Audax HM170C0 6.5" Carbon Fiber Woofer

I've owned Audax HM170C0 6.5" carbon fiber woofers for well over 10 years in my primary stereo DIY, ported MTM speakers: they are an exceptional value given the incredibly natural sound and flat frequency response they produce. Even after 10 years of use, when shopping for replacements, I have found nothing else (even costing two or three times as much) that can match the value and performance of these drivers, and will be replacing them with new HM170C0s.

I built my DIY MTM speakers in 2004 with these drivers, and as a first time builder, I found these woofers extremely forgiving with regard to driver selection/tweeter matching and port tuning, primarily due to the flat and sweeping frequency response curve: just look at it, I've never seen a 6.5" woofer with a curve so flat. At first I couldn't believe that a 6.5" carbon fiber woven woofer with a vented pole piece and generous magnet could exist at this price point with such a natural top end roll-off. The extended top end of this woofer is so natural that it can practically pair with any tweeter out there, at any crossover point and still sound great. My application is two HM170C0s sandwiching a Morel 28mm titanium dome tweeter, per speaker, crossed over at 2000Hz by an 18db 2-way crossover, using film capacitors, metal oxide resistors, and air core inductors (Madisound LEAP-configured and built for me in 2004).

These drivers sound so natural with vocal and orchestral music when positioned correctly on the baffle with the tweeter at ear height and the listener in the sweet spot. Bass response with two HM170C0s per speaker is also impressive, with solid response well below the typical 80Hz subwoofer crossover point. Because the 6.5" driver is so small, it makes the system fast and responsive to transients....making this driver ideal for anything from dedicated music to home theater applications. I think this driver really shines with bookshelf or MTM designs are front main speakers. This is truly an exceptional value and driver. Anyone who hears the Audax's in my DIY ported speakers is blown away by the midrange clarity and bass response.

There are two minor drawbacks which combined may rob my rating 0.5 of a star: first, there is a resonant peak at about 650Hz, which if not managed appropriately in your build, can cause a ring that will color sound. Secondly, one one of my units, the surround began to unravel to to lack of glue affixing it to the cone. It was a simple fix, but I was a little disappointed to see a manufacturing issue like that on a driver of this caliber. The other three units were fine. In the 10 years I've owned them, they still sound spectacular.