Multi-woofer 2-ways that AREN'T MTM?

[kevinp.]

Why is this frowned upon exactly? Is it because you have to take into account spacing between every driver and the tweeter, not just the top woofer and tweeter? If so, how do commercial companies get away with it (Klipsch RF-83's?).

[stinems]

It shouldn't necessarily BE frowned upon. It's all in the implementation. When you see a TMM or similar from a reputable commercial company, there is a good chance it's a 2.5way system, not a straight 2 way. In the case of the TMM, the bottom woofer is rolled off early and is used to fill in the baffle step quite nicely. A side benefit is that, because the bottom woofer is rolled off early, its acoustic phase is a bit different than the upper woofer and as a result you don't get near the power response dip (ie, off axis response nulls) at the Tweet/Midwoof crossover point like you'd get with the MTM 2 way.

In the case of your Klipsch RF-83, I would guess that's a TMWW from a crossover perspective, even though it may look like all three woofers are the same driver.

At any rate, driver spacing is really only an issue for the drivers that are being directly crossed over with one another. In a TMWW, T to W spacing shouldn't be an issue at all. In the classic D'Appolito 2 way MTM, both M's are being crossed over to the tweeter, so of course driver spacing is an issue. In the TMM 2.5way I described above, the bottom woofer isn't really crossed directly to the tweeter since it rolls off earlier (~600hz, usually at a 6db to 12db/oct slope) than the upper woofer to the tweeter (1.5khz-3khz). Since the bottom woofer isn't contributing as much to the frequencies around the Tweeter's crossover point, driver spacing isn't considered too much of an issue.

The worry surrounding driver spacing is off axis response, which in turn contributes to total power response of the system in the room. When drivers get much more than about a wavelength apart at their crossover frequency, you'll start to get severe nulls at the crossover frequency above and below the normal listening axis as destructive interference sets in. Closer together, the two drivers start to effectively act as a single source, at least as far as your ears are concerned.

Sam

[JonMarsh]

They do it by making 2.5 ways- one woofer runs full up to the tweeter crossover point, the other has a lower crossover point to provide mainly baffle step fill in, and is crossed out earlier, around 600-800 Hz depending on the cabinet baffle dimensions. The topological design of the network has to be done "the right way" or it's difficult to match up the LF phase of the two midwoofers.

[ThomasW]

Klipsch lists a single crossover point for that design, 1650Hz ...... 8O

[kevinp.]

thanks for the replies. I thought that might be the answer, but I could not find any verification anywhere that it was a 2 1/2 way.

[stinems]

I want to give Klipsch the benefit of the doubt and guess it was just a marketing decision to leave out the .5 way from their published specs rather than confuse the layperson. Besides, the .5 way low pass isn't really a "crossover point" per se anyway. I'm just incredulous that a reputable mid-fi company like Klipsch would employ a standard 2 way crossover in that TMMM layout.

Sam

[HareBrained]

It's been my understanding that most inexpensive commercial speakers don't account for the baffle step. They don't expect the buyer to put them into an "audiophile" listening position. They expect them put they'll be against the wall or next to the 50" TV. And I'd wager that the xover is the same for all woofers.

The 2.5-way xover would be employed at some price point but you're not going to find those at Best Buy, Frys, etc.

[kevinp.]

well, as much as I'd like to think speakers costing $3000/pair would follow general speaker design mantra, it seems these are actually only 2-way speakers according to users on the manufacturer forums. So why isn't the general public concerned with the issues this configuration reveals?

[JonMarsh]

Because they don't know any better, and because they don't go and listen to a variety of systems, and they may not have listening experience to give them the background to understand what they're hearing, or not hearing. The basic general public is most often initially attracted by boom/tinkle boxes.

Ok, lets turn off the cynicism. But seriously, look how the general public pimps out their ride, when they go into expensive car audio. In a lot of cases, it's got nothing to do with high fidelity, everything to do with sonic effects.

[jeffc]

attracted by boom/tinkle boxes.

:rofl:
nice!