Open Baffle musings

[Deward Hastings]

Re: Open Baffle musings

If the tweeter response is the issue with these dipole designs, why not put the tweeter into a waveguide and control the directivity that way

All the "normal" issues still apply, especially as one pushes the M/T crossover higher. A waveguide will (typically) increase the center-to-center spacing enough to cause beaming and response irregularities around the crossover frequency (the "sounds different when I stand up" effect), so the "fix" may be worse than the problem. OTOH if the M and T are moved far enough apart that they are completely decorrelated (which is not all that far at 4-6kHz.) it might work OK . . . that's an area where I have no experience and don't find much literature reference either.

[johnk...]

Re: Open Baffle musings

OTOH if the M and T are moved far enough apart that they are completely decorrelated (which is not all that far at 4-6kHz.) it might work OK . . . that's an area where I have no experience and don't find much literature reference either.

I would not advise that. Instead of "it sounds different when I stand up" you end up with "it sounds different when I move my head 3inches."

[Deward Hastings]

Re: Open Baffle musings

The Aura Whisper would be a better choice for that kind of thing,

I like the Aura too, but haven't found its behavior as a dipole all that encouraging. It's probably worth more experimenting, though.

Lots of things to try, not so much time and energy for the doing of it . . .

[fdieck]

Re: Open Baffle musings

I would not advise that. Instead of "it sounds different when I stand up" you end up with "it sounds different when I move my head 3inches."

Reminds of my Acoustat 2+2s..... move your ahead an inch and the whole soundstage moved around. I guess you could get one of those apparatus that you place your chin on at that optomitrist.:rolleyes: Very large acoustic sources at mid and high frequencies do a lot of weird stuff like bloating image size and poor spatial location not to mention comb filtering. This comes to placement as well, try moving a 400 pound Duntech Sovereign in 1/4inch increments to get the image focus right. Oh and on thick carpet it will change the set up again after a while when the carpet compresses under the weight and tilts the speaker. And all this despite attention to driver offset, symmetry, diffraction, and controlled directivity. Its designer, John Dunlavy was an antenna designer.

[johnk...]

Re: Open Baffle musings

Reminds of my Acoustat 2+2s..... move your ahead an inch and the whole soundstage moved around. I guess you could get one of those apparatus that you place your chin on at that optomitrist.:rolleyes: Very large acoustic sources at mid and high frequencies do a lot of weird stuff like bloating image size and poor spatial location not to mention comb filtering. This comes to placement as well, try moving a 400 pound Duntech Sovereign in 1/4 increments to get the image focus right. Oh and on thick carpet it will change the set up again after a while when the carpet compresses under the weight and tilts the speaker.

Speaking of the 2+2's, I had the Model III and a friend of mine had the Model IV with the Acoustat tubes. Long before the 2+2's came out we dismantled the IV's and stacked the panels in what eventually Acoustat released as the 2+2. We were on the phone frequently with a tech at Acoustat, I believe his first name was Jack. We could not help but wonder if we were where Acoustat got the 2+2 idea from. I recall that where the 2+2's came out we called and informed them that they made one error. The 2+2's were 8 ft tall. Here in New England, at the time, ceiling heights were commonly 7' 10" which was just enough for the stacked panel, but not the extra inch for the frames on the factory 2+2s. The versions we had made were mounted on 2x4's, floor to ceiling. The were backed up by RH Labs subs if you remember them. Did some things very well, but talk about beaming, as you note, like lasers.

[johnk...]

Re: Open Baffle musings

I like the Aura too, but haven't found its behavior as a dipole all that encouraging. It's probably worth more experimenting, though.

Lots of things to try, not so much time and energy for the doing of it . . .

Been there. Done that. Don't bother.

[Deward Hastings]

Re: Open Baffle musings

Been there. Done that. Don't bother.

Thanks . . . I'll bump it (even further) down the list :D I like as a (sort of) omni, but as an extended range "tweeter" I like the Peerless 2" thingies better . . .

It does highlight a more general "issue", though . . . that all our designs are constrained by what drivers are available "on the market". I know what I want, and it would often take only a few words to describe the changes I'd like to drivers that already exist which would make them far more suitable to my needs . . . but it ain't happening. Good things even disappear . . . I had a "poor mans dipole" design almost ready to "publish" a few years ago, but right when the prototype got "stable" the essential driver (AA-6.5) went nla. So much for that one . . .

And nowhere more true than if you're looking for a good upper-mid driver for dipole use . . .

[fdieck]

Re: Open Baffle musings

Thanks . . . I'll bump it (even further) down the list :D I like as a (sort of) omni, but as an extended range "tweeter" I like the Peerless 2" thingies better . . .

It does highlight a more general "issue", though . . . that all our designs are constrained by what drivers are available "on the market". I know what I want, and it would often take only a few words to describe the changes I'd like to drivers that already exist which would make them far more suitable to my needs . . . but it ain't happening. Good things even disappear . . . I had a "poor mans dipole" design almost ready to "publish" a few years ago, but right when the prototype got "stable" the essential driver (AA-6.5) went nla. So much for that one . . .

And nowhere more true than if you're looking for a good upper-mid driver for dipole use . . .

I don't know about that....

