604-8G DCR measurements?

Fran604g

Just Call Me Junior
Hiya folks,

Can any of my esteemed cohorts please remind me what the DCR for both the HF, and LF drivers ought to be? I should be able to remember, but I can't.

After spending a ton of time critically listening to my 604's recently, since installing my new Soundsmith Otello, I realized the L/R balance of the system was a little off.

I eliminated the cartridge (checked and double checked its setup, internal resistance, etc.), cables, preamp, and amps (G*S*G 6B4G w/604's & TAD 60 6550 w/AR3a's) by switching around ins and outs, and using my old tried-and-true Shure M97xE, etc.

I also reversed polarities of the ins, outs, and speakers, and used the Otello in another system - the problem did not follow the cartridge.

I eventually tracked down a possible explanation for the imbalance to be the following driver DCR measurements:

604 #1: HF = 6.2 ohms; LF = 6.2 ohms
604 #2: HF = 6.2 ohms; LF = 7.2 ohms

Using my PC - playing digital files through JRiver - I was able to determine (subjectively: i.e. with my ears) about a 2.5-3dB difference in channels - very slightly dependant on the recording(s) I used.

Here's how I did that, (first using the G*S*G/604-8G's; then the TAD 60/AR3a's):

1) Play a familiar record at preferred listening volume.
2) Correct the imbalance with the preamp balance control.
3) Switch preamp to PC, and return preamp balance to "neutral".
4) Play a familiar digital file.
5) Trim output volume at PC to be relatively the same system volume, as when using the TT.
6) Correct the imbalance using JRiver DSD "room correction" feature, and note channel dB difference.
8) Disable JRiver DSD "room correction".
9) Switch back to using the TT, with preamp balance control at "neutral" position, and note there's a channel difference again, just to be sure.
10) Correct imbalance again with preamp balance control.
11) All is good, channels are now balanced, and both the TT and PC are the same relative listening volume.

When using my TAD 60/AR3a's, it's the same relative difference in balance - albeit not quite as noticeable. I attribute this perceived difference to be noticeably less because of the much lower output of the G*S*G, and it's very different sound profile with the 604's. It's very revealing, whereas the TAD 60/AR3a's combination isn't quite as sensitive to minutiae.

I can equalize the channels with the balance control on my preamp, and things sound great, but you know: anal. :chin

What do you all think? Could the difference in Woofer DCR be the culprit? Would a ~16% difference in woof DCR account for ~3dB loss of gain in one channel?

I haven't tried a different preamp/phono stage yet, to absolutely eliminate the possibility it's the preamp, but it seems very unlikely that it is.
 
DCR is not relevant except as an easy-to-measure quantity vaguely proportional to IMPEDANCE, which is an AC quantity and the important thing as regards speaker/amp interface.

You would have to sweep the drivers with appropriate gear (such as DATS/Woofer Tester) to determine the impedance curve of the speaker.

My feeling is that a 1 ohm difference in DCR would not result in a hugely obvious difference in output, but this is somewhat dependent on the amplifier. A no feedback SE is more susceptible to impedance variation than a feedback amp would be...that's one of the reasons feedback is used, to eliminate this variability. Don't know what G*S*G means.

Another variable is the crossovers. If using original crossovers, the caps in some of those were quite junky--metallized paper caps in cardboard boxes potted in tar/wax or unimpressive Callins brand electrolytics. I can easily see a cap slowly going down the tubes and creating losses or response anomalies.

How is the room symmetry? Some rooms are just unbalanced architecturally and that is what balance controls are for.

Does the imbalance stay with the speaker if you swap speaker positions?

Another thing to try if in an testing mode is to play tones above and below the xover point and see if you can determine whether the HF or LF is unbalanced, or maybe it's both.

If it is HF, you can implement an attenuator in the louder channel so that the speakers are balanced with the preamp balance knob at mid setting. Or maybe one of the tweeters has a failing diaphragm.

It is not easy to get consistent reliable measurements in an average listening room but I often use an RTA app on my phone to try to get some idea of what is going on beyond simply ear testing. Basic left-right swaps will get you quite far along though.
 

