Using coaxial products for DIY monitors and home hi-fi applications

Eminence offers coaxial woofers in 8", 10", and 12", called the Beta-8CX, Beta-10CX and Beta-12CX, respectively. These woofers have a threaded pole-piece so that a screw-on, 1" exit high frequency driver can be attached to form a coaxial set up. The woofer has a screen type dust cap, which allows the output of the high frequency driver to pass through the center. A small, 60 degree conical horn is attached to the top of the pole-piece beneath the dust cap. In my experience, it seems that our coaxial products are misunderstood and do not have enough exposure.
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In this article, I hope to raise awareness by sharing my own experiences and show how you can use them to create a great monitor or home hi-fi speaker.
Several years ago, I was finishing my basement to add more living space for my growing family. My wife gave me permission on nearly half of the basement addition to build a man cave"/entertainment room. Since I work in engineering at Eminence Speaker (and my wife didn't really think through the prospect of turning me loose on our basement) I wanted to install an impressive, over-the-top sound system for home theater and general music purposes. I enlisted the help of Jerry McNutt, who is one of our design engineers, a passionate sound enthusiast, and a great box builder. We decided to use the Beta-10CX, combined with the ASD:1001 for the front, rear, and center channels. I have a 5.1 system (Yeah, it"s been a while!). We decided on a 1.52 cubic foot enclosure, tuned to 60Hz for the front speakers and center channel. We also added about a pound of pillow stuffing from Walmart for sound absorption. It was just left loose in the box. I mounted the rear speakers in the ceiling and used the space between the floor joists as an enclosure. We figured this would be sufficient, as there"s not much information sent to the rear channels, and they're right over my head when I sit on our couch to watch a movie. This setup sounded pretty good with our stock crossover, but we decided to make it even better. Jerry asked his crossover knowledgeable friend, Leo Frank, to assist. They used a spectrum analyzer to design an optimal crossover, which included padding for the tweeter. Eminence' stock board crossovers are nice for off-the-shelf products but they are not optimized for any particular system and do not include padding for the tweeter with the new crossover, my speakers sounded incredible.
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They were dynamic, articulate, and focused, which are all great advantages for the application. The high SPL of the system was also a plus. I only had about 30 watts per channel of power available. I also incorporated a 4x15" subwoofer enclosure, but with hand-built, custom woofers (still Eminence, of course) in a rather odd cabinet design. I apologize, but the full details of the sub will not be part of this article.

DYI stage monitors

A few years later, my band wanted to get away from in-ear monitors and decided we needed some really good floor monitors. Again, our coaxials came to mind as a great possibility. We preferred a 12" woofer for this application, so I decided to use the Beta-12CX and the ASD:1001. I also wanted to try the same crossover that we used in my home theater project.  

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Jerry built a test box that was sealed and 1.21 cubic feet. I was skeptical that a sealed enclosure would produce enough bass. However, we tested it with a lot of different types of music, and surprisingly, it stayed very clear, tight, and punchy. This was good news, because it kept the enclosures simple and in a smaller footprint than a ported enclosure would allow. We also stuffed the box full of fiberglass. This really cleaned up the mids. You could certainly use other acoustic absorption materials. I"m not sure exactly how much we used, and it"s basically a preference decision on how much to use. You need to add material until you"re satisfied with how it sounds. Jerry built 4 enclosures for me and we started using them in the band. We were very satisfied with the sound quality and how much better we could hear ourselves. We were actually able to lower our stage volume because we could hear so much better. Stage volume was always a struggle before.

The results were so good that Jerry built more for himself and a close friend that does a lot of sound projects. We also started sharing the design with customers that we felt could benefit from it. A local church camp was building a new worship center on their campus and came to us for help on the sound. We shared the design and they built monitors for their stage. They also hired one of our customers that designs and builds high-end line arrays to install their front of house. As they were sound checking the install, our customer heard the monitors and asked us about them. He was very intrigued and measured their performance with a hand-held spectrum analyzer. He was blown away by the response curve and said they were nearly perfect without any EQ. He eventually adopted the design and added it to his own product line. Jerry and I convinced our sales and marketing to add the crossover to our line. It"s now called the PXB2:2K5CX.