New two-way ALtec horn design, questions

Hi, I've only spent a little bit of time on this forum...but I appreciate the threads and knowledge of others.

I'm using stone horns from Stereolabs (Germany), 250Hz model crossed at 500Hz, plus a 1,000Hz tweeter horn crossed at 5,000hz. Drivers are two inch selenium and one inch respectively. Xover is Bob Crites unit for Klipsch.

Bass cabinet is 160 liter (5.6 cubic foot) in 25mm MDF, heavily braced and internal angled baffles, plus wool dampening on three sides. Ported to floor. Driver is 416-8C from GPA (should arrive next week).

Running two small tapped horns from 30Hz to about 60Hz. 300-watt O-Audio BASH amp.

Weston Acoustics (Melbourne) 300B "Time Machine" SET amp to drive the horns, plus a separate 100-watt pro-amp to drive the 416's.

Now, this multi way setup does sound good (even without the 416's installed)...but I want to change it to a full Altec "two way" system.

I want to run a GPA 902 one-inch driver into a horn (not yet decided)....and use the new GPA 1200 adjustable crossover. I'll keep the existing bass cabinets, and/or incorporate these into a new taller cabinet in order to house the horns. If I did this, I'd increase the cabinet volume to around 240 liters (8.5 cubic feet), which is better for the 416 to get down to a targeted 40Hz. I would use Euro birch ply (19mm) to build the 'outer' cabinet....and open up the top of the existing black cabinet.

I love the look of the Shindo design...and I could build that sort of cabinet. I previously built a Stonehenge V cabinet using a GPA 604 III, which sounded great.

I'd appreciate any thoughts/ideas on this.

Kind regards.

Andrew

Altec 1204B comes to mind for what I might end up with, size wise.

With the use of a 511 horn, I guess the Model 19 will be the closest overall sound/presentation....albeit taller/less narrow cabinet.

Do you still have the 604 III ?

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Originally Posted by Altec Best

Do you still have the 604 III ?

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No. A gent in Adelaide, South Australia has them in the Stonehenge cabs.

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Originally Posted by atilsley

...but I want to change it to a full Altec "two way" system.

I want to run a GPA 902 one-inch driver into a horn (not yet decided)....and use the new GPA 1200 adjustable crossover.

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The XO will limit you to either a M19 configuration or A7 with either a 511 or MR994, so if keeping your present cab, then it seems that the 811 with the same vertical and depth orientation of the drivers as the M19 is your only viable option without a larger horn extending proud of the baffle.

GM

Thanks GM, I was hoping you'd read this thread.

So, to understand, the 811 provides a higher xover advantage than the larger 511?

With cabinet depth, I don't have a real constriction...so I could accommodate the 511 if this was more desirable....!? The main objective for me is to try the two-way concept with a small format comp driver.

For bass, do you have an ideal cabinet size you'd accept for the 416? (remembering I can run the tapped bass horns (2) for the 20-40Hz range).

Also, have you had any experience with the new GPA adjustable xover? It seems like a pretty good investment for what is offered.

Kind regards

Andrew

You?re welcome!

Depends on the desired performance parameters. Both horns have the same HF design, only the LF sections are different.

The larger 511 will control directivity to a lower frequency with the trade-off of higher HF damping due to increased acoustic loading, collapsing directivity [beaming] in the process. With a high XO point, it will also have a flatter frequency/polar response due to less compression horn loading, acting more as a wave-guide.

If max efficiency isn?t a goal, then depending on the desired top octave response, the 511 can be the best choice overall for a high XO point.

You miss my point, it?s not cab depth that?s the issue, but the location of the horn?s acoustic center WRT the woofer?s that AFAIK is ?cast in stone? by the XO?s design. For a longer horn with the same vertical horn mouth/woofer physical alignment then, the XO would need to be designed for a different horn/woofer offset; otherwise the 511 must ?overhang? the woofer/cab by however much it?s longer than the 811.

My understanding of ?ideal? point source driver loading is that it wants to ?feel? a matching acoustical impedance on both sides of its vibrating membrane, so either an OB or its folded up compression horn variant as defined by Fs*sysQ/2 are the only two ?ideal? alignments.

