My Thoughts


On this page I am going to put down my thoughts as they appear, I hope more ideas will pop up, you never know!




Thought #1


When reading the Gradient SW-63 manual I noted that when you alter from 16 ohm mode to 4 ohm, there will be an increased output of 6 dB for the same input to the amplifier. This is of course true, but this made me think about the non straight impedance curves most speakers deliver. In Stereophile I have read some articles about single ended triode amplifiers, and John Atkinson's or was it Thomas J. Nortons conclusion that these are in fact tone controls because of their high output impedance. This is a stupid conclusion when you think a little more about it!
 
Let us discuss an amplifier that delivers an output of 10V into 8 ohms for an input of 100mV. This is the way an amplifier works, it amplifies voltages. If we let the impedance vary between 4 and 10 ohms in the midrange/treble area which is a quite common case, the amplifier will apply 10V for our chosen input regardless of the impedance. This gives us 25W at 4 ohm and 10W at 10 ohm, talk about a tone control! The single ended triode amplifier is as a matter of fact less of a tone control, as the high output impedance makes it deliver relatively  less power at 4 ohm than at 10 ohm.  What can we learn from this then ? We do not really know if the speaker is designed to give a flat frequency curve with constant power or with constant voltage. The only conclusion you can really make about single ended triode amplifiers way of treating loudspeakers with varying impedance is that it will be different, not if it is better or worse. This is only a matter of taste, and maybe a result of the choice of reference amplifier made by the manufacturer. Try with your own speakers, if you like it, it's OK. The high output impedance of SET amplifiers does however influence the filter characteristics quite heavily, so if you are going to use this kind of amplifier, it is probably wise to look at speakers with low order filtering (first or second order) or better still a loudspeaker without filter. If you are considering a SET amplifier, try putting a 2 Ohm resistor in series with your loudspeakers, if it sounds good it is probably OK to use a SET (if the output power is sufficient). 
 
If we take the discussion a little further, the real question is , use impedance correction or not. I think I will discuss this a little more in the 'Speakers' section.


Yes! I am not alone....


Some Common Amplifier Myths- Is tons of current better?


To get the correct perspective on the importance of the frequency alteration due to output impedance larger than zero I scanned a frequency response of a typical tube amplifier into a simulated load (not a good speaker design!) and I also scanned a response family showing how much the frequency response is altered by the speaker listening angle. I don't think I have to comment this, judge for yourself.




 



Thought #2


Concerning early reflections and their influence on box sound and speakers ability to 'disappear'.... I will return to this thought a little later. I am trying to find some papers from my acoustics classes containing the theory on which this is based. Sadly I have not found them yet, eventually I will find them.

 


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