Manley MAHI MONOBLOCK AMPLIFIER - Manual (Page 13)

Optimising Your Sound System
This section is full of Hutch's little hints that may help you get the most out of your stereo - and it may not
cost anything or cost very little. Probably, you know most of this, but hopefully some of it may be new or
refresh your memory or just be refreshing reading in a manual.
A very important factor is your speakers. Hopefully you have good speakers and they are appropriate for
your power amplifier. What is appropriate? Well, with 50 watt of tube power per side and probably a limited
budget we would hope for reasonably efficient speakers so that the system will get loud enough for the music
you listen to. The "spec" to look for is "sensitivity" or "efficiency". A speaker that is 95 dB efficient will
easily get as loud with 50 watts as 85 db speakers with 150 watts. "85" will do if you only listen to folk or
chamber music. Usually you pay about the same for high sensitivity speakers but in amplifiers more watts is
more $. By the way, many reviewers confirm that 50 tube watts is similar to 100 solid state watts. If you are
buying speakers, it is wisest to carefully listen to them before buying. You will most likely like them longer
if they tend to sound natural and real rather than over-emphasized in some area. In other words, think
"accurate reproduction" not "numbers" and "hype".
The price of speakers is often directly related to the low frequency response. Great lows generally require
deep pockets and plenty of power. Thanks to "home theatre" there are a lot of powered subwoofers available
that won't drain your resources. Get one that connects to speaker outputs so that it follows your input
selection and volume control. This makes connecting them pretty easy.
There are some very interesting speaker tricks. Most people just place them wherever it is convenient.
Spouse approval is a real factor. We suggest that you experiment with speaker placement, then when they
sound 100% better you bring in the spouse and demonstrate the difference. They should be able to hear the
improvement and may totally agree with your choice. You should aim for equal distances between your
listening position to each speaker and from speaker to speaker. The ideal is an "equilateral triangle". Try to
get the speakers off the floor, and away from the walls (both side and back). The angle of the tweeter or
speaker front panel to your face is also critical and experiment with that too. You should be getting a smooth
frequency response so that highs and lows are balanced and mids not too prominent or distant. It should
simply sound "natural". When we buy color TVs the first thing most of us relate to is flesh tones because it is
something we all relate to and know when they are right. The equivalent thing in audio is vocal tone. We
have evolved amazing discrimination for the varieties of human voice and much less for other instruments.
Use a few well recorded CDs with vocals and adjust the speakers to get the most natural voices. If you are
lucky, you will end up with a system that creates a 3D picture of the music that not only has left/right width
but a solid distinct center. It should also make some sounds seem in front of the speakers and some behind.
We have heard some systems with our amplifiers even give an illusion of the height of the individual
musicians. Most rooms are longer in one dimension. Some systems sound best with the speakers across the
short dimension and the listening position part way back but not right at the back wall. Some systems are
better across the long dimension. The only way to find out is to try.
If you are getting this amazing imaging and soundstage, you may be interested why you have it if you have a
nice vacuum tube amplifier. These are very audible effects that seem to be beyond normal measurement
technique or textbook electronic theory. This effect is directly related to the amount of negative feedback
used in a design. The less feedback the greater the imaging. In transistor amplifiers it has been common
practice to use more than 80 dB of negative feedback. Conventional designs need it because transistors are
not particularly linear devices and it forces the circuit to get low distortion figures as well as very high
damping factors. Tubes are much more linear and inherently low distortion. Tube amplifier designs use far
less negative feedback (less than 20 dB) as a result . We speculate that the negative feedback may have a
negative effect on transient accuracy. It is reasonably documented that the feedback does reduce the lower
order harmonics in distortion but can raise higher order harmonics that are more audible. Feedback also
makes the transition from clean to clipping very abrupt and abundant with high order harmonics. The best
audio devices always seem to be simple & aesthetically balanced, with form following function.
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