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Mass Loading ALTEC A7 VOTT 825 enclosures

71.50.22.23
Posted on February 18, 2016 at 10:17:57
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005






This is the neatest and cheapest way to mass load bone-stock A7 enclosures. These red concrete tiles come from Lowes, and cost $1.47 each, weigh 17.6 pounds each. I used about 26 by ear, to get the box to play best-to-my ears, without doing any bracing mods to the stock 825. That is about 440 pounds added to each A7 VOTT enclosure. I was using a 515B played full range, to make these determinations by ear. Next, I will add a tweeter to the mix. This was FUN to hear !!

Jeff Medwin

 

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RE: Mass Loading ALTEC A7 VOTT 825 enclosures, posted on February 18, 2016 at 12:17:54
Rafaro
Audiophile

Posts: 159
Joined: July 30, 2005
 About 600 lbs combined weight.....good luck moving it and keeping structure together! The problem with the Altec 825 is inadequate deep bass and poor greater than 10KHzs HF response. Once upon a time had a surround home system with five 825 cabs modified with 3/4" Plywood Oak veneer. The horn was reinforced and closed off from the bass reflex below. The bass reflex cab was then reinforced and an JBL 18" placed in as a subwoofer. A JBL horn supertweet was added and the system biamped. This gave 20Hz to 20Khz response and rivaled for pennies the $100K (at the time) Wilson WHAMM....actually won the bet ($1K) with the store owner that I could match the WHAMM "inexpensively". Highly recommend these mods but nowdays would place either a Danley tapped horn or a BillFitzMaurice subhorn in that bass reflex space instead of a direct radiator.

Best


Rafaro

 

RE: Mass Loading ALTEC A7 VOTT 825 enclosures, posted on February 18, 2016 at 18:34:43
Paul Joppa
Industry Professional

Posts: 7344
Location: Seattle, WA
Joined: April 23, 2001
 Like being too thin or too rich, you can't (in my experience) make high-efficiency speaker cabinets too heavy :^) Harder to mass-load the sides and back, but I expect that would be a help.

 

Might work great 4 hard rock but what about metal?, posted on February 19, 2016 at 06:20:10
Kloss
 Try baffles they sing with baffles..

 

RE: Might work great 4 hard rock but what about metal?, posted on February 19, 2016 at 10:03:10
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 No, there is something gained with added mass to the enclosure, that baffles will not get you !! It lowers greatly distortion and improves fidelity, when the box is massively loaded and held rigid.

Its very audible, suggest you try it out, and listen, using Lowe's tiles, etc., as I have done.

Have fun.

Jeff

 

RE: Might work great 4 hard rock but what about metal?, posted on February 19, 2016 at 10:34:38
Kloss



Baffles lower response mass does not and while it may be a good idea on a7 for my massive RCA bins not so much they already have mass. I can easily measure the extra bass the baffles add on the big RCA and my 1/2 w bins.

 

RE: Mass Loading ALTEC A7 VOTT 825 enclosures, posted on February 19, 2016 at 13:33:34
GM
Audiophile

Posts: 595
Location: Georgia
Joined: April 26, 2000
 You brace every panel and tie them all together so the cab can't 'breathe' and for an 825 cab + bracing, added mass set on top calculated out to around 246 lbs, so drlowmu's experiment gives some idea how much bracing helps.

Even small, tall MLTL cabs driven with dinky little 'FR' drivers, which are intrinsically well braced, require a lot more weight than I thought.

A RadioShack 40-1354 ~5.25" FR driver tuned to around 42 Hz in a ~7"x 8"x 48" MLTL built from a pre- Civil War era Southern Pine constructed barn, which cut more like metal than wood it's so hard/stiff, still required over 60 lbs of pennies in a wood wine box to 'anchor' it to a relatively massive 'floating'/suspended floor [hardwood floors over a crawl space].

FWIW, my test is it's enough when I can stand an old silver quarter on edge and it doesn't move when the speaker's driven with pure tones and pink noise as hard as it can handle from slightly below Fs to the XO point.

GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

 

If those were mine ..., posted on February 19, 2016 at 13:55:28
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 3041
Location: Atlanta
Joined: December 15, 2003
 I would add pockets to the sides and back of the cabinet that I would fill with sand.

Those side walls can radiate sound you do not want to hear and you quickly eliminate that.

Taking a cue for Bruce Edgar: place the cabinet in a sand box so the bottom is isolated from the floor.

THEN place the bricks on the top.

When I was using Edgars horns for the EV15 woofers I would do this and it does work very well. I did feel sorry for my floors! Makes moving the speaker impossible. I would use a ship vac to remove the sand.

Now using a round horn I cannot do as much mass loading. Maybe the round horn does not need as much help?

 

RE: If those were mine ..., posted on February 19, 2016 at 19:20:41
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 You are correct, a full sand load behind the curved bass horn would do two to four things simultaneously :

(a) add mass, AND
(b) infinitely brace the too-thin curved surface.
(c) brace the too-thin side walls in their middle section
(d) It also is directly damping the woofer's mounting plate.

My goal was to leave the A7 825 box 100% stock, and be able to disassemble the mass loading at will and quickly.

