I have 4 Pioneer Bofu's sitting around and just waiting for some projects. I was poking through the internet and came across the idea of pairing an open baffle with a ported box using identical drivers.
Here's what I was thinking for my Bofu's. A large OB approx 2' wide x 4' tall with a 3 cu. ft. ported box attached to the rear with a second driver firing up. See the pic if my description confuses you as much as did me when I wrote it.
Who here has he done it? What are the draw backs? Expense of the second driver? (I already have two pair so that's taken care of.) Will the output of the two be matched well enough? If it really works then why haven't I seen more of these?
I'm interested in hearing what the more experienced members have to say.
Here's what I was thinking for my Bofu's. A large OB approx 2' wide x 4' tall with a 3 cu. ft. ported box attached to the rear with a second driver firing up. See the pic if my description confuses you as much as did me when I wrote it.
Who here has he done it? What are the draw backs? Expense of the second driver? (I already have two pair so that's taken care of.) Will the output of the two be matched well enough? If it really works then why haven't I seen more of these?
I'm interested in hearing what the more experienced members have to say.
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Interesting
You could be cross omni driver for a 1.5way to compensate for dipole rolloff and BSC
Another thing is that driver Qts=0.5 pionts more in the direction of a closed design, rather than BR
To maintain your general design with omni bass, maybe make a cut below the OB baffle, so that OB baffle is positioned in the middle of the omni driver, so that it works more like real omni
You could be cross omni driver for a 1.5way to compensate for dipole rolloff and BSC
Another thing is that driver Qts=0.5 pionts more in the direction of a closed design, rather than BR
To maintain your general design with omni bass, maybe make a cut below the OB baffle, so that OB baffle is positioned in the middle of the omni driver, so that it works more like real omni
Just going by WinISD (for whatever that is worth) puts a sealed bofu at a F3 of approx 60hz and a F10 of 32hz. A ported box of 3 cu. ft. tuned to 35hz has an F3 of 32hz and a F10 of 26hz. I know extension isn't everything but the ported curve looks better to me and I've always liked the sound of ported boxes over sealed for the music I listen too. I believe Zilla has had the Bofu in both boxes so maybe he could comment on this.
Moving the baffle back to where it straddles the boxed woofer is an interesting idea. Would there be any weirdness having the two drivers firing into the listing area at 90 degrees out of phase with each other? I don't know that much about how these things behave really.
As you guessed the goal was to have the merits of the "Open Baffle Sound" coupled with real bass output without resorting to bi-amping or eq'ing. I already have the Pio's sitting around so I might as well give it a shot.
Moving the baffle back to where it straddles the boxed woofer is an interesting idea. Would there be any weirdness having the two drivers firing into the listing area at 90 degrees out of phase with each other? I don't know that much about how these things behave really.
As you guessed the goal was to have the merits of the "Open Baffle Sound" coupled with real bass output without resorting to bi-amping or eq'ing. I already have the Pio's sitting around so I might as well give it a shot.
I am using something vaguely similar ie ob + br
I have Saba 8"mid and 3" tweeter on open baffle with an 18" bass driver in a ported box.
It took a little while to arrive at this combo, as at first I trying ob for the bass in a u frame. I got frustrated and bought some ports and slapped a back on it and was shocked.It really sounds pretty damned good at this point, so I have been just enjoying it.
Ed
I have Saba 8"mid and 3" tweeter on open baffle with an 18" bass driver in a ported box.
It took a little while to arrive at this combo, as at first I trying ob for the bass in a u frame. I got frustrated and bought some ports and slapped a back on it and was shocked.It really sounds pretty damned good at this point, so I have been just enjoying it.
Ed
Gurley123
Maybe it's dependant on room size, but I have a pair of B20's in 1.94cu ft sealed boxes and I don't feel the need for a sub woofer with them. I don't know if I'm a bass head or not but I know I like confident extension into the high 30's low 40's and these are giving me that. My projected Fb was 59Hz and IINM my projected F3 was 57Hz.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=145213
Another thing I'd like to point out is that I'm in no rush to add tweeters to them. I have some PE Neo's for 'em. Unfortunately I didn't listen to them OB prior to doing this sealed thing so I can't comment on their sound in that regard, but I bet they will sound better than the sum of the parts would suggest.
