Beyond the Ariel

[Variac]

To answer the more general question from our gracious moderator, the top driver is going to be about -3 dB at 200 Hz, and the function of the other drivers is to extend the bass down to meet a stereo subwoofer at 60 ~ 80 Hz. A combination of EQ, staggered lowpass filters, and asymmetric panel width is what covers the gap between the subwoofer and the wideband driver.

Am I the gracious mod?

Your paragraph in the quote sounds pretty close from my limited experience with my open baffle mid. Don't be surprised if things come out more in your favor than you expect- that's one of the open baffle charms..

I'm stunned by how many possibly useful ideas our ongoing yap-a-thon has produced. Yes it's time for Lynn to get his lab set up and start living down there! Too many exciting questions to be answered....

 

[johninCR]

Is the shelf above the bass drivers required? It seems to be a pretty long ways to the top of the baffle in that location. That's not enough?

I suspect that two 12" drivers will go down lower than 300 hz. Is this a conservative estimate? a calc? or is it about the integration of the bass module?

John in CR has a big advantage here, he has actually done this stuff so should be given careful consideration.

P.S. please don't show more than 4 drivers- it's just too scary!

Thanks Variac,

I learned a tremendous amount in the past year and a half. I was seeing how far I could take a single point source with an OB, so experimentation was the only way due to a distinct lack of info online.

Plugging in Eminence's Beta12CX into Linkwitz's DipoleSPLmax spreadsheet, with a "D" of only 20cm (~7.5"), a single 12 doesn't become excursion limited at 120db until 225hz. However, 120db at only 80hz (too high IMO) would require 4 15's of similar excursion (3.5mm xmax) AND a large "D" of 60cm (a 12" deep U baffle). Now you understand why designers "cheat" by boxing the bass.

Personally, I think 80hz is way too high, because I believe OB bass is a huge benefit in room. It's directionality results in greatly reduced reflections that is perceptively different. Linkwitz calculates this advantage to be +4.8db, making me question whether flat OB bass is even desireable. Whenever I dial in what should be close to flat, it sounds very bass heavy on music with strong LF content, and I back off the shelving EQ.

Note that the numbers I toss out there don't consider placement, or floor reinforcement. The floor cuts it back to 2 15's for 120db at 80hz, plus placement can be used to significant advantage. There's a catch 22 regarding placement. Mids love the breathing room, making the rear wave just ambiance, however, closer placement can reinforce bass, not as boundary reinforcement, but as extra delay for the net rear wave as it travels to the wall and reflects back to combine with the front radiation at the listening position. This is one of the effects that I hope to quantify as part of my measurement regime.

 

[Lynn Olson]

Simple might be best

I might use this as my starting point, and see how much EQ this requires. I've heard the bass Gary Pimm gets from his cardioid/dipole W-boxes - down to 20 Hz with stunning resolution and tonality. This three-speaker setup ought to be able to meet the W-boxes or monopole subwoofers.

It is also simple enough to make a good test bed for the EnABL and Mamboni baffle and speaker-cone edge-termination systems. I'm thinking 18Sound, Radian, or Hemp Acoustics for the 12" wideband coax, possibly something as zany as the 12" Alnico Tone Tubby for the midbass, and a 15" high-Qts bass driver that is yet to be determined. (The new 15" Tone Tubby - who knows? Time to get better and start building!)

 

[Variac]

Now thats less scary but looks "right" somehow. Beautiful even.

I'm hoping that the coax works out, and the Hemp stuff is the most exciting, but there is another disadvantage to the coax because the "midbass" 12 will have a different response,-even if it is based on the same driver.

If the 12" and "midbass" 12 are exactly the same, then they should integrate better I'd think. But there is the possibility of different models canceling out each other's anomolies also... So either way there are possible pluses. Best to use the same brand though I'd think. At least the cones could then be similar stuff.

Considering the frequencies involved and the area needed, would an 18" be a better choice than the 15? A PA 18 is usually cheaper than two 15" but I don't see them used much. I guess the floor reflection will help here though...forgot about that..

