BudP said:
Hmm, I'd like to hear more about this interesting material. Where do you get it, what is it named, etc. "Good from infrasonic to 2 kHz" sounds pretty awesome to me, and certainly good enough for the purposes of edge termination on the HF dipole and bass units.
Reflecting on the previous mini-essay, we see the same kind of topological tricks used in microphones to create the desired polar pattern. Omni mikes have small enclosed chambers on the back side of the diaphragm, dipoles are left open on both sides, and cardioids use damping techniques on the back side of the diaphragm - and for variable-pattern mikes, anything from variable shutters to two sets of diaphragms and an electrical adjustment.
The real issue is edge termination, regardless of enclosure type. Loudspeaker designers who avoid the time domain like to dance around this, but I now think it's a combination of mind-set (freq resp uber alles), unwillingness to work in another domain, and unfamiliarity with the tools of the time domain - MLS, TDS, etc. The frequency-only mindset has significantly retarded progress in loudspeaker design over many decades - I can now understand better why Dick Heyser of Cal Tech met nothing but 100% opposition in his native Los Angeles, the home of Altec, JBL, and Cerwin-Vega. His work met a more receptive audience in the UK and Europe, but I'm still surprised how alien working in the time domain is for many high-end designers.
When you visualize the driver as a wideband pulse-emitting device with a dipolar radiation pattern, it's easier to see what the enclosure is really doing - storing and re-radiating energy. There are two things making this challenging relative to other fields: the awkward requirement for three decades of bandwidth - extraordinarily wide by RF standards - and the extreme dynamic range of the ear, which is very sensitive to the faintest decay products. The only reason we don't object more to the grossly artificial sound of hifi systems is we've been listening to these things for a long time.
Hi Lynn, and thanks for starting this thread. Pity about the leg, hope it mends well. But your pain has become our gain.
"Not to tease you guys too much" May not be the intention, but I think it's happening.
You have pointed out some interesting things often overlooked. In regard to stored energy in baffles, I was thinking only last week that the baffle could be tapered at the edges. But now I think that was wrong. The energy has only one place to go - air. You mentioned a conduit fixed to the baffle edge. It could be filled with something like cement or sand, to provide some mass to terminate the baffle.
Also, the whole concept of stored energy gets me thinking. This energy starts at the magnet. If we have a lot of mass at that point, less energy will go through the basket, which should be cast, with no sharp edges. File carefully!
Baffle treatment is also a problem. Nice high gloss finishes show off the quality of the timber, and radiate more....You mentioned a rough or textured surface. I wonder if a mix of bitumen paint and sand would help, how would you determine the size of the "lumps" in the texture?
I am very close to fitting some phase plugs to some little wide-rangers. Now I am wondering if I really want a reflective surface so close to the cone.
Regards,
Geoff
"Not to tease you guys too much" May not be the intention, but I think it's happening.
You have pointed out some interesting things often overlooked. In regard to stored energy in baffles, I was thinking only last week that the baffle could be tapered at the edges. But now I think that was wrong. The energy has only one place to go - air. You mentioned a conduit fixed to the baffle edge. It could be filled with something like cement or sand, to provide some mass to terminate the baffle.
Also, the whole concept of stored energy gets me thinking. This energy starts at the magnet. If we have a lot of mass at that point, less energy will go through the basket, which should be cast, with no sharp edges. File carefully!
Baffle treatment is also a problem. Nice high gloss finishes show off the quality of the timber, and radiate more....You mentioned a rough or textured surface. I wonder if a mix of bitumen paint and sand would help, how would you determine the size of the "lumps" in the texture?
I am very close to fitting some phase plugs to some little wide-rangers. Now I am wondering if I really want a reflective surface so close to the cone.
Regards,
Geoff
Lynn,
I can certainly attest to a mind set among transducer designers. NIH is the prevailing attitude and none of the designers I got to talk to over the life of the EnABL process had a clue what phase and time coherence might mean, and this includes some well regarded "designers" with published works and large followings. Might as well have been discussing making ice sculptures in Hades.
