Just an update for those who are interested. I'm slowly making progress on my dipole project. Here's a photo of where I'm at right now. The main panel that sits on top is pretty much as it's going to stay. Drivers are Seas 27TDFC and Vifa MG22. The bottom section is currently a stack of W-frame woofers. It will be rebuilt in a narrower form factor, 12.5" wide, to match the main panel. The woofer section will house 2 Madi 1252DVC drivers in a variation of the W frame. The active crossover is almost complete and ready for testing, it is pretty much SLs circuitry for the Phoenix, with some minor items changed. Peeking out from behind is my Titanic 1200, built into a box that slips flush into the Ikea bookshelf, powered by a PE plate amp. The bookshelf speakers are the first pair of speakers I ever bought, Mirage M290 I think is the model. Sounds like crap, but it's cheap HT. One day I may redesign the crossover to get rid of the big peak at 10K, plug the port and try to get rid of the tilted up bass.
RonS
RonS
Attachments
hi transducer,
I'm interested in that driver you used - the vifa mg woofer. How do you find it compares to other vifa drivers? What is it like in subjective terms regarding sound quality?
regards,
Paul
I'm interested in that driver you used - the vifa mg woofer. How do you find it compares to other vifa drivers? What is it like in subjective terms regarding sound quality?
regards,
Paul
I'm sorry, but the only other Vifa driver that I've used is a PL14, quite a different driver.
I can't comment on the MG driver's sound as I haven't been able to listen to it in a working system yet (troubles with the electronic crossover). I selected the MG series based on a friends recommendation. He works as a speaker designer for a very large Canadian speaker manufacturer, and apparently the MG series is the best of the Vifa drivers. It does have the new slimmer style chassis on it, as opposed to the Poly cone P series.
RonS
I can't comment on the MG driver's sound as I haven't been able to listen to it in a working system yet (troubles with the electronic crossover). I selected the MG series based on a friends recommendation. He works as a speaker designer for a very large Canadian speaker manufacturer, and apparently the MG series is the best of the Vifa drivers. It does have the new slimmer style chassis on it, as opposed to the Poly cone P series.
RonS
You haven't even tried it in a small box? ... hmmm
Interesting comments. It is very strange that it seems to have been featured in so few DIY speakers. It is very attractive, affordable and has a nice smooth response. I can't see why it hasn't been used more! (It looks a lot more interesting than the polycone drivers from an appearance point of view.)
regards,
Paul
Interesting comments. It is very strange that it seems to have been featured in so few DIY speakers. It is very attractive, affordable and has a nice smooth response. I can't see why it hasn't been used more! (It looks a lot more interesting than the polycone drivers from an appearance point of view.)
regards,
Paul
I bought the driver specifically for the dipole project. But lately I have been thinking of using it in a sealed box, since I'm having these problems with the electronic crossover.
Problem is that an 8" 2 way is not very practical, and if you do a 3 way you might as well use a 10 or 12" driver for the woofer.
I agree that they are good value, better than the poly cones. But I did notice some ringing in the higher frequencies that may be due to the stiff cone, or it might have been something vibrating during my measurements (the speaker was sitting on top of an aluminum ladder).
RonS
Problem is that an 8" 2 way is not very practical, and if you do a 3 way you might as well use a 10 or 12" driver for the woofer.
I agree that they are good value, better than the poly cones. But I did notice some ringing in the higher frequencies that may be due to the stiff cone, or it might have been something vibrating during my measurements (the speaker was sitting on top of an aluminum ladder).
RonS
12.5x15" with 3.5" wings on either side and top/bottom. Based on Linkwitz' Phoenix main panels (actually his prototype PMT1).
What do you mean when you say are you missing something?
RonS
What do you mean when you say are you missing something?
RonS
I've been reading everything I can on dipoles, and it seems that almost everything says you need giant baffles - like a 12 ft circumferance. But then you have the woofer separate, so I guess that's why the top panel is smaller. I want to build some small dipole surround speakers. but evidently "small dipoles" is an oxymoron. I just don't want 6 large speakers (and a sub) - there wouldn't be any room for the furniture! I'm also on a very limited budget - retired public school teacher.
MBOb: A couple of things make the baffle act bigger. The major one is that the vertical size of the baffle is all the way to the ground because it is on top of the bass box. Also he has small "wings"
at right angles going back a few inches.
