I’ve wanted to try an open baffle (dipolar) speaker design for a while. But I wouldn’t settle for less than a full range speaker system with excellent dynamics and sound presentation--no compromises. For simplicity I wanted to start with a two way system that marries a top notch wide range driver with a musical woofer.
I had used both the Mark Audio Alpair 10 and 10.2 (second generation) drivers in a MLTL enclosure as reported previously on DIYAudio. From hearing the new A10.2s in the MLTL boxes I heard improvements vs. the original A10s. Thus I thought that the A10.2 would be a good candidate for the mid/tweeter driver in the new project.
As most of you realize, full range open baffle coverage with a single driver—even one as remarkable as the A10.2—really limits the amount of bass you can achieve from the speaker design. Fortunately, the work by Martin J. King and followers show excellent results from the use of a large woofer—say 15 or 18 inches diameter—with a wide range driver to cover the mid and tweeter ranges of the frequency band. Martin analyzes various bass configurations on his website and I chose the H-frame design which yields good results with reasonable size for the overall speaker.
Normally, a high Q woofer is selected to provide essential EQ to boost the woofer output for bass frequencies if a passive crossover is used between the H-frame woofer and the broadband driver. For my project I planned to use an active crossover, so I looked for woofers that had good extension, high 90’s dBspl, and adequate response to below 40 Hz and reasonable overall Q. After a search I chose the Eminence Kappalite 3015LF Neo driver (Qts of 0.39, 99.8 dBspl, 9.6 mm extension, etc.). A low Q woofer like this one needs equalization to help assist its response so the crossover box so I anticipated EQ’ing across the frequency band to aid both the woofer and A10.2. For my crossover network I’m using the dBx DriveRack PA+ which features equalization over 28 bands. You can read other specs on the DriveRack and Kappalite 15 on the manufacturer websites.
Then I got to building. The H-frame for the Kappalite 15” driver is 18 x 18 inches high/wide and has a 16” depth (outside dimensions). The frame is built from 0.75” thick cherrywood (sides and top) and MDF. The A10.2 open baffle was sized to yield open baffle performance down to the low 100’s Hz. The A10.2 baffle is 18” wide and 19” high and has 3” thick hardwood side rims. With these dimensions the H-frame has a dipolar dip near 300 Hz so my goal was to crossover the woofer to the A10.2 so that their response would blend around 200 Hz.
I used a small Parasound preamplifier before the DriveRack and four channels of my Rotel 5-channel (125 watts) HT amplifier to power the speakers. RCA to XLR adaptors are used on the inputs and outputs of the crossover box. I have not heard any gain compression within the signal path for this gear so gain distribution seems in order.
When I finished assembly of the speakers the tweaking process with the crossover started. The tweaking with the DriveRack doesn’t take long as you can flip switches and twist controls to your desires. Initially, I tried to work toward flat response but the sound was a little off for my taste. I measured a slight rise in the frequency response that I suspected would need correction. With the DriveRack RTA microphone I tried the Auto EQ function with the mic across the room about 15 feet from the speakers. The Auto EQ process plays pink noise in the room and you get to choose between a set of contours. The flat response EQ wasn’t my cup of tea. Next I chose the live performance profile Auto EQ setting and bingo! I’m hearing the sound that I sought.
Now I’ve been playing my favorite CDs with these speakers and I’m pleased. The music is clean and tuneful without any excuses. Others have concurred about the natural sound and how it sounds like music. The Alpair 10.2 produces exceptional mids and the highs are spot-on without the need for a separate tweeter for my listening. Furthermore, I’ve become a devotee of dipolar bass. If you normally listen to closed or vented box speakers, you owe yourself a chance to hear open box bass. No muddy bass, no boxy sound, good integration with the room, etc. are just some of the benefits.
Last week I entered the speakers in the open unlimited category of the Parts Express Midwest Audiofest in Dayton, OH. My speakers won first place in this class so I was very pleased with the results and to know that others like what they heard.
Finally, it was fortunate that I purchased my Eminence drivers before the insane escalation in Neo driver prices this year. Other lower cost woofers are available that can do the job in this configuration so I encourage others to build it and tell us how your ears benefit.
https://picasaweb.google.com/102683...key=Gv1sRgCL3-uv2Z8KOgyAE#5627580330646289442
I had used both the Mark Audio Alpair 10 and 10.2 (second generation) drivers in a MLTL enclosure as reported previously on DIYAudio. From hearing the new A10.2s in the MLTL boxes I heard improvements vs. the original A10s. Thus I thought that the A10.2 would be a good candidate for the mid/tweeter driver in the new project.
