Control external speaker volume
I want to be able to change the volume a speaker via my basic stamp.· The speaker will have its input from a seperate CD player, I need to be able to change the volume from completely off(no sound)· gradually all the way to full blast.· Is this something feasible, and if so what should i do?·
Comments
http://www.electronic-circuits-diagrams.com/audioimages/audiockt11.shtml
I searched "circuit volume control" on google. It was tough finding anything using the word speaker in the search parameter, this is one of 15 million hits but it is number 1 in the 15 million.
After looking at the circuit it simply shorts the speaker output to ground to turn it off. I don't think an power amplifier would like that very much so better do some more digging. Speakers are rated in ohms, to low of resistance can blow an amplifier so I guess I would like to see how to do it right as well.
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Think outside the BOX!
Post Edited (metron9) : 10/4/2006 9:06:35 PM GMT
http://www.intersil.com/data/fn/fn8189.pdf
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Think outside the BOX!
It's usually not the best idea to try to control the low impedance, relatively high power signals at the speakers themselves, but control the levels upstream in the amplifier chain. It's also easier to switch signal sources there. Usually when you control speaker levels at the speaker, there's a low resistance pot (8-16 ohm) with multiple tracks/windings that's designed to maintain a constant load on the amplifier as you decrease the signal to the speaker (sometimes called an L-Pad or T-Pad depending on the design).
Thanks.
L-PAD
http://amps.zugster.net/articles/attenuation
T-PAD
http://www.uneeda-audio.com/pads/
The Thread I got that from
http://www.hawthorneaudio.com/forum/viewtopic.php?t=243&sid=59396f543251326675c471f732cd440e
Also on the impedance/resistance question
http://en.wikipedia.org/wiki/Electrical_impedance
My son plays guitar with a very loud amplifier, he constantly says he has to have it loud for the tone to be good, I am glad I researched this question maby I can get him to turn it down.
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Think outside the BOX!
Post Edited (metron9) : 10/5/2006 3:06:49 AM GMT
There are some nice little stereo amplifiers in kit form with a power output of several watts, enough for a small speaker. You could get 8 of them and do the digital pot thing on each of 16 channels.
I did a sound installation a couple of months ago with two independent channels switched among 4 speakers. The speakers were changed between sound bites (so there were no pops or clicks). It's not quite what you have in mind, but it was effective with the voices changing every 15 to 60 seconds or so and moving around the gallery.
Comments?
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Think outside the BOX!
Rather than using a modified speaker, you could just switch in a fixed resistor in parallel or series with the speaker to convert some of the energy into heat rather than sound. This would be smaller and cheaper than using a modified speaker.
The problem with controlling the sound at the speaker is that there's a significant amount of power involved, at least several watts. You could use 2 relays at each speaker to add more resistors in parallel with the speaker or in series with the speaker to reduce the sound volume. These relays would have to handle the power level at the speaker. With 8 ohm speakers and several watts of power, you may be talking about 1 amp of current with peaks higher than that. That's not huge, but a small reed relay may not handle it. More substantial relays typically need more than 20ma to drive, so you'd need a transistor between the Stamp and the relay or an I/O expander like the 74HC595 and the relay. You're now talking about 32 relays plus the I/O expander plus the transistors.
Reactance is similar to resistance, but is dependent on the rate of change of the electrical flow. There's capacitive reactance where there's little opposition to electrical flow initially, but this increases as time goes on. There's inductive reactance where there's huge opposition to electrical flow at first, but this becomes less with time. You can have both in the same circuit along with resistance and their effects combine. A capacitor impedes the flow of current at low frequencies, but passes high frequency current relatively easily. The opposite is true of an inductor.
If the OP is using 16 speakers and a higher power amplifier, he better check the impediance minimum of the amplifier, an array of 16, 8 ohm speakers, 8 on one side would only be 1 ohm impediance, not many amplifiers can drive that load. I have a 2000 watt crown that drives 2ohms I use 4 dual12 bass reflex speakers with horns for my outdoor sound system.
Hmmm I wonder if you could just cascade the speakers with potentiometers like picture attached. (Its 1AM and this is a quick idea sketch)
So the pots just bypass each speaker sending the voltage through the least resistive path.
Or just use transistors in linear mode!
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Think outside the BOX!