Nasty buzz from Energy 2.1e when fed a 300Hz tone

[SQLGuy]

Hi folks,

I recently bought a used pair of 2.1e’s at a local audio store for use as side surround speakers in my home system. The 2.1e’s auditioned OK, but, one use I have for my audio system is practicing bass guitar and I recently noticed that on a 19th fret D on bass (just about 300Hz), at even pretty low volumes, they make a really nasty buzz from the woofer. It’s not a signal issue, as the front speakers produce the same note perfectly cleanly. The problem occurs exactly the same in both 2.1e’s and production of notes above or below this fret is OK… it’s a really specific resonance of some sort.

I’m thinking that the voice coil windings have become separated, or maybe that the voice coil has become unglued somewhat from the cone.

Anyone experienced this issue before?

Any ideas on possible repair of the drivers? Or sources/prices for replacement drivers?

Lastly, I assume that foam ring over the driver mounting flange is a throwaway if/when you pull the woofer. Any sources for replacements for these?

Thanks,
Paul

[Iain McNeill]

so if you gently apply a little pressure to the cone by hand when playing the note (i know you need 4 hands) the buzz doesn't go away indicating the voicecoil is loose and buzzing?

It's more likely to be something loose in the cabinet or terminal panel/connectors.

If you replace the cone, the recone kit will come with a new foam surround.

[SQLGuy]

Hi Iain,

No, I don't think this is coming from the cabinet or connectors, especially not on both speakers. The cabinets of these speakers are very solid and non-resonant. No rattling or other "loose items" noise can be elicited by tapping or shaking the speakers.

Also, for the foam, it is not the driver surround that I'm talking about. It's the foam ring that goes over the flange of the frame where the woofer is mounted to the cabinet (see linked picture).

http://v5v.ca/forsale/energy/energy2.1e.jpg

Cheers,
Paul

[R-Carpenter]

loose screws usually vibrate exactly at 3oohz. Take the driver out, "lock tight" the screw holes and screw it back in.

[SQLGuy]

OK. I hooked up a function generator so I could set and hold the rattling signal. I then pulled off one of the foam rings and pulled the woofer.

The screws were not loose.

The problem is that there are four screws holding the 6.5" woofer in place, and about 290Hz is where the segments of stamped steel driver basket resonate against the cabinet. There is a gasket behind the woofer, but it is very thin and not enough to absorb this vibration.

I'm going to try cutting a new foam gasket and see whether that solves it.

[SQLGuy]

I ended up making some new gaskets out of relatively thick (about 1/8") weatherstripping (very spongy, easily compressible, foam rubber). I also found that I had to back off the four screws a tiny bit from fully tight in order to minimize the rattle. The final result is pretty good and a clear improvement from "before".

I think the truest solution would probably be to add four more screws, for a total of eight, to hold the basket to the cabinet. I may go back and do that if the rattles come back. A second possibility would be silicone sealant instead of a gasket... but I didn't really want to glue the baskets in place.

As for the foam ring that covers the screws: the glue holding them was dry enough that I was able to remove them without damage. I applied Duro spray glue to make for a temporary/removable bond in case I need to remove and reinstall them again.

BTW, since I was doing this bit of abusive testing (both with the function generator and with the bass), I decided to try out a speaker I'd built myself with an 8" Vifa 4 Ohm woofer (made for Mackie monitors) and a 1" Vifa metal dome tweeter. These woofers have cast baskets and they're held in place by eight machine screws with T-nuts (rather than wood screws). I'm happy to say that my speaker passed these tests with flying colors. Unfortunately, I've only built one so far... I've been waiting about a year to get around to doing the other one. Maybe I'll be a bit more motivated now ...? ;-)

Cheers,
Paul

[Iain McNeill]

Nicely done!

Oh, and BTW, build that 2nd speaker!!