[Vapor Audio]

Even a 6.5" woofer is nowhere near omnidirectional at 600 Hz - the output at 60 degrees off axis is already down a good 6-9 dB or so (depending on cone stiffness and geometry

I'm not sure where you get that idea ... I have a pair of Peerless 830884's here I'm planning on using in a waveguide, my own off-axis measurements are totally in-line with the spec sheet.  Just using it as an example.

http://www.tymphany.com/datasheet/printview.php?id=4

It's an 8" woofer, and is totally omni up to above 600hz, and is only 2db down at 1000hz.  Driver specifics play a small role in directivity, for the most part it's simply when the effective piston diameter becomes larger than 1/3 of a wavelength.

You are correct that breakup behavior of the woofer cone has to be taken into account, however SP Tech is crossing over their metal cone woofers far below the first breakup mode so a couple hundred Hz this way or that probably doesn't matter from a cone breakup standpoint.  But I could be wrong.

Those breakups manifest themselves lower as odd order harmonic distortions as well, so going as low as possible helps there too.  Also lower x-over can essentially negate any problems with center-to-center spacing and lobing effects.  And if you go with a 1000hz xover instead of 600hz, that's almost a full octave ... a simple LR4 slope likely won't push the breakups low enough in that case, and would require a notch.  Although he might be using one anyway, dunno.

I know a lot of people just don't believe a 1" dome tweeter can go as low as Bob is pushing them, but everything changes when loaded into a totally different environment like a waveguide as opposed to a flat baffle.  If the tweet measures well in distortion products and in the time domain at 600hz in the guide, then go for it!  I think the main concern at that point becomes excursion, I don't know how the guide affects excursion, but apparently it does or the SP speakers wouldn't be able to the reach level of dynamicism and pure SPL that everyone reports.

[ooheadsoo]

Duke's posts seem completely in the clear and I don't see any ill intent.

[phoenix_rising]

Thanks everyone for the replies. Can't wait to get your impressions Christoff if you manage to hear them.

Double Ugly: I am not getting the Infrawave as it is simply too large for me to put it anywhere. I will proably pair it with a Rythmik sub further on down the track.

[Double Ugly]

Geeze, Double - where in the world did I take a swipe at Bob?

In response to someone saying that they hoped the crossover of the Mini was down at 600 Hz, I posted that that there may well be valid reasons for it being higher.  In other words, if it turns out that Bob did use a higher crossover, I was defending him in advance!

Please tell me what I said that you interpreted as a "swipe" at Bob.

Thanks,

Duke

Hey Duke,

I understood all that, but this -

...so if they're a few hundred Hz higher than the lowest physically possible I'm sure it's with good reason.

is where I read - and then re-read - something... eh... not so nice.  Now that I've re-read it yet AGAIN, I can see clearly where I mis-read it.

If only it was the first mistake I've made today 

I apologize, Duke.  It's been a whale of a day and I've had way too little sleep.

-DU

[Double Ugly]

Double Ugly: I am not getting the Infrawave as it is simply too large for me to put it anywhere. I will proably pair it with a Rythmik sub further on down the track.

Nonsense, my boy!  Put that beast against a wall corner or nestled into ceiling/wall joint and all will be well! 

Seriously, pr, I understand.  Though I'm getting Revelations for a room too small for them, I understand.

Difference is, I don't always act on what I understand. 

[Duke]

To Turbo FC3S:

Well your questions are certainly fair.

I get my ideas of driver directivity from a loudspeaker text, from my own measurements (extrapolating from measurements of larger diameter woofers), and from a loudspeaker modelling program that has a solid track record in the industry.  Unless your measurements are time-gated to exclude reflections, they aren't giving you a reliable indication of the off-axis response because reverberant energy is being included in the measurement.   I use time-gated measurements for that and other reasons.