I am embarrassed to admit I do not know the commercial name of this damping pad material. At Perfect Fit McDonald, the local wholesaler to the auto interior restoration / repair industry in Seattle, they just call it carpet underlayment and ask you how many yards of it you want. I am sure Denver will have it's counterpart and I will call PFMcD and ask to talk to the purchasing people to see if I can get a line on trade names, grades, etc.
I use this material for selective damping in cabinets that have full EnABL pattern drivers installed. They are quite transparent to back wave energy from reflections and the damping pad material, just applied to discrete cabinet surfaces, rather than as a filler, effectively eliminates these reflections. I use 3M 99 spray adhesive to attach the pads in place.
One of the reasons I am interested in the Mamboni / EnABL experiment currently gong on in Tennessee is the likely hood of reducing the back wave transparency, without compromising room emitter surface coherence. The wave tank experiments I conducted years ago indicated that the waves emitted from an EnABL treated driver are phase and time coherent, as the wave tank pulses act just as Soliton waves do, in Norwegian Fjords. Having them terminate on the driver surface, on the back side of the driver, rather than emit into a box full force is quite an attractive possibility.
Another thought arises concerning the phase angle of energy emitted from back wave resonance couplers from bass reflex cabinet design. It appears that the energy being emitted is phase coincident to the energy emitted from the driver directly into the air. Can this same event be used with a back chamber scheme of Mamboni / multiple tuned vents to effect a Bipolar radiator of Bass?
Bud
I can certainly attest to a mind set among transducer designers. NIH is the prevailing attitude and none of the designers I got to talk to over the life of the EnABL process had a clue what phase and time coherence might mean, and this includes some well regarded "designers" with published works and large followings. Might as well have been discussing making ice sculptures in Hades.
I am embarrassed to admit I do not know the commercial name of this damping pad material. At Perfect Fit McDonald, the local wholesaler to the auto interior restoration / repair industry in Seattle, they just call it carpet underlayment and ask you how many yards of it you want. I am sure Denver will have it's counterpart and I will call PFMcD and ask to talk to the purchasing people to see if I can get a line on trade names, grades, etc.
I use this material for selective damping in cabinets that have full EnABL pattern drivers installed. They are quite transparent to back wave energy from reflections and the damping pad material, just applied to discrete cabinet surfaces, rather than as a filler, effectively eliminates these reflections. I use 3M 99 spray adhesive to attach the pads in place.
One of the reasons I am interested in the Mamboni / EnABL experiment currently gong on in Tennessee is the likely hood of reducing the back wave transparency, without compromising room emitter surface coherence. The wave tank experiments I conducted years ago indicated that the waves emitted from an EnABL treated driver are phase and time coherent, as the wave tank pulses act just as Soliton waves do, in Norwegian Fjords. Having them terminate on the driver surface, on the back side of the driver, rather than emit into a box full force is quite an attractive possibility.
Another thought arises concerning the phase angle of energy emitted from back wave resonance couplers from bass reflex cabinet design. It appears that the energy being emitted is phase coincident to the energy emitted from the driver directly into the air. Can this same event be used with a back chamber scheme of Mamboni / multiple tuned vents to effect a Bipolar radiator of Bass?
Bud
Geoff,
May I suggest that you think about how you can get the energy off of the baffle plate without attenuating it, without mass "STORAGE" damping, without any ringing of transient standing waves, without any diffraction artifacts and in phase and time coherence with the expanding polar wave front from the driver. That will get you much farther than damping of any sort and I believe is the point Lynn has been pushing towards with his comments. Unless you have a "perfect" damping scheme you will have reflected energy.
You might also look at the thread on Walsh drivers for some interesting information on wave termination from a surface without damping.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30689&perpage=10&pagenumber=5
For your phase plug concern I would personally urge you to make a smooth flat surface with a flat acrylic paint, or study and apply either the Mamboni or EnABL edge termination process, one will apply, and will satify your concerns.
