Fundamental Questions about Loudspeakers

When using a subwoofer, what exactly do you get by putting more money into your main speakers?

Let me clarify my question by being a bit more explicit:

It seems to me that the proliferation of the subwoofer has created a "sonic division of labor" allowing your main speakers to concentrate on reproduction above the subwoofer crossover point.

Now, since all DECENT speakers seem to give what is essentially totally flat frequency response above, say 80 Hz, what, if anything, is gained by going to very high-end speakers when employing an 80 Hz crossover. (80 Hz here is just picked as an example.)

So, why 340s over 170s if my crossover is at 80 Hz? Or, why Revel F52s over Ascend 340s? Do you just get to set your crossover lower? Is that it? Is there more to loudspeakers than frequency response, efficiency and dynamic range that I am missing? It seems like if you pay an extra $6,000 that should get you something other than setting your crossover 40 Hz lower (or whatever it is.)

On a related note, what is this business of "timbre matching"? If two speakers have a flat FR, then aren't they by definition timbre matched?

Only got a minute but a detailed reply to your question could take a long time. First, a truely flat FR is not common in a loudspeaker. Second, FR is just one of many variables and not the most important. What is the most important is argued endlessly but it's not FR.
Do a search on this Forum for posts by Dave F. He's tried to educate us on what's important to him in designing a speaker. I'm pretty sure that will answer your question.

David

As David said, there is more to the sound of a loudspeaker than FR. There are other measurable items like spectral decay, distortion, phase, off-axis response, etc. There is also argument about sound impact that doesn't show up in existing measurement techniques, but we'll set that aside for now.

In terms of the 170 vs 340, I think DaveF has noted specifically that the 340 can go louder before hitting distortion than the 170. This is useful for large rooms or people who really crank it up.

There are also arguments about when bass really becomes non-localized, so a lot of people prefer a pair of full-range speakers to a smaller pair of speakers and a single sub (or some use stereo subs).

Quote:

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Originally Posted by JackT

When using a subwoofer, what exactly do you get by putting more money into your main speakers?

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Not a whole lot if your usage is primarily HT, where the center channel does about 60% of the work. For 2-channel music, many people prefer the superior bass speed and accuracy of a good floorstander which can only be equalled by a truly musical subwoofer usually costing well above $1000 (of course such floorstanders also tend to require better amps to sound their best). Such floorstanders often have superior coherence across the entire frequency spectrum (lows-mids-highs) compared to a separate-sub(s) setup.

Quote:

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Originally Posted by JackT

So, why 340s over 170s if my crossover is at 80 Hz?

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If you have a large room, the 340s will provide a fuller sound at low/moderate volumes due to the extra mid-woof and wide dispersion tweeter. They will sound better if you ever listen to music full-range with the sub off. And last but not least, the 340s do have a more WAF-friendly form factor than the boxy 170s. :D

The best way I've heard it explained that actually makes sense to me goes like this: A small, inexpensive speaker may have a flat frequency response and low distortion when measured at a low volume. When we start approaching reference level, things change. That small speaker will be struggling to keep up at frequencies around 80Hz. A larger, more capable speaker with usable response down into the 40's or 50's can better handle loud, dynamic passages when crossed over at 80Hz. In HT, it's about the dynamics. A more bass capable main, center, and surrounds can handle these dynamic passages at much higher levels than a small speaker. So, it really depends on the volumes you want to achieve in your HT. If you listen at -20dB from calibrated reference level, then the added dynamics of a larger, more capable speaker may not mean much. If you want to push the envelope, then you need a speaker that can belt out an 80Hz tone (and lower...the crossover isn't a brick wall) just as easily as it can belt out a much higher tone.