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Author Topic: How bad is it to exceed the Xmax on a woofer?  (Read 27549 times)

Art Welter

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #20 on: January 06, 2009, 02:58:34 AM »

Elliot,

Sounds to me that the mechanical failures that you described would have happened even faster without a high pass.

They were caused by not having enough rig for the gig,(and/or too much power in the hands of idiots) unless you are suggesting that those rigs were capable of reproducing music at a decent level with “98% of your bass residing from 50 Hertz – down”.
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Elliot Thompson

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #21 on: January 06, 2009, 03:48:22 AM »

Silas Pradetto wrote on Tue, 06 January 2009 04:08



Well this isn't going to happen with these subs. First, I actually know what my subs are supposed to sound like, and I don't boost entire passbands when I know one frequency is lacking. I also employ RMS and peak power limiting with my amps. Second, I own 8 LAB subs, and if I need more bass, I have the weaponry.

I simply need a compact, lightweight, decent sounding drum sub/DJ monitor sub, and I HOPE these will fit the bill. The primary goal is to have plenty of bass within the first 10 feet or so of the subs to keep the drummers and DJs happy. I'll see on Thursday when the woofers arrive how the subs are going to work. Measured data will follow then.

Elliot, do you think you could explain some more about T/S parameters and what to look for in a sub driver? Or should I just search?



Providing you are babysitting you should be fine. You have the Lab Subwoofers as reinforcements if the DJs require more bass.

From past experience volume in the Mid-High section holds more value to them than a lot of bass especially if you have a large enough stack that can be easily heard where they are performing. Too much Bass creates a problem when they mix. Hopefully, the following will shed some light on what I mean.

In the summer of 2008, I provided a system for a small Rave. It was pretty simple. They brought their mixers, Turntables, and, Laptops while I provide everything else.

Since it was in a backyard I carried my smaller system, which comprise of six Double Fifteens getting around 7200 watts continuous and two tops being fed 1000 watts. The subs were lined up six across, right in front of their DJ Table. Throughout the event, they kept turning down the bass on their mixers. So, I asked them why are they turning down the bass in which I got no answer. I told them I brought more than enough bass so you can crank it up if you like, I don’t mind. I raised the bass back up (to flat) on the DJ mixer and walked away.

Around 5 minutes later, I hear the bass turned down again. I am assuming they are making a transition and going to raise it up shortly. However, it never comes to pass. So, I go over there and asked them why are turning down the bass? One of the DJs finally says, “The bass is too strong and, I can’t hear the music in the headphones.”

No problem! I walked over to the amp rack and turned two amplifiers off. The once six Double Fifteens offering 7200 watts turned into four boxes delivering 4800 watts. That made them happy. None of the DJs turned down the bass for the remaining hours of the event.

So as you can see, even DJs have a limit when it comes to bass. Laughing  

I always recommend this link to everyone getting into cabinet design.

http://www.speakerplans.com/index.php?id=faq1

If you have a specific question just let me know.

Best Regards,
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Elliot

Elliot Thompson

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #22 on: January 06, 2009, 05:23:10 AM »

Art Welter wrote on Tue, 06 January 2009 07:58

Elliot,

Sounds to me that the mechanical failures that you described would have happened even faster without a high pass.

They were caused by not having enough rig for the gig,(and/or too much power in the hands of idiots) unless you are suggesting that those rigs were capable of reproducing music at a decent level with “98% of your bass residing from 50 Hertz – down”.



It is combination of both although I wouldn't call them idiots. More to wards lack of understanding.

Many assume by high passing the subs they are fully protected and they can crank it as loud as they want without losing woofers to get the bass they turned down (50 Hz – below) back up providing the amplifier does not clip.

The next thing is get into situations where the system is not big enough assume, all they need to do is increase the volume and nothing will go wrong for the woofers are protected. Not understanding once the venue becomes full, human bodies absorb extra SPL from the sound bouncing around, they raise the fader even higher, launch their cones and wonder why there is no bass by the end of the event when the amplifiers never clipped. They always say “How could they be damaged, I never clipped the amp?”

Some may consider that comical. I’ve embarked 2-3 guys on a yearly basis for the pass fifteen years that fall into one of those categories and some of them are not new to the business.

Best Regards,


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Elliot

Art Welter

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #23 on: January 06, 2009, 04:21:50 PM »

Elliot,

Rog Mogale’s article you cited is good, but points out one of the measurement ambiguities noted in a prior post. Rog says:

“Note that the xmax figure is for one direction only, so an xmax figure of 5 mm means the cone can travel 5 mm outwards and 5 mm inwards past it’s resting place whilst still being under the control of the motor system.”

Then:

“Vd is Sd x xmax. It’s often overlooked but if moving lots of air at low frequencies is your game then you should know about it. I’ve put the parameter here after Sd and xmax because it ties in with both of these.”

Eminence specs the 4015 as Sd 872.9 cm square, Vd of 786 cc. The Xmax is rated at 9 mm (.9 centimeter)

872.9 x .9 = 785.61, rounded is 786 cc. Seems Xmax the way they measure, is peak to peak, or they would list the Vd as 1571 cc.

I know for a fact that the 4015 I have “clacks” at 16 mm peak to peak, and Eminence rates X lim at 15.5mm, so 9 mm for X max has to be peak to peak (the speaker physically won’t do 18 mm travel), which would only be a 4.5 mm X max the way Rog defines it.

