Various fun newbie questions

[parallax]

Hey guys. :-)

So this is my first DIY audio project. I'm designing a pair of bookshelf speakers (currently reading the LDC). Fairly simple, closed-box two-way design.

Just a couple initial questions.

1) Is it possible to "break" drivers by playing them too loud over too much time? Is this easy to do?

2) I'm not looking for any bass boost in this system, as I'm intending to buy a sub or build one next year or something. Ideally, I want to play classical and rock music fairly accurately. Is a Qtc of 0.707 recommended or should I go lower? Should I just target a Q of 0.707 and use fill to shape the sound?

3) Once the speakers are built and finished, how does one fix, say, a crossover network that breaks down later?

4) Do you have any recommendations for drivers, particularly tweeters that don't sound terribly sibiliant? I'm looking to spend ~$250 total on the crossover/drivers, plus whatever for wood and adhesives.

5) My tweeter doesn't have any part in my box design, right? I can just add it once I design the box for my woofer?

Thanks a lot.

[BillFitzmaurice]

1. Yes, and the same applies to your eardrums, so don't.
2. .7 is fine, a good compromise overall.
3. Mount the crossover on the outside of the box.
4. If the response curve is flat sibilence won't be a problem from the tweeter. More often the cause of sibilence is failure to compensate for the baffle step, which usually occurs around 2kHz or so; the 6dB response loss below the baffle step in effect can accentuate the audibility of frequencies around 2kHz, and make the speaker sound sibilent. Proper crossover design is far more important than the choice of the tweeter.
5. Yes, but make sure it has a separate subenclosure if it's not a sealed back unit.

[parallax]

Hey, for a 2nd order LR filter, LDC lists the formulae as

C1 = 0.0796 / Rh f
C2 = 0.0796 / Rh f

L1 = 0.3183 Rh / f
L2 = 0.3183 Rl / f

However some equations I'm seeing online list C2 as using Rl, not Rh.

What gives?

[bogoes]

Parallax -

You have much to learn in designing crossovers, and it is a difficult subject. I always hate to give this bit of advise, but I was there once before and did well with it. And that advise is this...the heart of all speakers is not the drivers, it's the crossover. For your first project or two, build a kit, study the crossover, maybe even venture to make changes to it to hear what happens. There are many more things that go into a crossover other than the crossover frequency... to get speakers that really sound nice, you need to incorporate bits for baffle step compensation, phase alignment, impedance, and breakup modes just to name a few.

Some kits to check out:
GR Research A/V-2
Seas L15RLYP / 27TFFC System by John Krutke
Parts Express Project Showcase - Lots of Projects, Check out the Triune

Good luck and have fun.

[parallax]

Thanks for the advice, bogoes.

However, I'm absolutely dead set on designing this thing from start to finish. I know you probably hear that a lot, but I don't mind going in circles (I've got a month with nothing to do before classes start again!) and this will probably be my last speaker project till next year due to time constraints.

I've already included baffle step compensation, phase alignment, and impedence (if you mean L-padding the tweeter appropriately, I guess) to the best of my knowledge. I'm sure I have more to do, but that doesn't bother me. Perhaps you could point me to a good reference on crossover network design...

Thanks a bunch,

- R