I want to build an H-Frame enclosure using a Dayton Ultimax UM18-22 driver. Specs HERE.
The baffle would be 20x20 and I am wondering what size for the depth.
The baffle would be 20x20 and I am wondering what size for the depth.
Thank you e_f.
I was familiar with that document, but I found it confusing. On your recommendation, I persevered. I would appreciate someone verifying my calculations and conclusions:
"The maximum length of the U and H frame geometry should be sized so that the first quarter wavelength resonance occurs above the low pass crossover frequency:"
Assuming Lmax is the length in metres, c is the speed of sound at 344 m/s, and the crossover is Hz, I derived the following:
"Adding length will not increase low frequency efficiency, it will only produce peaks in the SPL response. Efficiency of a U or H frame can be adjusted up or
down by increasing or decreasing the cross-sectional area of the cavities."
If I understand this correctly, the -3db point can be lowered by increasing the length or the cross-section, but if the length is increased below L max, then response peaks are created at the top of the usable frequency range. So for a 200Hz crossover, keep the depth of the cabinet less than 16.93"/43cm. To increase efficiency or to lower F3, increase the cross-section of the baffle.
What I find interesting is the recommended Lmax or depth of enclosure has nothing to do with the size of the baffle and too big is worse.
I was familiar with that document, but I found it confusing. On your recommendation, I persevered. I would appreciate someone verifying my calculations and conclusions:
"The maximum length of the U and H frame geometry should be sized so that the first quarter wavelength resonance occurs above the low pass crossover frequency:"
L maximum < c / (4 x crossover )
Assuming Lmax is the length in metres, c is the speed of sound at 344 m/s, and the crossover is Hz, I derived the following:
| Crossover (Hz) | Length (metres) | Length (inches) |
| 300 | 0.2867 | 11.29 |
| 250 | 0.3440 | 13.54 |
| 200 | 0.4300 | 16.93 |
| 150 | 0.5733 | 22.57 |
| 100 | 0.8600 | 33.86 |
"Adding length will not increase low frequency efficiency, it will only produce peaks in the SPL response. Efficiency of a U or H frame can be adjusted up or
down by increasing or decreasing the cross-sectional area of the cavities."
If I understand this correctly, the -3db point can be lowered by increasing the length or the cross-section, but if the length is increased below L max, then response peaks are created at the top of the usable frequency range. So for a 200Hz crossover, keep the depth of the cabinet less than 16.93"/43cm. To increase efficiency or to lower F3, increase the cross-section of the baffle.
What I find interesting is the recommended Lmax or depth of enclosure has nothing to do with the size of the baffle and too big is worse.
My driver (Dayton UM18-22) has a depth of 248mm or 9.76" from the front of the baffle. With a 200 Hz crossover max, the maximum depth of the cabinet can only be 16.93". In an H-frame, the baffle would need to be closer to the front to keep the driver inside the enclosure. Does it make more sense to use a U-frame?
Pretty much that.
Dipole is a dipole
the sides wont do much.
The room itself and floor do way more
and not much control over that.
otherwise sure 16.93 sounds great
Western Electric figured out the baffle size thing 100 years ago
Cabinet depth is 4x4s and 2x4 bracing.
Basically mount it to the wall
and solve most the problems.
Close to the floor helps lower F3 as well.