As a point of reference I own a pair of Hawthorne SI's matched up with a pair of Augies.
R/
Jim
Maybe it's dependant on room size, but I have a pair of B20's in 1.94cu ft sealed boxes and I don't feel the need for a sub woofer with them. I don't know if I'm a bass head or not but I know I like confident extension into the high 30's low 40's and these are giving me that. My projected Fb was 59Hz and IINM my projected F3 was 57Hz.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=145213
Another thing I'd like to point out is that I'm in no rush to add tweeters to them. I have some PE Neo's for 'em. Unfortunately I didn't listen to them OB prior to doing this sealed thing so I can't comment on their sound in that regard, but I bet they will sound better than the sum of the parts would suggest.
As a point of reference I own a pair of Hawthorne SI's matched up with a pair of Augies.
R/
Jim
This reminded me of another thread not too long ago, which is very similar. Refer to this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=142027&highlight=
If you go with that enclosure type, I am not sure how it would sound with a bass reflex enclosure. That thread is to eliminate the need for BSC, since when the OB driver moves outward, the BSC woofer also moves outward, thereby making the net displacement essentially zero in the rear. If you want to avoid something like this, I would just mount the BR speaker in the front. You can also invert the phase of one of the woofers, or just mount it inverted with the magnet sticking out.
Also, I would definitely recommend rolling off the BR driver somewhere in the upper midbass or lower midrange. There will be some cancellation due to the phase shift if you dont add a highpass to the OB speaker, but it won't be as bad as you think in the upper midbass
If you go with that enclosure type, I am not sure how it would sound with a bass reflex enclosure. That thread is to eliminate the need for BSC, since when the OB driver moves outward, the BSC woofer also moves outward, thereby making the net displacement essentially zero in the rear. If you want to avoid something like this, I would just mount the BR speaker in the front. You can also invert the phase of one of the woofers, or just mount it inverted with the magnet sticking out.
Also, I would definitely recommend rolling off the BR driver somewhere in the upper midbass or lower midrange. There will be some cancellation due to the phase shift if you dont add a highpass to the OB speaker, but it won't be as bad as you think in the upper midbass
I'm doing something similar using 3" visaton drivers (FRS8), and no ports.
http://www.diyaudio.com/forums/showthread.php?threadid=142027&highlight=
Wire both in phase, and the rear driver (LP around 500Hz), and it cancels the back wave of the OB driver.
The idea of this design is fairly simple: you get bass response better than the OB and the boxed driver would give separately (mine go an octave below Fs), and you get the airyness of an OB system.
Just noticed that someone found the same thread as me.
IMHO, go for it - it is a very rewarding system that isn't fussy about positioning.
If you still want to go for ports, fill up (temporarily) around 1/2 of the box (for reasons unknown, ported boxes tend to be twice the size), take some measurements. The de-fill the box, and put your port in, then sit back and enjoy.
Chris
EDIT - I wouldn't advise using ports, and they will affect the excursion curve of the cancellation box, meaning it will not cancel all the way down. This should be counteracted by the port's gain, but these two happenings would cancel (approximately), so, you have 2* box volume, and a tube, for something which would make little difference.
http://www.diyaudio.com/forums/showthread.php?threadid=142027&highlight=
Wire both in phase, and the rear driver (LP around 500Hz), and it cancels the back wave of the OB driver.
The idea of this design is fairly simple: you get bass response better than the OB and the boxed driver would give separately (mine go an octave below Fs), and you get the airyness of an OB system.
Just noticed that someone found the same thread as me.
IMHO, go for it - it is a very rewarding system that isn't fussy about positioning.
If you still want to go for ports, fill up (temporarily) around 1/2 of the box (for reasons unknown, ported boxes tend to be twice the size), take some measurements. The de-fill the box, and put your port in, then sit back and enjoy.