Some (Kwei) claim that wings don't help much. But they probably do in some circumstances.
In any case I'd guess the crossover to the woofers is around 300 hz - Ron- do you have a measurement or calc on this?
One infuriating thing about baffles is that to go one octave lower they need to be twice as big so if you don't mind using a sub woofer (actually a woofer!) the baffle can be a pretty reasonable size. I made my new baffles a little bigger than this though- to crossover to the woofer a bit lower- more like 200 hz. I think.
Mark
at right angles going back a few inches.
Some (Kwei) claim that wings don't help much. But they probably do in some circumstances.
In any case I'd guess the crossover to the woofers is around 300 hz - Ron- do you have a measurement or calc on this?
One infuriating thing about baffles is that to go one octave lower they need to be twice as big so if you don't mind using a sub woofer (actually a woofer!) the baffle can be a pretty reasonable size. I made my new baffles a little bigger than this though- to crossover to the woofer a bit lower- more like 200 hz. I think.
Mark
Mtn Bob,
There are two ways to go about a dipole:
1. conventional - use drivers with parameters specifically suited to open baffle use and use a large baffle. This approach is the more simple one
2. Linkwitz approach - use whatever drivers you want that have sufficient output and use eq/active filters to get the response right
Obviously transducer is taking the 2nd approach. Drivers that are suitable for #1 are much less well known to DIYers.
There are two ways to go about a dipole:
1. conventional - use drivers with parameters specifically suited to open baffle use and use a large baffle. This approach is the more simple one
2. Linkwitz approach - use whatever drivers you want that have sufficient output and use eq/active filters to get the response right
Obviously transducer is taking the 2nd approach. Drivers that are suitable for #1 are much less well known to DIYers.
Well, the Linkwitz approach is not going to work for anyone on any kind of a reasonable budget. He spends more on a pair of speakers then I can afford for the whole audio portion of a HT setup. But then I don't get to charge my toys off as a business expense!
Variac, the main panel sitting on top has sufficient size with the appropriate eq to extend to the crossover frequency. Which is by the way 100Hz LR4. The fact that it is sitting on the sub box does not make the baffle act bigger.
Kwei (or Thorsten Loesch as I know him) is wrong about the wings. The wings are simply the front baffle folded back to make the speaker a bit narrower looking, that's all. You could unfold them and the response would be the same. Only thing that might change is where the complete dipole cancellation occurs. With the folded wings, it's a bit further than 90 degrees off axis.
Paul, you are right, I am taking the Linkwitz approach.
MtnBob, take a look at Linkwitz' prototype speakers, they're under his Phoenix project, all passive crossovers and reasonably priced Vifa drivers. I'd suggest the PMTM1 as a good starting point for main channel speakers, add a dipole or sealed sub crossed over at 100Hz (preferably dipole for the full effect, it's where you really get the benefit of the design). You should be able to build it for a few hundred or so.
RonS
Kwei (or Thorsten Loesch as I know him) is wrong about the wings. The wings are simply the front baffle folded back to make the speaker a bit narrower looking, that's all. You could unfold them and the response would be the same. Only thing that might change is where the complete dipole cancellation occurs. With the folded wings, it's a bit further than 90 degrees off axis.
Paul, you are right, I am taking the Linkwitz approach.
MtnBob, take a look at Linkwitz' prototype speakers, they're under his Phoenix project, all passive crossovers and reasonably priced Vifa drivers. I'd suggest the PMTM1 as a good starting point for main channel speakers, add a dipole or sealed sub crossed over at 100Hz (preferably dipole for the full effect, it's where you really get the benefit of the design). You should be able to build it for a few hundred or so.
RonS
There's another intersting dipole project here:
http://www.geocities.com/kreskovs/NaO.html
It's been the source of much discussion at Madisound.
Steve
http://www.geocities.com/kreskovs/NaO.html
It's been the source of much discussion at Madisound.
Steve
Hello Transducer,
I wasn't aware whether you had EQ on the mid driver or not.
With EQ of course you can do it if you don't run out of Xmax.
100 hz really gets the crossover out of the way!
I meant compared a panel like yours floating in the air. I don't understand why the driver would act differently if there was a panel extending all the way to the ground or a bass box, this gives it an infinately longpath in one direction. In effect, your
driver is mounted of center in a very tall and narrow baffle ,no?