 

[Lynn Olson]

Now thats less scary but looks "right" somehow.

I'm hoping that the coax works out, but there is another disadvantage to the coax because the "helper" 12" will have a different response,-even if it is based on the same driver.

If the mid 12" and "helper" 12 are exactly the same, then they should integrate better I'd think. So either way there are pluses.

Considering the frequencies involved and the area needed, would an 18" be a better choice than the 15? A PA 18 is usually cheaper than two 15" but I don't see them used much. Or is this 15" a high excursion sub type as Linkwitz uses?

I'm planning on the midbass and bass driver sharing a steeper 12 dB/octave crossover set to about 1 kHz to prevent mid colorations from sneaking in. The cascade of 6 dB/oct lowpasses for the midbass and bass will control the degree of overlap between the drivers, and allow response shaping without massive EQ from the power amps.

I suspect mildly dissimilar widerange and midbass drivers might be a good thing, actually - remember, all of these drivers are working in the piston band, with intrinsically flat response, so what we're hearing are IM distortion signatures and unusual things like "magnet sound".

As for the bass driver, either a 15 or 18 would work fine. This depends on sonics as far as I can tell. High Q is a must, of course, along with good efficiency to complement the 97 ~ 99 dB/metre drivers upstairs.

 

[mige0]

variants

Hi

entertaining thread– and lots of input so far!

Thanks to all and special thanks to Lynn for bringing up here the very interesting point of cabinet coloration in an pinpointing and eloquent manner.

I am also on work to overcome this right now – though I am not through with reducing standing waves in closed boxes without the use of damping material. Its just an other attempt to make cabinet coloration "invisible". Every time I loose hope to finally manage to the point where I am confident with the results, I consider to make the step to dipole arrangement.


As for the changes in your route at the bottom end:

When you no longer consider a single low frequency speaker in order to compensate for the 6db roll off by doubling Sd every octave, it may come down to Sd and linear X against price per unit with a reasonable low resonance frequency. I found the Peerless sls 12"
http://www.tymphany.com/datasheet/printview.php?id=38
"http://www.tymphany.com/datasheet/printview.php?id=38"
to be a promising candidate in this respect.
When choosing 3 units, two of them could be placed close to ground one mounted at the side wing and the third one at the front in top of the other. The resulting shift in axis and directivity pattern at low frequencies might be welcome as it may give most certainly smother in-room response and extended flexibility for placing the OB in the room.


As for the changes in your route at the top end:

When looking for a high efficient tweeter instead of a coax driver, why not having a closer look at AMTs? These are not plagued by wear out like normal ribbons every time you over stress them a little bit.
Though not really at a bargain, the Mundorff's
http://www.mundorf.com/english/speakerschassis/index.htm
"http://www.mundorf.com/english/speakerschassis/index.htm"
might look interesting for example. They go up to 108dB, have good CSD, fairly flat FR and directivity may rather be a benefit than an issue for the intended application. Distortion is incredible low, which should fit nicely into a low coloration concept.
I doubt that the dipole feature of these devices can be used. Placing them closely to a potent midrange driver their diaphragm faces twice the pressure as normally, down to the cot off frequency of the mid unit. If possible though, you might want to break up the rear directivity pattern into a more chaotic behaviour. This should be an easy task at that frequencies. The small adjustable wings of BOSE (601?) loudspeakers come into mind immediately.
On the other hand, illuminating the room with rear tweeters might be not that demanding.
SONAB
http://www.carlssonplanet.com/oa14.php
" http://www.carlssonplanet.com/oa14.php"
also did this about three decades ago. In an appropriate environment this speakers created a smashing effect of "being there" at that time. SONAB
simply arranged several paper cone tweeters to fire in all directions at the top of the loudspeaker.
http://www.carlssonplanet.com/picture.php?p=365
" http://www.carlssonplanet.com/picture.php?p=365"

Greetings from the Alps,
Michael.


By the way , it is said that red wine is good for healing broken bones of elderly people - seriously!

