ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3 ... 7   Go Down

Author Topic: How bad is it to exceed the Xmax on a woofer?  (Read 11506 times)

Silas Pradetto

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3047
How bad is it to exceed the Xmax on a woofer?
« on: January 05, 2009, 01:21:10 pm »

I'm designing a custom double 15 cabinet and I'm using Eminence Definimax 4015LF woofers. I can either make the cabinet really small (4 ft^3) and not exceed the xmax (9mm) at rated power, or I can make it more ideal around 6 ft^3 but then I'm looking at a 12mm excursion at rated power.

What should I do?

index.php/fa/20019/0/
Logged

Ryan Garnett

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 536
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #1 on: January 05, 2009, 01:25:32 pm »

It's not xmax that you have to worry about exceeding, it's xmech.

Xmax is typically one way linear excursion.
Xmech is typically one way maximum excursion before something physically stops it, be it bottoming the coil, or the suspension, or whatever.
Logged

Silas Pradetto

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3047
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #2 on: January 05, 2009, 01:27:28 pm »

Well Xmech is like 15mm on these, and they're going to be high passed around 40Hz so the low bump on the graphs there doesn't matter at all.

So you're saying that even though I'm exceeding the Xmax a little, it should be OK with no appreciable increase in distortion?
Logged

Ryan Garnett

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 536
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #3 on: January 05, 2009, 01:43:25 pm »

Silas Pradetto wrote on Mon, 05 January 2009 13:27

Well Xmech is like 15mm on these, and they're going to be high passed around 40Hz so the low bump on the graphs there doesn't matter at all.

So you're saying that even though I'm exceeding the Xmax a little, it should be OK with no appreciable increase in distortion?


I'm saying you aren't likely to damage the woofer if you exceed xmax so long as you stay within xmech. Certainly there will be increased distortion above the linear range of the driver, but if you really need that much more output, your best bet would be to add additional drivers anyway.

Also, is that graph taking into account the change in impedance at different frequencies? You aren't always going to have a consistent 1400 watts from your amplifier across the entire frequency range.
Logged

Silas Pradetto

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3047
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #4 on: January 05, 2009, 01:49:28 pm »

I'm not sure how it's dividing up the power. I think it does take into account impedance and other factors, because depending on how I change the high pass the response above the high pass frequency changes, which wouldn't happen unless power was reallocated.

However, this would be powered with an I-tech putting out 4000 watts, so the 1400 doesn't matter, that's just the RMS rating of the woofers together.

I can increase the power to about 2500 watts without exceeding Xmech. In any case, I think a pair of these should be pretty nice for a drum sub.
Logged

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4874
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #5 on: January 05, 2009, 02:28:28 pm »

Silas,

With sine wave testing, at 16 mm peak to peak, the 4015 sounded noticeably “bad”, but at 12 was “OK”. Until 11 mm the sound quality is very clean. I think the 9 mm x-max rating is really conservative. That said, the speaker is so clean that with music you probably wouldn’t notice much distortion at all until the voice coil starts banging on the back plate.

If you can afford the larger box size, the extra efficiency down low will more than offset the excursion problem.

I built a 3.4 cubic foot box tuned to 38 HZ for a drum sub. Actual measured excursion with 100 watt sine wave at 30 HZ is 12 mm, which drops to 4 mm at 35, 1.5 mm at 40, 5 mm at 45, 7 mm from 50 to 70 HZ, then drops again.

Using a Crest CA-9 to drive it which does 550 watts at 8 ohms, have never heard any distortion or bottoming in drum sub use.  The only protection I use is pulling the 25 and 30 HZ bands down on the drum mix EQ, and that the clip light only flashes on a very hard kick hit.

I have also played a variety of really low frequency CD music material, and found nothing that could “flap” the cone below amp clipping. If you are going to use an amp with double the speakers power, you would need to be more concerned, of course.

By the way,  break in the cones before any testing. I ran the cone open air with a 20 HZ tone, turned the level up till it was about 10 mm peak to peak. I came back a couple (maybe four...) hours later, and could hear the dreaded clacking noise- the excursion had increased beyond  X lim,(15.5 mm published) but the speaker was unharmed!

