This blog is an attempt to document the design of a budget three way speaker. Although it may never be built, this blog will serve as my mental notepad where I can consolidate my thoughts and piece together some theory that will produce a speaker with the following attirbutes:
1.) Reference quality reproduction of only music. However, this is a very vague statement. Therefore, I will break down this requirement into the following sub-categories:
a.) Flat frequency response from 35Hz - 20kHz.
b.) Lowest possible harmonic distortion within the other given parameters.
c.) Best possible off-axis and power response.
d.) Best imaging and largest soundstage possible.
2.) The lowest cost drivers within the other given parameters.
3.) The simplest, yet most effective crossover, in keeping with the budget mentality.
4.) The ability to model and build without advanced measuring equipment.
Some of these goals appear to be at cross-purposes; specifically, lowest possible harmonic distortion and budget drivers. The goal will be to simultaneously maximize both.
One of the first decisions made was to make this a three-way. To make it a two way and achieve the extension desired would require a fairly large woofer. This in turn would require a robust tweeter that could be crossed low enough. The cost of these components would exceed the budget target. By making it a three way, there is more flexibility in choosing a low cost, high performing driver since it's required usable bandwith is smaller.
Three drivers have been chosen:
I decided early on that I need an 8" to get the extension I wanted at acceptable levels of distortion and excursion.
The SD215-88 Dayton 8" Shielded DVC Subwoofer. $28.48. Not only is this one of the cheapest 8" woofers out there, it also modeled the best of all that I played with, achieving the lowest extension and smallest enclosure, all staying within an acceptable range of xmax and group delay. It has a relatively high sensitivity and it's aesthetics are up to par having a stamped frame. It is the perfect woofer!
The B4N HiVi 4" Aluminum Midbass. $14.88. This may be the cheapest 4" Midbass out there. It was chosen for a variety of reasons: It shares the same cone construction as the B3N, which has been tested by Zaph Audio and found to have a favorable distortion profile. It's sensitivity is high enough to mate with the the SD215-88 even if full BSC were used, and the aesthetics are again favorable. Being a 4" cone, the idea was that it's frequency response wouldn't break up until higher so that a cheap neo dome could be used, while still being large enough to mate to an 8" without running out of xmax.
The ND20FB-4 Dayton Rear-mount 0.75" Neodymium Dome Tweeter. $5.88. Again, one of the cheapest neo tweeters out there. It was tested by Zaph Audio and found to have an easily workable frequency response.
Incedentally, this project is looking very similar to the Cinderella's found on Curt's website, except that he uses 4 B3N's, the Dayton Classic 8" and a slightly different neo tweeter. This makes me think I may be on the right track in my thinking, and is again, an instance of me finally understanding just how brilliant someone's existing design is.
Whether it is his influence or not, the enclosure I decided I wanted looks very similar to his:
It's footprint is only as large as it needs to be to accomodate the 8" near the floor and it tapers to the top where the midbass and tweeter are. The aesthetics, shape and form factor of the enclosure I've designed greatly appeals to me. The sketch is only preliminary, and the bracing and internal volume needs to be configured correctly still. I have questions yet to be found or answered about any adverse effects of having the woofer separated by such considerable distance from the midrange. Crossover points will be a major study.
More to come later.