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B&C 15" Neodymium Driver Rear Chuffing HELP!

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mitchiemasha View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Topic: B&C 15" Neodymium Driver Rear Chuffing HELP!
    Posted: 05 October 2022 at 4:50pm
I've picked up a B&C 15" 4 ohm Neodymium possibly a 15HPL76 350W, it looks exactly like that and the chuffing on the rear is horrendous, the worse I've heard. Is this normal? is this right? There's no coil rub, the driver moves very freely and sounds as expected apart from once cranked and the air start pushing through those tiny holes on the rear.

Any advice appreciated. Thank you




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Wikl109 View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Wikl109 Quote  Post ReplyReply Direct Link To This Post Posted: 05 October 2022 at 8:48pm
How are you testing it? If in free air i'd say it's probably normal.
If so try it in a box before starting to worry.
There was a thread on here a while back where I mentioned a loose coil on the former can cause problems (I've personally experienced this). That driver showed no coil rub when pushed, just had a rattle at certain frequencies.
Cheers, Chris.
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mitchiemasha View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 05 October 2022 at 9:32pm
I've got a cab with extra dampening so trying in that to night. This is definitely more a chuffing than a rattle, I may of had something similar to that before, it was quite frequency specific, this is more volume specific at all low freq. Comparing to a Fane 15, free air, the difference is insane.

Thank you
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Wikl109 View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Wikl109 Quote  Post ReplyReply Direct Link To This Post Posted: 05 October 2022 at 10:29pm
But does the Fane have a vented magnet assembly?
The JBL VGC models used to be noisy when pushed in free air so try it in a box first. The vents on that B&C seem pretty small so they'll make some chuffing sounds.
Cheers, Chris.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote singingfish Quote  Post ReplyReply Direct Link To This Post Posted: 05 October 2022 at 10:44pm
These were custom designed for FBT's compact abs reflex boxes by B&C.
I think you'll find when it's mounted in an appropriate cab this forced air cooling noise from the rear won't be an issue.
:-)
Matt
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Post Options Post Options   Thanks (1) Thanks(1)   Quote APC321 Quote  Post ReplyReply Direct Link To This Post Posted: 05 October 2022 at 11:48pm
So it is a 3" coil, relatively light cone, high efficiency woofer. Looked at the spec sheet and the Xmax is +/- 4mm.

Personally I wouldn't have said that the voice coil cooling arrangement on this woofer was a particularly clever design. Not surprised that you get "chuffing".

Look at the size of each of the cooling vents...like trying to force air through a drinking straw.

Sort of reminds me in concept to a JBL 2226, where instead of having a central cooling vent they have four smaller vents (at least bigger than the tiny holes on this driver) designed to allow heat to be taken from right up close to the voice coil. Great in principle, but actually leads to "hot-spots" on the voice coil where the vent "cut away" is.

Would love to see what is actually going on, hidden under the cast frame on this neo B&C.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2022 at 6:13am
I don't know how good an idea it is to "crank" any speaker if not in an enclosure. One "speaker guy" I knew (Mike Cotter, RIP) definitely said that it was a no-no. 


Earplugs Are For Wimps!
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mitchiemasha View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2022 at 12:42pm
Originally posted by Earplug Earplug wrote:

I don't know how good an idea it is to "crank" any speaker if not in an enclosure. One "speaker guy" I knew (Mike Cotter, RIP) definitely said that it was a no-no. 

I understand the driver isn't getting the air pressure resistance from the cabinet but I'd love to know more to the why of this... and, "cranked" was an over exaggeration, I wouldn't be taking the driver anywhere near max capacity. It was meant more as in slightly louder than just being on for a basic test. Most drivers today can take all sort of abuse I don't see how much of a short test out of cabinet can be a serious no no, but I'm open to more insight. Edit: also, yes, the sound would be rubbish, so not much good as a test of the quality of the speaker.

@APC321. I'll make sure to dissect it when it fails and get some pictures up.

@Wikl109. That's a good point, the fane is vented but it's the typical centre hole. Sovereign Pro 15, nothing fancy like what these B&C are trying to do.

@Singingfish. Yes, I'm hoping to get tested in the dampened cab tonight, didn't manage last night, ran out of time.




Edited by mitchiemasha - 06 October 2022 at 12:47pm
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mitchiemasha View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 07 October 2022 at 2:27pm
Some quick testing in a dampened box done and I can confirm the driver sounds good. I guess I was over panicking due to my Carlsbro rattling cabinet issue here 

https://forum.speakerplans.com/carlsbro-gamma-15-400-advice-needed-cab-vibration_topic107389.html  

1 is quite bad and the thinking was, there's no way the chuffing, as it's that loud, isn't going to be the same, especially on those minimal kick bass sections of dance tracks or happy DJ filtering moments.

Edited by mitchiemasha - 07 October 2022 at 2:30pm
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