Low xmax vs. high xmax??

[Steveopevo 10+ year member]

I've been trying to educate my self by reading and tend to find unclear answers about the pros and cons. Some say high xmax means more spl, and some say not necessarily. Some say it's allows better low frequency extension. Wheras low xmax is better for SQ. I've noticed brands like Hertz, DLS, and Focal are low xmax (9mm). My Polk mm's are (7mm) one way.

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[double 07 10+ year member]

My AA Havocs have 32mm and they get super loud and sound amazing while doing so. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[murph 10+ year member]

I've been trying to educate my self by reading and tend to find unclear answers about the pros and cons. Some say high xmax means more spl, and some say not necessarily. Some say it's allows better low frequency extension. Wheras low xmax is better for SQ. I've noticed brands like Hertz, DLS, and Focal are low xmax (9mm). My Polk mm's are (7mm) one way.

I believe you are talking about speakers not subs with those xmax sizes. Anyways higher xmax is usually ideal and all cases whether you want sq or spl. Higher xmax leads to lower frequency extension and more output throughout. I would not focus your options based on xmax, but would consider it on my choice.

 

[Kangaroux 5,000+ posts]

There are so many factors and variables there really isn't anywhere to start explaining because, frankly, it would be an answer that is pages and pages long. But I'll try and cover some basics. SQ and low xmax go well together for a couple of reasons. 1. Because SQ drivers aren't made to get very loud, they are designed to be accurate, so high xmax isn't an extremely necessary thing to have (keep in mind high xmax does NOT always equate to loud). 2. The higher the xmax of a driver, the harder it is to make sure the movement of everything remains linear once the driver starts to reach its limits. Here's a bad analogy of what I mean: is it harder to ride a bike in first gear and have to peddle very fast and uncontrollably, or is it harder to have it in 4th or 5th gear and have a much more smooth motion.

High motor force drivers by nature are great at SPL because of their ability to force the cone back and forth dare I say, violently. High xmax drivers on the other hand don't usually incorporate strong motors, because instead of relying on a strong magnetic force to generate SPL, they rely on moving a lot of air. Because of this, high xmax subs are great for setups that are geared towards moving a lot of air and, consequently, doing great on low end authority (also keep in mind that high xmax does NOT automatically mean the sub will do great on low notes. This is a combination of many other factors as well as the enclosure it is in).

 

[LosIsATool 5,000+ posts]

There are so many factors and variables there really isn't anywhere to start explaining because, frankly, it would be an answer that is pages and pages long. But I'll try and cover some basics. SQ and low xmax go well together for a couple of reasons. 1. Because SQ drivers aren't made to get very loud, they are designed to be accurate, so high xmax isn't an extremely necessary thing to have (keep in mind high xmax does NOT always equate to loud). 2. The higher the xmax of a driver, the harder it is to make sure the movement of everything remains linear once the driver starts to reach its limits. Here's a bad analogy of what I mean: is it harder to ride a bike in first gear and have to peddle very fast and uncontrollably, or is it harder to have it in 4th or 5th gear and have a much more smooth motion.
High motor force drivers by nature are great at SPL because of their ability to force the cone back and forth dare I say, violently. High xmax drivers on the other hand don't usually incorporate strong motors, because instead of relying on a strong magnetic force to generate SPL, they rely on moving a lot of air. Because of this, high xmax subs are great for setups that are geared towards moving a lot of air and, consequently, doing great on low end authority (also keep in mind that high xmax does NOT automatically mean the sub will do great on low notes. This is a combination of many other factors as well as the enclosure it is in).

High Xmas does always equal moving air either. Look at the W7, high Xmas and don't really move air. But they do pick up the low end strong. Like you said, you can go on all day. That is only one spec of many that have to line up.

 

[quackhead 10+ year member]

IMO, way overrated in most cases. But like murph says, I do consider it, along with BL, pe, sensitivity,mms....some always seem to sacrifice in one area to compensate for another.

 

[Julian 10+ year member]

You should not look at only one spec when buying a woofer.. People nut over a single spec but end up ignoring the other T/S parameters, If you are looking to compare I personally would model it up in winISD and go from there.. It will give you a level basis in comparing speakers but you have to realize when you put that same speaker in a car the specs may change.

 

[Steveopevo 10+ year member]

I believe you are talking about speakers not subs with those xmax sizes. Anyways higher xmax is usually ideal and all cases whether you want sq or spl. Higher xmax leads to lower frequency extension and more output throughout. I would not focus your options based on xmax, but would consider it on my choice.

Believe it or not these xmax ratings are subwoofers listed on there websites. My Polks are listed as 25mm, but that is actually xmech.

 

[quackhead 10+ year member]

High Xmas does always equal moving air either. Look at the W7, high Xmas and don't really move air. But they do pick up the low end strong. Like you said, you can go on all day. That is only one spec of many that have to line up.

let's see ..a 20hz wavelength is 56 feet long...

 

[THATpurpleKUSH 5,000+ posts]

high xmax doesnt mean shit if you can't keep the coil in the magnetic field.

Not to mention xmax is measured differently by every company out there. The best measurements are usually done with the coil in no less than 70% of the magnetic field one way.

 

[itsblown 10+ year member]

I feel like xmax is a loaded questions because of what kushy dreams said. Think about it. If you have a small *** voice coil it is going to be able to move farther within the magnetic gap then a larger voice coil before having mechanical issues. As to what Kangaroux said I tottally agree with larger voice coils lower xmax for complete controll over the cone. Thats why some of the best sound quality woofers in the world utilize such a large voice coil. For example the Morel ultime with a 5.1 inch voice coil.

