Modified 7' tall Altec Voice of the Theater cabinets

[RacerXtreme]

http://www.audioheritage.org/html/pr...altec/vott.htm



Hi everyone. Is anyone familiar with the 7' tall Altec Voice of the Theatre cabinets? I have 4 of the A4's complete with wings. Sold all eight of the Altec 515's and 12 Altec 288C's. Want to put 400 watt JBL 2225's in place of the 60 watt 515's. JBL's enclosure guide recommends 8 cubic feet of internal volume for two 2225's. Obviously the cabinet is a little too big. Thought about dropping a single 18" woofer in the bottom of the box and time-aligning it with my Rane AC 23 electronic x-over, but will probably try to find a way to reduce the overall internal volume instead.

Any suggestions as to how I can dial in both the internal and port volume to make the JBL's feel more at home in the big exponential horn loaded cabinets?

Thanks for the help.

Guy Strem
Shelby Township, Michigan

[wunhuanglo]

You'll want to post this on the Altec board.

http://www.hostboard.com/cgi-bin/ult...b=forum&f=3729

Many helpful people there.

Also, the A4 cabinet is the 210. Google "210 split" - there's a project to domesticate the 210 for home use.

HTH

[wunhuanglo]

http://www.users.qwest.net/~ccfrye/210.htm

[GM]

Originally posted by wunhuanglo
You'll want to post this on the Altec board.

He already did, but I guess he didn't like our thoughts on the subject: http://www.hostboard.com/cgi-bin/ult.../f/3729/t/1227

GM

[RacerXtreme]

One more thing......... What type of high freq. compression driver / horn combination will keep up with 8 15" JBL's ?

Tried the 288C's with Titanium diaphragms and they sounded o.k., but looking for something better.


Thanks,

Guy

[RacerXtreme]

Hi .........thanks, but I've already asked that question there. I'm a member of that board. Just thought I might find some different opinions here. I've seen that article about the 210 split before, and e-mailed him a few times also. I don't really want to head in that direction. It does seem like it would sound really good, but I may use these cabinets from time to time for large "occasions" and I think they will ultimately work better down low when at super high SPL's if the box is left intact. That's not to say that much work still needs to be done to stiffen them up and brace them properly........ It also gives me the option to put a single 18" woofer down there if I want.

Thanks for the help tho..........


Guy

[wunhuanglo]

I have some experience with building and tweaking the 828 cabinet, as well as modeling and using the various 515 driver incarnations and older JBL 15" drivers. I've also studied the 210 a bit.

On that basis, I feel fairly confident that what's true of the 828 is true of the 210 - there ain't no bass and you'd be wasting your time trying to get any. The box is just huge and designed to get at most poorly defined 50-60 Hz response from a hugely efficient driver pushed by tiny little tube amps.

It's the midbass - midrange projection that the Altec designs excel at, so why try to make them do something they really can't do? If you want to use the 210 for events you're looking at problematical logistics to say the least.

Acknowledging their strengths, cut down the cabinets to maximize their mid performance. Augment with some bass bins – Roger Mogale’s designs (http://www.speakerplans.com/) would be perfect.

Alternatively put the 2225’s into 10Pi cabinets (http://www.pispeakers.com/) and scrap the 210’s altogether.

At the bottom line my experiences tell me you’re barking up the wrong tree if your goal is a contemporary level of performance. You have the choice of accepting the design for what it is, in which case the 515G is probably the driver of choice, or essentially abandoning it by excising the midrange horn and discarding the rest.

HTH

[RacerXtreme]

Hi thanks for the help. You said you were familiar with the older 15" JBL drivers. How about the 2225's or 2226's ? Have you spent much time listening to the 210 cabinets? You said you've studied them a little. My 210's are on nice casters so they roll around easily when moving them. Experience has shown me tho, that the low end improves when you lay them on their side and stack them. There is just more of the cabinet surface sitting flat on the floor and they vibrate less when you push them hard. In a theater environment, the wings can and do help with mid-bass projection, but the casters should really come off for the best low end. They just make them so much easier to move around.


Guy

[simon5]

What the internal volume of the box you got?

[RacerXtreme]

That's the 64 thousand dollar question. I plotted 8 points on a graph to determine the area (or rather - volume) under the curve of the flared part of the horn. Some calculus and a litttle AutoCAD later........ I found out that the volume of air underneath the flared part of the horn is about 8.13 cubic feet. That excludes the bracing just below the flare of the horn and does NOT include the entire rectangular shaped area at the bottom part of the cabinet. That's about 16 cubic feet. Add another 8 for the top half of the horn and you've got 32 cu. ft. so far. There is some additional space unaccounted for just behind the 15" woofers too. It will take a while to accurately calculate the exact internal volume of the cabinet including all the internal bracing, but I'm guessing it will be around 37 or 38 cubic feet.......maybe a little more.

After reading Jim Dickenson's article on how to restore and modify 210 cabinets, one thing in particular stands out. He said: "There is no such thing as too much internal bracing.....".
Which obviously makes sense. So it's time to stiffen them up a bit, add some insulation, and figure out a way to substantially reduce the internal volume. Jim recommends blocking off the entire area behind the upper flare of the horn. And realistically, the entire chamber down in the bottom of the box can go too. Have to do more calculations do make sure.

How about some type of horn / compression driver combo that will keep up with the 15's?

Or a single 18 ?

If I stick a single 18" woofer in the bottom of the cabinet (totally blocked off from the space behind the 15's) do you think I will be able to "time-align" the 18 with the 15's above it? I have a Rane AC23 electronic x-over with that feature on it, but I'm not sure if it
can make up the difference in vertical displacement of the voice coils. In other words, I'm not sure if I can delay the signal going to the 18 enough to work in sync w/ the 15's. The 18 will be further forward in the cabinet (from a side view) than the 15's will be.

Stiffen up the box, dial in the proper internal volume for the JBL 2225's, get the port area in the ballpark, add an 18, and it should be one formidable low end cabinet.

That's a lot of work tho .........isn't it?

Argh.............

Thump ...........thump.........




Guy