I'm assuming this is the dipole he was recommending...
http://feandil.tripod.com/PartII/index.album?i=0&s=1
but with a t-line enclosure off the rear... correct?
http://feandil.tripod.com/PartII/index.album?i=0&s=1
but with a t-line enclosure off the rear... correct?
could someone create an isobarically loaded dipole 
like a normal dipole that woudl require the same distance from the wall... but adding an inverted sub (isobarik) to the front of the driver?
I wonder... I don't see why it wouldn't work... and you would get the benefits of the dual speaker dipole....
like a normal dipole that woudl require the same distance from the wall... but adding an inverted sub (isobarik) to the front of the driver?
I wonder... I don't see why it wouldn't work... and you would get the benefits of the dual speaker dipole....
JessicaG, forgive me if I have misunderstood something but I think I see some confusion in this thread and I suspect I know where is coming from.
In the context of this forum, generally speaking, a "dipole speaker" is exactly the same thing as an "open baffle speaker". That's what the people here are talking about, generally, when they talk about a dipole speaker. Picture a piece of plywood with a hole in it and a speaker mounted in the hole.
You may also see speakers with multiple drivers facing different directions referred to as "dipole" or "bipole" depending on the implementation, but those are a special case. If that's what you are after you may want to specify.
Again please accept my apologies if I am wrong in my assessment, but it looks to me like there is something keeping people in this thread from understanding each other and I think it may be just the usage of the term "dipole".
In the context of this forum, generally speaking, a "dipole speaker" is exactly the same thing as an "open baffle speaker". That's what the people here are talking about, generally, when they talk about a dipole speaker. Picture a piece of plywood with a hole in it and a speaker mounted in the hole.
You may also see speakers with multiple drivers facing different directions referred to as "dipole" or "bipole" depending on the implementation, but those are a special case. If that's what you are after you may want to specify.
Again please accept my apologies if I am wrong in my assessment, but it looks to me like there is something keeping people in this thread from understanding each other and I think it may be just the usage of the term "dipole".
HeatMiser said:
yes... that was my confusion earlier.
I didn't understand how both the push pull and that could be dipole... but I get it now
Thanks for clearing that up, however.
to reask my previous question. Is there any problem with isobarikly loading a speaker in the "classic" dipole manner
JessicaG said:
isobarik loading is a compound loading scheme and usually is push-pull (but it could be push-push). seen here:
http://www.jlaudio.com/tutorials/isobarik/
(the third pictoral, left to right, is almost never done because it doesn't effectivly limit driver "rocking" like the other methods.)
the method I suggested with the T-line would in fact be push-pull.
additionally the ability to place a dipole near or close to the wall depends on the where the dipole null is. Say you have a traditional dipole speaker "firing" straight ahead into the room - then the nulls are to the sides of the speaker and the out-of-phase rear radiation is "firing" to the rear of the speaker. The out-of-phase rear radiation is the problem and as such should NOT be located near a wall. The null side "radiation" however is perfectly acceptable to be placed near a wall (however you should never place an upper mid treble near a side wall). Back to the Isobarik 2nd order gradient T-line:
Now then, IF we dropped the T-line on the design I mentioned but kept the drivers operating in the same manner we would have the equivilant of a 2nd order gradient (though not really a second order gradient) in both front and back of the speaker BUT with BIpole operation (i.e. the rear radiation would be in phase with the front radiation), rather than operating as a dipole. This MIGHT be better than a dipole if placed near a wall, but I don't know and I don't think it would be much better..
**btw, as a historical note I believe the only commercial offering for this was from Celestion to acompany their areolam "6000" mini-monitor (and often incorrectly regarded as a dipole and incorrectly positioned in relation to the listener and mini-monitor - the correct orientation is seen in the left speaker in the picture).
http://tatooine.fortunecity.com/slaine/152/doc/cel6000.jpg It was however specifically made so that it could be rotated to acoustically "fit" the room the best (i.e. less interaction from walls).**
However when we add back in the T-line we are essentially shifting the rear radiation (of the bipole) to a lower freq. that is more monopole (omni-directional) in nature. If placed near a surface (any wall, floor and ceiling) you will have an increase in spl from boundry gain. In this case then placing the rear of the speaker with the "box" T-line near the wall should actually work to your advantage by increasing the spl of the lower freq.s. while maintaining (or bettering) the exclusion of room effects higher in freq. (55 Hz to 300 Hz) as a result of the increased side null of the true second order gradient in this freq. region.
