Axiom Home Page Forums General Discussion Technical Questions Speaker Resistance (Ohm) Wiring Question

Lets say that I have 8 speakers that are 4 ohms each.
I would like to set them up in groups of 4 speakers, so two groups of 4...

How can I get it so that they don't tax a basic stereo receiver that is only rated for 8 ohms/channel?


OK. So these are bass shakers, not speakers, but you get the idea.

I have a pair of wires running to my front row of seats, and a pair going to my back row of seats. Each row has 4 seats, each seat has a bass shaker.

I can wire them, it seems, so that I can get 8 or 2 ohms per pair and then combining two pairs (thus 4 seats) I can get 16 ohms, 4 ohms, 10 ohms (8+2), or 5 ohms (8+2/2)...

The receiver I was looking at was the Sherwood RX-4105. It costs all of $100 and offers 100 watts/channel (perfect match for two sets (channels) of four 25 watt shakers)...

If I go with a plate amp, they seem to all be mono output (which is fine), but when combining 8 shakers, I get 8 ohms (or other "odd" ohm numbers like the 5 & 10 in my first example)...

So either I need some help with the wiring to get something that won't tax the little $100 Sherwood (which I do NOT own yet) ohms wise but still utilize two channels to get the right wattage, or I need to find a mono amp that is 200 watts, not expensive, and can do 8 watts.

Ideas?

Resistance is futile.



Did that help?

LOL. No.

I was just searching and saw these.

AudioSource AMP100 - $99
Which the specs state...
"Output power 50 watts RMS per channel @ 8 ohms, 60 watts RMS per channel into 4 ohms, 160 watts RMS @ 8 ohms bridged mono"

And
Dayton Audio APA150 - $128
Which the specs state...
"Measured power output: 2 x 75 watts RMS (into 4 ohms @ less than 0.01% THD)"

I know that 75 watts is not 100 watts, but the trick I learned years ago about bass shakers is that they don't need to be "cranked up" to be effective, and in fact, they are more impressive at lower settings...

Other thoughts about any of this?

You need to make sure that the effective impedance of each branch or group is identical. Otherwise you will get level imbalances as more current will flow through the lower impedance branches. In other words you can forget about the 10 or 5 ohm options. If you need to use both channels, with 4 speakers per channel you can have 4ohms or 16ohms. With a single channel you can get 8ohms, as you have pointed out. The Sherwood will likely be fine with either the 16 or 4 ohm configuration, but there is no way to know for sure without trying it. Personally I would look for a cheap plate amp designed for DIY subwoofers.

Nick, have you already bought the bass shakers yet? i would try to find some 16ohm shakers.. That would allow you to get a nominal impedance of 8ohms.. In your 8 driver example.

Thanks Andrew. So many "diagrams" online show all sorts of configurations and odd ohm levels, thus my confusion.

Dakkon, yup, I've owned these shakers for years.

Here is a $120 plate amp. 250w at 4 ohms, 156w at 8 ohms...

Dayton Audio SPA250 Plate Amp

I would need to build some sort of "box" for it, but that wouldn't be a problem I wouldn't think.

Thoughts on this one?

I would just wire up each set of 4 shakers to either 4 ohms or 16 ohms, and then take the two wire runs that go back to where the amp would be and wire them in series or parallel (depending on which way I went - 4 or 16 ohm each set) and get 8 ohms.

I just want to make sure that I am thinking right before ordering something.

Nick, please do draw a map or take a picture or something. I'm interested in adding bass shakers, but the wiring has always baffled me.

Nick, you could always put a resistor in the circuit to increase the overall resistance.... It would be a "waste" of power, but would reduce the current draw from the amp.