Bud
May I suggest that you think about how you can get the energy off of the baffle plate without attenuating it, without mass "STORAGE" damping, without any ringing of transient standing waves, without any diffraction artifacts and in phase and time coherence with the expanding polar wave front from the driver. That will get you much farther than damping of any sort and I believe is the point Lynn has been pushing towards with his comments. Unless you have a "perfect" damping scheme you will have reflected energy.
You might also look at the thread on Walsh drivers for some interesting information on wave termination from a surface without damping.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30689&perpage=10&pagenumber=5
For your phase plug concern I would personally urge you to make a smooth flat surface with a flat acrylic paint, or study and apply either the Mamboni or EnABL edge termination process, one will apply, and will satify your concerns.
Bud
Thanks Bud.
I understand the requirement of absorbing the energy before it travels, hence the large mass at the magnet. It will only absorb a percentage of the energy, depending on how much mass we can have without it effecting the radiation of the sound wave off the back of the cone, and it becoming another source of reflection.
Thanks for the links.
Geoff.
I understand the requirement of absorbing the energy before it travels, hence the large mass at the magnet. It will only absorb a percentage of the energy, depending on how much mass we can have without it effecting the radiation of the sound wave off the back of the cone, and it becoming another source of reflection.
Thanks for the links.
Geoff.
Hi Lynn,
I guess you are discussing aperiod/resistive driver loading. Car audio exponents mount drivers in rigid containers little larger than the driver itself, the rear load with home made mesh enclosed glass fibre ARUs of half driver dia and vent externally to the cabin.
I guess we could cut 'vents' in wooden floors but not solid, so whether a graduated series of ARUs with the rear residual venting into a listening room would sound acceptable via a more normal sized cabinet might be worth considering.
Also I cannot begin to emphasise how simple rolls of dense carpet two to three turns thick and either side of a mounting baffle really do improve reproduction.
Cheers ........ Graham.
I guess you are discussing aperiod/resistive driver loading. Car audio exponents mount drivers in rigid containers little larger than the driver itself, the rear load with home made mesh enclosed glass fibre ARUs of half driver dia and vent externally to the cabin.
I guess we could cut 'vents' in wooden floors but not solid, so whether a graduated series of ARUs with the rear residual venting into a listening room would sound acceptable via a more normal sized cabinet might be worth considering.
Also I cannot begin to emphasise how simple rolls of dense carpet two to three turns thick and either side of a mounting baffle really do improve reproduction.
Cheers ........ Graham.
hi lynn
am enjoying the thread, tho I will readily admit that the majority of it goes WAY over my head ha ha. Only recently discovered your ariels, but alas those vifa mids seem to be over the hills and far away.
Can I quickly make a clarification/correction?? Back in post 111 you cautioned against using a low fi device like the Behringer deqx in any application other than bass duties. (However, I have heard the Behringer DEQ 2496 make significant improvements in systems, yet admit that there would certainly be systems in which you wouldn't use it!)
There is no such unit as the Behringer deqx, there is for example a dcx(2496), or a deq(2496).
However, there is a unit (company) known as deqx, which do indeed do active eq and room correction. I think would be unfair on this unit to describe it as low or mid fi, indeed it is used in many very expensive and high end systems. Unless it indeed was the deqx you were referring to, what seems to have happened is that the two were somehow mixed together into some hybrid beast now known as the behringer deqx, which could be unfortunate on the deqx as it is a very good system indeed.
I use the deqx in my tri amped system and so can vouch for it's quality. That, of course, is only my opinion.
am enjoying the thread, tho I will readily admit that the majority of it goes WAY over my head ha ha. Only recently discovered your ariels, but alas those vifa mids seem to be over the hills and far away.
Can I quickly make a clarification/correction?? Back in post 111 you cautioned against using a low fi device like the Behringer deqx in any application other than bass duties. (However, I have heard the Behringer DEQ 2496 make significant improvements in systems, yet admit that there would certainly be systems in which you wouldn't use it!)
