Dual 416-8b MLTL design

[Mercury3]

Hey everyone I just signed up to ask a few questions. I don't really know what I want to do so I'm still contemplating options. Please bare with me and I'll explain where I'm coming from.

I'm getting old now but remember way back in the olden days (1981 actually) I bought my first pair of really nice and new speakers - Altec Model 19's. They were nice but as many of you who has this audio bug in our blood know eventually we want to move on to try new and other things. So I sold them and went on over the years to own many other nice speaker designs some bought and some built.

I've always missed the big and effortless sound that my old model 19s had. They weren't without issues though - I'd bi-amped mine at 800hz with an 18db electronic crossover which did improve the sound. That large 416 struggled to do a good job up to 1200 hz. Likewise it struggled to go low. I bottomed the woofers out once (ya learn your lesson after once) trying to get them to go lower but they just couldn't do it. Regardless I still consider those to have been excellent speakers that did a lot right.

So I've wanted to build something again and have spent a few days reading as much as I could find on Altec's with special interest in the Transmission line design. Others have mentioned how the 416 generally cannot go low but I gather it can in a properly designed transmission line cabinet. Excursion might be an issue which is why my thought would be to use two 416s per channel. From what I've read 24 cubic feet. That's tough but doable.

If I do proceed with such a design I'd probably need to run them up to 600 or 700hz to some 511 horns.

One question I have - I'm old school and remember the old transmission lines were just open at the end of the line. Maybe tapered but open. The newer designs I've read about recently (I think a few I saw designed by GM) have a port towards the end of the line rather and being open. Would this port be tuned similar as we would tune a bass reflex port? I'm guessing it would have the necessary quarter wave length delay due to the port being towards the end of the line and the tuned port would provide better back pressure for the woofer (limit excessive cone motion at cutoff) hence raising power handling a bit. Better control over the woofer. Again I'm just guessing.

Another question would be I could make the cabinets wide but feel it would look strange having the two woofers mounted horizontally hence I would prefer to mount them vertically. However the first thing that comes to mind with them vertical is the two woofers would be at different points along the transmission line. I'm not sure how much that matters.

3rd question is it looks like the GPA 416-b models a little better than the Altec 416-b. I wish I could but I can't afford 5k for four woofers. I had no idea the GPA 416's were so expensive and wish I'd had the fore-site to have bought a whole bunch of them 15 years ago when they were less expensive.

That's all my thoughts so I appreciate incite from others.

Thanks,
Mark

[RonSSS]

Welcome Mark!

I can't answer your questions because I don't know doodly squat about transmission lines!

I've had my 19's for maybe 20 years? I'm old and can't remember.
I augment the low end with Altec 8184 18" subs. Crossed at 80hz. I run the 19's full range, with only 25w of tube power, the amps wad up before I could ever bottom the cone.
Agree with you on the 19's short comings. Always thought of scoring some 299-8A drivers and horns and crossing much lower than 1500hz. But prices on Altec stuff is just nuts, as you said should have bought more stuff 15 years ago! I pain $1100 for my 19's...??.

Hope the box guru's chime in

Ron

[Mercury3]

Thanks for the welcome Ron. I did think about the possibility of building some 19s again and use subs for the lows. I'm glad there seems to be a renewed interest in these vintage speakers. I saw the company building cabinets for them. It looks like they will build one slightly larger to fit a 511 instead of an 811 horn.

I have a very nice pair of subwoofers now that I built about five years ago so that is still an idea. I'm not sure because I keep tossing different ideas around in my head.

I'm going to retire sometime next year so this is going to be a retirement project for me. I have to check my finances to see what I can really afford. If money were no object I'd be ordering some GPA 416s.

Mark

[alancohen]

Thanks for the welcome Ron. I did think about the possibility of building some 19s again and use subs for the lows. I'm glad there seems to be a renewed interest in these vintage speakers. I saw the company building cabinets for them. It looks like they will build one slightly larger to fit a 511 instead of an 811 horn.

I have a very nice pair of subwoofers now that I built about five years ago so that is still an idea. I'm not sure because I keep tossing different ideas around in my head.