 

[Lynn Olson]

Re: variants

Hi
When looking for a high efficient tweeter instead of a coax driver, why not having a closer look at AMTs? These are not plagued by wear out like normal ribbons every time you over stress them a little bit.
Though not really at a bargain, the Mundorff's
http://www.mundorf.com/english/speakerschassis/index.htm
"http://www.mundorf.com/english/speakerschassis/index.htm"
might look interesting for example. They go up to 108dB, have good CSD, fairly flat FR and directivity may rather be a benefit than an issue for the intended application. Distortion is incredible low, which should fit nicely into a low coloration concept.
I doubt that the dipole feature of these devices can be used. Placing them closely to a potent midrange driver their diaphragm faces twice the pressure as normally, down to the cot off frequency of the mid unit. If possible though, you might want to break up the rear directivity pattern into a more chaotic behaviour. This should be an easy task at that frequencies. The small adjustable wings of BOSE (601?) loudspeakers come into mind immediately.
On the other hand, illuminating the room with rear tweeters might be not that demanding.
SONAB
http://www.carlssonplanet.com/oa14.php
" http://www.carlssonplanet.com/oa14.php"
also did this about three decades ago. In an appropriate environment this speakers created a smashing effect of "being there" at that time. SONAB
simply arranged several paper cone tweeters to fire in all directions at the top of the loudspeaker.
http://www.carlssonplanet.com/picture.php?p=365
" http://www.carlssonplanet.com/picture.php?p=365"

Greetings from the Alps,
Michael.


By the way , it is said that red wine is good for healing broken bones of elderly people - seriously!

Thanks for the tip - maybe I should start drinking red wine - it would make the time go faster, if nothing else! One of these days I plan to return to Zurich, such a beautiful city, and such a friendly place.

The Mundorf 2530 certainly looks like a good complement to the 18Sound 12NDA520. So many choices! It's nice that we're not limited to the usual suspects from Scan-Speak, Vifa, Dynaudio, and Seas anymore.

I'm afraid to ask the prices from Mundorf, though - just how expensive are these new-generation AMT's? I've heard AMTs sound wonderful - the big problem with the US-made versions was variability, with no two alike, and some later-generation versions with serious FR problems. I imagine the Mundorf versions are very, very good - the specs are certainly better than anything I measured from the US versions. I couldn't find the prices anywhere, though - who distributes these products in the EU or the USA?

P.S. Very interesting article on clock jitter, by the way. This is much more audible than people realize, and part of the reason I'm not a huge fan of casually passing audio through a Behringer digital EQ - it's hard enough to build one good DAC in the system, much less a bunch of cheapo Chinese-made ones.

 

[planet10]

Re: Simple might be best

I might use this as my starting point,

The ladder structure at the back doesn't feel right, there must be a more elegant way of achieving the same ends.

dave

 

[mige0]

AMT from mundorf

Hi

the Mundorf AMTs are available in europ from HIFISOUND
http://www.hifisound.de/oxid/oxid.php/sid/x/shp/oxbaseshop/cl/alist/cnid/469431430ea6a1c48.83684768
"http://www.hifisound.de/oxid/oxid.php/sid/x/shp/oxbaseshop/cl/alist/cnid/469431430ea6a1c48.83684768"

or Lautsprechershop
http://www.lautsprechershop.de/hifi/index.htm?/hifi/baendchen.htm
"http://www.lautsprechershop.de/hifi/index.htm?/hifi/baendchen.htm"

also from Madisound
http://www.madisound.com/cgi-bin/index.cgi?cart_id=324141.6232&pid=1962


As for the Behringer DCX: they have messed the unit in the analoge part by iferiour capacitors, inferiour layout and inferiour bypassing. Nothing that could not be fixed at low cost if you have time and skills. But there are lots of threads about it somewhere else.

Thanks for your comment on clock jitter! I fully agree.

Greetings
Michael


Yes, drinking red wine stimulates the production of an specific glue for the bones which is in deficency the older we get.

