BobGardner said:
The speaker doesnt care what the source impedance is, and the amp doesnt care
what the load impedance is, so an L pad is unneccessary in this case.
I can't find the original thread to which this re. refers, but I have to say
that this is incorrect. The speaker and amp output impedances should be
matched for greatest power transfer and, failing that, the impedance of the
speaker should be greater than that of the amp output, to avoid distortion
in the output stage of the amp. Since the nominal (very nominal) impedance
of a speaker is 8 ohms, the amplifier output impedance should be 8 ohms or
lower. Since most amplifiers are designed to drive a nominal 8 ohm load,
providing them with such a load avoids distortions.
An L pad can provide attenuation between the amplifier output and the
speaker and provide a correct load for the amplifier. However, for each
volume setting you will need different resistor values.
http://www.goldpt.com/schm_ml.html shows a circuit diagram of a switchable
attenuator. If you click on the DIY reference box, you will get access to a
whole lot more info as well.
This is incorrect. If the amp is clipping, it will sound fuzzy, but not because
the amp is operating into a hi impedance load, but because its turned up too
loud. Regular old resistor will attenuate the signal.
Depending on the design of the output stage, the use of "regular old
resistors" can cause distortion. If the resistor in question is in the
hundreds of ohms range, which would be necessary to reduce the volume of an
8 ohm speaker by 40 or so dB, then the amplifier will clip at much lower
output levels than it would if it were driving its design load. Presumably
the original intention was to have a volume control between amp and speaker,
not to have to adjust the amp volume.
A switched L attenuator will avoid these problems and provide volume control
between the amp and speaker.
John