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Peak to Peak Excursion ratings?

post #1 of 18
Thread Starter 
Do the majority of manufacturers of subwoofer drivers use peak to peak excursion specs?

Polk's budget db series lists 18mm peak to peak excursion and i'm curious if they are just trying to win the numbers game by publishing mechanical limits or if it's the same rating other manufacturers use.

What ratings do most of the more recognized companies like Dayton normally use?
post #2 of 18
Center to peak is the norm for reporting xmax (linear excursion) and xmech (mechanical limits).
post #3 of 18
Marketing departments use peak to peak. Engineers use xmax, which is half the peak to peak.
post #4 of 18
Ain't peak-to-peak just Xmax times two? ...
post #5 of 18
Thread Starter 
So those polks would actually be around 9 mm xmax then...
post #6 of 18
That would appear to be the case if this is the driver we're looking at:
http://www.polkaudio.com/products/db1240dvc
post #7 of 18
Thread Starter 
Yeah that's the one. They list it as "Xmax Linear .728 inch/18.5 mm (peak to peak)" under the t/s parameters section.
Edited by Mik James - 4/29/13 at 4:46pm
post #8 of 18
Quote:
Originally Posted by BeeMan458 View Post

Ain't peak-to-peak just Xmax times two? ...

exactly how does that differ from "half the peak to peak?" They taught me in fourth grade they're the same thing. Is B is two times A then A HAS TO BE half of B.
post #9 of 18
Quote:
Originally Posted by JHAz View Post

exactly how does that differ from "half the peak to peak?"

It doesn't. Hence the purpose of the whistling emoticon.
post #10 of 18
Thread Starter 
Also on the subject Ive seen mention of particular Dayton subs having underrated xmax specs, is it a similar situation where people are confusing peak to peak with xmax or are some Dayton subs actually under spec'd?
post #11 of 18
Quote:
Originally Posted by Mik James View Post

Also on the subject Ive seen mention of particular Dayton subs having underrated xmax specs, is it a similar situation where people are confusing peak to peak with xmax or are some Dayton subs actually under spec'd?

Josh Ricci found the Dayton 18" HO driver to have a fair bit more useful excursion than its rated xmax, 18-20mm vs 12.5mm. In that case I suspect it is a genuine matter of being conservatively specified versus a matter of confusion.

http://www.data-bass.com/data?page=system&id=89
post #12 of 18
Thread Starter 
Someone should test some more Dayton's to see if it's a common theme smile.gif
post #13 of 18
Quote:
Originally Posted by Steve1981 View Post

Josh Ricci found the Dayton 18" HO driver to have a fair bit more useful excursion than its rated xmax, 18-20mm vs 12.5mm. In that case I suspect it is a genuine matter of being conservatively specified versus a matter of confusion.

http://www.data-bass.com/data?page=system&id=89
It depends on how you determine the figure. The traditional method was to subtract the plate thickness from the coil depth and divide by two. The modern method is via Klippel Analysis, which measures excursion at 10% THD. The latter is more accurate in real world applications, but not every manufacturer has laid out the cash for a Klippel rig.
post #14 of 18
Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by Steve1981 View Post

Josh Ricci found the Dayton 18" HO driver to have a fair bit more useful excursion than its rated xmax, 18-20mm vs 12.5mm. In that case I suspect it is a genuine matter of being conservatively specified versus a matter of confusion.

http://www.data-bass.com/data?page=system&id=89
It depends on how you determine the figure. The traditional method was to subtract the plate thickness from the coil depth and divide by two. The modern method is via Klippel Analysis, which measures excursion at 10% THD. The latter is more accurate in real world applications, but not every manufacturer has laid out the cash for a Klippel rig.

I don't think you need to invest in Klippel's technology in order to determine Xmax. For example you can infer a driver's Xmax from how it produces bass when mounted in a common kind of box and operated in a simple but large space. Since that Xmax number is probably going to be infer performance in a similar box in a listening room, its not an invalid approach. The specifics of the box and the room relate more to SPL than Xmax. You can measure maximum displacement using ordinary shop tools or laser-based devices that are now becoming reasonable to obtain.

http://www.laserlinc.com/specs_single-axis/160s_specs.html
post #15 of 18
Quote:
Originally Posted by arnyk View Post

I don't think you need to invest in Klippel's technology in order to determine Xmax. For example you can infer a driver's Xmax from how it produces bass when mounted in a common kind of box and operated in a simple but large space. Since that Xmax number is probably going to be infer performance in a similar box in a listening room, its not an invalid approach. The specifics of the box and the room relate more to SPL than Xmax. You can measure maximum displacement using ordinary shop tools or laser-based devices that are now becoming reasonable to obtain.

http://www.laserlinc.com/specs_single-axis/160s_specs.html
It's certainly easy enough to measure a speaker and find the 10% THD level, anyone with an $85 mic and measuring freeware can do it. If you have sufficient skill you can use a speaker modeling program to calculate excursion at that point, or if you happen to have a laser handy you can use that. The question raised is what are you seeing when you look at a manufacturer's data sheet? It may be a measured xmax at 10% THD, it may be a calculated xmax. Or it may be a peak to peak figure that some marketing hack decided to use instead of xmax. Caveat Emptor.
post #16 of 18
JL Fathom F113 says it has a peak-to-peak excursion of 4 inches.
......does it mean that the woofer can go up from the resting position 2 inches. and go down 2 inches. altogether 4 inches?

it's so mind-blowing.
post #17 of 18
Yes. When manufacturers list the excursion as Xmax in T/S parameters, it is one way excursion @ Lord knows what THD number. P2P is double the Xmax, which is more eye catchy for a buyer when shopping for a driver.
post #18 of 18
Quote:
Originally Posted by narutium View Post

JL Fathom F113 says it has a peak-to-peak excursion of 4 inches.
......does it mean that the woofer can go up from the resting position 2 inches. and go down 2 inches. altogether 4 inches?

it's so mind-blowing.

It is meaningless because it will probably sound like @&$$ if you figure out how to actually make the cone do that. Its proper name is probably Xmech. Xmax rules!
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