Have you ever seen speaker designations such as 2-way, 3-way or even 2.5-way, and asked yourself what this actually refers to? On this episode of Ask The Expert Otto explains it all!
Your questions are what that keeps the Ask The Expert concept alive, so please keep them coming, and we'll keep on answering them! You can do this via the form at the bottom of this page "Send us your questions."
To answer the first part of the question, let's talk about what a two-and-a-half-way speaker is. First of all, a two and a half way speaker is typically a speaker where you have one tweeter and two identical woofers. The reason for doing such a design is to mitigate a problem known as baffle step.
Baffle step is what happens when the woofer produces a more omnidirectional sound (figure 1), due to it producing lower frequencies, and this causes the bass to emanate in all directions from the speaker like a sphere. The result of this is an inconsistent presentation, because most of the energy in the high frequencies is sent directly towards the listener whilst the lower frequencies are spread out into the room, causing the level of the bass to taper off somewhat and causing an imbalance between the bass compared and the midrange and tweeters.
To mitigate this problem you could tweak the crossover crossover and essentially decrease the levels of the midrange and tweeter to match the woofer output. However, this sacrifices sensitivity, and therefore the better solution is to use a two-and-a-half-way speaker design. As mentioned above, a 2.5 speaker uses two identical woofers, and by simply adding a second woofer, it's possible to increase the bass output to better match the level of the tweeters.
This is an extremely simple yet effective way of mitigating the issue of baffle step. It doesn't require a crossover redesign, it doesn't sacrifice the sensitivity of the speaker, and it's also relatively cost effective because all you're doing is making a bigger cabinet and adding an extra woofer, which isn't as costly as one might imagine.
Reasons for choosing a 2.5-way speaker versus a 3-way speaker can be cost, but also the simplicity of the speaker has its part to play. A simpler design can provide benefits in terms of sound whilst keeping costs down. If you have a true 3-way speaker, the crossover becomes more complicated, as does the design of the baffle, and you actually still have the issue of baffle step, so you would still need to figure out how to increase the bass level.
That's typically done by using two woofers in a three way speaker, so now it's your actually using four drivers and not three, again increasing the cost and the size of the speaker.
This is why a 2.5-way design is a great option, since it offers a great balance of cost versus performance, as well as remaining a relatively compact loudspeaker.