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Diezel Impedance mismatching / EVM12L Impedance issue

Thu, Jan 10, 2019 6:12am

I tried to find a good answer here and around but still have a question mark over my head.
I hope i don't repost this topic...

I have a 4x12 Cab with Stero Input 2x8 Ohm and Mono 1x12 Ohm from Factory!
Yes 12 Ohm its has 2x8 and 2x16 Ohm Speaker in it by Factory.
So i hooked up the Cap with 2 Speaker Cable as 2x8 Ohm Cabs.
Not sure if that makes a different.

Now i've bought 4 new EVM 12L Speakers with 8 Ohm Factory Print on it.
When i measure the Impedance of the Speakers i measure 4.3, 5.3, 5.0 and 4.7 Ohm.
When i measure other 8 Ohm Speakers from other Manufacture i measure around 6.8 and 7.4 Ohm.
I contact Electronic Voice and asked if that really correct and they say when they have
a Impedance Value everything is ok.

Of course the direct measured Impedance Value is lower than the real Impedance,
but that low for 8 Ohm Speaker and so different Values???
I found in the web more which have measured these Values... even 5.3 for a 16 Ohm labelled.

When i'm correct the Impedance Value of a Speaker is attached to the Frequency of the Signal
with a Range between the direct measured Value as Minimum and even over 40 Ohm and more as Maximum?

Now i asked myself how to hock up Speaker like this to my Herbert.
In a Manual from one of my other Amps (from another Company) i found:
The Amp is not very sensitive to impedance mismatching and therefore
we encourage experimentation with regards to speaker loads.
You may feel free to try an 8 Ohm load on the 4 Ohm jack or a 16 Ohm load
on the 8 Ohm jack as you may discover a characteristic that the mismatched
load imparts on the sound that is desirable.

Our 4x12 cabinets are wired in Series/Parallel and are rated at 8 Ohms and
these should normally be connected to the 8 Ohm jack.
When using two of our 8 Ohm 4x12 cabinets, connect them each to a 4 Ohm jack
as doubling the load on each jack produces a total load of 8 Ohms
and is a proper impedance match.

Feel free to use speaker cabinets built by other manufacturers and
these are often wired to produce a 16 Ohm load which you would want
to connect to the 8 Ohm jack. Two 16 Ohm cabinets would be connected
each to an 8 Ohm jack.

Overall our Amp is very impedance friendly and most speaker loads will
work great with the exception of slightly shorter power tube life occurring
when a mismatch in the low direction (two 4 Ohm cabs - each in a 4 Ohm jack
to produce a total load of 2 Ohms) is used for long periods of time.

Of course i want to know how "dangerous" is a Impedance mismatch for a Diezel
especially for the Herbert.

Is there a Rule for this?

Measured Impedance > Amp Output?
Measured Impedance = Amp Output (only?)
Measured Impedance < Amp Output?

And perhaps what is so special about Electronic Voice to have so different low measured Impedance...?

Best Regards
Last edited by Plattfuss on Fri, Jan 11, 2019 9:33am, edited 2 times in total.

Re: Diezel Impedance mismatching / EVM12L Impedance issue

Thu, Jan 10, 2019 6:13am

Sorry for the long Question... :/
I hope my Question isn't that stupid...

When i right the rule is:

Speaker > Output => save for the Tansfomer / not very good for Tubes / less Power / less Range of Sound
Speaker = Output => like it should be
Speaker < Output => dangerous for the Transformers

Re: Diezel Impedance mismatching / EVM12L Impedance issue

Fri, Jan 11, 2019 11:38am

I'm not sure how to wire up the 4 EVM 12L

Option a) 2 parallel / serial => expected 8 Ohm
Option b) 4 parallel => expected 2 Ohm
Option c) 4 serial => expected 32 Ohm

Normally i would have to go option a) to get 8 Ohm out of 8 Ohm Speakers.
But when i read that i can destroy Parts within 4-16 Ohm Range
and you measure 4.7 instead of -+ 15% from 8 Ohm i get worried.

Measured Values are 4.3, 5.3, 5.0 and 4.7 Ohm.

Option a) => (1/(((1/4,3) + (1/5,3))) + (1/(((1/5,0) + (1/4,7)))) => 4,79 Ohm
Option b) => 1/((1/4,3) + (1/5,3) + (1/5,0) + (1/4,7)) => 1,19 Ohm
Option c) => 4,3 + 5,3 + 5,0 + 4,7 => 19,3 Ohm

So the best would be to use Option a) and use the 4 Ohm Output?

At the moment i think i am to stupid to understand the Realtime Values of a Speaker
and go with the Company Label and use Option a) with the 8 Ohm Output...

Sorry :(

Re: Diezel Impedance mismatching / EVM12L Impedance issue

Fri, Jan 11, 2019 2:17pm

Those measured values do not matter. It's an 8 Ohm speaker.

1/(8 + 8) + 1/(8 + 8) = 1/8


(1/8+1/8) + (1/8+1/8) = 1/4 + 1/4 = 1/8

Re: Diezel Impedance mismatching / EVM12L Impedance issue

Mon, Jan 14, 2019 10:55am

Thanks i will ignore the measured values und hope they are like labelt.
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