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Old 18th July 2007, 08:20 PM   #1
JRace is offline JRace  Canada
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Location: Vernon, BC
Default Timer controlled speaker switch...

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Last edited by JRace; 21st August 2012 at 02:07 AM.
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Old 19th July 2007, 03:27 PM   #2
KISS is offline KISS  United States
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2 speakers per channel probably isn't a problem. You would nned to check the minimum permissable load for the amp.

1/Rp = 1/(1/R1+1/R2+...1/Rn)
R= Parallel combination of n speakers

Rs= R1 + R2 + ... +Rn)
Rs = The series combination of n speakers


Two 8 ohm speakers in parallel is 4 ohms and if I did it right three in parallel would be 2.6 ohms which could be a problem for some amps.
In parallel, the volume should stay about the same, but series combinations will vary the volume.

Timer controlled relays will work fine as long as the AMP can handle it.
We probably could provide more info with more information:

1. wattage of amp
2. Max Listening level (Rms voltage across any given speaker)
3. Minimum load allowed by amplifier


If you had a 1 KW amp stable into a 2 ohm load then not a problem.
If you had a 10 watt amp with an 8 ohm minimum load then a problem.

Of course, the answer lies somewhere between these limits.

You could, however, buy L-pads for each of the speakers. Wire 2 speakers in parallel and place that combination in parallel or series with another speaker so you would then have 4 ohm in parallel with 8 or 8 ohms in series with 4 ohms.

For each speaker, wire a DPDT switch that will select a resistor or speaker for the load. Have thes controlled by timers.

A second AMP.

Just can't evaluate cost-effective options without more information.
Even maximum speaker switches (total) during a day might help help.
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Old 19th July 2007, 03:50 PM   #3
AndrewT is offline AndrewT  Scotland
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Well, we all know that Prince Charles talks to the plants, but this is bordering on the insane.

The plants don't even get the pleasure of hearing the gardener's dulcet tones.
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Old 19th July 2007, 04:00 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
a number of solutions.
Wire two sets of the relay controlled speaker in series, giving 16ohm. Then wire in the third pair in parallel to the first two sets.
The worst impedance is 5.3ohms. Care with the series set to avoid both relays going to straight through and shorting out the amp.

Unfortunately, the volumes are not matched.

What about using transformer coupling as in PA work.
2:1 transformers will convert the speaker impedance to an effective 32ohm. Then you can wire as many as four sets in parallel and still stay at 8ohm or above.

2:1 audio transformers that can handle wideband speaker currents will not be cheap retail, but there are bargains out there.

Or is it the timers that you are enquiring about?
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Old 19th July 2007, 04:31 PM   #5
JRace is offline JRace  Canada
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Finding the proper timer device is the concern. as it needs to be turned on/off at percise pre-determined times.

The sound system is only to provide audio for plants to listen to so output and sound quality are not a priority, nor is volume matching from room to room.

As well, we may end up running three speakers in total (1 per room) if it makes the wiring easier.

For the record I am not making any claims as to whether or not this will improve the quailty of the plants - I am just trying to help my friend with his project.


The amp will be a Luxman m-113 2ch power amp, I think it was rated around 50w/ch @ 8ohms RMS.

Thanks for the input...
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Old 19th July 2007, 04:48 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
a DIY adjustable timer that is precise and three independent channels and repeatable from day to day will be quite a project.

Those plug in timers intended for table lamps etc, are fairly precise.

Wire two speakers in series on one channel.
Wire the next two series speakers to the second channel. I've heard that plants can't tell if it's not stereo.
Finally wire the last series pair to one or other channel.
Each series pair can be connected at will by a relay.

Now just work on the control.
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Old 20th July 2007, 02:24 AM   #7
dangus is offline dangus  Canada
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Get some 120V timers or X10 relay modules. Cut some traces and isolate the switch (or relay) contacts from 120V. If using the X10 module, use an X10 controller (the one that looks like a digital clock) or a computer with a serial or USB X10 interface to control the modules. X10.com always has some kind of package deal going, or you might find some ex-Radio Shack house brand X10-compatible stuff at a liquidator.

I think there are X10 modules with dry contacts, but they'll be harder to find. And it's the appliance modules that have the relay contacts, not the lamp modules (which are dimmable). Of course, if you have some 120V AC coil relays you could just plug those into either style of X10 module and save some hacking around.
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Old 20th July 2007, 02:57 AM   #8
KISS is offline KISS  United States
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Do it the way everybody else does it. You don't need a full blown PLC, but something like this might do:

http://www.idec.com/Products/ENG/PDF...Relay_2004.pdf

Again, your missing specifications.

Precise: down to the nano second?, Relative to each other?
Same schedule for a day, a week, a month, a year, a century
How easily does it have to be changeable?
How many times a day does it switch: 1 on, 1 off; right?
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Old 20th July 2007, 03:47 AM   #9
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use three mechanical time switches to switch relays on a distribution board.
Thats a fast implemented, cheap, reliable and safe solution (at least, if you are familiar with 115/230V circuitry ).
If not, plug cheap walwarts into the time switches to serve 12V relays.
regards
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Old 20th July 2007, 04:52 AM   #10
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Quartz alarm clocks, digital or analog can be used to get the real time reference. U will have to dig in them a little. They are cheap and easily available. Then it is a matter of one hour pulse from a crystal controlled time base and dividers. Connect a CD4017 to go further.

Gajanan phadte
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