As most of you realize, full range open baffle coverage with a single driver—even one as remarkable as the A10.2—really limits the amount of bass you can achieve from the speaker design. Fortunately, the work by Martin J. King and followers show excellent results from the use of a large woofer—say 15 or 18 inches diameter—with a wide range driver to cover the mid and tweeter ranges of the frequency band. Martin analyzes various bass configurations on his website and I chose the H-frame design which yields good results with reasonable size for the overall speaker.
Normally, a high Q woofer is selected to provide essential EQ to boost the woofer output for bass frequencies if a passive crossover is used between the H-frame woofer and the broadband driver. For my project I planned to use an active crossover, so I looked for woofers that had good extension, high 90’s dBspl, and adequate response to below 40 Hz and reasonable overall Q. After a search I chose the Eminence Kappalite 3015LF Neo driver (Qts of 0.39, 99.8 dBspl, 9.6 mm extension, etc.). A low Q woofer like this one needs equalization to help assist its response so the crossover box so I anticipated EQ’ing across the frequency band to aid both the woofer and A10.2. For my crossover network I’m using the dBx DriveRack PA+ which features equalization over 28 bands. You can read other specs on the DriveRack and Kappalite 15 on the manufacturer websites.
Then I got to building. The H-frame for the Kappalite 15” driver is 18 x 18 inches high/wide and has a 16” depth (outside dimensions). The frame is built from 0.75” thick cherrywood (sides and top) and MDF. The A10.2 open baffle was sized to yield open baffle performance down to the low 100’s Hz. The A10.2 baffle is 18” wide and 19” high and has 3” thick hardwood side rims. With these dimensions the H-frame has a dipolar dip near 300 Hz so my goal was to crossover the woofer to the A10.2 so that their response would blend around 200 Hz.
I used a small Parasound preamplifier before the DriveRack and four channels of my Rotel 5-channel (125 watts) HT amplifier to power the speakers. RCA to XLR adaptors are used on the inputs and outputs of the crossover box. I have not heard any gain compression within the signal path for this gear so gain distribution seems in order.
When I finished assembly of the speakers the tweaking process with the crossover started. The tweaking with the DriveRack doesn’t take long as you can flip switches and twist controls to your desires. Initially, I tried to work toward flat response but the sound was a little off for my taste. I measured a slight rise in the frequency response that I suspected would need correction. With the DriveRack RTA microphone I tried the Auto EQ function with the mic across the room about 15 feet from the speakers. The Auto EQ process plays pink noise in the room and you get to choose between a set of contours. The flat response EQ wasn’t my cup of tea. Next I chose the live performance profile Auto EQ setting and bingo! I’m hearing the sound that I sought.
Now I’ve been playing my favorite CDs with these speakers and I’m pleased. The music is clean and tuneful without any excuses. Others have concurred about the natural sound and how it sounds like music. The Alpair 10.2 produces exceptional mids and the highs are spot-on without the need for a separate tweeter for my listening. Furthermore, I’ve become a devotee of dipolar bass. If you normally listen to closed or vented box speakers, you owe yourself a chance to hear open box bass. No muddy bass, no boxy sound, good integration with the room, etc. are just some of the benefits.
Last week I entered the speakers in the open unlimited category of the Parts Express Midwest Audiofest in Dayton, OH. My speakers won first place in this class so I was very pleased with the results and to know that others like what they heard.
Finally, it was fortunate that I purchased my Eminence drivers before the insane escalation in Neo driver prices this year. Other lower cost woofers are available that can do the job in this configuration so I encourage others to build it and tell us how your ears benefit.
https://picasaweb.google.com/102683...key=Gv1sRgCL3-uv2Z8KOgyAE#5627580330646289442
The crossover relieves the Alpair 10.2 from most of any bass handling issues. I can touch the surround and I don't feel significant energy nor feel/hear over driving of the 10.2.
Frankly, you will want to turn-up the volume as the sound is clean and clear. Fortunately, my drivers have several hundred hours on them so they are well broken-in.
Frankly, you will want to turn-up the volume as the sound is clean and clear. Fortunately, my drivers have several hundred hours on them so they are well broken-in.
