Which 2x10? Mesa vs Revsound vs Barefaced

[agedhorse]

The top photo is an accordion surround but is has an improved cone edge attachment. The top of the older style cones was flat (parallel to the mounting surface) and the bend in the cone to the cone angle was a particularly vulnerable aspect of this design for bass guitar use.

 

[dawind99]

@dawind99 @agedhorse I must admit, I'm not a speaker designer. Nor do I play one on TV!

But the Celestion BN10-200X does not look to have an M-Roll surround. Do they have different variations of it?

View attachment 3171460

Smaller radius on the Celestion but "M-rolls" indeed. When I think of M-rolls the most obvious is the foam or butyl surrounds used on HA or auto drivers. But, it in the end it's radiused. I think the M roll is a misnomer as well. I think sine wave rolls would be a better description albeit confusing. Or, perhaps U and upside down U roll. But not a V roll which M sort of insinuates.


I thought the M-Roll looked like this but I really don't know. Trying to learn here.

View attachment 3171464

 

[agedhorse]

M-roll works differently than the simple accordion surround, M-roll is the slang term, because it can be a 1, 2 or even 3 roll profile.

An accordion type suspension displaces differently, more of a stretching motion whereas the rolled suspension has more of a displacing motion where the movement is parallel to the "legs" of the roll. This progressive motion tends to be more linear that the simple accordion, especially noticeable at higher displacement rates. The other big difference comes from the vibrational transmission across the surround from the cone edge to the basket juncture and back to through the surround (a form of reflection standing wave), the attenuation coefficients are quite different.

Looking at the top driver, I would have to characterize the geometry as accordion, but as I mentioned earlier it has specific improvements to address the chronic weak points that older versions of this style suffered from. Rolling the accordion pleats also addresses the weaknesses at the apex of the pleats under higher excursion applications but it still moves differently than a true rolled surround.

I remember when this geometry came into being, originally in home audio where designers wanted a high compliance woofer with reasonably high excursion, the old style surrounds simply couldn't deliver so a variety of foams were tried (first unsuccessfully in an accordion fashon, and later formed in a single roll as this gave better control over progressive displacement motion). After trying this approach in pro audio drivers used in sub applications mostly, it was found that the foam materials were not as durable and the switch was made to linen (cloth). Single roll was not stable enough (the roll had to be too large for the needed displacement) so they split the single larger roll up into 2 smaller rolls that looked like an "M". My experience with this was first with JBL drivers like the 2220 and 2240 and such where the earliest versions were a hybrid between the accordion surround and the true rolled surround but later versions (including the 2241, 2242, 2226) became true rolled surrounds. All of this was due to the need for better controlled excursion at the higher and higher power levels these drivers were encountering. Rolled suspension tooling was more expensive and the need was not there in the MI industry until later when bass amps became more powerful and traditional surround driver failure rates skyrocketed.

If you look at the profile of a true rolled suspension, it's almost the opposite of a sine function at the apex, where it's almost spherical. That's the key to how the rolled suspension works differently, steeper legs with a spherical apex.

 

[dawind99]

M-roll works differently than the simple accordion surround, M-roll is the slang term, because it can be a 1, 2 or even 3 roll profile.

An accordion type suspension displaces differently, more of a stretching motion whereas the rolled suspension has more of a displacing motion where the movement is parallel to the "legs" of the roll. This progressive motion tends to be more linear that the simple accordion, especially noticeable at higher displacement rates. The other big difference comes from the vibrational transmission across the surround from the cone edge to the basket juncture and back to through the surround (a form of reflection standing wave), the attenuation coefficients are quite different.

Looking at the top driver, I would have to characterize the geometry as accordion, but as I mentioned earlier it has specific improvements to address the chronic weak points that older versions of this style suffered from. Rolling the accordion pleats also addresses the weaknesses at the apex of the pleats under higher excursion applications but it still moves differently than a true rolled surround.