Chris
EDIT - I wouldn't advise using ports, and they will affect the excursion curve of the cancellation box, meaning it will not cancel all the way down. This should be counteracted by the port's gain, but these two happenings would cancel (approximately), so, you have 2* box volume, and a tube, for something which would make little difference.
No more replies?
Shame, but I've a feeling that some people just don't like the idea, although I have no idea why...
Using PRs behind the OB driver wouldn't work, as it would only absorb a small portion of the rearwave, meaning the rest would still go around the front and cancel the front wave.
I've got my Visaton drivers now, going to make a stereo pair today (if the weather holds up), and will let you know how that sounds.
BTW - you wouldn't need a big baffle to mount the OB speaker, the one I'm using is 7" by 12", and there's a one or 2 dB drop around 300Hz, and that's all, as below that, sound becomes omnidirectional, and above it becomes directional.
IMHO, mess around a bit first. Just me saying the baffle doesn't need to be big might not persuade you, whereas if you try it yourself, the evidence is before you, not hundreds of miles away on a small, wet island called the UK.
Shame, but I've a feeling that some people just don't like the idea, although I have no idea why...
Using PRs behind the OB driver wouldn't work, as it would only absorb a small portion of the rearwave, meaning the rest would still go around the front and cancel the front wave.
I've got my Visaton drivers now, going to make a stereo pair today (if the weather holds up), and will let you know how that sounds.
BTW - you wouldn't need a big baffle to mount the OB speaker, the one I'm using is 7" by 12", and there's a one or 2 dB drop around 300Hz, and that's all, as below that, sound becomes omnidirectional, and above it becomes directional.
IMHO, mess around a bit first. Just me saying the baffle doesn't need to be big might not persuade you, whereas if you try it yourself, the evidence is before you, not hundreds of miles away on a small, wet island called the UK.
If my idea with the passive radiator did work to cancel out just a small amount of the low frequency radiation I think it would be worthwhile. I think in Lynn's thread he mentions that he is not interested in cancelling out or absorbing all the rear radiation but reducing it slightly would be a benefit. Hardly anything will absorb the lower frequecies which is the are of interest so I though that maybe a passive radiator arranged in this manner might help enough.
jamikl
jamikl
It was a crazy weekend full of birthdays and family reunions so I haven't had much time to look through these responses.
paulfk, that speaker is the one that got me thinking about this. I saw someone selling those on the Obad import site and I thought I could make it on a larger scale.
I have some inductors that will cut the BOFU at 500Hz that I can use. I may just start out running the speakers both full range and in phase and then change things from there (change phase, add tweets, add lowpass, try the cabs sealed, ect.) After I try as many combos as I can stand, I will then just chose what sounds best to me. I don't have any way to take measurements so I'll have to rely on my ears.
I need to settle for a final design and make a cut sheet. What kind of equation do you use to figure the rolloff of an open baffle. I'm guessing it's a function of wavelength. I'll do some digging but if any one could point me in the right direction, I ould really appreciate it.
paulfk, that speaker is the one that got me thinking about this. I saw someone selling those on the Obad import site and I thought I could make it on a larger scale.
I have some inductors that will cut the BOFU at 500Hz that I can use. I may just start out running the speakers both full range and in phase and then change things from there (change phase, add tweets, add lowpass, try the cabs sealed, ect.) After I try as many combos as I can stand, I will then just chose what sounds best to me. I don't have any way to take measurements so I'll have to rely on my ears.
I need to settle for a final design and make a cut sheet. What kind of equation do you use to figure the rolloff of an open baffle. I'm guessing it's a function of wavelength. I'll do some digging but if any one could point me in the right direction, I ould really appreciate it.
Yeah, I was playing with EDGE within twenty minuets of posting that question. I should have googled before I asked? Oh well, validation is good too.
BTW, with EDGE I came up with a baffle of 40"(tall) x 12"(wide) with the driver centered 34" up and 7.375" over from the far edge. I resized the box accordingly.
BTW, with EDGE I came up with a baffle of 40"(tall) x 12"(wide) with the driver centered 34" up and 7.375" over from the far edge. I resized the box accordingly.
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