8 ohm cab measures 5.3 ohms

denton57 · #1 03-13-2013, 09:00 PM

Just hooked up 4 eminence s2012's in my V4 cab and the resistance reads 5.3 ohms. I seem to remember that it is normal for an 8 ohm cab for some reason. Can anyone confirm this?

Speakers are 8 ohms each.

Vince Klortho · #2 03-13-2013, 09:01 PM

Yes, that is the typical DC resistance of an 8-ohm speaker(s). Speakers have voice coils which are basically inductors so their impedance will vary according to frequency.

T-Bird · #3 03-13-2013, 09:17 PM

Hi.

A bit on the low side IME, but still well within' the range.

Regards
Sam

Vince Klortho · #4 03-13-2013, 09:36 PM

Yes, you are right. Upon further review I found some things that say it will usually be between 5.4 and 6.6 ohms so that is at the low end of the range. This can be explained by many factors though. The meter used to measure it is one factor, the strength of its battery is another.

fdeck · #5 03-13-2013, 09:53 PM

I've noticed that most of the 8 Ohm Eminence drivers used in DIY and custom bass cabs range from 5 to 6 Ohms at DC.

two fingers · #6 03-13-2013, 09:55 PM

Quote:

Originally Posted by Vince Klortho

Yes, that is the typical DC resistance of an 8-ohm speaker(s). Speakers have voice coils which are basically inductors so their impedance will vary according to frequency.

This.

denton57 · #7 03-14-2013, 05:26 AM

Thanks all. I know the battery in my meter is over 3 yrs old. I'll switch it out and see if there's a difference.

So..V4B has 2, 4, and 8 ohm selector. Stay with 8 ohms on the head?

funnyfingers · #8 03-14-2013, 05:41 AM

You can see impedance chart here: http://www.eminence.com/pdf/Basslite_S2012_cab.pdf

As you see most of the individual frequencies do give 5 ohm.

Bassmann1968 · #9 03-14-2013, 06:15 AM

Stay with 8 ohm on the amp.

mmbongo · #10 03-14-2013, 06:30 AM

Hook up the meter, watch it, and move one of the speakers. Watch it jump to 16, 1, 4, 8, 3, 12, and everything in between with just a nudge of the cone.

funnyfingers · #11 03-14-2013, 06:38 AM

Quote:

Originally Posted by mmbongo

Hook up the meter, watch it, and move one of the speakers. Watch it jump to 16, 1, 4, 8, 3, 12, and everything in between with just a nudge of the cone.

Ah interesting idea. You could probably face another speaker to it and play music as well...

mystic38 · #12 03-14-2013, 07:54 AM

There is nothing wrong with the speaker...you are measuring resistance... not impedance...it is an 8 ohm nominal impedance speaker, as you can see from the chart funnyfingers linked to it is measuring well within parameters...

Additionally, for techno-giggles, Note that you meter has an accuracy specification.. and the % figure quoted is the % of full scale, not % of the reading so when measuring an exact 8 ohm a meter with 3 1/2 digit display and a spec of 2% +/- 1 digit it would read:

on 200 Ohms scale : anywhere from 3.9 Ohm to 12.1 Ohm
on 20 Ohm scale : anywhere from 7.59 Ohm to 8.41 Ohm

beans-on-toast · #13 03-14-2013, 08:23 AM

If you want a better picture of what is going on, disconnect your speakers and measure them individually. Maybe they are all the same, maybe one is a lot lower. You won't know unless you look at them one at a time.

And yes, get a fresh battery for your meter.

Here is some info related to driver DC resistance:

Re
Measured in ohms (Ω), this is the DC resistance (DCR) of the voice coil, best measured with the cone blocked, or prevented from moving or vibrating because otherwise the pickup of ambient sounds can cause the measurement to be unreliable. Re should not be confused with the rated driver impedance, Re can be tightly controlled by the manufacturer, while rated impedance values are often approximate at best.. American EIA standard RS-299A specifies that Re (or DCR) should be at least 80% of the rated driver impedance, so an 8-ohm rated driver should have a DC resistance of at least 6.4 ohms, and a 4-ohm unit should measure 3.2 ohms minimum. This standard is voluntary, and many 8 ohm drivers have resistances of ~5.5 ohms, and proportionally lower for lower rated impedances.

So as a general rule of thumb, DCR should be at least 80% of the drivers impedance. That doesn't have to be the case since the manufacturer can control what the DCR will be.

T-Bird · #14 03-14-2013, 12:24 PM

Hi.

Quote:

Originally Posted by mmbongo

Hook up the meter, watch it, and move one of the speakers. Watch it jump to 16, 1, 4, 8, 3, 12, and everything in between with just a nudge of the cone.

Yes, but then You're not actually measuring anything, just creating MMF voltage that interferes with the measurement bridge voltage, and therefore the reading.

Regards
Sam