Comb filtering at those frequencies isn't an issue because the narrow notches fall within the ERB (equivalent rectangular bandwith), so it is essentially inaudible.
Likewise, "phase issues" are really a non-issue because at those same frequencies the human auditory system is not phase locked anymore.
I agree that a horn that maintains directivity control up to 15kHz certainly reduces some of the benefits of using a super-tweeter, but other benefits still remain, such as the superior transient behaviour and reduced post-ringing of the super-tweeter's smaller and lighter diaphragm.
In my experience, the only compression drivers that can give top-octave results of comparable subjective quality to those afforded by a dedicated high-quality super-tweeter (such as the one I am using) are the TAD TD-2001 and TD-2002. Both use small-format Be diaphragms, and are less suited to being crossed over at 5-600Hz than the larger format drivers we were discussing. So, it's swings and roundabouts.
And to me, the best compromise is still a large-format Be-dia driver for 600-6k and a dedicated super-tweeter above that.
YMMV.
Cheers,
M.
If you cross over at 6 Khz comb filtering is certainly an issue IMO. Also higher in frequencies. But that's another debate.
The drivers will not sum, there will be superposision. What you're basically saying is that these phase issues aren't audible in this region but lower distortion with a smaller driver is.
I wouldn't draw that conclusion considering phase issues are normally far more audible than distortion. With a crossover as low as 6KHz and fairly close to a very sensitive area you definitely loose something IMO as well as also potential benefit some, and those have to be weighed up against each other. Personally I would never cross over that low but much higher if I considered an extra tweeter.
In a nutshell, yes.
I think it depends on the frequency range, and one cannot generalise (i.e., "normally" doesn't mean much, one needs to be specific).
Agreed. There's no such thing as a free lunch. Pick your poison. Etc. Etc. ;-)
Marco
So I'm pretty sure after what I can tell about the polars of the the horns I looked at, a Tractrix 350 horn is has about the best polars.
I bought a pair of JBL 2451 and will replace the diaphragms with Aquaplas coated titanium.
Very good treble from what I've seen. If I see it make sense, in the long run, I'll get beryllium.
520-630Hz for a xover.
I haven't been convinced to move from an Acoustic elegance 15" simply because it seems to have the mid bass sq I want and the bass extension I need. for a 15" a ka=2 is 573hz so it seems to line up.
I kinda wanted to run dual 15's....I also had dreams of running sealed subs......which should conclude to enough bass and tight at that.
I bought a pair of JBL 2451 and will replace the diaphragms with Aquaplas coated titanium.
Very good treble from what I've seen. If I see it make sense, in the long run, I'll get beryllium.
520-630Hz for a xover.
I haven't been convinced to move from an Acoustic elegance 15" simply because it seems to have the mid bass sq I want and the bass extension I need. for a 15" a ka=2 is 573hz so it seems to line up.
I kinda wanted to run dual 15's....I also had dreams of running sealed subs......which should conclude to enough bass and tight at that.
Nice! Sounds like a great recipe. I know that I've mentioned this, but I found woofer selection to be very difficult with my horns. The carbon fiber and paper cone woofers I first tried just didn't play with the same voice. I had much better luck with an aluminum cone woofer. Maybe a rigid compression driver diaphragm doesn't match a flexible cone woofer? Who knows. I also tried to integrate a horn subwoofer and I went back to the woofers only because it was much more coherent and tighter bass. Lucky for me the woofers provide ample output all the way down. Anyway, don't be shocked if your first woofer isn't your last.
Well thats some wise information. Cspieker you run a xover of 500hz, don't you? The Aquaplas coated titanium diaphragms should play nicely into a paper or similar woofer, I am only hypothesizing, but that coating should give it character, slightly more in the direction of paper, and similar materials versus an aluminum one. They actually have a very smooth high register. The damping affect can be seen clearly in the measurements. They are dryer than beryllium by more than a little bit.
Truextent diaphragms measurements
So I'm not saying its a hole in one, but I think its hedging the bet in my favor. I think that the material characteristic is a direct influence on matching two drivers. I wish he had of used also an aluminum diaphragm for comparison, but all together, really appreciate POS, hes done a crap ton of investigation into the compression drivers and horns that can be researched by the rest of us.
At 350 a driver, and planning to use 4 total.....they will match....even if they don't.....they will. XD
Someone on another forum was suggesting I used the SEOS horn over the Tractrix but I am sold on the how linear...or should I say, how neutral the off axis response is, of the tractrix...it continually looses treble the farther you go but beyond that, it stays linear. The SEOS 24 wouldn't be a loss either, just different, wider dispersion, but more colorful off axis, especially the vertical axis. I think sometimes choices like these come down to personal taste rather than one being better than the other. I sweep a high pass filter across a mix in order to expose peaks and nulls, so the way a tractrix responds is right up my alley.
Looking to pick up a cts 3000 to run the dual 15's =)
Truextent diaphragms measurements
So I'm not saying its a hole in one, but I think its hedging the bet in my favor. I think that the material characteristic is a direct influence on matching two drivers. I wish he had of used also an aluminum diaphragm for comparison, but all together, really appreciate POS, hes done a crap ton of investigation into the compression drivers and horns that can be researched by the rest of us.
