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Old 5th January 2004, 08:59 PM   #201
Bose(o) is offline Bose(o)  Canada
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Simon,

Are those the Seas P17RCP08 and the "up" model from the 19TNF08s? Currently I'm using the aforementioned drivers in my Open baffle project. I don't think I'll ever go to anything other than OB again, except for maybe a systme I design to sell to someone. The OBs are unusally "cold" almost dry they are so crystal clear. To the untrained ear this is a bad thing though, to many of our ears it's a new beginning.
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Old 6th January 2004, 01:29 AM   #202
MarkMcK is offline MarkMcK  United States
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While researching how to make an improved 2-inch loudspeaker driver, I experimented with a Tang Band polypropylene driver sold by Parts Express with the model number W3-881S. My experiments involved structuring the cone and designing what is inaccurately called a phase plug for this driver. Those experiments were so successful that I built a little system using this modified driver. I have been happily listening to the system for five months now.

There is nothing special about the system except it performance. It is just one 10 inch MFB woofer crossing over just below 200 Hz to a pair of the modified W3-881S’ in a couple of little boxes. The boxes are constructed of an outside shell of quarter inch thick oak veneer plywood, a damping layer of silicon-based caulk, then an inner shell of half inch MDF with internal bracing. The combination produces a cabinet that sounds a little less like a wooden box when tapped, and that radiates a little less energy than a box of ¾ inch MDF sheets.

Despite the low cost of the system, and while admittedly limited in maximum volume, there are not a lot of loudspeakers available that will outperform it. The system produces little sound of its own. Resonant structures in the modified 51 mm polypropylene cone are well controlled and markedly reduced from the stock driver. The characteristics of the system are best labeled by the words “clean, open, clear, and detailed.” Although the descriptor was mainly applied to electronics and has fallen out of favor, the loudspeaker excels at inter transient silence. Even while the violins are playing fortissimo, and the tympani are pounding away, the woodwinds still have presence and excellent distinctness.

In the rock genre, sounds, even when overdubbed and modified by the heavy use of effects, are well separated and distinct. Every layered and overdubbed effect and instrument has its own distinct space and soundstage. Wall of sound recordings start to break down into individual components. Peter Gabriel’s Up becomes a listening event worth spending an hour of your life just to listen to the production.
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Old 6th January 2004, 01:30 AM   #203
MarkMcK is offline MarkMcK  United States
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The stock W3-881S has some problems. Most egregious is too much unit-to-unit variance in performance. The driver’s frequency response needs to be rated at plus or minus 6 db. Yet the 12 db of total frequency response variance is never the same from driver to driver. Beyond that, the common characteristics are a rising response peaking between 8 and 12 kHz and then generally rolling off above that. Onset response is not bad, although showing unit-to-unit variance and showing the rising high frequency response. Decay response is not nearly as good.

Despite these flaws, the W3-881S was the best of the small diameter cone drivers I tested. Because of their price, now well over $100 US each, I do not include the Jordan 53 or Bandor drivers in a comparison with the $14 US W3-881S.
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Old 6th January 2004, 01:32 AM   #204
MarkMcK is offline MarkMcK  United States
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Polypropylene is a marvelous plastic. Its semi crystalline structure allows one to manipulate the characteristics of this material as you can no other plastic. Combine this with the chaos theory and you can devise techniques to control cone resonance with only small changes in beginning conditions. For me, this meant heating small sections of the material to slightly below the melting point of polypropylene and dimpling the surface at critical points. This modification, accounting for over 80% of the improved performance, consists of 16 small dimples whose combined area is only about 2 % of the total area of the cone. The custom “phase” plug and two small beads of glue measuring 5/8 inch by 3/32 inch near the outside edge of the cone completes the last 20% of the improvement.

After modification, the driver’s frequency response, even using the highest resolution testing and no smoothing, can be rated from 130 Hz to 19 kHz plus or minus 3 db. Many of the drivers will measure plus or minus 2.5 db. Of course, when no driver varies by more than 6 db, there is less unit-to-unit variance.

While the flat and more consistent frequency response is important for tonal balance, the real improvement comes from decay reduction. From 7 kHz to 20 kHz, the decay reduction is close to a 20 db improvement.
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Old 6th January 2004, 02:42 AM   #205
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Can you post some driver close-ups? Your mods sound VERy interesting.

dave
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Old 6th January 2004, 09:10 AM   #206
SimontY is offline SimontY  United Kingdom
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Bose(o)

Quote:
Are those the Seas P17RCP08 and the "up" model from the 19TNF08s?
No, and I don't think so, but I don't know! The tweeter is the noFerro 900, a sort of mid-range priced thing, but sounding very nice, only after it has a proper capacitor and nice wiring. Otherwise it sounded bleached and wiry. I think it has an excellent/smooth frequency response. The midbass is W17 PPI/H571/CB17RCY/P (pick a model number, any number!). I think this driver has a very low QTS, which I gather is inappropriate for open-baffle use. But I am curious about this 'loading' type.
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Old 6th January 2004, 04:25 PM   #207
chops is offline chops  United States
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Things are a bit messy right now, but oh well. Here's a couple pics of my system. If you remember how my old set-up looked, you can tell there have been quite a few changes since then.

Left side of rack:
Reciever - Yamaha RX-V740
Sub Amplifier - Carver M-400t
AudioControl RitcherScale Series II

Right side of rack:
Scientific Atlanta Explorer 2100 Cable Box
Sony DVP-NS755V SACD/DVD Player
Sony SLV-575UC VHS Deck
Panamax 1000 Power Conditioner

In front of rack:
Main Amplifier - Aragon 2004 Mk II

Loudspeakers:
Front Center Channel - Acoustic Energy Aegis One
Main Channels - Tannoy Mercury m3
Subs - DIY Twin15 Dipoles
Surround Channels - DIY 3-way towers
Rear Center Channel - Optimus PRO-X77

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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Old 7th January 2004, 09:24 PM   #208
MarkMcK is offline MarkMcK  United States
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Default W3-881S mod

I hope Dave was talking about my little system when he asked for a driver close-up.

Once the drawings (I hope to have some help from a 3D CAD pro this weekend) and writing is done, I plan to submit a manuscript of the modification procedure to AudioXpress. I don't want to go into too much detail until the manuscript is accepted for publication. If it is rejected, then much more detail will be available immediately. Otherwise, die temperature, dimple placement, and plug shape are all serious but not critical items.

Well, maybe they do tend more toward critical. It does take a modicum of skill to properly stress the polypropylene skin during dimpling and the plug profile that Tang Band uses is not the optimal shape.

From the attached picture you can get a good idea of the dimple placement and where the two glue lines are placed on the underside of the cone.

I apologize for the fuzziness, my focus depth is really shallow at this distance.

Enjoy,

Mark
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Old 7th January 2004, 09:46 PM   #209
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Default Re: W3-881S mod

Quote:
Originally posted by MarkMcK
I hope Dave was talking about my little system when he asked for a driver close-up.
He was

Thanx. If you need any help with the aXp article, i've proofed a couple others.

dave
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Old 8th January 2004, 12:18 AM   #210
Nielsio is offline Nielsio  Netherlands
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Default Re: W3-881S mod

Quote:
I apologize for the fuzziness, my focus depth is really shallow at this distance.
Maybe you could back up a bit (and zoom in) to be able to get it sharp? Also aiming a lamp at it for more light helps the camera focus and you'll get less noise.
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