| Good grief. The 80 watts you have now, with 89db/w @1m speakers, should
be more than adequate, unless you listen in an aicraft hangar, or plan
to use them for raveups in a 40 acre field. Your note sounds like you
have some basic misconceptions about power rating and loudness.
Before the lecture ;-).......
The speakers sound like they're a Wilmslow Audio kit. Wilmslow's number
is in this conference somewhere - they're nice helpful people.
Going up to 100 watts only gives you 1.25 times the power. Sound
pressure diminishes by the inverse square law, so 1.25 times the power
will only give you the-square-root-of-1.25 times the sound pressure at
the same distance; I don't know what that works out at, just over 1
somewhere. So if you only select your amp on its ability to deliver 100
watts, you may as well save your money and buy CDs or LPs with it.
In practice, a good modern 40-50 watt amp like the Pioneer A400 will
probably show your old Technics the way home. That should fit in your
budget, along with a few home grown models. Don't be deceived by RMS
power ratings, it's the amp's ability to deliver rapid surges across
the frequency band into a real loudspeaker, whose impedance can range
from 4 to 16 ohms on vaerage depending on frequency, in response to a
real music signal that counts. RMS power has very little relationship to
that, it is more down to the amp's ability to reproduce dynamic range,
and that is in turn dependent on the same capability of the source of
the signal.
Also, don't be deceived into thinking that 100 watt speakers need a 100
watt amp, it's the sensitivity that counts. Your speakers will sound
twice as loud as a pair with a sensitivity of 86db/w @1m, for any given
power input, or half as loud as a 92db/w @1m. A pair of 50 watt
speakers can take three or four times that in power surges, provided
they are fed with a clean signal; on the other hand, a 100 watt pair
will go into self-destruct mode with a 30 watt amp cranked up so high
it clips and distorts the signal.
And the quality of the signal ultimately depends on the quality of your
sources, especially if you plan to run at full power.
End of lecture....
Dave
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| Dave,
Thanks for the lecture, all constructive criticism gladly accepted. Well I went
back and checked the spec sheet I got with the speakers and they are definitely
made by Kef in Maidstone. However I erred on some of the ratings I quoted off
the top of my head. These are 86db/w @1m units and 8 ohm nom. impedance.
Now I do understand the 3db factor and the inverse square law factor, as I am
an engineer, although I've spent the last few years writing software instead of
designing great loudspeaker systems like I should have been. However I'm
perplexed at the way equipment manufacturer's rate their amplifiers. As you
point out in .1 the difference in amplifiers actual power handling abilities and
their quoted RMS abilities can be startling due to things like poor transient
response and "holes" in their power output spectrum. However I would like to
bring up the point in case of Technics.
As described I have a Technics 80W amp, however I've heard 50W amps perform as
well as them, probably for all the reasons outlined in .1. Now, I have a
friend who had a Sony 40W amp and replaced it with a Technics 70W amp and he
nearly cried when he pumped up the volume. It was nowhere near as "powerful" as
the Sony. This may sound ludricous but do Technics calculate RMS values
differently to the rest of the engineering community or are these just
aberrations on a normally good record.
Back to my Kef/Technics setup: The volume on the amp is displayed in digital
form in dB from -70 to 0. Average CD's played off an old but excellent Ferguson
CD player sound clean up to -14. After that the sound quality goes to hell.
Surely the THD exponential point can't be hit so far from Max volume. Could the
amp be clipping so early? Even though the volume ain't stupendous at this point
I avoid going above this point to avoid tweeter blowout from distortion.
So as you can see I have serious misgivings about Technics, so does anybody
want to defend them.
Joe.
PS any body listened to the Pioneer A68(?)6 amp. Any opinions vis a vis the
above?
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| Joe,
86db isn't particularly sensitive, but you should still get respectable
volumes in an average room with a *good* 80 watts amplifier.
Regarding the Sony vs. Technics issue you mention, manufacturers
measure RMS power into 8 ohms, usually at a fixed frequency. How two
different amplifiers work with a real music signal into a real load
depends on the amp power supply's ability to deliver current, and on
the supply's bandwidth and output impedance as seen by the output
stage. Give an amplifier an easy, simple signal and a "budget speaker"
load, and it will sound OK; however, a demanding signal, even with easy
speakers, will sort the men out from the boys.
Regarding your distortion, I suggest you check the speaker drivers for
damage, that they're screwed in tight, and that there are no loose
connections or dry joints. Also, cabinet air-tightness can affect
volume and dynamics - hence perceived volume; you can check this by
gently pushing the cones of the bass units in - you should feel lots of
resistance and they should spring back immediately you take your hand
away. If they're reflex speakers you will need to temporarily block the
port, of course. Then make sure you have the speakers on appropriate
stands and that they are postioned correctly. If you still have
distortion at the level you suggest, try a different amp and source.
Remember that high sound pressure levels can reveal all sorts of ills
in a system that are inaudible at "normal" listening levels, as can
more revealing speakers than you're used to.
Good fun this hobby, ain't it?
Dave
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