Aura NS6-255-8A 6" sub for AA-6.5

potential mids for dipoles

Vifa TC6FC00-04 2" Full Range Paper Cone Woofer 4 Ohm (Pair)
Vifa TC9FD-18-08
Celestion Neodymium 5" Full Range Woofer
Dayton Audio DS90-8 3" Designer Series Extended-Range
Aurasound NS3-194-16A 3" Paper Cone 16 ohm (Pair)
Fountek FR88EX 3" Full Range

I think most of these would work very well without pay "silly money" for a driver which in my mind is over about $50. Save some money in your speaker budget for good crossover parts. I look for sales and got Vifa NE123W-04 for about 40 bucks apiece. I am ruthless on Ebay and usually pay half what the going high bid for used stuff is. Ebay is like the Stock market... buy low sell high. You have to look for trends or something that might be good deal for you but not others (single drivers, missing parts, stuff that needs repair.) Scratch and dent or returns to a big retailers are often great deals.

I you have been good you could ask Santa for:


Vifa NE180W, 6.5" Woofer, 4 ohm

Vifa NE123W-08 4" Full Range Woofer Speaker 4" Full Range Woofer Speaker

Both are on sale.

[Deward Hastings]

Re: Open Baffle musings

Vifa TC9FD-18-08

I like the TG9FD more . . . it's even on my "maybe" list, along with a couple Tang Bands. The others, not so much . . .

[fdieck]

Re: Open Baffle musings

I like the TG9FD more . . . it's even on my "maybe" list, along with a couple Tang Bands. The others, not so much . . .

I really like neo magnets and damped (mod podged) paper cones. I have a lot of what's on my list and they sound very good. I think the
Celestion Neodymium 5" Full Range Woofer would be great with some cone treatment. Neo magnets being small help open up the back of driver the driver for less reflections and better rear polar response.

I don't like alot of the very stiff cone materials unless they are well damped. I don't like using notch filters high order crossovers to bury resonances. A drivers with a 12dB or more peak at cone break up just asking for problems to design with to me. I just feel like the driver design has not done his job. Ted Jodan and Rudy Bozak designed aluminum cones decades ago with better damping than a lot what is out there now. They didn't have Finite Element design software and actually listened to what they were designing.

[Pete Schumacher]

Re: Open Baffle musings

All the "normal" issues still apply, especially as one pushes the M/T crossover higher. A waveguide will (typically) increase the center-to-center spacing enough to cause beaming and response irregularities around the crossover frequency (the "sounds different when I stand up" effect), so the "fix" may be worse than the problem. OTOH if the M and T are moved far enough apart that they are completely decorrelated (which is not all that far at 4-6kHz.) it might work OK . . . that's an area where I have no experience and don't find much literature reference either.

What's wrong with pushing down the XO point to 1KHz using a dipole tweeter in a waveguide? CTC issues would be almost nil at that frequency, and those larger AeroStriction Tweeters from Aurum Cantus are more than up to the task of reaching 1KHz cleanly. The Beyma TPL150 is another that has great performance that low in frequency, and would easily work in dipole mode.

[Deward Hastings]

Re: Open Baffle musings

What's wrong with pushing down the XO point to 1KHz using a dipole tweeter in a waveguide? CTC issues would be almost nil at that frequency,

There's nothing wrong with pushing the XO point down, but it doesn't cure the CTC problem because the necessary waveguide (to maintain pattern control) grows bigger proportionally. If I had my druthers I'd put the M/M (both appropriately baffled cones) cross down around 600-700, and the M/T cross up at 5000-6000, but a driver that isn't beaming (too badly) at 5000 and has enough excursion at 600 is, as far as I can find, mia.

[Pete Schumacher]

Re: Open Baffle musings

There's nothing wrong with pushing the XO point down, but it doesn't cure the CTC problem because the necessary waveguide (to maintain pattern control) grows bigger proportionally. If I had my druthers I'd put the M/M (both appropriately baffled cones) cross down around 600-700, and the M/T cross up at 5000-6000, but a driver that isn't beaming (too badly) at 5000 and has enough excursion at 600 is, as far as I can find, mia.

Only if you're looking to control directivity in both the horizontal and vertical. A big planar like the Beyma or AC 30100 will have limited vertical window anyway, but their horizontal window is large. Making a waveguide that is cylindrical rather than circular would allow closer spacing of the mid and tweeter.

[Deward Hastings]

Re: Open Baffle musings

Only if you're looking to control directivity in both the horizontal and vertical. A big planar like the Beyma or AC 30100 will have limited vertical window anyway, but their horizontal window is large. Making a waveguide that is cylindrical rather than circular would allow closer spacing of the mid and tweeter.

That leads ultimately to the argument for a dipole line array (if one can make that work over a wide enough range). Short of that solution one still gets a loss of overall pattern control, and generally still at a crossover. In effect that's what the original (single tweeter) ORION did . . . trading the back lobe (mid) for side lobes (tweeter) while maintaining overall flat on-axis and in-room power response. The change from front wall to side wall reflection proved detrimental to generating a conherent "acoustic scene", however, which led to the rear tweeter. Managing those front wall reflections seems to play a significant part in "tricking" the brain to believe that a sound actually coming from two separated (left and right) sources is coming from between them, and provicing the illusion of "stereo" from only two channels of signal.

The other end of that "design spectrum" is, of course, point source omni . . . that gives uniform power response and consistent reflection from all angles.

It's also all dependent on proper encoding in the recording . . . capturing and conveying in two channels the necessary cues to re-assemble the "scene" on playback.

[Mayhem13]

Re: Open Baffle musings

Have to disagree with you here Deward as most certainly a waveguide loaded ribbon/planer coupled to a cone woofer can result in an M/T with constant directivity. It's been done.