Unibox Volume Calculation Question

[lcolbur1]

Correct me if I'm wrong, but once I input the required driver specifications into Unibox, it calculates a recommended volume, be it for sealed, ported, etc. I'm assuming this volume is accurate, but based on what? I input Dayton's 5" reference driver specs and got a suggested volume of 2.6 liters for two drivers working in parallel. That seems awfully small to me. Raising the volume changes the accompanying graph, but does it do so detrimentally? Should I just stick with calculated volume? I would like these drivers to eventually be used as a midrange.

[5th element]

The trouble is that there is no perfect single alignment for any one driver it's all about what it is you want the driver to do and how you want it to do it, ie how it's going to integrate with the rest of the system. Unfortunately this is something that you pick up over time.

Usually when one wants to use a driver for midrange duty the size of the box is chosen more to optimise how the rearwave of the driver will interact with the cabinet, rather than going for a specific bass alignment. While it is true that the inherent roll off of the box can be tuned and added into the highpass filter to arrive at a specific acoustic target, it is also true that it is very easy to modify the high pass around any size of box you may wish to use. For this reason people usually ignore the box size and build to a size of box that will allow the drivers rear wave to breathe properly.

Some midrange drivers, in optimised boxes, require boxes that are ridiculously small, like 0.5 litres or so and this doesn't really give you a lot of wiggle room with the cabinet, so as to allow you to keep all side walls and rear wall a decent distance away from the driver. Having the driver mounted too close to these causes problems that you'd rather avoid. Certainly not catastrophic problems, but ones you'd rather prevent. In this case most people would ignore the optimum cabinet volume, oversize the cabinet and design around giving the driver room to breathe. On the other hand some midrange drivers would require a ridiculously large box, or maybe wouldn't even have a 'standard' optimum box solution, given their parameters. These are usually drivers with an unusually high Qts. There is certainly nothing wrong with this, the driver will still need a decent amount of space around it to allow it to breathe and the high Qts will be handled in the xover.

Usually speaking you are much better off using a bigger box with a midrange driver as it will also push the drivers resonance lower and if pushed low enough will make designing the high pass filter easier.

[---k---]

Matt gave you the long answer.
Short answer, I think Unibox for sealed calculates a volume based on a Qts=0.7 . Is that the right alignment for you??? Maybe maybe not. Especially for a mid, the roll off likely doesn't occur until below the crossover.

Also, make sure you're hitting the recalculate button frequently. IIRC, Unibox sometimes autoupdates values and other times not.

[fbov]

... I would like these drivers to eventually be used as a midrange.

Unibox and other simulators are intended to model bass response. In your case, a midrange will hit it's highpass filter far higher in frequency than it's natural low frequency roll off. The only thing I'd look at for a sealed midrange compartment is to insure it wasn't so small it limited driver excursion near the HP filter's active range.

5th gets into this discussion...

Frank

[JonMarsh]

Unibox will calculate the volume based on however you set the system alignment, that is, the net Qts. Keep in mind, that is the net volume, you must account for driver volume, ports if used, etc. For sealed, I usually prefer something in the range of 0.5 (critically damped) to 0.6, depending where I want F3 and F10 to be, and the boundary placement and how that can be used to lift the low end.