Unfortunately, both are normally impractical at best in any confined space smaller than a typical school auditorium/channel, so like most things, you choose your performance goals, then which trade-offs you?re willing to accept to get as close as practical to them.

The ideal? then is to find the alignment that is flattest in room at the listening position all the way down to Fb, but without mapping the room?s response, this usually boils down to making the cab as large as practical and tuned to some low frequency, which is usually Fs for a sysQ < ~0.4 and lower if > ~0.4, then using some form of EQ to individually dial in each speaker.

No experience with any of the Altec/GPA adjustable XOs beyond playing with settings on some Altec consumer model speakers and not liking what I hear when any 15? is used this high with a separate horn, no desire to get any.

GM

GM, thanks.

I now get the point re location of horn.

So, to simplify our discussion, I want to cross over at 1200. As such, is my project like a M19 albeit slightly taller?

With the 1200 xover point, is there any gain in going for the larger 511?

Oh, one other thing, I asked about ideal cabinet volume for the 416. Any thoughts? At present I have 160 liters, but with a rebuild, this can go to 240.

Kind regards

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Originally Posted by atilsley

Oh, one other thing, I asked about ideal cabinet volume for the 416. Any thoughts? At present I have 160 liters, but with a rebuild, this can go to 240.

Kind regards

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Another consideration in building new cabs....the 511b will require a minimum of 24". Using the 811b you can narrow the cabs another 5"-6". I prefer the 511b in larger rooms but regardles of which horn I would focus much effort on EQ ing the horns(a tip from GM in the past). IMO this is where the mod.19's crossovers came in to play and were so responsible for that great sound! (love to hear the GPA's too) However, as GM pointed out phase alignment may suffer a little with the 511b. A crossover mod could help though.

You?re welcome!

Again, if using the GPA XO, then only if you use an 811 in the same location referenced to the woofer location.

I already answered this and don?t know how to explain it any simpler, so with what few details you?ve posted, I?m guessing not in your app.

Huh?! I gave you my thoughts! Guess I gave you too many, so if 240 L is as big as you can go, then do it and initially tune it to ~32 Hz and fine tune it from there if required.

GM

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Originally Posted by rontec

Another consideration in building new cabs....the 511b will require a minimum of 24". Using the 811b you can narrow the cabs another 5"-6". I prefer the 511b in larger rooms but regardles of which horn I would focus much effort on EQ ing the horns(a tip from GM in the past). IMO this is where the mod.19's crossovers came in to play and were so responsible for that great sound! (love to hear the GPA's too) However, as GM pointed out phase alignment may suffer a little with the 511b. A crossover mod could help though.

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Thanks...my existing cabs are 24 inches deep...so I'm ok there. When you say you prefer the 511 horn in larger rooms, what do you define as a large room? My listening room is an open lounge/family...approx 20 feet x 14 feet, then opens up bigger. Ceilings are tall also, 11 feet. Distance from audio to seating is 16 feet.

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Originally Posted by GM

You’re welcome!

Again, if using the GPA XO, then only if you use an 811 in the same location referenced to the woofer location.

I already answered this and don’t know how to explain it any simpler, so with what few details you’ve posted, I’m guessing not in your app.

Huh?! I gave you my thoughts! Guess I gave you too many, so if 240 L is as big as you can go, then do it and initially tune it to ~32 Hz and fine tune it from there if required.

GM

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Thanks again, GM...I'm trying to keep up with your tech detail...so it's all a learning for me at the moment. I appreciate you've been in the game a long time.

As an aside, for your own system (or previous ones), do you run any subs? I ask this because I have the two small tapped horns I can use for the 20-40Hz range if needed. For me, I guess I'm working through the issue of building an Altec system that is strictly two-way (ie, no subs), or with subs. If the latter, then I don't need to tune the cab down as low, hence, not build it as big. Just talking out loud here....

Thanks again.

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Originally Posted by GM

No experience with any of the Altec/GPA adjustable XOs beyond playing with settings on some Altec consumer model speakers and not liking what I hear when any 15? is used this high with a separate horn, no desire to get any.

GM

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Thanks....just to clarify your point, are you saying you do not like the sound of a 15-inch woofer approaching/exceeding 1200Hz? Does this mean you do not like the sound of the Model 19, which crosses over at this frequency?

