From the HOQS community. Originally posted in the HOQS Facebook group and republished here with permission. See the original post with measurement videos.
The finishing touches that fully optimized the HOQS Playa Edition Type “O” Paraflex CRAM! 2×18 subwoofer were worked out in the real world, through experiments carried out by Justin Spinks of Dux Audio, Noah Johnson of Subcaste Sound (both in Colorado), and Eric Ross of WAAT (Wiggly Air Audio Technologies) in Florida.
As it turns out, shifting the baffle forward a bit (as these Playa Edition designs do) more than compensates for the change in air volume caused by the forward-facing driver mounting. Because of this, the cabinet’s front panel needs to be extended downward (in this case about 7 inches) to lengthen the HTR path. That brings the resonator tuning relationship back into the optimal range, since the cabinet’s fundamental tuning has shifted lower in frequency and the cross-sectional area of the HTR section has been reduced somewhat.
This optimization has a profound effect on performance in the time domain. The waterfall comparison below shows decay time much reduced (improved) between 80 and 100 Hz, centered around 90 Hz. What was previously seen and heard as stored energy, or “ringing,” around 90 Hz is now greatly reduced, practically alleviated, and basically resolved.
The result is more accurate reproduction of music (or live reinforcement), which subjectively can be expected to sound cleaner and tighter, more detailed and musical, and less fatiguing at high levels. The crossover point can also be set higher without running into problems. Most people don’t use that extended upper bandwidth, but it’s there if you need it.
What we learned here has been applied to the new “O” CRAM! 2×21 subwoofer, also a Playa Edition style. Its PDF was produced by Robert Moon of Exxotic Audio (just like the 2×18 version), with support from Ty Cention of HOQS Australia and Kaironex Audio and Visual; Robert continues to build the PDFs in Ty’s format.
A 9-inch front panel extension was also tested, but it offered little additional benefit. We preferred to keep the mouth area on the large side of optimal so that adding a grille to the cabinet won’t noticeably harm performance.
The measured frequency response produced by the F185C is a little different from that of the N185C. The N185C has a slightly stronger motor and doesn’t displace as much air in the first section of the LTR, so it looks mildly underdamped in comparison. Keep in mind these measurements are taken at very low power. At higher power (typical operation), the N185C’s curve is expected to look more like the F185C’s, due to inevitable parameter shift as the coil moves away from center and warms up. Consider it a form of headroom for the N185C: a fair amount of parameter shift can occur before its curve resembles the small-signal F185C measurement.
With the baffle and drivers arranged this way, the additional air volume in the first section of the LTR path should benefit the 2×21 cabinet nicely, since 21″ drivers (such as those recommended in the 2×21 plan) typically prefer a little more air volume to work with.
Note: in the “O” CRAM! 2×12 subwoofer, the same real-world optimization required a small adjustment to the size and position of the cabinet’s mouth. That change is in the current revision of the PDF.
Original posts
- This update, with measurement videos (HOQS group)
- Type O CRAM! 2×18 Playa Edition (HOQS group)
- Type O CRAM! 2×21 Playa Edition (HOQS group)
The Type O CRAM! 2×18 and 2×21 Playa Edition plans are in the HOQS Knowledge Base, and WAAT cuts both as CNC flat packs. Ask a WAAT builder about yours.
