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-   -   ? What to do,Slight damage to Woofer ordered from MCM (http://www.diyaudio.com/forums/subwoofers/226205-what-do-slight-damage-woofer-ordered-mcm.html)

Justhappytobehere 22nd December 2012 12:37 AM

? What to do,Slight damage to Woofer ordered from MCM
 
I ordered 4 15" Polypropylene Cone Woofers from MCM Electronics ( MCM Part #: 55-2974 ) . 2 of the 4 speakers arrived with a slight dent on the edge of the flat part that seals the speaker to the mounting hole it (unless straightened the speaker will not seal properly) . I'm wondering if I should go through the hassle of returning the 2 speakers ? Or does anyone think this is a minor issue that could be fixed by straightening out the slight dent or might there be other issues caused by the impact that caused the dent . Other than the slight dents the speakers seem to be unharmed.
I apologize in advance for this totally newbie question but any advise would be greatly appreciated.

Andrew Eckhardt 22nd December 2012 01:10 AM

This is a common problem when ordering house brand low buck merchandise from MCM. Often the order cost is low enough compared to shipping that it interferes with the option of sending something back unless MCM will eat it. I recently ordered 4 55-2963's and they all had the surrounds glued on so cattywampus that I'd be lucky to get 3 cone distorting milimeters of excursion before extreme nonlinearity sets in. The speakers actually have a "datasheet" where 7mm Xmax is specified. Rather than just sending them back I asked if they could investigate whether the rest of their current stock had this issue. No reply received..

If you post pictures of the damage somebody here might be able to make a recommendation.

Kindhornman 22nd December 2012 01:18 AM

Just,
Do everyone and yourself a favor and post a jpeg picture of the damage. I am assuming that you are talking about a stamped frame loudspeaker as it is hard to imagine this being a cast frame with the damage you are describing. I would worry about a couple of issues besides the sealing issue. One is if the center pole piece was shifted when the speaker was dropped and the other is if the frame is still round and not damaged in any way to make it out of round. If the damage is outside of the surround and the frame is still round you could just straighten it out, but I would probably want to return the devices just to be on the safe side. Once you mount it you may have a problem when you pull the frame back into shape as it could tweak the frame and then you probably won't be able to return the speakers. Better to be safe than sorry.

Steven

Andrew Eckhardt 22nd December 2012 01:28 AM

Definitely inspect the magnet assembly for cracked glue or magnet. Usually when something lets go between the top plate and basket you can see it by grabbing hold of the magnet and wanking on the basket. You can also tap the magnet with a the grip of a screwdriver and listen for one that doesn't ring like the others. Extra damping usually means a flapping gap somewhere it shouldn't be. If it actually chatters there isn't a lot you can do without just the right amount of an adhesive with good capillary action properties. At that point sending it back would be most reliable for sure.

▀art West-VL. 22nd December 2012 09:24 AM

And listen if the voice coil is rubbing inside the magnet assembly.
push carefully and straight on the cone and listen, you should hear nothing.
Or better; put a sine wave of ▒15hz through them at no more then 5W for a short period and listen carefully.

mattlong8 22nd December 2012 07:47 PM

I damage MCM drivers just from tightening the mounting bolts. I assume the frame is bent. you can pay to send them back or try bending them back with some vices. Over all one must expect a high out of box defect rate from MCM but some of their stuff is ok. Always measure the T/S for each individual driver as they can widely vary.

Best of luck to all this coming year with your designs and builds,

-Matt


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