Seas U16RCY/P + Seas 27TBCD/GB-DXT = Prestigious Two – Monitor DXT - diyAudio
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Old 12th June 2012, 07:31 PM   #1
gornir is offline gornir  Sweden
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Default Seas U16RCY/P + Seas 27TBCD/GB-DXT = Prestigious Two – Monitor DXT

Hi everyone,

I’ve started a new build project called “Prestigious Two – Monitor DXT” and currently I’m in the fine tuning, listening test and final measurement project stage.

This time I’ve used less expensive driver units from the “Seas Prestige line” The mid-woofer used is the U16RCY/P, which has a woven polypropylene cone and phase plug. The mid-woofer has a smooth extended frequency response with a controlled roll-off, without nasty cone break-ups. For its size it has a large radiating surface (99cm˛) and the bass performance is very good.

A variant of this mid-woofer is used in the “Sonus Faber Liuto” loudspeaker series as well as in the "Abrahamsen FS401" loudspeaker.

The tweeter used is the well-known and among DIY:ers popular 27TBCD/GB-DXT tweeter, with its unique DXT lens and great off-axis frequency dispersion.

For further details and measurements on these driver units see:
SEAS H1499 27TBCD/GB-DXT
SEAS H1520 U16RCY/P

I’ve used both these drivers in active as well as passive loudspeaker designs before, but I haven’t been fully satisfied with the end result and I have always thought they could perform even better and now I think I’ve succeeded!

The DXT tweeter isn’t the easiest tweeter to work with. Don’t misunderstand me, it’s not that hard to shape it in to a working cross-over that on paper looks good, but in my opinion this tweeter has a tendency to become dull, un-engaging and less musical in certain configurations.


I found this tweeter to work and sound the best in a second-order LR filter topology (acoustically). This means that in order to use a simple electrically first-order filter it needs to be crossed-over a bit higher up in frequency to ensure that it operates within its “comfort zone”. In this case I’ve targeted a 3kHz cross-over point for the design.

On the other hand, this requires a mid-woofer capable of a 3kHz cross-over point without sacrificing any off-axis dispersion (beaming) and to match the DXT tweeters excellent and controlled off-axis frequency characteristics. The Seas U16RCY/P fulfills that together with a very smooth and controlled frequency slope roll-off, without the need to do corrections for nasty cone break-ups.

To sum up, this all ended up in a very simple cross-over design, which was one of the goals of this loudspeaker design.

Click the image to open in full size.

Picture4: The mid-woofer cross-over filter section is an electrical first-order and is very simple and consists only of a large coil (L1) that shapes the cross-over slopes to a LR2 roll-off with a targeted 3kHz cross-over point. The inductor (L1) also tunes the “Baffle Step Compensation” (BSC).

The tweeter cross-over filter section consists of a single tweeter padding resistor (R1) and a first-order electrical filter (C1) that shapes the cross-over slope to a LR2 roll-off with a targeted 3kHz cross-over point. The value of (R1) can be changed to tailor the tweeter level to personal preferences.

The tweeter is connected with reverse polarity and (C2+R2+R3) shape the tweeters frequency response and flatten the response at higher frequencies.

Click the image to open in full size.

Picture5: Simulated 15deg off-axis frequency response with a targeted second-order LR topology (acoustical). Cross-over point at 3kHz. Note the tweeters sharp peak at the hard dome break-up frequency!

More info coming soon….

Regards

/Göran
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Last edited by gornir; 12th June 2012 at 07:40 PM.
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Old 12th June 2012, 07:54 PM   #2
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Did you buy or build that enclosure? The finish is quite nice.
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Old 12th June 2012, 08:36 PM   #3
gornir is offline gornir  Sweden
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Quote:
Originally Posted by 454Casull View Post
Did you buy or build that enclosure? The finish is quite nice.
No sorry, it's the Dayton Audio Curved Cabinet Gloss Black 302-721 enclosure. Nowadays I usually use prefabricated enclosures if it fits the loudspeaker design.

By using and re-using prefab cabs I have time to build more designs, which is for me the more fun part in the loudspeaker design, than the woodworking.

Regards

/Göran
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Old 12th June 2012, 08:51 PM   #4
sreten is offline sreten  United Kingdom
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Hi, Looks pretty good to me, simple result, due to synergistic design, rgds, sreten.
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Old 13th June 2012, 03:22 AM   #5
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Interesting, I'm curious to know how it compares to other 2 designs with the same tweeter, Markk's ER18dxt, and, especially, Seas's own Idunn, which use U18RNX/P
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Old 13th June 2012, 08:51 AM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Albrerta View Post
Interesting, I'm curious to know how it compares
to ...... Seas's own Idunn, which use U18RNX/P
Hi,

Its obviously different :

Click the image to open in full size.

with a more complex c/o and a lower c/o point :

Click the image to open in full size.

The x/o is not near LR2 acoustic as used here.

rgds, sreten.
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Last edited by sreten; 13th June 2012 at 08:53 AM.
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Old 13th June 2012, 10:05 AM   #7
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Nice crossover on the tweeter, remarkably simple! One inductor and two caps per channel - beautiful! Have you ramped up the SPL and to see how the tweeter retains its composure in the crossover region at high volumes?
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Old 13th June 2012, 10:17 AM   #8
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Excellent job Goran! I'm also curious to know if the tweeter will hold up at louder volumes.
Perhaps the X-max of the woofer will run out before the tweeter starts getting harsh.
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Old 13th June 2012, 01:15 PM   #9
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Very interesting project!
Please keep us updated about the sound and the values of the crossover components, if you don't mind (as well as cabinet size, port length and so on).
Since there already is a project with the DXT tweeter and the ER18RNX woofer, what do you think is the main sonic signature of the U16RCY? Did you also try the ER18?

Thanks!
Martin
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Old 13th June 2012, 03:04 PM   #10
boris81 is offline boris81  United States
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It will be interesting to compare the off-axis response to other designs. The Application Notes on the DXT Technology show excellent results with a 4" woofer. It seems that the DXT tweeter can be made to work well with a good range of midwoofers without compromising it's great directivity.
The design compromise in choosing a midwoofer would be that larger drivers will give better low-end extension while some smaller ones might offer lower distortion in the upper midrange.
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