Changing speakers

[dan stanton]

Sorry, but my brain isn't functioning well today. If I have 200 watts out into 2 ohms @ 20 volts = 10 amps, right? So, if I change to 16 ohms @ 20 volts = 1.25 amps = 25 watts?

 

[Rick Auricchio]

Theoretically, yes. But we're dealing with impedance, which changes dramatically with the frequency. So it isn't a constant resistance like you're assuming. Impedance and power change with frequency.

As for the higher impedance cutting power, this is generally true of solid-state amplifiers. Tube amps get adjusted to match the impedance, so they deliver the same power level in all cases.

 

[dan stanton]

It's solid state. Peavey.

 

[Rick Auricchio]

A SS amp will put out more power into a lower impedance load, and less to a higher impedance.

For example, it might be 400w/2ohm, 200w/8ohm, 100w/16ohm.

 

[dan stanton]

Thanks, Rick.

 

[Rick Auricchio]

That said, many folks try to switch to a lower-impedance cab "to get all the power from the amp." Doubling power gets you about 3dB louder, which is almost insignificant (assuming the cab can take it.)

The far better solution is to add a cabinet, which immediately increases loudness. The second cab naturally drops the impedance, which gets higher power.

Just in case that might have been on your mind.

 

[dan stanton]

Actually, I'm tring to get less power out, so I can use it until I get a new speaker cabinet built. All I have now is a 50 watt rms cabinet.

 

[Rick Auricchio]

And I assume you can't just turn down the volume on the amp or the bass?

 

[billfitzmaurice]

Doubling power gets you about 3dB louder, which is almost insignificant (assuming the cab can take it.)

Halving the impedance load gets you 3dB at small signal levels, not at full power. The full power capacity of an amp drops with a lowered impedance load, so a 100 watt amp at 8 ohms won't deliver 200 watts into 4 ohms, 160 watts is more like it. That translates to perhaps 2dB additional output at full power, so if you're rig isn't loud enough going to a lower impedance load alone isn't going to make a worthwhile difference, you have to do so via adding more speaker to get higher sensitivity as well as more power.

And I assume you can't just turn down the volume on the amp or the bass?

+1.

 

[dan stanton]

Turn down? How do you do that? I was stuck more on the math than anything. Thanks for the help!

 

[Rick Auricchio]

That's kind of like:

"Back up my hard drive? How do I put it into reverse?"

 

[smogg]

Turn down? How do you do that? I was stuck more on the math than anything.

LMAO,
That's a sig if I ever saw one.

 

[B-string]

That's kind of like:

"Back up my hard drive? How do I put it into reverse?"

Reverse the 12volt power to the hard drive, but then all the hidden messages from the devil come out!

 

[billfitzmaurice]

Reverse the 12volt power to the hard drive, but then all the hidden messages from the devil come out!

"Turn me on, dead man!"

 

[Pilgrim]

Reverse the 12volt power to the hard drive, but then all the hidden messages from the devil come out!

"Paul is still dead...Paul is still dead...."

 

[avantflow]

Hello!
I am about to change speaker on my Marshall Bass state 150W combo. The original was a 15 inch, 8 Ohms speaker and that's all i know. Then the second user replaced it with a RCF 75 W speaker and it's not working well with my combo.
I found a 500w celestion for a good price cca. 50 €, but it's a full range speaker. I was wondering if this is a good or bad thing.
-> Invalid Link Removed

 

[dan stanton]

Steal it smogg.