No it doesn't. The H baffle double driver dipole has 1 driver facing front and 1 driver facing the rear.
http://www.diyaudio.com/forums/showthread.php?postid=177932#post177932
One driver mounted forward and the other reversed, but the polarities are inverted so both cones are moving the same direction.
I'd have to agree with LineSource...I think that thing would be walking around the room unless constrained in some way.
Cheers,
Davey.
I'd have to agree with LineSource...I think that thing would be walking around the room unless constrained in some way.
Cheers,
Davey.
Thanks. Yes, I would agree with that too. Wow, I don't see any option without some significant compromise in this case.
Sand chamber H-baffle
A speaker motor has push vs. pull non-linearities due to the cone surround and spider mechanical forces, as well as minor non-linearities in the motor. In addition, for a dipole there is rear wave blockage from the magnet assembly and the rear frame structure that keeps the front - rear summation from full dipole cancelaion. For an H-frame, by mounting one driver facing forward and the second driver facing backward, these motor and dipole radiation non-linearities tend to cancel out. This arrangement does "smear" the time coherence of the wave launch by having two different cone attach distances, and it also "messes" up the front launch with resonances and reflections from the magnet and frame supports. I always mount all dipole speakers facing forward because I believe time coherence and non-obstructed front wave launch are more important than trying to reduce non-linear and dipole summation distortions.
I have built a dipole baffle with sand filled volumes running along the vertical sides and got great results. This both absorbs baffle vibration and adds useful weight to counter the cone Mms.
OO----baffle-----OO
The OO is the 6" x 3" oval shaped rib defining the sand volume
Cut several 6" deep and 3" wide oval shaped ribs from plywood with 1" holes to allow the sand to flow, and dado them into the baffle side edges at at 8"-12" spacing. Create a top and bottom baffle cap that follows the baffle plus oval ribs to contain the sand. Glue Formica onto the baffle front, wrap it around the ribs, and glue the Formica to the baffle rear. The Formica contains the sand. This design puts the sand in direct contact with the baffle edge, and hence allows the vibrating sand to efficiently absorb the vibrations through heat.
My width baffle
6" rib + 18" baffle + 6" rib = 30"
A speaker motor has push vs. pull non-linearities due to the cone surround and spider mechanical forces, as well as minor non-linearities in the motor. In addition, for a dipole there is rear wave blockage from the magnet assembly and the rear frame structure that keeps the front - rear summation from full dipole cancelaion. For an H-frame, by mounting one driver facing forward and the second driver facing backward, these motor and dipole radiation non-linearities tend to cancel out. This arrangement does "smear" the time coherence of the wave launch by having two different cone attach distances, and it also "messes" up the front launch with resonances and reflections from the magnet and frame supports. I always mount all dipole speakers facing forward because I believe time coherence and non-obstructed front wave launch are more important than trying to reduce non-linear and dipole summation distortions.
I have built a dipole baffle with sand filled volumes running along the vertical sides and got great results. This both absorbs baffle vibration and adds useful weight to counter the cone Mms.
OO----baffle-----OO
The OO is the 6" x 3" oval shaped rib defining the sand volume
Cut several 6" deep and 3" wide oval shaped ribs from plywood with 1" holes to allow the sand to flow, and dado them into the baffle side edges at at 8"-12" spacing. Create a top and bottom baffle cap that follows the baffle plus oval ribs to contain the sand. Glue Formica onto the baffle front, wrap it around the ribs, and glue the Formica to the baffle rear. The Formica contains the sand. This design puts the sand in direct contact with the baffle edge, and hence allows the vibrating sand to efficiently absorb the vibrations through heat.
My width baffle
6" rib + 18" baffle + 6" rib = 30"
Well, if you are willing/able to build a baffle with extra weight like sand, then the H dipole will still work well for you, whether you use traditional front/rear driver facing or front/front like LineSource. Note that your baffle does not have to get as fancy as LineSource's if you don't have tools/skill to do it. You can use all flat pieces, and just have cavities in the 2 vertical sides to hold sand. Note that this will be *very* heavy. I built my Tempest sub out of 1" MDF, no extra ballast, and it is just about the limit of what 1 person can lift.
Estatic,
I'm interested in dipoles as well. I have a pair of AV12's and have tried them in a dipole - I made just a quick and dirty box to see how it sounds, not with the intention of keeping it at this stage as I can't live with the placement issues of a dipole at this stage.
There are two approaches to designing a dipole:
1. conventional simple approach - use drivers designed for dipole use with a high Qts and low fs, which need little or no eq
2. actively filtered approach - use any driver you like which has sufficient displacement and is free of turbulence
You are much more limited in your selection of drivers with #1. I understand that you can still get some Lambda drivers, which I have heard are the lowest distortion drivers you can get, also very expensive of course. Regarding low distortion, another option is to get PA high efficiency drivers with parameters suitable for dipole - I believe it is easier to get low distortion when you have a number of 18" drivers moving less. PA drivers are designed for low distortion and compression. Or perhaps a stack of 15" drivers. .... yes your options for getting low distortion drivers with sufficient displacement are all expensive ones!
Going with approach #2, the Tumult seems ideal, but check that all of its excursion is actually useable, regarding turbulence. I'd want to know from someone who has tried that it is actually silent. I know my AV12's make more noise when they are moving in free air than I was expecting. Playing 10 Hz tones they do make some noise, if there was music playing it would probably mask the turbulence but it is very difficult for a driver to move so much as the Tumult without some air noise. My point - find out from someone who has the Tumult and has got it to move at xmax in free air with 20 hz tones.
