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Old 17th January 2013, 06:29 PM   #6051
Julf is offline Julf  Europe
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Quote:
Originally Posted by ds23man View Post
The discussion was: if you have high sensitivity compression drivers and you want to use an overpowered Ncore without hiss, should you reduce the gain of it ( 3 db) or is it possible to use a lpad or series resistor without serious quality loss.
And within those narrow confines, yes, I am willing to admit that there probably won't be serious quality loss.
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Old 17th January 2013, 06:33 PM   #6052
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Quote:
Originally Posted by Julf View Post
OK - as I stated, my experience with horns is mostly in the PA area. One of the horns I was involved in long ago was a 3 m x 2 m x 1 m concrete horn, with 2 15" drivers. They definitely benefited from damping.
I confirm. I was talking about compression drivers. Long time ago, I used JBL cones drivers in horns enclosures at the time i was in charge of a big rental PA company and indeed, they needed good electronic damping.
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Old 17th January 2013, 10:36 PM   #6053
Henkjan is offline Henkjan  Netherlands
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[offtopic]
Quote:
Originally Posted by Julf View Post
Wasn't familiar with that one - haven't lived in Finland for 15 years. But the cover of the magazine from -89 was a nice nostalgic reminder - I got my Linn Isobariks (still going strong!) from Kruunuradio around that time..
I lived in Finland also at that time (Oulu)
[/offtopic]
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Old 17th January 2013, 11:14 PM   #6054
ChrisPa is offline ChrisPa  United Kingdom
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Quote:
Originally Posted by Esperado View Post
a high efficiency horn is a high efficiency microphone.
For my understanding, if this is the case

Quote:
Originally Posted by ds23man View Post
horn speakers are acoustical damped devices, they do not need any electrical dampening by the amplifier.
then how can this be the case?

Quote:
Originally Posted by Esperado View Post
a high efficiency horn is a high efficiency microphone.
This signal is seen by the amplifier, and will be added in the feedback loop of the amp.
Isn't that exactly the reason why you want a high damping factor/low output impedance, to absorb currents from the driver that are nothing to do with the signal being fed to the driver?

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Originally Posted by Esperado View Post
More than that, as the Ncore is a class D amp, it would be stupid to loose its definition. Limiting its power is like reducing a digital delta sigma DAC to the first bits, in a way. The good way to adapt its power would be to reduce the power supply voltage.
No it's not. A class d amp doesn't have any quantisation in its amplitude, it is completely linear. It could be argued that there is quantisation in its frequency resolution because of its switching frequency, but not in its amplitude

Lowering its power supply voltage won't change its gain or noise characteristics, it will lower its maximum power because it will clip earlier. It may/will also change its open loop linearity at the desired (low) operating power. If we assume that the amplifier is more linear about its centre point, then it is more linear at lower amplitudes than higher amplitudes and so lowering the supply voltage lowers the point/power at which these 'higher amplitude' non-linearities will occur
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Old 18th January 2013, 12:31 AM   #6055
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ChrisPA, a class D amp is a width modulation of a square pulse. The width is set by a comparator between a triangle signal and the input signal. Its precision (so its definition or distortion) depend of the internal noise and the level of the input signal (you get better precision if you compare V than µV).

Reducing the voltage of the pulses (reducing the voltage feeding the power Mosfet) reduce the power (less voltage) without changing the widths of the pulses. The output noise will be reduced in the same time.
It is obvious.
It will not clip 'earlier' with the input signal. It will just reduce the acoustic power, Like if you used a less efficient speaker. That we want with a high efficiency speaker like a compression driver+horn.

Look at the distortion+noise curve of an amp: it will increase as the level decreases, at least because the amp's noise.

To explain the things with other words, instead of using 0 to 5% of the modulation range in normal work, you will use 0 to 30% for the same acoustic level. See what i mean ?

About compression driver, the membrane is damped by the high pressure a little like if it was in water. The little volume of air between the phase plug and the membrane oppose a great force against movements. The excursion of the membrane is very little, for the same acoustic level compared at the one you would need in free air.
http://www.meyersound.com/news/press...yer_diag.l.gif
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Last edited by Esperado; 18th January 2013 at 12:45 AM.
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Old 18th January 2013, 06:32 AM   #6056
Julf is offline Julf  Europe
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Originally Posted by Esperado View Post
Reducing the voltage of the pulses (reducing the voltage feeding the power Mosfet) reduce the power (less voltage) without changing the widths of the pulses. The output noise will be reduced in the same time.
Why would reducing the voltage reduce noise? What you want to do is decrease *gain*.

Quote:
It will not clip 'earlier' with the input signal. It will just reduce the acoustic power, Like if you used a less efficient speaker.
If you reduce the voltage, the point where the amp will clip (by running out of ability to produce the required amplitude/power) will happen sooner if you keep the gain constant but reduce the voltage available.

Reducing the *gain* will produce less acoustic power, but that has nothing to do with the available voltage.

Quote:
Look at the distortion+noise curve of an amp: it will increase as the level decreases, at least because the amp's noise.
Yes. And noise does not decrease with decreasing voltage, it decreases with decreasing gain.

Quote:
To explain the things with other words, instead of using 0 to 5% of the modulation range in normal work, you will use 0 to 30% for the same acoustic level. See what i mean ?
And why would that affect noise and/or distortion?
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Old 18th January 2013, 07:13 AM   #6057
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Originally Posted by StigErik View Post
In this:

Click the image to open in full size.


(digital volume control, before the DAC's)
Aha, the real one
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Old 18th January 2013, 10:35 AM   #6058
Julf is offline Julf  Europe
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[offtopic]
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Originally Posted by Henkjan View Post
I lived in Finland also at that time (Oulu)
Ouch - it's cold and dark up there! :-/

[/offtopic]
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Old 18th January 2013, 10:45 AM   #6059
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Quote:
Originally Posted by Julf View Post
Why would reducing the voltage reduce noise? What you want to do is decrease *gain*.
when you decrease gain, you decrease noise, because the same modulated noise will be carried by a lower voltage.
i don't understand why this is so hard to understand.
If you want to reduce the output level of a DAC, you have 3 solutions
1- Set an attenuator. (But you will increase output impedance after-it).
2- Reduce the level in the digital domain, but it will reduce the definition (less bits)
3- Reduce the analog voltage reference: each bit will have a lower voltage, but you will keep the definition.
Ok, that's enough about the question, i think.
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Last edited by Esperado; 18th January 2013 at 10:47 AM.
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Old 18th January 2013, 10:49 AM   #6060
akasha is offline akasha  Denmark
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Originally Posted by fas42 View Post
The dilemma of low distortion equipment, or systems, is that you can then listen "deeper" into the sound without effort: mediocre sound smears everything with a relatively uniform patina, which may be pleasant, or unpleasant, and one tends to listen to the outside surface of the musical happenings. So, if you can listen further into the mix then your ear adjusts, and realises that something that didn't register before is very clear, and in fact is "wrong", could be improved. Hence the journey continues ...

Frank
So true!

everyone is listening for different parameters with different ears

most speakers loose 99% of whatever you feed them

seems like the overall sport in hi-fi engineering these days lies in solving errors everywhere else than where they occurs in the first place
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