the image shows a high quality midbass unit unfortunately being marketed as a subwoofer

Some thoughts on subwoofer parameters

By Mehta | Audeo | 30 Apr 2021

10" and larger woofers with bandwidth potential <60hz are the only types of drivers making suitable subwoofers for non-ported systems.

Mathematically (and therefore physically), it is possible to create a ported system tuned in such a way that even a 4" driver gives deep bass. I'd advise against thin and tough plastic ports. My 2nd design for low SPL was a 4" tang band FR in a damped 6L bass-reflex box. I decided to try some port loss calculations, and realized a partially damped cardstock port would offer more natural extension and very low distortion. Now, where to find a 4cm diameter cardstock tube?

My domestic partner eventually insisted that we start throwing away toilet paper rolls again. She's exceptionally tolerant of my antics. Admittedly, having empty TP rolls collected all over the house in the name of sonic enterprise should be embarrassing for anyone. Something to note is how Onken ports model very poorly if the traditional port losses aren't accounted. Although Onken ports are not relevant anymore in their original form, it's helpful to understand how much flexibility there is in terms of porting systems.

Some recent 4" and 5" drivers have goofy marketing departments calling them "subwoofers." They are excellent midbass units, and a good designer can get a bit of sub-bass response from a midbass driver, sure. It's not just a matter of F3. Overall sensitivity and power handling affect the performance significantly. 

Bandwidth potential can be more or less equated with F3. <60hz will give a much deeper response than traditional woofer F3 of ~100hz. I'm using a 10" driver with an F3 of 55hz, 12" with 48hz, and another 12" with 40hz. The 12" drivers are superior, with easily 3 - 5dB sensitivity over the 10.

There is a pair of 15" drivers with F3 ~33hz sitting in my workshop. 12" is manageable, 15" the VAS starts to get seriously unruly, especially with a high quality factor, so I have not deployed them as of yet. Losses and damping have a huge effect on box size requirements. Read Edgar Villchur's patents. EV (??) blatantly ripped him off and easily defended themselves in court a decade into his patent, so no worries there.

Have fun, and always trust your ears more than the calculator. I will share my thoughts on "accurate measurements" and how much they matter in terms of creating a working design in a future post. 

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