Sound City 4-12 w/9.4 Ohm Speakers

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Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Wed Jun 17, 2015 7:43 pm

Hello, I have a Sound City 4-12 w/ Sound City speakers that are labelled as 15 ohm, but test as 9.4 to 9.6 ohm. I was hoping to use the cab as a 16 ohm. Can anyone shed some light?

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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Wed Jun 17, 2015 10:09 pm

A speaker's voice coil resistance will invariably be lower than its nominal impedance.
Your report indicates a larger than expected discrepancy though; what do other speakers measure?
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Wed Jun 17, 2015 10:25 pm

Thanks for asking. Before trying the cab I plugged a speaker cable into the lower input and got a reading of 22.4 ohms, and then tried the upper input and got a reading of 9.4. Then I unsoldered all 4 speakers and tested them individually. They all gave readings in the 9.4 to 9.6 ohms range.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Thu Jun 18, 2015 3:26 am

I looked a bit closer and found the "Hi-Fi 8" stamp. Now I'm wondering if these are recones or were a special factory order to be used as 8 ohm. The term Hi-Fi has me thinking they might be factory, but I won't get my hopes too high. I'd like to know more if anyone has info., or can direct me to someone who might.

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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Thu Jun 18, 2015 2:36 pm

Have you got access to any different speakers whose resistance can be measured?
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Thu Jun 18, 2015 5:23 pm

Yes, I've been testing a 16 ohm cabinet that I recently put new speakers in and its been reading 15.8 ohms. That's all I've used the multi meter for so far. I'm not brainy enough to be a tech. I read a few things last night to make sure I was using it right. It was bought primarily for testing cables, measuring ohms and biasing. Amp Protection 101.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Thu Jun 18, 2015 10:52 pm

What about if you short the probes together?
A looky over Celestion spec sheets indicates that 16 ohm types have a resistance around 12-14 ohms, eg http://celestion.com/product/24/Heritage_Series_G12M/
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Fri Jun 19, 2015 3:09 am

After moving the probe ends around on each other I got it down to 00.1. Does that sound about right? Maybe I should try another meter.

I re-measured the 16 ohm cabinet mentioned above (Orange 2/12 w/Hot 100, 8 ohm) through a 20' CSI 16/2 speaker cable and the lowest reading I could get by holding the probes onto the 1/4" male with my fingers was 16.3. I tried another cable and got the same reading.

I measured the 2, 8 ohm Vintage 30 that I removed from the Orange by holding the probes directly onto them and got measurements of 6.8 and 6.9. I did the same to a Hot 100 that arrived with a bent frame and it measured 7.7 ohms.

Then I measured a Marshall 1960AHW 4/12 loaded with the stock Historics through one of the cables mentioned above and got a reading of 15.1.

I've only pulled one of the Fane/Sound City. It measured 9.4 with the probes directly on it. The other 3 were measured through the wires that are soldered on them. They all measured in the range of 9.4 to 9.6.

The humidity is 60%, Temp 73 F, if that matters.

I want to use the Sound City with some 100 watt heads that I can't afford to damage. I was planning to use it paired with other 16 ohm loads at all times to minimize the chance of blowing something when recording the amps dimed and boosted. That probably isn't possible. The Sound City speakers are labelled "40 watts." I hope that's correct. But even if it is, I'd rather use it with another cabinet to share the load.

I don't have much experience with this, so I have a lot to learn. Any help will be appreciated.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Fri Jun 19, 2015 1:42 pm

If I wire the 4, 9.4 ohm speakers series/parallel and run them as an 8 ohm load, will they damage a Plexi 100 watt head being run wide open and boosted for long periods?
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Fri Jun 19, 2015 7:01 pm

Your 9 to 10 ohm readings are strange.
Speakers are made in other impedances, I think 12 ohm types may have been used in column type PA speakers. I guess they would be about 9 to 10 ohms resistance.

Let's hope your's are a more normal type, and perhaps the solder joints have gone bad.
Have you got a soldering iron? If so try re-soldering the tinsel wire to speaker terminal joints, using fresh fluxed solder.
Put an alligator clip on the tinsel wire just behind the terminal to prevent solder wicking along the tinsel wire, thereby making it solid rather than flexible.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Sat Jun 20, 2015 12:09 am

Thanks for the lesson on soldering tinsel wire. I would have learned that the hard way.

I got some fresh ends on the wires, twisted them together in series/parallel, and took a reading of 9.7 from the top jack. It read 9.4 before I rewired the speakers. Then I tested the lower jack that originally measured 22.4, and some kind of magic happened. I got a reading of 14.5. That made my day. I didn't touch the wires on the jacks. Maybe one of the speaker wires was wrong. I'm going to test it out with a solid state amp before soldering it back together. I should probably pull a speaker and photograph the jacks. I'd like to know how the ohms are being raised in the lower jack. I hope it's safe for my amps.

This is my first experience with a front loaded cab. I think I prefer rear loaded. I didn't get it to toy with though. So once it's situated it should be fine.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Sat Jun 20, 2015 7:38 am

The jacks should be in parallel, and the lower reading will invariably be the most accurate; maybe the other socket has a tarnished surface or bad solder joint.
I would re-wire the cab with new sockets before using it.
Realistically, if all speakers are in individually measuring 9 to 10 ohms, then if everything is good, then array must also measure 9 to 10 ohms.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Sludge on Sun Jun 21, 2015 2:20 pm

I cleaned the jacks and now they both give readings of 9.6 ohms. Watts rating aside, can this cabinet be safely used as an 8 ohm load with a cranked 100 watt amp? I'll gladly pair it with another 8 ohm cabinet to save speakers. What I'm asking about here is possible amp head damage.
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby Baron Von Machinenmann on Sun Jun 21, 2015 10:14 pm

You will lose a slight bit of power and low end with the mismatch but are in no danger of frying anything running it this way, go for it. :jam: :cheers:
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Re: Sound City 4-12 w/9.4 Ohm Speakers

Postby pdf64 on Sun Jun 21, 2015 10:38 pm

Yes, if the actual nominal impedance is around 12 ohms, then using it as if it were 8 ohms (rather than 15/16) would probably be the best option.
Bear in mind that if you pair it with another 'real' 8 ohm cab, that 8 ohm cab would get a bigger share of the amp power.
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