Greetings
For the last year and a half, I've been happily enjoying my single tumult in a sealed 120L enclosure.
There seems to be a 'cult-like' following indicating that di-pole configuration is the way to go for bass nirvana.
I would like to try this out for myself.
I am looking for a design to build a di-pole sub with one tumult driver.
I have read countless threads, visited linkwitz's site and I am now ready to start the process. Hopefully with some help from this forum I can build an awsome di-pole.
First question, the 'H' design. Can one use a cylinder with the driver mounted in the centre (half the length) to obtain a '3D' H ? Effectively the driver would 'see' the same 90-degree baffle.
Also, how do you determine the ideal dimensions for the H ?
Will I need an EQ?
Thanx in advance
Dan
For the last year and a half, I've been happily enjoying my single tumult in a sealed 120L enclosure.
There seems to be a 'cult-like' following indicating that di-pole configuration is the way to go for bass nirvana.
I would like to try this out for myself.
I am looking for a design to build a di-pole sub with one tumult driver.
I have read countless threads, visited linkwitz's site and I am now ready to start the process. Hopefully with some help from this forum I can build an awsome di-pole.
First question, the 'H' design. Can one use a cylinder with the driver mounted in the centre (half the length) to obtain a '3D' H ? Effectively the driver would 'see' the same 90-degree baffle.
Also, how do you determine the ideal dimensions for the H ?
Will I need an EQ?
Thanx in advance
Dan
Hi Dan,
A Tumult sounds like a good main ingredient for your first dipole recipe.
However, I'd say ixnae on the ylindercae. By positioning your driver at a cylinder's midpoint, you're pretty much getting the worst of both or however many worlds. Not only is the front-to-back path length identical in all dimensions, guaranteeing you a sharp peak followed by deep nulls, you'll also be begging for cavity resonances unless you lowpass it early.
These are the same reasons why round baffles with centrally mounted drivers are generally to be avoided, as are unnecessary cavities--again, unless you're planning to cross very low and steeply. To spread Fp, you want a variety of front-to-back path lengths. This is why people on this forum often arrange their drivers off-center in flat baffles. I've often thought a driver mounted in the center of a star-shaped baffle would be pretty ideal since the deep cuts and long legs of the star would present such a great range of front-to-back path lengths.
Obviously, you don't have to go to extremes, but just don't forget that there is wisdom in a multitude of path lengths. ...Did that sound a little Buddhist to anyone else?
A Tumult sounds like a good main ingredient for your first dipole recipe.
However, I'd say ixnae on the ylindercae. By positioning your driver at a cylinder's midpoint, you're pretty much getting the worst of both or however many worlds. Not only is the front-to-back path length identical in all dimensions, guaranteeing you a sharp peak followed by deep nulls, you'll also be begging for cavity resonances unless you lowpass it early.
These are the same reasons why round baffles with centrally mounted drivers are generally to be avoided, as are unnecessary cavities--again, unless you're planning to cross very low and steeply. To spread Fp, you want a variety of front-to-back path lengths. This is why people on this forum often arrange their drivers off-center in flat baffles. I've often thought a driver mounted in the center of a star-shaped baffle would be pretty ideal since the deep cuts and long legs of the star would present such a great range of front-to-back path lengths.
Obviously, you don't have to go to extremes, but just don't forget that there is wisdom in a multitude of path lengths. ...Did that sound a little Buddhist to anyone else?
Bill F. said:Hi Dan,
A Tumult sounds like a good main ingredient for your first dipole recipe.
However, I'd say ixnae on the ylindercae. By positioning your driver at a cylinder's midpoint, you're pretty much getting the worst of both or however many worlds. Not only is the front-to-back path length identical in all dimensions, guaranteeing you a sharp peak followed by deep nulls, you'll also be begging for cavity resonances unless you lowpass it early.
These are the same reasons why round baffles with centrally mounted drivers are generally to be avoided, as are unnecessary cavities--again, unless you're planning to cross very low and steeply. To spread Fp, you want a variety of front-to-back path lengths. This is why people on this forum often arrange their drivers off-center in flat baffles. I've often thought a driver mounted in the center of a star-shaped baffle would be pretty ideal since the deep cuts and long legs of the star would present such a great range of front-to-back path lengths.
Obviously, you don't have to go to extremes, but just don't forget that there is wisdom in a multitude of path lengths. ...Did that sound a little Buddhist to anyone else?
I think you should use the dipole woofer only at frequencies below the resonance point. Linkwitz is doing that as well. Myself have a dipole woofer in a H-frame and it has total dept of 40cm, so 20cm at both sides. It has a nasty resonance at 200-250Hz or so but if you filter well below that, say 120Hz or so with sufficiently steep filters, then you don`t see that resonance. Of course you need EQ to correct for the 6dB/Oct roll-off that you get with a dipole.
