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Author Topic: clearance needed in front of woofer  (Read 3980 times)

David A. Parker

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clearance needed in front of woofer
« on: November 21, 2010, 10:17:35 pm »

my sub drivers, eminence 3015lf, have an xmax of 9.6mm, xlim of 17mm. How much clearance do I need between the cone and the grille? Is xmax total movement, peak to peak, or is it a one way measurment, meaning the peak to peak is 2x xmax, and the cone will actually travel out 9.6mm?
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David Parker
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John Halliburton

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Re: clearance needed in front of woofer
« Reply #1 on: November 22, 2010, 09:45:16 am »

It could, Xmax is not the limit of mechanical travel of the driver.  Check with Mr. Jerry McNutt at Eminence if you can't find a mechanical limit spec on the website page for that driver, or just add .75-1" of depth to the baffle board from the front edge.  Recessing it even farther is not going to hurt either.

Best regards,

John
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Art Welter

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Re: clearance needed in front of woofer
« Reply #2 on: December 21, 2010, 02:07:57 pm »

David A. Parker wrote on Sun, 21 November 2010 20:17

my sub drivers, eminence 3015lf, have an xmax of 9.6mm, xlim of 17mm. How much clearance do I need between the cone and the grille? Is xmax total movement, peak to peak, or is it a one way measurment, meaning the peak to peak is 2x xmax, and the cone will actually travel out 9.6mm?

David,

Missed this one while traveling, so you have probably addressed the grill situation, but here goes anyway:

Xmax and Xlim are one way travel, peak to peak is double that.

The 3015LF cone can travel 17mm (just under 3/4”) one way before damage.

If the driver is front mounted, it would be a good idea to leave that much room in front of the at rest front extreme of the cone or surround.

A 6 dB increase in level will double the excursion when in the linear operating range of the speaker, that is up to Xmax.

If you are using a large box, the driver will hit Xmax with around 400 watts about 1/3 octave above Fb (box tuning), so if you have 1600 watts available you could possibly exceed Xlim.

That said, the motor has less “push” past Xmax, so hard to say what it would actually take to exceed Xlim. Below Fb, it may only  take a fraction of the rated power to exceed Xlim, which is why we use HP (low cut) filters.
In the area above Fb, usually in the heart of the kick drum fundamental, some empirical experimentation is needed to see how much power drives the cone too far.

It is easy to measure cone movement with a white dot on the cone, always good to see if Fb (where the cone movement is at minimum) came out as predicted.

Some cones don’t want to move that last little bit before Xlim, some looser cones seem to just keep on moving further till they rip or knock.

I use fabric grill, setting the distance a bit past Xmax allows me to see if I’m hitting the speaker too hard as the grill starts to flap without damage to the speaker.

If you are using a metal grill, contact with it is like running the surround past a cheese grater, not a good idea  Laughing .

Art Welter
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David A. Parker

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Re: clearance needed in front of woofer
« Reply #3 on: December 21, 2010, 07:52:57 pm »

Art Welter wrote on Tue, 21 December 2010 13:07

David A. Parker wrote on Sun, 21 November 2010 20:17

my sub drivers, eminence 3015lf, have an xmax of 9.6mm, xlim of 17mm. How much clearance do I need between the cone and the grille? Is xmax total movement, peak to peak, or is it a one way measurment, meaning the peak to peak is 2x xmax, and the cone will actually travel out 9.6mm?

David,

Missed this one while traveling, so you have probably addressed the grill situation, but here goes anyway:

Xmax and Xlim are one way travel, peak to peak is double that.

The 3015LF cone can travel 17mm (just under 3/4”) one way before damage.

If the driver is front mounted, it would be a good idea to leave that much room in front of the at rest front extreme of the cone or surround.

A 6 dB increase in level will double the excursion when in the linear operating range of the speaker, that is up to Xmax.

If you are using a large box, the driver will hit Xmax with around 400 watts about 1/3 octave above Fb (box tuning), so if you have 1600 watts available you could possibly exceed Xlim.

