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Designing the DIY 'Big Reds'

toxcrusadr

toxcrusadr

Omelette au Fromage
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I'm hoping to get some speaker design gurus interested in this one. As some of you may recall I have a rather large shop building - metal barn with a concrete floor. Lots of room to play around. I plan to build some speakers that are 1) large and 2) use stuff that I have around as much as possible.

The first part of the design is just general topology.

I have a pair of Altec VOTT cabinets, 828H that take 15" woofers. I have some vintage 15" 4 ohm CTS woofers that should work well. They are early 70s, very heavy and I've tested them with WT3.

I don't have the Altec horns, but I have a lot of decent midranges and a pair of Heil AMTs (the big ones). My thought was to build a mid/tweeter enclosure (or repurpose other speaker cabinets) to use a pair of mids with the AMT in the center. For the upper cabinets, I've read that a vertical array sounds better, but it would get kinda tall and the Altecs are already washing machine sized.

1) Should the mid/tweet array be vertical or horizontal?

If the mids are 8 ohm I can parallel them for 4 ohms if need be. I have lots of paper cone mids from consoles and scrapped speakers, nothing high end, but I could upgrade later if I get this working. Crossovers would be outboard, DIY allowing for bi/triamping later. It seems Heils come in 4 and 8 ohm so I'll need to figure out which I have before I can tackle that part.

I've read several AMT DIY threads and I don't think I have to worry about how low the AMTs will go in a 3-way speaker. At least to start with, I thought crossover points of 800 and 5000 Hz would be OK.

2) Suggestions on crossover frequencies?

I already know how complex speaker and xover design can be and that I'm shooting in the dark with this. It's a garage system after all. :D

Any and all tips are welcomed on the above topics or anything else you can think of.
 
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What color are they going to be?

The MTM topology depends on what you want for dispersion. A vertical array will have limited (useful) vertical dispersion but very good horizontal coverage. A horizontal arry is just the opposite (and why the horizontal MTM center channel speaker is generally a bad idea).

Crossover will really depend on the drivers and where they are well behaved.
 
It's basically a garage with high ceilings, about 35 x 60 ft. No one will be sitting in one spot listening to these, rather there is a lot of moving around. Maybe good horizontal dispersion is best?

I'm calling them the Big Reds as a working title because these beat-up Altecs are painted red. They'll get stripped, dings filled in and painted something close to Altec gray, with reproduction VOTT stickers on the sides. :yes:

I have impedance curves on the woofers and their TS params, but nothing on the AMT's other than what I've seen here (1500 Hz seems to be the bottom end for a two-way, IIRC). Haven't chosen the mids yet from my driver piles. The WT3 was borrowed so I don't have that option for testing mids. I do have a digital db meter and sig gen (uh, when I fix it, it's an old HP tuber and it's motorboating). This is how I got to SWAG'ing the crossover points: I have little to go on. Suggestions welcome for low tech methods of doing something better. :D
 
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Here's the original thread where I was considering using the CTS woofers, and Gordon W thought they might work out OK.

http://audiokarma.org/forums/showthread.php?t=374718&highlight=CTS+woofers

The TS params in that thread were posted by another AKer for very similar woofers. I don't think I ever went back to pull my #s out of the computer to make sure they match, need to do that. I tested all 4 that I have.

Would it help in selecting the lower xover point to load these into the cabinets and do some in-room freq response tests with a sig generator?
 
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I dug out the T/S params for the woofers I'd like to use from the WT3 tests I did awhile back. This is an average of 4 woofers, all pretty close. They are a bit different from the CTS woofers in the other thread I linked, Fs a bit higher and they are 4 ohms instead of 8.

Re 2.96
Fs 32 Hz
Qt 0.170
Vas 26.2 cu ft
SPL 102 db/1w/1m

I have other params in case they're needed. Just thought I should post these for the record, in case anyone comes along looking for data on these since they are not that rare. I'll try to get a pic of the woofers up too.
 
Do you really need dual mids? If you're not crossing over low, it shouldn't be hard to get a single to go as loud as the other drivers can manage.
 
toxcrusadr said:
but nothing on the AMT's other than what I've seen here (1500 Hz seems to be the bottom end for a two-way, IIRC).
Click to expand...

Do you have these Heils (see specs):
http://www.parts-express.com/pe/showdetl.cfm?partnumber=264-600

I have these in a 2-way crossed at 1 KHz (or 1.2 KHz, I'm still messing with them) 18 db / octave and they work well for me. I've read the posts on AK that suggest against using them in a 2-way. They sit atop the cabinet with an Altec 416 woofer/Mid.
 
Mine are vintage and look like these:
Heil_AMT_tweeters.JPG


I found a note I had left myself awhile back that said they aren't that great under about 2 KHz, according to EchoWars. Also, I have a buttload of mids sitting around, nothing real special but I'd like to put them to work. Finally, I have a huge room to fill with sound and a boxfull of inductors. Thus the three-ways with dual mids. :D But, I'm open to suggestions.
 
Chris, there is a Pioneer SF700 3 way electronic crossover a friend has for sale nearby. It has selectable 300, 500, 700, and 1K woofer points. I would source a pair of Altec 511s and drivers and run these biamped.
 
Hey, that's MY pet speaker name! :D

attachment.php


I think you can guess which one it applies to, in that picture. :D

For those who haven't seen that picture before- yes, those are two 18" woofers per cabinet. And the cabinet is over 6 feet tall.

I even built some "Little Reds":

attachment.php


... which are still about 4 feet tall, with two 15" each.

But seriously, I don't care about the name. Unless you're working Anime Weekend Atlanta setup- then I DO care, because I want to make sure these particular Big Reds go to the right ballroom in the hotel!

Regards,
Gordon.
 
toxcrusadr said:
Mine are vintage and look like these:
Heil_AMT_tweeters.JPG


I found a note I had left myself awhile back that said they aren't that great under about 2 KHz, according to EchoWars. Also, I have a buttload of mids sitting around, nothing real special but I'd like to put them to work. Finally, I have a huge room to fill with sound and a boxfull of inductors. Thus the three-ways with dual mids. :D But, I'm open to suggestions.
Click to expand...

I concur with the opinion, that these Heils are much better when restricted to 2K and up. A 2K crossover is about the lowest I'd go, to avoid breakup.

Regards,
Gordon.
 
GordonW said:
I concur with the opinion, that these Heils are much better when restricted to 2K and up. A 2K crossover is about the lowest I'd go, to avoid breakup.

Regards,
Gordon.
Click to expand...
Gordon - What specifically have you heard when you crossed them lower?
I ask because I have a pair crossed at 1200 Hz mated with the 416s and they sound fabulous. I drive them with a 2A3 SET amp to no more than 95 db-c or so, usually in the mid 80s db-c. Maybe you hear breakup at very loud volumes? I just don't hear any of the nasty stuff that I've read about more than a few times.
You can see my pair in my avatar.
 
sheltie dave said:
Chris, there is a Pioneer SF700 3 way electronic crossover a friend has for sale nearby. It has selectable 300, 500, 700, and 1K woofer points. I would source a pair of Altec 511s and drivers and run these biamped.
Click to expand...

I may get to that eventually, just thought it'd be fun to play with some of the stuff I have sitting around. Actually have a Behringer crossover bought from another AKer already. This garage system is kind of an experimental lab. At the rate I'm going with it though, I may find some horns at the curbside before this is all done anyway. :D
 
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