Polk CS1 and R50 Impedance for JLH Supply Voltage and Bias Current

[kozard]

I am using a pair of CS1 on my test bench as I build and modify a JLH Class A amplifier. They are advertised as 8 Ohm impedance however I suspect they might actually be lower.

Does anyone know what the impedance is of the Polk CS1 and R50 (beyond the claimed specs)? Based upon any measurements? Or use with Class A amplifiers?

I don't have anything setup to measure speaker impedance, however just my voltmeter on the back terminals of the CS1 reads close to 4 Ohms.

Polk Audio CS1 (Black) Center channel speaker at Crutchfield

Polk Audio R50 Tower speakers at Crutchfield

 

[AllenB]

You're probably right. If you sweep them with larger resistor in series you'll see it all.

 

[kozard]

I tried to measure the Polk CS1 impedance today and I get 4.3 Ohms but with huge spikes to 16 Ohms.

Does this look right? I have never measured speaker impedance before. I am using REW and an 8 Ohm sense resistor.

 

[kozard]

By the way I measured test load resistors with REW to try to make sure my measurements were valid. They seem to be ok for a 1/4W 10 Ohm Metal Film resistor and (8, 4 and 2 Ohm) 100W test load resistors. (Attached.)

I guess I need to re-bias my JLH and increase the heat sinks.

 

[AllenB]

It looks as though you've done an excellent job.

 

[kozard]

Today I improved the cables and calibration with lower resistances and entry of the test lead resistance.

In case it is helpful for anyone else with a JLH or other Class A amplifier I have enclosed REW speaker impedance measurements for the Polk CS1, CS2, Monitor 70 and R50.