Guitar Cab - 2 Speakers, Different Power Ratings

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Guitar Cab - 2 Speakers, Different Power Ratings

Postby Ax1 » Sun Oct 12, 2014 6:55 am

I am putting together a guitar cab for my 30W tube amp, and have been told that at full volume it outputs up to 55W of power.

My questions is, I want to use a 20W 8ohm speaker in parallel with a 50W 8ohm speaker. Will this work? - This should give me a 70W load at 4ohms right? - but as they are both the same resistance, they take half the current each which would be too high for the 20W speaker?
The reason for this is I want to mix 2 different brand and models of speaker to get a unique tone.

I just want someone to confirm. My calculations show that with a 55W output, without knowing anything else, each speaker would need to handle 27.38 Watts (is that correct?)
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Re: Guitar Cab - 2 Speakers, Different Power Ratings

Postby DeathRex » Mon Oct 13, 2014 9:22 am

Yep, each one will get 27.5 watts. Easy way to fix that is the put a resistor in series with the 20 watt speaker. Something like a 3.3 to 4.7 20 watt resistor. Of course more power will goto the 50 watt speaker. Don't know if it will be louder than the 20 watt, that depends on the sensitivity of each.
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Re: Guitar Cab - 2 Speakers, Different Power Ratings

Postby Ax1 » Thu Oct 16, 2014 1:24 pm

I thought about just putting a resistor in series with the 20W speaker, but wasn't sure if that was allowed, best practice?

The sensitivity for the 20W is 98db, and the 50W is 100db. So the 50W will be louder, but not by that much. Is that correct?

I think I will put a switch on the cabinet, so I can run it with the single 50W with resistor, or on both speakers with a resistor on the 20W.
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Re: Guitar Cab - 2 Speakers, Different Power Ratings

Postby DeathRex » Thu Oct 16, 2014 4:58 pm

All home speakers that have more than one speaker in them and not biamped have resistors in the crossover.

Well with a 4ohm resistor in, the speaker will be getting even less, since 1/3 of the power will be absorbed by the resistor.

I would like to see the speakers rated a bit higher than the amplifier, like 2X. Could you turn the power down of the amplifier, like to 20 watts?
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