# Speaker volume control

Discussion in 'Electronic Basics' started by Andrew Howard, Sep 24, 2003.

1. ### Andrew HowardGuest

What is the best way of controlling a speaker's volume directly? (not
adjusting the amp). I have a single 8ohm speaker, and I have tried a
variable resistor, but the volume decreases too quickly. Any suggestions?

Andrew Howard

2. ### John GGuest

Get a Variable resistor about 50 ohms.
Probably very hard to find though.
An nderstanding of OHMS law would be a great advantage for the future.

5. ### BaphometGuest

You need either an L or a T pad which Radio Schlock sells. An L pad consists
of two ganged rheostats and the T pad three. This is to provide a constant
impedance as seen by the source, load or both. Additionally, a regular one
section variable resistor will cause serious distortion.

6. ### JeffMGuest

Additionally, potentiometers come in 2 tapers: linear and logarithmic.

The human ear's response to sound intensity is a logarithmic function
so that's the taper required for those applications.

There's 1 caveat: a _pad_ needs to have a REVERSE logarithmic taper.

L L PPPPPPPP AA DDDDDDD
L L PPPPPPPPP AA DDDDDDDDD
L L PP PP AA AA DD DD
L L PP PP AA AA DD DD
L L ===== PPPPPPPPP AA AA DD DD
L L ===== PPPPPPPP AA AA DD DD
L L PP AAAAAAAAA DD DD
L L PP AA AA DD DD
L LLLLLLL PP AA AA DDDDDDDDD
LLLLLLLLL PP AA AA DDDDDDDD

7. ### Baronvonrex420Guest

I used an "L" pad from the Shack. I believe it was a stereo volume control.
Large rheostat that would mount in a standard wall plate. Works Great!

8. ### BobGardnerGuest

This is to provide a constant
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.
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.

9. ### John FortierGuest

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
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