Speaker Wiring Impedance Question

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Rotus623

Member
2010-09-20 4:34 am
Alright fellars, so I just bought a KMD cabinet, with with four 16ohm Celestion speakers. Everything is working well, but the owner told me that the speakers were wired for a 16 ohm load. I have an impedance switch on my amp(4,8 and 16ohms), and don't want to blow anything up.

Seems to me like two speakers were run in series, and 1 speaker was run off of each of the two, in parallel. The wiring is a little hard to explain, maybe this is called a series-parallel, so I am posting a picture. One other thing, if I plug into one, or both of the amp input jacks, does that change the load? Any help, as always is appreciated!!y
P.S. even though the pics say 4 ohms, the speakers are actually 16 ohms.

http://i803.photobucket.com/albums/yy317/rotus623/Audio/wiringdiagram2.jpg
 
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Yep, those are wired in a series-parallel arrangement. The two on the left are wired in parallel with each other....likewise the two on the right. The two pairs are then wired in series with each other. Total impedance of the four is the same as single driver would be (16 ohms in your case.)

Cheers,

Dave.
 

Rotus623

Member
2010-09-20 4:34 am
Cool thanks Dave. One little thing though. I thought for it to actually be run in series-parallel, it had to tie in the bottom two speakers as well. Also, the amp can in fact push 4 ohms (since it is switchable) so do you think there is a point to run the circuit in parallel to make it 4 ohms(maybe for some more wattage). Last thing, is it possible to run this load in 8 ohms? (Just curious)
 
Cool thanks Dave. One little thing though. I thought for it to actually be run in series-parallel, it had to tie in the bottom two speakers as well. Also, the amp can in fact push 4 ohms (since it is switchable) so do you think there is a point to run the circuit in parallel to make it 4 ohms(maybe for some more wattage). Last thing, is it possible to run this load in 8 ohms? (Just curious)

You could run them all in parallel and get 4 ohms but your amp won't put out any more power at 4 vs 16 ohms and at 4 ohms you'll have more power lost in the wiring from speaker to amp. I²*R and R is a constant. Doubling the current quadruples the loss and you're quadrupling the current from 16 to 4 ohms so 16 times more loss.

A solid state amp that puts out constant voltage (most are) _will_ deliver more power at lower impedances, a 'trick' some speaker manufacturers have used to make sensitivity seem better. Your transformer coupled amp (presumably tubes since transformers are easily avoided with solid state) changes the voltage/current relationship so that the power doesn't change with impedance - except for already mentioned cabling losses at lower impedances.

 

Rotus623

Member
2010-09-20 4:34 am
"Your transformer coupled amp (presumably tubes since transformers are easily avoided with solid state) changes the voltage/current relationship so that the power doesn't change with impedance - except for already mentioned cabling losses at lower impedances."

Yes sir, it is a 100W valveking head. Thanks for the great answer. I still am wondering though, if my speaker configuration is in fact run in series-parallel. I thought in order for this to be the case, the bottom two speakers had to be run together. (And mine are not) And does it change anything or make a difference if I fun my amp into one of the cabinet inputs or both?
 
"Your transformer coupled amp (presumably tubes since transformers are easily avoided with solid state) changes the voltage/current relationship so that the power doesn't change with impedance - except for already mentioned cabling losses at lower impedances."

Yes sir, it is a 100W valveking head. Thanks for the great answer. I still am wondering though, if my speaker configuration is in fact run in series-parallel. I thought in order for this to be the case, the bottom two speakers had to be run together. (And mine are not) And does it change anything or make a difference if I fun my amp into one of the cabinet inputs or both?

If your rotated the group 90 degrees the sides would be in parallel rather than the bottom/top. It's all perspective. To prove it to yourself, disconnect one speaker and measure the DC resistance which will likely be less than 16. Reconnect it into the network with the other 3 in series/parallel and measure the group. It should be very nearly identical to the single driver. Reasons for a difference is possible variations between the drivers plus the wiring.

 

Rotus623

Member
2010-09-20 4:34 am
If your rotated the group 90 degrees the sides would be in parallel rather than the bottom/top. It's all perspective. To prove it to yourself, disconnect one speaker and measure the DC resistance which will likely be less than 16. Reconnect it into the network with the other 3 in series/parallel and measure the group. It should be very nearly identical to the single driver. Reasons for a difference is possible variations between the drivers plus the wiring.


So why am I measuring 4 ohms if the speakers are in fact 16 ohms? The resistance is measuring as if the whole setup is being run in parallel. Are you guys sure that the wiring is in series-parallel?
 

Rotus623

Member
2010-09-20 4:34 am
Cal, the wires on the left are going right to their respective destinations, identical to the ones on the right. I swear I thought for that setup the speakers on the bottom had to be run together instead of the speakers recieving the main input signal, but I guess it doesnt matter. Right? Only reason Im questioning it is because of my odd ohm readings.
wwenze, I am measuring + to - with a digital multimeter across a single speaker. Should I use the multimeter in a different location?
An externally hosted image should be here but it was not working when we last tested it.
kmgwiring.jpg

wwenze, I am measuring + to - with a digital multimeter across a single speaker. Should I use the multimeter in a different location?
 
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The wiring seems correct. You must disconnect the input wires from the amp and measure there. If those are 16 ohm drivers you should read 16 ohms. If you measure at one driver as it stands with disconnecting anything you should read 4 ohms. The diagram you show is the same as what you have as far as the speakers are concerned.
 
If you measure on a single driver you'd see 8 ohms not 4 (since there's another driver still in shunt.) IF these drivers really are 16 ohms. :)

Rotus,

Remember, 16 ohms is probably the rated nominal impedance of these drivers and not the DC resistance, which is what you're measuring with your ohmmeter. Most likely it would measure something less than 16 ohms.

Also, maybe I missed it, but you MUST disconnect the red/black wires from your amplifier while making these measurements or you will get an incorrect reading.

Cheers,

Dave.
 
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Rotus623

Member
2010-09-20 4:34 am
Okay Cal, Davey, you want me to measure the ohms at the input jack of the speaker cab, or the output of the amplifier? When I measured at the (disconnected) speaker input jack, I get all sorts of crazy numbers. When I measure directly across each speaker, it is 4 ohms.
Conclusion is that the multimeter which measures DC Impedance is not going to properly measure this, correct? And also, this is in fact a series-parallel, so I should be at 16 ohms and just set my amp output impedance to that, right?
 
Run it at 16 ohms. If you put a meter on the input jack to the cabinet and it says somewhere around 12 to 14 ohms then it is a 16 ohm cabinet. There is not any way to get 8 ohms from 4 16 ohm speakers.

But if you disconnect the speakers and put a meter on them each one should read in the area of 12 to 14 or so ohms.
 
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