I remember when this geometry came into being, originally in home audio where designers wanted a high compliance woofer with reasonably high excursion, the old style surrounds simply couldn't deliver so a variety of foams were tried (first unsuccessfully in an accordion fashon, and later formed in a single roll as this gave better control over progressive displacement motion). After trying this approach in pro audio drivers used in sub applications mostly, it was found that the foam materials were not as durable and the switch was made to linen (cloth). Single roll was not stable enough (the roll had to be too large for the needed displacement) so they split the single larger roll up into 2 smaller rolls that looked like an "M". My experience with this was first with JBL drivers like the 2220 and 2240 and such where the earliest versions were a hybrid between the accordion surround and the true rolled surround but later versions (including the 2241, 2242, 2226) became true rolled surrounds. All of this was due to the need for better controlled excursion at the higher and higher power levels these drivers were encountering. Rolled suspension tooling was more expensive and the need was not there in the MI industry until later when bass amps became more powerful and traditional surround driver failure rates skyrocketed.

If you look at the profile of a true rolled suspension, it's almost the opposite of a sine function at the apex, where it's almost spherical. That's the key to how the rolled suspension works differently, steeper legs with a spherical apex.

 

[dawind99]

An "accordion" surround has a saw-tooth pattern. The Celestion does not. It is rolled and as you say "M" roll has never been defined exactly and has been thrown around for years covering every driver from the foam surrounds of yesteryear that have all disintegrated by now, to what some refer to as the M roll, which as you said can have 2 to as many as 6 "pleats"...and probably more down the line as the wheel is yet trying to be reinvented. As a description "sine" wave (only IMHO) works better than "spherical" as a sine wave is most often imagined in the XY axis. A sphere XYZ, a ball, which a surround's ribs are not. I thought "sine" wave made it easy to visualize.

 

[agedhorse]

The cross-section of the apex of a rolled surround is semi-circular, which is the same cross-section as a sphere.

On the m-roll surrounds that I have seen, I haven't seen more than 3 rolls. Another way to describe the difference between an accordion and a rolled surround is that if you look at the section at the neutral plane of an accordion driver it's almost symmetrical, whereas the section of the rolled surround is very asymmetrical.

The motion of the rolled surround is more angular while the motion of an accordion surround is more linear. The difference in the math describing the two motions is profound.

Since I design and also recone (or used to) drivers, I have a number of different parts around the shop, so maybe some pictures of what I am trying to describe might be helpful here...

Double-roll surround (top side)

Double-roll surround (back view):

Accordion surround (front view):

Accordion surround (back view):
(note the angle the cone makes with the surround at the edge, this is the old style cone-surround interface, that angle is a huge weakness)

 

[dawind99]

The cross-section of the apex of a rolled surround is semi-circular, which is the same cross-section as a sphere.

On the m-roll surrounds that I have seen, I haven't seen more than 3 rolls. Another way to describe the difference between an accordion and a rolled surround is that if you look at the section at the neutral plane of an accordion driver it's almost symmetrical, whereas the section of the rolled surround is very asymmetrical.

The motion of the rolled surround is more angular while the motion of an accordion surround is more linear. The difference in the math describing the two motions is profound.

Since I design and also recone (or used to) drivers, I have a number of different parts around the shop, so maybe some pictures of what I am trying to describe might be helpful here...

Double-roll surround (top side)
View attachment 3171692


Double-roll surround (back view):
View attachment 3171693

Accordion surround (front view):
View attachment 3171695

Accordion surround (back view):
(note the angle the cone makes with the surround at the edge, this is the old style cone-surround interface, that angle is a huge weakness)
View attachment 3171696

What I see on the back of your "double Roll" is a significantly more acute angle then on the back of the "accordion". The math is not profound, just one of the last "truths" you can count on when used correctly. And, it's physics supported by math that try to explain what's going on in an enclosure which is the most important part of the equation in my eyes. The driver is useless in free air as you know with air vibrating in 3 dimensions.
Anyway, m-roll or accordion, it comes down to application and performance in that application and the proof is always in the ear of the listener.

 

[agedhorse]

The motions are completely different, the results are measurably different, that's WHY the rolled suspension evolved and was so widely adopted for high excursion applications.

Nothing wrong with using what you prefer, but imo it's misleading to call it something that it's clearly not.

 

[Jhass]

Those surround photos are cool - thanks for sharing them.

I am certainly NOT an expert on bass drivers, so all I can do is trust my ears. I love the way the Celestions in my RS210 sound. I've been playing everything from Bach to Badfinger, Pettiford to Petty, Sinatra to Stones, and they do it all brilliantly.