# xmax or linear excursion?



## ALL OR NOTHING (Mar 9, 2008)

from my understanding, the higher the efficiency the driver the less xmax(throw) the speaker produces. right? here's the problem... i'm highly interested in the Hertz hv 200 8" midbass drivers. on the data sheet they look perfect for compresion drivers. when i looked at the excursion they look pretty weak compare to the dynaudio mw172's. the mw172's are 9mm and the hertz hv 200's are 5mm. is the hertz being tested at 1 way linear excursion or is the dynaudio 2 way? i see the dynaudio said max excursion at 15mm. i'm kinda concerned because i don't want an 8" driver that is super loud as hell that doesn't produce some serious midbass. i remember those older kicker shallow mount 8"... those drivers had zero midbass but were loud as hell....

these hertz 8"s look a lot like a pro audio driver... spec wise...

http://www.hertzaudiovideo.com/Doc/pdf_hv200.pdf

http://www.dynaudio.com/eng/auto/esotec/tech_mw172.htm


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## ALL OR NOTHING (Mar 9, 2008)

moving down... please read and respond, if you want


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## 89grand (Nov 23, 2006)

See to me, I would think xmax would have a lot to do with midbass output.

A number of people have said it's not important, but a speaker has to move to produce sound, and the louder it gets the more it has to move and the lower it gets, it has to move even more. Using that logic, I would think xmax does matter quite a bit.

I could be wrong about this, since some people say xmax doesn't matter much. I just can't seem to grasp how it's possible that a low xmax speaker can get loud and low.


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## Abmolech (Nov 2, 2006)

Sensitivity is motor strength (BL) versus mass (principally mass surface area of the cone)

You can have a strong motor and higher surface mass cone, and this will allow a smaller volume enclosure at the expense of sensitivity.

Conversely you have a weak motor and low surface mass cone, which requires a large volume enclosure, which has high sensitivity.

Xmax should be rated a 70 % of the BL strength. IE how far it can more before the BL force has dropped by 30 %.
It is considered the maximum distance the motor should move the voice coil while still having some degree of control. (NOTE at 70 % BL the motor requires TWICE the wattage as it does at 100 %).
Beware, manufactures have different ways of measuring xmax, and you may not be comparing drivers on the same playing field.

Look at the VAS (suspension compliance versus air compliance) to help you decide if the sensitivity is real. IE high VAS and sensitivity indicates real world figures.

xmec is the total amount of movement before you hit the backing plate with the voice coil. Anything above xmax is bad.


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## ca90ss (Jul 2, 2005)

Hertz listed xmax is 1 way while the Dyn's are listed p-p.


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## ALL OR NOTHING (Mar 9, 2008)

ca90ss said:


> Hertz listed xmax is 1 way while the Dyn's are listed p-p.


thanx...

just talked to one of jeff smith's installers, he said something about the hertz space 8". they cost 500 more bucks than the hv200's. i figured they cost more because space 8"s are more installer friendly. i need to pull the specs up on those space 8"s


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## ~thematt~ (Sep 14, 2007)

ALL OR NOTHING said:


> from my understanding, the higher the efficiency the driver the less xmax(throw) the speaker produces. right?


Nope. They're not actually directly related. 

Efficiency is basically how much power it takes to do work. 

Xmax is more how stiff the suspension is for the speaker to reach a limit with a certain amount of power. 

Volume of output is based purely on cone area and movement. No efficiency at all. You want lots of midbass? Buy a large cone that moves a lot. 

Or a larger cone that moves less. 
To compare, work out the Vd or volume displaced. Its simply cone area times one way xmax. Lets say the Vd of the dyn is 400cubic cm, and the Hertz is 500cubic cm. 

The hertz is louder in the same frequency band. Efficiency will tell you how much power you need to get it there.


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## solacedagony (May 18, 2006)

Abmolech said:


> Xmax should be rated a 70 % of the BL strength. IE how far it can more before the BL force has dropped by 30 %.
> It is considered the maximum distance the motor should move the voice coil while still having some degree of control.
> 
> xmec is the total amount of movement before you hit the backing plate with the voice coil. Anything above xmax is bad.





~thematt~ said:


> Nope. They're not actually directly related.
> 
> Xmax is more how stiff the suspension is for the speaker to reach a limit with a certain amount of power.
> 
> ...


Like Abmolech said, xmax is simply the distance a cone can move before losing 30% BL strength (assuming that's how the manuf made that measurement). There's no power measurement at all since box volume (and tuning) will change the amount of excursion your driver will use.

Remember that the lower you want your driver to play, the more xmax you're going to need. Higher efficiency will help you to get more output out of your driver without having to drive it as hard (read: less distortion).

Also consider that these are small signal parameters. What you're actually getting at 50W of power may not correlate directly.