Here is a link to additional photos of my speakers.
https://picasaweb.google.com/108320796621723128031/Jul112011?authkey=Gv1sRgCMKFxZnUlNrfrQE#
https://picasaweb.google.com/108320796621723128031/Jul112011?authkey=Gv1sRgCMKFxZnUlNrfrQE#
Offset or not is a good question. I did not complete a study for this design so there is no offset.
However, I would be in good company if I did not use an offset. Dr. Linkwitz points out that while an offset may help diffraction on the main axis, it causes some problems off axis, especially for an open baffle driver.
However, I would be in good company if I did not use an offset. Dr. Linkwitz points out that while an offset may help diffraction on the main axis, it causes some problems off axis, especially for an open baffle driver.
Yes, I read your comments on the matter on the PE forum. That's an interesting point, and furthermore, at least one can say that centering the speaker is good aesthetics.
I wonder what would be required to produce your results using just passive components. It would first require a higher-q woofer for the H-frame. I wonder how the beta-15 would model in an H-frame? I think its sensitivity would be a good match, so hopefully no need to pad either driver...
I wonder what would be required to produce your results using just passive components. It would first require a higher-q woofer for the H-frame. I wonder how the beta-15 would model in an H-frame? I think its sensitivity would be a good match, so hopefully no need to pad either driver...
If you are interested in other Eminence or Goldwood woofers, go to Martin J. King's website as he has several white paper/projects on various woofers and specific configurations. He has a passive crossovered Eminence 15" Alpha or Goldwood 18" and I think specific examples of Jordan JX92S or Fostex full range drivers on his site as well. He talks about various Eminence woofers in another white paper.
If you have his spread sheets, you can plug in your choice of woofer and full range driver and see how your variation functions. For open backed woofers, the dipolar configuration eats up sensitivity so it would be best to work the details to see if you choice of woofer and wide range drive can be passively crossed. Generally, a higher Q woofer needs less low end EQ which makes passive crossovers do-able. But an active crossover can solve a lot of aliments for this kind of configuration plus permits other choices of drivers.
If you have his spread sheets, you can plug in your choice of woofer and full range driver and see how your variation functions. For open backed woofers, the dipolar configuration eats up sensitivity so it would be best to work the details to see if you choice of woofer and wide range drive can be passively crossed. Generally, a higher Q woofer needs less low end EQ which makes passive crossovers do-able. But an active crossover can solve a lot of aliments for this kind of configuration plus permits other choices of drivers.
And you know, as much as I love the idea of the alpair OB, there's still something irresistibly sexy about that big *** mid!
My view is that it is mostly about the woofer configuration that you choose. The dynamics of the open baffled Alpair 10.2 when paired with a musical open back woofer like the Eminence 3015LF is impressive. My point is that we accept compression in our vented and sealed boxes but an open baffled system will unleash the sound when properly designed.
Nice build
Nice work there! A couple of questions if you don't mind. Is that felt on the surface of the baffle? Have you experimented with lower x/o points, perhaps 120Hz or even as low as 90Hz? You have quite capable drivers and thought you might prefer the overall presentation with a slightly lower crossover point. I finished a similar 3-way build and found that to be the case, perhaps the difference being that I had a little extra help in the upper bass region.
Nice work there! A couple of questions if you don't mind. Is that felt on the surface of the baffle? Have you experimented with lower x/o points, perhaps 120Hz or even as low as 90Hz? You have quite capable drivers and thought you might prefer the overall presentation with a slightly lower crossover point. I finished a similar 3-way build and found that to be the case, perhaps the difference being that I had a little extra help in the upper bass region.
Attachments
Matevana Asked: A couple of questions if you don't mind. Is that felt on the surface of the baffle? Have you experimented with lower x/o points, perhaps 120Hz or even as low as 90Hz?
No felt. I'm using a textured paint on the baffle to try to conceal my limited painting skills.
Crossover points for my design were established by several considerations. First, the size of the top baffle housing the Alpair 10.2 determines how low that driver can play--in my design around 200 Hz before rolloff. You have the dipolar rolloff effect of 6 dB per octave because of this factor. Second, the H-baffle depth (16" in my case) causes a dipole dip around 300 Hz so you need to cross before that point. When I measured the performance of each driver as mounted, the natural crossover frequency is 200 Hz. To cross the upper baffle any lower in frequency would necessitate a larger frame.
No felt. I'm using a textured paint on the baffle to try to conceal my limited painting skills.
