Ultra-Scrooge Home Theater - 5 piece
I present these "fiscally conservative" Home Theater speakers using inexpensive
drivers from Parts Express .
They consist of the Onkyo 3/4" textile dome tweeter which cost a whopping 69 cents each and the 4" extended range shielded Pioneer driver which cost $.1.25 (.87 as of 12-1-04). These drivers are so inexpensive because they are special "buyouts" from the manufacturer.
I flush mounted these unusual shape tweeters by cutting the round hole for magnet clearance first and placing the tweeter on the face of the speaker. Then I traced the outline of the tweeter, removed it and freehand routered with a 3/8" straight bit to the edges of the traced outline. OR . . . you could just cut the round hole and surface mount it.
The Pioneer driver is loud and rowdy, the Onkyo is smooth and fairly quiet. Not a good match but we can even things up by using an inductor large enough to bring the Pioneer down near the Onkyo's level.
Since this is a ultra low-budget project, I used a simple 1st order crossover with impedance compensation on the Pioneer drivers. I designed several 2nd order crossovers with Speaker Workshop using the PE posted frequency response files but after doing many actual acoustic tests with Speaker Workshop and then listening to several types of music back and forth, I have come to the conclusion that the 1st order crossovers shown here will work just fine for the use they are intended for - inexpensive home theater speakers.
NOTE: The 2 Pioneer drivers are connected in series (minus of first woofer connects to plus of second woofer) for the MTM version. The reason for series connection is with typical parallel wiring, the NSB's gain more volume and they are already louder than the little Onkyo tweeter. Also in keeping with the low budget approach, the series connections make for a friendlier load on low end amplifiers.
I initially did not use an impedance compensation circuit (Cz1 & Rz1) on the crossovers as I could not hear much difference and it added over $1 (gasp!) to each speaker. If you are a genuine scrooge you can leave those components out, but after doing impedance tests, I could see that the overall impedance absolutely skyrockets after about 3000 Hz. While this does not make or break the design, it does affect the crossover point and the speakers do have a slightly smoother sounding upper end with the compensation.
Use the cheapest crossover components you can buy. Simple 20 ga. coils, NP caps and wirewound resistors (5 watt for Rz1) will suffice. The shown component values do not have to be exact. If you have 5.6uF or 8uF caps on hand, use 'em. Got some used .6mH or .8mH coils, they'll work too - I doubt you would hear the difference.
You WILL need a subwoofer for full "home theater" effects - or even
most music with these little guys.
Construction is simple butt joints with carpenter's glue. I had some 3/4" particle board which I used for the fronts since I wanted to flush mount the tweeters. The rest is 1/2" MDF. I plan to router the edges, make grille covers and paint them satin black. DONE! See pic at top of page.
Again, nothing has to be exactly as I've presented it here. The boxes could (and should) be bigger, but normally "home theater" speakers are small so they are easier to place and blend in .
As an option, I've finally constructed compact rear channel boxes with a simple full range (no tweeter). With just an inductor coil of .7mH in series with the driver and a box size of 6x6x8, these actually sound much better than I thought. The enclosure is sealed with a fistfull of polyfill stuffing. These small boxes would be nearly invisible tucked in the upper corners of the room.
Don't expect these to be audiophile quality speakers. However, they do sound quite good for what they are and most "consumer grade" ears would be impressed with them. I consider this a fun project which can then be given away as a gift. You can be a scrooge with a heart!
If you really want to make silk purses out of these sow's ears drivers and can stand to part with a few more dollars, step up to Dan Carroll's UBHT speakers which are proper MTM speakers with the NSB's wired in parallel. This requires a better LOUDER tweeter and a bit more crossover cost as well as a decent amp to handle the impedance load.
Better yet, check out Parts Express for some of their other Buyouts and special deals. There is always plenty to pick from.