I think such a narrow baffle probably doesn't go much lower than
one less tall but I would think it picks up some advantage.
Well, I think I might have a middle ground theory on this. I carefully drew the path of travel around a flat baffle and one with wings when I was deciding how to make my speakers.
2" wings on each side don't add 4" to the width because the sound travels from the back edge of the baffle wing to the back of the cone in a straight line, a hypotenuse- it doesn't follow along the inside of the baffle to the inside corner and then to the driver. Small wings (1.5") didn't really change much as far as path of travel on my drawings. I was surprised by this.
I'm not saying I'm right, it would just explain why wings work, as you and many others say, but not as well as you would expect as Kwei/Thorsten/Whoever says.
What do you think of this?
Mark
I wasn't aware whether you had EQ on the mid driver or not.
With EQ of course you can do it if you don't run out of Xmax.
100 hz really gets the crossover out of the way!
I meant compared a panel like yours floating in the air. I don't understand why the driver would act differently if there was a panel extending all the way to the ground or a bass box, this gives it an infinately longpath in one direction. In effect, your
driver is mounted of center in a very tall and narrow baffle ,no?
I think such a narrow baffle probably doesn't go much lower than
one less tall but I would think it picks up some advantage.
Well, I think I might have a middle ground theory on this. I carefully drew the path of travel around a flat baffle and one with wings when I was deciding how to make my speakers.
2" wings on each side don't add 4" to the width because the sound travels from the back edge of the baffle wing to the back of the cone in a straight line, a hypotenuse- it doesn't follow along the inside of the baffle to the inside corner and then to the driver. Small wings (1.5") didn't really change much as far as path of travel on my drawings. I was surprised by this.
I'm not saying I'm right, it would just explain why wings work, as you and many others say, but not as well as you would expect as Kwei/Thorsten/Whoever says.
What do you think of this?
Mark
To me, one of the beauties of an open baffle speaker is the simplicity. With the cost of an LM3875/LM3996 amplification channel so low, a simple active crossover could get rid of that passive monstrosity and improve things quite a bit!
I'm a little puzzled by the woofer in that system. If it's not a dipole woofer because the driver is positioned at the front of the baffle, how far back does it have to go before it becomes a dipole?
Mark,
You are correct re:Xmax. But remember that the 8" woofer is only being used from 100Hz to 1500Hz. Probably using two of them in an MTM format would be better, we'll see. Linkwitz only uses 1 in his Orion with a LR4 crossover at 100Hz, I've heard it and it doesn't have any problems. The Vifa has almost as great an Xmax as the Seas driver.
The fact that the main panel sits on the woofer box doesn't do much if anything for the baffle size because the rear radiation of the woofer sees an obstruction from the top of the woofer box. Also, the panel in front on the woofer box is only about 6" wide, although about 3' high. Really, I don't think it enters into the equation.
The radiation pattern of a dynamic driver on a folded baffle is quite complex, especially it's rear radiation. I think we're agreed that in the front the sound travels along the baffle front and around the corners, right? (in addition to straight ahead as well, and every point in between) In the rear, the sound is hampered by the basket structure and magnet. And while it does go straight back, and also straight to the corners of the wings, it also travels along the back of the baffle and then around the corner. It should be easy enough to test. Make a flat baffle 18" wide, centre a driver on it and measure it's on axis and 90 degree off axis response. Then take the same baffle but fold back some wings 3" each, so that the baffle is now only 12" wide from the front. Repeat the measurements and see what happens. I suspect that the off axis null will move somewhat behind 90 degrees, I think Linkwitz in a stereophile review mentioned 135 degrees or so. If the wings didn't do anything, I don't think he'd bother to use them, would he? He has worked on dipole speakers for many many years, he really knows his stuff.
Nuuk, I think you're missing the point of the NaO speaker. The designer is a friend of mine, and we've discussed his speaker a bit. Part of your assumption is incorrect, in that a simple active crossover is not sufficient to perform the corrections necessary for an open baffle dynamic driver dipole speaker. Just look at Linkwitz' web site, his Phoenix speaker uses something like 6 opamps for each driver! And that doesn't include all of the caps and resistors around them for all of the eq. needed. Further you are assuming that a simple LM3875 type amp is sufficiently high in quality to not desire anything better. John's design, while large in number of passive components, requires only 1 amp for the main panel and 1 for the woofer system, and reduces the count of opamps to 3 for both the mid and tweeter and 3 for the woofer. I might be trying a completely passive crossover design and power it with a large Bryston 4BST. I think I'd rather have 10-12 passive parts in my crossover than 18 opamps and a whole bunch of passives!
