Speaker Impendence Question

rictified · Post by **rictified** » Sun Jan 23, 2005 8:11 am

to the square root of the square.

billikenn · Post by **billikenn** » Sun Jan 23, 2005 5:24 pm

I second that, Im quite oblivious to anything but simple circuits.
They make all engineer disciplins cross over and take intro classes to the other disciplines. I struggled through my circuits class.
Although impendance matching seemed pretty easy.

aristeas · Post by **aristeas** » Sun Jan 23, 2005 10:36 pm

Well i've only understood about one word in four so far, but here's my question. My Laney tube amp has an impedance switch that changes the level from 8 (as a combo) to 4 ohms with an extension cabinet. Does this mean I can use any extension cab as long as it's rated at 8 ohms?

rictified · Post by **rictified** » Mon Jan 24, 2005 2:42 pm

Yes, because that means you have to have an 8 ohm speaker load in your combo, with an extension speaker also of 8 ohms in parallel with your combo speaker the total impedance is 4 ohms. I should have just said yes.

leftyguitars · Post by **leftyguitars** » Mon Feb 21, 2005 7:47 am

Hi there, Can I put my oar in? I'm a sound engineer (not that that makes me an expert). The golden rule is valve (tube) amps must not be run at a higher impedance than the output setting (or run open circuit, i.e. no speaker connected), and solid state (transistor) amps must not be run at a lower impedance than the output setting (or short circuit). Also impedance is different to resistance so you can't accurately measure impedance with an ohm meter as impedance alters with the frequency of the input signal, therefore you need a special impedance meter which "injects" a frequency (typically 1k) into the line. The best way to work impedance out if you don't have an impedance meter is by the series and/or parallel formula i.e. 8 + 8 in series = 16ohms, 8 + 8 in parallel = 4 ohms. Hope this helps, Peter.

leftyguitars · Post by **leftyguitars** » Mon Feb 21, 2005 8:00 am

Lee Kear, yes, if your speaker in the combo is 8 ohms and you use an extension speaker which also is 8 ohms then you would set the amp output to 4 ohms. Provided that they are wired in parallel.
To check if they are in parallel or series look at the wires in the jack socket and combo speaker, if the are connected + speaker to + jack and - speaker to - jack, they are parallel.
If they are wired "daisy chain" i.e. one wire goes from amp to one speaker terminal then from the other speaker terminal to one jack terminal then from other jack terminal back to amp they are in series. I hope this clarifies rather than confuses. Peter

thx1955 · Post by **thx1955** » Mon Feb 21, 2005 8:54 am

Herer is one of the best, if not the best impeadance and load calculators I've come across. Duncan Amps Impedance Calculator

It not only calculates the overall impeadance for most of the combinations out there, but it will also show how the amp's load is spread across the motors.

It's a nice little Exel spreadsheet and can be downloaded from the Duncan site. For those of you who like me are still in love with tube amps this is also a good site for information and tools for building and maintaining tube amps.