accordion surround

[thinking]

Was talking to a friend who is more seasoned in the history and use of speakers than myself, and he made the comment that "those Altecs use that accordion surround" as the reason that he didn't like them too well (i.e. 604's).
Question I have then, is there a reason other than limiting Xmax that the accordion surround would be a drawback? Any advantages that it afforded?

[gamalot]

I have lots of 30 year old altec speakers that have accordion surrounds and never needed to have them replaced or repaired. Foam deteriorates!

Gary

[bowtie427ss]

I'd ask your friend to provide some basis for his opinion if he can.

I'm pretty sure that in a well engineered and executed speaker excursion is and should be limited by the damper, NOT the surround. I'm pretty sure that in a speaker with an enormously powerful motor like the 515 that severe cone buckling, cracking, tearing would occur if the surround limited the excursion.

Xmax, i'm pretty sure is a parameter used to specify the limit of voice coil travel that can occur while maintaining a linear power response.

Take my comments with a grain of salt as i'm neither an engineer or technician. Hopefully others will chime in.

[bowtie427ss]

I should also add that the mechanical resistance of an accordian surround remains more constant. The mechanical resistance of the single roll foam surround increases proportionally the further it's moved from it's center or neutral position.

I can think of 2 advantages of foam over accordian. First foam is cheaper, secondly it doesn't require doping or sealing to be airtight.

The biggest disadvantage in my mind is that it's not a stable compound giving it questionable durability over time.

Just my additional 2 cents worth..............

[DNV47]

No scientific answer here, just experience. I will say that the best cone drivers I've ever heard happen to use an accordian surround. Plus the Altec 755A, one of the most sought after cone drivers ever uses an accordian surround and some say it's the best cone driver of it's size ever made. On the other hand, I don't think you can judge a driver just by one design characteristic. There are drivers out there with big magnets that fall short of drivers of better overall design with lesser magnets as there are drivers with accordian surrounds that are only suitable for AM table radios. The accoridan surround just happens to be associated with some very fine cone drivers.

[DNV47]

Before someone calls me on my error above, the 755A was really a Western Electric product.

[bowtie427ss]

I will say that the best cone drivers I've ever heard happen to use an accordian surround.

<font size="2" face="Verdana, Helvetica, sans-serif">I'll second that, not all Altecs either. However it seems those i would say have been the best sounding to my ears when not Altec brand "borrow" much from the altec design and are likely the products of designers/engineers that at one time or another were part of the Altec history. ie Renkus/Emilar, Stephen's tru-sonic, JBL, Frazier (Ed May and Jack Frazier were personal friends). It always seems to turn out that my favorites can all be traced back to show roots in Altec.

[bfish]

Originally posted by thinking:
Was talking to a friend who is more seasoned in the history and use of speakers than myself, and he made the comment that "those Altecs use that accordion surround" as the reason that he didn't like them too well (i.e. 604's).
Question I have then, is there a reason other than limiting Xmax that the accordion surround would be a drawback? Any advantages that it afforded?

<font size="2" face="Verdana, Helvetica, sans-serif">As Bowtie inferred, a cone driver's suspension has nothing to do with xmax (or shouldn't), which describes the length of axial travel before the driving force becomes non-linear. In the case of Altec's with underhung coils (coil depth less than front plate thickness), this is the point where the coil begins to leave the gap. The physical limit of travel caused by the suspension (xmech) is considerably beyond xmax in most cases.

The type and properties of suspension components in a given design are selected as carefully as the cone, magnet and all other parts to acheive the design goals. Also, the components need to be able to maintain their performance without signifigant change for the expected life of the driver. Altec's philosophy seems to have been to control the lightest unrestricted moving mass with the greatest practical driving force to provide efficient, linear, high output. A pleated, doped cloth surround met those requirements best in the models that used them, and there's now no question as to their durability. In fact, I've never seen a bad one that wasn't punctured, shredded or burnt by accident or abuse. Nor can I think of a single pleated Altec that would be improved with any other type of available surround. I wouldn't use a pleated surround in a driver with a longer throw, but then Altec didn't either. Most early designs had paper surrounds, and several later models used foam, both materials that fatigue with age and eventually crack or rot.

[dhook17322]

Another example of the problems of a foam surround is the condition you see many, if not most used 3182's that turn up for sale. Most have to be reconed because the foam surround has rotted and disintegrated. GPA has solved this shortcoming with a fine redesigned cone with pleated surround. Probably they will last much longer and perform as well.

[thinking]

Thanks for the comments. I didn't mean to imply that the surround limited the Xmax, but that if you had a driver with a very large excursion, it seems that you would be less likely to use the accordion surround. Yes, the underhung voice coil does result in a limited Xmax, as compared to the overhung, but I wouldn't make that trade. IMO until you get to very high spl levels, or subwoofers where you really need to move some air, Xmax is a numbers war for marketing.