The woofer is not a dipole but rather a cardiod at most frequencies. For it to be a dipole you would have to add equal length to the front as at the back to make the path length the same both front and back. In either case, both cardiod and dipole are both velocity sources (as opposed to pressure sources for ported or sealed boxes) and John feels that that is where the benefit lies. I haven't had a chance to test his woofer design, but he makes some strong claims for it.
RonS
You are correct re:Xmax. But remember that the 8" woofer is only being used from 100Hz to 1500Hz. Probably using two of them in an MTM format would be better, we'll see. Linkwitz only uses 1 in his Orion with a LR4 crossover at 100Hz, I've heard it and it doesn't have any problems. The Vifa has almost as great an Xmax as the Seas driver.
The fact that the main panel sits on the woofer box doesn't do much if anything for the baffle size because the rear radiation of the woofer sees an obstruction from the top of the woofer box. Also, the panel in front on the woofer box is only about 6" wide, although about 3' high. Really, I don't think it enters into the equation.
The radiation pattern of a dynamic driver on a folded baffle is quite complex, especially it's rear radiation. I think we're agreed that in the front the sound travels along the baffle front and around the corners, right? (in addition to straight ahead as well, and every point in between) In the rear, the sound is hampered by the basket structure and magnet. And while it does go straight back, and also straight to the corners of the wings, it also travels along the back of the baffle and then around the corner. It should be easy enough to test. Make a flat baffle 18" wide, centre a driver on it and measure it's on axis and 90 degree off axis response. Then take the same baffle but fold back some wings 3" each, so that the baffle is now only 12" wide from the front. Repeat the measurements and see what happens. I suspect that the off axis null will move somewhat behind 90 degrees, I think Linkwitz in a stereophile review mentioned 135 degrees or so. If the wings didn't do anything, I don't think he'd bother to use them, would he? He has worked on dipole speakers for many many years, he really knows his stuff.
Nuuk, I think you're missing the point of the NaO speaker. The designer is a friend of mine, and we've discussed his speaker a bit. Part of your assumption is incorrect, in that a simple active crossover is not sufficient to perform the corrections necessary for an open baffle dynamic driver dipole speaker. Just look at Linkwitz' web site, his Phoenix speaker uses something like 6 opamps for each driver! And that doesn't include all of the caps and resistors around them for all of the eq. needed. Further you are assuming that a simple LM3875 type amp is sufficiently high in quality to not desire anything better. John's design, while large in number of passive components, requires only 1 amp for the main panel and 1 for the woofer system, and reduces the count of opamps to 3 for both the mid and tweeter and 3 for the woofer. I might be trying a completely passive crossover design and power it with a large Bryston 4BST. I think I'd rather have 10-12 passive parts in my crossover than 18 opamps and a whole bunch of passives!
The woofer is not a dipole but rather a cardiod at most frequencies. For it to be a dipole you would have to add equal length to the front as at the back to make the path length the same both front and back. In either case, both cardiod and dipole are both velocity sources (as opposed to pressure sources for ported or sealed boxes) and John feels that that is where the benefit lies. I haven't had a chance to test his woofer design, but he makes some strong claims for it.
RonS
Please keep in mind that I'm not attacking your speakers 😉
I agree that the 8" prob is fine, I never said it wouldn't work,
in fact I just don't know. I know Linkwitz uses just one in his current speaker. I'm just reminding people that x-max is an issue. Often I've heard people state that when they raise the cutoff they discover that the driver sounds a lot better and that in retrospect, they were getting close to the x-max. So I think it is
a good idea to calc the x max and/or do a crossover test at various frequencies if you aren't copying an existing design.
On to the sub as a baffle:
It seems to me that you just argued that a folded back wing
acts like a baffle, so the top of the woofer box would act like a wing baffle then. So the sound has to go around this baffle then down towards the ground, then can't get through the ground to the front. I'd say that's a pretty big baffle.
