[corloc]

John,

A few quick questions,  How high are the baffles?  I assume that boxes are acting as baffle.  So, just putting your baffle on posts will not work.  What is the width of the baffle?  22" square isn't to bad.  I think the baffle for the iris 15" is 22"  have you tried Planet 10's phase plugs?  Through my experimentation I've only come up with eq'ing or larger baffle.  Sorry if you have answered these questions before, but I have been on hiatus from audio for a couple months or so.

Chris 

[JohninCR]

John,
A few quick questions,  How high are the baffles?  I assume that boxes are acting as baffle.  So, just putting your baffle on posts will not work.  What is the width of the baffle?  22" square isn't to bad.  I think the baffle for the iris 15" is 22"  have you tried Planet 10's phase plugs?  Through my experimentation I've only come up with eq'ing or larger baffle.  Sorry if you have answered these questions before, but I have been on hiatus from audio for a couple months or so.
Chris 

Chris,

I hesitate to call them baffles because the driver mounting baffles are not much larger than the driver, and the design functions much differently than just a baffle.  The boxes they're on are more like pedestals, but only about 8" tall, so I'm definitely getting significant floor benefit with them too low.  Though they're only 22" wide the average distance differential for the front and rear waves is an average of almost 20", not including the floor effect.  I only got as far as cutting the dustcap off one of my B200's, but I don't have anything the right size to act as a phase plug, so I haven't tried that yet.  This pair seems to be working fine with stock drivers, but I plan to test phase plugs too.

Here's what I'm talking about for those who didn't see the pics in the other thread.  I believe the correct term for them would be Constant Directivity Dipole WaveGuides, so I'll coin a new acronym now, CDDWG.

[corloc]

pheeew.... perdy

I can see that building the diffraction ring will be a real treat.

Well I'll just through out my xbaffle program.  Having the drivers that low and no midrange problems?   On my winged baffles I couldn't get below 24" off the for without muffling the mids. 

[JohninCR]

That height is only temporary, but I have a table that blocks direct floor reflections in the temporary position.  Without it you're probably right that it would be a mess.  Bass will go away too.  The real answer is a 15" in the base.  Then about 50lbs or more of sand.  I'm going to have to enclose the space between the front/rear 4" dia roundovers I made out of laurel 2x4's, because the darn things are vibrating an amount I don't understand.  The plywood panels are dead even before covering with foam and material, but the roundovers vibrate enough that they have to be hurting the sound.  I've always wanted to do really massive OB's, so I guess these will be the ones.  They'll need it to mount a 15, though I'll probably make the 15 a slide in unit to decouple it from the rest of the speaker and be able to magnet mount the 15.  That strategy is working slick on some other projects.

[corloc]

Is laurel hard and light?  Maybe using pine might keep the vibrations down few hz.  Or decoupling the detraction ring from the CDDWG with a gasket.  I completely agree with decoupling the 15" from the B200 baffle. 

[AJinFLA]

Here's what I'm talking about for those who didn't see the pics in the other thread.  I believe the correct term for them would be Constant Directivity Dipole WaveGuides, so I'll coin a new acronym now, CDDWG.

That looks suspiciously like a tapered H-baffle to me. I discussed just such a thing with John K many moons ago, lessening the impedance mismatch at the TL terminus. JohninCR, why is that not a H-baffle? Because you have tapered the TLs?
Can you show us some measurements on and off axis to clarify exactly how constant that directivity really is? What frequencies are being wave guided? At what frequency is the measured dipole peak within the operating passband of the driver?
Have you considered putting a hole in the rear TL that leads into another TL so that we could have the worlds first and only CDDWGOB/RLH? I think the fans here might be even more impressed with that one
C'mon John, point a mic at that thing from about 2m out and rotate it 15, 30, 45, etc. degrees.
Post some graphs. Looking forward to seeing it.

cheers,

AJ

[corloc]

Hay, AJ

Why don't yo head over to Rodolf's thread on H-baffles and give a hand and learn.  I would enjoy your help here, but you only seem to be interested in being a sniper.