Have fun
Gertjan
Thanx for the replies
I find this baffle stuff somewhat baffling.
Bill F.
I would only have a baffle diameter large enough to mount the driver onto. The cylinder enclosure I envisioned I read from the Linkwitz site He uses a cylinder for his analysis of the H-frame dipole woofer. I guess it could be a square. Linkwitz states: “L=d1+d2 and width and height W”. When width = height the cross-section is either a square or a circle. From his graphs with his dimensions he shows a +6db peak at 283Hz. If I use similar dimensions I should receive similar results (in free space that is). And as quemink suggests, the sub will be crossed over 24db per octive below 80Hz so the peak shouldn’t be an issue.
So, the only filter requirement would be to replace the 6db/oct that i will lose because of the configuration? A BFD could do this, no? or I guess i could modify my AVA250 plate amp.
Dan
Dan
I find this baffle stuff somewhat baffling.
Bill F.
I would only have a baffle diameter large enough to mount the driver onto. The cylinder enclosure I envisioned I read from the Linkwitz site He uses a cylinder for his analysis of the H-frame dipole woofer. I guess it could be a square. Linkwitz states: “L=d1+d2 and width and height W”. When width = height the cross-section is either a square or a circle. From his graphs with his dimensions he shows a +6db peak at 283Hz. If I use similar dimensions I should receive similar results (in free space that is). And as quemink suggests, the sub will be crossed over 24db per octive below 80Hz so the peak shouldn’t be an issue.
So, the only filter requirement would be to replace the 6db/oct that i will lose because of the configuration? A BFD could do this, no? or I guess i could modify my AVA250 plate amp.
Dan
Dan
You should also look into the U-frame dipole design by John Kreskovsky.
And the Tumult should be just great for this application.
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And the Tumult should be just great for this application.
Is infinite baffle an option for you? If you *do it right* you can get all of the performance or a dipole without losing output.
* ie. room treatment and / or room eq and experimenting with positioning
Have you tried the tumult out of the box for turbulence? I find it hard to imagine that you could use all that excursion without a lot of turbulent airflow.
* ie. room treatment and / or room eq and experimenting with positioning
Have you tried the tumult out of the box for turbulence? I find it hard to imagine that you could use all that excursion without a lot of turbulent airflow.
tg3 said:
Yes, the U-frame is very interesting as well, I was thinking of doing an U-frame for my next project. The advantage of the U-frame is as you can see that you radiate less to the back so the reflections from the back-wall will be less disturbing. You also should get a maxiumum of 6dB more output for the same cone movement. So more soundpressure before bottoming.
To get the best effect, you have to make sure that at the back of the speaker, sound from the back side of the woofer and the front side at the same time. You can see that the path length from from front of the woofer to the back of the enclosure and from back of the woofer to back of the enclosure is longer. So I guess it would be best to place a sort of labyrint in the enclosure so that the back sound arrives at the same time as the front sound. So basically you create a very short transmission line at the back.
At least, the above was my plan, hane not build it yet.
Best regards
Gertjan
paulspencer said:
From the Adire Audio web site:
All of this is attached to a 12-spoke cast aluminum basket; combined with the 1.375" diameter pole vent the Tumult has no audible air noise in operation. The ultimate speaker for dipole use (where high excursion is mandatory).
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An externally hosted image should be here but it was not working when we last tested it.
Paul
The IB has definite appeal to me. The problem is where do you cut the hole for the driver, ceiling? floor? wall?. And at which location on the ceiling/floor/wall? Is this an important consideration?
I guess I do have a old intake vent on the floor in the corner I could experiment with....anyone using the basement won't particulaly like it though
The U-Frame seems like a good choice as well.
Damn too many choices.
The IB has definite appeal to me. The problem is where do you cut the hole for the driver, ceiling? floor? wall?. And at which location on the ceiling/floor/wall? Is this an important consideration?
I guess I do have a old intake vent on the floor in the corner I could experiment with....anyone using the basement won't particulaly like it though
The U-Frame seems like a good choice as well.
Damn too many choices.
tg3 said:From the Adire Audio web site:
All of this is attached to a 12-spoke cast aluminum basket; combined with the 1.375" diameter pole vent the Tumult has no audible air noise in operation. The ultimate speaker for dipole use (where high excursion is mandatory).
I have heard similar comments about my sub driver - the Stryke AV12 but I can tell you it isn't silent when moving with 10 Hz test tones, far from it. Normally with music this won't be a problem as turbulence will be masked, but I would prefer "silent." The AV12 has a similar basket design - very open with a decent size vent. I doubt that the Tumult could be silent given it has so much more excursion.
