Rear Magnet Support for a 515B in a A7 enclosure. QUESTIONS

[GM]

1] Extensively, from small ?full-range? drivers to 18? subwoofers and not to put too fine a point on it, the first AFAIK to try and enlighten DIYers on the subject when I got on line back in ?96.

2] To mine and the folks who made the effort to compare, yes, regardless of the size/type of driver and cab loading.

3] Yes. The plumber?s strap/hanging support is better than nothing I guess, but neither addresses the reasons for bracing drivers and why you haven?t seen one done this way. Regardless, the industry?s proper pattern placement for four bolts renders it moot AFAIK as it?s not primarily done for cosmetic?s sake as most folks apparently assume. Had [horn] DIYers wondered why Altec used a different bolt pattern on the 825 [and its screw block before the ?bean counters? put it on a ?diet?], they might have come to realize the real reason or done a bit of ?due dilience? to learn more about the ?physics of the situation? as one early WWW audio BBS forum ?techno-weenie? referred to the underlying math of all things technical.

4] Yes, but your strict limitations as to what you?re [not] willing to consider and especially your reason why, renders it moot, so this will be my only post on the subject. FWIW, quite awhile back I promised Phil G. I?d collect all the bracing info [including for drivers] that me and others have posted over time into one document, but it?s proving far more frustrating/time consuming than I anticipated, which combined with yet another year [so far] of spending most of my quality time ?putting out fires? for a variety of reasons beyond my control, it?s still a way?s off.

Hmm, stiffness increases at the cube of thickness, so going from 5/8? to ?? is a ~3.11x increase, definitely worth the effort, but some bracing is still required. ?? ? 1? = ~4.267x still can?t compete with bracing?s up to ~10x local area increase, so doesn?t seem worth the total cost to me, especially since I can take a 5/8? cab and bond a bunch of old tiles ripped out of a kitchen/bathroom rehab, which combined with a bit of bracing will be at least as ?stiff?/?dead? as your high $$$ one. Worst case $$$ wise, I?d use new cheap vinyl stick-on tiles, but that?s just me since I came from a place where to build something meant straightening a lot of discarded nails in advance.

Anyway, looking forward to how it all pans out. For sure, it?s bound to be at least an order of magnitude better than most factory cabs. It would be interesting to compare it to a properly braced one though to determine if there was any subjective or outright audible difference, especially beyond 1.0 m/2pi [half] space.

GM

[LowOhms]

1] Extensively, from small ‘full-range’ drivers to 18” subwoofers and not to put too fine a point on it, the first AFAIK to try and enlighten DIYers on the subject when I got on line back in ’96.

2] To mine and the folks who made the effort to compare, yes, regardless of the size/type of driver and cab loading.

3] Yes. The plumber’s strap/hanging support is better than nothing I guess, but neither addresses the reasons for bracing drivers and why you haven’t seen one done this way. Regardless, the industry’s proper pattern placement for four bolts renders it moot AFAIK as it’s not primarily done for cosmetic’s sake as most folks apparently assume. Had [horn] DIYers wondered why Altec used a different bolt pattern on the 825 [and its screw block before the ‘bean counters’ put it on a ‘diet’], they might have come to realize the real reason or done a bit of ‘due dilience’ to learn more about the ‘physics of the situation’ as one early WWW audio BBS forum ‘techno-weenie’ referred to the underlying math of all things technical.

4] Yes, but your strict limitations as to what you’re [not] willing to consider and especially your reason why, renders it moot, so this will be my only post on the subject. FWIW, quite awhile back I promised Phil G. I’d collect all the bracing info [including for drivers] that me and others have posted over time into one document, but it’s proving far more frustrating/time consuming than I anticipated, which combined with yet another year [so far] of spending most of my quality time ‘putting out fires’ for a variety of reasons beyond my control, it’s still a way’s off.

Hmm, stiffness increases at the cube of thickness, so going from 5/8” to ?” is a ~3.11x increase, definitely worth the effort, but some bracing is still required. ?” – 1” = ~4.267x still can’t compete with bracing’s up to ~10x local area increase, so doesn’t seem worth the total cost to me, especially since I can take a 5/8” cab and bond a bunch of old tiles ripped out of a kitchen/bathroom rehab, which combined with a bit of bracing will be at least as ‘stiff’/‘dead’ as your high $$$ one. Worst case $$$ wise, I’d use new cheap vinyl stick-on tiles, but that’s just me since I came from a place where to build something meant straightening a lot of discarded nails in advance.

Anyway, looking forward to how it all pans out. For sure, it’s bound to be at least an order of magnitude better than most factory cabs. It would be interesting to compare it to a properly braced one though to determine if there was any subjective or outright audible difference, especially beyond 1.0 m/2pi [half] space.

GM

Dear GM,

Thanks for the detailed answers to my original post's four questions. Very kind of you to respond, and helpful.

I looked over the Cooper Industries pipe hanger catalog "mah" referred us to. The problem was that the 515B rear slug is about 6 1/2 inches in diameter, and the pre-made industrial hangers are either for 6 inch or 8 inch OP pipes, so the magnet would "swim" on a 4 inch radius hangers IMHO.

Back to a DIY plumber's strap!! All I want is a little support on the rear of the driver, maybe just two pounds of tension, upwards. But I wanted to find something minimally magnetic and strong. other than the inexpensive standard plumber's straps.

There is a perforated Stainless Steel strap sold by McMaster-Carr. It would have minor magnetic effects, being austenitic, and would be strong. 304 Stainless Steel 3/4 inch wide strapping that is 3/64th inch thick, with alternating 1/8th and 1/4 inch perfroated holes on half inch centers. Ten feet for $11.49. URL is as follows:

McMaster-Carr

I think I will make a "sling loop", a few inches larger than the 515B's rear body, and run a long bolt upwards through the A7 enclosure's top surface, and have a large fender washer to spread the load. Use a nylon centered "safety " nut to adjust tension conservatively. I'll be very careful not to over torque the bolt, and goof up the driver internally. Just help it some with gravity-relief at the woofer's rear.


Others may want to experiment with this, I have not even hired a carpenter to cut the A7's wood !! To future experimentors : please report back to us all, as to any listening results, and I will do likewise in the future. Thanks to Dennis Fraker for his input and to all others for contributing to this thread.

Special thank you GM for your experienced input.

LowOhms.......Jeff Medwin

[westend9]

Internal brace supporting Altec 416 in DIY MLTL cabinet. I chose to use a very stiff foam rubber between the magnet cover and the wood brace as it mostly does away with any resonance issues and affords a compressive fitment. Disruption of sound waves was secondary to affording a continuous brace, between panels, to these large cabinets (15.5 cu. ft.).

[tomt]

What is the diameter of the 515 magnet cover

actually, the 515 has no magnet cover.

it's all part of the magnetic circuit .

[bowtie427ss]

actually, the 515 has no magnet cover.

it's all part of the magnetic circuit .

No argument here. Too bad Altec didn't have a cutaway of a 515 somewhere in the literature like they do of the 604-8G.

Here's an image i scrounged with a 515 magnet slug, pole piece, and return pot(on the right of course);