There is no such unit as the Behringer deqx, there is for example a dcx(2496), or a deq(2496).
However, there is a unit (company) known as deqx, which do indeed do active eq and room correction. I think would be unfair on this unit to describe it as low or mid fi, indeed it is used in many very expensive and high end systems. Unless it indeed was the deqx you were referring to, what seems to have happened is that the two were somehow mixed together into some hybrid beast now known as the behringer deqx, which could be unfortunate on the deqx as it is a very good system indeed.
I use the deqx in my tri amped system and so can vouch for it's quality. That, of course, is only my opinion.
terry j said:
did you mean you can't locate them????..
if so, heres an example
http://www.speakercity.com/Merchant...&Product_Code=P13WH00-08&Category_Code=VifaCL
Regards
Ed
-me too
Thanks to this thread I am starting to visualize my next loudspeakers. Most of what I intend to use I either already own, or will fit within a meager budget.
I own a set of Eminence Beta 12CX and psd2002 compression drivers. I personally don't like the way they sound (surprise) but maybe there is hope. I think I've picked up a couple of things along the way here.
The 12CX woofer has a terrible peak at 2k -it's major flaw I think - maybe I could notch that out. I could cover the rear of the 'horn' with felt to lower reflection. Also, I could perf near the edge or put a ring of felt on the very edge of the horn, or both. I could damp the 'room side' of the compression drivers' phase plug with some type of coating. The tweeter and 12cx horn combo simply isn't very good, but efficiency is very good - too good. The curve takes a dive out to 20k. I would have to somehow create a rising response and attenuating lower frequencies would be OK due to the 105dB efficiency.
I can see this driver in a modest dipole baffle on top with a W dipole down below using a pair of the Pyle PPA15 15" per side. I am thinking of doing what Infinity did on the old RS series using wood slats to reduce diffraction and make it look good.
The 15" drivers run by an Adcom 555II actively crossed to the Eminence. The top either active or passive (??) run by a Pass or Krell clone.
Am I on a good track?
vital states, yes, that was exactly what I meant ie I couldn't find the vifa mids used in the ariels after maybe not exhaustive but nonetheless considerable use of the google search function on the computer. Boy that came out all contorted didn't it! ha ha.
Thanks for the link, will reconsider my options now.
Thanks for the link, will reconsider my options now.
WMTMW with 21" woofers
I'm a builder that uses dipoles with pro drivers. This WMTMW uses two 21" woofers, two JBL 2123J mids and a Heil Air Motion Transformer - it was tri-amped plus a horn loaded sub. These have been retired.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=83282
Now I'm using 3-way dipole line arrays with six pro ten inch woofers, twelve 5.25" mids, and thirty neodome tweeters a side plus a horn sub. Multi-amped. 120 db no problem - low compression and simply fantastic imaging with my latest 'mods'
The large line-array open baffles are the best overall speaker I have built or heard to date. crossover is at 180 and 4k with a wideband 'notch filter on the mid (ypu need to play with a line array a bit) and configured to keep cross talk cancellation at a minimum from the midbass up. Kinda like large headphones but bigger, better and more natural from a listeners perspective.
I'm a builder that uses dipoles with pro drivers. This WMTMW uses two 21" woofers, two JBL 2123J mids and a Heil Air Motion Transformer - it was tri-amped plus a horn loaded sub. These have been retired.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=83282
Now I'm using 3-way dipole line arrays with six pro ten inch woofers, twelve 5.25" mids, and thirty neodome tweeters a side plus a horn sub. Multi-amped. 120 db no problem - low compression and simply fantastic imaging with my latest 'mods'
The large line-array open baffles are the best overall speaker I have built or heard to date. crossover is at 180 and 4k with a wideband 'notch filter on the mid (ypu need to play with a line array a bit) and configured to keep cross talk cancellation at a minimum from the midbass up. Kinda like large headphones but bigger, better and more natural from a listeners perspective.
