Understanding Excursion

[DevilDriver]

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Understanding Excursion

Quote: Originally Posted by DevilDriver

It's been a while since I've put anything meaningful together, so it's time for another fun technical article! Excursion is a large contributor to high output in any driver on the market. Typically, larger excursion (seen visually as how far the cone moves in and out) means more sonic output. However, with excursion come challenges.

[lowxpectationz20]

that was good shit man, ..and i thought i knew alot about audio..

[sdime98]

cool, i'mma have to go read up now.

[Bama]

very informative. good job

[DJDAudio]

Well done man!,

Is there a way to use the back EMF of the system as a shock absorber of sorts to help save the speaker?

Last what of the magnetic pole was 10" long and the voice coil was 2" that way it could travel 8" without ever leaving the magnetic field?

Also What if the surround was removed and a Teflon style piston ring was used and polished cylinder wall. as well as a uniform spring return.

Ok little of topic but If you have a 12" driver with 12" of excursion capabilities would this be better or worse for you SPL? I would think worse for the time it would take to traverse this distance,.

[DevilDriver]

Quote: Originally Posted by DJDAudio

Well done man!,

Is there a way to use the back EMF of the system as a shock absorber of sorts to help save the speaker?

Last what of the magnetic pole was 10" long and the voice coil was 2" that way it could travel 8" without ever leaving the magnetic field?

Also What if the surround was removed and a Teflon style piston ring was used and polished cylinder wall. as well as a uniform spring return.

Ok little of topic but If you have a 12" driver with 12" of excursion capabilities would this be better or worse for you SPL? I would think worse for the time it would take to traverse this distance,.

Well, the first problem with back EMF is that it causes substantial second order harmonic distortion. We want to keep EMF and eddy currents to a minimum.

With a long gap, short coil (LGSC or in this case, underhung) design, there are a few inherent issues. First problem is that production would be very very expensive. With a short coil, BL will drop very quickly as it moves towards the outer limits of the gap. The flux density and saturation would fall well short of our goals as well; these designs are typically very inefficient (in terms of actual flux used) and, as such, not as highly sought after, particularly considering the production costs. Yes, LGSC is capable of lower distortion in some regards (inductance is wonderfully low and there is less flux modulation until you reach the outer limits of the gap) but the cost of producing a driver like we are suggesting here is extremely expensive. Machining aside, the cost of raw materials would be quite high.

Surround changes are interesting to note. A surround is an important part of the suspension, but the spider is very very critical. The Arachnid from Adire Audio is actually a very ingenious step in this direction. HERE is a good thread on distortion generated from suspension non-linearities which also touches on underhung vs Adire's XBL^2 gap technology (US Patent 7,039,213)

In terms of raw SPL (from an engineering standpoint), massive excursion in a sealed enclosure is the way to go. There are a few basic issues with this so far, the first being availability. Right now, there are absolutely no stock parts to create anything near this level of excursion; it would have to be extremely custom and extremely expensive (Adire's Parthenon as well as Richard Clark and David Navonne's giant sub are two of very very few subs that are capable of doing well and are also extraordinarily expensive). Secondly, subwoofer drivers are highly inefficient (typically converting ~3% of input electrical power into acoustic output) and, thus, we would have extremely large power demands.

High spl is currently attributed to subs with large BL (and BL^2/Re) that are used in a bass reflex enclosure, as the use of the out of phase port causes it to be much more efficient than a sealed enclosure while still not requiring the large amount of room required by any 4th or higher order bandpass enclosure.

Hope that addressed some of your questions; I know you always have lots

Neil

[DJDAudio]

Quote: Originally Posted by DevilDriver

Well, the first problem with back EMF is that it causes substantial second order harmonic distortion. We want to keep EMF and eddy currents to a minimum.

With a long gap, short coil (LGSC or in this case, underhung) design, there are a few inherent issues. First problem is that production would be very very expensive. With a short coil, BL will drop very quickly as it moves towards the outer limits of the gap. The flux density and saturation would fall well short of our goals as well; these designs are typically very inefficient (in terms of actual flux used) and, as such, not as highly sought after, particularly considering the production costs. Yes, LGSC is capable of lower distortion in some regards (inductance is wonderfully low and there is less flux modulation until you reach the outer limits of the gap) but the cost of producing a driver like we are suggesting here is extremely expensive. Machining aside, the cost of raw materials would be quite high.

Surround changes are interesting to note. A surround is an important part of the suspension, but the spider is very very critical. The Arachnid from Adire Audio is actually a very ingenious step in this direction. HERE is a good thread on distortion generated from suspension non-linearities which also touches on underhung vs Adire's XBL^2 gap technology (US Patent 7,039,213)

In terms of raw SPL (from an engineering standpoint), massive excursion in a sealed enclosure is the way to go. There are a few basic issues with this so far, the first being availability. Right now, there are absolutely no stock parts to create anything near this level of excursion; it would have to be extremely custom and extremely expensive (Adire's Parthenon as well as Richard Clark and David Navonne's giant sub are two of very very few subs that are capable of doing well and are also extraordinarily expensive). Secondly, subwoofer drivers are highly inefficient (typically converting ~3% of input electrical power into acoustic output) and, thus, we would have extremely large power demands.

High spl is currently attributed to subs with large BL (and BL^2/Re) that are used in a bass reflex enclosure, as the use of the out of phase port causes it to be much more efficient than a sealed enclosure while still not requiring the large amount of room required by any 4th or higher order bandpass enclosure.

Hope that addressed some of your questions; I know you always have lots

Neil

Thanks man you do know a damn lot to you,

and you did answer all my questions and thanks for the link!

[DevilDriver]

It makes me wish I paid more attention when I was in high school. I have learned more in the last year than I think I have the whole rest of my life, and my way towards EE starts in a week.



Neil

[robertlamont80]

The cones mass also plays a large part in the frequency and force of a driver.

[juddspaintballs]

ah, I love all this technical crap. That short article reminded me a lot of the first couple chapters of the LDC

[BudRacing]

Quote: Originally Posted by DevilDriver

It makes me wish I paid more attention when I was in high school. I have learned more in the last year than I think I have the whole rest of my life, and my way towards EE starts in a week.



Neil

I was a member of some car audio boards when I was in high school and when physics class came around it was a breeze.

[beandip]

this is like the 8th time i have read this article, it never gets old