So then, is there any problem to isobarikly load a dipole?
Answer:
Push-Pull: Yes - without a complex wave guide you end up with a bipole. However WITH a complex wave guide you have reduced (to non-existant) nullification higher in freq. AND have added cavity resonance(s).
Push-Push: No, and radiation should become more second order gradient"ish" (i.e. the side nullification should increase and make both the in-phase front driver and out-of-phase rear driver a bit more directional for their respective outputs).
*A comercial design of this nature can be seen from Legacy Loudspeaker's Whisper reviewed here:
http://www.stereotimes.com/speak040300.shtm
picture of the back here:
http://www.legacy-audio.com/2004/whisperis2.htm
running vertically on the speaker top to bottom on the right side of the picture you'll see two vertical bands of wood that span the length of the speaker with a "black band" in-between them (the wood bands are actually 2 different baffles). The "black band" is the gap where the rear driver's in-phase output is "colliding" with the front driver's out-of-phase rear output (effectivly canceling). They could have chosen to pressure load the compound drivers by making the "black band" enclosed BUT they would suffer a decrease in spl.*
Seems to be a slightly odd thread... I'm not quite sure what is being asked, but I have been playing with some Celestion 6000-style spaced dipoles recently, and looking at the NaO and SLs Orion system recently. As far as I can tell, the Celestion 6000 clone I have is a dipole, without any particular qualification. As to 'H' frames and 'W' frames, there will be a limitation if you try to run these up too far into the midrange, due to cavity resonances inside the frame. A NaO-style box with the bass driver on the front should allow a higher crossover point than the 100Hz or so usually implemented with 'H' and 'W' frames, 'cos the cavity resonance doesn't directly effect the frontal output. The NaO isn't a true dipole as such, but the sound quality is supposed to be very similar. Rotating a dipole sub so that the rear radiation doesn't bounce of the wall behind and cancel the frontal output will work, but there are some complications depending on where the side walls are for example. You don't want to end up listening to the null...
Looking at the thread again with a little more time I remain a bit perplexed. Scott, the Celestion 6000 is just a regular dipole to all intents and purposes. You seem to be implying that isn't and requires different placement compared to other dipoles. I can't see why this should be. the fact that you have two drivers with a space inbetween won't change the radiation pattern significantly. With enough space around it, the best thing would be to fire it right at the listener so that they are directly on axis. In real rooms, particularly small ones, the situation is complicated by the reflections off nearby walls. It may be that in some situations you would need to fire the drivers at the side walls, but in a big enough room, in which the reflections were significantly weaker in amplitude than the direct output of the dipole sub., you'd simply be sitting in the null, the same as with any other dipole bass system.
I'm also struggling a bit with the hybrid dipole/ t-line idea. If I'm visualising it right, isn't that just an isobaric t-line with the isobaric chamber open to the air? This wouldn't work properly as an isobaric and certainly not as a dipole. Perhaps I'm not imagining it properly...
An isobaric, or at least a compound driver dipole would work OK, and has been used in SLs larger commercial designs like the Beethoven, IIRC. Probably a better bet would be to just have one above the other and accept a larger baffle/ frame, particularly if the idea is to run up to 300Hz or so. At higher frequencies compound driver pairs are not coupled together as solidly by the air mass between them, and cancellations can apparently occur.
In the system I'm experimenting with at the moment, only the bass from about 40Hz to 100Hz is dipole loaded, with the rest of the range handled by a conventional sealed box two-way speaker. Even in this rather rough lash-up, the bass sounds far better than most box speakers, and like some other posters I'm beginning to suspect that that dipole (or in the case of the NaO, cardioid) bass is much more of a qualitative improvement than dipole operation through the midrange- although that's nice too.
A Peerless XLS 10 or 12" driver in a NaO-style box run up to 200Hz should still be sounding fine, and could either be used with a comparatively small mid-bass unit in a sealed box, or perhaps a 6.5" driver in a shallow U-frame, which would require very little eq for a flat response- perhaps none if the driver Q was high enough. This is the path I'm heading off on next...