 

[quackhead 10+ year member]

stepping outside the car for a minute..some of the loudest and best sounding concerts use subs with large vc and >15 mm xmax on kw's of power each..in multiples, of course.

 

[sundownz Pro Seller]

The question of how much x-max you need really depends on the application... often times in a ported box the highest x-max is not necessary as the port reduces excursion at tuning and 1/3 octave in either direction. For example... tuning to 30 Hz reduces cone excursion from 25 Hz to 40 Hz quite a bit. In a sealed box it becomes much more important.

You really want the RIGHT amount of x-max for your power rating and box application... in development of the SA-8 v.2 we measured full bandwidth SPL in the suggested enclosures from 25 to 80 hz. If we made the coil any longer (for more x-max) we lost output across the board at at rated or even 20% above rated power. We tried four different lengths -- the settled upon length and thus x-max offered the best output across the board at the rated power levels. So there is no reason to "fluff" the spec sheet with a super high linear x-max if all it does is REDUCE output at any reasonable power level.

These days with super powerful amps readily available it is pretty amazing how much people can get a sub to full excursion even AT tuning... for instance in my Jeep SPL box I can bring an NS v.2 to full surround limits of about 38mm or so one-way AT box tuning of 53 Hz (156dB). Allowing more movement would increase it's SPL potential -- in this case it would take a new surround / spider to do that (which I am working on).

 

[T3mpest 10+ year member]

The question of how much x-max you need really depends on the application... often times in a ported box the highest x-max is not necessary as the port reduces excursion at tuning and 1/3 octave in either direction. For example... tuning to 30 Hz reduces cone excursion from 25 Hz to 40 Hz quite a bit. In a sealed box it becomes much more important.
You really want the RIGHT amount of x-max for your power rating and box application... in development of the SA-8 v.2 we measured full bandwidth SPL in the suggested enclosures from 25 to 80 hz. If we made the coil any longer (for more x-max) we lost output across the board at at rated or even 20% above rated power. We tried four different lengths -- the settled upon length and thus x-max offered the best output across the board at the rated power levels. So there is no reason to "fluff" the spec sheet with a super high linear x-max if all it does is REDUCE output at any reasonable power level.

These days with super powerful amps readily available it is pretty amazing how much people can get a sub to full excursion even AT tuning... for instance in my Jeep SPL box I can bring an NS v.2 to full surround limits of about 38mm or so one-way AT box tuning of 53 Hz (156dB). Allowing more movement would increase it's SPL potential -- in this case it would take a new surround / spider to do that (which I am working on).

Very good post.. Xmax is only important if the design you'll be using runs out of it.. Xmax in general is when a subs moves far enough that it loses 70% of it's BL value when vs when the coil is centered. Keeping within this range is important. First reason is ANY drop in BL is a loss of motor force, hence loss of effeciency. The further the coil can move without losing BL the more effecient the subwoofer is (not effeciency in the "rated" sense, but TRUE effeciency".. Also any loss of BL is a form of non-linear distortion and is generally the highest contributor to a subs distortion. If your going past xmax your making the sub have more distortion and putting more power to the coil for less actual speaker output, BL compression is very real and hardly EVER talked about

Secondly, SPL is ALWAYS about displacement.. The further a speaker canmove the louder it will be all things equal.. SPL subs may have smaller xmax ratings, but they have alot of motor force.. Xmax only says how far a coil can move before it loses BL.. If you don't have enough BL to move the cone that far without frying the coil in the first place then it's USELESS.. Most SPL subs have high BL for this reason. They can overcome the ports damping effect near tuning. A SQ sub with 35mm of xmax but very little BL can't do that in many cases, hence alot of people think SPL has nothing to do with xmax. However, since a high xmax limits BL compression, it's actually a good thing even for an SPL woofer. Once you can hit the supsension limits of a subwoofer near tuning, you've effectively maxed out how loud the box is. You can't generate any more air movement at that frequency by adding more power.. The less power you need to do this the better off you are.

Anyway some things said by certain people in this thread really isn't true.. A high xmax is good for a SQ woofer. The woofer can move further, meaning it can play lower, with less BL compression and do so with less distortion than a low xmax woofer... Xmax is king in a sealed design and many times SQ designs used sealed drivers (not a great idea in my opinion either, but it does happen). High xmax drivers are generally well controlled beyond xmax as well. At worst we can say, they are better behaved at any displacement before any driver with a lesser xmax, hence the lower xmax. Beyond xmax is when a speaker begins to lose composure, by definition it's 70% BL or 10% distortion, whichever comes first, with 70% being 10% thd in most cases... Some designs like XBL^2 for example actually are VERY linear in BL and VERY nicely behaved beyond it.. XBL^2 drivers BL drops like a rock after 70% BL, but exhibit almost no loss through 90% of their stroke. Meaning a woofer that can move 32mm would have basically NO TSP changes until 25mm or so.. Beyond 25 it slowly loses a bit of BL until 32.. Right at 32 it's nearly impossible to even get the driver to go beyond xmax as it's losing BL so fast it can't move any further.. That's why you never see any brahmas or XXX's with mechanical damage.. It's too hard to make them bottom or even go outside of their comfort zone.. They sound fine no matter how much power you put on them until you smoke the coil lol..