Author Topic: Passive radiator help? (Read 307 times)

jagerphan84 · « **on:** July 20, 2005, 08:51:12 AM »

Hi folks,

Somewhat un-Alembic related, but I'm hoping someone here will be able to help out with an audio problem I'm having.

I've got a couple of speaker cabs which each contain four 5 drivers as well as a 15 passive radiator. One of the cabs is fully functional and sounds beautiful, but the other appears to have some kind of problem with the passive radiator. I'm getting some very prominent 'crackly' distortion from the radiator whenever I venture into the low frequencies. I replaced all four of the 5 drivers hoping one of them was the culprit, but no luck.

So is it possible to 'blow' a passive radiator, or could it be that the cabinet needs a good cleaning inside? I'd sure like to try and fix it up myself before shelling out for a new PR, but I don't want to go poking around without any clue as to what I'm doing.

Any thoughts would be greatly appreciated!

Adam

kungfusheriff · « **Reply #1 on:** July 20, 2005, 09:06:22 AM »

Have the voice coil looked at--I got an SWR through the mail earlier this year that had been dropped, knocking one of the speaker's coils off-axis and causing similar-sounding distortion even with the leads disconnected, causing the speaker to become a passive radiator.

jagerphan84 · « **Reply #2 on:** July 20, 2005, 09:55:02 AM »

Hey KFS,

Thanks for the idea, but methinks the passive doesn't have a voice coil at all! From what I've read about them, a PR is just a frame and cone, without the voice coil or magnet. I could be wrong though; stranger things have happened!

Adam

keith_h · « **Reply #3 on:** July 20, 2005, 10:06:26 AM »

If I recall from many many years ago, some PR's have dampening mechanisms to limit the cone travel and even out the tone. The ones I recall seeing were mecahnical and had a counter balance weight. So you could have dirt or wear in whatever your PR uses for dampening. I say giving everything a good cleaning is worth the effort and cheaper than buying a new one.

Keith

lbpesq · « **Reply #4 on:** July 20, 2005, 11:38:06 AM »

Adam:

Since you also have one that works, you might try opening both up and eyeballing the innards to see if there is any difference. If not, try swapping the PRs and see if the problem follows the PR or stays with the cab. This might help you narrow down the possible culprit.

Bill, tgo

jagerphan84 · « **Reply #5 on:** July 20, 2005, 12:04:32 PM »

Hey Bill,

I've checked out the guts, and all seems to be identical between the two. I'd love to swap the PR's, but unfortunately they're glued in! The drivers are screwed in like all my other cabs, but for whatever reason, the manufacturer opted for glue on the PR's.

I guess I'll have to dig out the old vacuum cleaner and see if I can't suck the problem right out.

Adam

(PS Bill - yep, great minds sure DO think alike!)

foth · « **Reply #6 on:** July 20, 2005, 01:33:51 PM »

I once found a little plastic space monster wedged between the cone and frame of a distorting speaker (in a Super Reverb). Look for the unlikely with your best Sherlock Holmes mindset, especially if open-back cabinets and children are involved!

keith_h · « **Reply #7 on:** July 20, 2005, 01:42:38 PM »

And don't forget the Lite Brite pegs pushed into the input jacks.

Keith

lbpesq · « **Reply #8 on:** July 20, 2005, 04:13:15 PM »

Crayons too!

Which reminds me of the time I gave my wife a cell phone when she first moved in with me in Oakland. She was constantly getting lost, so I figured a cell phone was the solution, so she could call me for directions. She lost it the second day. After I had turned the house updside down and checked the cars without any luck, I cancelled the service. Then I had an idea. I showed her 4 year old son (later my stepson) my phone and asked him if he had seen one like it. He said sure, under my bed. I ran upstairs and, lo and behold, there it was. Thus was born a family motto: If you can't find it, ask the 4 year old.

Adam: You might try muting the PR with your hand or something while playing something through the cab and see if it has any effect on the crackling.

Bill, tgo

bigredbass · « **Reply #9 on:** July 22, 2005, 09:26:09 PM »

As regards passive radiators ( . . . doesn't the name make you wonder if the AGGRESSIVE radiators are locked up in some Federal facility?), MESA has launched the WALKABOUT SCOUT cabinets with (you guessed it) passive radiators to reinforce the deep end in these small venue cabinets.

www.mesaboogie.com

J o e y