Should be 2B
From this article by JBL could someone tell me if underhung is figure 2b and not 2c . Thank you !
Should be 2B
Hello from Australia
This my first post here having been banished years ago for unknown reasons. Good reasons for becoming unbanished have emerged. I have been trawling many sites as a guest, seeking info aligned to my projects.
I was fortunate to have visited old cinemas in the 1970's and collected a number of Altec horns and drivers for small money. (2 x 288C with 803 multicellulars, Western Electric field coil drivers, the 515 & 604D drivers which are the subject of this post, some cabinets and motley collection of horns and drivers, all for $379 of '70's AUD. About $3000 today!!) Most didn't come close to any +ve WAF so were relegated to workshop duty or worse, stored for 45 years. Some still keep company with BIG horns built for pop concerts and Altec and JBL hardware all of which has been home to a long line of spiders.
Now to the point....
I'm in the process of re-coning a pair of Hollywood 515s and a 604 duplex with aftermarket (of course) coils and cones. These drivers appear to have the same front plate geometry with the plate tapered to 8mm at the VC gap.
515 PROJECT
These 515's will be fitted to some local copies of an Altec VoTT enclosure. I reconed these 515s in the 70's with genuine 15 ohm cone/coil assys which have VC windings of 7mm height. I have since bought after-market 8ohm re-cone kits as a trial (not from GPA). Their VCs have windings of 8mm height.
The kit of parts also includes "C" stiffness spiders. These seem to be much stiffer than the original cones' concertina fabric 'spiders'. (Same material as the outer surround.) I'm reluctant to commit to these if the more compliant "B" or "A" spiders are available. The supplier needs another prod to produce this info.
The 1970's recone kits included Altec doping compound which was applied as instructed to the middle valley of the outer cloth surround so it did not completely seal the surround. My reading has found a few emphatic advices that the 515 should have its cloth surround completely sealed by a thin coating of EVA or PVA sealant/adhesive. The doping material of old may not be appropriate or available. GPA couldn't ship it as it's now considered HazMat. I'm unsure on how to proceed.
The recone kit supplier claims that the 515's will be transformed to 515B specs, but, upon inspection, I now doubt it.
So, Dear Reader,
1. what is the likely modification to performance with coil height that matches the gap height rather than being slightly under-hung? (8mm vs. 7mm). Better or worse distortion? Better or worse anything else?
2. Should I attempt to match spider compliance?
3. Should I seal the cloth outer surround completely or some variation of that idea?
Should the current plan not be such a good one, the 1970's cones can be refitted.
604D PROJECT
This is an indulgence. I can't leave this driver in its current state. The original 604D cone has its original Bakelite spider and VC is intact but the cone is beyond recall. This decrepit cone Assy may have to contribute its VC as no after market coil I can find has a 10mm coil height.
In this case the spider compliance is pretty stiff. Not sure if this was the best they could do back in the '40's or is it deliberately so to prevent the cone colliding with the coaxial horn?
Any advice on how to proceed with this work will be greatly appreciated
Rog (aka Roj.)
Hello Rog ! I'm curious as to why you were banished ? As you don't know either, I went back to see what user names you may have had in the past. Nothing shows up, it may have been too long ago.Do you recall what user name you had at the time of banning or is it the same (Rog) ? The board doesn't ban folks for no reason.The board has only banned a half dozen members in it's entire existence and most of them for spamming...Originally Posted by Rog
But anyway Rog "Welcome Back to the Board" ! I would only use GPA parts for them.. Do you know anyone in the USA who could purchase for you from GPA and then ship it out to you somehow ?
The cloth surround has to be completely sealed with the doping compound...Otherwise air could leak through the cone..
1] It will have basically 0.0 mm Xmax Vs 0.5 mm, so too little to make much in the way of audible difference.
2] Wasn't aware of any spider options other than the early phenolic spring and later impregnated cloth, but due to these being designed for horn loading Vs the later reflex cabs, stiffer is better overall.
3] Surround should always be sealed for any sort of [mid] bass cab alignment.
