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The Return of the Holosonic(sort of)by Craig Schmidt Many years ago, when I was a teenager, Infinity came out with a Loudspeaker called the Holosonic (at least that’s what I think it was called. It’s been almost thirty years!). These speakers were unique in the fact that most of the drivers were firing up from the top of the cabinet out of a hole. I thought this was really neat and wanted a pair but could not afford them at the time. The speaker quickly faded into obscurity and I forgot about them until I read JBL’s cabinet suggestions for the LE8T-H driver. (In my opinion they give good cabinet advise for this driver and in general.) Anyway they stated that the port (they recommend one for this driver) could be put anywhere as long as there were no obstructions. This got me thinking – why not put the port on the top of the cab! So I did. The JBL LE8T-H is a nice full range driver. One area that I feel it excels is in regards to the bass response. It can go deep for what is really a six and half inch driver in an eight-inch frame. The down side (if you want to call it that) is the unit requires a fairly large cabinet up to 4 cubic feet. I decided on a small tower configuration of about 3.4 cubic feet. My choice for material this time was three quarter inch veneer plywood surfaced with red oak. I braced the interior of the cabinet per JBL’s recommendations and used fiberglass and one other material to dampen the innards (see if you can figure out what it is. Look at the photos).
The front panel was doubled to one and one half inches. I installed a four-inch port for this project (which is what JBL recommends). I went a little crazy though with what I used. Parts express sells what must be the top of line port assemblies. They cost about fifteen dollars each and they are flared on both ends. The manufacturer goes into detail as to how and why these are better than plain old tubes (they supposedly reduce distortion). I figured, what the hell, I’ll try them. I am glad I did. They work very well indeed!
Now I was all set to finish things (sanding and staining) when I started reading our one and only website in regards to using what I call helper drivers to augment full range drivers. I decided to try this out on another project that I was building at the time (MCM revised). When I found that it worked well with the little MCM driver I made up my mind to put one with the mighty JBL. After all, I could turn the unit off if I did not like the sound. The problem was I had already cut the hole for the LE8T-H. It was necessary to mount the tweeter on top of the cab. This limited my choice of drivers. Fostex came to the rescue with the T90A (that "a" is for alnico). These units are unreal. They are very small yet weigh a ton. They are built like a fine watch (I’m not kidding). Plus they come with these neat little stands that sit right on top of the cabinet! I used the now famous Fostex R80B L-pad so there was some adjustment to the tweeter output. I also used a 1uf. capacitor per Fostex’s recommendation for the crossover (I know this is a bad word but loosen up, it’s a hobby). The best I could find was a Solen (I had read that there are some paper in oil caps around in this size and voltage range that are designed specifically for this application but the cost is high. Audio Note makes one).
As you can see by the photos, I put everything on top that I could. It worked out very well.
I finally stained the cabinets in cherry satin. I think they look pretty good. Note the beveled front edges. I will not be discussing the sound qualities of the completed units. Someone else will do this (hopefully) in the near future but I would like to give my opinion in regards to the bass response of this so-called speaker system. Having the port on the top of the speaker cabinet may be ugly to some but I think it is a big improvement over putting it near the floor or near the main driver. The bass is exceptional in depth and cleanliness. For what it is worth, this driver can move a lot of air and do it accurately but on the other hand the upper bass to the midrange (where it doesn’t have to move a lot) is also handled quite well. It’s hard to describe. Suffice it to say it’s the best yet for me. I have had many emails about this driver and how to get it. Well if you are thinking about trying a set you better act fast. I talked to JBL the other day and they only had 40 left. I had just purchased an extra set two weeks ago and they had 89 on hand. They are moving fast! One fellow hobbyist bought five! To try and bring this project to the max (?), version two, "Holosonic Minus the Hole" will use passive radiator and Heil motion transformer. Now if you thought the T90A was heavy!
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