amplifier's "slam-factor"

Sean, thanks for validating my previous statement and for adding some of the detail that I overlooked. It is my understanding that Moncrief really knows his stuff about audio.

Two other questions, Sean:

1. You're probably really kicking yourself for not purchasing that Primare P30, aren't you? heh, heh.

2. Why not enter your system into virtual systems here on AG?

Aball, the damping factor is calculated by dividing the resistance of the speaker by the output impedance of the amplifier: DF= Z(load)/Z(out). For an amp to have a damping factor of 100 into an 8 ohm load its output impedance would have to be .08. Since a speakers load/resistance changes with frequency (most anyway) the damping factor of an amplifier varies with frequency too. Above 100 is pretty good. When the numbers start getting really high they kind of get trival/splitting hairs. The difference between a damping factor of 175 and 1750 is a 0.5% change in control over the speaker. Some claim those really high damping factor start becoming marketing hype--particularly if other aspects of the design may have been neglected. Concern rises when an amp has an output impedance of say 2 ohms and into an 8 ohm load we now have a DF of 2, worst case (and it does happen with those SET's) things can actually go into the negative zone. (The equation is simplified: to account for the speaker cable, its resistance is added to the output impedance of the amp and then that sum is divided into the aformentioned equation.)

(Current drive amps are the only time one tries to match the output impedance of the amp directly to the speaker for a DF of 0: this in only done in active systems and rarely to my knowledge. Any other time the amplifier aspires to an ouput impedence of 0)

Slew rates matter: its an important spec. However, their worth has to be interpreted in the context of power and load resistance too. A less powerful amp doesn't need as high a slew rate as a bigger one. Into an 8 ohm load an 11V/us is acceptable for a 32 watt amp; for a 1,000 watt amp 64V/us is appropriate. It does depend on the bandwidth of the amp. And if slew rates get too high it can cause new problems.

This article briefly attempts to correlate some of the electrical/measurable aspects of amplifiers performance to subjective impressions.

http://sound.westhost.com/amp-sound.htm

An output impedance of 2 into an 8 ohm load gives a DF of 4, not 2 as incorrectly stated. (This is ignoring the change caused by the cable) Although if you look at tube amp specs you'll often see ones claiming DF's of <2. I believe the Cary 300SEI (from mid '90's) actually went up to a 3.8 ohm output impedance.

Sean, I use the Rockport Syzygy speakers in a 16 x 23 x 8'6" room and can hear the transition to Class B on musical peaks when running just 10w of Class A and can't hear the transition with about 30w of Class A via a switch on the JC-1s....

Stehno: As to the Primare piece, i would have liked to have grabbed it, especially at that price, but i'm not upset about it. Then again, i don't know what i missed either : )

As to listing my systems, i had done that at one time on AA and had one of them listed here. Quite honestly, i pulled them down for security reasons. I and several others discussed this privately and came to the same conclusion i.e. we didn't need to advertise what we had. Quite honestly, i do not live in what is the best part of town, hence my desire to relocate. Two houses on our block have been burglarized in the last year, so no sense in pushing the matter if you know what i mean.

Bob: Thanks for the response. The point i was trying to make was that others may have different ideas of what they think is "loud" and have lower efficiency speakers AND have bigger rooms. While that is a tough situation ( big room, low efficiency speakers, high spl requirement ) for sure, i'm sure that it does exist. Just as i would have laughed if someone would have told me that i needed 1200 wpc to power a set of speakers before owning a set of them, i no longer rule things like that out anymore. Each situation is different and we all have different goals / priorities as to what is most important to us within our own systems. Sean
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