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Old 26th August 2012, 05:02 PM   #1
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Default So how important is xmax?

Im thinking about all the sighing that goes on over drivers with small xmax and its limitation of output.

i'm thinking of an instrument like a cello, how much is its xmax? They get pretty loud!

Or a violin? Heck a clarinet has an xmax of 1mm so an xmach of 2mm and they get LOUD! I know i played one.

Bass clarinet plays down to 35hz or so and has an xmax of 1.5mm, its horn loaded i know.

Hey im gonna do a horn resp layout of a bass clarinet. Its front loaded wit a back chamber of about 5cc, and s1 of 25mm2 and an s4 of about 5525mm2. As for the transducer properties its numbered stiffness bamboo reeds so pick a compliance and giver! I think the thing is about 1.5m long if my memory serves me.
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Old 26th August 2012, 05:45 PM   #2
tvrgeek is offline tvrgeek  United States
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Pleas quit speculating and go read real physics. Even a free program like WinISD will show you some nice and easy to understand charts.

You also need to consider the DISTORTION. This depends on motor design. Many drivers Xmax is way past their linear operation. Has it occurred to you that if it was only about Xmax that all speaker would be an inch across and eq'd to flat?
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Old 26th August 2012, 06:08 PM   #3
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Sigh.

Xmax is a value given to moving coil loudspeakers. It is simply an attempt to describe / indicate the linear operating range of the motor, or powertrain as it is probably more accurately described. However, there is no universal derivation.

Probably the most popular method, or at least the most consistent, is to measure a drive unit under load, and set Xmax as the point at which it reaches 10% THD.

An alternative method, which does not require measuring the driver, is to take the absolute value of the magnetic gap height minus the height of the VC winding & divide that by 2. Unlike the above, this does not set Xmax to any one particular value, since motor designs vary dramatically and this has a significant effect upon drive unit linearity. There have been several other suggestions for setting a value on linear operating range too, if memory serves.

As a general rule, manufacturers rarely state the method / criteria they used to establish the figure given in their datasheets. Therefore, IMO the exact numerical value listed should be viewed as part of a wider context, and it is arguably less significant than the general indication it provides, i.e. it may assist in narrowing down a list of possible options for a given application.

Last edited by Scottmoose; 26th August 2012 at 06:22 PM.
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Old 26th August 2012, 06:11 PM   #4
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Not quite sure of what your asking.

im sure that within its xmax most drivers exhibit minimal distortion.

I know that the sound of a clarinet changes drastically if you overblow.

What aspect of physics would clarify my understanding, being specific.

Im also aware that most of the sound, 70% perhaps, is composed of harmonics.

Ah well i kind of forgot where that whole thread came from anyhow.
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Last edited by Etocynned; 26th August 2012 at 06:13 PM.
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Old 26th August 2012, 06:27 PM   #5
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Quote:
im sure that within its xmax most drivers exhibit minimal distortion.
Not necessarily. As I noted above, there is no single definition for Xmax. One of the most popular ways requires the drive unit to be measured, and sets Xmax at point at which 10% Total Harmonic Distortion (THD) is reached. That is at least a consitent method, although note that a driver may be at anything up to 9.999% distortion below this point.

Another purely mathematical method of providing a figure that can be called Xmax does not set it to a specific distortion figure at all, so unit X may be at 10% THD at the value obtained, while unit Y would be at 5% THD, and unit Z could be at 40% THD.

Last edited by Scottmoose; 26th August 2012 at 06:34 PM.
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Old 26th August 2012, 07:18 PM   #6
tsiros is offline tsiros  Greece
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your thought/question can be summed up as:

"how can a bass clarinet/cello produce 35Hz so easily while a speaker can't?"

well

one is a musical instrument

the other is not.

the musical instrument does not reproduce sound. It produces sound. The sound you hear is "distorted" (one would say). It can not produce any kind of sound. It can produce only that specific sound.
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Old 26th August 2012, 08:08 PM   #7
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Quote:
Originally Posted by tvrgeek View Post
Pleas quit speculating and go read real physics.
Geez, give him a break. He's just posting a theory, not spreading lies.

To the OP......
You need more excursion with small radiating surfaces, because they can't rely on the characteristics of the actual instrument.
Things like resonating of panels and such, like a piano. Sure, they are just strings but, they are exciting the whole instrument. This moves more air than the string itself.
Or like you said, the horn loading of a ummm......a horn
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Old 26th August 2012, 09:16 PM   #8
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a titanium 'reed' in an oboe or clarinet would be a totally different instrument, but probably a great experiment, also likely a poor instrument. . The goals of an instrument and a reproducer are obviously at the opposite ends of an imagimary scale. One end being to maximise colouration and give timbre, colour tone etc. The other end being to minimise harmonic distortion.
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Old 26th August 2012, 09:22 PM   #9
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cone excursion behavior can vary in the passband under transient conditions, from beat-tones between instruments or a bass instrument's fundamentals and harmonic content, enclosure type and its input impedance valley(s) placement/magnitude and Z below the passband. Sometimes a longer xmax driver such as W8-1772 will do less useful work and behave worse than say FE206EN as the Tangband has lower average impedance and draws more current below the useful range of the enclosure. I've seen drivers such as Nirvana Super10 in a 70 liter 41Hz tuned reflex go chaotic. Use of better loading such as a Karlson coupler will keep things under control longer.

one rough estimate of xmax is by the 70% BL point (Lc - Hg)/2 + 1/4(Hg) = x-max (70% Bl)

if a driver is seen moving much at a high overall rate then it can "gargle" which is highly disconcerting - even 15" coaxial will gargle on some material at modest listening levels.
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Old 26th August 2012, 09:33 PM   #10
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Etocynned View Post
e.

Bass clarinet plays down to 35hz or so and has an xmax of 1.5mm, its horn loaded i know.
yes, its horn loaded
try without, and blow just the mouth piece
you know it sounds like a duck


hmm, thinking about adding compressed air to a horn speaker

playing a horn instrument, the 'air blow' is always in the same direction
but when a woofer reproduces its sound it will move both back and forth to do it funny stuff
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