However, I do see what you mean from the curves on that Peerless woofer!  I wouldn't say that the woofer is omnidirectional at 600 Hz based on those curves as they only go out to 60 degrees, but they certainly do seem to contradict what I have posted.  Now if Peerless took their measurements on a one-meter wide baffle that would account for some of the discrepancy, but not all of it.  Unfortunately I don't have a way to post the curves run by my simulation program (LMP by LinearX).   

Loudspeaker cones behave as rigid pistons at some frequencies but then transition to the breakup region.  In the breakup region, the radiation pattern can be over twice as wide as rigid piston theory would predict.  While that may apply to the Peerless cone, I don't think it applies to the Seas aluminum cones within their operating passband.

I definitely believe that a low-resonance tweeter can go as low as Bob uses them because I understand what collapsing the directivity does for a driver.  Now if the waveguide is too small to properly load the driver, that introduces problems in terms of directivity, frequency response and power handling. 

Duke

Edit - I just thought of another reason why that Peerless woofer could have a much wider pattern than what I would have expected:  The bullet-like pole-piece extension.  From what I understand such features are claimed to reduce beaming, and maybe that's true - I haven't really studied much about them.

It looks like the woofer in the Mini has a similar feature, which (if it really does widen the pattern significantly) would mean that you were probably more right than I was regarding the radiation pattern similarity between woofer and tweeter below the frequency where the waveguide loses pattern control. 

[Duke]

Double explained:

"...but this

...so if they're a few hundred Hz higher than the lowest physically possible I'm sure it's with good reason.

is where I read - and then re-read - something... eh... not so nice.  Now that I've re-read it yet AGAIN, I can see clearly where I mis-read it.

"If only it was the first mistake I've made today 

"I apologize, Duke.  It's been a whale of a day and I've had way too little sleep. "

Duke replies:

Apology cheerfully accepted - if ever we meet, have a beer on me!  Thanks for being willing to reconsider your initial interpretation.  And evidently my choice of words was poor - I'll try to learn from my mistake, as I really didn't mean anything derogatory about what Bob is doing. 

Let me try to explain what I meant by that statement:  Suppose that it's physically possible for Bob to cross over the Mini at 600 Hz (meaning, tweeter power handling is still acceptable).  But suppose that tweeter harmonic distortion, on-axis response, power response, or some combination thereof (and therefore sonics) are compromised if he does so.  In this case, it makes sense to put the crossover where it sounds best, even if it's a couple hundred hertz above the power-handling-limited minimum.  Well, that's my opinion anyway.

Best wishes,

Duke

[Vapor Audio]

I just had a big reply typed up for Duke, but deleted it all ... I don't want to hijack Bob's thread. 

The only thing I want to say is off-axis response is predominantly determined by piston diameter alone, that goes for both woofers and tweeters. 

[lonewolfny42]

Hey Jim....

I've met Duke and his wife...and heard his speakers at RMAF '06...he's a good guy....and a fan of Bob's from way back. I've seen that in print.... he's OK.....

You'll get to meet him at RMAF '07.....

Now get some rest.....if you have trouble sleeping....count watts....one watt....two watts....three watts....four watts....etc......

[Double Ugly]

Hey Jim....

I've met Duke and his wife...and heard his speakers at RMAF '06...he's a good guy....

Hey Chris,

Yeah, I know; I simply misinterpreted his post...twice.   As I said above, would that it was the first time today, but what're ya gonna do? 

I'll try to find him in Denver and apologize in person.  If he (or you for that matter) are looking for me, you may recognize the guy I'm hangin' with. 

And maybe I'll try that sleep trick.  Goodness knows I can use about 12 hours of dead-to-the-world sleep. 

[phoenix_rising]

Nonsense, my boy!  Put that beast against a wall corner or nestled into ceiling/wall joint and all will be well! 

Seriously, pr, I understand.  Though I'm getting Revelations for a room too small for them, I understand.

Difference is, I don't always act on what I understand. 

Thought I would tell you I ordered 3 for LRC duty.

I will post a review when I get them.

[Double Ugly]

Thought I would tell you I ordered 3 for LRC duty.

I will post a review when I get them.

That should certainly make for an excellent system.  I'm look forward to your comments.