CHR 70A Gen3 Dual Driver for Pensil - Page 3 - diyAudio
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Old 1st February 2014, 05:33 PM   #21
JoeyGS is offline JoeyGS  Philippines
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Great idea! Got belden CAT 6 lying around. Thanks



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We happily ise 2 strands pulled from solid core CAT5.

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Old 28th February 2014, 09:00 AM   #22
JoeyGS is offline JoeyGS  Philippines
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Default Dual CHR70a gen3 on Pensil R70.3 box

I have progressed in nearing completion of my dual chr70a gen 3 and R70.3 combo.

My build utilized the existing R70.3 dimensions and added a second driver. I just proceeded despite the advices given in this thread as the holes were already made prior to the consultation. And since my ultimate purpose is to play around with Mark's excellent driver and really see what it can do, this also gave me the opportunity to experience the possible effects if the box design was not followed to the letter.

My purpose of adding another driver is to increase the SPL and comfortably fill my room with sound. More low bass was not in the priority as I am comfortable with working the main speakers with subs. I was more interested in producing the best highs and mids with ample bass probably until in the 45-50hz range. The rest of the bass can be handle by subs.

19mm birch plywood was used for the box. No damping was used, but instead polyfill sheets were teased to give it a good spread and thickness of about 1 to 1-1/2inches (25 to 38 mm) and lined along the top, back and side walls. What I thought of the poly lining was that, if I provide enough thickness and not too dense, I would be able to eliminate the box internal reflections, prevent the walls from resonating negatively and allowing the drivers to work naturally and still allow the bass to travel smoothly from the box into the port. In this way, I wanted to create a, sort of, infinite baffle and that while I have doubled the drivers without doubling the volume and port size, the supposedly undersized box will still allow the drivers to perform optimally.

After 150++ hours of burn-in, I hear smooth and detailed highs, palpable mids and surprisingly tight and articulate bass which I hear to be within the 40-30hz range. I was so happy with the results. The cymbals and the drums were even better than my Magnepan SMG-c as they are heard to be very organic and raw. Decays are very natural and with most of my music material, I may not need the subs. I can feel the thud of the bass on dynamic passages, the soundstage is wide and deep and layering or presentation of the performers are easily discerned.

I ended with both drivers per channel powered. While having one of the drivers as a passive driver also yielded good results, its better to power both as the frequencies are more balanced and dynamic.

The paint finish still has to be completed ........ the back portion has no finish yet due to the tuning process.

Attached are some build photos for your appreciation.......

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image by jgseverino, on Flickr

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image by jgseverino, on Flickr

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image by jgseverino, on Flickr

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image by jgseverino, on Flickr

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Old 28th February 2014, 07:35 PM   #23
chrisb is offline chrisb  Canada
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nice wall diffusers, and I assume "bass traps" of some type - any particular formula for those
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Old 28th February 2014, 08:09 PM   #24
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Look like QRD diffusors to me:
QRD diffusers: Technical Overview
QRDude: Quadratic Residue Diffuser calculator
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Old 1st March 2014, 12:31 AM   #25
JoeyGS is offline JoeyGS  Philippines
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Scott is right. They are QRD diffusors, 1ft x 1ft in size and interlocked to form the wall
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Old 3rd March 2014, 07:55 AM   #26
JoeyGS is offline JoeyGS  Philippines
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Mark, Chris, Scott, Dave and all pensil users........

My Pensil/CHR70.3 build has deviated from the CHR70.3 and have no clue if it's performance now is optimal apart from it sounding very good to my ears. I have not heard or built this box with a single driver, so I have nothing to compare with.

So theoretically, when I just added the second driver but have not increased the box volume, have not adjusted the driver alignment and have not increased the port area ...... what is the expected behavior of the speaker based on the original computations and tests?

Would be nice to learn the science from the experienced and expert builders and users.

Thanks
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Old 3rd March 2014, 02:53 PM   #27
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Since Vas has doubled, the alignment significantly changes from what was designed, with attenuated LF gain. As noted, it is not something I recommend doing, although I'm glad you are happy with the results. There is a dedicated twin driver enclosure design which I have finished however & is in the queue for drawing up.
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Old 3rd March 2014, 04:47 PM   #28
JoeyGS is offline JoeyGS  Philippines
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Thanks Scott for the insight.

Will await for the twin driver enclosure.


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Since Vas has doubled, the alignment significantly changes from what was designed, with attenuated LF gain. As noted, it is not something I recommend doing, although I'm glad you are happy with the results. There is a dedicated twin driver enclosure design which I have finished however & is in the queue for drawing up.
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Old 3rd March 2014, 04:51 PM   #29
JoeyGS is offline JoeyGS  Philippines
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Would it help if the port is increased double of its original size?
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Old 3rd March 2014, 05:12 PM   #30
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No, considerably worse.
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