I'm just asking as the Model 19 is something I'm trying to determine if that's the 'sound for me.'

Kind regards.

Anybody near Sydney got a Model 19, or similar, for auditioning by Atilsley?

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Originally Posted by atilsley

Thanks...my existing cabs are 24 inches deep...so I'm ok there. When you say you prefer the 511 horn in larger rooms, what do you define as a large room? My listening room is an open lounge/family...approx 20 feet x 14 feet, then opens up bigger. Ceilings are tall also, 11 feet. Distance from audio to seating is 16 feet.

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I think 511b's could work well in this sized room. The 24" I mentioned is the minimal width of the cabs being that the 511b's are about 23" across. Again if you're keeping the cabs as narrow as possible.

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Originally Posted by rontec

I think 511b's could work well in this sized room. The 24" I mentioned is the minimal width of the cabs being that the 511b's are about 23" across. Again if you're keeping the cabs as narrow as possible.

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Ok thanks. The HF's are similar for 511 and 811....given I'm aiming to cross higher, wouldn't the 811 be the default choice? Obviously, if I was building a VOT A5/7, the lower xover point would make this horn choice more critical.

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Originally Posted by atilsley

Distance from audio to seating is 16 feet.

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Just so we're all on the same 'page', for horn design [polar response] selection it's the 'line of sight' distance, so depending on how wide the 'sweet spot', the 511 may be preferred in this app.

GM

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Originally Posted by GM

Just so we're all on the same 'page', for horn design [polar response] selection it's the 'line of sight' distance, so depending on how wide the 'sweet spot', the 511 may be preferred in this app.

GM

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Thanks.

If I went with the 511 and dropped the notion of the GPA adjustable two way N1200 xover, what would your preferred xover point be? (assume I will use the 902 comp driver and have bass cabinet of 240 liter.)

Yes, I'm asking for personal opinions.

Thanks very much.

I thought GM was saying you could still use the 1200 xover with the 511 , but you might need to physically move the 511 a few inches forward into the listening room so to more align the voice coils of the woofer and HF driver again to maintain a closer phase alignment...?

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Originally Posted by rontec

I thought GM was saying you could still use the 1200 xover with the 511 , but you might need to physically move the 511 a few inches forward into the listening room so to more align the voice coils of the woofer and HF driver again to maintain a closer phase alignment...?

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Thanks...yes, I understood the point about moving the horn to get the optimum alignment. My q was more around the bass driver running up to 1200Hz...as GM had made a comment earlier that he wouldn't like that....hence my q to him about the Model 19, with the 1200Hz xover point.

Kind regards.

YES....!!! Finally got the 416's today from Great Plains Audio.

Wonderfulyl packed...very professional.

They look absolutely fantastic....heavy, very well machined...just a piece of art.

I was keen to get them into their custom boxes...so, after only 15 minutes, I had them playing. What a relief.

Without run-in, they are sounding very good. The cabinets are around 160 liters, so bass extension is good, most likely getting a flat response to 40Hz, then gradual roll off. I'll check this on the weekend with my signal Hz CD.

Running the separate 100-watt pro amp to drive the woofers, with a 500Hz passive xover.

On the weekend, I'll disconnect this amp and run the drivers through the Bob Crites 500/5000 xover from the 300B SET...but I suspect I'll have to attenuate the horns down somewhat.

The tapped horn subs were hardly needed...but if I run the drivers with the 300B, I'll probably retain the subs.

The blue horns will go on sale so I can start on the 511/811/902 project.

Better pic attached.

Sounds better WITHOUT the solid state amp...now running all through the SET 300B. I need to attentuate the horns down 3 or 6dB. Subs are hardly needed.

Removed legs and sealed up the port to floor, then created another port on the front elevation, reducing size by 1/3. Greatly tighter and improved bass.

Also, tonight, I tested some miniDSP settings for the bass...adding low shelf rise to the 20-80Hz range by 6dB....plus used a Butterworth 24dB crossed 550Hz.....

Better filling of bass throughout the range...but probably too strong down low. Sounds more like a permanent sub woofer turned on.

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Originally Posted by atilsley

Removed legs and sealed up the port to floor, then created another port on the front elevation, reducing size by 1/3. Greatly tighter and improved bass.

