SSD and xmax

[DUAL10S 10+ year member]

Just noticed the SSD's are back up. Anyway........

When looking at xmax: it is peak to peak unless noted as one way?

For example, JL15wo states 12.7mm one way linear (.50"). So would that be 25.4mm peak to peak? Sonic just states 12.7mm and the manual says one way linear.

Another example is Massive Audio Rebel 15 - Sonic and Massive states 20mm peak to peak.

And finally, the SSD stated 20mm xmax. I assume this is peak to peak.

Not nut hugging JL but if this is correct the JL has more linear xmax than the Massive and the SSD with less power?

I know there is more to it than xmax but when comparing subs I do take that into consideration. These subs are within $40 of each other and the xmax would not be the deciding factor here. As the SSD will take 1000w, JL 300w and the Massive 500w. 300w vs 1000w would be more noticeable than 5mm of xmax I would think.

Can be misleading if not digging for all the details.

Thoughts

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[Kangaroux 5,000+ posts]

xmax is how much it can move "safely" one way whereas xmech is how much it can move overall

 

[RAM_Designs 5,000+ posts]

Xmax is one way unless otherwise noted. The SSD has 20mm one way, 40mm total...which is about 1.6" of total clean excursion.

 

[hispls 5,000+ posts]

An honest x-max is how far it can move one way with 80% of bl. How many companies are honest, who knows? JL probably is, Fi, Soundsolutions, etc. probably are. Companies that rate their amps at "peak" (hit by lightning) power probably would use peak to peak number. x-mech is how far it will travel one way before bottoming out the coil or the spiders slapping the basket, or the coil jumping out of the gap or some other mechanical limit.

I wouldn't let 5mm be a deal breaker when buying a woofer. Really you need to consider your application. Usually higher x-max comes at the cost of a longer (heavier/less efficient) coil. In the case of some of the super x-max linear technologies, the exotic coils are really very inefficient compared to other drivers except at high excursion very low frequencies.

 

[audioholic 5,000+ posts]

xmax is never peak to peak, unless the company is flat out lying. xmax is defined as one-way linear. Peak to peak usually refers to physical clearance allowances, and is always expressed as two-way, not one-way. So the terms peak to peak and xmax should never be compared.

xmax is how much it can move "safely" one way whereas xmech is how much it can move overall

No, xmech is how far it can move 'safely'. xmech refers to how far the cone can move before stuff starts running into each other (coil bottoming out, spiders contacting the frame, etc). xmech is also suppose to be expressed in one-way terms, again assuming the company is being honest. xmax is a spec that relates to distortion output. Even if not measuring distortion levels directly to derive xmax, but instead using the loss of BL method, the only reason they measure the loss of BL is because BL distortion (caused by losing motor force as the coil leaves the gap) accounts for the vast majority of distortion a speaker produces. This is why BL curves are almost a direct relation to distortion levels when discussing motor designs.

xmax is sometimes derived using the loss of BL method someone mentioned above, but its also sometimes measured with distortion thresholds as its limiting factor. Both of these methods are considered acceptable, so often times companies use which ever one makes their product appear better, and makes comparing specs from one company to another somewhat misleading, even if both companies are being relatively honest about their xmax figures (because they were derived using different methods).

 

[Kangaroux 5,000+ posts]

xmax is never peak to peak, unless the company is flat out lying. xmax is defined as one-way linear. Peak to peak usually refers to physical clearance allowances, and is always expressed as two-way, not one-way. So the terms peak to peak and xmax should never be compared.


No, xmech is how far it can move 'safely'. xmech refers to how far the cone can move before stuff starts running into each other (coil bottoming out, spiders contacting the frame, etc). xmech is also suppose to be expressed in one-way terms, again assuming the company is being honest. xmax is a spec that relates to distortion output. Even if not measuring distortion levels directly to derive xmax, but instead using the loss of BL method, the only reason they measure the loss of BL is because BL distortion (caused by losing motor force as the coil leaves the gap) accounts for the vast majority of distortion a speaker produces. This is why BL curves are almost a direct relation to distortion levels when discussing motor designs.

xmax is sometimes derived using the loss of BL method someone mentioned above, but its also sometimes measured with distortion thresholds as its limiting factor. Both of these methods are considered acceptable, so often times companies use which ever one makes their product appear better, and makes comparing specs from one company to another somewhat misleading, even if both companies are being relatively honest about their xmax figures (because they were derived using different methods).

woops...mixed that up. sorry, was tired last night //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

 

[audioholic 5,000+ posts]

No problem.