You can cut the hole for infinite baffle in any part of the envelope. Your choice will be determined by:
*how it couples to room modes in that position
*aesthetics
*practicality
*sound isolation (if you have a tiled roof space behind it and neighbour issues then you might consider your options)
*vibration issues
You can actually make a very large sealed box in the room - if it is large enough relative to the VAS then it may be considered IB still.
IB drivers are normally mounted so that they cancel the mechanical vibration that is transferred to the structure to a certain extent, so you may consider using two Tumults.
IB is a very interesting area and I suggest you do some searching both on google and on this forum.
paul
This is obviously not an a easy thing to determine. Short of cutting a 15" diameter hole, test for response then move to next spot and repeat.....not my idea of fun
Could be a lot of holes in the end.
Is there any software out there that would help determine IB placement??
Also, how do the room modes couple to a IB configuration?? Is it the same as a sub box in a room. Ive read that dipoles donnot couple to the room like a box does so how does an IB compare.
This is obviously not an a easy thing to determine. Short of cutting a 15" diameter hole, test for response then move to next spot and repeat.....not my idea of fun
Could be a lot of holes in the end.Is there any software out there that would help determine IB placement??
Also, how do the room modes couple to a IB configuration?? Is it the same as a sub box in a room. Ive read that dipoles donnot couple to the room like a box does so how does an IB compare.
I'd start with playing around with simulation with the Room Reflection Response Calculator which shows the effect of room modes. This will give you an idea.
To do actual tests you don't need to built it! Imagine your room were flipped so the floor now became the ceiling and vice versa. Now put your microphone where your ears would be relative to the floor. Put your sub on the floor in the position equivalent to where you would put it on the ceiling. It does not matter that you are not putting it in the ceiling - sound waves don't understand "ceiling" and "floor."
Dipoles have three main advantages in the bass:
1. no box - the air spring is removed and the driver movement is controlled by the signal, driver motor and suspension system so the transient response is as good as the driver itself will allow
2. velocity source rather than pressure source - monopoles are pressure source, which means they couple to room modes differently, hence bass traps in the corners where pressure develops in a monopole won't work for a dipole in the same way
3. dipole figure of 8 polar response pattern - monopoles are omnidirectional and excite more room modes, dipoles less - they tend to be more limited to longitudinal modes
An infinite baffle only has the first of the three advantages. However, with a combination of room treatment and eq, I think IB can be just as good as dipole regarding accuracy with some added advantages:
* much higher output
* no intrustion into the room
* cheaper - you don't need so many drivers
I can help with the simulation side of things if you like, although I can only do it properly for a rectangular room.
To do actual tests you don't need to built it! Imagine your room were flipped so the floor now became the ceiling and vice versa. Now put your microphone where your ears would be relative to the floor. Put your sub on the floor in the position equivalent to where you would put it on the ceiling. It does not matter that you are not putting it in the ceiling - sound waves don't understand "ceiling" and "floor."
Dipoles have three main advantages in the bass:
1. no box - the air spring is removed and the driver movement is controlled by the signal, driver motor and suspension system so the transient response is as good as the driver itself will allow
2. velocity source rather than pressure source - monopoles are pressure source, which means they couple to room modes differently, hence bass traps in the corners where pressure develops in a monopole won't work for a dipole in the same way
3. dipole figure of 8 polar response pattern - monopoles are omnidirectional and excite more room modes, dipoles less - they tend to be more limited to longitudinal modes
An infinite baffle only has the first of the three advantages. However, with a combination of room treatment and eq, I think IB can be just as good as dipole regarding accuracy with some added advantages:
* much higher output
* no intrustion into the room
* cheaper - you don't need so many drivers
I can help with the simulation side of things if you like, although I can only do it properly for a rectangular room.
Paul
Sure
Dimensions are: Height 7'11" Width 14'0 Length 17'7"
Walls are plaster on top of drywall (very solid). There is a fireplace centred at 7' on the longest wall. The connection from walls to ceiling are coved. Doorway with door at one end and 4' by 5' window at other end. 4' by 10' window opposite of fireplace.
In a corner on the floor, opposite the fireplace, on the same side as the doorway and the largest window, there is a vacated 16" by 20" vent. This vent could house a sub for a IB.
Oh yah and just to complicate things more there is a open archway to another room in the corner opposite of this vent. The room is 11' by 11'.
Nice rectangle room eh!
In advance, thanks for your interest in my audio project.
Sure
Dimensions are: Height 7'11" Width 14'0 Length 17'7"
Walls are plaster on top of drywall (very solid). There is a fireplace centred at 7' on the longest wall. The connection from walls to ceiling are coved. Doorway with door at one end and 4' by 5' window at other end. 4' by 10' window opposite of fireplace.