Also, tonight, I tested some miniDSP settings for the bass...adding low shelf rise to the 20-80Hz range by 6dB....plus used a Butterworth 24dB crossed 550Hz.....

Better filling of bass throughout the range...but probably too strong down low. Sounds more like a permanent sub woofer turned on.

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Setup correctly the 416 is a mean woofer... You don't need a sub with them in the right setup (Cabinet,Crossover). My favorite Altec woofer 416-8B's.

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Originally Posted by atilsley

Thanks....just to clarify your point, are you saying you do not like the sound of a 15-inch woofer approaching/exceeding 1200Hz? Does this mean you do not like the sound of the Model 19, which crosses over at this frequency?

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No and no. Frankly, I was stunned to learn how highly regarded it is among the ?faithful?. Technically, it?s a poor ?marriage?, sonically coupling the tail end of the driver?s break-up modes to the HF horn?s compression loaded BW. The 416, and especially the 515, are better than most WRT controlling break-up modes, but????

Run the 416 full-range by itself and with various XO points/slopes and let your ears decide. Altec knew they needed to use either the 515 or a custom, but between budget constraints and the desire to keep up with the competition bass ?thump? wise????

GM

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Originally Posted by atilsley

Ok thanks. The HF's are similar for 511 and 811....given I'm aiming to cross higher, wouldn't the 811 be the default choice?

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Yes, if there?s no need for the larger horn?s ?tighter? polar response and/or not in a prosound app where the bigger horn better protects the driver below the XO point.

GM

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Originally Posted by GM

No and no. Frankly, I was stunned to learn how highly regarded it is among the ‘faithful’. Technically, it’s a poor ‘marriage’, sonically coupling the tail end of the driver’s break-up modes to the HF horn’s compression loaded BW. The 416, and especially the 515, are better than most WRT controlling break-up modes, but…………

Run the 416 full-range by itself and with various XO points/slopes and let your ears decide. Altec knew they needed to use either the 515 or a custom, but between budget constraints and the desire to keep up with the competition bass ‘thump’ wise…………

GM

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Understood. Why didn't Altec cross the 19 around 700Hz...given the 511's LF range? Wouldn't this have solved the criticims you raise re HF distortion of the woofer....?

??? The M19 uses the 811, presumably to limit cab depth, cost, plus wanted to bypass the sectoral horn's 'honk' and get a good blend off axis at around 90 deg through the XO BW with a nominally 15? point source [cone driver], hence the need for it to be so high.

They did a great job with what they were forced to work with [PA horn] and in some ways superior to earlier consumer designs, but it's fundamentally flawed based on my understanding of what constitutes ?best? compression horn, point source LF speaker design for use in a high SQ, wide BW app, especially when max efficiency isn?t the prime goal.

GM

Thanks GM

For home audio, how would you compare the compromised M19 with the 604? I've had a GPA 604 in a large 250 liter Stonehenge cab and like the overall presentation. Appreciate your opinion on the 604 'sound.'

You?re welcome!

The 604 is a near-field monitor and the M19 a far-field one plus designed to handle much more power, so pick the one that is the best ?fit?, though the ?rub? here is that neither one is optimum for most HIFI apps, though historically, the few that have converted the M19 concept to a low tuned MLTL were much happier overall, making the choice between the two a ?no-brainer?.

Factor in that to get a proper comparison the 604 needs to either be at ear height and the M19 adjusted for distance/slope to get the center of its horn?s ?sweet spot? at ear height or bring the 604 down and adjust it to have the same HF ?sweet spot?, doing it in a typical HIFI room would also require rolling off both speakers fairly high up due different cab tunings, room interaction [I?m guessing around 250-300 Hz].

Compared this way and fiddling with the M19?s tone controls to minimize horn size differences [?fullness?], I imagine that in a narrow ?sweet spot? there wouldn?t be a significant difference sonically, but run wide range and optimized for in-room response it?s going to be enough different to be an apples n? oranges choice to me.

Anyway, there are folks here with both, so they are the ones to best answer this one.

Really, based on your stated performance goals, thoughts, and not wanting to stray too much from the ?conventional wisdom?, it seems to me that a 604 MLTL with a 511 perched on top to make a three way is a good way to ?have your cake and eat it too?, and if you add the 416 as a helper mid-woofer, then system sensitivity can be 3 - 6 dB higher/channel.

