They appear to be later-model ferrite Altec hardware, GPA software, and Urei (JBL?) horns. Seems like if they were so particular, they'd have posted some test plots though....
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They appear to be later-model ferrite Altec hardware, GPA software, and Urei (JBL?) horns. Seems like if they were so particular, they'd have posted some test plots though....
I have a hard time getting this question answered..so here goes another try w/o as many words to clutter.
Speaking of paper cone speakers...
BobR or anyone. I was hoping to get a defination of a term that an Altec competitor used in the 70's when they mentioned Altec's almost exclusive use of the 4-fold "Accordian" Cloth Surround.
The term is "Rim-Resonance Dip" problems.
What does this mean & does the heavy doping on that type of surround negate this entirely
Thank you for that insight..That leads me to questions about dampening.
Theoretically, if you use a thinner, lighter; yet stiffer sealant for Doping.. Just enough to close or fill the gaps in the cloth surround..to prevent the air from passing thru..how will that effect the sound. Altec & GPA use a heavy..thick..rubbery dope. Does this effect the dampening?
"the openings between the threads. When properly applied, this compound has minimal effect on the surrounds' flexibility properties (damping, compliance), as it never completely dries or stiffens the surround. It does however, add signifigant weight to the moving mass, so must be applied with a "just-enough" frame-of-mind"
[QUOTE]Originally posted by 417 - Alnico:
[QB]Thank you for that insight..That leads me to questions about dampening."
Ah, the next logical question.....BTDT
"Theoretically, if you use a thinner, lighter; yet stiffer sealant for Doping.. Just enough to close or fill the gaps in the cloth surround..to prevent the air from passing thru..how will that effect the sound."
Only to the extent that the altered surround deviates the force/deflection characteristics from design. Could be a little or a lot. My first experimentation along these lines was a real flop, and reminded me that others with far more smarts than myself had already spent lots of time to determine the best way to do it. The doping concoction I made up (being out of Airflex, which you can't get anymore...), was as you describe, thinner, lighter, and stiffer, as it did dry, though it had the wet, shiny, appearance of the real McCoy. Satisfied that I was a genius, I proudly stuffed the 421-8HII back in its' cab, and ran a sweep.....ooops....all thoughts of patents vanished......LF response dived at 240hz, was off the scale (nonexistant) at 180. I meekly cut out my work (and a $65 kit), recleaned the frame, and set it aside to redo when I had the right materials. http://www.hostboard.com/forums/
The lesson? If you're reconing/repairing a speaker and want it to sound like it was designed to, use identical methods and materials as the factory....period. If you want to experiment with design, use your frame of choice, and have a large quantity of software at your disposal, so you can build, test, record, rebuild, retest, etc....to your hearts content.
" Altec & GPA use a heavy..thick..rubbery dope. Does this effect the dampening?"
Yes. Intentionally. The current product has the appearance and consistency of honey...or STP, and seems to perform as Airflex used to. Don't expect to learn the exact method other than by experimentation and experience, as this is one of the few bits of proprietary information a builder can keep to himself, as most other parameters can be easily reverse-engineered.
TIP; for those of you with Altec doped surrounds as described, which exhibit drips or localized puddling. Don't try to remove or redistribute the doping by brushing, solvents, etc., except in extreme cases. Instead, rotate the drivers mounting a quarter or half turn in the cabinet, to allow heat and gravity to slowly do the job. For old drivers that have been mounted in the same position for 20 years or more, a half turn can have other benefits, too. In the old days, it wasn't uncommon to open a cab and find a penciled schedule, with the dates and initials of the driver rotations! http://www.hostboard.com/forums/
Your question could best be completely answered by someone actually involved in the design of the speakers in question, that understands the engineering goals of the specified construction methods (like Bill).
My understanding is that rim resonance is an unwanted component of speaker design that can add peaks and dips in the response plot of a given driver. It seems to be a minor or non-issue with a one-piece, paper, cone/surround. However, paper surrounds are very stiff, and therefore, unsuitable for high-efficiency designs.To fully understand the advantages of a multi-fold cloth surround, it would really help to see one before doping. Made from fine-thread, open-weave cloth, (with a high percentage of open area), the threads are impregnated with a "setting agent", then molded into the multifold shape. The finished surround is extremely light, offers a progressively increased resistance to cone travel, and will flex repeatedly without changing properties (compare repeated foldings of a tee-shirt to a paper bag..). The open-weave design provides the weight advantage, since the large, open areas between the threads weigh nothing, but it's here that the old trade-off gremlin raises his head. As you know, LF transducers require a baffle to separate the front and rear waves to avoid cancellation. Since an open-weave cloth surround is acoustically transparent, the baffle effect is lost, as LF waves easily pass through, causing cancellation. Sooooo...special doping compound is sparingly applied to close and seal the openings between the threads. When properly applied, this compound has minimal effect on the surrounds' flexibility properties (damping, compliance), as it never completely dries or stiffens the surround. It does however, add signifigant weight to the moving mass, so must be applied with a "just-enough" frame-of-mind.
