New member here, great Forum! I haven't built a box since the 70's, and things were simpler then... I've got a design in mind, but I can't seem to get consistent results with any programs I've tried (WinIsd, etc), and was hoping for some assistance. Here's the driver and specs:
HiWave BMR12 Compact 2" Full-Range Square Speaker 12W 8 Ohm 299-208
Power Handling (RMS) 12 Watts
Power Handling (max) 24 Watts
Impedance 8 ohms
Frequency Response 150 to 16,000 Hz
Sensitivity 83 dB 1W/1m
Voice Coil Diameter 1"
Resonant Frequency (Fs) 164 Hz
DC Resistance (Re) 8.13 ohms
Voice Coil Inductance (Le) 0.12 mH
Mechanical Q (Qms) 2.37
Electromagnetic Q (Qes) .89
Total Q (Qts) .65
Compliance Equiv Vol (Vas) 0.0063 ft.³
Maximum Lin Exc (Xmax) 3 mm
Surface Area of Cone (Sd) 17.2 cm²
My plan is to use 16 of these in each enclosure vertically as a line array. The usage will be low power PA for live music in a very small venue. BTW, I don't expect miracles in low end response.
Could anyone give me their calculations for sealed and ported boxes?
Thanks much!
HiWave BMR12 Compact 2" Full-Range Square Speaker 12W 8 Ohm 299-208
Power Handling (RMS) 12 Watts
Power Handling (max) 24 Watts
Impedance 8 ohms
Frequency Response 150 to 16,000 Hz
Sensitivity 83 dB 1W/1m
Voice Coil Diameter 1"
Resonant Frequency (Fs) 164 Hz
DC Resistance (Re) 8.13 ohms
Voice Coil Inductance (Le) 0.12 mH
Mechanical Q (Qms) 2.37
Electromagnetic Q (Qes) .89
Total Q (Qts) .65
Compliance Equiv Vol (Vas) 0.0063 ft.³
Maximum Lin Exc (Xmax) 3 mm
Surface Area of Cone (Sd) 17.2 cm²
My plan is to use 16 of these in each enclosure vertically as a line array. The usage will be low power PA for live music in a very small venue. BTW, I don't expect miracles in low end response.
Could anyone give me their calculations for sealed and ported boxes?
Thanks much!
It's a good job that you're not expecting miracles in LF response, because you won't have any. 
Stock sealed Qtc 0.707 = total 15.2 litres for 16 drivers. They don't need much; they're not really full range drivers (no 2in unit is).
Like most tiny drivers with a high Fs, they're not well suited to vented boxes. If you felt you really must do that, I'd be inclined to 12 litres total tuned to a nominal 125Hz; 2 x 5cm diameter vents, & then line those vents with damping material (carpet underlay or similar) to damp the peaking response. Since you've got 16 of the drivers in place excursion is not horrific if you go easy with the volume knob & avoid feeding them too much LF content.
Attached, yellow = above mentioned sealed, blue vented before the vents are damped. FWIW.
Stock sealed Qtc 0.707 = total 15.2 litres for 16 drivers. They don't need much; they're not really full range drivers (no 2in unit is).
Like most tiny drivers with a high Fs, they're not well suited to vented boxes. If you felt you really must do that, I'd be inclined to 12 litres total tuned to a nominal 125Hz; 2 x 5cm diameter vents, & then line those vents with damping material (carpet underlay or similar) to damp the peaking response. Since you've got 16 of the drivers in place excursion is not horrific if you go easy with the volume knob & avoid feeding them too much LF content.
Attached, yellow = above mentioned sealed, blue vented before the vents are damped. FWIW.
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I appreciate the responses! Scott, your graph agrees with what I'm getting in WinISD, so it must be correct. I'm having a hard time wrapping my head around those numbers, it seems drivers have advanced a lot since I last worked with this.
I'm guessing it's the Xmax - this is much higher than I recall from way back when!
I'm guessing it's the Xmax - this is much higher than I recall from way back when!
No argument on that one Greg, although based on a quick look through Unibox (I didn't do the manual math as I had to go listen to a paper) modest damping only drops it by a litre or so. That said off the top of my head I can't remember how they define 'light'. I suspect I'd want a bit more than that, so I'll take your Vb as read. Out of interest, which equation did you use? One of these days, I'm going to have to get around to writing an Excel file based on WML... I might even do that in the morning. Time I did.
I suspect I'd want a bit more than that, so I'll take your Vb as read. Out of interest, which equation
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Within the inherent compromises, sort of. As GM & I were discussing, you could probably lose a bit off the depth in practice assuming it's well stuffed & you want the flattest possible sealed box alignment. The larger volume, stuffed, will drop Q somewhat.
Couple of points: you'll need ear-height to be lower than the top of the array, or the HF will vanish since (at least in the Fresnel zone) arrays are highly directional vertically. It will probably already be a bit attenuated through the usual output lobing, although the small size & physical character of the BMR units should compensate for a reasonable proportion of that. And if you can make a longer array with a few more drivers, so much the better.
You're welcome!
This isn't necessarily a good assumption, especially if you're using the basic WinISD instead of the Pro version, which yields a flatter response over a wider BW [the response goal of a max flat alignment] with the smaller M/S calculated net Vb [box volume] than the Pro's calculated 15.13 L one.
Yeah, materials and manufacturing advances in recent decades now allows for some pretty awesome designs, especially WRT power handling. I have a pair of old Babb prototype 'full-range' drivers that are truly 'full-range' down to 20 Hz/F3 in a 1 ft^3 sealed cab thanks to having a 32.48 mm Xmax and can handle 400 W transients! A pity it's now a long time stillborn project since there's been some huge advancements since 2003.
GM
Right, I was just wanting us to be on the same 'page', not necessarily saying the smaller, minimally damped cab would be the best overall choice for the intended app, though in this case it is from a power handling POV.
GM
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