They could do better, but the performance requirements back when these drivers were designed didn't include any real bass and little mid-bass, so reproducing the lower mids on up bandwidth at high speech, instrument intelligibility was the goal where the human vocals and acoustic 'bass' instrument's harmonics that define them resides, so keeping them as close as practical to stock [stiff] and enjoying them for what they are and adding separate sub, super tweeter systems to handle a modern recording's much wider bandwidth is the best of both for bridging this 'generation' gap.
Period correct electronics will of course bring out the best in them since they were designed as a closed system Vs today's where the speaker is just basically a damping resistor.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Hello Altec Best
I am sorry to be so late to reply. I waited on my local supplier for info by email and eventually phoned them. The discussion was far from useful to me and I'm still waiting for the info on available stifnesses of spiders.
I can still buy direct from GPA but, in a response from Bill H years ago, the old doping compound could not be shipped to Australia. I am currently assuming that the sparing application of EVA sealant is an appropriate means of treating the outer suspensions.
I'm busy with a full time job, that of servicing scientific equipment, so have less time than I'd like for this absorbing hobby. Retirement isn't far off so that will change.
Thanks
Rog
- - - Updated - - -
Thanks GM
In terms of bandwidth, I have expected too much of my two 515s. It's doubtful that I will use them in the way in which you have generously described but I'm happy to learn from the wealth of experience from you and others here and elsewhere and modify what function these drivers can realise.
I haven't established which stiffness spiders are on offer through my local supplier (Queensland Speaker Repairs) but those supplied with their recone kits are of the impregnated coarse cloth type, yellow/orange in colour.
I feel the need to attempt to match the compliance of the assembled cones purchased as original Altec parts 40+ years ago. Those supplied to date are much stiffer.
Do you have any estimation of whether and by how much an impregnated cloth spider will 'relax' in early use?
Rog
Hmm, by the '70s, '80s the spiders were quite limp, relatively speaking, allowing mid 20s Fs, 20+ ft^3 Vas and due to all these 'old tech' motors having such limited Xmax, Xmech, you can't drive any of them hard enough to really loosen them up much without risking either bouncing the VC off the backplate or 'cocking' it in the gap, which usually requires a re-cone IME.
Even my mid '50s ~20 Hz, 20 ft^3 Vas 515Bs were still meeting spec circa 2000 'close enough', the last time I measured them. If you can get the proper re-cone kit for the ~20 Hz, 20 ft^3 Vas 515B like mine, it's the best overall performing one WRT wide bandwidth [BW] box loading IME, though no clue what the kit number is.
The diaphragms OTOH has changed over time due to the dramatic weather changes in my house since I don't have a central heat/AC system to maintain some semblance of average temp, humidity year round, so in an attempt to offset this a bit I treated them with a light 'dusting' of Dammar to block out moisture. Unfortunately, it didn't block out he Summer's sun UV, so now need to be 'dusted' with paint if I want them to look ~ like new.
Anyway, when I want to loosen up a driver I just set it outside in the Summer sun with a scrap of plywood to protect it from UV/roaming animals as it gets hot enough in my locale to bottom it out in a few hours or 'uncock' them if they've been stored upside down too long. Will be doing this for the 'umptheenth' time this year to a ~NIB pair of 1st run 421-8H.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Not to hijack the thread, but something GM said made me think. I have wondered about how speakers and other electronics are affected by heat/humidity. My main listening area is not heated/cooled also. It stays pretty cool in the winter but gets damn hot in the summer. I can't "hear" a difference between the seasons. The only time I have heard speakers sound different is when it was below zero.
Anyways I always wonder about the long term affect of having my stereo in a non climate controlled area. From what GM says it sounds like the woofers are not really affected.
I don't run my Altecs in the shop anymore but do have smaller drivers that see really steep swings in temperature/humidity. I haven't noticed any difference in presentation. I live in MN so if the shop isn't heated (it happens, occasionally in Winter) temps are very low. The shop doesn't have A/C so the Summer brings ambient seasonal conditions. I should remedy that with a spare A/C unit or buy one of the more efficient new ones and work in comfort. Glad I read this thread and added to my to-do list.
BTW, GM--
My MLTL cabs you designed are still singing. I can't thank you enough for your input during the construction. I enjoy them immensely!
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