Resurrecting Old 1501-4 Speakers

[Bob Snelgrove]

Found a few at my storage. only 3.2 ohms ,no load. Is that bad? On one the basket voice coil is super clean and nothing in the gap but it still sounds distorted. Testing out of cabinet but still shouldn't sound that bad. Where to start? Mix and match baskets to magnets?

thx

bob

[Dave Meis]

The 4 ohms rating is *impedance*, when you use a VOM to check ohms, it's telling you *resistance*, and 3.2 is a normal reading. Resistance will read lower than impedance....I can't address the distortion, but the 3.2 is a good number.

[Marty Nemanick]

Bob, did you check for any voice coil rub when lightly pressing down on the cone? Your resistance measurement is good.

Marty

[Bob Snelgrove]

I did and after cleaning the gap, I still am getting rubbing, even tried rotating the magnet. I'm testing the speaker in the open with a stereo system, Mcintosh 100w amp, FWIW?

bob

[Dave Grafe]

I did and after cleaning the gap, I still am getting rubbing, even tried rotating the magnet. I'm testing the speaker in the open with a stereo system, Mcintosh 100w amp, FWIW?

bob

How are you "cleaning the gap"? How are you realigning the coil in the gap after pulling the magnet? Normally the coil is carefully centered in the magnet's gap before gluing using paper shims, there is no way to do this once the cone is in place, and removing/rotating the BW magnet after the cone is installed is most likely to result in a bad fit, very possibly why the speaker has issues now - someone may have pulled the magnet "because they could" and when they put it back it did not line up properly. If it ain't broke we can fix that too...

"Rubbing" i.e. scratchy sounds when the cone is moved by hand come from the voice coil rubbing on the sides of the gap, either from loose windings, misaligned coil, or a warped coil former. Be careful to apply even pressure when pressing the cone to preserve its shape. The only repair option for a scratchy coil is to replace the cone.

[Bob Snelgrove]

I did and after cleaning the gap, I still am getting rubbing, even tried rotating the magnet. I'm testing the speaker in the open with a stereo system, Mcintosh 100w amp, FWIW?

bob

How are you "cleaning the gap"? How are you realigning the coil in the gap after pulling the magnet? Normally the coil is carefully centered in the magnet's gap before gluing using paper shims, there is no way to do this once the cone is in place, and removing/rotating the BW magnet after the cone is installed is most likely to result in a bad fit, very possibly why the speaker has issues now - someone may have pulled the magnet "because they could" and when they put it back it did not line up properly. If it ain't broke we can fix that too...

"Rubbing" i.e. scratchy sounds when the cone is moved by hand come from the voice coil rubbing on the sides of the gap, either from loose windings, misaligned coil, or a warped coil former. Be careful to apply even pressure when pressing the cone to preserve its shape. The only repair option for a scratchy coil is to replace the cone.

I'm using masking tape and a business card. No debris, foam, or shavings were present and the gap looks clean. There are no shims and the 3 screw holes dictate the magnet alignment. Can rubbing be tested pusing only one edge or should it be done pushing parallel with 2 hands, 180 degrees?

thx

bob

[Dave Grafe]

Pushing one edge only warps the cone and is not a reliable test, you need to apply uniform pressure across the entire cone. Also the three bolt holes that align the magnet are not at all an accurate way to center an installed cone. Once the magnet has been removed re-coning is required to restore it.

[Bob Snelgrove]

Pushing one edge only warps the cone and is not a reliable test, you need to apply uniform pressure across the entire cone. Also the three bolt holes that align the magnet are not at all an accurate way to center an installed cone. Once the magnet has been removed re-coning is required to restore it.

I marked the original mag/cone alignment so maybe I'll put it back. I still don't see any shims? And it doesn't seem to be rubbing now if I push evenly. A 1.5 v battery will move the cone both ways depending on polarity.

bob

[Dave Grafe]

I marked the original mag/cone alignment so maybe I'll put it back. I still don't see any shims? And it doesn't seem to be rubbing now if I push evenly. A 1.5 v battery will move the cone both ways depending on polarity.

bob

When installing a speaker cone the inner and outer surrounds are set into place with small paper or plastic shims placed between the inner surface of the voice coil and the walls of the gap. Glue is applied with these shims in place, and once the glue is set the shims are removed before gluing the dust cover in place. Removing the magnet destroys the alignment and it is virtually impossible to put it back with tolerances the thickness of a piece of paper in all directions. To further complicate things the actual wires are on the outside of the bobbin, the part NOT shimmed in construction so even if you got lucky and restored the alignment any deformation of the wires will reduce the clearance even more.

A sad story but this is true science. While it can be a convenience for repair technicians Peavey never intended the magnets to be removed unless the speaker was being rebuilt.

[Jerry Overstreet]

Have to disagree there Dave. I've swapped back and forth, AB'ed, replaced, handled Peavey BW mags tons of times. They are designed to be serviced that way.

This is a different design than most speakers as you describe.

The 3 bolts align the magnet on the basket coil when re-installed. There is no need for shims provided the motor has not been broken loose from the adhesive.

That is a condition that would only happen with a severe blow or as the result of being stuck to another similar magnet of the same strength. Something I found out too late.

The other issue with BWs is deteriorated screen foam getting into the gap and coil former discussed here:
viewtopic.php?t=213959&highlight=mainta ... aintenance

[Marty Nemanick]

I agree with Jerry, I've carefully swapped BW magnets dozens of times without any problems. It may be possible that the voice coil itself may be just slightly out of round. Try rotating the magnet to another position.

[Bob Snelgrove]

Update, There is NO rubbing when pushing the cone evenly, 180 degrees near the surround. I was trying to find rubbing by pushing on one edge. I'm still getting distortion playing (bass) test tones through my home stereo, no cabinet just the speaker in the open air. If that is flawed, I can mount it back in a cabinet but I was hoping what I'm doing was a fair test?

Thanks for all the replies

bob

[Jeffrey Maxwell]

Bob,
Are you sure that the test signal from your home stereo is not distorted? Maybe try another speaker on the stereo to make sure it is outputting a clean signal?

Jeff

[Bob Snelgrove]

Confession time

I have been leaning the speaker(s) against a dresser to face them into the room. While trying another known good speaker that was also rattling (distorting), I pulled it away from the dresser and all the bad noise was gone. Tried the 1501's and all was well. It takes a big man to admit he messed up, I'm only 5'6", but I'll take the win, LOL !

[Jeffrey Maxwell]

Mystery Solved!

[Dennis Detweiler]

When removing the magnet, I cut the heads off of longer bolts and screw them down into the basket before removing and when re-installing. This makes sure the magnet is lining up evenly while removing it and lowering it back onto the basket. Less chance of tilting the coils and boogering the coil.