I'm going to retire sometime next year so this is going to be a retirement project for me. I have to check my finances to see what I can really afford. If money were no object I'd be ordering some GPA 416s.

Mark

I have a pair of VOTT A5s with braced and insulated 828 cabinets. They sound amazing, but still don't go loooooow, even with the 515Bs I have in them.

I made a pair of these bucket subs Bucket Sub and haven't looked back. I know...they look pretty cheesy, but the 28-53Hz they supply blends perfectly with the 515Bs. Do not knock it until you've tried it. I use a Crown XLS 1500 to power and crossover. The beauty is you can't even tell they are playing, that is, until you turn them off; then the bottom drops out and the 515Bs sound like mids.

[GM]

Dual 416-8b MLTL design

Hey everyone I just signed up to ask a few questions. I don't really know what I want to do so I'm still contemplating options. Please bare with me and I'll explain where I'm coming from.

I'm getting old now but remember way back in the olden days (1981 actually) I bought my first pair of really nice and new speakers - Altec Model 19's. They were nice but as many of you who has this audio bug in our blood know eventually we want to move on to try new and other things. So I sold them and went on over the years to own many other nice speaker designs some bought and some built.

I've always missed the big and effortless sound that my old model 19s had. They weren't without issues though - I'd bi-amped mine at 800hz with an 18db electronic crossover which did improve the sound. That large 416 struggled to do a good job up to 1200 hz. Likewise it struggled to go low. I bottomed the woofers out once (ya learn your lesson after once) trying to get them to go lower but they just couldn't do it. Regardless I still consider those to have been excellent speakers that did a lot right.

So I've wanted to build something again and have spent a few days reading as much as I could find on Altec's with special interest in the Transmission line design. Others have mentioned how the 416 generally cannot go low but I gather it can in a properly designed transmission line cabinet. Excursion might be an issue which is why my thought would be to use two 416s per channel. From what I've read 24 cubic feet. That's tough but doable.

If I do proceed with such a design I'd probably need to run them up to 600 or 700hz to some 511 horns.

One question I have - I'm old school and remember the old transmission lines were just open at the end of the line. Maybe tapered but open. The newer designs I've read about recently (I think a few I saw designed by GM) have a port towards the end of the line rather and being open. Would this port be tuned similar as we would tune a bass reflex port? I'm guessing it would have the necessary quarter wave length delay due to the port being towards the end of the line and the tuned port would provide better back pressure for the woofer (limit excessive cone motion at cutoff) hence raising power handling a bit. Better control over the woofer. Again I'm just guessing.

Another question would be I could make the cabinets wide but feel it would look strange having the two woofers mounted horizontally hence I would prefer to mount them vertically. However the first thing that comes to mind with them vertical is the two woofers would be at different points along the transmission line. I'm not sure how much that matters.

3rd question is it looks like the GPA 416-b models a little better than the Altec 416-b. I wish I could but I can't afford 5k for four woofers. I had no idea the GPA 416's were so expensive and wish I'd had the fore-site to have bought a whole bunch of them 15 years ago when they were less expensive.

That's all my thoughts so I appreciate incite from others.

Thanks,
Mark

Greets!


Yeah, from a technical POV, ~1 WL across is the limit so ~900 Hz for a 15".


FWIW all of the Altec [ML = vented] TLs I've designed/built are tuned to Fs.


You don't necessarily need duals to go low, just depends on how loud you want, room and max speaker size and whether or not you have two good corners, otherwise best go dual or a < 100 Hz sub system for a GPA 416-8C at rated power.


Based on some measured specs, ~10.92-15.73 ft^3/driver depending on whether there's a separate sub system, so 2x for duals. Of course they can be smaller, it just means less TL loading of the vent and even then we can get some of the 'lost' gain back by inverse tapering it [ML-TQWT] like I did with my dual 515Bs.



Vents are tuned the same, just can't be calculated like a reflex, i.e. must either be calculated with a horn designer program or with measuring equipment.


You guessed right.


