passive crossover for waveguide tweeter/horn & 15alpha

[Angaria]

I'm trying to build a relatively compact full-range OB speaker for a friend as a graduation gift. While it will sound better than anything he's heard, the hitch is that I have to be satisfied with the sound quality

After playing around with a pair of 15" SI coaxials, I just can't take the sort of mid-range hollowness and ragged response of the tweeter. Not bad for the price, but those issues are just to noticeable for me.

Was thinking about an audio physic cs2-like design with a wave-guided tweeter, or a pro-tweeter and a horn crossed around 900Hz. Woofer would be 1 Eminence alpha. Does this sort of design necessitate an active crossover/high slopes to sound decent?

Most of the related work I've seen has been active, so I wondered if anyone had luck with a similar design and a passive network. This seems to be the place for related designs...

[Saurav]

Check the Isiris thread, that's the most comprehensive design discussion I've seen here involving a WG-loaded compression tweeter (and it's an OB too). It does have a midrange driver. I've been trying to design a passive crossover for my own project (OB with CD/WG) and am pretty close to giving up and going active. I'm having a hard time getting the phase to line up, since the tweeter signal is delayed quite a bit compared to the midrange. With a bigger/deeper driver, this may not be an issue, but then you'll have worse center-to-center spacing issues. Also, I'm not sure what WG/tweeter maintains dispersion control down to 900Hz... it would need to be pretty big to do that, I would think.

I haven't heard the CS2, and I don't know how much shaping/EQ the Alpha15 needs to work with a 1kHz crossover. It may need pretty sharp slopes as well. AFAIK the CS2 uses a DCX2496. It has received some very good reviews, but 2 15" woofers crossed to a tweeter at 1kHz... does make you wonder. Some of the Lambda drivers might work well with that kind of design, but they're spendy.

Also, you might want to read the long threads on DIYAudio by gedlee. He's one of the world's foremost authorities on waveguides, and recently started selling a kit version of his speakers (not an OB). If nothing else, that might give you some design issues to think about. The few reviews I've read of his speakers are very good.

Audiocircle has an open baffle forum, and there are some designs there that might work for you.

Couple more comments... MJK (Martin King) has a couple of articles on his website about OB design, and some MathCAD worksheets to help design them. He likes the Alpha15, but he uses it up to ~200Hz, with a wideband/midrange above it and a tweeter if necessary. If you haven't looked at the Linkwitz and MusicAndDesign websites yet, you probably should - lots of good info on dipoles.

Also, search DIYAudio for "Manzanita" (I think I spelled that right) - it's a small OB with a 12" Peerless woofer crossed straight to a (I think) SEAS tweeter. It looks like a "stick a coil on the woofer and call it good" design, but if you find the main thread where he talks about it, there's a little more thought put into it than that. Also, it was taken to RMAF and a couple other audio shows and got good reviews, so it's more 'proven' than "These are the best speakers I've ever heard (and I've only heard Bose)", if you know what I mean. This design might be close to what you're trying to do, but at a lower efficiency target.

[ThomasW]

Something to reference in the Isiris thread is the tweeter zobel. IMO these are mandatory when a passive crossover is being used.

It's problematic finding a 1" compression driver and corresponding horn/waveguide that works well in the 900Hz range.

One driver to consider is the Radian 465PB. It should be noted that some purists don't like the design of the Radian diaphragms. IIRC it's something about the suspension causing modes in the dome ....

[Angaria]

Thomas - thank you for the comprehensive reply. It's really a fine assessment of the best projects I've seen.

The modified DCX used in the cs2 sells for $1600, so perhaps it's use is more of a sound quality choice as opposed to an absolute necessity when dealing with the slopes. Though as you say, crossing so high would appear to necessitate some response shaping.

If you've been having issues perfecting a passive OB design, I'll take that as a sign that I either need to go 3-way, or perhaps work on a 2-way with a woofer that will get down to 100 Hz and then use the alpha with a plate amp/crossover.

[Saurav]

If you've been having issues perfecting a passive OB design, I'll take that as a sign that...

No, you take that as a sign that this is just the 2nd set of speakers I've tried to design, and I barely have a clue about what I'm doing. I'm not Thomas And FWIW, I am trying a 3-way.

The modified DCX used in the cs2 sells for $1600, so perhaps it's use is more of a sound quality choice as opposed to an absolute necessity when dealing with the slopes. Though as you say, crossing so high would appear to necessitate some response shaping.

I don't know for sure, I'm speculating that it might.

[ThomasW]

If you've been having issues perfecting a passive OB design, I'll take that as a sign that I either need to go 3-way, or perhaps work on a 2-way with a woofer that will get down to 100 Hz and then use the alpha with a plate amp/crossover.

My Isiris is the first and only operational pair using a passive network. Normally we don't publish the 'alpha' version of any design. In this instance we did and now people are seeing what goes on during the development of a finalized design.

Usually development of a final design is a fairly quick process. With the Isiris project finalization of the design came to an abrupt halt due to Jon's insane work schedule.

Historically I've not needed advanced testing tools since those were supplied by Jon. Lately I've been building, rewiring, adding equipment and rearranging equipment so I can do more advanced measurements and testing. This isn't a minor task given the complexity of the my system, and the fact that the front end equipment is in one room, and all the amps and EQ are in the basement below... 8O

One cool thing is I now have the B&K 4133 with it's associated 200watt phantom power supply/pre-amp... :B

Regarding the DCX2496, as a $250 developmental tool I don't think it can be beat. Spending $1000 or more to have one modded unit strikes me as a poor investment given the build quality of the basic unit.

[Saurav]

Oops, maybe you were talking to Thomas and not me ops: :P

[ThomasW]

Since we both have been having issues maybe he was talking to both of us...

[Saurav]

Well, we all know you have issues...

[JoshK]

Who's this Jon character?

[Mazeroth]

Who's this Jon character?

Oh no you didn't.