 

[slowmotion]

Sorry 'bout the long quotes, but I just thought this could be repeated....
I have to agree with panomaniac, to me some of the big hornsystems I've been lucky to hear here in Norway sound more like real music that anything else....

I think that I agree with you there. Because the most neutral, uncolored, realistic systems I have ever heard were horn based. Compared with the very best planars, e.g., Quad ESLs and Magnaplanars, the horns always sounded more like real music to me. All other direct radiating systems sound like speakers to me, as nice as they may be.

When I lived in Paris I was lucky enough to hear, use and live with a number of high end speaker technologies. At the time I also worked in the music business and lived with a cellist . My ears were full of live music every day, all day long. As great as some of the systems I heard were, none sounded more like real music to me than the horns. It was not a matter of nuance, the horns nailed it.

The very big horn systems that we put together at the Kiron Theatre demos (designed by J.Hiraga) were by far the best imaging of any system I've heard before or since. Absolutely no problem with mass choral or strings. In fact, that's where they really shone.

So when I was in the thick of live music every day, all day, the good horn systems were by far the most life-like, the most realistic to my ears. Lack of coloration and dynamic ease where where they stood out. No direct radiator was as good, tho many were still quite wonderful to listen to.

But maybe horn colorations just don't bother me. I certainly did not hear them in those systems. I do hear them in lesser horn systems, i.e., most P.A. systems. Is it a matter of taste, or do we actually hear differently?

There's nothing wrong with your hearing, there's nothing wrong with mine, and similarly for Linkwitz and Geddes. People really do hear differently, although the academic community sometimes says otherwise - again, it's very easy to make a study reach a pre-determined conclusion, especially if Philips or Sony are backing it.

My guess is that working with certain types of audio systems sensitizes us to certain faults, just as people who make color prints in a photo studio can see color differences that are invisible to most of us. I know I am very sensitive to stored energy, having battled against it in loudspeakers since 1975. I'm much less critical of IM distortion and high-level compression, an area where horns are dramatically superior to all other systems.

I find the horn coloration gross and immediately obvious, and not a pleasant euphonic one. But I am aware the dynamic compression and IM distortion congestion of direct-radiators (and electrostats) is completely unacceptable to horn enthusiasts. For them, horns are the only way to go.

I have come to believe that. Perhaps it's at the root of so many audio arguments. Some of it is condtioning, some of it innate.

But it's a subject that mertis a whole thread to itself. I'll start one later today.

 

[Salas]

I'm planning on the midbass and bass driver sharing a steeper 12 dB/octave crossover set to about 1 kHz to prevent mid colorations from sneaking in. The cascade of 6 dB/oct lowpasses for the midbass and bass will control the degree of overlap between the drivers, and allow response shaping without massive EQ from the power amps.

I suspect mildly dissimilar widerange and midbass drivers might be a good thing, actually - remember, all of these drivers are working in the piston band, with intrinsically flat response, so what we're hearing are IM distortion signatures and unusual things like "magnet sound".

As for the bass driver, either a 15 or 18 would work fine. This depends on sonics as far as I can tell. High Q is a must, of course, along with good efficiency to complement the 97 ~ 99 dB/metre drivers upstairs.

The 18inch is mainly used to save some excursion for +3 to +4dB on top of a 15 inch territory output. It is generally heavy, slow, and beams from 100-150Hz and up. Generally its parameters don't give lower enough bass than a 15''. Main reason of use is max SPL. We are talking outdoors reinforcement levels now. There, room gain is absent and ground image is the only aid. Thus you get em in twin 18'' side by side mounted format in wide and low 200lt and over reflex or bass bin boxes. Processors cut like hell under 35Hz to save excursion limit, and system phase goes south.
I have put 18 and 15 together in shared box volume, only there they time better. I would choose no more than 15'' in the speaker under discussion (no enclosed volume to use the shared timing trick anyway) and if I needed more stuff for EQ and raw level, I would just double up.

 

[planet10]

Re: Re: Simple might be best

The ladder structure at the back doesn't feel right, there must be a more elegant way of achieving the same ends.

