Hey Guys,
You caught me in a rare moment here. After jumping through a bunch of hoops to get brochures printed at the very last minute in time for RMAF, I forgot one very important printing task - BUSINESS CARDS! Argrrgghhh!!! So here I am at 11:30PM CST, waiting for my son Jason to update the logo file and insert it into the cards, then waiting forever for them to print. I only have to get to Chicago Midway by noon tomorrow in order to catch my flight. And I still have packing to do. Duh...I must be some kind of glutton for punishment or...just STUPID!!!
So...while I wait for my dinosaur printer to spit out cards, I might as well try to answer
brj's question.
OK, what's with that stupid lip? The stupid grill frame - that's what. Of all the darn things that are a pain to make, you wouldn't believe what a pain in the neck a stupid little grill cover can be. We had to include one in this series as seeing that it's targeted as a more affordable product, more younger families are likely to purchase them. Young families have little kids. Enough said...gotta have a grill.
Didn't want to include the cost of building one out of individual sticks - easier to program the CNC and make one out of 1/8 inch hardboard. Cover it with 3/16 inch acoustic foam and you have a frame. Problem is...the edge of the hardboard would show if it's not recessed. Hence, the recess. And NO, I'm not going to stretch cloth around them - too much fuss at this price-point.
BLASPHEMY!!! What about all that nasty edge diffraction? What edge diffraction? We ain't got no stink'n edge diffraction - at least not at any wavelengths that little recess will affect. That's the beauty of the waveguide. By the time the wavefront reaches the mouth, it's total surface area is large compared to the dimensions of the recess. I could get more technical and talk about how the acoustic impedance of the wavefront is lower and therefore more immune to boudary effects, but I think you get the point.
Essentially, the waveguide allows the wave to "launch" away from the front panel without ever really "seeing" the edges of the enclosure. One evidence of that is the controlled beam-width. If the dispersion of the tweeter was wider, as in a conventional baffle mount, then the wavefront would see the dicontinuity at the enclosure edge and diffract off of it. The increased directivity of the off-axis response pretty much proves there's no energy reaching the enclosure edges. The enclosures outer edges reside outside the "window" being illuminated by the waveguide.
Of course if the wavefront did reach the enclosure edges, then you'd have all the nasty little ripples in the magnitude response and also a correspondingly smeared envelope response in the time-domain. You know, the same problem almost everybody else has.
Now, at longer wavelengths there is some baffle step/diffraction effects, but the wavelengths are so long that that getting rid of that little recess will have virtually no effect in eliminating them. That's where compensation in the crossover comes in. Do our systems have zero diffraction? No, but it's as low as theoretically possible in enclosures the size most people are willing to accept in their homes.
In fact, that's why the Timepiece 2.1 and all the other products in the Millennial Reference Series are basically boring rectangular boxes. A simple box such as that is the easiest/least expensive to build - it offers the most bang for the buck though. But it also produces just about the worst possible level of diffraction if it's used with a conventional baffle. We can get away with it though because of the waveguide and pass the savings on to the customer. Well, the waveguide adds cost, but at least you're paying for an optimal solution, not a half-a**ed one.
But there again, that's why you see so many companies rounding the edges of their enclosure or making pyramid shapes, using felt rings or foam around the tweeters, and even more exotic forms. They're all desperately trying to reduce diffraction effects. Besides - they look cool - right?
Don't kid yourself though, you're paying for all that artistic balogna, and if it was an optimal solution, I guess it wouldn't be so bad. But all that stuff is little more than a Band-Aid on a severed artery. None of those methods fully correct for the problem over the entire bandwidth of the tweeter. Don't get me wrong, those methods do have a positive effect at some range of frequencies, but they don't have the ability to "get them all."
Think about it, if some other method to eliminate edge diffraction was actually superior to a properly designed waveguide, then our waveguide or any other for that matter, would be fundamentally inferior. They're too darn hard to make to be inferior right out of the gate. Basically, our speakers might be good, but they would forever be flawed in their very concept. That's no way to start a small company when your up against established giants.
And then there's the history factor. The first Edison cylinder had a horn on it. Engineers have known that Horn Theory offers superior performance for over a century. It's just that early on they over-engineered the things to get the most efficiency/sensitivity in order to make up for their lack of available amplifier power. We don't have that problem anymore these days so we can back off on the high compression ratios to avoid the air non-linearities that otherwise result, and capitalize on all the other benefits that Horn Theory offers.
So why do we roud-over the front panel edges in the Millennial Reference Series then? Well, because it looks cooler. They already look boxy enough for cripe's sake. That, and otherwise we'd have to edge-band the side panels. It's actually less work to round-over the front panel and cover up the edges of the side panels with it. That little roud-over does virtually nothing to reduce edge diffraction. And when other companies tell you that's why they do it - take it with a grain of salt. Well, I guess it does helps when the wavelengths are pretty short to begin with.
Most companies cross-over somewhere around 3kHz, so they might reduce diffraction effects a bit by using a round-over. Even then, it will only effect frequencies about 1/2 octave above and below that frequency. Higher than that, the tweeter starts beaming anyway so the wavefront never really reaches the enclosure edges to begin with - at least not much energy from a percentage standpont.
I'll back up and say that all of the above is highly dependant on the individual design, and the results of any technique can vary considerably but...the fact remains that no other method can compete with a properly designed waveguide with regards to the diffraction issue. Then when you throw in all the other benefits of reduced driver excursion and controlled directivity, well...let's just put it this way. You'll never see SP Technology produce a product that is intended to offer superior performance that doesn't use a waveguide of some kind. I mean, there's no point. The world already has plenty of cookie-cutter boxes out there. I just have this egotistic need to be different.
So there's my little dissertation on the subject. I hope all this makes sense and doesn't sound too much like marketing hype. Printing seems to be about done now and it's only 12:30AM. Maybe I should go home and get some sleep. I have a party at Steve's in Denver to attend tonight so that might be a wise thing to do. Hope to see a lot of you guys this weekend. Have a good night.
-Bob
