Two-Way vs. Three-Way Component Speakers
Is One Better than the Other?
http://caraudiomag.com/articles/two-...onent-speakers
I thought it would be interesting to present this, especially while we're thinking about component speakers in ourForum poll. Not that I want to complicate the discussion. But this is something people ask about quite often. Here's Derek Lee's take on the issue below. Feel free to post your comments at the end of the article. —Ben Oh
Question: My question is why did so many companies go away from 3-way components and are 2-way components better for sound competition than the more expensive 3-way components?
[B]Derek Lee: The manufacturers will have their own position as to why they shifted away from three-way components—I have my own view, which is based on what happens at the install bay level and how that is translated up the chain to the manufacturers and marketers.
First, from the acoustic science side of the topic, it is accepted as fact that the best speaker is a single point source speaker or emitter. You have one mouth on your face, and when you speak or sing, all frequencies involved emit from the same source. Compare that to a loudspeaker and we hit a couple of snags: a speaker cannot cover all of the audible frequencies, so we need to use a low frequency device called a woofer, and a high frequency device called a tweeter.
Put a woofer and tweeter together, and you can now cover the complete musical band from 20 Hz bass notes to 20,000 Hz at the treble end respectably. Problem solved? Not so fast—the singer has one sound source, which takes two speakers to equal. If you place the speaker components beside each other, the brain can decode the presence of two sound emitters instead of the expected one source. They are duplicating efforts in that the woofer is playing a bit into the tweeter’s range and the tweeter is trying to cover some high bass notes. This duplication of signals causes “phase errors” which is the foundation of how creatures localize the source of a sound whether prey or predator or punk band.
So we add a circuit called a crossover, which is a filter set that blocks high frequencies from the woofer and low frequencies from the tweeter. Now the sound has become more precise but still doesn’t sound exactly like it is from only one emitter, especially when the song transitions from a low note to a high note and the sensitive ear notices that the source of the sound has changed position slightly.
The black art of building a perfect loudspeaker is frustrating enough to drive speaker designers to go postal. The loudspeaker is like a guitar—the longer you play guitar, the more you know that it is impossible to tune and keep in tune. It can be maddening! So far, we have only covered a two-way speaker. Now you want to go three-way? Who needs the aggravation?
From the physical installation side, cars today are just too cramped to offer spaces that are suitable for speaker locations. We prefer to have two locations that are equally distant in path length between the speakers and the ears, forming an equilateral triangle, known as the “imaging triangle”. The speakers must also be “on-axis” or perpendicular to the listener so the speaker is firing directly at the listener. That’s tough to get in cars of the last 20 years. Keep in mind that we also need to ensure the speaker elements are within one-half wavelength at the crossover point according to many, including Vance Dickason, the renowned author of the [I]Loudspeaker Design Cookbook. That means the tweeter, midrange and woofer all must be very close together or you get all kinds of phase and timing problems.
Most installs wind up consisting of a woofer in the door and a tweeter in the dash. According to the half wavelength rule, a woofer and tweeter should be less than an inch or two apart from center to center, depending on the crossover frequency! Where do we put the midrange? Break out the plasma cutter and fiberglass, and let’s fabricate a new dash! It seems that there is little chance of getting naturally good speaker placement in a car. Even the carmaker that has absolute control over the shape of the dash ALWAYS designs the speakers to be in bad positions.
Which sounds better? Audiophile philosophy says that simpler is better, and I agree in the broad sense. It takes more work to make three components work like two, yet never really succeeds. I have heard many stunningly sweet systems using two-way home speakers, and find that if you triple the price tag, you can get a three-way to equal a two-way system if done by a very skilled designer. Just watch out for the voodoo that comes up as an extension of sound physics and true common sense. Those who claim they can hear grass growing are typically found on the Internet forums promoting all kinds of weird concepts as if they are industry veterans.
In the sound competitions I have judged starting with Car Audio Nationals back in the mid 1980’s, two-way systems always seemed to be the most natural and cohesive. The reason always made sense to me: if you drop a stone in a calm lake, you can see circular waves propagate outward from the center. Drop two stones close together and the waves appear to blend into one. Drop several stones and you get a mess. Audio follows a similar parallel in that if we can get the sound wavefronts from a woofer and tweeter to blend in time and phase, it will sound like the highly valued “point source”.
Keeping the woofer and tweeter as close as possible is a major key to success, followed by aligning the voice coils on the same plane. That one is a lot more difficult. If you were able to mount a tweeter in the middle of a woofer (creating, ironically, a coaxial speaker), you would still need to embed the coil of the tweeter back inside the coil for the woofer to approach perfection. This is not possible at the installation level, and even if you did, the coils would induce energy into each other and you are back to having the equivalent of no crossover.
This is where new technology comes in to play. Since we have the ability to digitally delay signals, we could use a processor to delay the signal destined for the tweeter amplifier so it arrives at the voice coil a fraction of a second behind what the woofer receives. Now you have a point source that can be time aligned, resulting in the closest thing to a natural emitter like a musical instrument or voice. Again, in a two-way world, this works, but in three-way speaker systems, it is much more difficult.
Manufacturers recognize that it is important to make things that people want to buy, and speakers have evolved to the point where there are clear preferences. There was a time when “more is better” ruled, resulting in three way, four way, five way 6x9 speakers all feeding off of the enthusiasts mistaken notion that if it had more, it must be better.
Limited speaker mounting options in new cars helps to influence the manufacturers to simplify their offerings, and the additional benefit is passed on in the form of lower installation labor costs to you. Less to build, lighter to ship, more reliability and improved sonic performance all drive the decision. Quality counts—high-grade components are essential whether you choose to build a two way or three-way system but I agree that a two way will always perform better with less work.
[I]Derek Lee is the former instructor and co-owner of Mobile Dynamics, Toronto, Canada, and contributing tech editor to Car Audio and Electronics [I]magazine.
This was an article i posted long time ago from car audio magazine which is closed now. This is the article i was refering to on the phone Baig sahab.[/I][/I][/I][/B]