Here are some pics of other efforts... these thou, just brace the baffle, but could be adapted with the addition of a magnet clamp amd a tripod structure on the front/baffle end with driver mounting rings... (somewhere on this forum is a Thorsten L supravox baffle with a metal L for driver mounting and a floating plexi baffle)

The big new Jamo flagship:

An externally hosted image should be here but it was not working when we last tested it.

MDF -- not the ideal material...

and a rendering that preceded the above....

dave

 

[LineSource]

Lynn, have you considered a 2-structure baffle to separate the dipole woofers?

Dipole woofers will generate baffle vibration that can audibly modulate the higher frequencies unless special attention is paid to the baffle design. Counter balanced W-baffles are one good solution for deep bass from multiple dipole woofers. My earlier post illustrated how sand cavities can be built into the edge round-overs to maintain forward facing dipole woofers. I favor forward facing dipole woofers, but always physically separate the bass structure from the mid-tweeter structure.

 

[Graham Maynard]

http://www.jamo.com/Default.aspx?ID=2250&M=Shop&PID=15707&ProductID=17862

 

[johninCR]

"MDF -- not the ideal material..."

I'm starting to think that for OB's it may be pretty close.

Dave, I like the spine approach, especially if you connect it to the magnets. Add a couple of sacks of steel shot to the base and you're in business.

I agree with linesource regarding firing the woofers on axis with physical separation of the woofer section. Also plan on mass even in the upper section if you want a vibration free baffle. It's surprising the forces at play even in the null of the woofer section, and I'm not even talking about high output like Lynn's goal. They only net to zero there, not actually cancel.

It's great to see all you box guys finally coming around. The next step is to get you away from the flat baffles and H's, especially in the LF section. That's where the opportunity lies for design advancement. Anyone can XO and EQ a multiway flat if I can. As a group I'm sure we can figure out how to optimize my dual pathway approach in the LF section, or are you guys going to leave me on my own for another year. If I go it alone, I may become averse to sharing and go commercial.

 

[Lynn Olson]

Lynn, have you considered a 2-structure baffle to separate the dipole woofers?

Dipole woofers will generate baffle vibration that can audibly modulate the higher frequencies unless special attention is paid to the baffle design. Counter balanced W-baffles are one good solution for deep bass from multiple dipole woofers. My earlier post illustrated how sand cavities can be built into the edge round-overs to maintain forward facing dipole woofers. I favor forward facing dipole woofers, but always physically separate the bass structure from the mid-tweeter structure.

The catch here is that I'd like to run the wideband driver pretty much full range, without a 200~300 Hz highpass. If I was going to use a highpass filter - and make an honest midrange of it - the obvious candidate is the 18Sound 8NMB420. Note the response curve and power handling. For a classic 3-way speaker, this is an obvious design choice, and gives more freedom to select the tweeter since a higher tweeter crossover can be selected.

Since the 12NDA520 is the target driver, and I plan to let it "free run", it will be generating some cone-reaction vibration. Not as much as the drivers below it, of course, and that's a good argument for physically isolating the wideband driver from the midbass and bass drivers.

Planet10, thanks for the posts at #448 and #452. Good ideas there, and the 3D illustration is a slick visualization tool for the driver-support framework.

It's interesting - a conventional enclosure is like a monocoque, or exoskeleton, with the outer shell bearing the structural weight but also unfortunately acting like a large-area radiator for all internal vibrations, whether reaction products from the driver, or standing waves from internal box modes. The large area is much of the reason minimonitors have less cabinet coloration than even the most advanced construction big speakers - there's just less area to radiate, thus less coloration.

By contrast, the driver-support structures we're seeing here are external, but are specifically designed to have low radiating area combined with stiffness and rigidity. The trick is to have the large-area baffle not flop around and resonate from the back pressures, which although low, are certainly present in close proximity to the drivers.

"MDF -- not the ideal material..."

I'm starting to think that for OB's it may be pretty close.

Dave, I like the spine approach, especially if you connect it to the magnets. Add a couple of sacks of steel shot to the base and you're in business.

