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If Xmax shouldn't be exceeded, why have a Xlim?

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audiomik View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2011 at 10:44pm
Interesting idea - but it will do nothing much in terms of addressing IMD products!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wayward91 Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2011 at 11:21pm

Well. Interesting reading. all I can add it that in my opinion a speaker is (usualy) designed or should be designed to reproduce a sound and not alter it. I kinda destroyed a speaker quite badly (shown below) so i wouldn’t purposely aim to over extend a driver on a regular basis. To me it seems to be asking for trouble.  Smile









Edited by wayward91 - 01 March 2011 at 11:21pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S DeXter Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2011 at 12:36am
Originally posted by wayward91 wayward91 wrote:

Well. Interesting reading. all I can add it that in my opinion a speaker is (usualy) designed or should be designed to reproduce a sound and not alter it. I kinda destroyed a speaker quite badly (shown below) so i wouldn’t purposely aim to over extend a driver on a regular basis. To me it seems to be asking for trouble.  Smile



A case of exceeding Xmech... not xmax...! Smile
Enjoy your self...... It's later than you think.......
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audiomik View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2011 at 1:26am
Think there could be something here worth considering which comes from early mathematical models of the 'ideal' Horn loading for a cone loudspeaker and still holds true today.

This is that the ideal loading for a driver occurs with zero cone movement as it models as the ideal drive condition since the throat coupling volumes remain constant.

Now we know that in the real world this isn't very practical; but to best match our driver to our horn loading then the cone displacement should be as small as possible to achieve a result closest to the theoretical ideal....

For greater deviation from this ideal, distortion rises whilst when exceeding Xmax, distortion rises substantially more.

So rather than trying to extract the 'maximum' from a single driver/cabinet design; the use of multiple under-driven cabinets are the better solution in terms of the system being capable overall of reproducing the original program source whilst minimising 'colouration' of the original program material it is reproducing....

Ok - other factors apply but the principle is valid as posted by others in this thread earlier
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Post Options Post Options   Thanks (0) Thanks(0)   Quote greeef Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2011 at 3:38am
Originally posted by snowflake snowflake wrote:

as below 200Hz the human ear rapidly loses sensitivity (at 24dB/octave I think) a couple of percent distortion will make the perceived sound twice as loud.


The rate of sensitivity loss varies with loudness. At home listening/conversation levels your figure is probably accurate, but as the system gets louder, the response flattens out. 

fltcher munson contour

I wouldn't trust this to the letter, there are a lot of different equal loudness contours out there, but they all show the same theme, a (erm...) less reduced sensitivity to bass notes as a sound becomes louder.

In my view, distorted bass usually sounds quite brash and undynamic (compressed). I prefer a subtle, understated bass tone that you feel rather than hear, but i listen to poncey music a lot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2011 at 5:48am
Originally posted by greeef greeef wrote:

I wouldn't trust this to the letter, there are a lot of different equal loudness contours out there,


That old Fletcher-Munson chart is extremely inaccurate, with the current standard being ISO 225:2003 - see here and here.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 26 April 2014 at 11:23am
this thread was interesting to read : )

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Post Options Post Options   Thanks (0) Thanks(0)   Quote fourway hornloaded Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2014 at 8:34pm
(a bit of a trhead hack, but it's on Xmax and i thought it appropriate to post this here)

The other day I replaced one of my beloved PD186 that had started scratching (for whatever reason?) and put in an 18Nd9300, which is a neo version of 18LW1400. Similar T/S, checked for plausible response and mech. movement using hornresp. I'm used to giving my bass bins 500 Watts each whole night long, so they should move about 8...10 mm in each direction which has proven totaly fine. Not too much power here.

Now what happens: that particular bin with the neo driver beats like it's hitting something. But only on high excursion, on loud drum beats. It was in parallel to a PD186 that had no problems. Turning down that particular amp by ~6dB cured the problem.

Do I just have a bad one? It's second hand, but I tested it with a tone generator, no scratching even at large displacement wo I thought it should be fine.

The 18Nd9300 is one of those 'new' drivers with 15mm gap and 24mm coil winding height. PD186 is one of those 'old' drivers with 8mm gap and 24mm vc. But then they promise similar Xmax figures and some say that having a less steep BL-curve leads to a larger controlled displacement anyway. There's also the DDS spider, where the PD has an 'old fashioned' double spider.

Has anyone had similar experience with 'modern' drivers?

Thanks in advance,
Robert





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2014 at 8:45pm
Yup. It's the cooling air noise when it exits from the plateset.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2014 at 9:44pm
If you really want to know the answer, measure the TS Parameters of both drivers in question. You are overlooking many things that play a factor on how the loudspeaker is reacting in the box. Measure the TS Parameters of both drivers.

Best Regards,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark James Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2014 at 9:49pm
also i may be well off here but if you sim in horn response say for example a stack of four identical cabs versus say 8 identical cabs same power per driver the 8 stack suld have lower excursion at same power input and acoustic output levels???? what im suggesting is with te stack feauturing alot of pd186 tat you are comparing to a single 18sound wich may not be coupling up with the oter bins maybey thats causing te driver to go over xmax? JUST a thought though can you say load four 18 sound and compare to 4 pd?????
me so horny me love you long throw
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fourway hornloaded Quote  Post ReplyReply Direct Link To This Post Posted: 28 April 2014 at 10:53pm
thanks!

@Pasi: Maybe that's why they discontinued a seemingly sound driver? 15"ers and a 12"er are still available with the same magnet structure that the 18Nd9300 has, but no 18"er.

@Elliot: Point taken, i did not measure T/S. Still, such entirely different behaviour is a little bit unexpected, judging the datasheets, isn't it? 500W in any enclosure that properly loads the driver should be ok with this type of driver (35Hz HPF was set, just plain-old techno beats on and on). In the end of the day, the Nd9300 is quite high-tech compared to PD186 and you wouldn't expect 18sound to totally screw up the datasheet, would you? (I admit that PD kind-of did exactly that).

@Mark: They were in 3 stacks of 2 bins each, with only half a meter between stacks. So that shouldn't have been the problem. I'm going to have to do what you suggested though: have a direct stacked comparison between drivers. Because if this behaviour is structural, I can't use such drivers. Hopefully just one bad driver.

I must say I do like this forum for the type of discussion you can get here. Thanks again. This might also be interesting regarding the recent change of T/S on the much-used PD186.

Is there anyone else who can comment on 'new-fashioned' drivers, say 'P300 or 'LW1400 against PD186?

regards, robert
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