You can find it in my post #2277
To link to a post, click on the post # in the top right and then paste.
Her is a link to your post
(1) Review and Measurements of Benchmark AHB2 Amp | Page 114 | Audio Science Review (ASR) Forum.
It is a bit odd to paste a chart from Dr. Floyde Tool's article titled: "DAMPING DAMPING FACTOR AND DAMN NONSENSE" and claim it proves the importance of damping factor
If you think a wiggly chart with no axes, the discussion should just end here. If you don't care about linearity into load or distortion buy a Parasound. If you care about those and want to buy on Damping Factor (output impedance), but a Purify amp. I have not heard them but they are intriguing.
There have been many informative posts concerning Damping Factor including this one by t@DonH56 that examines the effect at different DF and frequencies:
(1) Review and Measurements of Benchmark AHB2 Amp | Page 111 | Audio Science Review (ASR) Forum
If you are seriously interested in learning about this topic the Benchmark article is excellent:
Audio Myth - "Damping Factor Isn't Much of a Factor" - Benchmark Media Systems
This must be read carefully. The Focal speaker used in the analysis is specified at 8 Ohms but has a minimum impedance of 2.6 Ohms. Benchmark uses 2.6 Ohms during the article not 8 Ohms. 0.1 dB is used as the target response range that could be identified in a ABX test. There are reasonable values.
The effectiveness of higher damping factor is limited by cables:
SPEAKER CABLES SET A PRACTICAL LIMIT ON THE DAMPING FACTOR
A typical set of 10-foot 12-AWG speaker cables will have a round-trip series resistance of 0.0318 Ohms. If these were driven by a zero-ohm amplifier (if such an amplifier existed), the damping factor would be 200. Benchmark offers 11-AWG cables that have a round-trip series resistance of 0.0252 Ohms. These would limit the damping factor to 317 if driven from a zero-ohm amplifier.
In other words, damping factors greater than 200-300 can rarely be achieved at the speaker terminals. If damping factors near 1000 were important, we would need to place the amplifier very close to the drivers and/or use some very large conductors. However, don't go out and buy welding cables; large conductors have inductance problems. Skip the welding cables, as this paper will show that we don't need a damping factor of 1000.
If you think DF of 2000 is going to make any difference, DF of infinity is not more than 317 with 12 foot 11 gauge wire.
Stereophile's simulate speaker has a minimum impedance of 6 Ohms which is not stressful.
Real-Life Measurements | Stereophile.com
However, they describe their cables as well since they know cables limit DF.
Here is a summary of the discussed measurements and specifications:
AHB2 DF and measurements:
- 0.09 ohm at 20Hz and 1kHz
- 0.22 ohm at 20kHz
- Simulated speaker deviation: ±0.1dB
- Damping Factor 130 at 20Hz with published curve
- DB loss into 4 Ohms up to 2 kHz: 0.2 dB
- DB loss into 2 Ohms up to 2 kHz: 0.25 dB
A21 DF and measurements:
- 0.077 ohm at 20Hz and 1kHz
- 0.1 ohm at 20kHz
- Simulated speaker deviation: ±0.1dB
- -3dB point close to 100kHz
- Damping Factor 1100 at 20Hz, other frequencies not specified
- DB loss into 4 Ohms up to 2 kHz: 0.5 dB
- DB loss into 2 Ohms up to 2 kHz: 0.75 dB
The Stereophile simulated speaker has a minimum impedance of 6 Ohms.
So what would be the likely impact comparing these amplifiers with a speaker that has a minimum impedance of 2 Ohms?
That can be inferred from the above measurements because we can see the effect of lower impedance and simply multiply simulated speaker (and cable) deviation by 3.
For argument's sake, lets only apply the simulated speaker deviation to the AHB2 and not to the A21. In reality, the A21 will probably incur increased deviation.
So here are the estimated effects in the bass frequencies for each amplifier using the Stereophile measurements:
Estimated deviation of the AHB2 into 2 Ohms DF + Load: -0.3 (DF) + -0.25 (Load) =
-0.55 dB
Estimated deviation of the A21 into 2 Ohms DF + Load: -0.1 (DF) + -0.75 (Load) =
-0.85 dB
Based on DF and linearity into the load, the AHB2 should perform better into more difficult loads by .30 dB minimum (greater than the .1 threshold).
I agree, that dynamic measurements into load would be a useful addition but the AHB2s power supply holds up better for difficult loads so should do better at such a measurement.
There is no evidence (or math) that supports audible improvements from amplifiers effective damping factors > 100.
- Rich