Hi Thanks for readings. In a 3-way open baffle speaker it is recommended to use a bass driver with a high qts, 0.7 or greater to ensure good bass response.
Are there any specs to ensure suitability of a driver for midrange duties, over 120hz - 3khz. Low qts is supposed to give a more snappy mid, so is a low qts specification necessary, or are there any other specs to be taken into consideration
Are there any specs to ensure suitability of a driver for midrange duties, over 120hz - 3khz. Low qts is supposed to give a more snappy mid, so is a low qts specification necessary, or are there any other specs to be taken into consideration
The high Q idea really only applies if you are planning to use the driver into the range of its resonance and want to use its natural response to compensate for dipole roll-off.
If you are planning to use active or passive filters to deal with dipole cancellation, the driver Q is less relevant.
Going that far down with the midrange, you need to consider the volume displacement (Sd x Xmax) and baffle size to ensure that you can produce adequate SPL. Linkwitz's site has an Excel spreadsheet to calculate that. It also has lots of other information about what makes for a high resolution driver.
https://www.linkwitzlab.com/spl_max1.xls
https://www.linkwitzlab.com/mid_dist.htm
If you are planning to use active or passive filters to deal with dipole cancellation, the driver Q is less relevant.
Going that far down with the midrange, you need to consider the volume displacement (Sd x Xmax) and baffle size to ensure that you can produce adequate SPL. Linkwitz's site has an Excel spreadsheet to calculate that. It also has lots of other information about what makes for a high resolution driver.
https://www.linkwitzlab.com/spl_max1.xls
https://www.linkwitzlab.com/mid_dist.htm
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120 Hz to 3kHz is a very ambitious range for an OB driver. Getting a driver to play up that high with decent dipole behavior and linear response means something like a 4" diameter driver on a minimal baffle, and that small a driver won't have a prayer of getting down to 120 Hz with any appreciable volume regardless of Qt. A bigger driver would go lower, but with unavoidable response ripples at the top of its range. I generally think that 2 - 2-1/2 octaves is all you can get out of a cone-type OB driver, so lots of OB systems wind up as 4-ways. In my case that means an ESS Heil tweeter above 1500, an 8" from 400 - 1500, a 15" from 400 to under 100, and a pair of sealed subs below that. (The Heil, not being a cone driver, manages a wider range at the expense of a more erratic off axis response beyond 45 degrees, a tradeoff I'm happy to make).
To cover 120 to 3000ish well, I suspect it would take a 12" plus a 6" driver (like an SB17xxx?) crossed around 600.
Bill
To cover 120 to 3000ish well, I suspect it would take a 12" plus a 6" driver (like an SB17xxx?) crossed around 600.
Bill
You’re going to want to extend your OB bass response higher as a design criteria template. 250-400hz is a good target, but the higher you go, the more expense expected for the driver(s) whether it a large cone premium or multiple smaller drivers who’s native response extends higher without breakup and a directivity discontinuity.
If your mid/tweeter desired XO point is 3k, stick with that and design downward……the importance of phase and response clarity from 800hz to 8k cannot be overstated….THIS is what’s between the bread slices and should be your primary design goal. 3-4” mid drivers would be ideal, but 5” mids are acceptable IMO if you’re willing to accept some tradeoffs. My suggestion for those who need the power handling of a 5” cone driver think strongly about a planar/ribbon tweeter solution where the limited vertical dispersion of the tweeter won’t be as destructive to the mids phase pattern. In lies the tradeoff……this is a sit down and enjoy speaker with incredibly wide horizontal response and deep soundstage from the rear facing radiation.
As was mentioned earlier, many designers including my guiding light on OB development, Linkwitz finalized their design template for OB systems as a 4 way. OF COURSE, that template was developed around the choice of preferred, favored or familiar drivers that made sense to the designer to meet specific and often subjective goals for dispersion and timbre. Different choices for different spaces can certainly work within a 3 way solution……..and OB listeners when they’re not lying to themselves are always wishing for that lower extension that an enclosed sub can deliver……just a little bottom end filler so a 3 way OB with near ultrasonic sub support is another way of slicing the bread.