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

So all I have to do is put a hole(s) in the horn near the mouth? Maybe model the holes as port from a cavity like a bandpass?

IFF the vent exits into the horn, then the vent holes should be as far forward as possible.

But that isn't necessary. With a relatively low tuning, the vent could exit anywhere else. That could be done to direct vent pipe resonances away from the listener or simply to avoid compromising the horn polars.

Personally, I can't see spending 100's of hours of effort on choosing a horn contour and then implementing it only to cut large holes in it. Isn't that the benefit of the AXI, that it covers down low enough you don't need to synergize? If synergizing, there are lots of cheaper drivers that will do as well.

The compromise on that for me would be sealed mids on the horn with their bandpass ports sized to support only down to 100 Hz and at home levels, not PA levels. Such holes can be small enough to not seriously disrupt the pattern. Combine this with MTM woofers and you have a winner. The woofers will stay in time alignment horizontally and you will notice very little phase shift at 100 Hz in sitting vs standing.

I would say the same thing about an AXI crossed at 250 Hz even. My home synergy crosses to a bass bin at 250 Hz and shows excellent time alignment through the crossover frequency. The issue at the higher crossover frequencies is more one of vertical lobes due to CTC. You can minimize CTC by slot loading the woofers so you add only half the slot with to half the horn's height to get CTC.

Have you listened to an AXI playing down to 250 Hz?
 
IFF the vent exits into the horn, then the vent holes should be as far forward as possible.

But that isn't necessary. With a relatively low tuning, the vent could exit anywhere else. That could be done to direct vent pipe resonances away from the listener or simply to avoid compromising the horn polars.

Personally, I can't see spending 100's of hours of effort on choosing a horn contour and then implementing it only to cut large holes in it. Isn't that the benefit of the AXI, that it covers down low enough you don't need to synergize? If synergizing, there are lots of cheaper drivers that will do as well.

The compromise on that for me would be sealed mids on the horn with their bandpass ports sized to support only down to 100 Hz and at home levels, not PA levels. Such holes can be small enough to not seriously disrupt the pattern. Combine this with MTM woofers and you have a winner. The woofers will stay in time alignment horizontally and you will notice very little phase shift at 100 Hz in sitting vs standing.

I would say the same thing about an AXI crossed at 250 Hz even. My home synergy crosses to a bass bin at 250 Hz and shows excellent time alignment through the crossover frequency. The issue at the higher crossover frequencies is more one of vertical lobes due to CTC. You can minimize CTC by slot loading the woofers so you add only half the slot with to half the horn's height to get CTC.

Have you listened to an AXI playing down to 250 Hz?

I haven't touched mine yet.
You can minimize CTC by slot loading the woofers so you add only half the slot with to half the horn's height to get CTC
I think you are suggesting a vertical slot loading.
My home synergy crosses to a bass bin at 250 Hz and shows excellent time alignment through the crossover frequency.
Well thats encouraging. It would seem a high order hp filter on the horn and a lower order Lp filter on the 15" would make sense.

The compromise on that for me would be sealed mids on the horn with their bandpass ports sized to support only down to 100 Hz and at home levels, not PA levels.
- Compromises are great, I've made so many already lol. We are just theorizing at this point. Its fun. In this case it would be one sealed 15"....playing down to 100hz is perfect. Is it worth it, you think? The formula as it stands is a 20" plus, tall horn, on top of a box just tall enough for the 15", we'll say 250hz is a safe starting place for the xover considering others have crossed at 300hz on a horn that loads twice as high as the one I propose.
 
On a more serious note, I have continuously come across information that repeatedly suggest that the characteristic that I spoke of, at the beginning, of this project, is directly tied to efficiency/high sens. I've read countless times that systems with great dynamic capability present the most uncompressed listening experience....this has always been one of the leading aspects, that I wanted to tie into the design.

So far I have been blessed. The horn/driver combo and the woofer/enclosure combo should have around a sens of 95db or higher. Considering that is all the way down to 30hz....aint bad.

Strauss 2.1 for comparison
Sensitivity 93 dB / 1 W / 1m
Impedance 8 Ohm
Power 200 W RMS
Frequency range 23 Hz – 26 KHz (-* 6 dB)
Crossover frequency 400 Hz
Distortion THD < 0.3 % (93 dB / 1m / 100 Hz – 26 KHz)
 
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Camplo, are you aware of Keele's formula for pattern control?

The one that says:
1,000,000 = coverage angle in degrees x speaker width in inches x frequency in Hertz.
Same thing for vertical using speaker height of course.

So pattern control at 90 degrees and 250Hz is like 44 inches wide !!

I ask because I'm not sure if your goal is to get pattern control, or just to get a CD like the AXI to work low enough to pass off directly to a woofer....
 
just to get a CD like the AXI to work low enough to pass off directly to a woofer....
This

Yes. No need for the 15m if you're crossing that low to the Axi.
It just seems like a good Idea to keep the sub excursion away from the xover...


I've found wood. I just need to find someone to cut it into squares, I'll do the rest.
 
