Duke, you see, the lowering of output impedance is great but once again “how it was used”. When we hear the result do we hear the effect of a more infinite dumping or we hear the problem that coming with application of feedbacks, or we hear the problem with the fundamental fault of the drivers?
I few years ago a friend of mine (Geoff Cook) turned me to think and to experiment with negative output impedance when a negative output impedance cancels out the mechanical and electrical suspension of the LF drivers. I would not comment if the lower Zout sounded better or worth. There are many conditions to consider starting form the way that the amps used and ending with the specific characteristics of the drivers/enclosures. I found at that time (I think it was 2001) a guy – he was professor in some kind of university in Mid West who wrote in beginning off 90s his PhD papers about a contribution of an amp’s negative output impedance for linearizing of the LF drivers performance. I spoke with him a few times and it was hugely educational. All this made me to feel that a dropping out impedance is a hugely powerful tool if it properly used. You might see a few commercial products from 80s that use it but it was not properly done and it was in context of the very wrong drivers.
You see, the biggest and the most magnificent thing when you introduce an infinite damping with lower or negative impedance is getting rid of the damn primary resonance on the driver. We all sucked in the wisdom of building LF sections heavily relaying on the damn Fs. But the primary resonance is a fundamentally crappy thing! The impedance do up, the amplifier’s output stage become instantaneously underloaded and the cone moves not according to the signal but according of God know what (mechanical suspension of the driver, air damping and so on…)
Audio people are not familiar with bass reproduction when the Fs do not exists and I feel that it is very unfortunate. My experiments did indicate that with no Fs we get completely different type of bass, the real bass! I have to admit that I did not get better sound in context of the speakers and the amplifiers that I used. You see, I did not listen the Sound itself but rather the specific strictures of the sound and that lead me to my conclusions. In fact in a few weeks I am planning to return to those experiments with the LF channel of my “Super Melquíades” project and to see if I would be able to get an “interesting” result by dropping the output impedance to approximately minus 2Ohm. I consulted with Dima and we sumized that with Melquíades I would not be able to cancel the driver impedance completely because the Melquíades has no enough power (my former experiments suggested to use minus 80% of DCR). However I would be able to get a “minus little bit” and will see where it will lead me.
I think it should work fine. When I experimented with the negative Zout in past I used different (wrong) woofers. Today, although my woofers are not underhanged but they are very “smartly” overhanged and the coil in it’s Xmax still does not jumps across the magnetic transient. I pay a fee of having no sensitively but I have many drivers… and ... a “beneficialy” small room. My preliminary experiments indicated the Melquíades could loose approximately 4-6dB and still drive my room to the necessary loudness. In addition I change the gain in my line-stage from 3dB to ~8dB (thanks, Dima). So, I will have some Melquíades power to burn in the dumping…
When I reach some conclusive results I will post them around here….
Duke, here are are some observation for you to think.
| Duke wrote:|
| The soundstage collapses; the presentation becomes dry, lifeless and even edgy; and any emotion in the music is completely lost. When the output impedance control is dialed back up (damping factor down), the soundstage blooms, the music becomes "wet", and the emotion in the music begins to move you again. |
What I’m hearing in your description is your drivers are flatting out the primary resonance. If you do not use any barbarian impedance normalization network (that must not be used anyhow) then you might easily detect that with dropping output impedance the rise of the speakers impedance become less aggressive. (With the conventual woofers) So, what the Morons (means we) recognize as “bass” is in fact a situation when an amp begin to pump hundreds presents of its typical power to the drivers that temporarily lost a control over themselves. With the Negative Zout since the driver’s shaking begun to be slightly reduces via the force of the amp’s output stage then you loose subjectively what we call “bass”. Keep dropping the impedance while you run your real time spectral analyzer and you will see the actual result of bass disappearing (actually it is not bass disappearing but the amplitude around the Fs)…
Anyhow, any single adjective that you used in your description of the effect you heard is an exact representation of a gradual removing LF component from Sound. So, if you want to hear the clear effect of damping increasing with drooping of Zout then you should in parallel with dropping of Zout to EQ the LF up.
This of course introduce a whole bag of own problems…
Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche