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

Quote:
Originally Posted by LTD02

the surface area of a coil is its height multiplied by its circumference (x2 if you want both sides, but for now we can use just one).
circumference is diameter * pi.
the height will be held constant.
3" * 3.14 = 9.42" circumference for a 3" diameter coil.
two of those give 2 * 9.42" circumference, which is 18.84".
18.84" of circumference divided by 3.14 = 6" diameter.
so, two three-inch diameter voice coils has the same area as one six-inch diamter voice coil.
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?

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Quote:
Originally Posted by LTD02

i recant this post as i suspect he was talking about excursion not thermal properties.
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.
Quote:
Originally Posted by Scott Simonian

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.
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.
Quote:
Originally Posted by Scott Simonian

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.

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?

I can shrink the box to protect them if need be, but I'd be giving up some efficiency, 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?
Edited by Gorilla83 - 10/27/12 at 7:02am
"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.
Quote:
Originally Posted by Tom Bley

"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.

Doh! Autocorrect strikes again, ugh.

Dual opposed it is and I'm 85% sure on the 5cu ft design.
Quote:
Originally Posted by Gorilla83

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?
xmax is xmax. How can it be a conservative number? Or are we only worrying about xmech now?
Quote:
Originally Posted by LTD02

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".
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%
Quote:
Originally Posted by LTD02

yeah, you missed the part where i said holding all other things equal.
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.
Quote:
Originally Posted by LTD02

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%
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?
Quote:
Originally Posted by LTD02

"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.
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.
Was planning on cutting some wood for this project today, but as luck would have it my sunroom was flooded due to a clogged/leaking toilet. FAIL.

If I have some time I may wrap up a few more room treatments and then resume this project some night this week and/or next weekend.

Back to the box debate - should I stick with 5 cubic feet or should it be shrunk some to prevent over excursion? I guess it's tough to tell since we don't exactly know what xmax mech is just yet. Anyone in here have an answer from Dayton?

I guess Josh R. has one on the way as well so maybe he can shed some light.
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
Quote:
Originally Posted by NicksHitachi

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

Thanks Nick, it probably could have been a lot worse had we not found it in time. Water is cleaned up and the ceiling is drying out now. Going to replace the toilet, fill and reseal the ceiling, then paint.

Quote:
Originally Posted by Sibuna

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

I'm really curious to see how they sound too - they should easily outperform the empires by a good margin, at least on paper. I'm ALWAYS on the search for more bass - especially since we didn't succeed at bringing the house down.
What would be the best enclosure size for single RS18's and a 1000 watt amp?
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