I'm also struggling a bit with the hybrid dipole/ t-line idea. If I'm visualising it right, isn't that just an isobaric t-line with the isobaric chamber open to the air? This wouldn't work properly as an isobaric and certainly not as a dipole. Perhaps I'm not imagining it properly...
An isobaric, or at least a compound driver dipole would work OK, and has been used in SLs larger commercial designs like the Beethoven, IIRC. Probably a better bet would be to just have one above the other and accept a larger baffle/ frame, particularly if the idea is to run up to 300Hz or so. At higher frequencies compound driver pairs are not coupled together as solidly by the air mass between them, and cancellations can apparently occur.
In the system I'm experimenting with at the moment, only the bass from about 40Hz to 100Hz is dipole loaded, with the rest of the range handled by a conventional sealed box two-way speaker. Even in this rather rough lash-up, the bass sounds far better than most box speakers, and like some other posters I'm beginning to suspect that that dipole (or in the case of the NaO, cardioid) bass is much more of a qualitative improvement than dipole operation through the midrange- although that's nice too.
A Peerless XLS 10 or 12" driver in a NaO-style box run up to 200Hz should still be sounding fine, and could either be used with a comparatively small mid-bass unit in a sealed box, or perhaps a 6.5" driver in a shallow U-frame, which would require very little eq for a flat response- perhaps none if the driver Q was high enough. This is the path I'm heading off on next...
Toaster said:
well 200 hz is also acceptable, I'm planning on Audax's PR 6.5" for the midrange line so it should be ok... also that would keep the vocals to one area (well most vocals)
Also the NaO- style is the classic front of driver to back of next driver correct??? I'm unsure about this...
let me read up on it.... is there any sites that have NaO calculators or dipole instrustions
Toaster said:
sorry for the confusion (late night writing can do that sometimes..)
yes, i did screw up a bit here.. I was thinking that isobarik was essentially another name for compound loading - it is in fact a bit more complex in that it is not only compound loaded but DOES require an encapsulated "pressure" chamber (like a pipe). Therefor my "answer" would be in reference to compound loading (not isobarik loading)..
JessicaG's orginal question was:
"Is there any problem with isobarikly loading a speaker in the "classic" dipole manner?" (which was correctly represented in her drawing.. I didn't see the 180 deg phase change on the pic originally)
Yes: You suffer a drop a 3 db theoretical drop in spl because of increased mass. Remove the "pipe" (that makes it isobarik), where it will become just a compound dipole, and you should remove most of your loss in spl (that the isobarik had).
again, sorry for the confusion
Toaster:
I think the celestion is NOT a dipole but rather a null-directive bipole. There COULD be important differences with respect to proximity to boundries. Consider that with a dipole it is the out-of-phase rear output that would have gain from the boundry. The null-directive bipole however has IN-PHASE rear output that would have gain from a boundry. As I mentioned previously, I think it might be better than a dipole near a boundry. Additionally because it is more directive you'll need to angle it properly in relation to the listener (a dipole will have a wider radiation pattern and will need less "aiming"). (Btw, you do not listen to the null portion of a dipole.)
As to the T-line thing..
You are right, it wouldn't work properly as an isobarik (as I mentioned above). Nor would it work properly as a dipole - instead directivity would increase, (become more directive), from that of a dipole and act more like a second order gradient (at the sacrifice of a theoretical 3db of spl). This however is BETTER than a dipole in-room (i.e. less room interaction in the operating freq. range). Additionally of course below this passband the t-line's operation would be omni.
Note: The NaO's sub response becomes increasingly omni-directional as you go higer in freq. (which is NOT advantageous with regard to room resonances). Below 50 Hz however it may well be better than the typical dipole solution. (note however that the gain in spl is a little exagerated on JohnK's site because of air flow resistance, of the fiber mass, and the resulting increase in driver mass - BUT this will lower the freq. and perhaps enable greater extension provided the driver is capable of increased excursion.)
so if you are interested in the benefits of dipole midbass (in the freq. range we discussed) - the NaO is NOT the solution.
so if you are interested in the benefits of dipole midbass (in the freq. range we discussed) - the NaO is NOT the solution.