With multiple drivers along a TL line, this driver 'line array's midpoint is where a single driver would normally go since acoustically it's just a single oval driver until long enough to be an 'infinite' one that mimics a long ribbon speaker [~71% of room height].


Technically, whether drivers are vertical or horizontal is a function of desired polar response, how far away the listening distance [Lp] is and XO point/slope, so make a scaled floor plan of where the LP, speakers, other furniture, windows, doors [swing] will be and Lp width, i.e. the more info the more optimized we can make it.


In general though, we want vertical for widest polar response and vice versa with horizontal allowing closest horn/woofer spacing, so combined with narrowest 'sweet spot' is best overall for short Lp distances and or narrow sound walls.


Re height, [ML] TLs are normally designed around average seated ear height [~38" default] aligned to the [super] tweeter, so in general around 60" high, but with large horns this makes the cab too short to have any useful 1/4 WL TL vent damping, so have to put the horn centerline somewhat higher, angled down as required.


FWIW me and some others prefer a more prosound woofer placement centered somewhere in the face/chest area, allowing more vent loading, sense of 'live' performance.


Also, unless the cabs are hard in corners, they need to be ~26-30" W depending on its depth to offset baffle step loss and ~40" wide for horizontally opposed 15".


Well, if I'm remembering the timing right, then GPA's products 15 yrs ago were made from worn out tooling and configured ['voiced'] to what EV was pumping out at the end, so not the low Fs, Qts, high Vas drivers of the 'glory' days, but more prosound centric for EQ'd, high continuous power, low dynamic headroom apps. The upside was they handled a minor amount of more power and performed better with high DF amps, i.e. more [mid] bass at the expense of lower system efficiency.


Nowadays for USA Altec/GPA type apps I recommend AE drivers, preferably with the Apollo upgrade; not cheap, but ~what ferrite GPA prices use to be IIRC: AE Speakers by Acoustic Elegance


For a pretty comprehensive listing of similar products around the world, recommend spending some quality time researching these threads:


Beyond the Ariel - diyAudio


Is it possible to cover the whole spectrum, high spl, low distortion with a 2-way? - diyAudio

GM

[Mercury3]

Thanks for the reply GM - I have read as many of your other postings as I could find so I was hoping you would chime in.

I'm not familiar with those AE woofers but I'll have a look. Nice thing about the Altecs is they sound good into the lower midrange which is tough for large woofers. If I go with 511-b I probably be close to 700 hz.

Yeah I'm old school and was always comfortable tuning the ports the old fashion way with a signal generator / resistor while measuring the two impedance peaks. Some say it's antiquated but crap I've built some damn good subs in the past that way.

Having said that some of my best subs were of aperiodic designs. I've got a pair of those 6 cubic feet cabinets in each corner now. With room gain those are only a couple of db down at 20hz. There great but I'd have to ditch those to make room for the transmission lines. If I kept those I wouldn't be able to go with wide cabinets. I've thought about it though but then I'd scale down the 416 boxes.

I need to think on this thoroughly as at 64 these will be my last build.

[GM]

You're welcome!


Ah! Didn't realize you had them; the worst one is on a par with some EV era 416 driver/recones with up to 0.7+ Qts, with a high Fs/huge Vas to help keep efficient up, hence ideally sealed alignments for HIFI/HT apps. 515s weren't much better according to the distributor, but again suitable for PA apps with the now vintage/obsolete prosound [mid] basshorns, so only bought a pair of 802 diaphragms, while they switched to marketing B0$3 prosound, which was/is pretty impressive, but [much] too pricey, so personally only seen them used in trade shows where [super] high speech intelligibility is 'job one'.



With a separate sub system, best to either go low Qt sealed or maybe a pipe horn similar to mine, just depends on what the max width/depth is available. Another option would be making new sub cabs with smaller footprints if going tall is an option, Ditto are the drivers suitable for down firing? Anyway, really need a floor plan and any SAF/whatever restrictions, etc..