In a corner on the floor, opposite the fireplace, on the same side as the doorway and the largest window, there is a vacated 16" by 20" vent. This vent could house a sub for a IB.
Oh yah and just to complicate things more there is a open archway to another room in the corner opposite of this vent. The room is 11' by 11'.
Nice rectangle room eh!
In advance, thanks for your interest in my audio project.
Ok here's my attempt:
firstly since your room is very solid, the modes will be nasty as shown in the chart. With some treatment, it looks a lot more tame.
This is shown for a guessed seating position a little further back from the middle of the room, sitting 3.5 m from the rear wall with the longest axis being from the front to back walls. This response is for your main speakers placed out from the rear wall and in from the corners.
firstly since your room is very solid, the modes will be nasty as shown in the chart. With some treatment, it looks a lot more tame.
This is shown for a guessed seating position a little further back from the middle of the room, sitting 3.5 m from the rear wall with the longest axis being from the front to back walls. This response is for your main speakers placed out from the rear wall and in from the corners.
Attachments
Now for some options. Assuming extensive treatment is used for the bass ...
IB works best if you are relatively close ie. if you are 3.5 m from the wall behind your speakers and the IB is in the rear corner. I also showed (green line) what would happen if you placed your sub directly behind the couch - not as good as I expected.
If the room is treated then the IB option seems to work about as good as anything you will likely find.
The room treatment would need to be extensive to get the results as shown. I modelled the room firstly with a reflectance of 0.9 for the floor, 0.7 for front and back walls and 0.8 for all other surfaces as the room is solid. With treatment I modelled with 0.5 for all but the floor. If you don't use treatment then you would need eq no matter where you place your sub. Probably best to do both.
IB works best if you are relatively close ie. if you are 3.5 m from the wall behind your speakers and the IB is in the rear corner. I also showed (green line) what would happen if you placed your sub directly behind the couch - not as good as I expected.
If the room is treated then the IB option seems to work about as good as anything you will likely find.
The room treatment would need to be extensive to get the results as shown. I modelled the room firstly with a reflectance of 0.9 for the floor, 0.7 for front and back walls and 0.8 for all other surfaces as the room is solid. With treatment I modelled with 0.5 for all but the floor. If you don't use treatment then you would need eq no matter where you place your sub. Probably best to do both.
Attachments
"2. velocity source rather than pressure source - monopoles are pressure source, which means they couple to room modes differently, hence bass traps in the corners where pressure develops in a monopole won't work for a dipole in the same way"
A bass trap works exactly the same with a dipole or a boxed speaker.
/Peter
A bass trap works exactly the same with a dipole or a boxed speaker.
/Peter
It´s true as you say that a dipole and box speaker are slightly different in how they set the air in motion. However a bass absorber see no difference in how the sound (pressure wave) was created.
No matter if you use a dipole or box the pressure will build up in the corners as a function of direct radiation and energy build up/resonance/standing wave.
The reactive function of a helmholtzabsorber or a panel/membrane absorber (or the resistive function of a pile of fiberglass) will be the same for a pressure variation
(= soundwave) that builds up on it no matter what thingy we have to create the sound in the first place.
Even though we call dipoles velocity sources and boxes pressure sources, they are still both devices that creates waves of pressurized air that fluctuate and travels in space.
The only thing that separates the two types of speakers from eachother once we are "outside" of the speaker itself, is the radiation pattern.
/Peter
No matter if you use a dipole or box the pressure will build up in the corners as a function of direct radiation and energy build up/resonance/standing wave.
The reactive function of a helmholtzabsorber or a panel/membrane absorber (or the resistive function of a pile of fiberglass) will be the same for a pressure variation
(= soundwave) that builds up on it no matter what thingy we have to create the sound in the first place.
Even though we call dipoles velocity sources and boxes pressure sources, they are still both devices that creates waves of pressurized air that fluctuate and travels in space.
The only thing that separates the two types of speakers from eachother once we are "outside" of the speaker itself, is the radiation pattern.
/Peter
Peter,
what you say is true - if it's there, the bass trap will absorb it but ...
as I understand, monopoles have maximum pressure in corners in particular, while dipoles create maximum pressure in different parts of the room ... hence bass traps will not work as effectively for dipoles, and you may need more of them to achieve the same effect.
Now that I'm writing this, I realise that I don't really know if this is true or not, I obviously need to look into this more ...
what you say is true - if it's there, the bass trap will absorb it but ...
as I understand, monopoles have maximum pressure in corners in particular, while dipoles create maximum pressure in different parts of the room ... hence bass traps will not work as effectively for dipoles, and you may need more of them to achieve the same effect.
Now that I'm writing this, I realise that I don't really know if this is true or not, I obviously need to look into this more ...
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