[krips]

Hello all. I've been reading up on OB for a while now, as it's what I want to do for my next project. Ever since I put my CCS FR125s in OB just as an experiment I've loved it! My plan is to do a L/C/R matching set of OB speakers (similar to Bob in St. Louis'), using active crossovers and gainclones (35w each, already in the works). These will be used in my HT, and because of this, I have a maximum height of 36", although I would like to be below that it possible. Hopefully some of you will be kind enough to share your wisdom with me .

1) Modeling - In WinISD, when you enter the volume of the enclosure, it would be the size of the room, would it not? When I do this, specifically for the midrange, output drops significantly (~4dB). Is this because the midrange I'm modeling has a low QTS (.232)? With a smaller woofer the effect is even more extreme. I had assumed that while a low qts woofer would  begin to roll of earlier than a high one, it wouldn't begin this until it was in the bass region, not before the 1500Hz WinISD is showing me.

2) Sensitivity - Just how important is it to be of a very high sensitivity, and should all drivers be of the same sensitivity? I believe I read somewhere that the woofer should be significantly more sensitive.

3) Tweeter Design - Should tweeters also be dipolar for OB speakers? I've seen all different types, from planers which I believe are true dipoles, to opposing tweeters wired out of phase (I'm assuming) to a single monopole tweeter.

4) Tweeter Height - This is not specifically related to OB, but I'm curious how important tweeter height with reference to ear level is. I believe it was the older fellow who runs realtraps that said it was more important to have a matching front 3 than to have two tweeters at ear level and your center lower. If my tweeters are at say 30" and my ears are at 42" would this be detrimental to the experience?

5) Crossover Frequencies - I believe from what I've read that the woofers should be crossed over at about 200-300Hz, and the mid at about 1500Hz ish. Are there any reasons why one couldn't cross over higher? Is this just to get the XO point out of the area where our ears are most sensitive?

My current plan is to run an Acoustic Elegance OB15 15" as the woofer (91.4dB@1w sensitivity, $100), a Silver Flute W20RC38-04 8" (91dB@1w sensitivity, $37), and the Vifa DX25TG05-04 (93.5dB@2.83v, $31, fs 650Hz). Apparently this particular tweeter is open-backed? That is what I got from reading John's blurb on it on the Zaph site.
Here is a picture of what I'm envisioning.

As shown this would be about 31.5" tall. I was thinking 3/4" MDF on the front with an additional two sheets of sand filled 3/4" plywood and a single 3/4" MDF sheet on the back, with all edges rounded over. I'm not quite sure how to make it stand up though .
I've very open to input as you are all infinitely more knowledgeable about this than I am. I'm looking forward to any and all comments . Thanks.

[Rudolf]

1) Modeling - In WinISD, when you enter the volume of the enclosure, it would be the size of the room, would it not?

Before modeling the drivers for OB, you should model the baffle with EDGE. Please get aquainted with the dipole-roll-off phenomenon to understand the output drop.

2) Sensitivity - Just how important is it to be of a very high sensitivity, and should all drivers be of the same sensitivity? I believe I read somewhere that the woofer should be significantly more sensitive.

Since you will use active crossovers, differencies in sensitivitiy can easily be adjusted. You should focus on the maximal excursion instead, because usually that is a limiting factor in dipole designs

3) Tweeter Design - Should tweeters also be dipolar for OB speakers? I've seen all different types, from planers which I believe are true dipoles, to opposing tweeters wired out of phase (I'm assuming) to a single monopole tweeter.

You could start with a monopole tweeter and add a second one later. Generally a true dipole configuration for the tweeter is noticeably better than just monopole.

4) Tweeter Height - ... If my tweeters are at say 30" and my ears are at 42" would this be detrimental to the experience?

It would be no problem for me. But it looks like different people feel different about it.

5) Crossover Frequencies - I believe from what I've read that the woofers should be crossed over at about 200-300Hz, and the mid at about 1500Hz ish. Are there any reasons why one couldn't cross over higher? Is this just to get the XO point out of the area where our ears are most sensitive?

Those crossover points look reasonable. But your driver parameters and the baffle size will dictate where you need to cross.

My current plan is to run an Acoustic Elegance OB15 15" as the woofer (91.4dB@1w sensitivity, $100), a Silver Flute W20RC38-04 8" (91dB@1w sensitivity, $37), and the Vifa DX25TG05-04 (93.5dB@2.83v, $31, fs 650Hz). Apparently this particular tweeter is open-backed?

Probably not. I don?t know of any dome tweeters with open back.