604E not equal volume

[280SL]

I have a pair of 604E that were built the same year but in the cabinet one has significantly lower volume that the next. I do not detect any voice coil rubbing on the lower volume speaker. I am wondering if the low volume speaker needs to be recharged. Is there any way to discern if an alnico needs to be recharged? Currently I am using a pot between the preamp and amp to reduce the gain on the higher volume speaker.

[Earl K]

First thing I would do is make sure that the cones ( are original & ) have the same printed number on them ( 21184-2 is original ).

That's the number to look for ( the assumption when you see those numbers is that the voice-coils are also identical and original ):

http://img.usaudiomart.com/uploads/large/1503345-vintage-altec-604e-super-duplex-speakersmatchedexfresh-pulls.jpg

- If you see 2 different numbers on your cones then you will possibly need to recone one or both at GPA (https://greatplainsaudio.com/) ( to obtain a matched pair ).

One can ( with the woofer section of the crossover unhooked ) measure the DCR ( ie; dc Resistance ) of each voice-coil > looking for a close match of +/- 0.5 ohm .


A weak magnetic system will manifest itself in the Qes value of the woofers Ts parameters > the Qes value of matched woofers should be near identical ( if the woofers both have the same cone numbers & voice-coils ) .

The most straightforward approach to measuring a speaker's Ts parameters is to buy something like a WooferTester gizmo such as DATS 2 from P.E. (https://www.parts-express.com/dayton-audio-dats-v2-computer-based-audio-component-test-system--390-806) or WT2 from S&L (http://www.woofertester.com/wt2product.htm).

:)

http://www.audioheritage.org/photopost/data//500/Altec_604-605ts.png

[280SL]

Both speakers have the same cone. One speaker measure DCR woofer 11.5 and 8.8 and the other is 13 and 9 ohms. The louder one is 13 and 9.

[Earl K]

Have you tried swapping the crossovers from one cabinet to the other ?

:)

[280SL]

Yes I have tried swapping crossovers.

Below are the Fs of the speaker. The Fs of the 27.1 is the louder the other less volume.
78729

[Earl K]

Both speakers have the same cone. One speaker measure DCR woofer 11.5 and 8.8 and the other is 13 and 9 ohms. The louder one is 13 and 9.

What were the cone numbers that you found on your 604E's ? ( over the decades, there were a few possible replacement cone numbers ).

An upward shift in Fs can be caused by the surround Goop drying up ( though typically raising the Fs a few hz won't change overall output levels ).

A lower than expected DCR can sometimes be caused by a partially shorted voice-coil ( the woofer will continue to work, but at a reduced level ).

:)

[Earl K]

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=78729&d=1508613409

Since you are obviously handy with a signal generator, sense-resistor & DVM, I would recommend that you download REW to perform some more extensive parameter testing ( click the pic ).

https://www.avnirvana.com/images/rew_300x300_banner.gif (https://www.roomeqwizard.com/)

Additionally, the most up-to-date Beta Versions are available at AVNirvana ( REW Forum ). (https://www.avnirvana.com/forums/official-rew-room-eq-wizard-support-forum.10/)

REW will ( among other things ) allow you to setup a jig to measure your woofer's AC impedances ( as well as obtain Ts Parameters ).

From the looks of your above pic, your woofers have different voice-coils ( you'll need actual AC impedance traces to either verify or debunk that opinion ) .

:)

[280SL]

The cone numbers are the same. They are in a cabinet so I don't have immediate access to them. One of the speakers was bought new by my father and I know the cone is original. That speaker has the higher volume.