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## St. Dark (Mar 19, 2008)

Abmolech said:


> Xmax should be rated a 70 % of the BL strength. IE how far it can more before the BL force has dropped by 30 %.



I had it in my head for some reason that it was the distance one way a cone could travel while keeping an equal number of windings in the coil. Dunno where that came from, but the definition you supplied makes sense from the standpoint of other things I've heard.
Thanks!


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## Neil (Dec 9, 2005)

~thematt~ said:


> Nope. They're not actually directly related.


Well, that is pretty debatable. Generally speaking, yes, you do lose efficiency as you increase Xmax. There is a reason that we don't see 10+mm Xmax 6.5" drivers with 95+ dB efficiency.



~thematt~ said:


> Efficiency is basically how much power it takes to do work.


Can also be looked at as how much output with a given input...same general concept, though.



~thematt~ said:


> Xmax is more how stiff the suspension is for the speaker to reach a limit with a certain amount of power.


I wouldn't say Xmax is that at all....Xmax is the smaller of Xmag and Xsus; both the suspension and the motor are key here.



~thematt~ said:


> Volume of output is based purely on cone area and movement. No efficiency at all. You want lots of midbass? Buy a large cone that moves a lot.


Not completely true either. Efficiency plays a very key role in output with a given input, particularly above 80-100 Hz.

Displacement is good, but so is efficiency; a lot of displacement is useless if it is not efficient enough to use it before melting the coil.


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## Neil (Dec 9, 2005)

St. Dark said:


> I had it in my head for some reason that it was the distance one way a cone could travel while keeping an equal number of windings in the coil. Dunno where that came from, but the definition you supplied makes sense from the standpoint of other things I've heard.
> Thanks!


That used to be the standard. Generally speaking, for overhung drivers it was (Voice Coil Height - Top Plate Height)/2. For underhung, it was (Top Plate Height - Voice Coil Height)/2. It was realized after this that considerable flux lies in the fringe field (the area just above and below the gap) and that it was possible for BL to remain linear even as windings leave the gap. So the generally accepted value for Xmag in subwoofers is 70% BL; mids are typically more tightly regulated as the distortion is more audible (ie. Voice Coil mag uses 82% BL).


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## ALL OR NOTHING (Mar 9, 2008)

DevilDriver said:


> That used to be the standard. Generally speaking, for overhung drivers it was (Voice Coil Height - Top Plate Height)/2. For underhung, it was (Top Plate Height - Voice Coil Height)/2. It was realized after this that considerable flux lies in the fringe field (the area just above and below the gap) and that it was possible for BL to remain linear even as windings leave the gap. So the generally accepted value for Xmag in subwoofers is 70% BL; mids are typically more tightly regulated as the distortion is more audible (ie. Voice Coil mag uses 82% BL).



i get it now... my choices are....

1. high xmax driver low efficiency , requires booko power
2. decent xmax high efficient driver, high spl less power

the question is... if you want high spl, good midbass, sound clean... whick drivers to pair up compression drivers?


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## 89grand (Nov 23, 2006)

How about some Hybrid L8's?


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## Neil (Dec 9, 2005)

To pair with compression drivers, you need to find a driver that is highly efficient with enough Vd for low frequency output. That is most likely to come from a large driver (8" or larger) but these are pretty hard to integrate in a vehicle. You could also go with a dual 6.5" or dual 7" approach, but that takes a little more care and electronic compensation.


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## chad (Jun 30, 2005)

One thing people refuse to do is look at how much power they have and decide how loud something will get with that power regardless of excursion, too many people get caught up in that spec (Xmax). Also remember that the more power you toss at something the more power compression you will have to deal with generally AND the more sag you will encounter with the vehicles electrical system. Also remember that you are getting into an area where transfer function helps tons, so an anechoic sensitivity can generally be assumed higher for the "bass in mid-bass"

So pick a point in the mid-bass region, look at the sensitivity and plug it in to Sens+10LogPower, then decide which driver suits your needs more while ignoring X-Max figures but yet comparing drivers, if the higher sens one just gets nudged out by a tad, I'd still shoot for that one.

Xmax can actually harm you in terms of fidelity, remember where they are playing up to, 250-350 maybe, you don't need huge x-max for that so at the same time a really inefficient driver is stroking like crazy, remember it has to modulate the upper frequencies on top of that, think inter-modulation distortion.


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## St. Dark (Mar 19, 2008)

DevilDriver - thanks for the additional info.



dang, been here only a few days and already done learned something.


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## St. Dark (Mar 19, 2008)

chad said:


> so at the same time a really inefficient driver is stroking like crazy


I'm with you on most of that post- but the part I quoted. For a given size of driver, playing at a given frequency and a given volume, wouldn't less efficient speaker A be moving the same amount as more efficient speaker B? Just consuming more power to do so?


