Richard_s
Second Unit
- Joined
- Nov 25, 2000
- Messages
- 267
Below I have included some text from a Q&A that I found while researching sibilance on the internet. My system sounds great as I have talked about in other posts but exhibit moderate but anoying sibilance (JBL N26 fronts, N-center). My next purchase will be a new receiver with DPL II in addition to DD5.1 as a minimum (the DPL II is to improve my sound from my "digital" cable service which does not give me SPDIF output only downconverted L&R analog). The DD5.1 etc is for my DVD movies/music.
OK now my question
I really don't understand the information presented below but it does make me beleive that not all receiver amplifiers will be the same with regard to sibilance. The last thing I want to do is make this worse. Given your experience or based on the following information Is there a particular brand/model that would be best. I can wait for the new models that are comming out.
The Text:
Could it be said that amplifiers with high damping factors use a lot of negative feedback, and therefore, would be expected to have excessive sibilance?
A We can say that a high-damping factor, by definition, means a low output impedance. The benefits of negative feedback are lower distortion, wider bandwidth, and lower output impedance, at the cost of reduced gain. That, in itself, would not increase sibilance. However, in some situations where the "designer," usually not qualified for the term engineer, will twiddle with the negative feedback circuit in order to either try to cheat the gain/bandwidth tradeoff by using the negative feedback circuit to apply what turns out to be positive feedback on the upper end, creating a slightly rising frequency response in the audible range and a peak in the ultrasonic portion of the amplifier's bandwidth, which then suffers from very poor phase response and poor stability because of it. In such a case, it would be very possible that the rising response, or more likely, distortion elicited by driving a reactive load which made the amplifier unstable, would add a harshness or edge to the upper mid-range and treble, making it appear perhaps fast or revealing, or simply, sibilant. It may also be that the "designer" simply used negative feedback to get good numbers for a spec sheet out of low quality parts and a poor design, and that the amplifier, if measured intelligently, would test very poorly, exhibiting a significant ratio of its distortion spectrum in the higher harmonics. Lots of negative feedback can lower the overall amount of THD, but add some harmonics up around the fifth or seventh, which are very noticeable and very irritating. That is one big reason why class A single ended triode amplifiers, using no negative feedback at all, can have THD of 1% and the listener is in heaven, while a mass market receiver with 0.001% THD and significant amounts of negative feedback, sounds bad.
So while it may be accurate (or may not) to say that some amplifiers with very "good" damping factors may be sibilant because of the particular and individual use of negative feedback in that model, I don't think one could say that an amplifier that uses a good deal of negative feedback and has, as a result, a "good" damping factor, would be necessarily sibilant. The sibilant amplifier would be sibilant because of poor engineering, or rather a poor engineer. I think that it's interesting to note that after testing a bunch of DVD players in Redmond, Washington a few weeks ago, although the specs provided by the manufacturers in the manuals are probably quite similar in nature, NONE of them measured the same. This not only raises questions that measurements aren't sensitive enough to characterize sonic differences, and challenges the usefulness of manufacturer's "specs" as well. Personally, I think they're pretty useless (manufacturer's specs, that is). Lastly, there are lots of very fine amplifiers that use a little negative feedback. It is the overuse of negative feedback that gives it a bad name
OK now my question
I really don't understand the information presented below but it does make me beleive that not all receiver amplifiers will be the same with regard to sibilance. The last thing I want to do is make this worse. Given your experience or based on the following information Is there a particular brand/model that would be best. I can wait for the new models that are comming out.
The Text:
Could it be said that amplifiers with high damping factors use a lot of negative feedback, and therefore, would be expected to have excessive sibilance?
A We can say that a high-damping factor, by definition, means a low output impedance. The benefits of negative feedback are lower distortion, wider bandwidth, and lower output impedance, at the cost of reduced gain. That, in itself, would not increase sibilance. However, in some situations where the "designer," usually not qualified for the term engineer, will twiddle with the negative feedback circuit in order to either try to cheat the gain/bandwidth tradeoff by using the negative feedback circuit to apply what turns out to be positive feedback on the upper end, creating a slightly rising frequency response in the audible range and a peak in the ultrasonic portion of the amplifier's bandwidth, which then suffers from very poor phase response and poor stability because of it. In such a case, it would be very possible that the rising response, or more likely, distortion elicited by driving a reactive load which made the amplifier unstable, would add a harshness or edge to the upper mid-range and treble, making it appear perhaps fast or revealing, or simply, sibilant. It may also be that the "designer" simply used negative feedback to get good numbers for a spec sheet out of low quality parts and a poor design, and that the amplifier, if measured intelligently, would test very poorly, exhibiting a significant ratio of its distortion spectrum in the higher harmonics. Lots of negative feedback can lower the overall amount of THD, but add some harmonics up around the fifth or seventh, which are very noticeable and very irritating. That is one big reason why class A single ended triode amplifiers, using no negative feedback at all, can have THD of 1% and the listener is in heaven, while a mass market receiver with 0.001% THD and significant amounts of negative feedback, sounds bad.
So while it may be accurate (or may not) to say that some amplifiers with very "good" damping factors may be sibilant because of the particular and individual use of negative feedback in that model, I don't think one could say that an amplifier that uses a good deal of negative feedback and has, as a result, a "good" damping factor, would be necessarily sibilant. The sibilant amplifier would be sibilant because of poor engineering, or rather a poor engineer. I think that it's interesting to note that after testing a bunch of DVD players in Redmond, Washington a few weeks ago, although the specs provided by the manufacturers in the manuals are probably quite similar in nature, NONE of them measured the same. This not only raises questions that measurements aren't sensitive enough to characterize sonic differences, and challenges the usefulness of manufacturer's "specs" as well. Personally, I think they're pretty useless (manufacturer's specs, that is). Lastly, there are lots of very fine amplifiers that use a little negative feedback. It is the overuse of negative feedback that gives it a bad name