TOA and JBL seem to follow the same convention as Eminence. It would be interesting to find out how other manufactures shows this important parameter, “no replacement for linear displacement!”

Looking at a B& C 15TBX100 driver, it lists “+/- 9 mm” for X max, but does not list Vd, so I can’t tell which way they figure.

Art
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Silas Pradetto

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #24 on: January 06, 2009, 10:58:24 PM »

Well if Eminence specs their xmax peak to peak, but xmax is defined as one-way travel, how does Eminence Designer interpret the spec? If Designer uses the definition of xmax it will be showing double the actual xmax of the woofer, meaning my excursion plots are wrong, and in reality, the woofer isn't even going to come close to the expected xmax and will handle far less power than I think.

Which means these woofers might suck.
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Elliot Thompson

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #25 on: January 07, 2009, 06:51:58 AM »

Art,

You would know better than I when it comes to Eminence Speakers for I own none. My Eminence experience stopped in 1995 so, I have no clue how Eminence measures out these days.

I used to use B&C when no one paid any mind to B&C (1996 - 1997) but have moved on to Beymas, RCFs, and Electrovoive.




Silas Pradetto wrote on Wed, 07 January 2009 03:58

Well if Eminence specs their xmax peak to peak, but xmax is defined as one-way travel, how does Eminence Designer interpret the spec? If Designer uses the definition of xmax it will be showing double the actual xmax of the woofer, meaning my excursion plots are wrong, and in reality, the woofer isn't even going to come close to the expected xmax and will handle far less power than I think.

Which means these woofers might suck.


Like I mentioned in my earlier posts, expect 700 watts per driver maximum before things start going downward. I didn't take xmax in account for it wasn't the limiting factor. It was the electrical side where power compression came into play before exceeding the xmax.

Eminence Designer offers all the information needed to understand the symbols in the Online Manual located in the Help section. Bare in mind Eminence Designer is Bass Box Lite, which is a stripped-down version of Bass Box Pro.

Here is the root of Eminence Designer's source. http://www.ht-audio.com/

Best Regards,

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Elliot

Art Welter

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #26 on: January 07, 2009, 03:56:03 PM »

Silas,

I don’t have any predictive software other than a calculator and formulas.

Here is what I measured outside using sine wave tones and a dB meter 10 meters from the source (didn’t have SMAART last winter..) so you can equate these to a real 1 watt 1 meter figure.

The voltage was  22.8@30 HZ to 26.3@160.  CD player with recorded tones, CA9  amp. Amounts to about a 1 dB loss in the bottom from the top, but is a 2 db drop from 28.3 volts, so these figures are a little lower in the bottom than they should be:

4015      25   30   35   40   45   50   55   60   70   80   90   100   110   125
3.4’38 FB   83   86   89   91   86   91   95   96   95   96   99   99   98   98
Excur      16   12   4   1.5   5   7   7   7   7   6   5   3   2   1.5   

You are doing 2) 2x15”, so add 9 db to the above figures for what they would do at 10 meters (100 watts) and another 20 dB to that for level at one meter and you see you can do 125 dB at 60 HZ with only 400 watts total into four 4015.

Using a slightly smaller box with a higher FB will also give you another couple dB.

Also, this is sine wave testing. As I said, with music, live or recorded, I have not seen anywhere near that much cone movement with around 500 watts.

Whether you think those levels “suck” I guess depends on what you are trying to do, with the amp you have you should be able to do in the 135 dB range for your DJ or drummer.
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Silas Pradetto

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #27 on: January 08, 2009, 07:12:11 PM »

I completed the subs today. First impression is they ROCK. I'm limiting with the I-Tech to 1000w RMS per pair with a 4 second attack and also limiting to 90 volts peak with a .01 second attack. They stay clean right up to the limiters.

Many measurements to come. Was getting about 110dBC at 50 feet today inside the shop.
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Elliot Thompson

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #28 on: January 08, 2009, 07:55:07 PM »

Silas Pradetto wrote on Fri, 09 January 2009 00:12

I completed the subs today. First impression is they ROCK. I'm limiting with the I-Tech to 1000w RMS per pair with a 4 second attack and also limiting to 90 volts peak with a .01 second attack. They stay clean right up to the limiters.

Many measurements to come. Was getting about 110dBC at 50 feet today inside the shop.



What you could do is play a mix Trance CD for 1 hour at those levels. If the woofers survive, they are DJ Ready Laughing


Best Regards,
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Elliot

Silas Pradetto

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Re: How bad is it to exceed the Xmax on a woofer?
« Reply #29 on: January 08, 2009, 07:57:16 PM »

Elliot Thompson wrote on Thu, 08 January 2009 19:55

Silas Pradetto wrote on Fri, 09 January 2009 00:12

I completed the subs today. First impression is they ROCK. I'm limiting with the I-Tech to 1000w RMS per pair with a 4 second attack and also limiting to 90 volts peak with a .01 second attack. They stay clean right up to the limiters.

Many measurements to come. Was getting about 110dBC at 50 feet today inside the shop.



What you could do is play a mix Trance CD for 1 hour at those levels. If the woofers survive, they are DJ Ready Laughing


Best Regards,



I was testing with Elvis Presley - Rubberneckin' (the Paul Oakenfold Remix). Talk about a bass track! My pant legs were flapping.

I also broke them in for an hour or so with a 20Hz sine wave.
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