Chris

[Rudolf]

Hay, AJ

Why don't yo head over to Rodolf's thread on H-baffles and give a hand and learn.  I would enjoy your help here, but you only seem to be interested in being a sniper.

Chris

I might have said it with other words, but John really is overdue to have some measurements going along with his verbal descriptions. I´m sure he knows it himself. So this is no teasing, just a friendly reminder once in a while.
And I´m sure there is not much to learn for AJ in that H-baffles thread. But bringing in his experience certainly would help.

Rudolf

[corloc]

Sorry, AJ I was a snarly. 

Rudolf, I agree John should get measurements to help himself.   I'm intrested, How long of a learning curve is there to get usefull mesurements?  In my mind, you don't point a mic at a speaker and get all thethe information you are looking for.

Chris

[corloc]

Never mind the measurement question was off topic.

[Rudolf]

That looks suspiciously like a tapered H-baffle to me. I discussed just such a thing with John K many moons ago, lessening the impedance mismatch at the TL terminus.
AJ

AJ,
if this was discussed somewhere on the Internet, could you lead us to the source?
If the discussion was private, could you give us a rough view of any conclusions you came too? Particularly - does it help to taper a H-baffle and to what extend?

Rudolf

[AJinFLA]

Hay, AJ

Why don't yo head over to Rodolf's thread on H-baffles and give a hand and learn.  I would enjoy your help here, but you only seem to be interested in being a sniper.

Chris

I might have said it with other words, but John really is overdue to have some measurements going along with his verbal descriptions. I´m sure he knows it himself. So this is no teasing, just a friendly reminder once in a while.
And I´m sure there is not much to learn for AJ in that H-baffles thread. But bringing in his experience certainly would help.

Rudolf

Rudolf this is simply not true, there is always something for me to learn when someone like yourself shows measurements of a system that they have built.

Corloc, no need to apologize, no offense was taken. These are internet chat boards, I regard them as such. Pointing a mic at a speaker is not intended to tell you everything, it is intended to tell you something. It is an accumulation of measurements and the practice of repeated measuring before one starts to associate what is being measured with audible correlation.
Surely you can look at the free space FR of a small bookshelf speaker and a large floorstander and "see" the much deeper more extended bass response and know that when placed in a room, one will have deeper more powerfully extended bass than the other?
What won't be seen is the room response when both are placed inside (excitation of modes, etc.), the quality of the bass, etc, etc.
So each measurement tells you something, but not everything. Lots more measurements are needed and then, yes, listening. Skipping the measuring and only listening leaves you flying blind.

Rudolf, that discussion was a while ago, on Madisound IIRC. It may have stemmed from my advocating WG's for tweeters and lowering the acoustic impedance mismatch. I think I asked John if he had considered flaring his U-baffle to allow more damping material and transitioning the TL terminus more gradually. I believe he said he had not. At very low (subwoofer) frequencies, this would probably have limited if any effect.
JohninCR's case is different, because he is using a midrange driver in an H-baffle. Frequencies will certainly be higher. I have no idea how he figures it will have more controlled directivity than the dipole cancellation on a flat baffle, but John has promised to suprise me with measurements of his various builds, so I guess we'll see. I would be particularly concerned with increasing D to that length, not to mention reflections within the horn from various points on the cone.

Lots of times it will take days for me to respond because I am often busy listening to music rather than mucking about with a computer keyboard

cheers,

AJ

[scorpion]

I'll contribute with the link to the ARTA measurement software which I wrote about in another thread: http://www.fesb.hr/~mateljan/arta/news.htm .
As Rudolf probably knows this software is subject to a favourable review in the current issue of German Hobby HiFi. They also used it for
guite a number of measurements presented in other articles in the magazine. 

/Erling

[JohninCR]

Rudolph,

If Thuneau doesn't come out with their measurement app soon, I will give something else a go.  I've been doing a lot of construction while patiently waiting, and was really looking forward to the direct tie in to their active XO/EQ system, which I use. 


