Overnight Sensation Center Channel... Bipole... What? When?
Post date: Dec 4, 2011 7:10:24 AM
At the request of Meniscus, I designed a matching thin center channel and bipole surround for the Overnight Sensation family. I guess I forgot to mention it to the public. So let's take a look at what we have. Both speakers are available as kits from Meniscus, or you can buy them piecemeal. And no, I have no plans of doing a Dayton ND20 version, because I'm tired.
First, the center channel is meant to be very thin to compliment a modern flat screen home theater setup. It uses four of the HiVi B3N and the HiVi T20 tweeter. I am exceptionally pleased with how this speaker sounds. I even left it on mono and listened to music through it for a few days just 'cause it could do it. The cabinet is pretty simple, and calls for 1/2" stock
The crossover for the MMTMM is a 2.5-way, which means that the outside woofers only play "bass duty," while the inside woofers play both mids and bass. The crossover is relatively simple. For inductor L3, you can use an iron-core and it should be no problem.
The other request was for a "bipole" surround. The idea with these speakers is that they are meant to be wall-mounted (typically rear or side walls), and to get the maximum amount of horizontal dispersion possible. They are sealed and are intended to be paired with a sub.
The cabinet with this design follows suit with the "bipole surround" speakers you tend to see in many mid- and high-end THX home theater designs. This means that the cabinet requires some angles. Cutting angles isn't as difficult as you might think; heck I can do them on a cheap circular saw. I tried to be as clear as possible with the cabinet drawing (which assumes butt joint construction. If you're into mitre joints, you're on your own!) The tweeters' orientations are flipped on the cabinet I used, however this is optional. In fact, you could orient the drivers TM/TM or TM/MT or MT/MT, and it would still be fine.
The crossover for the bipole surround shares some similarities to the MTM version of the Overnight Sensations. Basically, we have both woofers run in parallel, as well as having both tweeters run in parallel. So you may notice that the woofer filter is remarkably similar to the MTM. The tweeter filter, however is different. The voicing is very similar to the rest of the Overnight Sensations (of course).
The Frequency Response of the bipole is basically flat when you're OFF-axis (which is going to be most seats in the room). However, if one were to listen to it straight ON-axis, it would probably sound rolled off and a bit muted. (That's Comb Filtering for ya) Again, this is to create the widest dispersion possible.
OFF-AXIS Frequency Response
ON-AXIS Frequency Response