November 2011

Merrill DCA5.5 (Almost) Full Range Driver
Article By Tom Dooling

Difficulty Level

  I always look forward to evaluating a new speaker. It requires critical listening for extended periods which is something I really I enjoy. The Merrill DCA5.5 is a roughly 5" diameter full range speaker available from diyparadise.com. This driver was recently redesigned and features a much heavier cast frame than it’s’ predecessor.

Background
For this review, I constructed a tried and true folded line transmission line enclosure out of 0.75" medium density fiberboard (MDF). I flush mounted the driver in the top of the enclosure which was 24" tall overall. The cutoff frequency was approximately 65 Hz (set slightly higher than the 60 Hz free air resonance of the driver) with a line length of 52". I did not taper the line, and it was stuffed with polyester fiberfill. All listening was done with the speaker on stands to elevate them to ear level with a 10 to 15 degree toe in. I chose the transmission line enclosure since Yeo wanted a non-resonant enclosure and I have experience with folded lines. It is possible that a much larger horn enclosure would provide deeper and extended bass response, but the small cone size of the driver will still be the limiting factor.

In theory, full range speakers provide sound that radiates from one coherent point and avoid the difficulties inherent in a crossover network. Unfortunately, physics works against the one driver approach; a large driver that produces deep bass is not well suited to high frequencies and a small high frequency driver will be subject to high levels of distortion reproducing very low frequencies. The challenge is working out an acceptable compromise for both.

This driver holds tremendous potential for the do it yourselfer. Be advised that you are buying a raw driver, not a completed speaker, but it truly is an exceptional driver. Yeo at diyparadise asked me to design a non-resonant enclosure and keep it as small as possible with 24" as a maximum height.

The low sensitivity (88dB/W/m) has to be considered when selecting or evaluating amplifiers that will work well with this driver. I evaluated these speakers in three different rooms in my house and used amplifiers from 15 to 110 watts RMS with excellent results.

Set Up
My main listening room is fairly “live" with hardwood floors, with not a lot of furniture and a listening position 9 feet away from the speakers that were 8 feet apart. They were driven by custom made 25 watt push-pull 300B triode amplifiers that feature cathode feedback on the custom wound output transformer.  I also evaluated them in a secondary listening room which is 12 by 22 feet and is carpeted and has more furniture. The Merrill’s were again eight feet apart and slightly toed in. Listening position is closer to 12 feet in this room and the speakers were driven from a Sansui AU-D11 solid state 110 watt per channel integrated amplifier. The third listening position was in my home office where they were driven from a 12 watt per channel MOSFET output amplifier that is biased heavily into class A operation. The speakers were slightly above ear level and 4 feet away, 4 feet apart, 10 degree toe in. In the office the source was my computer Prodigy HD2 soundcard.  (Note: I would not recommend very low power SE amplifiers that are frequently paired with high efficiency full range drivers be used with the Merrill’s. The 12 watt amplifier I used drove them quite well, but I never really pushed the SPL.)

Listening Test
While it is difficult to describe the sound of a speaker; I think the best way to describe the Merrill DCA5.5 is effortless when it is reproducing what it does best. Mounted in their transmission line enclosures, the Merrill’s provided outstanding imaging and presentation. They have a very fast dynamic attack and no evidence of ringing on the decay. The high end is silky smooth with a delicate presentation.

Where these drivers really excel is on solo piano music, acoustic music and in their vocal presentation. Their midrange compares favorably to any speaker I’ve heard regardless of price or size. I listened to these speakers for over 4 months in the rooms I have described and with a range of program material that would take 20 pages to list in its entirety. In a brief summary, selections from k.d. lang Hymns of the 49^th Parallel, Linda Ronstadt Cry Like a Rainstorm and Howl Like the Wind Court, Joni Mitchell’s Court and Spark and Sarah McLachlan U Want Me 2 were breathtaking in their lush reproduction. Male vocals were outstanding as well. The Rolling Stones Has Anyone Seen My Baby? [Bridges to Babylon], as well artists like Neil Young, Bruce Springsteen, Mott the Hoople, U2, Blues Traveler and many others were exceptional. Piano tracks form Jim Brickman showcased the attack and decay properties of the driver.

The biggest shortcoming of the DCA5.5 is the bass response, and again that may be of special interest if you like to experiment with drivers. I believe the bass response could be improved at least somewhat in a horn type enclosure. But ultimately the small physical size and limited excursion would limit its’ performance in a full range speaker. I realize there will be people that disagree, but from my experience, you can’t cheat physics and strong bass requires moving lots of air and a larger driver. When I auditioned the Merrill with tracks from both the Titanic and Master and Commander soundtracks, the lack of the lowest octave was very evident. The performance of the Merrill’s was improved considerable when I turned on the powered subwoofer I have in my main system.

When I compared the Merrill DCA 5.5’s to my two reference speakers, the DCA5.5 had equal or better midrange and high end but lacked the low end. Their low efficiency required also fairly substantial drive power but so do my main speakers. My main loudspeakers are two-way Morel drivers in a sealed enclosure with a similar sensitivity. My secondary system has an 8 inch Dynaudio woofer in a transmission line with an ESS Heil AMT-1 handing the midrange and high end.

My office system has Fostex full range ported speakers. The Merrill’s were a big upgrade in clarity and attack compared to the Fostex speakers and the difference in the bass response was not as much compared to my other speakers.

Conclusion
This is a little difficult since you are buying a driver and mounting it in the enclosure of your own design and I can only rate it from my experience. As a pure full range driver, the Merrill DCA5.5 ultimately comes up a little short as the bass is lacking enough that on some material they just sounded too thin. I think it would be well served as the front and center speakers in a home theater application. I also think it could be an outstanding main speaker in a home music system if you have sufficient power and couple it with a low frequency driver that can handle the program material below 60 Hz. I would go with a bi-amp set up and active crossover in that application. Or it could be used with a fast low frequency driver and crossed over at closer to 500 Hz with a passive crossover.

Since it is after all aimed at the DIY market, it should get a lot of props for the tremendous potential and versatility it provides to a speaker designer.

Associated Equipment
Amplifiers:
Custom made 25 watt push-pull 300B triode amplifier
Sansui AU-D11 110 watt solid-state integrated amplifier
Custom made 15 watt solid-state amp, JFET input, MOSFET output.

Marantz CD-63SE CD player
Modified Kenwood Preamplifier drives the 300B amplifier.

15 inch closed box subwoofer with an active crossover and dedicated 200 watt amplifier was used for some of the listening tests.

Specifications
Type: full range driver in a transmission line enclosure
Driver: Merrill DCA5.5
Frequency Response: 65 Hz to 20 kHz
Sensitivity: 88dB/W/m
Nominal Impedance: 8 Ohm
Power Handling: 50 to 100 watts
Available From: diyparadise.com/...products_id=133
Price: $145/pair