In several instances on ASR, it has been stated that the Purifi's new 6 inch woofer is best with a passive radiator. They may answer this soon as I understand SPK6 will use its passive radiator (pr). Rick Craig used the SB 5x8 pr with the Purifi woofer in his Purezza. He also used it in his Integrity. Since I built the Integrity, I have the same SB pr. Now that I have a SPK5, it was not all that hard to create a new back baffle with the SB pr instead of the S-shaped port. It was a bit challenging due to the pr height, but moved the speakon towards the corner to fit. Also, note that I had removed the SPK5 brace (as cabinet is already solid, did not find any indication that altered results at middling SPLs used here.)
While have been building subwoofers for about 3 decades, had never designed one with a pr. Since I use Bassbox Pro and it can model pr alignments, thought I would start with modeling the SPK5 with the SB pr. The vented SPK5 has an f3 of just below50 64 Hz, so was pleasantly surprised to find the pr model f3 was lowered to 40 48 Hz. Along with no major indication of the port resonance exhibited by the vented SPK5 model, the initial checks looked promising. Here are my baseline SPK5 measurements with REW...
SPK5 frequency response (1 meter, 75db, 3ms gate)
Ignoring the low bass (gated out), this aligns well with other public frequency response measures of the SPK5.
SPK5 woofer nearfield (0m, output level maintained, no gating, 1/24 smoothing)
Using105 dB line as reference, 3 dB down is 50 Hz See later post, but the updated f3 is 64 Hz. So, seems to match well with Bassbox modeling...
SPK5 port (0m, output level maintained, no gating, 1/24 smoothing)
Note the prominent port resonances at 400 Hz, 800 Hz and 1.2 kHz (all projected in the Bassbox model). While not shown, even without gating, there is no obvious sign of the 400 Hz port resonance affecting the on-axis response. However, given that the port is on back baffle and room modes likely dominate, this is not a definitive measure. Will have to wait for Amir to remeasure to see what Klippel NFS finds.
While have been building subwoofers for about 3 decades, had never designed one with a pr. Since I use Bassbox Pro and it can model pr alignments, thought I would start with modeling the SPK5 with the SB pr. The vented SPK5 has an f3 of just below
SPK5 frequency response (1 meter, 75db, 3ms gate)
Ignoring the low bass (gated out), this aligns well with other public frequency response measures of the SPK5.
SPK5 woofer nearfield (0m, output level maintained, no gating, 1/24 smoothing)
Using
SPK5 port (0m, output level maintained, no gating, 1/24 smoothing)
Note the prominent port resonances at 400 Hz, 800 Hz and 1.2 kHz (all projected in the Bassbox model). While not shown, even without gating, there is no obvious sign of the 400 Hz port resonance affecting the on-axis response. However, given that the port is on back baffle and room modes likely dominate, this is not a definitive measure. Will have to wait for Amir to remeasure to see what Klippel NFS finds.
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