 

[Fi Car Audio 10+ year member]

As mentioned above, 1 way.

Deriving/measuring Xmax comes from two values, mechanical and magnetic. You take the smaller of the two as the Xmax (as the smaller is the limiting linear factor of the sub). Most subs have more linear mechanical throw than motor/coil linearity. So usually the coil and motor geometry are the linear limiting factors.

 

[DUAL10S 10+ year member]

That makes some sense as most of that is over my head.

So when comparing the xmax specs of the JL, FI and Massive it would seem Massive's (peak to peak xmax) although not dishonest - but misleading to make their product look at least as good as the SSD and JL product when it actually has the least amount of linear excursion between the three.

I could not find the BL parameter for the JL or the Massive. Even if I did all I would know is which motor was stronger. Starting to get a small understanding of the loss of BL and xmax.

Is this why the subs with lots of xmax have a large motor (higher BL)? I notice the FI Q15 (Bl is 19.65) with 28mm xmax and at the other end the FI X15 (Bl is 13.2) with 18mm xmax. This makes sense to me but the FI 15BL (Bl is 22.7) with 18mm. Why not in the 30mm or more range?

I know the BL15 is not for the same application as the Q or the X but to derive the xmax the method should be the same especially for the same Company. Not picking on FI as their parameters are some of the few that are available for comparison. If anything that would lead me to purchase from them over mainstream. Just trying to get a better understanding.

 

[audioholic 5,000+ posts]

We just talked about this the other day, but its worth discussing again.

The majority of distortion a speaker creats is BL distortion. BL is, basically speaking, the motor force of the speaker. BL distortion is distortion that is caused when BL is lost as the coil moves and exits the sweet spot in the magnetic field the motor generates. In other words, the further the coil/cone excurts, the less force the motor has on it, so loss of cone control occurs. Less cone control from less motor force means higher distortion levels. This would imply that the speakers with the highest BL ratings would have the least distortion and highest xmax potential, but that is not the case.

BL is rated in a static fashion. But BL is not static. As I said above, BL changes depending on the position of the coil within the gap (or outside it). So one sub might be rated for a higher BL than another speaker, but loses it faster as the coil/cone moves. A fairly recent development in speaker tech is BL optimization, which is the process of utilizing various methods to maintain constant BL throughout the cone/coil's motion limits. Typical motor designs like the tradition overhung type have a BL 'curve', while BL optimized drivers have a flat 'curve'. Flat meaning BL stays constant. The advantage of a linear BL curve, if you haven't guessed already, is constant cone control no matter how much excursion is occurring. Less distortion. This is why you cannot look at one individual spec like BL, and derive too much useful information about the over all performance of a speaker. A single t/s spec can almost never be looked at without considering other t/s specs to see the big picture. BL is no exception, as is xmax.

Hope that helps.

 

[DUAL10S 10+ year member]

Yea, I read through that thread (lots of info)

Thanks for the info here as well. I will have to read through them a few more times to sink in.

So if I have some understanding of this: linear xmax is the "sweet spot" (little to no distortion not losing Bl) - where as xmech is safe mechanical travel but with distortion (loss BL)?

 

[audioholic 5,000+ posts]

Yea, I read through that thread (lots of info)
Thanks for the info here as well. I will have to read through them a few more times to sink in.

So if I have some understanding of this: linear xmax is the "sweet spot" (little to no distortion not losing Bl) - where as xmech is safe mechanical travel but with distortion (loss BL)?

As Fi Car Audio was suggesting above, xmech and xmax can be the same in some designs, if mechanical limits are less than magnetic limits (BL loss).

 

[RAM_Designs 5,000+ posts]

An honest x-max is how far it can move one way with 80% of bl.

If I'm not mistaken, it's normally measured within 70% of the static BL spec.

 

[RAM_Designs 5,000+ posts]

An honest x-max is how far it can move one way with 80% of bl.

If I'm not mistaken, it's normally measured within 70% of the static BL spec.

 

[DUAL10S 10+ year member]

^^^^ Lost me on that one.

If xmax and xmech are the same wouldn't that be linear all the time?

And why BL loss when mechanical is less than magnetic - wouldn't the coil stay in the magnetic field as mechanically it would not travel as far? I understand the lower xmax but not the BL loss.

Or am I completely misunderstanding this?