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I think you are suggesting a vertical slot loading.

Actually not, although that is what you will see in the thread in my signature.

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but given the 20" tall horn dimension you just mentioned (not necessarily for the first time), there is no CTC issue with even an 18" direct radiator, so no need for slot loading. I'm guessing you would get 500 mm ctc with direct radiator and about 350 mm slot loaded as done in thread below.

Companion Woofers for my Synergy Horns

My motivation in the above design was to see if I could get to Danley's single point summation limit center to center distance with woofers outside the horn with a concept, since abandoned, that I was considering. Of course one can if the XO frequency is lowered sufficiently and with slot loading you don't have to lower the XO quite so far. 500/350 = 1.42

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This

It just seems like a good Idea to keep the sub excursion away from the xover...

That is a good idea.

Equally good, perhaps better, is to use enough subs (4 18's may be enough) so no individual driver needs a lot of excursion. The imperative is to limit the excursion of drivers responsible for the medium and high frequencies - the AXI, which is why some of us are nervous about crossing the AXI too low. But do you really want to allow the TD18's to hit their Xmax of 14 mm? By one of the definitions used for Xmax, that implies 10% THD. If you have enough subs so that they don't go beyond say half Xmax, then there is no need for the TD15Ms.
 
I've found wood. I just need to find someone to cut it into squares, I'll do the rest.

Try this guy, he will do as much or as little as you want and has a local source for baltic birch plywood. Shipping isn't that bad..

Custom Speaker Designs and Kits | Speaker Hardware

I got a really reasonable quote from him on one project but aborted in favor of a local CNC shop that charged me twice as much. If all you really want is the sheets of ply cut down to size, the supplier should be able to do that.
 
4 18's would uncomplicated things but sacrifice of space. These enclosures aren't small lol.

I am really digging whats depicted in the picture. Could I take my TL design, Face the driver upwards, and fold the Terminus over the top of the driver? I'm not sure exactly what slot entails...I'm guess I could keep the terminus and still some how slot load the driver?

I need to find a different supplier then....
 
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Uncomplicating things is usually a really good idea. With 4 18's you get the performance of two 18s in a TL which is a complication. The TL is harder to build and it might not come out precisely as modeled.

Four 18's up front like I drew (mine are 15's) does indeed look impressive. I've done the drawings and built the woofers but I've never lifted the 2nd woofer on top of the stack out of fear for my back. I've found I'm satisfied with just the lower woofer working with subs out in the room.

I don't see why you couldn't add slot loading to the TL, but I think its an unnecessary complication. At the XO frequency being considered, CTC isn't an issue. It does minimize the height for a MTM stack but its not necessary to get a lobe free forward beam at the XO we are talking about.

If keeping things simple becomes your goal and 4 18's up front is within the realm of possibility, then consider side by side direct radiator woofers below the horn. I think the pair of 18" woofers will be a good match to the horn in both width and height for a better directivity match at XO. That can be made to work well aesthetically as it did for JBL back in the day.

Size shouldn't be an issue with sealed TD18s, definitely would be for bass reflex.
 
Right now you've got me interested in slot loading the 15M in a sealed box. I don't know how to model this in hornresp though. What type of effect is the slot going to have on the FR.

Currently I am dedicated to the TL. I mean that if I build it and don't get it right, I will not give up until it is right, which is pretty much standard when building a TL thats never been built before.

I don't see why you couldn't add slot loading to the TL, but I think its an unnecessary complication. At the XO frequency being considered, CTC isn't an issue. It does minimize the height for a MTM stack but its not necessary to get a lobe free forward beam at the XO we are talking about.

CAn we talk about this....are you suuuure? How am I figuring this? I might have used xdir to confused myself but at 250hz from the center of the 15" to the center of the horn will be....18.5-20"...I am not talking about mtm though.
 
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A slot loaded woofer is modeled as an offset driver horn. A pure slot is such a horn with no expansion. But if you build it as I did as a very high aspect ratio conical horn it will play higher. You can see the HR model and the effect on the FR in post #3 of my Companion Woofer thread.

I agree with direct radiators you will get 20", about 500 mm, or less CTC. Here is what XDIR showed me

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Do I need 4?

Based on all that I've read [not all], the 'tone' of your project eschews Synergy concept, so I meant multiple compression drivers on a combiner/phase plug attached to a suitable horn with one full range and three low passed to get the necessary extra power handling to get down to 150/whatever Hz you want/need to make a nominally two way system.

I just said [4], I haven't researched it; may need more to keep excursion at a < 1/2 power for high SQ. Otherwise Synergy concept, my preference for all things high SQ, till something better comes along of course. ;)

GM
 
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I am sorry to jump in, but GM, could you please clarify a bit for me?

If one combines 4 compression drivers, they can go theoretically lower to half the frequency with the same SPL? And any compression driver on a sufficiently large horn can be used with 1/4 the power with every octave down from the manufacturer specified value? Even below the resonant frequency? If one would want to go to extremes and provided that the combination is perfect, a large number of smaller compression drivers could be used to play as low and one large compression driver?