AJ,

Don't worry, I've already been plotting how to pull off a CDDWG-RLH.  My problem remains a suitable driver.  I have no doubt that measurements will help toward optimizing my OB-RLH's, because I don't really understand exactly how they function.  They definitely add significant bass extension, but whether or not there's horn or TL action going on or that they simply syphon off some of the lowest frequency content of the rear wave and apply a longer delay to it, I don't know.

The CDDWG's are a different story.  I'm just borrowing the work of others who figured out the physics and applying it in a different way.  It's actually pretty straight forward, and if any flat baffle dipole designs came close to Geddes' Summa in terms of controlled directivity, they would of course display those results prominently.  For my design the real question is, did I go with the correct waveguide size to provide a good transition from waveguided directivity to dipole directivity in the lower frequencies?  Even if I missed the mark, I'm clearly obtaining some significant benefits, especially by correcting the HF beaming of a fullranger.  This greatly broadens the area of prime listening.  Also, I have to believe that eliminating the midrange prominence of output way off axis is a good thing, because it means that reflections of that output have better frequency balance which is the concept behind Dr. Geddes' design.  His OS waveguides may well be the optimum, but I can't determine how much they reduce HOM's compared to a conical shape until I figure out how to build some and do so.

Until I get around to measuring go ahead and snipe away.  Try to come up with flaws in my ideas or execution, or even more stuff like Beranek's Law...  something that might be useful.  I believe that totally discounting ears as our most sensitive design instruments is a real mistake.  Do you really think that I just build a wacky speaker idea, play some music, and then spout off about how wonderful it is?

[Bob in St. Louis]

Do you really think that I just build a wacky speaker idea, play some music, and then spout off about how wonderful it is?

No, I don't believe for a second that you would John..............
.........But I might.  aa

Finally finished, sans a little tweeking here and there.

Bob

[Viridian]

John,
Is there a "rule of thumb" that you used to get the dims for your cddwg/rlh or was it just intuition? I ask because I wonder if anyone would be willing to do what you have done but with a different driver. I was thinking of the SI's. Huge, I know. I understand that you had abandoned using styrofoam since the fiberglass resonated too much, but what if someone were not averse to it being unfinished? If I were to laminate that stuff together and carve it into a solid sphere then cut out the wg apertures front and rear... What do you think? how big of a sphere would it need to be? 90deg opening front and rear or is it not constant? Perhaps a silly idea, but then why not?

I am creeping into this OB thing very slowly. I just won and am soon to receive a pair of 12" Corals(not FR, alas) from eBay. Hooray. BTW, do you know if there exists the sort of software you are using as xover for Mac? Otherwise I will have to go with a Pro Xover like MJ's DBX or something to pair with my DEQ2496.

This has been fun reading and seeing what you guys have been doing. Thanks for sharing with us lurkers.

Erik

[gooberdude]

Hey Bob,

When you can crank those baffles out for $20 each, put me high up on your list!!!        i need 2....

With my recent Silver Iris experiences it seems like them big drivers could sit in a food pantry powered by a loaf of bread and still kick out marvelous jams.  Pun intended??   

OB lovers need to have a pair of these around for the rainy days.   Is OB a PITA?  Just SI....

So how do your new baffles sound Bob??   


matt

[opnly bafld]

Hey Bob,

When you can crank those baffles out for $20 each, put me high up on your list!!! 

Matt,
If you can drive down to St. Louis and back on $40 of gas, just wait a few weeks and Bob will probably GIVE them to you.

Lin

[Bob in St. Louis]

Matt, they sound good. I spent some time last night listening to 2 channel, and watching a movie. They do seem less thin, a bit more full than the baffleless stop signs. Time will tell whether or not they're sonically right, but visually I'm less than ecstatic.

If you can drive down to St. Louis and back on $40 of gas, just wait a few weeks and Bob will probably GIVE them to you.

Yup. aa

Bob

[gooberdude]

i wonder if the metal brackets close to the magnets is affecting things?  just kidding!!!

you really aren't that happy with them??


Are they grounded, felted & de-screen'd?    If not, start there.   

Mine work best pointed towards the sky - up, up & away...about a 40 degree angle in their baffles is good.