Please explain amplifier output impedance

Success? I would consider damping over 20:1 to be excessive. I use master tapes for reference and one thing has become clear over the years: high damping factor equates to not getting the bass right; retentive (not in a good way) IOW punch without real definition and the first thing to go is always low frequency ambience.

Some speakers are intentionally designed for amps of higher output impedance (new paradigm, BTW) in order to take advantage of the benefits such amps offer. IOW there is no *ideal* value for output impedance- it all depends on the speaker...

The lesson here is that you have to pay attention to the speaker/amplifier interface regardless of the amplifier or speaker that you have chosen. To ignore this means you could flush thousands of dollars away to no good effect.

No success?

Oh well. I've learned a lot. You guys have fun.

Hi Gregm,

No problem, that's a fair question. I won't give a highly specific answer, but hopefully the generalities will be useful.

You can design a crossover with the values optimized to produce the desired transfer function with a minimum number of parts. Or, you can design a more complex crossover that uses what looks like redundant circuitry, such as parallel resistor legs at different places within the circuit. The more complex crossover gives you more options when you start trying to juggle the impedance without spilling the frequency response.

I worked within the minimum-parts-count topology to smooth the impedance, but at best was only able to keep it between 7 and 27 ohms above the bass peaks (a nearly 4-to-1 spread). The 27 ohm maximum was at about 3 kHz, which is not a good place to have a response anomaly.

Switching to a what-the-heck-high-parts-count topology, I got the impedance down to between 8 and 13 ohms above the bass peaks, and the 13 ohm maximum is at 400 Hz where an extra dB or so helps offset the baffle step a bit.

The topology and combination of values that produced a good impedance curve without spoiling the frequency response was largely the result of trial and error. My modelling program did not do a very good job of predicting what the impedance curve would be, perhaps due to non-ideal behavior of the components. So I spent a lot of time changing crossover parts, measuring frequency response, and measuring impedance. I'm sure there's a better way.

Duke

Success. I think we all agree if you accept that my persepctive is "old school" (from electronics text books, linearity, accuracy etc.)

Furthermore, I fully agree with Atmasphere that a low frequency ambience or bass definition is what a tube amp or an amp with a lower damping factor does to the sound.

I have been following this thread with interest and doing my own novice research on this topic and it seems that there is no right answer here in terms of whether or not damping factor is a relevant spec. Here are some of the tidbits I have picked up:

1. The mechanical damping of the speaker plays the largest role in terms of how the cone movement is damped

2. The effect of any damping factor above 10 is impossible for humans to hear

3. A static damping factor number does tell the entire story since both amp and speaker impedance changes with frequency.

4. A high damping factor is misleading as it could mean the use of a lot of negative feedback which could have adversely affect the sound

These are just some bits of info I have picked up from reading about dampiing factor so please refrain from blasting me with flames. I am by no means an expert in this area.

I think there is no real good rule of thumb. Everyone has to just listen to the amp/speaker combo and decide for themselves.