First DIY project for a guy looking to upgrade - multiple sealed 18s? - Page 2

You've shown the circumference is the same. Isn't a 6" voice coil likely to be longer than a 3" voice coil and have a larger surface area and also a thicker coil?

Yes, I was referring to excursion.

Models line up. It's about on the line or 1mm over rated Xmax in a 4cuft cab and about 3mm over Xmax in the 5cuft at 1,250w per driver.

"You've shown the circumference is the same. Isn't a 6" voice coil likely to be longer than a 3" voice coil..."

yes.

"...and have a larger surface area and also a thicker coil?"

that depends.

holding all other things equal, a 6" coil will be two times longer than a 3" coil. it will have two times the surface area. so two 3" coils will have the same surface area as one 6". as for which has the thicker coil, number of windings, shape of the wire, etc., those are all factors outside comparing diameters. there are 4" coils with thin wire and next to no height. there are 2.5" coils with 8 layers of thick wire and lots of height.

Is that 4cu-ft or 5cu-ft per driver or per pair of drivers?

For a pair. This was mentioned in Ricci's post #8 on page one.

It wouldn't be my choice for a box design. With 5cu-ft for a pair you exceed xmax at 50Hz.

Not mine either, really but it works. I'd rather go with less power, larger boxes but...

Anyway, it does go over rated Xmax but not by a lot and it's a controlled excursion profile and not one that rises much below.

"Also - I believe it was stated that the stated Xmas was likely a conservative number as well. Even at 15-16mm of excursion under the full 1250 watts, is this really an issue?"

Xmas is on December 25th.

Looking forward to you build. My vote is for the Daytons in dual opposed config.

xmax is xmax. How can it be a conservative number? Or are we only worrying about xmech now?

So, I must be missing something here. Two 3" voice coils that are say 2" long do not have the same surface area as a single 6" voice coil that's 4" long.

Two 3" diameter voice coils:
pi*3"*2" x 2 (drivers) = 37.7in^2

One 6" diameter voice coil:
pi*6"*4" = 75.4in^2

So, there we have it... Two 3" voice coils are not equal to a single 6" coil. They're equal to a single ~4.25" voice coil.

"So, I must be missing something here. Two 3" voice coils that are say 2" long do not have the same surface area as a single 6" voice coil that's 4" long."

yeah, you missed the part where i said holding all other things equal.

you could just as easily say that two 3" voice coils that are 4" high have twice the surface area as a single 6" voice coil that is 2" high. it is kind of a goofy argument.

"xmax is xmax. How can it be a conservative number? Or are we only worrying about xmech now?"

xmax is NOT xmax.

there are many ways to calculate it and/or measure it.

i have seen all these and they are all fair:

(height of the coil - height of the gap) / 2

(height of the coil - height of the gap) / 2 + 1/4 gap height

(height of the coil - height of the gap) / 2 + 1/3 gap height

displacement where bl is 70% of resting bl

displacement where distortion is 10%

Right, so I held everything else equal and made the surface area comparison of the two voice coils.

"Guys - what is the likelihood my amp is actually delivering a constant 2500/channel to each channel - at least long enough to really put the drivers in any danger?"

tough to say without measuring the amp. also, there tends to be some rolloff in amps below 20hz vs. stated power in the spec sheet, not always, but often.

"I can shrink the box to protect them if need be, but I'd be giving up some efficiency, right?"

yeah, that is right.

"Also - I believe it was stated that the stated Xmax was likely a conservative number as well. Even at 15-16mm of excursion under the full 1250 watts, is this really an issue?"

while i don't know, my guess is that is well within the safe operating limits of the driver. i've asked dayton if they could provide xmech, but haven't heard back yet.

"Right, so I held everything else equal and made the surface area comparison of the two voice coils."

no you didn't. you doubled the height of the 6" coil and then claimed that the surface area was double.

So then the theory here is that Dayton is using the most conservative xmax measurement method to avoid sales and make their driver seem less capable than it really is?

You're the one who said the 6" coil would be twice as long so I used your number. Now you're complaining that I doubled the length and compared them.

the confusion seems to be around the use of the word length.

what you are referring to as length is more commonly referred to as height.

what i am referring to as length is how long the wire would be if you unwound the coil and measured how long it is.

"So then the theory here is that Dayton is using the most conservative xmax measurement method to avoid sales and make their driver seem less capable than it really is?"

that is certainly one way to see it, but in my estimation represents short term thinking.

another perspective is that by providing conservative data, dayton will win the trust of its users and build a strong reputation, and that over time will trump exaggerated claims and provide for a more enduring business.

Either way it doesn't seem like a good strategy to intentionally push the driver past xmax regardless how it's determined.

I honestly don't see the problem here. A couple mm over Xmax isn't going to hurt the driver.

"Either way it doesn't seem like a good strategy to intentionally push the driver past xmax regardless how it's determined."

it really depends on the driver stereodude. some drivers have an xmech fairly close to the xmax (or even under it), while others have a ton of running room past xmax. member 'not noted that xmax on the lms5400 at 38mm is kind of aggressive and that it is excursion limited to about 33mm physically. meanwhile alpine swr 12 has a 20mm xmax, but 36mm or xmech.

Gorilla,

man that sucks major! A friend of mine just had the exact same thing happen to his theater. Many condolonces upon you......

Nicholas

when you get these built id be really curious to see how they sound vs your dual emps. I also find it humorous that after we tried to bring down your house you are in search of more bass

What would be the best enclosure size for single RS18's and a 1000 watt amp?