohm speaker is safer, but likely to blow at some point.

If I remember well you can go sligtly upwards in Ohm (amp to speaker) since that happens when connecting cabinets/speakers of different impedance... I think this is difficult stuff to remember laugh.gif
EDIT: Ok, tonymiro replied already. Anyway, one extra post to warn about impedance cant hurt so i will leave mine aswell tongue.gif


Its the other way around for tube amps - too high an impedance gets reflected back through the ouput transformer to the power tubes and they can end up arcing. This happens for sure if you have no speaker connected, you would probably be ok for a while with 16 vs 8 but I wouldn't chance it for a tube amp - solid state amp should be ok, with the caveats mentioned above.


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MickeM
post Oct 8 2007, 03:46 AM
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QUOTE (Andrew Cockburn @ Oct 8 2007, 04:27 AM) *
Its the other way around for tube amps - too high an impedance gets reflected back through the ouput transformer to the power tubes and they can end up arcing. This happens for sure if you have no speaker connected, you would probably be ok for a while with 16 vs 8 but I wouldn't chance it for a tube amp - solid state amp should be ok, with the caveats mentioned above.

Da...sh. Dash! Really? Why can't I get this into my head, Ive been trying to 15 years. blink.gif Please supply me with a simple rhyme that I can fall back on next time I stand there with the speaker cable in my hand scratching my head (amp head that is) biggrin.gif

This post has been edited by MickeM: Oct 8 2007, 03:47 AM


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Andrew Cockburn
post Oct 8 2007, 04:34 AM
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QUOTE (MickeM @ Oct 7 2007, 10:46 PM) *
Da...sh. Dash! Really? Why can't I get this into my head, Ive been trying to 15 years. blink.gif Please supply me with a simple rhyme that I can fall back on next time I stand there with the speaker cable in my hand scratching my head (amp head that is) biggrin.gif


Ohms too high, you're amp will fry smile.gif


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MickeM
post Oct 8 2007, 05:01 AM
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QUOTE (Andrew Cockburn @ Oct 8 2007, 05:34 AM) *
Ohms too high, you're amp will fry smile.gif

laugh.gif laugh.gif Good one! But I will be wondering - Ohms to high, but where?


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Andrew Cockburn
post Oct 8 2007, 06:01 AM
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QUOTE (MickeM @ Oct 8 2007, 12:01 AM) *
laugh.gif laugh.gif Good one! But I will be wondering - Ohms to high, but where?


Damn, thought I was clever for a minute there sad.gif


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Andrew Cockburn
post Oct 8 2007, 06:17 AM
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Speak too high and your head will fry ?


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MickeM
post Oct 8 2007, 07:19 AM
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QUOTE (Andrew Cockburn @ Oct 8 2007, 07:17 AM) *
Speak too high and your head will fry ?

laugh.gif laugh.gif laugh.gif that's priceless!!! laugh.gif

Just to make sure I got it right, i will not sneak peak on the earlier posts. wink.gif
So I'm standing there with my amp plugged in the 8 Ohm jacket, I look at the cabinet that has 4 and 16 Ohm. I say out a loud - Speak too high and your head will fry! - and then plug it into 4 Ohm.

Rock or electric shock? We'll rock now! Right? cool.gif


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Andrew Cockburn
post Oct 8 2007, 07:26 AM
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Exactly!


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MickeM
post Oct 8 2007, 07:27 AM
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QUOTE (Andrew Cockburn @ Oct 8 2007, 08:26 AM) *
Exactly!

Thanks mate! I will remember that excellent rhyme. biggrin.gif


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Saoirse O'Shea
post Oct 8 2007, 07:59 AM
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QUOTE (Andrew Cockburn @ Oct 7 2007, 08:27 PM) *
Its the other way around for tube amps - too high an impedance gets reflected back through the ouput transformer to the power tubes and they can end up arcing. This happens for sure if you have no speaker connected, you would probably be ok for a while with 16 vs 8 but I wouldn't chance it for a tube amp - solid state amp should be ok, with the caveats mentioned above.


My stupid - with trannies a higher impedance speaker is fine but if you do the same with a tube you may well overload the transformer and end up with arced out tube sockets as Andrew says. (I think I was reverting to 'a' level physics and tranny amps.)

Nonetheless speakers are variable impedance rather than constant load and if you run with a lower impedance speaker (lets ignore blown tubes and higher impedance for now) your tone will suffer. Still poorer tone is still better then a dead, fried amp though. All in all with a tube amp you should impedance match the amp and speakers.

Cheers,
Tony


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Cranesong Avocet II Monitor Controller, Dangerous Music Liasion Insert Hardware Router, ATC SCM Pro Monitors, Lavry Black DA11, Prism Orpheus ADC/DAC, Gyratec Gyraf XIV Parallel Passive Mastering EQ, Great River MAQ 2NV Mastering EQ, Kush Clariphonic Parallel EQ Shelf, Maselec MLA-2 Mastering Compressor, API 2500 Mastering Compressor, Eventide Eclipse Reverb/Echo.
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Andrew Cockburn
post Oct 8 2007, 08:46 AM
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QUOTE (tonymiro @ Oct 8 2007, 02:59 AM) *
My stupid - with trannies a higher impedance speaker is fine but if you do the same with a tube you may well overload the transformer and end up with arced out tube sockets as Andrew says. (I think I was reverting to 'a' level physics and tranny amps.)

Nonetheless speakers are variable impedance rather than constant load and if you run with a lower impedance speaker (lets ignore blown tubes and higher impedance for now) your tone will suffer. Still poorer tone is still better then a dead, fried amp though. All in all with a tube amp you should impedance match the amp and speakers.

Cheers,
Tony



No, no, not stupid, I naturally assumed you meant transistor amps and complemented your excellent advice with some information around tube amps smile.gif


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Live long and prosper ...

My Stuff:

Electric Guitars : Ibanez Jem7v, Line6 Variax 700, Fender Plus Strat with 57/62 Pickups, Line6 Variax 705 Bass
Acoustic Guitars : Taylor 816ce, Martin D-15, Line6 Variax Acoustic 300 Nylon
Effects : Line6 Helix, Keeley Modded Boss DS1, Keeley Modded Boss BD2, Keeley 4 knob compressor, Keeley OxBlood
Amps : Epiphone Valve Jnr & Head, Cockburn A.C.1, Cockburn A.C.2, Blackstar Club 50 Head & 4x12 Cab
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