Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Cabinets-Speakers => Topic started by: markvalluzzi on July 04, 2012, 05:29:48 pm

Title: Impedance of speakers
Post by: markvalluzzi on July 04, 2012, 05:29:48 pm

I recently was reading someones posting for a speaker for sale.  He said it was a 16 ohm. The photo verified that by the manufactures label. He went on to say he had a DCR of 6.9    What does DCR stand for ?

Title: Re: Impedance of speakers
Post by: John on July 04, 2012, 07:20:53 pm

If I had to guess, DC resistance.

Title: Re: Impedance of speakers
Post by: markvalluzzi on July 05, 2012, 02:53:24 pm

I thought that might be the case. SOoooo  If the speaker label says 16 ohms,  Why would a meter read 6.9 ohms ?  It doesn't make sense.

Title: Re: Impedance of speakers
Post by: John on July 05, 2012, 03:03:42 pm

Hah. Somewhere there is a discussion about that, but I forget what the answer was. Short answer is, it really doesn't matter that much. For instance, my little SE is supposed to have a 4 ohm attached to it, but I'm running an 8 instead. Might not be as efficient, but as long as I don't run it with no load at all, or hook it to a 16ohm speaker at full bore, no biggie.

Title: Re: Impedance of speakers
Post by: Willabe on July 06, 2012, 09:01:00 am

Quote from: markvalluzzi on July 05, 2012, 02:53:24 pm

I thought that might be the case. SOooo  If the speaker label says 16 ohms,  Why would a meter read 6.9 ohms ?  It doesn't make sense.

I don't think a 16 ohm speaker is supposed to read that low when you take a resistance reading? I think it's supposed to read only at most a few ohms off/lower than the 16 ohms.

I think that could mean a partially shorted voice coil?

If you have any other 16 ohm speakers measure them and see if they are close to 16 or closer to 6.9. I bet closer to 16.


                                    Brad      :think1:

Title: Re: Impedance of speakers
Post by: Willabe on July 06, 2012, 09:16:52 am

I just measured a Tubby Tone 12" 8 ohm and got 6.4 ohm. Jensen 12" re-issue 16 ohm and got 12.2 ohm.

I'd say your speaker is either an 8 ohm or it's voice coil is partially shorted, if that's possible?


                        Brad      :think1:

Title: Re: Impedance of speakers
Post by: markvalluzzi on July 06, 2012, 06:08:11 pm

Thanks Brad.  I've spoken with several people and they gave the same info. you provided to me. A 16 ohm speaker would NOT have a resistance reading of 6.9  The guy I was talking about, probably had a recone and wasn't acurate with his information.  Maybe he thought having a 16 ohm speaker was an easier sell. You never know. Alot of people give out info. when they shouldn't.

Title: Re: Impedance of speakers
Post by: HotBluePlates on July 06, 2012, 10:18:27 pm

Quote from: markvalluzzi on July 06, 2012, 06:08:11 pm

Thanks Brad.  I've spoken with several people and they gave the same info. you provided to me. A 16 ohm speaker would NOT have a resistance reading of 6.9

Not true.

Impedance = Resistance + Reactance. Resistance of the wire, whichis then wound in a coil having mostly inductive reactance.

Except it's not plain addition, but vector algebra; Resistance² + Reactance² = Impedance²

Gerald Weber suggested there was a fixed ratio of d.c. resistance for a given speaker impedance, but that's just wrong. There is a typical range, but it really depends on how the speaker manufacturer designed and constructed their speaker.