Fran604g

Just Call Me Junior
Hi J-Rob,

Thanks for prompting me to try an RTA app. I don't know why I didn't do that before, I've used one in the past.

I did a rudimentary RTA with my phone, using the TT and my old Stereo Test Record (Stereo Review model SRT14) with the "Broadband test signal" (random phase signal), and only detected about a 1dB difference between the 2 speakers. Phone was held same height/distance - centered with driver, 30 inches away - same volume setting, preamp balance at "neutral".

My sense was (past-tense, now) that the problem was associated with one of the speakers, in that I'd tried reversing the connections at the amp, and the same speaker (R) exhibited the attenuation. I no longer think the room, or the equipment is to blame for the difference, I now think it's my right ear. :(

G*S*G = Get SET Go, it's a simple SET 6B4G amp that was engineered over at DIYTube.com about 10 years ago: http://www.diytube.com/phpBB2/viewtopic.php?f=14&t=1566

I built Jeff Markwart xovers for the 604's in 2007 using all new parts. The drivers are in stock Altec 620 cabs.

Thanks again.
 

TubeHiFiNut

Administrator
@Fran604g - When was the last time you had your ears professionally cleaned by an ENT doctor?

My right ear canal builds up wax faster than the left - residual effect of having a bone spur removed from the right canal 40 years ago.

I use hydrogen peroxide regularly (usually at least once per month) and visit my ENT at least twice a year for professional cleaning and inspection.

Your imbalance might be nothing more than ear wax.
 

Fran604g

Just Call Me Junior
I never have been to an ENT. I've cleaned them myself the same way - with H2O2 - I'll do that, and hope it helps.

I think it's probably (past) a good time to see a doc, too.
 

John Frum

Secret Society Member
Oh, no, the dreaded audiogram! Mentally brace yourself for some hard truths.

If your ENT offers it, take a full-range test. Many occupational tests will only top out at 10K, if you're lucky.
 

Fran604g

Just Call Me Junior
Oh, no, the dreaded audiogram! Mentally brace yourself for some hard truths.

If your ENT offers it, take a full-range test. Many occupational tests will only top out at 10K, if you're lucky.
Yeah, I've been putting off the inevitable - at least in my mind. :beat
 

Fran604g

Just Call Me Junior
After this last post, I cleaned my ears, but noticed no improvement in my hearing. I just committed myself to having the balance control compensate for the sound.

So, "hear's" a strange observance:

A couple of weeks ago I bought a 7-1/2" RTR tape of Simon and Garfunkel's Wednesday Morning, 3 A.M.

Once I received it, I put it onto my TEAC A6010, and had a listen, with my preamp balance skewed to attenuate the left channel, as I have needed to do recently.

When I reached the end of side 1, I reversed play, and noticed that the left channel had dropped out...a lot.

I thought "crap, a dud tape". The player has always worked flawlessly, even very recently with other tapes. I advanced the tape forward and checked the sound. Futher "up" the tape, the left channel seamed fine.

I considered other possibilities, like head alignment, for instance, but I thought that wouldn't explain what I had just done, so I dismissed that hunch.

I repeated playing the tape from the beginning, but it was still wonky.

Then I remembered that a while before I bought this tape -- when I was messing around with my new Otello -- for some unknown quirky reason (as I am wont to do occasionally), I had added a ground wire from my pre to power "conditioner". Years ago, I had everything similarly linked together, but had removed the deck out of system, had only put it back in earlier this year, and never ran all the ground wires I used to have.

Anyway, it suddenly dawned on me that I had very recently attached this new ground -- so out of pure curiosity, I detached it.

Guess what? I no longer have any difference in volume between the 2 channels with any source. My pre balance is now set back to neutral, and everything is perfect as it has always been.

What could explain this?

Crappy interconnect connections, maybe? :chin
 
Anyway, it suddenly dawned on me that I had very recently attached this new ground -- so out of pure curiosity, I detached it.

Guess what? I no longer have any difference in volume between the 2 channels with any source. My pre balance is now set back to neutral, and everything is perfect as it has always been.

What could explain this?


Did you use the detached end of the ground wire to clean out your ear canals? That might be your answer right there...
 
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