Diagnosing Allison One problems

I recently inherited a pair of Allison One speakers from the late 70s or early 80s. They belonged to my stepfather, and I remember their room-filing sound, although I don’t think they’ve been used in years.

I attached them to my system, and they output mostly trebly sound, with just a hint of mid or bass. The connections have the correct polarity, and the receiver (Harmon/Kardon 3390) is capable of driving the aging pair of KLH speakers previously attached. I removed the grilles, and the speaker cones appear to be intact and operational. The speakers can handle power, and the sound is not distorted, just trebly. My guess is that some of the internal crossover electronics may be the cause, but I don’t know how to diagnose or what the fix would be.

Any suggestions or advice would be most welcome.

Hi! Welcome to HFGF!

I suggest removing the grilles and watching the drivers while music is playing. Do the woofers move? If not, then yeah there is a broken connection somewhere. If they do move but not very much (crank the volume), then there’s probably a dying component in your crossover network. If either of these happen, see if
can you pull the drivers out and give us pics of the crossover network.

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Make sure they’re against a wall.

After what you described, I would guess the capacitor in the crossover network went bad.

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Thanks for all the replies. I do have the speakers against a wall. Is the capacitor issue something that could happen to both speakers at once? Could a power surge cause this?

Short Aanswer: Yes.

Longer Answer: Capacitors are the one component in electronics that age and fail. Under the same conditions (as in: same room or on the same circuit board), they will either fail in one long cascade (old computers usually die like this), reach their expected life time (commonly rated in hours @ 85°C or 105°C) or just by age.

A power surge would kill an amplifier or power supply, the speakers would probably be fine.
Should be as easy as pulling the crossover out and looking at the numbers on the capacitors.

For example:

You want the same uF (or nF) capacity, and the same or higher Voltage rating.