20 replies to this topic

[Bassaholic]

At what volume? I mean if still kept in its linear range, then the distortion would be low, so the overall BL curve would not be an issue. So a XBL2 motored subwoofer would not automatically sound any better. The IDMAX is still a pretty decent sub IMO.

Secondly, since when does having a XBL2 motor have anything to do with sensitivity? I mean the BL of the Brahma (for example) was likely specifically chosen, rather than forced to be at that level due having a XBL2 motor.
The bandwidth (F3 in a given Qtc enclosure for example) and required enclosure volume has a bit more to do with the sensitivity though.

[Blackrazor]

Bassaholic said:

At what volume? I mean if still kept in its linear range, then the distortion would be low, so the overall BL curve would not be an issue.

The whole point of the XBL2 motor is the motor strength is the same at near full excursion as it is at rest point. The IDMax's are like most subs, the motor strength deteriorates the further the cone moves from resting towards its XMax... i'm not saying they sound bad, they sound bloody wicked, but i still like that silky smooth Brahma sound BTW, apparently BL non-linearity accounts for 70-80% of subwoofer distortion (or so i read somewhere, may have even been Dan Wiggins saying that

Bassaholic said:

Secondly, since when does having a XBL2 motor have anything to do with sensitivity? I mean the BL of the Brahma (for example) was likely specifically chosen, rather than forced to be at that level due having a XBL2 motor

For a given magnet size and strength, the XBL2 tech will have less sensitivity, simply because they have to remove some of the magnet internally... its hard to increase the strength of certain areas of the magnet by changing the magnet composition, so both the Brahma and XXX start with a huge magnet and remove some areas of the magnet at strategically located areas to reduce the motor force slightly at those areas... thats how they get the flat BL Which means better SQ but less SPL I'm not saying you cant have a high sensitivity XBL2 sub, just that for a given magnet size the XBL2 motor has less sensitivity, hence why the XXX and Brahma's have utterly massive magnets

[Bassaholic]

Blackrazor said:

The whole point of the XBL2 motor is the motor strength is the same at near full excursion as it is at rest point. The IDMax's are like most subs, the motor strength deteriorates the further the cone moves from resting towards its XMax... i'm not saying they sound bad, they sound bloody wicked, but i still like that silky smooth Brahma sound BTW, apparently BL non-linearity accounts for 70-80% of subwoofer distortion (or so i read somewhere, may have even been Dan Wiggins saying that

The whole point of XBL2 is a to optimise the motor for a longer linear range for a given coil height and top plate height.

I agree that BL non-linearity is a significant contributor to subwoofer distortion. Obviously, within a particular range, the BL spec will not deviate that much, regardless of the motor topology. Hence why I said "At what volume? I mean if still kept in its linear range, then the distortion would be low".

Blackrazor said:

For a given magnet size and strength, the XBL2 tech will have less sensitivity, simply because they have to remove some of the magnet internally... its hard to increase the strength of certain areas of the magnet by changing the magnet composition, so both the Brahma and XXX start with a huge magnet and remove some areas of the magnet at strategically located areas to reduce the motor force slightly at those areas... thats how they get the flat BL Which means better SQ but less SPL I'm not saying you cant have a high sensitivity XBL2 sub, just that for a given magnet size the XBL2 motor has less sensitivity, hence why the XXX and Brahma's have utterly massive magnets

They don't remove any of the magnet. It is the gap that is altered. This will of course have an effect on the BL, but the resulting BL value (at whatever point on the curve) depends on the optimisation of the motor. In fact, in one of the technical articles on the Adire Audio website there is a comparison of the split gap design vs a long gap long coil design, with the same basic parts, only a different voice coil (XBL2 motor had a shorter coil) and obviously a different gap design. The gap width, magnet and top plate height etc all remained the same. In this example, the XBL2 motor had a larger BL value at all points on the BL curve.

But the fact remains, the resulting sensitivity spec of the Brahma, is likely a side effect of optimising the driver for a particular frequency response in a particular size enclosure. Dan could have made the BL (for a given coil resistance) a lot higher, if that was his goal.

Feel free to ask Dan to clarify. If I am wrong, then post/get him to post his reply here and perhaps I will learn something. :wink:

[Blackrazor]

OK, yeh my bad, i knew they made a hole somewhere from reading the tech paper but i thought it was in the magnet, tis in the top plate like you said

[web:61ffaf6599]http://www.adireaudi...etailsPaper.pdf[/web:61ffaf6599]

[Mr_Bob]

IMO the sensitivity is reduced in XBL2 drivers as the the large excursion involved (64mm p-p) requires a large roll surround which decreases the effective piston area and thus reduces efficiency.

i also guess that due to the low frequencies that they're also designed for, the spider need to be fairly stiff to retain control at high xmax.
but i may be wrong on that one

[Bassaholic]

Mr_Bob said:

IMO the sensitivity is reduced in XBL2 drivers as the  the large excursion involved (64mm p-p) requires a large roll surround which decreases the effective piston area and thus reduces efficiency.

This is also a good point. For example, the difference in efficiency between the large surround of the 12" brahma is probably somewhere around 0.8dB less than the smaller surround on the shiva.

Yes, decent suspension is definitely required to prevent coil rocking at high xmax - no point having a large linear BL range, if the coil ends up scraping at high xmax.....