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philw44 View Drop Down
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    Posted: 30 June 2010 at 11:42pm
This is going to be difficult to explain or diagnose over the net but i'll give it a try.

Nearly finished my B&C Sub 15 build from 18mm Bgrade Birch Ply w/JBL 2226h and can't seem to isolate this buzzing noise - It almost sounds like it's coming from the actual driver/cone itself.

It only happens when I'm pushing them hard and at certain frequencies during playback. You don't notice it when the mid/tops are playing with it  but it's fairly obvious when they are not.

We've opened the top up and had it playing without the lid to see if the driver was catching the terminals or something but it's not. Handle, terminal plate, top hat, tnuts and screws are all tight as can be. We have yet to glue the top of the cab on but it's very secure with 14 screws.

Frustrated :(


Edited by philw44 - 01 July 2010 at 12:04am
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jbinks View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2010 at 11:54pm
Is it possible that the driver isn't loaded (air) properly in an unfinished cab?

You might be exceeding xmax (and hitting the backstop) because the cabinet isn't loading the driver as designed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philw44 Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2010 at 11:57pm
Originally posted by jbinks jbinks wrote:

Is it possible that the driver isn't loaded (air) properly in an unfinished cab?

You might be exceeding xmax (and hitting the backstop) because the cabinet isn't loading the driver as designed.


Sorry, i don't understand. Any chance of breaking that down for a newb? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 12:11am
If you take a driver and operate it in "free air", as in... on a bench, or fixed to a simple baffle (no box), it's basically "unloaded". If it's in a box, the design of the box normally means that in order for the cone to move forwards, the air it displaces (infront, or behind) needs to move some distance. Because "moving" air requires force, this is called "loading" the driver. In otherwords, the driver has to work to push and pull the air in and out of the cabinet.

At low frequencies, especially around the "resonant frequency" of the driver (the frequency that the driver can most easily operate at), the amount of physical movement of the cone can become quite large, for a relatively small amount of input power. This causes the driver to move too far and hit the endstop in the magnet, causing a "pop" or "click" type noise each time. This is bad, avoid it!

When the driver is in a cabinet, the movement of the driver is reduced because it has to push and pull the air through the cabinet. This additional "load" prevents the driver from being able to move as far for the same input power. This in turn means you can apply more power before you start hitting the endstop again.

So to sumarise, when your box is "open", the driver is basically unloaded. Even with a small amount of power, you are probably seeing the driver move too far and hit the stop resulting in the noise you described. If you put the top on and the box is complete then the driver becomes "loaded" and no longer suffers from that problem.

Bottom line:
Put the box together. Stuff a load of power into it over a range of different frequencies.
If you hear anything odd: investigate.
If you don't: all is well.
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philw44 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philw44 Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 12:12am
Cheers, I understand what your saying now.

Unfortunately it was still doing it with the box fully constructed
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 12:20am
Ah right.

Do you have any other boxes that you could put the driver in to test if the noise is really coming from the driver?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philw44 Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 12:32am
Unfortunately not - although i have built two Sub15's using two diff drivers and they both seem to exhibit this problem.

I know I'm not helping too much really am i :(

Err other info - amp is Matrix XP3000 - 1000W into each driver @ 8hom and HP set to 35hz with X-over at 100hz.

It buzzes really badly on whatever the second bass note is to the chorus of Michael Jackson's Billie Jean LOL - F sharp.


Edited by philw44 - 01 July 2010 at 12:48am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bass traffic Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 3:44am
It could be something in your room that is vibrating or it could just be that the box is tuned to that frequency.
I used to have this problem with some dodgy synergy speakers whenever I was making drum n bass, the low notes would always rattle.
Try the box in a different room if possible if it doesn't solve it you might have to eq it out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2010 at 8:32am
If you are getting the same problem with two boxes, then you need to eliminate all the common factors.
In this case the common factors are the amp and the room. So run them off a different amp first, then try in a different location. Outside would be ideal if it's practical where you are.
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