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

[LowOhms]

Q1 : Has anyone experimented with a rear magnet support, in an A7 enclosure, to be used in addition and in conjunction with the standard four front speaker frame mounting bolts?

Q2 : Does this additional rear support "sound better" - as oppossed to when the stock ALTEC speaker is supported and mounted from the front of frame only ?

Q3 : Is there a benign way ( as far as not obstructing airflow and creating minimal turbulences with the cone's back wave ) to execute said rear magnet support?

I have been thinking of using a heavy duty "plumber's pipe strap", looped in a diameter just a little larger than the OD of the 515Bs rear slug, and line the strap, where it supports the driver, with felt. Use a pair of bolts ( one upwards from the plumber's strap holes, and one downwards through the top of the A7 enclosure ) and have each bolt connected by a common threaded coupler, so I can re-torque the support over time, as the plumber's strap stretches. Stop nuts will be used against the threaded coupler.

I've never seen this done anywheres in such a manner.

Q4 : Does anyone out there have direct "doing or listening experience" with a hanging support system that is re-torquable??

If you do a wood brace from the rear cover of the enclosure, ( pressing against the rear of the 515G's frame ), you add lotsa cabinet resonaces into the driver, which should sound bad, and this effect will not occur as prominently IMHO with a hanging support.

The air-disturbance "footprint" of the hanging support I've outlined herein would be minimal.

I am in the planning stages of building a 24 mm ( almost one inch ) Baltic Birch plywood pair of A7 enclosures. No wood has been cut yet, but I have the B.B. wood on hand, waiting.

Conceptually, this rear support design approach could apply to a 604 driver in a MLTL, etc. also.

Experienced doers/listeners, what can you share with me on this idea?

Linkwitz discusses magnet mounting, but fails to address the large footprint that obstructs the cone's rear wave !! So, this as a start...makes the plumber's strap hanging method - suggested to me by Dennis Fraker of Serious Stereo, look better to me !!

http://www.linkwitzlab.com/frontiers_2.htm#N

Thanks friends.


DrLowOhms ..... Jeff Medwin

[VolvoHeretic]

Don't know anything , but I like to invent. What is the diameter of the 515 magnet cover which is all that the brace would be supporting?

[LowOhms]

Hiah,

No large area wood braces behind the cone wanted.

Trying to avoid all internal braces, hence 24 mm Baltic Birch construction. Everything will get dadoed and screwed together.

All the rear wave "sees" in my original post is "a 5/8ths metal strap around the driver, and a couple of bolts and a inner-threaded coupler, and stop nuts", rising to the top of the cabinet ( but WAIT !!! - in an A7 there is not much distance to add ALL of that hardware ) .

In fact, visualizing it some more, in a A7 there may ONLY be needed ONE long bolt, rising upwards through the strap, and penetrating through the A7 's top enclosure surface, with an adjustment nut, and a load bearing fender washer on top, outside of the enclosure. Be a good idea to snug a washer and nut on both sides of the enclosure. Yes, that is it !!

For a 604 MLTL, the threaded coupler and stop nuts may come into play, since it usually has more vertical distance existing above the driver !

Jeff

[bowtie427ss]

Brace externally such that the 515 can be/is mass loaded with a simple block between it's magnet and the cabinet back.

Damp the 515's basket.

[LowOhms]

Hi BowTie,

I addressed that in my original post. Nixed it. See this paragraph :


" If you do a wood brace from the rear cover of the enclosure, ( pressing against the rear of the 515G's frame ), you add lotsa cabinet resonaces into the driver, which should sound bad, and this effect will not occur as prominently IMHO with a hanging support. "



I prefer to avoid that rear cover - wood brace approach. It "sounds worse" I have been told by one acoustical engineer.

It reminds me of an out-of-time negative feedback loop, only acoustical.

But then, I am no expert. Just have my thoughts. Thank you for posting, and of course, you certainly can disagree with my viewpoint and reasoning. Respectfully,

Jeff

[bowtie427ss]

If it hasn't been demonstrated via listening or measurement, the claims are meaningless to me, with all due respect of course.

Adequate bracing and damping is mandatory.

Add more mass to the back panel to tune the resonance below the LF driver's operational BW.

I would be inclined to experiment with different back panels, full removable, half removable, even perhaps a fixed rear panel with an "access door" only for the LF driver.

You should be able to find an effective way to skin this cat.

[Old Guy]

I would have to call that engineer. The back cover could be braced externally to reduce resonances to almost nil. It may have sounded worse because he expected or wanted it to. Honestly, you waste a lot of time on strange thinking. Eliminate all cabinet braces to not disturb airflow in the cabinet then hang a metal strap in the cabinet?

[tomt]

Don't know anything , but I like to invent. What is the diameter of the 515 magnet cover which is all that the brace would be supporting?

last time i measured mine i got 6" diameter.

not exactly tho ....


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perhaps something like this -



these come in a variety of sizes,

i forget what they are called .

certainly less airflow restriction

than the more common lumber bracing ....

[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);