Looking into exploring open baffle subs with existing 18" Faitals, in an active system. I have a couple 12" sealed servo subs playing the lowest end so don't necessarily need the OB subs to get to 20Hz. I envision having the four subs playing the lower end and the OB subs playing alone above 50 or 60Hz up to 100 or 120Hz.
I'm thinking H or U shaped. Pros & cons or recommendations?
I understand the cavity behind the U or in half the H shouldn't be too long to avoid resonances. How shallow is enough? If I use a 24"x24" baffle should I keep it under 50% wing, so 12" for the U or 6" each way for the H?
How do I model an H baffle on Basta or Edge? 24" from driver center to baffle edge, plus 6" wing one way, plus another 6" for the sound to come around the back of the wing and meet halfway, so 36"x2=72" baffle?
I ran a couple of searches in this forum thinking others would have posted o something along these lines before, but didn't get much. If you are aware of another thread where this was addressed, I'd be happy to get the link and read up.
Thank you!
I'm thinking H or U shaped. Pros & cons or recommendations?
I understand the cavity behind the U or in half the H shouldn't be too long to avoid resonances. How shallow is enough? If I use a 24"x24" baffle should I keep it under 50% wing, so 12" for the U or 6" each way for the H?
How do I model an H baffle on Basta or Edge? 24" from driver center to baffle edge, plus 6" wing one way, plus another 6" for the sound to come around the back of the wing and meet halfway, so 36"x2=72" baffle?
I ran a couple of searches in this forum thinking others would have posted o something along these lines before, but didn't get much. If you are aware of another thread where this was addressed, I'd be happy to get the link and read up.
Thank you!
A good way to model these structures is using HornResp. It does a decent job of predicting both the dipole response and the 1/4-wave internal resonance in the frequency response.
Edge is only flat baffle, I'd have to look at Basta again to see if you can do H. You didn't see it, right?
It seems strange to use the Faital 18s for only an octave. They should be happy up to ~500Hz. at which point you cross to a mid or fullrange. I've done that with 21a and 18s.
It seems strange to use the Faital 18s for only an octave. They should be happy up to ~500Hz. at which point you cross to a mid or fullrange. I've done that with 21a and 18s.
Yeap, I didn't see the H baffle option in Basta.
Faitals indeed go up to 500Hz easily and are today used as midbasses from 70 to 350Hz baffleless. But lately I'm wondering if they are really clean/transparent above 200Hz or so. That is why I want to test them for sub duties and maybe use a 12" or 15" for midbass.
I can get to 60Hz baffleless, so hoping an H-baffle will allow getting to at least 40Hz - maybe 30Hz? So 40 to up to whatever makes sense/sounds good. Maybe it goes higher than 120Hz and I can go for a 12" midbass with minimal baffle.
I never used Hornresp for H-baffle - actually didn't know it was prepared to handle this!
Looking into wizard, I set it to free space, CH=1, Vrc=Lrc=Vtc=Atc=0, and S1=S2=S5=S6=3600cm2 (24"x24").
How do I model the wing length? If I want to model 12" wings with the baffle midway, so 6" each way, how should I enter it into Hornresp?
Thank you in advance!
I have been experimenting with various 12" to 18" pro audio drivers this past 9 months or so. This is for the "woofer" role in a nude dipole system. After building up several (five?) different versions with different drivers ($ to $$$) I found that I was never satisfied by any of them above about 350Hz or so. I think the lightweight cones and other design tradeoffs that are needed to exceed 96dB/W SPL result in too many cone resonances and other issues, and these were always audible to some extent at the upper end of that passband.
With some careful choice of driver the 80-350 Hz range can work pretty well. I just cross over to sealed subs below 80Hz. This is without any baffle, but that is the main point of the system design, and one that avoids any and all resonances that are created by the folded "frames" (U/H/M, etc.). You could probably use a 24x24" planar baffle and a 15 or 18 and still go up to 350Hz nicely.
Set the lengths L12 and L56 to 15.24 cm, as shown in the attachment.
Attachments
Hi David,
Great to have you back on line. Hornresp is great for dipole sims. Thanks.
Can I ask some basic questions?
When Hornresp models an H-baffle does it assume the cross section is square or circular?
With SPL where is the reading taken from in space eg out to the right of the Schematic? How far out?
Hornresp also give this slider wizard option for rapidly changing the H-frame dimensions. It even allows the H-frame to turn into a U-frame. Big thanks to David.