Crossover points for my design were established by several considerations. First, the size of the top baffle housing the Alpair 10.2 determines how low that driver can play--in my design around 200 Hz before rolloff. You have the dipolar rolloff effect of 6 dB per octave because of this factor. Second, the H-baffle depth (16" in my case) causes a dipole dip around 300 Hz so you need to cross before that point. When I measured the performance of each driver as mounted, the natural crossover frequency is 200 Hz. To cross the upper baffle any lower in frequency would necessitate a larger frame.
Jim,
If your 10.2 starts to roll-off at 200Hz, it should be down 6dB at 100Hz. Conversely the helper woofer, if rolled off at 100Hz instead, depending on the slope used, should achieve half-point around 200Hz. Summing in the occurrence of floor bounce, again depending on where this occurs in your design, you might find that you aren't lacking any in the 100-200Hz range. (I find I often have to cut frequencies in this range with many dipole designs).
SL discovered the benefits of lowering his x/o to 90Hz (from 120Hz) in his latest Orion-4 build and remains convinced that lower is better. His baffles are only 13" wide! You might want to give it a try. I'd be interested in your thoughts if you do.
Matevana... love that tea!
Interesting thing about these open baffle projects, to me anyway, is that they are easy to blend with bass systems. I have H-frames and one of my sons has small open baffles (maybe 14" wide with an 8" full range driver on it) blending nicely with a sealed powered sub.
When i simmed these open baffles the roll off is gradual. The charts never looked like ported boxes that peak then dip drastically. Crossing ported boxes to a sub is more challenging to get right than open baffle.
Does anyone know the slopes produced by ported, sealed and open baffle? I thought it was 18db per octave for ported but not sure. Regardless, simply plopping a full range driver into a baffle large enough to produce output into the mid 100hz zone can easily be mated to a sub of some kind.
IME, drivers with higher qts (close to 1 or higher) will produce more bass on an open baffle compared to a driver with a lower qts (.5 or lower) on the same sized baffle.
Having said that, many drivers, regardless of qts, will produce bass to 300hz or lower on resonably sized open baffles.
I hope i don't ramble like this in person...
If i were to build a simple ob with a single driver without bass support i'd look for something 8" or larger with a qts of close to or greater than 1.
If using bass support, just about any driver, large or small over say 4" seem to produce bass to about 300hz... some go lower than others... allowing a lower crossover frequency... which usually sounds better to me.
It's amazing to me how many high excusion subwoofers are out there... and how expensive they can be! I used to drool over their heavy duty construction. Then i built H-frames with relatively innexpensive Alpha 15's... that looked like the were going to fall apart having to produce loud low bass... now i drool at home listening to musical ob bass thru these paper coned, puny Xmas drivers. Maybe one day i will explore better built drivers and EQ... but not until i get my fill of these!
Zilla
Interesting thing about these open baffle projects, to me anyway, is that they are easy to blend with bass systems. I have H-frames and one of my sons has small open baffles (maybe 14" wide with an 8" full range driver on it) blending nicely with a sealed powered sub.
When i simmed these open baffles the roll off is gradual. The charts never looked like ported boxes that peak then dip drastically. Crossing ported boxes to a sub is more challenging to get right than open baffle.
Does anyone know the slopes produced by ported, sealed and open baffle? I thought it was 18db per octave for ported but not sure. Regardless, simply plopping a full range driver into a baffle large enough to produce output into the mid 100hz zone can easily be mated to a sub of some kind.
IME, drivers with higher qts (close to 1 or higher) will produce more bass on an open baffle compared to a driver with a lower qts (.5 or lower) on the same sized baffle.
Having said that, many drivers, regardless of qts, will produce bass to 300hz or lower on resonably sized open baffles.
I hope i don't ramble like this in person...
If i were to build a simple ob with a single driver without bass support i'd look for something 8" or larger with a qts of close to or greater than 1.
If using bass support, just about any driver, large or small over say 4" seem to produce bass to about 300hz... some go lower than others... allowing a lower crossover frequency... which usually sounds better to me.
It's amazing to me how many high excusion subwoofers are out there... and how expensive they can be! I used to drool over their heavy duty construction. Then i built H-frames with relatively innexpensive Alpha 15's... that looked like the were going to fall apart having to produce loud low bass... now i drool at home listening to musical ob bass thru these paper coned, puny Xmas drivers. Maybe one day i will explore better built drivers and EQ... but not until i get my fill of these!
Zilla
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.