The problem with this hobby (and many others) is that we are always striving for that extra 10%. I suppose you might conclude that IS the thing that makes DIY fun!
Simulations are a great place to start. They will help prevent many costly mistakes. That being said, when you ARE down to that final 10%, there seems to be no substitution for experimentation. Active systems really lend themselves to this, as in most cases you are tweaking settings as opposed to substituting components.
Jim, it is not without problem to put a driver at the center of a square (or circular) baffle as you probably know. Linkwitz has it: Electro-acoustic models here and Joihn Kreskovsky gives the picture here: Dipoles and Open Baffles .
A simulation of your design with MJK's models result in this on axis response (I have used your dimensions, cross bass at 100 Hz L-R 12 db/oct and Alpair HP at 200 Hz likewise):
Off axis response will be more even. Offsetting the driver horizontally can also even out response but at the expense of assymetric horizontally polar response. Keeping the driver horizontally centered but moving its centre up to 15" on the 19" baffle will give this simulation:
A bit more even frequency chart and preserved symmetric horizontal polar.
32 watts input would give 100 dB SPL at 40 Hz well within X-max limits for the woofer also the Alpair can take this input according to specifications.
Building passive also seems possible given these results.
I am not at all astonished by your appreciation of the H-bass sounds. The Kappalite has a very suitable Q-value for use in H-baffle together with ample cone movement. Bass should be clean and well defined.
/Erling
A simulation of your design with MJK's models result in this on axis response (I have used your dimensions, cross bass at 100 Hz L-R 12 db/oct and Alpair HP at 200 Hz likewise):
An externally hosted image should be here but it was not working when we last tested it.
Off axis response will be more even. Offsetting the driver horizontally can also even out response but at the expense of assymetric horizontally polar response. Keeping the driver horizontally centered but moving its centre up to 15" on the 19" baffle will give this simulation:
An externally hosted image should be here but it was not working when we last tested it.
A bit more even frequency chart and preserved symmetric horizontal polar.
32 watts input would give 100 dB SPL at 40 Hz well within X-max limits for the woofer also the Alpair can take this input according to specifications.
Building passive also seems possible given these results.
I am not at all astonished by your appreciation of the H-bass sounds. The Kappalite has a very suitable Q-value for use in H-baffle together with ample cone movement. Bass should be clean and well defined.
/Erling
OMG, that Kappalite 15" driver is expensive!
http://www.parts-express.com/wizard...bPage_ID=3&searchFilter=Kappalite+15&x=29&y=7
Multiply that by 2! It better sound good. I'm used to seeing Alpha and Beta prices. Plus you need the electronics to make it work. I'm sure it all sounds fantastic.
http://www.parts-express.com/wizard...bPage_ID=3&searchFilter=Kappalite+15&x=29&y=7
Multiply that by 2! It better sound good. I'm used to seeing Alpha and Beta prices. Plus you need the electronics to make it work. I'm sure it all sounds fantastic.
Ideal slopes are: Ported boxes fall-off at a 4th order rate--24 dB per octave. Sealed boxes fall-off at a 2nd order rate--12 dB per octave. Open boxes fall at a 6 dB per octave because of the dipole effect which increases to 18 dB per octave lower below the resonant frequency of the driver. Thus for open baffles you have the 6 dB for the dipole effect plus the inherent 12 dB per octave for the below Fs decline.
Yeah neo driver prices have gone crazy because of the market/China situation/monopoly. The 3015LF has gone from $180 to $325 at Parts Express. I was lucky enough to obtain my woofers at the old price.
The Kappalite 3015LF is a favorite for the Tapped Horn entusiasts and rightly so. Just have a look in the Subwoofer part of this Forum. However it's parameters also makes it almost ideal also for H- or U-baffle use. A bit more so than used on a flat baffle. The extra air load in especially an H-baffle just makes it do its best and the H also helping in EQ by itself. If you haven't heard a well constructed Tapped Horn you still miss an experience. But be aware that the Open Baffle bass is the only one to match it in cleanness and dynamics, set aside that it won't match the SPL figures.