Another good driver is the Titanic - 19mm xmax, it has a shorting ring and I believe it has low distortion. Well designed basket. I'm told from one guy who has 4 of them in sealed boxes that it is a very articulate driver, very compliant suspension and reproduces bass with some subtlety.
The AV15 is hard to beat in terms of displacement/cost ratio but you can't really compare it to the Tumult.
Regarding some earlier comments on power handling - it doesn't require much power to drive a dipole woofer. With test tones I could easily reach xmax (23mm one way) with my AV12 with a tiny 50 watt amp!!! It was 10 Hz tones I must admit. In a box that amp could barely get the driver to move at all a few mm in a sealed or vented box. I dont know how much power the Tumult needs in a sealed box or a dipole (but it will be less than the thermal power rating probably). As I recall, Linkwitz recommends having only as much amp power as you need to prevent overexcursion with dipoles. I'm not sure how you are really going to determine that, the best way is probably to ask someone who has used the Tumult in dipole. I doubt you would need 1kw, which sounds more appropriate for a sealed box.
regards,
Paul
I'm interested in dipoles as well. I have a pair of AV12's and have tried them in a dipole - I made just a quick and dirty box to see how it sounds, not with the intention of keeping it at this stage as I can't live with the placement issues of a dipole at this stage.
There are two approaches to designing a dipole:
1. conventional simple approach - use drivers designed for dipole use with a high Qts and low fs, which need little or no eq
2. actively filtered approach - use any driver you like which has sufficient displacement and is free of turbulence
You are much more limited in your selection of drivers with #1. I understand that you can still get some Lambda drivers, which I have heard are the lowest distortion drivers you can get, also very expensive of course. Regarding low distortion, another option is to get PA high efficiency drivers with parameters suitable for dipole - I believe it is easier to get low distortion when you have a number of 18" drivers moving less. PA drivers are designed for low distortion and compression. Or perhaps a stack of 15" drivers. .... yes your options for getting low distortion drivers with sufficient displacement are all expensive ones!
Going with approach #2, the Tumult seems ideal, but check that all of its excursion is actually useable, regarding turbulence. I'd want to know from someone who has tried that it is actually silent. I know my AV12's make more noise when they are moving in free air than I was expecting. Playing 10 Hz tones they do make some noise, if there was music playing it would probably mask the turbulence but it is very difficult for a driver to move so much as the Tumult without some air noise. My point - find out from someone who has the Tumult and has got it to move at xmax in free air with 20 hz tones.
Another good driver is the Titanic - 19mm xmax, it has a shorting ring and I believe it has low distortion. Well designed basket. I'm told from one guy who has 4 of them in sealed boxes that it is a very articulate driver, very compliant suspension and reproduces bass with some subtlety.
The AV15 is hard to beat in terms of displacement/cost ratio but you can't really compare it to the Tumult.
Regarding some earlier comments on power handling - it doesn't require much power to drive a dipole woofer. With test tones I could easily reach xmax (23mm one way) with my AV12 with a tiny 50 watt amp!!! It was 10 Hz tones I must admit. In a box that amp could barely get the driver to move at all a few mm in a sealed or vented box. I dont know how much power the Tumult needs in a sealed box or a dipole (but it will be less than the thermal power rating probably). As I recall, Linkwitz recommends having only as much amp power as you need to prevent overexcursion with dipoles. I'm not sure how you are really going to determine that, the best way is probably to ask someone who has used the Tumult in dipole. I doubt you would need 1kw, which sounds more appropriate for a sealed box.
regards,
Paul
34mm Xmax excursion limited SPL
24" wide H-baffle with two Tumults
34mm Xmax excursion limited SPL
no room gain or room resonance considered
Freq.....monopole....dipole
Hz......dB SPL......dB SPL
20......109..........95
28......115.........104
40......121.........113
57......127.........122
80......133.........131
113.....139.........140
160.....145.........149
226.....151.........158
320.....157.........163
453.....163.........169
24" wide H-baffle with two Tumults
34mm Xmax excursion limited SPL
no room gain or room resonance considered
Freq.....monopole....dipole
Hz......dB SPL......dB SPL
20......109..........95
28......115.........104
40......121.........113
57......127.........122
80......133.........131
113.....139.........140
160.....145.........149
226.....151.........158
320.....157.........163
453.....163.........169
Hey line source, much thanks for the figures. They do make me feel better about the rationality of the initial design.
Paul Spencer wrote:
"I'm interested in dipoles as well. I have a pair of AV12's and have tried them in a dipole - I made just a quick and dirty box to see how it sounds, not with the intention of keeping it at this stage as I can't live with the placement issues of a dipole at this stage."
Oh dear, now I'm really confused. I was under the impression that placement was least critical with dipoles.... That idea was one of their main attractions. I would be grateful if you would expand your statement regarding placement.
eStatic
Paul Spencer wrote:
"I'm interested in dipoles as well. I have a pair of AV12's and have tried them in a dipole - I made just a quick and dirty box to see how it sounds, not with the intention of keeping it at this stage as I can't live with the placement issues of a dipole at this stage."
Oh dear, now I'm really confused. I was under the impression that placement was least critical with dipoles.... That idea was one of their main attractions. I would be grateful if you would expand your statement regarding placement.
eStatic
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