I agree with linesource regarding firing the woofers on axis with physical separation of the woofer section. Also plan on mass even in the upper section if you want a vibration free baffle. It's surprising the forces at play even in the null of the woofer section, and I'm not even talking about high output like Lynn's goal. They only net to zero there, not actually cancel.

It's great to see all you box guys finally coming around. The next step is to get you away from the flat baffles and H's, especially in the LF section. That's where the opportunity lies for design advancement. Anyone can XO and EQ a multiway flat if I can. As a group I'm sure we can figure out how to optimize my dual pathway approach in the LF section, or are you guys going to leave me on my own for another year. If I go it alone, I may become averse to sharing and go commercial.

I was thinking again about user-adjustable hinged baffles - with the simple addition of airtight tape on the back side, a piano hinge would indeed work to create a variable-angle side wing. Any kind of wing is going to create a short horn. In this application the de facto "horn" is working far below its passband, and moreover is looking directly into a room corner!

As you've been mentioning, JohninCR, this rotates the null of the dipole polar pattern, which in turn changes the interaction with the room, which is nowhere close to flat at these frequencies anyway. Cheaper than EQ, and certainly saves on the amplifier power.

The sheer strangeness of combining a TQWT in acoustic parallel with a leaky open-ended box has an appeal, although how it could be modelled as a complete in-room system escapes me. The people doing the heavy-duty competer modelling appear to have their hands full with simple dipole baffles interacting with a room. The simplest possible model of the TQWT+lossy-box would seem to shift from a monopole to cardioid to a dipole as the frequency increased, but that's just a wild guess. It's going to interact with the room in a very different way than conventional monopoles or even large-panel dipoles.

As JohninCR has mentioned earlier, measurements don't correlate well with subjective impressions at these frequencies, so the merit of going to the trouble of modelling all that is open to question. And I thought TL's and Karlson enclosures were controversial!

 

[johninCR]

Lynn,

The problem with hinges is bracing. This is without question the most common flaw I see in virtually every folded open alignment. The result is panel vibrations that would never be acceptable in any decent box speaker. Do these people really not put their hands on the construction to feel the significant vibrations. Apparently the common thought process is that since it's opened, there is no pressure, however, boxes don't vibration from a change in absolute pressure in the box. It's the pressure waves striking them. If you constrain that rear wave to a significant extent those rear edges "flap in the wind". Bracing may be even more important than a box, because at least a box has the structural support of the rear corners.

 

[Lynn Olson]

Vibration Control

Just wanted to throw out some information on vibration control, looked at from two different angles:

First, the "mainstream" approach of using every known method to get it as low as possible. Thanks to "jzagaza" at http://www.diyaudio.com/forums/showthread.php?postid=1165952#post1165952, we have some very interesting links to Fujitsu's advanced audio research project at:

http://www.timedomain.co.jp/tech/tech_e.html

http://www.timedomain.co.jp/tech/theory/td_theoryA4_eng.pdf

And a rare Stereophile review that actually describes the real-world results of this project - compared to something completely different, an Avante-Garde all-horn system!

http://stereophile.com/standloudspeakers/107fuj/

By the way, the Fujitsu Ten Eclipse TD712z speaker is about as close to an ideal monopole - in terms of extremely low diffraction and fully decoupled vibration control - as any speaker I've ever seen. This seems to represent the limiting case for the "mainstream" method of rigorous isolation and mechanical sinking of vibration from the driver. The physically small size of the single-driver speaker also limits unwanted emissions from the cabinet, something that is quite troublesome in big audiophile (and dipole!) speakers.