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## ALL OR NOTHING (Mar 9, 2008)

i'm learning too much here... my hat doesn't fit anymore


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## T3mpest (Dec 25, 2005)

St. Dark said:


> I'm with you on most of that post- but the part I quoted. For a given size of driver, playing at a given frequency and a given volume, wouldn't less efficient speaker A be moving the same amount as more efficient speaker B? Just consuming more power to do so?


For a speaker to cause a given pressure change at a given frequency it requires it to displace a given amount of air. At lower frequency, where the cone is movign less times/second, it needs to either be a large cone or move very far at each trip. For each time you drop 1 octave (1/2 your given frequency) you need to displace 4x the amount of air to keep the same pressure variation.

The opposite is also true, as frequencies increase, the excursion needed to reach a given SPL drops, becuase the cone is moving many more times per second. again, for each doubling of an octave, we need 1/4 the excurison. THis is why effeciency is important. For each time we double power, we gain 3db's. This is because the speaker cone moves further, increasing displacement. A given effeciency tells us, essentiall, how far a speaker is moving with a given amount of power. Let's say we have two tweeters, one rated at 88db's another at 91db's. The 91db moves 2x as far as the 88 with the same amount of power applied. Meaning if we put 100 watts on each of them, assuming neither driver runs out of excursion, the 91db driver will be louder, it's still moving further. The key here is that the tweeter will rarely run out of excursion 1/2 an inch is a good distance to move when you doing it 10,000 times a second. The limiting factor in higher frequencies is the amount of power you can apply, or moreover, the effeciency of the driver.

If your tweeter has 3/4 an inch of excursion, it'll never it if it's playing up high. The fact that it is 88db's effecient will limit it's output, given an RMS wattage. Let's say it can handle 128watts. That's 109db's of max output, that probably requirs less than 1/3 an inch of excursion. 


That's why effeciency is important. A hlcd can easily have 109db of effeciency, 1 watt of input!! It might only have say 1/2 an inch of excursion, but that's not our limiting factor here. The fact that the 88db tweeter can move further doesn't matter, it can't handle the power needed to reach the excursion it's capable of.

Now some would say, oh well, powers cheap, just throw a big amp on it, we'll use that 3/4 of an INCH! The issue here is power compression. As the coil heats up impedence rises. We now have a driver that while the power is going to the coil, it's not causing a direct change in the strength of the magnetic field. Most of the energy is simply going towards heat. Again,it gets'hotter, and we have an viscious cycle. Lots of heat, no real change in excursion. In SPl based events competitiors have actually tripled or quadruples power only to see less than 1db of gain. 

Midbass frequencies, true midbass, not subass from your mids, tends to be power and effeciency limited. Just a couple inches of xmax is enough for stupidly painful levels at 150hz, assuming your midbass can handle the power it needs to reach that excursion level at that frequency. Again,it's not alot of distance to move, a lighweight driver that can do it with only a little bit of power is at the advantage here.


With all that said, your absolutely right. If each speaker is reaching the same SPL at a given frequency and they are the same size, then they did move the same amount as well. The key was how much power it took to get there, which as I just noted above, can be a very imporant thing. If you saturate the coil to move that relatively short distance, then no amount of overhang is going to help you.


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## ALL OR NOTHING (Mar 9, 2008)

T3mpest said:


> For a speaker to cause a given pressure change at a given frequency it requires it to displace a given amount of air. At lower frequency, where the cone is movign less times/second, it needs to either be a large cone or move very far at each trip. For each time you drop 1 octave (1/2 your given frequency) you need to displace 4x the amount of air to keep the same pressure variation.
> 
> The opposite is also true, as frequencies increase, the excursion needed to reach a given SPL drops, becuase the cone is moving many more times per second. again, for each doubling of an octave, we need 1/4 the excurison. THis is why effeciency is important. For each time we double power, we gain 3db's. This is because the speaker cone moves further, increasing displacement. A given effeciency tells us, essentiall, how far a speaker is moving with a given amount of power. Let's say we have two tweeters, one rated at 88db's another at 91db's. The 91db moves 2x as far as the 88 with the same amount of power applied. Meaning if we put 100 watts on each of them, assuming neither driver runs out of excursion, the 91db driver will be louder, it's still moving further. The key here is that the tweeter will rarely run out of excursion 1/2 an inch is a good distance to move when you doing it 10,000 times a second. The limiting factor in higher frequencies is the amount of power you can apply, or moreover, the effeciency of the driver.
> 
> ...


now my ****in football doesn't fit... thanx for the info

i guess people would rather spend money on power than a high efficient driver. those hertz hv 200 8"s are 94db with 5mm xmax 1-way. i think i'm gonna go with these...


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