Re: WMTMW with 21" woofers
Magnetar,
How bad was/is dipole baffle vibration from the front radiating woofers? W-baffles with mirrored moving mass compensation are often considered necessary, as you can see from this thread. So, how much rock and roll is generated in your baffles? Over the years I've become a big fan of WMTMW topology when the room allows the size.
Magnetar said:
Magnetar,
How bad was/is dipole baffle vibration from the front radiating woofers? W-baffles with mirrored moving mass compensation are often considered necessary, as you can see from this thread. So, how much rock and roll is generated in your baffles? Over the years I've become a big fan of WMTMW topology when the room allows the size.
Re: Re: WMTMW with 21" woofers
They were heavily braced and made froma layer of birch ply, plus underlayment backer board plus marine ply. Then braced and reinforced with pine and MDF. I started out with just the birch and kept adding layers to quiet the beasts down.
The new open back line arrays are better in all respects.
I haven't read the whole thread yet -
LineSource said:
They were heavily braced and made froma layer of birch ply, plus underlayment backer board plus marine ply. Then braced and reinforced with pine and MDF. I started out with just the birch and kept adding layers to quiet the beasts down.
The new open back line arrays are better in all respects.
I haven't read the whole thread yet -
I can't believe I almost missed this thread about my 2 favorites OB's and OB line arrays.
Some interesting possible solutions to edge diffraction, which I think is the most ignored subject in speaker design. I'm not from the camp believing that diffraction is a moot point with dipoles, since it's caused by the pressure change at the edge which is double compared to a monopole. An infinitely thin baffle may help the front and rear components cancel, but I believe they are in large part directional so diffraction can't be ignored.
I was disappointed to see in the last few pages the idea to turn the bass section into a monopole through heavy absorption of the rear wave. Just build an aperiodic box if you want that.
Instead let's have discussion about how to eliminate the TL resonance via construction shapes. It's my understanding that the fundamental resonance is caused by the air mass behaving as a lumped mass at very low frequency, then transitioning to more normal behavior higher in frequency. The tangled mass of damping material breaks up the lumped air mass behavior, thus eliminating the resonance (this is why damping is required to make U-baffles function properly according to JohnK). I've had some success with using staggered cross bracing and expanding CSA's to break up the lumped mass behavior and reduce resonance.
Magnetar, it's good to finally get some feedback about your OB arrays. I'm glad they're working out for you. How well damped is the area behind your speakers? At high SPL's I prefer the rear wave to roll off early, because too much HF in the rear wave sounds congested to me.
With my latest project, I've decided to go with Dr. Geddes' approach but in dipole form for constant directivity from top to bottom. Dipole radiation controlling things up to 500hz or so, which transitions to waveguided control above that. I really like the results so far, because I find that typical dipoles have toostrong an emphasis well off axis.
My upper section will accomodate up to an 8" driver as pictured below, with a 15" planned for the bottom. I plan to fill voids with a lot of sand to eliminate my only problem, which is significant vibration in the 4" diameter solid wood roundovers (a testament to the energy causing edge diffraction). The foam and material lining is absolutely required to eliminate colorations resulting from HOM's despite the minimal horn loading of the waveguides.
Here's a pic of my CDDWG's, Constant Directivity Dipole WaveGuides.
Some interesting possible solutions to edge diffraction, which I think is the most ignored subject in speaker design. I'm not from the camp believing that diffraction is a moot point with dipoles, since it's caused by the pressure change at the edge which is double compared to a monopole. An infinitely thin baffle may help the front and rear components cancel, but I believe they are in large part directional so diffraction can't be ignored.
I was disappointed to see in the last few pages the idea to turn the bass section into a monopole through heavy absorption of the rear wave. Just build an aperiodic box if you want that.