Hmm, after 15 sec. of thought, this is my ?official? recommendation as it satisfies the XO point issues once the XO is dialed in phase wise [horn tilt + vertical driver offset] at the listening position to account for the large c-t-c spacing.

GM

I have both. My opinions are non-audiophile in nature. I like the 604-8G for jazz and small classical or the occasional folk album. The 19's are my everyday players because they can do jazz but also shine on metal and classic rock. Neither do low bass or extended high frequencies so they won't be a good choice if you listen to techno or synth music. I have fairly eclectic tastes and a relatively large collection of music of varying styles and both speakers can work well within their limitations. If you want to party, the 19's are the answer. If you want to engage with the performers, the 604's are a better choice. I've had both in rooms varying from tiny to moderate in size (10 x 12 to 14 x 25) and I think they will both play well in these types of spaces. They could be better in a larger setting but it shouldn't turn you off just because your room isn't ideal. Do some room treatments and enjoy the sound.

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Originally Posted by zelgall

I have both. My opinions are non-audiophile in nature. I like the 604-8G for jazz and small classical or the occasional folk album. The 19's are my everyday players because they can do jazz but also shine on metal and classic rock. Neither do low bass or extended high frequencies so they won't be a good choice if you listen to techno or synth music. I have fairly eclectic tastes and a relatively large collection of music of varying styles and both speakers can work well within their limitations. If you want to party, the 19's are the answer. If you want to engage with the performers, the 604's are a better choice. I've had both in rooms varying from tiny to moderate in size (10 x 12 to 14 x 25) and I think they will both play well in these types of spaces. They could be better in a larger setting but it shouldn't turn you off just because your room isn't ideal. Do some room treatments and enjoy the sound.

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Thanks...good to hear that sort of response. I've also enjoyed the 604's.

GM, I had an email from Bert Doppenberg (Oris) who's built up a pair of very large bass horns, but using open baffle. Too big for me, but a dual driver version is very attainable. I thought I'd just include here in our discussion, as my quest has been for a mid-bass horn of a particular size. If this horn catered from 100Hz to, say, 800Hz, then I'd be on a winner. I also like the look of it.
Kind regards.

Bert discusses them on his forum: http://forum.bd-design.nl/index.php?id=17095

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Originally Posted by atilsley

If this horn catered from 100Hz to, say, 800Hz, then I'd be on a winner.

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Again, you don't have the depth plus 800 Hz is too high unless you roll one driver off or accept the lobing issues of a MTM that will be compounded by horn loading; or, if you put the horn on top, then at your listening distance you'll have the same problem as I did, hearing the vertical scale of the music move up and down because of the super wide c-t-c of a large horn, woofer TMM.

Anyway, I'm down to repeating myself, so I'm done until if/when you may need some cab design help.

GM

Ok thanks. I feel I need to go to college for 5 years just to keep up. I'm no closer to a decision. For some reason, I sense better to stick with stock standard gear, lest you stray into unacceptable compromise.

Regards.

You don't need 5 years of appropriate college education to get into speaker system design but recognising one's limitations is a good start in a learning curve. Frankly, I don't know why beginners think they can do better than established quality products without doing the 'hard yards'. Grasshopper, I think you have had a revellation. By the way, I have an understanding of the basic principals, math and physics but have no inclination to spend my time and money 're-inventing the appropriate wheel'.

Master. Thank you.

Another gent provided a simple yet clear breakdown of the 604 vs 19. That's the sort of help I needed...matched my understanding.

GM is a pro...no issue there....I just couldnt keep up.

Yet, I love altec, and want to build cabinets...that's my hobby.

Kind regards

Not a Master but maybe an an initiated apprentice Journeyman. :rolleyes:

It's good to journey.

Oh, the db design ob horn does fit my requirements....depth 535mm, mouth width 1230mm, throat width 170mm, radius 950. I don't yet have height, but I'll anticipate 1000mm.

What appeals is the cabinet-free problems.

I get the detail and slam of mid bass, without farting around with ports, vents and undue cabinet resonances. The low q 416's would be in their element.

Thats a journey...

http://www.hostboard.com/forums/hbmc...2013/01/21.jpg

Amazing-looking speaker!