Pairing Amps with Speakers

[anm]

Originally Posted by CharlyD

The interaction between an amplifier and a speaker can be quite complex. While speaker sensitivity is the most critical factor, parameters such as speaker impedance and phase can also be critical. The JBL's you're considering, however, have very well-behaved impedance and are easy to drive. If the speaker sensitivity is rated at 90dB/1W/1m, and you'd like to achieve a volume level of 110dB (quite loud) you'll need at least 100WPC. The easy calculation is:

Pout = 10 ^ ((dBmax - dBsens) / 10)

If dBsens (dB out at 1W) = 90dB and dBmax (SPL goal) = 110dB

Pout = 10 ^ ((110 - 90) / 10) = 100Watts

Wow! That's a great response! Thanks! Now I can do a maths while looking at various amp/ receivers.
Question - if I buy an AVR with 40WPC for now, could my speakers fry the AVR? Or vice versa?

Can someone also advice me on how to reuse an old AVR when upgrading with a new one? Here is the post - http://www.avrevforum.com/showthread.php?t=1921
thanks and regards

[CharlyD]

Originally Posted by anm

Question - if I buy an AVR with 40WPC for now, could my speakers fry the AVR? Or vice versa?

With only 40WPC, it's more likely that you'll encounter distortion (clipping) when attempting to achieve realistic volumes for your movie soundtracks. Clipping causes high levels of high frequencies that can damage tweeters. Using 90dB/W/m sensitive speakers with 40WPC should get you to about 106dB or about half the volume you'd get with 100WPC. On the other hand, your other posting describes your living space as "a matchbox". In that environment and if used prudently (don't crank the volume up to the point where it's obviously distorting), 40WPC may serve your needs well until you can find a larger domicile and upgrade your receiver.

[wes]

Originally Posted by perion

I was wondering how one goes about pairing amps and speakers ... do you settle on an amp first and then try to find a speaker that "matches", or vice versa? Paul

Paul,

Here is the order on allocation of budget from more$ to less

1. Speakers (spend the most amount of money here)
2. Amplification, (Class A, Class A/B)
3. Source (CD, SACD, iPod with uncompressed files)
4. Processor (direct Audio feature is best)
5. Cables (10% of system, Canare or Belken)

Have fun.

[anm]

Originally Posted by CharlyD

The interaction between an amplifier and a speaker can be quite complex. While speaker sensitivity is the most critical factor, parameters such as speaker impedance and phase can also be critical.

I went through this site http://www.soundandvisionmag.com/spe...tem-page2.html which says

Nominal impedance for the L820 and LC2 measured unusually low at 4.3 and 4.4 ohms, respectively — something to note when matching them with an amplifier or receiver.

Is lower impedence than the rated impedence a good or a bad thing?

How does impedence fit into the calculation? Some amps say power is X WPC at 4 ohms, while Y WPC at 8 ohms, where X > Y. Does it mean that speakers with lower impedence can be used with a less powerful amp, and hence better return on investment?

regards

[CharlyD]

Sorry, I was trying to simplify things and went a bit too far. Speaker sensitivity is measured with a standard voltage (not power) input. The voltage used is 2.83VRMS which would equate to 1 Watt at if the speaker was 8 Ohms (P = (V^2)/R). I only looked at the JBL spec page for these speakers which lists their impedance at 8 ohms. Since the JBLs are actually closer to 4 ohms, the power input would be closer to 2 watts at that voltage. Make sure the amplifier you're considering will drive 4 ohms and don't cut corners on power. The amp will still have to drive considerable current through these speakers.

[anm]

Originally Posted by CharlyD

Sorry, I was trying to simplify things and went a bit too far. Speaker sensitivity is measured with a standard voltage (not power) input. The voltage used is 2.83VRMS which would equate to 1 Watt at if the speaker was 8 Ohms (P = (V^2)/R). I only looked at the JBL spec page for these speakers which lists their impedance at 8 ohms. Since the JBLs are actually closer to 4 ohms, the power input would be closer to 2 watts at that voltage. Make sure the amplifier you're considering will drive 4 ohms and don't cut corners on power. The amp will still have to drive considerable current through these speakers.

Still can't understand.
Does it mean that the same AVR would be able to send more power to the speakers that have lower impedance, and hence would perform better with speakers with lower impedance?

Or does it mean the speakers with lower impedance would suck out more power and AVR would be screaming for mercy?

Can this also be put into the formula you mentioned earlier?

regards

PS (edit of post) - I think I understand. Lower the impedance, more we are heading towards a short circuit scenario. Speakers sucking out loads of current and the AVR may not be able to keep up with that kind of current flowing through its own circuit.
To express the equation again - P=I^2 * R or I = sqrt(P/R). Max power an amp can provide, in terms of watts is fixed. So if R goes down, I goes up.