And for the other view - instead trying to completely get rid of vibration, over at Mother of Tone, they're aiming for "consonant" vibration, using selected woods and varnishes:

http://www.mother-of-tone.com/mother.htm

http://www.mother-of-tone.com/lacquer.htm

This isn't as ridiculous as it sounds. Thom Mackris and I auditioned identical compressed-carbon (not carbon-fibre) record mats with, and without, a common woodworking varnish in a direct A-B test. The difference was equivalant to the difference between a $500 and $5000 tone-arm, or a $200 and a $2000 phono cartridge. More musical, as you'd expect, but also much more lifelike and a remarkable absence of "mechanical" or metallic coloration. Instead of adding a "musical" coloration, it removed quite a bit of harsh and grainy "mechanical" coloration, and revealed much more of the musical dynamics, tone colors, and timbre. The impression of space was also quite a lot better, remarkably so, and it didn't sound like a coloration to me, more like the removal of a number of resonances.

Are the "absolute" and "consonant" approaches in conflict? Not as much as it appears. Yes, it's good to get coloration as low as possible, but there's always going to be a residue. That residue might as well be musically consonant, so it can subjectively disappear. The Mother of Tone approach using solid woods and selected lacquers (not C37, by the way, but conventional wood lacquers) seems like a direct and cost-effective way to build agreeable-sounding speaker systems using commonly available materials.

 

[ScottG]

While the 12NDA520 is a fantastic driver.. I'm not so sure this is the driver that should be run fullrange.. Dispersion becomes poor about 1.4 kHz, and it looks like at 1.8 kHz you start into time domain problems.

Now of course you *might* be able to modify the driver to an extent to clear things up (in time).. but that still won't do anything for the dispersion pattern.

It could be that the Tone Tubby is FAR better with time at the top of its passband.. don't know. I also don't know about its horizontal dispersion (which, including price, is why I didn't mention it to Paul in his thread).

One possibility to improve in-room power response while even further limiting dispersion, (creating a more linear off-axis response), and near time room reflections would be a hypercardoid based on a free air bipole with a pair of 12" drivers (mounted back to back). It would however need a very similar dispersion pattern at higher freq.s - which could be accommodated via those 18 sound horns. (in a paired bipole config.). Note that such a config. for the free air bipole would significantly reduce frame energy build up, (provided the two drivers were connected physically via a high transmission material), and mildly reduce 2nd order distortion. More importantly though, it should reduce time problems at the top of the driver's passband (..when compared to virtually any other mounting scheme). Additionally, you could always vary the rear in-phase output for most of the passband with a simple acoustic trap.

(Note that such a bipole will NOT have the side combing problems of traditional bipoles).

Well, it's an idea.

 

[berm]

I’m curious about the worth of this approach, but I’ve been intrigued by a woofer design in Speaker Builder
2/93, “The Flexible Dipole Woofer”, by Michael Allen. It’s part of a 3-way dipole, and covers the range between 40 and 135 (?) Hz. The whole system he claims to be + or - 2dB, 40 to 20kHz, with tight, tuneful bass.
He constructed the woofer on a frame 33” by 22”. On that he glued a very thin sheet of mylar, then on that glued a 29” by 18” piece of polyurethane foam (soft foam, I’ve assumed), then another piece of mylar glued over that to form a sandwich. He then takes a 10” woofer, cuts off most of the basket save for two legs, removes the cone and dustcap, leaving it as a motor. He mounts this on a double bracket on one side of the frame, and attaches it to the foam sandwich, using the neck of a 2 liter pop bottle inserted into the 1” voice coil, then glued to the mylar. He goes on to write that he was surprised to find that Museatex has a patent on a similar device, but he sees his as a “soft piston” and the Museatex as a “bending wave” transducer. I believe the Museatex design is the Melior One, a single-driver point souce which I think moves a mylar film without the foam sandwich feature.
This is one of those projects that I never got around to trying. This design should have several applications, and it seems like this particular thread was the best place to drop this in as one way among many to get decent dipole bass. I’ve been amazed at how occasionally some ideas seem to take fire, and the recent threads - this one, EnABL/Mamboni, the fourteen inch handmade cone, the Walsh thread - are enlightening and fun to read, to say the least. I should have dropped this in earlier, as the discussion seems to be going in a different direction, but I thought it still might prove useful to someone - if it does merit consideration.
Keep all that gray matter churning. Great read on this thread.