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Help with X-Max Max linear excursion or Max Mechanical?

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robh3606

I have been trying several alignments for a pair of LE14A-s and at 40-60Hz I am seeing an X-max problem for the larger boxes. I can safely stay within these requirements for a smaller box but would like to lower F3. Is it "safe" to do a box where you exceed Xmax. I think the answer will be NO but I have to ask. I do not want to damage the drivers but the P max is the max available from my amp. I am not using PE for the driver as the peaks could be higher especially in that frequency range. Now is P max the highest Linear limit the motor can drive the cone or max mechanical excursion before driver damage?
Thanks

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Re: Help with X-Max Max linear excursion or Max Mechanical? - PeterS 16:42:42 09/26/01 (1)
As PJ points out, exceeding the driver's X-max will utimately damage it. Two ways to get more bass; bigger driver or multiple drivers, you have to move more air.
PS
- Re: Help with X-Max Max linear excursion or Max Mechanical? - robh3606 19:14:47 09/26/01 (0)
  Thanks Pete
  That is the last thing I want to do. Just confused about what limits to use and it is at max power. Under normal conditions I would think I would have a hard time getting up there but as you say I do not want to ruin a driver for a marginal increase in bass extension.
Re: Help with X-Max Max linear excursion or Max Mechanical? - PJ 15:40:10 09/26/01 (3)
To maintain a given SPL, excursion increases, as frequency drops.
Pmax is supposed to be the rating of the VC of the driver. Higher than this, you MAY run the risk of literally burning it up. Usually a problem with tweeters, and basically, this is what happens during clipping. The insulation melts, and essentially you get smoke..
You can run into excursion problems well before you run into power problems. The driver has been pushed to it limits once you pass either the excursion limits, or the VC power rating limit.
After Xmax, the driver is no longer linear. If memory serves me correct, its when BL is down 3dB. Xmech is the physical linear limits. It is usually VERY audible (ie banging). If you hit it hard/long enough, you will damage the driver.
- Re: Help with X-Max Max linear excursion or Max Mechanical? - Robh3606 19:10:01 09/26/01 (2)
  Thanks PJ
  The problem is not power but Xmax as you said. My confusion is what to use. The driver is rated at 5mm peak. All thinks being equal its peak to peak is 10mm. When I look at the graph for X-max at maximum input power I have a problem as it goes to 5.5mm. If the peak to peak is the "real number" than all is fine with the alignment I would like to use. Is the peak 5mm the correct limit or should I be using peak to peak?
  - Re: Help with X-Max Max linear excursion or Max Mechanical? - Panj2107 22:06:27 09/26/01 (1)
    Xmax is supposed to be given as a 1-way measurement, but some sub drivers are often given as p-to-p. I would think yours is 1-way.
    I am not 100% sure on this, and you would probably want to get an opinion of someone who knows more than me, but I am guessing you would be fine. At x-max levels its going to be very loud, and its unlikely you would reach it that often. Unless you hit x-mech, chances are if you exceed x-max by 0.5mm, at a msssive SPL, you wont even notice...but again, you are better to get someone who knows something about those particular drivers, which I do not.
    What input power are you using?
    - Re: Help with X-Max Max linear excursion or Max Mechanical? - robh3606 07:19:08 09/27/01 (0)
      Thanks PJ
      With the pe for the driver of 100watts I am OK. With the rms value of my amp @120watts I exceed the limit. I think you are correct. I started to look at the other drivers I am and have used and my main woofers have a lower xmax and a lower eficiency and I have never bottomed them even using full range in an HT setting, So i think I am chasing ghosts with this and will just build the box and be careful.
      Thanks Again

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