Hey guys,
Actually, I've been keeping an eye on D&D 8C active monitor speaker for a while now and after Erin's Audio corner YT review, I'm tempted to try my luck designing a similar active speaker to see what would come up at the end.
I have access to many sample drivers so it's needless to buy drivers in the first place. I'll use Hypex DLCP with some Ncore NC252MP (rated 250watts@4ohms). I have also miniDSP 4x10HD if needed. For now, my biggest concern is about maintaining a controlled cardioid pattern from about 100hz give or take for the midbass/midrange driver. I'll use one or two subwoofers at the rear side as boundary coupled bass drivers just like 8C. I have also some options for a tweeter that I think will be of lower significance for now. I'll take care of that later.
It will be a big profile bookshelf type of speaker, not a floorstanding.
Hary F. Olson has an article "Gradient speakers" AES Volume 21 Issue 1; January 1973 I'm sure I had downloaded it many years ago but can't find it on my laptop and I have no active membership for now. If anybody has access to this article I would be grateful to have it. It would be much of help to read that article.
For now, I'm thinking about some drivers. for subwoofers, I'm considering SEAS L26RO4Y. I don't know one or two. I'm gonna have two on the prototype enclosure so I can test both ways. I have no smaller than a 10" driver for this region. for the midbass/midrange region I have a couple of choices. this is the most critical driver within others. Due to gradient cancellation, it will have about 6dBs lower SPL so a high dynamic and high excursion driver is more suited to have the same acoustic output after the cancellation. A driver with resonance frequency close to the lowest midbass frequency will be needed and I may have to use some EQ to boost lowers frequencies to have a flat response around 100hz.
I've never design anything with a flow resistor port to get a passive cardioid pattern. I'm gonna use polyester felt, natural ship wool or Ecco felt, I don't know for now. I have not much idea about the port itself. I have to figure a way out to measure the delay needed for phase cancellation. I think it could be measurable by the impulsive response in the time domain but I have no idea about the size of the port and the ratio between it and the SD of the back of the diaphragm.
Faital Pro 8PR200 and 10PR410 are my first choices. High excursion and good dynamic range. there are a pair of SEAS U22REX/P-SL also available. I have also Beyma 12P80ND but I think that would be oversize for the project. for the tweeter, I'm considering Beyma TPL-150/200H or Aurum Cantus G1 or AST25120 or maybe a BlieSMa T34B with a waveguide. I have a 3D printer at hand and can print a waveguide for the dome if needed.
that's it for now. I will make my mind and any idea is much appreciated. I'm totally new to this kind of speaker design so I like to hear opinions. I hope in the end it will be a good project with justified and measured results so anyone interested could build it as a DIY.
Actually, I've been keeping an eye on D&D 8C active monitor speaker for a while now and after Erin's Audio corner YT review, I'm tempted to try my luck designing a similar active speaker to see what would come up at the end.
I have access to many sample drivers so it's needless to buy drivers in the first place. I'll use Hypex DLCP with some Ncore NC252MP (rated 250watts@4ohms). I have also miniDSP 4x10HD if needed. For now, my biggest concern is about maintaining a controlled cardioid pattern from about 100hz give or take for the midbass/midrange driver. I'll use one or two subwoofers at the rear side as boundary coupled bass drivers just like 8C. I have also some options for a tweeter that I think will be of lower significance for now. I'll take care of that later.
It will be a big profile bookshelf type of speaker, not a floorstanding.
Hary F. Olson has an article "Gradient speakers" AES Volume 21 Issue 1; January 1973 I'm sure I had downloaded it many years ago but can't find it on my laptop and I have no active membership for now. If anybody has access to this article I would be grateful to have it. It would be much of help to read that article.
For now, I'm thinking about some drivers. for subwoofers, I'm considering SEAS L26RO4Y. I don't know one or two. I'm gonna have two on the prototype enclosure so I can test both ways. I have no smaller than a 10" driver for this region. for the midbass/midrange region I have a couple of choices. this is the most critical driver within others. Due to gradient cancellation, it will have about 6dBs lower SPL so a high dynamic and high excursion driver is more suited to have the same acoustic output after the cancellation. A driver with resonance frequency close to the lowest midbass frequency will be needed and I may have to use some EQ to boost lowers frequencies to have a flat response around 100hz.
I've never design anything with a flow resistor port to get a passive cardioid pattern. I'm gonna use polyester felt, natural ship wool or Ecco felt, I don't know for now. I have not much idea about the port itself. I have to figure a way out to measure the delay needed for phase cancellation. I think it could be measurable by the impulsive response in the time domain but I have no idea about the size of the port and the ratio between it and the SD of the back of the diaphragm.
Faital Pro 8PR200 and 10PR410 are my first choices. High excursion and good dynamic range. there are a pair of SEAS U22REX/P-SL also available. I have also Beyma 12P80ND but I think that would be oversize for the project. for the tweeter, I'm considering Beyma TPL-150/200H or Aurum Cantus G1 or AST25120 or maybe a BlieSMa T34B with a waveguide. I have a 3D printer at hand and can print a waveguide for the dome if needed.
that's it for now. I will make my mind and any idea is much appreciated. I'm totally new to this kind of speaker design so I like to hear opinions. I hope in the end it will be a good project with justified and measured results so anyone interested could build it as a DIY.
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Here's the Dutch & Dutch development thread.
Here's a thread on a DIY Dutch and Dutch 8C inspired design by Jag768
Here's a thread on a DIY Dutch and Dutch 8C inspired design by Jag768
There is quite a bit of information in the Dutch & Dutch patent
EP3018915A1 - Directional loudspeaker
- Google Patents
EP3018915A1 - Directional loudspeaker
- Google Patents
Pressure takes a massive "hit" with these designs.