Instead let's have discussion about how to eliminate the TL resonance via construction shapes. It's my understanding that the fundamental resonance is caused by the air mass behaving as a lumped mass at very low frequency, then transitioning to more normal behavior higher in frequency. The tangled mass of damping material breaks up the lumped air mass behavior, thus eliminating the resonance (this is why damping is required to make U-baffles function properly according to JohnK). I've had some success with using staggered cross bracing and expanding CSA's to break up the lumped mass behavior and reduce resonance.
Magnetar, it's good to finally get some feedback about your OB arrays. I'm glad they're working out for you. How well damped is the area behind your speakers? At high SPL's I prefer the rear wave to roll off early, because too much HF in the rear wave sounds congested to me.
With my latest project, I've decided to go with Dr. Geddes' approach but in dipole form for constant directivity from top to bottom. Dipole radiation controlling things up to 500hz or so, which transitions to waveguided control above that. I really like the results so far, because I find that typical dipoles have toostrong an emphasis well off axis.
My upper section will accomodate up to an 8" driver as pictured below, with a 15" planned for the bottom. I plan to fill voids with a lot of sand to eliminate my only problem, which is significant vibration in the 4" diameter solid wood roundovers (a testament to the energy causing edge diffraction). The foam and material lining is absolutely required to eliminate colorations resulting from HOM's despite the minimal horn loading of the waveguides.
Here's a pic of my CDDWG's, Constant Directivity Dipole WaveGuides.
An externally hosted image should be here but it was not working when we last tested it.
JoninCR,
You might want to re-read the last few pages. They aren't actually about bass monopoles at all. Some cardioid bass was mentioned by Lynn, Gary Pimm's flat to 16 Hz system specifically, and then some slight discussion of how to use a specialized, infinite edge simulation pattern, with multiple, in this case likely hundreds, of ports in an attempt to make a perfectly terminated rear bass chamber for possible bipolar operation, as an alternate to the cardioid bass was also mentioned. I am not at all sure why more bass might be needed, Gary Pimm appears to have shown a clear path for integrating bass and bipolar mid and upper drivers.
Your point on the amount of power that is available at the null zone of a driver is important to note. There are some edge terminations that remove reflected energy from the cone edge, being experimented with in another thread here, the Walsh thread after page 6.
I can report that the EnABL process narrows the null zone at the periphery of a driver to just a handful of degrees. Would that help or hinder your damping procedure as shown in your pictures? This process will also eliminate edge diffraction from a baffle, regardless of it's shape, and even large radius edge contours can benefit from a less lossy termination.
The Mamboni process spoken of in earlier pages in this thread, will also remove edge diffraction by making the terminus infinite. The use of both of these tools to control driver and baffle plane reflections and energy storage, without significantly damping any of the active or passive surfaces with further energy storage mechanisms, might interest you in your future experiments.
Bud
You might want to re-read the last few pages. They aren't actually about bass monopoles at all. Some cardioid bass was mentioned by Lynn, Gary Pimm's flat to 16 Hz system specifically, and then some slight discussion of how to use a specialized, infinite edge simulation pattern, with multiple, in this case likely hundreds, of ports in an attempt to make a perfectly terminated rear bass chamber for possible bipolar operation, as an alternate to the cardioid bass was also mentioned. I am not at all sure why more bass might be needed, Gary Pimm appears to have shown a clear path for integrating bass and bipolar mid and upper drivers.
Your point on the amount of power that is available at the null zone of a driver is important to note. There are some edge terminations that remove reflected energy from the cone edge, being experimented with in another thread here, the Walsh thread after page 6.
I can report that the EnABL process narrows the null zone at the periphery of a driver to just a handful of degrees. Would that help or hinder your damping procedure as shown in your pictures? This process will also eliminate edge diffraction from a baffle, regardless of it's shape, and even large radius edge contours can benefit from a less lossy termination.
The Mamboni process spoken of in earlier pages in this thread, will also remove edge diffraction by making the terminus infinite. The use of both of these tools to control driver and baffle plane reflections and energy storage, without significantly damping any of the active or passive surfaces with further energy storage mechanisms, might interest you in your future experiments.
