Altec 414Z (Malibu) woofer distortion, what HAVE I done?

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02-06-2018, 12:34 AM
TW14MB

Altec 414Z (Malibu) woofer distortion, what HAVE I done?

Hello all,

I've had this pair of Malibu's for several years and haven't used them for over a year. I used to use them on McIntosh MC-30s. They always sounded good.

I recently hooked them up to a Bryston 8B (using only 2 of the 4 channels.) They sounded good for a few minutes, I did NOT turn them up loud, but now one woofer in each cabinet (the lower woofer in the left and the upper woofer in the right) are distorted. The other woofer in each and the horn sound fine.

The DC voltage on the 8B is less than 1mv. Apparently they have a circuit to protect from any DC output. The amp tested fine on other speakers.

I am assuming I am in for a hefty repair bill. Was this caused by the Bryston amp directly somehow from "too much power?" I was always told that clean power is what is most important so I am not understanding how this could happen. I'll break this down into a few questions, I appreciate any help you all can offer:

1. Does anyone know offhand the price to repair a 414Z? I have "Midwest Speaker" here in MN who I like dealing with, but should I send them to GPA for full service?
2. I have not disassembled anything yet. Any advice from Malibu owners? It looks like I need to detach the crossover from the back panel, (so I can set the panel aside), and then desolder and remove the woofers from the cabinet face. Am I correct that the woofers are soldered and there is not some kind of clip or other method I am missing?
3. Is it possible that some crossover issue has contributed to the problem? I would expect poor performance but not distortion, and certainly not from a different speaker in each channel.
4. Lastly, these cabinets have the die-cut wood grille which I was never a huge fan of. is it possible to remove those without doing permanent damage to the cabinetry? I can not tell from a visual inspection if they are framed in from the back, although I do see screws holding the front panel braces in, but are they also glued?

Sorry I know this is a lot of questions but any help is appreciated. This really is a great group of people in vintage audio.

Thank you!
02-06-2018, 07:36 AM
Earl K

I highly doubt that simply hooking up a different amplifier ( functioning correctly I assume ) would result in the symptoms you've described .

It's more likely a case of aged woofer suspensions finally giving it up ( and allowing the voice-coil to start rubbing ).

These old woofers have very narrow gaps. They also have a pretty loose compliance ( comprising the surround and the spider ).
With time ( & gravity ) a little bit of cone migration is bound to happen ( leading to VC rubbing ) .

A temporary fix ( often ) is to simply rotate the woofers 180deg ( to see if the cones migrate back onto a non-rubbing position ).

If that doesn't work, reconing will be necessary ( I'd use GPA ).

:)
02-06-2018, 03:49 PM
TW14MB

Thanks Earl, I will try the rotation and see what happens. You mean after 50 years of reliable service they might be out of spec? Who can I call to complain?

I was REALLY enjoying the way they sounded until I noticed the problem.

Regarding "burnt" voice coils, would that change overall DCR of the whole system? Is there a signature to that distortion vs. rubbing voice coils vs. torn paper?

At the speaker terminals on the cabinet the DCR is 6.6.
02-06-2018, 04:32 PM
Earl K

Quote:

Originally Posted by TW14MB

Thanks Earl, I will try the rotation and see what happens. You mean after 50 years of reliable service they might be out of spec? Who can I call to complain?

I was REALLY enjoying the way they sounded until I noticed the problem.

Regarding "burnt" voice coils, would that change overall DCR of the whole system? Is there a signature to that distortion vs. rubbing voice coils vs. torn paper?

At the speaker terminals on the cabinet the DCR is 6.6.

The DCR ( at the terminals is about right ).

There's no reliable way to describe the differences in sounds so that the in-experienced can make an accurate diagnosis ( a slightly bubbled voice-coil former is going to sound the same as a more benign rub ) .

Sorry, as far as I'm concerned it'll just lead to a case of a whole lot of false positives .

What's needed is some test gear and the experience to interpret the test results .

Try the woofer rotations , if that doesn't remedy the situation, try your local reconer for a diagnosis .

:)