The critical element is how close the reflecting rear of the internal cabinet wall is to the driver: basically get the rear wall as close as possible to the driver's magnet, and keep the baffle as narrow as possible (not much wider than the driver itself).
Generally, use a higher Qts driver with a fair bit of Vas to derive some gain lower in freq. to combat the pressure loss. Of course that's not necessary assuming enough eq./power/excursion.
The critical element is how close the reflecting rear of the internal cabinet wall is to the driver: basically get the rear wall as close as possible to the driver's magnet, and keep the baffle as narrow as possible (not much wider than the driver itself).
Generally, use a higher Qts driver with a fair bit of Vas to derive some gain lower in freq. to combat the pressure loss. Of course that's not necessary assuming enough eq./power/excursion.
Thanks!
I don't think I go that way. it would be something like Kii Three. in active mode with one or two woofers at back it would be much easier to obtain the cancellation somewhere in side of the cabinet, it's about changing the delay of back woofers in DSP. but that will be no option for me as the woofers at the sides of the cabinet would play to about 220-250hz or so. The 8C genius is to have an 8" driver to cover most of the frequency band with controlled directivity in the critical area where the upper frequencies will also be directional corresponding to shorter wavelength to diaphragm size ratio.
I still don't know how Kii Three controls the directivity of midrange after crossover frequency where there is no out of phase response in that area to interact with the diffracted sound of midrage toward the back of the cabinet. I suppose the woofer at the side of the cabinet cover the similar range (+250hz) out of phase to do that! I think that would be possible with FIR Eq.
Thanks!
good points. I can simulate the mid driver and the cabinet and hopefully the resistive fibers in Multiphysics Comsol to see everything in action but after all, I think there will be a lot of experimental tries the errors to get the right amount of cancellation so the simulation might not come handy at all. that will not be an easy job to do right but I'm gonna do it. takes some time and huge amount of measurements.
light me up about this. the denser the material the higher the speed of sound, right? So why would a composition of fiberglass or polyester fibers (with air in between ) which obviously are denser than air alone, make the sound travel slower?!
I also have no idea about how much material will be need in the back chamber of the driver to make the delay needed and how that much material will effect the driver tuning. I'm gonna start with filling the whole chamber as I think materials with such density are not very good at damping frequencies this low. at least no in this volume. and I think there should be some space between the fiber stuff and the backside of the diaphragm so there is enough air to be compressed to start moving.
I also have no idea about how much material will be need in the back chamber of the driver to make the delay needed and how that much material will effect the driver tuning. I'm gonna start with filling the whole chamber as I think materials with such density are not very good at damping frequencies this low. at least no in this volume. and I think there should be some space between the fiber stuff and the backside of the diaphragm so there is enough air to be compressed to start moving.
This has been researched thoroughly. Simple explanation is that the moving fibers cause that the 'normal' laws for speed of sound in materials don't apply. A just as simple calculator can be found on the excellent site of MH Audio
The denser the material - the higher the speed of sound inside the material itself. It is not he same as the speed of sound through the air between the fibers of the denser material. Sound waves propagate through the air, not through the fibers.
Thanks
I googled but didn't find anything about it. if you can give some more specific details I can find it. is this a kind of metal wool or mesh?
Thanks for the explanation. Great calculator! I'm familiar with mh-audio but I had not seen this particular calculator.
Thanks for the explanation. that's right. I just read something about it in an article.
I also took a glance at this article. it seems the resistive material will also alter the resonance itself.
https://www.jhbrandt.net/wp-content/uploads/2018/07/Sound-waves-in-Air-and-Fiber.pdf
I haven't been able find it again, and cannot quite remember. I think the company or the product had straightforward name like wovenmetal or metalmesh or something like that. Can't remember if it was actually woven or some fibrous stuff but I remember it was in a sheet form and remember thinking if D&D used something like that in their product. I was sure I bookmarked the site somewhere but haven't been able to find it ps. Google finds plenty of companies that provide metal mesh / perforated / woven products and list acoustics as application but not much more info. Anyway, maybe it is nothing important
ps. Google finds plenty of companies that provide metal mesh / perforated / woven products and list acoustics as application but not much more info. Anyway, maybe it is nothing important
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If you are really trying to clone the 8C you might as well use what they do
achieving constant directivity as low as 200Hz using really large drivers?
I think this is the actual product
Akotherm - MaterialDistrict Utrecht
achieving constant directivity as low as 200Hz using really large drivers?
I think this is the actual product
Akotherm - MaterialDistrict Utrecht
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the resistive material should also act as a low pass filter to not allow higher frequencies to get outta ports at frequencies that could not be diffracted toward the back of the cabinet from the positive sine of the diaphragm due to the shorter wavelength. this material should also have a pretty linear effect on the sound.
in a couple of days, I'm gonna concoct the cabinet to start measuring things. I have to figure out how to get a relatively consistent group delay for the resistive port.
I also ran into this driver from Scanspeak and it seems a perfect choice for cardioid:
21WE/4542T00 – Scan-Speak A/S
I also ran into this driver from Scanspeak and it seems a perfect choice for cardioid:
21WE/4542T00 – Scan-Speak A/S
I really like the D&D design and no doubt it is really well implemented and a super high performance speaker.
But I'm a little amazed they where able to obtain a patent on this .... isn't this the same concept Amphion has been using for many years? E.g. the Krypton3.