It was FASCINATING to hear the differences between mass loading with 100 pounds, 150, 250 300 and ultimately about 440 pounds. I was listening " full range" on the 515Bs, with a VERY good SET amp of my own design ( two stage Type 45 direct coupled - ultra DYNAMIC ).

The determinations I made "full range" may not be valid or needed for operating the 515B as a simple two-way, up to 800 HZ only. But that is OK, at least I now very-well know the enclosure's limit when playing " full range ". It was awesome to experience all of this Rick.

Jeff Medwin

 

RE: If those were mine ..., posted on February 19, 2016 at 19:25:50
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Throw some 25 pound bags of Kitty Litter on top of the round horn first !!

HEAR that.

If better, build a square box around that round horn, sand load it, it will likely help it.

Jeff

 

RE: If those were mine ..., posted on February 20, 2016 at 08:00:12
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 3041
Location: Atlanta
Joined: December 15, 2003
 My horns are fairly substantial - over one inch wall thickness - I think the round shape helps to mitigate the need for as much damping weight as the rectangular Edgar horns.

I must admit that I have made a nod to "prettiness" with not placing anything on top of them, though the kitty litter idea has me intrigued. had never heard of using that, not even sure what it is made of!

The throat of the horn has been reinforced with a mixture of BONDO and sand and is over five inches thick and the baffle is four inches thick in most places.

Have to admit I was worried that too much weight might damage them but the kitty litter sounds safe enough.

Back when I was using ACOUSTATs (before discovering how good horns could sound twenty years ago) - the double height ones - I had them wedged between the floor and the ceiling and this made a massive (pun intended) difference in how they sounded. Keeping the speaker locked in position, as you well know, is one of the most important things we can do.

Thanks for the advice.

I would think filling that cavity behind the horn part of the ALTECs would be very advantageous. With what, knowing you want to keep them so they can be returned to original state, is the trick.

 

RE: If those were mine ..., posted on February 20, 2016 at 09:56:46
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Kitty litter is fuller's earth AFAICT.

JM

 

i tried one better, posted on February 20, 2016 at 14:06:42
merdy
Audiophile

Posts: 1710
Location: New paltz,ny
Joined: July 25, 2001
 after reading your posts i went to the local weight watchers and convinced three really wholesome women that they would have the best time of their lives.
after loading them up in my trusty saab wagon and proceeding to my audio workshop i noticed the effect right away, the car severely under steered and the turbo did nothing but whine,we finally reached the studio after using half a tank of gas for a few miles ,everything was going well so i decided to feed the lovely lonely ladies some food and vino as the extra weight would help after a case of wine 3 chickens,2 legs of lamb,beef wellington,mac&cheese,20 pounds of creamed spinach and 7 layer cake for desert we began the experiment
i had sally sit on top of one speaker facing backwards so her butt cheeks clamped the horn well her thighs gripped the a7 like a vice and the added 400 lbs worked its magic ,next did the same with Helen on the right speaker
victoria being the smaller one with a cherubic face i made sure she sat on a 2 inch maple stool on top of my tube amp i could see her admiring my big tubes
i pressed play and right away i was mesmerized in a trance all the cliches of the last 40 years of came to me ,blacker than white,deeper than space,i was now one with the musicians not only was i foot tapping i was lap slapping and crying with joy.
suddenly it all came to a abrupt end as Vicky just farted.
p.s i thought mass loading was a mechanical driver parameter
Silence is golden duct tape is silver

 

RE: Mass Loading ALTEC A7 VOTT 825 enclosures, posted on February 20, 2016 at 15:21:04
hifipaul
Audiophile

Posts: 739
Location: NY
Joined: December 22, 2008
Your experiment with mass loading matches my experiences. I didn't go that far though......Have you ever played around with extending the horn to get the rolloff lower?

 

....too Funny !..(nt), posted on February 20, 2016 at 18:18:19
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

 

RE: If those were mine ..., posted on February 20, 2016 at 20:00:01
Phil-G
Audiophile

Posts: 1
Location: florida
Joined: February 20, 2016
 A year or so ago in a fit of insanity I scratch built a pair of 828 cabinets. i braced and stiffened the box as well as i could.
But I also fabricated ultra stiff fiberglass composite horn flanges and bedded them in silicone. i also installed an 8" dia x 7" round port instead of the stock rectangular port. not getting any odd noises and my RTA indicates a strong 35 hz. I still need a sub though.
Sonic Barbarian

 

RE: Might work great 4 hard rock but what about metal?, posted on February 21, 2016 at 08:52:20
Don Reid
Audiophile

Posts: 935
Location: Rural NW Georgia
Joined: February 2, 2001
 Kloss, I'm just curious. What is the Fc of the big RCA bins?
I dream of an America where a chicken can cross the road without having it's motives questioned.

 

RE: Might work great 4 hard rock but what about metal?, posted on February 21, 2016 at 09:35:58
Kloss
 Don in my room with baffles 38hz my 1/2 w bin with a bit smaller baffles 50hz baffles add +-8 hz extension this I can easily measure not just hear.

 

RE: Mass Loading ALTEC A7 VOTT 825 enclosures, posted on February 24, 2016 at 09:09:14
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 No, but I have owned very nice large format bass horns in the past. I had six RCA Ubangie cabinets, all at one time, a couple decades ago.

Jeff

 

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