How this type of surround effects rim resonance is beyond my understanding. If used by a competitor as an example of problems with Altec design, I doubt if they were taking into consideration Altecs' strict requirements for uniformity and excellence of cone construction, a parameter that minimizes rim resonance from the start, meaning that you don't have to fix a problem that doesn't exist.
It seems as though I am on a roll here..Let me ask you this.. On my avatar is a 414.
This driver, like the 515 etc.. has a Vented w/ screen Voice Coil cover/cap/dome..What is the function of this vented design in relation to the LF preformance of the 414? If I used that kind of dome on a 417 for example, would that have ant effect on the frequency response or...?
<font size="2" face="Verdana, Helvetica, sans-serif">The properties of every component in a speaker are (or should be) selected for the effect it has on performance as related to the design goal. Changing any of them will change the speaker's performance. Even seemingly minor differences can have a major impact. The upper range of a LF drivers response is largely produced at the smallest area, i.e. the dust cap. LF HIFI drivers intended for flat FR and limited BW, and to crossover from 500-1200hz use the softer, oversize (4" cap over a 3" coil) to remove the HF element, which can cause IM distorion in this app. The vented center serves dual purposes, eliminating the highest element produced at the tiny center of the cap, and providing some ventilation to aid coil cooling. Altec 12" and 15" MI/PA drivers have different needs, as they're often used alone to provide "full range" (of the instrument) response. Thus, a rigid, coil-size, aluminum cap is used to accentuate the HF response in this app. While a guitar's highest fundamental is around 1KHZ, the essential harmonics (that make it sound like a guitar) lie in the 1KHZ-8KHZ band, and are reproduced to a large degree by the aluminum cap.Quote:
Originally posted by 417 - Alnico:
It seems as though I am on a roll here..Let me ask you this.. On my avatar is a 414.
This driver, like the 515 etc.. has a Vented w/ screen Voice Coil cover/cap/dome..What is the function of this vented design in relation to the LF preformance of the 414? If I used that kind of dome on a 417 for example, would that have ant effect on the frequency response or...?
Since there are also differences in the makeup of other components, (cone, coil, spider), the answer to the next question (can I make a 414 out of a 417 by changing dust caps?) is no. Yes, many Altec components are used in multiple applications, but if used in the wrong combinations give bad results. Even components that appear identical may not be. For example, many spiders are available in at least three degrees of "stiffness", and cannot be told apart by looking at them.
Excellent! That is what I thought. I appreciate your replies.
Jeff
What is your opinion on the performance of Alnico vs Ceramic magnets? Do the Alnico units really have some kind of special compression after high volume exteneded use..effecting the Low end?
Or is this a myth like BobR says about Tube superiority vs SS amps etc..
<font size="2" face="Verdana, Helvetica, sans-serif">While I've read lots of opinions touting the 'power compression/Alnico magic', I've yet to see any supporting test data. Even if there's some truth to those statements, musical instrument applications would be the only legit uses to take advantage of such sound-altering traits. One thing I do know regarding the al/cer debate on "old" speakers is this; given two identical, all-original 30+ year old drivers, one Alnico, the other ceramic, the ceramic one is far more likely to sound just like it did when new, having retained its' magnetic strength far better than the Alnico counterpart.Quote:
Originally posted by 417 - Alnico:
What is your opinion on the performance of Alnico vs Ceramic magnets? Do the Alnico units really have some kind of special compression after high volume exteneded use..effecting the Low end?
Or is this a myth like BobR says about Tube superiority vs SS amps etc..
My opinion on tubes vs SS is very similar, in that tubes still have the edge for musical instrument amps/effects, while SS (and some newer digital) rules for accurate REproduction. The reason is simple;
To date, ALL AF amps add an element of harmonic distortion to the signal. The TYPE of harmonics is where the difference lies. The HD of a tube amp, while generally at higher levels than SS, is, by nature, pleasing to the human ear, as the individual harmonics are "in tune, musically" with the original signal (think Whitney Houston). This accounts for the "warm, full" descriptors often applied to tube sound. SS HD, on the other hand, is, also by nature, of an order that is dischordant with the original signal (read; sounds nasty, think Edith Bunker).
The other main difference lies in the clipping characteristics of tubes vs SS, but this parameter is of use to musicians only, as listeners should never drive their stereo amps into clipping, no matter what type.
The damping factor (the ability of an amp to completely control cone motion by offsetting inertia) is many orders of magnitude better in most SS amps than tube amps. HOWEVER, many pre-SS speakers were designed to operate accurately on low-DF tube amps. This is where the progressive damping of multi-fold surrounds can really shine.
Back in the 50s, musician's gear and home hifi gear all used the same technology (and many of the same parts!). Evolving technology has changed everything, IMO, improving in the field of sound reinforcement and home listening, and, again IMO, taken the new tools for musicians to all-time lows! There's a good reason most of us listen to "old" music, and it's not just nostalgia.....