/Erling
/Erling
These are below the box Fs or driver Fs. On open baffles, below the dipole peak, bass will fall off at 12-18 db/octave. And the dipole peak will be determined by the distance from the front to rear of the driver, basically by baffle size. It is usually much higher than the driver Fs.
skorpion said:
This is spot on.
i think this high Q super clean driver would also be well suited to mating to the Mark Audio
Designed specifically for open baffle/dipole use
Underhung motor for extreme BL linearity
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Designed specifically for open baffle/dipole use
Underhung motor for extreme BL linearity
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Otto,
I substituted Eminenca Alpha15 for AE IB15 in my Blindstone OB The BlindStone OB earlier this year. It's effect was quite fantastic soundwise.
Later I had a discussion with Martin J King about the AE Dipole15 and Eminence Alpha 15 in his OB with Fostex 108E Zigma Yahoo! Groups .
He didn't seem to have the same revealing experience as I had with the IB15s in my set up.
/Erling
I substituted Eminenca Alpha15 for AE IB15 in my Blindstone OB The BlindStone OB earlier this year. It's effect was quite fantastic soundwise.
Later I had a discussion with Martin J King about the AE Dipole15 and Eminence Alpha 15 in his OB with Fostex 108E Zigma Yahoo! Groups .
He didn't seem to have the same revealing experience as I had with the IB15s in my set up.
/Erling
Jim, I built much the same thing, using the A7 in place of the 10 as you used. I had a bit of offset on the speaker instead of being in the center, I was lazy to use EDGE, but in the end they model ok.
I found a few things that I didnt like about imaging, and am wondering what your experience was. My room isn't the biggest, 4x4.5x4m, and could definitely use some acoustic treatment, being brick walls and hardwood floor...
First, I found that localization wasn't as precise I've had from other builds. I tried the drivers at about .75 - 1 meter from the back wall, but had to use a sheet of 1" polyfill behind the FR to get the imaging to be more clear.
What ruined it for me though was that the soundstage "bunched up" at the speakers. While there was imaging to some extent, to my ears the sound was coming largely from the speakers. I was thinking to try felt on the front surface, or trying to chamfer the edges a bit, but haven't gotten around to it yet. I still have a nagging feeling in the back of my mind that perhaps this could be simply a psychological effect from the largeness of the baffle, I didn't do any blind testing and I try to be critical of perception of changes.
In the end I put the A7's in Dave's Slim classic GR dMar-Ken7 (a slim ported enclosure). Dramatically better imaging and also lets me run a really low xo point (approx 60/150, 1st order pllxo, biamping). Keeping the Eminence 15a bottom end in the H frame of course sounds wonderful and adds a real sense of scale.
With so many people raving about the alpairs in OB, Im wondering if my issues are unusual, for example due to room problems, or if they are just a compromise that OB people are willing to deal with?
I found a few things that I didnt like about imaging, and am wondering what your experience was. My room isn't the biggest, 4x4.5x4m, and could definitely use some acoustic treatment, being brick walls and hardwood floor...
First, I found that localization wasn't as precise I've had from other builds. I tried the drivers at about .75 - 1 meter from the back wall, but had to use a sheet of 1" polyfill behind the FR to get the imaging to be more clear.
What ruined it for me though was that the soundstage "bunched up" at the speakers. While there was imaging to some extent, to my ears the sound was coming largely from the speakers. I was thinking to try felt on the front surface, or trying to chamfer the edges a bit, but haven't gotten around to it yet. I still have a nagging feeling in the back of my mind that perhaps this could be simply a psychological effect from the largeness of the baffle, I didn't do any blind testing and I try to be critical of perception of changes.
In the end I put the A7's in Dave's Slim classic GR dMar-Ken7 (a slim ported enclosure). Dramatically better imaging and also lets me run a really low xo point (approx 60/150, 1st order pllxo, biamping). Keeping the Eminence 15a bottom end in the H frame of course sounds wonderful and adds a real sense of scale.
With so many people raving about the alpairs in OB, Im wondering if my issues are unusual, for example due to room problems, or if they are just a compromise that OB people are willing to deal with?
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Imaging is different with ob for sure. I enjoy the wider, more diffuse soundstage. Instruments and vocals occasionally pop and float in space more often than boxed speakers, imo. But with boxed speakers there's the ability to pinpoint things a bit better... at the expense of the wider, bigger soundstage.