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Here is a specific page on SL's site I think will help you...read very carefully as there is quite a lot to absorb. Also SL's dipole calculator is linked from that page.
recommended Linkwitz page
recommended Linkwitz page
Hmmmm...
Ok, well as far as the Celestion 6000 is concerned, it is a dipole. There's lots of info on it on the web, but if you just Google 'Celestion 6000', as I just did, the first page of hits gives a link to Martin Colloms Stereophile review of it, and a link to Celestions own website. It is definitely a dipole. Odd thing though, its not the first time someone has suggested it's a bipole to me, so some article somewhere may be steering people wrong.
Apart from that, the NaOs directivity pattern vs a 'normal' dipole is more a matter of degree than kind, I think. Both systems significantly reduce room interaction compared to a monopole. Slightly different considerations apply with how you place them/ rotate them relative to the listener and room boundaries. The exact radiation pattern is not the only issue anyway- there's also the lack of (most) enclosure colouration to consider. I still think that cavity resonances are likely to be an issue for a dipole like an 'H' or 'W' frame. It's not an issue if you've built it into a flat plank baffle of course. Also, I'm still stuggling a bit with this 'second order gradient' from a dipole/TL hybrid. Isn't a gradient another term for a cadioid directivity pattern? That's what the NaO is supposed to be doing isn't it? I'm still doubtful a dipole/TL would really work this way anyway, although I'd be interested to know more about how this would work. Have you built something like this Scott? If not, how do you visualise the interaction of the units and the resultant directivity pattern?
And also... My understanding is that compound and isobaric loading were the same thing, not that a compound system is one in which the drivers are imperfectly coupled.
And Jessica- as you've probably seen by now, the NaO bass system just consists of one driver per channel in an open backed box. If you aded more for increased output, you'd just stack more open backed boxes up...
Ok, well as far as the Celestion 6000 is concerned, it is a dipole. There's lots of info on it on the web, but if you just Google 'Celestion 6000', as I just did, the first page of hits gives a link to Martin Colloms Stereophile review of it, and a link to Celestions own website. It is definitely a dipole. Odd thing though, its not the first time someone has suggested it's a bipole to me, so some article somewhere may be steering people wrong.
Apart from that, the NaOs directivity pattern vs a 'normal' dipole is more a matter of degree than kind, I think. Both systems significantly reduce room interaction compared to a monopole. Slightly different considerations apply with how you place them/ rotate them relative to the listener and room boundaries. The exact radiation pattern is not the only issue anyway- there's also the lack of (most) enclosure colouration to consider. I still think that cavity resonances are likely to be an issue for a dipole like an 'H' or 'W' frame. It's not an issue if you've built it into a flat plank baffle of course. Also, I'm still stuggling a bit with this 'second order gradient' from a dipole/TL hybrid. Isn't a gradient another term for a cadioid directivity pattern? That's what the NaO is supposed to be doing isn't it? I'm still doubtful a dipole/TL would really work this way anyway, although I'd be interested to know more about how this would work. Have you built something like this Scott? If not, how do you visualise the interaction of the units and the resultant directivity pattern?
And also... My understanding is that compound and isobaric loading were the same thing, not that a compound system is one in which the drivers are imperfectly coupled.
And Jessica- as you've probably seen by now, the NaO bass system just consists of one driver per channel in an open backed box. If you aded more for increased output, you'd just stack more open backed boxes up...
Sorry, that's added, not 'aded'... Jessica, the relative dimensions of a Nao isn't exactly a rule, the NaO is a specific product with a few variations rather than a generic type of bass loading- although the principles used can be used with other drivers. For the 10" XLS driver, the designer recommends a 18" deep open box, and seems to scale the box depth to the driver size. Mind you, since only two drivers are recommended, the Peerless XLS 10" and 12" drivers, this may not be a design priciple as such, it may just relate to these specific drivers. How far you can take a NaO-style box up into the midrange is mostly a drive unit issue, the same as it would be in a conventional box. The only other issue I can think of is how the bass boost is designed in. If the boost starts at 100Hz, where the NaO crossover is usually set, there may be problems created if the crossover ends up higher than where you start to boost it- at least if you modify the existing NaO crossover rather than start from scratch. What sort of complete system are you aiming for?
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