Bud
EnABL and Mamboni are interesting indeed, and there may be something I can use there, though I'm really liking the 80-90deg wide null I've created at each side of my WG's. Added presence like a horn but without the coloration, a bit more sensitivity too, while they seem to retain much of the sense of space of a wide open dipole.
Re monopole, I have to disagree. If you start attenuating the rear wave at low frequencies in the bass section, there's a shift toward monopole. My room construction is primarily concrete, so I'm very sensitive to things that get away from a net pressure of zero introduced in the time domain below 200hz or so. Dispersion patterns whether dipole or hybrid with a shift toward cardiod both work for me with proper placement.
If you want more bass in an open alignment, I see only 2 choices, more drivers making EQ a requirement or lengthen the rear wave path. Before you cry foul "that's just a TL", if you use a TL only well below it's fundamental then isn't it just a U-baffle? My solution is to send the lowest frequencies on a longer path by using a Helmholtz slot to separate a portion from the rest of the rear output.
I've built 2 of these. One uses the Hawthorn coax 15, but the Qts is probably too high because cone control is lost too quickly for really high SPL. The other uses a cheap Selenium coax 15, and is in daily use at a friend's beach hotel outdoors. The 2m pathlength differential of the portion of the rear wave that enters the slot means that it actually helps reinforce the front wave down to below 30hz instead of cancelling it. The slot size and shape determine what frequencies enter the longer path. I use only 5 staggered cross braces, a little damping, and a tapered terminus with a Kslot shape in the shortest panel to prevent resonce in the 16" short pipe....nothing in the longer pathway.
Re monopole, I have to disagree. If you start attenuating the rear wave at low frequencies in the bass section, there's a shift toward monopole. My room construction is primarily concrete, so I'm very sensitive to things that get away from a net pressure of zero introduced in the time domain below 200hz or so. Dispersion patterns whether dipole or hybrid with a shift toward cardiod both work for me with proper placement.
If you want more bass in an open alignment, I see only 2 choices, more drivers making EQ a requirement or lengthen the rear wave path. Before you cry foul "that's just a TL", if you use a TL only well below it's fundamental then isn't it just a U-baffle? My solution is to send the lowest frequencies on a longer path by using a Helmholtz slot to separate a portion from the rest of the rear output.
I've built 2 of these. One uses the Hawthorn coax 15, but the Qts is probably too high because cone control is lost too quickly for really high SPL. The other uses a cheap Selenium coax 15, and is in daily use at a friend's beach hotel outdoors. The 2m pathlength differential of the portion of the rear wave that enters the slot means that it actually helps reinforce the front wave down to below 30hz instead of cancelling it. The slot size and shape determine what frequencies enter the longer path. I use only 5 staggered cross braces, a little damping, and a tapered terminus with a Kslot shape in the shortest panel to prevent resonce in the 16" short pipe....nothing in the longer pathway.
An externally hosted image should be here but it was not working when we last tested it.
johninCR said:
John, can you post the measurements to show proof of concept?
Please post the measurements at varying angles so we can see that this is really taking place, instead of, perhaps mere speculation?
johninCR said:
So you have evidence of reduced HOM's here. Can you present it in the form of measured data please? Thanks.
johninCR said:
That looks an awful lot like a midrange in an H-baffle, where the TL's are simply tapered, instead of constant cross section, as one would have in a typical H-baffle subwoofer.
Can you post your measurements where you confirmed this to have constant directivity? What frequencies are being wave guided? Why are high frequencies from different parts of the cone simply not reflecting around in this horn?
I guess I'll have to wait for the post of your measurements to see what might really be going on here.
Thanks in advance.
BTW, I've been following the thread from the beginning. Lots of good information - along with some good 'ol golden earred fantasy, all mixed into one. Quite entertaining so far
.cheers,
AJ