16 Ohm Mesa V30 Measure 7.1 Ohms

[Heavymetal66]

I came across (2) Mesa V30's and since I don't like that speaker I'm looking to sell them. One of them needs a recone as it has voicecoil rub. The part # (T4416) indicates it's a 16 ohm Vintage 30 that came from a Mesa amp (I confirmed with Celestion). When I check it with my DMM it measures 13 ohms which is what I'd expect from a 16 ohm speaker.

The other speaker, same part #, is physically in good shape, but measures 7.1-7.4 ohms yet it supposed to be a 16 ohm speaker. 7.4 ohms is close to what I'd expect for an 8 ohm speaker - maybe on the high side. I asked Celestion about this and they said without knowing the history it could have been reconed as an 8 ohm speaker. If that's the case they did a great job as it looks like it came from the factory.

The cone and dust cap look great, there's no voicecoil rub, the spider is in great condition and the speaker jumps as expected when I touch a 9v battery across the terminals. Is there anything else I can check to confirm if this is actually an 8 ohm speaker, or a problematic 16 ohm speaker? If it was reconed why not indicate it on the speaker (it still shows 16 ohm). Also, these came out of the same 2x12 cab so why would anyone have a 16 ohm and 8 ohm together?

The first speaker is easy - sell it cheap noting it needs to be reconed. But I'm not sure what to do about the second one. I don't want to sell it as good with a little higher price only to have it go bad on someone, or worse yet possibly ruin their amp. Yet, I don't want to give it away if it's a perfectly working Vintage 30.

Anything else I'm not thinking of to check this speaker? Thanks!

 

[Steppin' Wolfe]

I think Celestion answered your question to some extent in that they accepted the ohmmeter reading as establishing that you have an 8 ohm speaker there regardless of what the part number says. Could someone in the factory have made a mistake and stamped the wrong part number? Anything is possible. Could it have been reconed as an 8 ohm. Anything can happen...but a good reconer would have noted the change, imho. also imho, the reality of the impedance needs to be noted on the speaker at this time.
Good luck with it.. fwiw, I have little use for that speaker myself. I pulled one from a Mesa MKIV and 8nstalled an Altec Lansing 417-8H.. Huge improvement...worth the weight.

 

[J M Fahey]

It´s clearly an 8 ohm speaker.
Trust your meter and not the label.

 

[Heavymetal66]

Thanks for your replies. Just wanted to double check before I sold it.

 

[Pete Cage]

I've seen more than a few mis-ohm-labeled Celestions over the years.

 

[gldtp99]

I'd put my money on the speaker being an 8 ohm that was mislabeled and has gone through its working life as a mismatch--- paired with the "real" 16 ohm speaker in the 2x12

Sometimes things slip through the cracks and no one is the wiser until years later, if ever

 

[Motterpaul]

Since 16-ohm speakers in 2x12s are wired in parallel - together you could be hitting about 12-ohms. I am thinking that with your amp set at 16-ohms you are close enough that you would never notice an audible problem (or an electrical one) as long as you kept them as a set.

 

[pdf64]

Since 16-ohm speakers in 2x12s are wired in parallel - together you could be hitting about 12-ohms. I am thinking that with your amp set at 16-ohms you are close enough that you would never notice an audible problem (or an electrical one) as long as you kept them as a set.

8 // 16 = 5.3

 

[TimDude88]

It might be worth noting what impedance actually is. "Impedance is a more complex type of resistance, where the resistance and phase between the input and output signals change with frequency," (Megantz, 6).

Megantz, R. (Y2009). Design and Construction of Tube Guitar Amplifiers. TacTec Press.

 

[Steppin' Wolfe]

when an 8 ohm speaker is paired with a 16 ohm, the 8 ohm speaker will be worked harder than the 16 ohm.

 

[pdf64]

Impedance is a more complex type of resistance, where the resistance and phase between the input and output signals change with frequency

But what if, as here, there is no input / output in that sense probably meant in the context of that quote?
Rather we're looking at an electrical source (the amp) and its load (the speaker cab). Here, relationship between the voltage across the load and the current flowing through it will vary, significantly, over the frequency range, not only in regard of the relative magnitude of each to the other, but also in regard of the phase (time relationship) of one to the other, which will flip one way then the other a couple of times.
It's a rather complex interaction

when an 8 ohm speaker is paired with a 16 ohm, the 8 ohm speaker will be worked harder than the 16 ohm.

That's true when, as here, they're connected in parallel; twice the current flows via the 8ohm than the 16ohm, whereas the voltage across them is the same.
Whereas that flips around if connected in series; in that case, the same current must flow through each but twice the voltage will appear across the 16ohm than the 8ohm, so the 16ohm speaker will be working harder.
Of course, the latter would only be likely if it had been an 8ohm speaker mislabeled as being 16ohms.

 

[HotBluePlates]

It might be worth noting what impedance actually is. "Impedance is a more complex type of resistance, where the resistance and phase between the input and output signals change with frequency," (Megantz, 6).

Megantz, R. (Y2009). Design and Construction of Tube Guitar Amplifiers. TacTec Press.

But what if, as here, there is no input / output in that sense probably meant in the context of that quote?

If the quote is accurately lifted from Megantz, it's a bad way of expressing the idea.

Impedance is opposition to current, composed of Resistance and Reactance.​

​

Resistance is opposition to current that doesn't vary with frequency, with a phase angle of 0º.​

​

Reactance is the opposition to alternating current that varies with frequency, with a phase angle of 90º (Inductance) or -90º (Capacitance).​

So it's bad to try to explain a frequency-dependent opposition of current by describing it as "resistance" which is itself independent of frequency.

 

[TimDude88]

If the quote is accurately lifted from Megantz, it's a bad way of expressing the idea.

Impedance is opposition to current, composed of Resistance and Reactance.​

​

Resistance is opposition to current that doesn't vary with frequency, with a phase angle of 0º.​

​

Reactance is the opposition to alternating current that varies with frequency, with a phase angle of 90º (Inductance) or -90º (Capacitance).​

So it's bad to try to explain a frequency-dependent opposition of current by describing it as "resistance" which is itself independent of frequency.

Interesting stuff.

 

[HotBluePlates]

Interesting stuff.

Check out NEETS Module 2, and scroll to Section 4. It explains combining Resistance & Reactance to arrive at total Impedance.

Some of the other NEETS Modules are handy, but they're often a starting point for understanding other stuff.

 

[TimDude88]

Check out NEETS Module 2, and scroll to Section 4. It explains combining Resistance & Reactance to arrive at total Impedance.

Some of the other NEETS Modules are handy, but they're often a starting point for understanding other stuff.

Wow! I'll be sure to bookmark this one! Thanks. I'm taking my time and starting to go through books about how tube amps work, learning the different stages, components and all of that fun stuff. This is good stuff. Thanks.