At 350 a driver, and planning to use 4 total.....they will match....even if they don't.....they will. XD
Someone on another forum was suggesting I used the SEOS horn over the Tractrix but I am sold on the how linear...or should I say, how neutral the off axis response is, of the tractrix...it continually looses treble the farther you go but beyond that, it stays linear. The SEOS 24 wouldn't be a loss either, just different, wider dispersion, but more colorful off axis, especially the vertical axis. I think sometimes choices like these come down to personal taste rather than one being better than the other. I sweep a high pass filter across a mix in order to expose peaks and nulls, so the way a tractrix responds is right up my alley.
Looking to pick up a cts 3000 to run the dual 15's =)
Hard to say on driver synergy, my limited experience has certainly not given me an explanation I can hang my hat on. Just guesses. But the experience has taught me that specs and other's endorsements don't tell the whole story by far. I do cross at 500, but I've moved to some overlap with the woofer helping up a little higher so I'm doing less eq boost on the tweeter there. Not for any audible differences, just in response to some suggestions here and to play around. I have 4 different xo types loaded in the minidsp to switch and compare on the fly. They're all measured and tweaked for response and phase. Ill never be "done". Not till I die. 
I completely agree with the Tractrix! The directivity falling off slowly to match up with the woofer makes for nice polars on the completed system, and for whatever reason, the Tractrix just sound right to me. Congrats on starting the process!
I completely agree with the Tractrix! The directivity falling off slowly to match up with the woofer makes for nice polars on the completed system, and for whatever reason, the Tractrix just sound right to me. Congrats on starting the process!
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Hmm, add another ~300 L to the AE TD15H's Vas spec, drop Mms down to ~50 g and you'd have an Altec 416 with ~4x the Xmax, which is one of the reference drivers for matching paper drivers to compression drivers.
Ka = 2 is its ~160 deg [theoretical 180 deg] point,which is ~1 WL across or ~900 Hz for a 15".
GM
Altec used a curvilinear cone with a raised lip at the surround that combined with selective doping, differing dust caps was used for all 15" apps from bass/lead guitar to 30 Hz bass horns with usable HF out to 5+ kHz to ensure plenty of woofer 'speed'. Really stiff at the rim and down in the flared throat, but flexible in between for creating the 'snap', woofer 'speed' required to keep up with a compression horn.
??? horn sub details?
GM
That's my gripe with tractrix, once you can no longer see the full throat, it's over...........
To my way of thinking, you're not 'seeing the forest for the trees' since what's critical is the primary response and use foam/whatever mouth damping to control off axis 'color', so would definitely choose the SEOS over a tractrix, though with dual 15s [preferably in tandem], beryllium and 500 Hz XO would opt for the SEOS 30.
GM
If you plan to add subs (later), why would you choose a TD15H?
This is a subwoofer of the 'air pump' type > designed to go low in small enclosures.
It's not a driver I would want to use above 150Hz and definitely not below a horn/wg.
I would consider a TD15M instead, which is a major step towards the Altec drivers GM referred to.
This is a subwoofer of the 'air pump' type > designed to go low in small enclosures.
It's not a driver I would want to use above 150Hz and definitely not below a horn/wg.
I would consider a TD15M instead, which is a major step towards the Altec drivers GM referred to.
I don't plan on adding a subwoofer, thats the main reason, otherwise, I'd definitely run a smaller woofer....so the xmax is needed....other wise the specs and materials, motor etc, are so close, why would the td15m make for better upper register than the td15h. I'd like to have a better understanding, they both have the same inductance, which plays a huge role in upper range limit. Are you thinking about the excursion and its affect on the top register?
This is a quote from a person I don't quite trust, if you won't explain your philosophy theres a good chance you are just repeating what someone else told you and you yourself do not understand the workings behind it.
I don't see the sense in making sure my horn can support the half point of the chosen xover freq. The tractrix 200 and 350 have a minimal spec of 350hz and 530hz...(also makes the names make no sense) ...he thinks the tractrix 200 would be the better option if I'm crossing at say 600hz, because I need a horn that supports half of that, which is 350hz....but I always use a 48db/oct slope....at 350hz I'd be down more than-30db.....wtf is his reasoning? I'm asking here because he was to high and mighty to explain his thought process.....or he just doesn't know wtf hes talking about lol
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There are measurements available of the Td15m. The descriptions on the AE website provide enough clues for the intended application of respective drivers. In Short: lf you need a driver for a small subwoofer cab, capable of moving lots of air, which would probably be crossed to a midwoofer above 100hz > TD15H.
For midwoofer duties, a TD15M is the better option. In a large cab it will play down into the low 30s.
It's not surprising Ae suggests the 15M as replacement for the Altec 416 ao.
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Whoever said that, has a point.
A pure Tractrix horn - not a hybrid of sorts - isn't constant coverage.
You may want to read this thread.
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I tend to agree, but seems like the H with the Apollo option would be best of both option and allow the sub woofer to be just that now that movies, some recorded music has some serious infra bass that I wouldn't want modulating any ~27.5 Hz-up BW, though assume at a hefty price increase.
GM
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