Re the AE drivers; now decades long story short from before there was GPA and AE, the goal was creating modern drivers to replace vintage HE Altec, EV, etc., plus expand the line for high end consumer apps. It's been a long time coming and still have long lead times, but with Facebook now driving prosound components for DIY, etc., around the world, hopefully this market will grow again like vinyl.


GM

[Mercury3]

Thanks for the reply again GM,

fyi I opened up a separate thread on the four 416'b woofers I sent off to GPA to be remag / reconed:
Altec 416-8b woofers

Do to the above I'm kind of committed to using the 416-b woofers. It isn't imperative but after the recones I've quite a bit invested in them now.

Another snag I've realized is with a tall dual woofer MLTL it would probably be to tall to mount a 511 horn on top of the cabinet. (It'ed be up there aiming down) There isn't any way I can see to easily put the horn inside in a MLTL box without it still being high.

I could keep my subs and change my plans to a MTM design which could be made sealed since the subs would handle the lows. For sure that design would be easier. If I did that I would probably like to roll off the 416's a little which would help protect those magnets from becoming discharged again.

Or - I could ditch the subs and make the MLTL cabinets with the 416's horizontal rather than vertical. Cabinets would need to be about 40 inches wide but then not need to be so tall. 511's could be mounted on top that way. Woofers side by side wouldn't look as nice visually.

So much to think about!

Yes if I do get rid of my current subwoofers I would have two corners and could go with 40 inches wide cabinets. Depth wise I should probably limit to 24 inches max due to some furniture on the left might get in the way.

My room is fairly narrow (guessing maybe 16 feet wide) but very long because the dining room and kitchen are back behind the living room (no walls in between) Sofa is probably about 15 feet from the wall so would be about 12 feet back from the speakers. Ceiling is high and vaulted which does help my room a lot. Currently I have several bass traps and a bunch of acoustic panels I bought and put up. I think those don't really do a lot for lows but help a bit in the mids/highs.

I've got a Dayton omnimic which I've used for other designs and my room isn't to bad. I get good gain at the lowest frequencies which helps. I do have a slight null at 60-70 hz right at the listening sofa but I never considered that a very big issue.

Mark

[GM]

You're welcome!

OK then, unless the cabs can be quite large, 'we' can't go any further till you have actual T/S specs on all four since what's published at GPA can allegedly be far off enough to ideally require [much] larger cabs.

This is a problem because? I mean the ideal is getting the woofers to be in a room's vertical odd harmonic plus the performance can 'feel' more 'you are there' when the speaker's acoustic center is in the face/chest area.

Regardless, if there's enough depth available this can be an advantage in that more acoustic path length is available by folding it ~ in half since no matter what the woofer cab's configuration, the horn must be in a separate space to allow max TL loading of the vent, be it open on top or in a massive sand/whatever filled sealed box.

Trust me, assuming a typical HIFI/HT app and a proper drain/rezap back to spec, you can't heat up these big AlNiCo motors enough to drain any audible amount out of them over time unless you plan to live at least another 64 years of daily use with them max EQ'd to get the most output from them at hearing damage levels. I mean look at how many years of cinema sound apps running the better part of 12 hrs daily, sometimes more, it takes to flatten them since their low power VCs can't 'sink' enough current for any length of time without acting as an expensive fusible link.

Indeed, the 'beauty' of AlNiCo versus ferrite [mud] motors is that one acts as a heat sink, keeping performance more efficient over time while the other is an insulator that quickly goes to thermal power EQ/distortion for a more linear performance over time. It's obvious then that it's better overall in a prosound app and not so much in a HIFI/HT app other than a separate sub/LFE system.

The real danger is causing them physical damage since it can alter their performance, ability to restore them to anywhere near spec.

GM

[Mercury3]

Thanks GM,

That's encouraging news concerning the woofers. No there isn't any physical damage and all four even look almost new. It'll be interesting to see how they test when I get them back.

Makes sense also about keeping the woofers vertical. I was remembering those large JBLs with the two 15's side by side but I think they crossed those over real low. Visually I never liked the looks very much.

Well with holidays coming up it'll probably be sometime next month before I get the woofers back. I'm busy with work to so no hurry.