I've never heard the alpairs but am more curious than ever just to understand if what you are describing is unique to them. Also, if you were to try another set of drivers in your open baffles just to see if you get the same effect... I wonder what drivers fit the same opening?
I've never heard the alpairs but am more curious than ever just to understand if what you are describing is unique to them. Also, if you were to try another set of drivers in your open baffles just to see if you get the same effect... I wonder what drivers fit the same opening?
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Wider sound stage is ok. But it doesn't need to be diffuse. Just trade efficiency for accuracy. Get rid of those overly wide baffles, which control the bass efficiency of your FR driver, and regain precise imaging.
Rudolf
My Alpair 10.2s image just fine on open baffle. My setup has the open baffles on the H-frames with the front wall 2 meters behind them. I am impressed with how the sound floats in the air between the speakers and does not stick to the baffles as you often hear from some box speakers. In fact you can walk toward the speakers and you have very little directional clues as to where the sound originates until you are within a meter or so of them. Without a doubt these speakers present an out of box image.
Like Rudolf says, if you want an accurate soundstage in OB, you have to get rid of the wings and big baffles. Go for a naked OB basically. But that takes a toll on the power, excursion and max SPL capability.
All the drivers that I have tried on OBs, including alpairs, always produced a diffuse soundstage. But OB is still very easy to listen to compared to boxed.
All the drivers that I have tried on OBs, including alpairs, always produced a diffuse soundstage. But OB is still very easy to listen to compared to boxed.
Wider is not better !
I would like to support Rudolf's statement above and also qualify if further by postulating that a more narrow baffle doesn't suffer from efficiency loss compared to the wide one.
Using comparatively small membran area for our mid/fullrange and putting it well above floor there won't be much bass produced by such unit anyhow.
It is no use trying to crossover this unit lower than 200-250 Hz because it will very seldom give you any output lower.
Let's use Jim's speaker and the Alpair 10 as an example. In the first MJK simulation I used my version from above, that is 18" wide baffle, unit 15" up centred on the 19" tall baffle. Alpair is running fullrange:
Next example has a baffle 6.5" wide, unit 15" up centred on the 19" tall baffle and it is running fullrange:
QED
/Erling
I would like to support Rudolf's statement above and also qualify if further by postulating that a more narrow baffle doesn't suffer from efficiency loss compared to the wide one.
Using comparatively small membran area for our mid/fullrange and putting it well above floor there won't be much bass produced by such unit anyhow.
It is no use trying to crossover this unit lower than 200-250 Hz because it will very seldom give you any output lower.
Let's use Jim's speaker and the Alpair 10 as an example. In the first MJK simulation I used my version from above, that is 18" wide baffle, unit 15" up centred on the 19" tall baffle. Alpair is running fullrange:
An externally hosted image should be here but it was not working when we last tested it.
Next example has a baffle 6.5" wide, unit 15" up centred on the 19" tall baffle and it is running fullrange:
An externally hosted image should be here but it was not working when we last tested it.
QED
/Erling
Thank you for the sims. I need to get my ob simulator onto my new pc but worry i will end up simming a couple hours a day and lose my job. Your sims do suggest a loss of output in the critical range where the sub would meet the main driver so i think your example (tho meant to be drastic) would be audible. But if you went for a 12" or 14" baffle it may suggest barely an advantage over the wider baffle. Proof is in the listening of course.
When i simmed for the beta 12lta i simply selected the width of the H-frames they were sitting on top of (19.5"), made room for the drivers to be stacked one on top of the other (22") and the sim went down to around 200hz so i felt i was in good shape.
I think we can put a lot of drivers onto a baffle the width of our H-frames (using either 15 or 18" drivers) and create a relatively clean looking, great sounding open baffle.
When i simmed for the beta 12lta i simply selected the width of the H-frames they were sitting on top of (19.5"), made room for the drivers to be stacked one on top of the other (22") and the sim went down to around 200hz so i felt i was in good shape.
I think we can put a lot of drivers onto a baffle the width of our H-frames (using either 15 or 18" drivers) and create a relatively clean looking, great sounding open baffle.
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