Art Welter
Logged

Silas Pradetto

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3047
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #6 on: January 05, 2009, 02:34:09 pm »

Art Welter wrote on Mon, 05 January 2009 14:28

Silas,

With sine wave testing, at 16 mm peak to peak, the 4015 sounded noticeably “bad”, but at 12 was “OK”. Until 11 mm the sound quality is very clean. I think the 9 mm x-max rating is really conservative. That said, the speaker is so clean that with music you probably wouldn’t notice much distortion at all until the voice coil starts banging on the back plate....
Art Welter


Wouldn't 16mm peak to peak be 8mm each way, which is less than the 9mm Xmax? or are you referring to 16mm each way, 32mm peak to peak?

My box (with 2 woofers in it) is going to be 6.5 cubic feet tuned to 42Hz and high passed around 35Hz. I definitely think a pair is going to be fine for a drum or DJ monitor setup.
Logged

Elliot Thompson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1573
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #7 on: January 05, 2009, 03:09:26 pm »

Silas Pradetto wrote on Mon, 05 January 2009 19:34

Art Welter wrote on Mon, 05 January 2009 14:28

Silas,

With sine wave testing, at 16 mm peak to peak, the 4015 sounded noticeably “bad”, but at 12 was “OK”. Until 11 mm the sound quality is very clean. I think the 9 mm x-max rating is really conservative. That said, the speaker is so clean that with music you probably wouldn’t notice much distortion at all until the voice coil starts banging on the back plate....
Art Welter


Wouldn't 16mm peak to peak be 8mm each way, which is less than the 9mm Xmax? or are you referring to 16mm each way, 32mm peak to peak?

My box (with 2 woofers in it) is going to be 6.5 cubic feet tuned to 42Hz and high passed around 35Hz. I definitely think a pair is going to be fine for a drum or DJ monitor setup.



To get a better understanding of what is going on with your design, look at the Normalised gain, & Maximum Acoustic Power.

You also may want to check a thread where I mentioned how rolling off lower frequencies can cause more harm than good.

I would suggest you re-design that box for you will indeed exceed the xmech of the driver.


I've used Eminence Designer/Bass Box Pro for nearly 10 years so, I know excactly what the measurements mean.

Also, if I remember correctly, that driver is a woofer and not a sub which offers an FS around 50 Hertz or so. So, the cabinet is tuned too low.

Best Regards,
Logged
Elliot

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4874
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #8 on: January 05, 2009, 03:15:41 pm »

As far as I can tell, Eminence measures X max and X limit are peak to peak.

I use a silver sharpie and mark a dot on the cone, and then hold a ruler next to the cone. Persistence of vision makes it easy to see how far the cone moves.

At 16 mm peak to peak (8 mm each way) the 4015 starts to clack. That's about 5/8”, which is a lot for this type of cone. With a sine wave tone, the 4015 really started to change character (distort) at 12 mm.

I have measured the Lab 12” at 26 mm peak to peak without bottoming, though it is rated at 22 X-lim. That was fun, at that level the unloaded ports could blow a piece of paper across the room.

Interestingly, in ported cabinets the Lab 12” do not seem to change character much at all even at that excursion, which is probably why we hear of people popping them.

Anyway, a 2x15” 4015 should be happening for a drum sub, but personally I think high passing above the low B on a bass is a little high for a drum monitor.
Logged

SteveKirby

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2106
Re: How bad is it to exceed the Xmax on a woofer?
« Reply #9 on: January 05, 2009, 04:20:58 pm »

Silas, if you're high passing at 35, then there will be some attenuation where the cab unloads the cone.  So you shouldn't get that full excursion, at least from the signal input.

That said, I agree with Art that you're trying to tune the cabinet too low.  Also, from my playing with Bassbox Pro, the only way to get that sort of high Q response down low is to put unrealistic cabinet stiffness values in.  You won't get that in real life.
Logged
Pages: [1] 2 3 ... 7   Go Up
 

Page created in 0.101 seconds with 20 queries.