Adding MASS to an A-7 825 enclosure

[LowOhms]

Over this end-of-year time, I am putting together my FIRST ALTEC system , a A7/800 system, and experimenting quite a bit.

With a stock 825 box, loaded with only a 515B, with good wiring between amp and driver ( minimum of 9 AWG ), and driving the woofer full range, direct ( no crossover, with attendant losses ) I find that the more MASS I load it with, the better it sounds. I am ( temporarily, to experiment ) using my L.P collection's storage boxes, filled with LPs, as progressive 53 pound mass increments.

Listened to two L.P. boxes added to an 825 ( 106 pounds ), three boxes ( 159 pounds ), four boxes ( 212 pounds - see photo ) and finally, most recently five boxes ( 265 pounds ). Easily, and beyond any doubt, the most mass added sounded the cleanest and most dynamically contrasted, and lowest in perceived distortion.

I THINK, for DECADES now, people have missed the boat, towards getting their ALTEC speakers, A7 variety to perform to full potential. 265 pounds, once heard, makes it HARD for me to go back to 212 pounds. I have figured out, between adding mass behind the woofer's curved side flairs, and making / adding TWO triangular sand ( or kitty litter ) boxes to place on top of the A7, adjacent to each side of the tweeter horn, one can get the weight needed to " extremely " MASS-load the enclosures. Behind each curved-horn side is really a GOOD location, because, in addition to bracing the curved sides infinitely, it is also in INTIMATE contact with the woofer's mounting board.

I also plan to build a second pair of 825 (upper) rear woofer-access panels, out of one inch Baltic Birch Europly material, as this panel directly absorbs the back wave, and is an EASY mod to execute and install !!

Stay tuned over this next month. I am loving what I am hearing, with 515B directly driven, and 265 pounds on the top. Exciting to me. !!

People will say, well, just brace it better, stock box is too flimsy. Yes, but I have a sneaking suspicion that adding mass, in addition to bracing, will easily give higher fidelity than bracing alone !!

This is fun, hearing these 53 pound increments. Kiddie litter bags can be bought for as low as $2.99 in my town, and that is 25 pounds to experiment with. Buy more than one !!

Merry Christmas,

Jeff Medwin....LowOhmsAttachment 2817

[GM]

Well, you brace first since it increases stiffness at a much lower increase in mass, but adding mass is still desirable in a bass cab [my ~20 ft^3 cabs weigh a calculated ~245 lbs with dual 515Bs]. That, or bolt it to a massive concrete floor or at least pedestal. Since stiffness goes up at the cube of thickness, the easiest way to add mass/stiffness is to double up on the exterior panels and triple up the top of the horn in the A7's case. If the total weight is too much to move around, then of course a concrete, marble or similar removable plate will work as long as it's rigidly attached.

Note that if one has a 'suspended'/'floating' floor like I do then long term sagging can occur and why I now have extra wood 'spanners' with screw jacks in the 'crawl' space under my cab's sections of floor.

GM

[LowOhms]

Well, you brace first since it increases stiffness at a much lower increase in mass, but adding mass is still desirable in a bass cab [my ~20 ft^3 cabs weigh a calculated ~245 lbs with dual 515Bs]. That, or bolt it to a massive concrete floor or at least pedestal. Since stiffness goes up at the cube of thickness, the easiest way to add mass/stiffness is to double up on the exterior panels and triple up the top of the horn in the A7's case. If the total weight is too much to move around, then of course a concrete, marble or similar removable plate will work as long as it's rigidly attached.

Note that if one has a 'suspended'/'floating' floor like I do then long term sagging can occur and why I now have extra wood 'spanners' with screw jacks in the 'crawl' space under my cab's sections of floor.

GM

Dear GM,

Perfect. This was a very kind and helpful response. You are very kind to many people.

I will take it as my Christmas present from you and the Board, and USE it.


G-d bless you, G-d Bless you ALL, and Merry Christmas.

Jeff Medwin