Hornresp allows checking the SPL output ( via the drivers Xmax and power)
Its worth comparing the sim for a flat baffle versus a H/U frame. Benefits and costs with bass extension vs upper reach and impulse/phase etc.
Hi kazap,
Thanks, it's good to be back 🙂.
The pressure response can be specified at a given off-axis angle, and is also normalised to a distance of 1 metre.
Kind regards,
David
Thanks, it's good to be back 🙂.
Circular (axisymmetric).
The power response is independent of position, and is normalised to a distance of 1 metre.
The pressure response can be specified at a given off-axis angle, and is also normalised to a distance of 1 metre.
Kind regards,
David
Thank you David!! You've added a lot of new functionality into Hornresp. Congrats!!
To evaluate different wing and baffle dimensions and the resonances the cavity might create, should I be looking at ripples in the acoustical power curve, acoustical impedance, or something else?
Thanks for including this!
I couldn't find the parametric sliders. From Window>Schematic Diagram. What next to get to the sliders?
I have a similar current setup: sealed subs to 70Hz, naked 18" to 350Hz, 8" to 1700Hz and dipole AMT above.
Besides this OB sub experiment, I've been thinking about adding two more subs for a distributed bass array.
Back to OB sub: I agree the midbass can go to 350Hz on small (12" driver) or naked driver. My Faital 18hp1010 is rated 98dB @ 1W so probably suffering what you describe. I was considering Eminence 2512 or even AE LO12 for midbass, but before spending on new drivers I'm thinking they would need crossing higher that 70-80Hz and hence want to experiment making dipole subs and see how high they get playing nicely.
Let me try and work through the Hornresp chain for an H-frame on the floor
First save the driver specs: go to www.Loudspeakerdatabase.com , find your driver, see the Hornresp data file and download it into the Hornresp> Driver folder
Hornresp>Help>Input Wizard> Half space (on the floor)>Direct radiator>H-frame>finish>
Window>Input parameters> Tools> Loudspeaker Wizard > No to mask > sliders
S1 - driver baffle area cm x cm - eg 18" driver = 46cm outer diameter will need eg 50x50=2500
L12 - front extension in cm - make it 0cm and theres the U-baffle
L52 - rear extension in cm
save>File > paste driver > calculate >Window>Acoustic Power >Tools>Max SPL > OK
Check out the impulse and displacement too.
If you are using a QTs < 0.5 driver check out the power needs compared to eg an Acoustic Elegance Dipole or other high QTs OB woofer.
First save the driver specs: go to www.Loudspeakerdatabase.com , find your driver, see the Hornresp data file and download it into the Hornresp> Driver folder
Hornresp>Help>Input Wizard> Half space (on the floor)>Direct radiator>H-frame>finish>
Window>Input parameters> Tools> Loudspeaker Wizard > No to mask > sliders
S1 - driver baffle area cm x cm - eg 18" driver = 46cm outer diameter will need eg 50x50=2500
L12 - front extension in cm - make it 0cm and theres the U-baffle
L52 - rear extension in cm
save>File > paste driver > calculate >Window>Acoustic Power >Tools>Max SPL > OK
Check out the impulse and displacement too.
If you are using a QTs < 0.5 driver check out the power needs compared to eg an Acoustic Elegance Dipole or other high QTs OB woofer.
Have you checked out the Fi Audio IB318v2? This can work very well in a dipole sub with high Xmax and high Qts. I have one loaded into an H-frame that has a 24x24" mouth and is 16" deep on front and back (32" total length). Nice, but still needs some EQ for dipole losses and 1/4 wave resonance.
kazap: Can you plot the frequency response for 2.83 (or 1W or whatever) input instead of max SPL? If you are indeed looking for "max SPL" then a dipole sub is not where you should be looking for that! 😀 But I guess it's not a bad idea to know the excursion limited SPL.
Thanks for doing this!! I thought I had it, but your explanation showed I was missing some things.
Interestingly, a 60x60cm baffle with 30cm H wings to each side shows the 18" reaches the 9.8mm Xmax by 32Hz at 12W reaching 101dB SPL. While using 15cm wings (each side), at 12W it still bottoms out at Xmax at 31Hz but at 96dB. And a 60x69 flat baffle doesn't bottom out at 12W and gets to 94dB SPL at 31Hz.
Simply adjust the S1, L12 and L56 slider controls in the Loudspeaker Wizard and observe how the response changes.
