New two-way ALtec horn design, questions

[GM]

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

[atilsley]

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

[rontec]

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

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.

[atilsley]

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.

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.

[rontec]

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.

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.

[atilsley]

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.

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.

[GM]

Distance from audio to seating is 16 feet.

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

[atilsley]

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

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.

[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...?

[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