| It was as far back as 2010 that I presented the Merlin. The Merlin is an interesting design in that it is a DCR (a Dual Chamber Reflex). Internally, there are two chambers with three tuning ports altogether. The net result is you not only get the low bass as in a normal bass reflex, but the other chamber produces a wonderful mid-bass.
Since I’m in the process of testing horns, it would be a good opportunity to test out the Merlin again. This time round, instead of the Seas 27TDFC dome tweeter, I will replace it with a Pyle PH565/PDS182 combo and time align it with the Dayton RS180S midwoofer. |
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| Non-Time Aligned Response
Fig 1 shows the summed response of the Merlin-II without time alignment. Electronic crossover was set at 2kHz (24dB/oct). No CDEQ was used. From the plot, we can see there’s strong cancellation to the right of the crossover frequency. |
 (Fig 1) Merlin Frequency Response. Vertical Scale = 5dB/DIV |
| Reversing Phase of compression driver
Fig 2 is the summed response with the Pyle PDS182 wired in reverse phase. Now, cancellation is seen on the left of the crossover frequency. |
 (Fig 2) Summed Response with PDS182 in Reverse Phase |
| Applying Delay
With the compression driver still wired in reverse phase, a delay was added to the RS180S until a deep notch appears (Fig 3). This is an indication that the two drivers are time-aligned. |
 (Fig 3) Delay Added to Dayton RS180S with PDS182 in Reverse Phase |
| Time Aligned Response
In Fig 4, the compression driver is re-wired back to normal phase. The summed response (Red trace), shows no cancellation on either side of the crossover frequency. |
 (Fig 4) Summed Response with PDS182 re-wired back to normal phase |
 (Fig 5) Time-Aligned Frequency Response of Merlin-II. Microphone at 1 meter tweeter axis, 5 msec Gating, No Smoothing. |
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| Merlin-II Time Aligned Frequency Response
Fig 5 shows the expanded view of the Merlin-II response. Disregard measurement below 500Hz as they are out of the gating range. The missing chunk of frequencies from 100Hz – 200Hz is due to floor bounce. Nothing to worry about. What is interesting is from 50Hz – 100Hz. This is without any electronic bass boost. You won’t get this amount of bass with a 7″ midwoofer in a normal bass reflex. This is where the Dual Chamber design shines. |
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| Sound Quality
As I was hoping for, the slight grittiness in the highs vanished when the drivers are time aligned. Sibilance sounds much smoother too. The Merlin-II can’t get better than this. And the best part, it’s only a two way. No subwoofers needed. |
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December 12, 2016Projects