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In Reply to: RE: Most speakers posted by Jon L on October 15, 2014 at 14:47:13
"A speaker advertised as "87 dB and 4 Ohms" more often than not actually measures more like 84 dB dipping into 2 Ohms easily in large portions of the frequency response."
This is another reason the Ncore's ultra low output impedance is helpful, being 1 milliohm at 16kHz and below. Note it is reportedly not affected by frequency throughout most of the audio band, raising to only 2.5 milliohm at 20kHz.
The first time I had the Atsah's here, I hooked them up with good quality Furutech cords with Oyaide connectors, placed them on amp stands and used large brass pucks on top to help control resonance. I am sure the milled aluminum enclosures also help control resonances, and may be one reason some report those larger amps to sound better than the 200 wpc NC400's.
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> This is another reason the Ncore's ultra low output impedance is helpful, being 1 milliohm at 16kHz and below.
That seems awfully low to me. It equates to a damping factor of 8000. I've never heard of anything like that. Have you actually measured it?
That seems awfully low to me. It equates to a damping factor of 8000.
Given the design, I'm not surprised. As Nelson Pass once observed:
"Class D amplifiers are switches with tons of feedback."
"Tons" of feedback buys you very low source impedance.
Oops...a small error.
The DIY module NC400 has an output impedance of 1mohm, but
the larger OEM module NC1200 has an output impedance of 3mohm at frequencies less than 20K Hz, and 2mohm at less than 1K Hz.
Yes, the damping factor is high and a couple of reviewers have reported that, on some speakers, this can result in the perception of less bass.
With my Aerial 9s, the bass was outstanding with a nice balance of sounding full, deep and tight, and excellent drive.
Specs for the NC1200 are covered on the linked datasheet.
Three milliohms gives you a DF=2666 with a nominal 8 ohm load. Anything over about 50 isn't really needed and that data supports the notion that it has significant amounts of NFB.
I'll pass.
Well Bruno Putzey is on record as saying that if you use negative feedback you should use LOTS and LOTS of it. So I wouldn't be surprised to find a boat load in an amp he designed.
Not sure I agree with him but I found the difference between DF200 and 400 subtly audible.
As it happens in every publication I've read which said that a DF above 50 is meaningless they assumed speaker cable with a resistance a couple of orders of magnitude higher than my cheap 11AWG cable.
Not surprising that it does not make much difference in those circumstances or when using passive speakers (that wire in the almost inevitable series inductor on the woofer screws it up).
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