That said, the motor has less “push” past Xmax, so hard to say what it would actually take to exceed Xlim. Below Fb, it may only  take a fraction of the rated power to exceed Xlim, which is why we use HP (low cut) filters.
In the area above Fb, usually in the heart of the kick drum fundamental, some empirical experimentation is needed to see how much power drives the cone too far.

It is easy to measure cone movement with a white dot on the cone, always good to see if Fb (where the cone movement is at minimum) came out as predicted.

Some cones don’t want to move that last little bit before Xlim, some looser cones seem to just keep on moving further till they rip or knock.

I use fabric grill, setting the distance a bit past Xmax allows me to see if I’m hitting the speaker too hard as the grill starts to flap without damage to the speaker.

If you are using a metal grill, contact with it is like running the surround past a cheese grater, not a good idea  Laughing .

Art Welter


Thanks for the reply. I have already redesigned the front part of the cabs to allow for the xlim. In the initial comparative tests, the new cabs with the kappalite 3015 drivers outperformed my old subs with the omega 18's. The 3015's went lower and louder with the same voltage applied. The new cabs are 2/3 the size of the old cabs, so that's a big plus. I used an eminence design for the cab, and it appears that these drivers respond well to the HUGE ports. each cab has two drivers and 6-6" port tubes each 11" long. First time out with them doing a live band they exceeded my expectations. All I needed them to do was come close to my old double 18's. They in fact outran them.

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David Parker
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Art Welter

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Re: clearance needed in front of woofer
« Reply #4 on: December 21, 2010, 08:05:32 pm »

Nice when things turnout better than planned.

Did the 6 ports put the Fb at 44 Hz?
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David A. Parker

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Re: clearance needed in front of woofer
« Reply #5 on: December 21, 2010, 10:01:28 pm »

Art Welter wrote on Tue, 21 December 2010 19:05

Nice when things turnout better than planned.

Did the 6 ports put the Fb at 44 Hz?


I ran the numbers before I built them, and it all came out pretty much the same as what the eminence plans said. Six ports seemed extreme, but supposedly it was to reduce port velocity. As far as testing what the FB actually was, I'm not sure how to go about testing that. Using a port calculating program it came out right.

http://www.parts-express.com/pdf/290-598c.pdf


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David Parker
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Mike Caldwell

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Re: clearance needed in front of woofer
« Reply #6 on: December 22, 2010, 08:40:29 am »

David A. Parker wrote on Tue, 21 December 2010 22:01

Art Welter wrote on Tue, 21 December 2010 19:05

Nice when things turnout better than planned.

Did the 6 ports put the Fb at 44 Hz?


I ran the numbers before I built them, and it all came out pretty much the same as what the eminence plans said. Six ports seemed extreme, but supposedly it was to reduce port velocity. As far as testing what the FB actually was, I'm not sure how to go about testing that. Using a port calculating program it came out right.

http://www.parts-express.com/pdf/290-598c.pdf





That's an easy test to do, you just need a tone generator with some form of calibrated read out and your eyes. Send the output of the tone generator to an amp connected to the sub. Sweep it around the range the cabinet should be tuned to while looking at the speakers cone excursion/movement. When you hit the tuned frequency of the cabinet the cone excursion will be the least. This only works in the frequency range where you can actually see cone movement.

Art Welter

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Re: clearance needed in front of woofer
« Reply #7 on: December 22, 2010, 10:37:17 am »

David A. Parker wrote on Tue, 21 December 2010 20:01

Art Welter wrote on Tue, 21 December 2010 19:05

Nice when things turnout better than planned.
Did the 6 ports put the Fb at 44 Hz?

I ran the numbers before I built them, and it all came out pretty much the same as what the eminence plans said. Six ports seemed extreme, but supposedly it was to reduce port velocity. As far as testing what the FB actually was, I'm not sure how to go about testing that. Using a port calculating program it came out right.
http://www.parts-express.com/pdf/290-598c.pdf



Port calculations generally don't take port position in the cabinet into account, other than assuming they are about a port width away from walls.
The Eminence box alignment does not show where the ports should be mounted, though you chose a logical front mounting.

Port proximity to walls will affect tuning, usually making it lower.

This exchange might refresh your memory  Laughing :

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