Planar/Ribbon Tweeters vs Domes

[FnAudioDog]

Looking for opinions in sound and dispersion differences between  Dome and Ribbon tweeters.

[richidoo]

Larger stiff domes are the ultimate, imo. Diamond is a boy's best friend. But they are expensive. Scan has a beryllium model now that is reasonable price for the performance. Eton has a magnesium dome coated with ceramic that intrigues me. Being round direct drivers, dispersion varies with frequency from omni to laser beam, so baffle angle, crossover design, room treatment and placement are critical to the sound quality you perceive. 

Ribbons offer higher sensitivity and excellent transient response for a reasonable price but they can sound thin in the lower and middle frequencies like 5-10K. The clarity and realism is extreme on RAALs. Dispersion pattern is wide horizontally and very narrow vertically. The fatty 20mm RAAL is a little better on vertical. Controlled vertical dispersion minimizes ceiling reflections which is a big advantage. Ribbons' very low impedance requires a transformer, which adds its own influence. RAAL has transformer versions with high inputZ so a triode can drive them directly. That might fatten up the sound to be one of the best possible tweeters if you can stand the complexity and price.

Compression drivers are another variety of tweeter that is catching on in audiophile circles. With an aluminum or even beryllium diaphragm the sound can be sweet, natural, extremely detailed and very low distortion, plus very high sensitivity, but they require a horn to function and that can create its own problems and opportunities. The SEOS type horn is new, and available in all sizes from 6" to 24". An 8" would allow crossover at 2k like normal tweeter, but offers ideal dispersion 90x50.

I am playing with 12" SEOS now, and I enjoy it very much even with a moderately priced CD. With a high end beryllium CD I might be in heaven. But I still am haunted by the memories of two tweeters, the accuton 1.2" (from Gemme Katana) and the RAAL 5" (from Selah Mejor.) I'd like to play with those in future projects.
Rich

[_Scotty_]

If you are considering  building your own speakers I would lean toward a Hi-Vi Research planer magnetic tweeter. Specifically I would recommend the RT2C-A,RT2-Pro and the RT1-WE.
Scotty

[FnAudioDog]

Thanks Scotty,

I'm looking at building Troels Gravesen's AT-SWs to replace my
top MTM cabs.The AT-SWs use the Swan RT2H-A ribbon.
No one has built this project from Troel's site that I know of.
Just wondering if it may be brite compared to my sea's 1" dome T25CF001. I have no experience with ribbon's.



Steve.

 

[Face]

Personally, I'm a fan of smaller ribbons more due to their better dispersion, but they can't be crossed as low and need a small mid.  IMO, the OEM RAAL is the best of both worlds, but are difficult to acquire by themselves. 

I would check out Selah Audio's selection of kits.  If you decide to purchase a set of finished speakers, both Clearwave and Selah would be excellent choices.

[BobM]

For a home built speaker I always preferred a good silk dome. They are easier to integrate with the mid/woofer and sound more "of a whole" than a metal or ribbon tweeter. Those always seem to stand out from the mid/ woofer in a discontionuous way, IMO. Also, you lose vertical dispersion with small ribbons - they just don;t seem to energize the room the way a done does.

Now the ultimate to my ears is a full length planar ribbon. No skimpy vertical dispersion, plenty of detail and space and speed. Matching it with anything though can be problematic, and it is not for a DIY project. The ultimate implementation is on the old Apogees, but then, I'm a bit biased toward those now.

[_Scotty_]

FnAudioDog, I took a look at Troels Gravesen's Tweaking the RT2H-A page and found very detailed measurements of the driver's impulse,ETC and Distortion plots as well as other measurements. My speakers use the RT2C-A in an WMTMW design with 12/oct. crossover slopes.
The superb measurements of the RTxxx design seem to actually correspond to excellent sound from the driver which is not always the case. I have always loved the sound of my speakers and it is gratifying that there is some kind of relationship between the perceived sonic performance and the objective measurements.
I think you will like the sound of the completed ATSW speaker. What I would like to see is a MTM design using two of the AT 18H52, this should allow you to use the RT2H-A without any attenuation and allow the elimination of the in-line resistors which rob any tweeter of the dynamic life it could have had. An MTM with these drivers could have a potential sensitivity of as high as 95dB.
One of the particular strengths of the Hi-Vi planer magnetic tweeters is their preservation of the dynamic life that might be present in the recording. This also seems to be a quality shared by some other Hi-Vi drivers, the F and D series of woofers seem to have an amount of dynamic life that is comparable to Hi-Vi's isodynamic tweeters.
The ATSW should sound okay as far as having a satisfying amount of body to the sound of instruments where the tweeter plays a major part in reproducing the sound of the instrument. I think one of the keys to not having a thin sound from Hi-Vi planer tweeters is to resist the urge to cross them over as low as it appears that you can based what the published frequency response looks like.
As you can see the ATSW has a crossover of about 3kHz instead of 1.5kHz which is the lower response limit of the RT2H driver. My speakers have the crossover between the mid and tweeter set at 3.5Khz.
This is a very nice cookbook loudspeaker project and with suggestions for enclosure damping that works correctly it it should be easy to build and achieve a good sounding loudspeaker.
Lets us know how it turns out if you go ahead and decide to tackle the ATSW project.
Scotty

[_Scotty_]

Please see image below:
http://www.audionervosa.com/index.php?action=media;sa=album;in=130

FnAudioDog, you can control the horizontal dispersion of the RT2H-A and how it loads the room above the crossover point by how closely you place felt to the tweeters slot. The tweeter's vertical and horizontal radiation is accomplished in part by the diffraction of the sound wave when it exits the slot.
By varying the distance of the felt from the edge of the slot you can radically alter how the tweeter loads to the room and how much HF sound is radiated to the sides. If you build the ATSW and you feel that the balance is tipped to the HF side of the equation you can push the felt in closer towards the edge of the slot. In the picture I tried to unsuccessfully to upload to my gallery you can see the spacing I used on my RT2C-A.
The felt is slightly over 3/8in away from the edge of the slot, in my case this does not reduce the apparent HF output of the speaker. I can reduce how loud the tweeter sounds by moving the felt closer to the edge of the slot. If the felt is inside 1/4in. the highs are noticeably reduced and the highs sound more polite than they should.
The felt offers a very powerful means of dialing in the sound of the speaker and matching the speaker to the room and the room's acoustics. 
Whether the felt is used to reduce the tweeter's output or just used to minimize HF diffraction from the sides of the cabinet, its presence greatly improves how smooth the speaker sounds and how well the speaker disappears.

Scotty