Altought the front panel is only 6" wide, if there isn't a slot all the way through the woofer box then the entire width of the box counts as a baffle. I guess an experiment could be done to check this too: It would be easy: try suspending your top baffle in the air away from the woofer box a couple of feet and see if the lower mids change.
I don't think I said that the wings don't do anything, I said they are not the same as a flat baffle and that Kuei says they don't. I also never argued that the radiation doesn't change. Your experiment is fine, but I don't have measurement equipment, so I'll leave it up to you. Perhaps you could make the 2 baffles you are mentionaing and just listen to them and see if there is any difference. Should be easy since you have 2 drivers.
Since you are pretty much copying the Linkwitz design you will probably come out fine. Does he makes the wings curved in depth to get rid of peaks and notches, or maybe it's just an appearance issue- Another question!
I agree that the 8" prob is fine, I never said it wouldn't work,
in fact I just don't know. I know Linkwitz uses just one in his current speaker. I'm just reminding people that x-max is an issue. Often I've heard people state that when they raise the cutoff they discover that the driver sounds a lot better and that in retrospect, they were getting close to the x-max. So I think it is
a good idea to calc the x max and/or do a crossover test at various frequencies if you aren't copying an existing design.
On to the sub as a baffle:
It seems to me that you just argued that a folded back wing
acts like a baffle, so the top of the woofer box would act like a wing baffle then. So the sound has to go around this baffle then down towards the ground, then can't get through the ground to the front. I'd say that's a pretty big baffle.
Altought the front panel is only 6" wide, if there isn't a slot all the way through the woofer box then the entire width of the box counts as a baffle. I guess an experiment could be done to check this too: It would be easy: try suspending your top baffle in the air away from the woofer box a couple of feet and see if the lower mids change.
I don't think I said that the wings don't do anything, I said they are not the same as a flat baffle and that Kuei says they don't. I also never argued that the radiation doesn't change. Your experiment is fine, but I don't have measurement equipment, so I'll leave it up to you. Perhaps you could make the 2 baffles you are mentionaing and just listen to them and see if there is any difference. Should be easy since you have 2 drivers.
Since you are pretty much copying the Linkwitz design you will probably come out fine. Does he makes the wings curved in depth to get rid of peaks and notches, or maybe it's just an appearance issue- Another question!
Mark, I know you're not attacking my speakers, I didn't take it that way at all 😀
I really don't know what to say about the woofer box as an extended baffle. It's almost impossible to measure since we're dealing with very low frequencies, which are difficult to measure at home, especially in the far field. I'll leave the hard work to Linkwitz 😉
I'm really not interested in whether the wings sound different than a totally flat baffle, as a flat baffle of sufficient width is unacceptable to me visually (or my wife!).
I think Linkwitz uses the curved wings on the Orion as an asthetic element. You'll notice that at it's shallowest point it is pretty much in line with the midrange. I'm not sure, you'd have to ask him.
Cheers,
RonS
I really don't know what to say about the woofer box as an extended baffle. It's almost impossible to measure since we're dealing with very low frequencies, which are difficult to measure at home, especially in the far field. I'll leave the hard work to Linkwitz 😉
I'm really not interested in whether the wings sound different than a totally flat baffle, as a flat baffle of sufficient width is unacceptable to me visually (or my wife!).
I think Linkwitz uses the curved wings on the Orion as an asthetic element. You'll notice that at it's shallowest point it is pretty much in line with the midrange. I'm not sure, you'd have to ask him.
Cheers,
RonS
I agree those wide baffles are hard to take!
For my experiment I suggested you hang one open baffle from strings (putting it on the floor won't do!)with the woofer box off to one side a bit and leave the other on the woofer box. Then switch an identical signal between them and Listen for a difference. It might be quite obvious. Of course I can understand not wanting to bother with this also, but you were the one suggesting an experiment.
For my experiment I suggested you hang one open baffle from strings (putting it on the floor won't do!)with the woofer box off to one side a bit and leave the other on the woofer box. Then switch an identical signal between them and Listen for a difference. It might be quite obvious. Of course I can understand not wanting to bother with this also, but you were the one suggesting an experiment.
Ah, I see now what you meant for your experiment. Tell you what, once I finish the bloody things, I'll try it and report here. If I can only get the electronic crossover working properly!
RonS
RonS
- Status
- Not open for further replies.