Hi all,
After the warm welcome in the introductions section I decided to post something that resembles a build log in this section of the forum.
This thread is meant to document the process of a recently finished build, but since this is my first rodeo with this driver I would also like to compare notes with those of you who have experience with the GPA driver or Altec predecessors. Also, please feel free to ask me questions about the process or result.
The idea is to keep updating this thread to reflect changes made to fine tune the cabinets.
A summary of build details:
Well, this is about it for now. Hope I didn't bore you to death. Will keep listening and enjoying for now!
After the warm welcome in the introductions section I decided to post something that resembles a build log in this section of the forum.
This thread is meant to document the process of a recently finished build, but since this is my first rodeo with this driver I would also like to compare notes with those of you who have experience with the GPA driver or Altec predecessors. Also, please feel free to ask me questions about the process or result.
The idea is to keep updating this thread to reflect changes made to fine tune the cabinets.
A summary of build details:
- The cabinets have a net volume of about 349 liters or roughly 12 cubic feet. (Calculated the net volume displaced by bracing and driver to the best of my abilities which is more of a guesstimate than anything else)
- They were designed by Scott Lindgren by my request. He was very patient with me and instrumental in turning this duplex fantasy into a reality.
- All panels are doubled 18mm baltic birch and I copied the bracing scheme from another one of Scott's designs, the Bison cabinet.
- The driver is mass-loaded by the bracing structure and consequently by the entire enclosure. The magnet brace construction is based on these pictures @shoshin posted some time ago.
- For lining the cabinets I used 20mm thick denim insulation. I lined the top, one side, and back panel down to about 70% of the length of the cabinet.
- I finished the cabinet in walnut veneer and used Rustins Danish Oil to finish. It was my first serious attempt at veneering and overall I'm pleased with the result. I used the iron on method with PVAC wood glue.
- Crossover is the Werner Jagush one with autoformers for the HF driver.
- I'm using teflon coated 16 AWG silver plated stranded copper wire. Double runs from amp to crossover and single runs from crossover to both LF and HF section.
- At first I was a little bit underwhelmed by what I was hearing. Everything sounded pretty flat and lifeless and double bass and bass guitar as well as some kick drums had no meat on their bones. Besides, they had to compete with unreasonably high anticipation that had been built up over the past few months (years if you count the time from first design pass to finished result). I attributed this to sub optimal speaker placement, to driver break-in, and everything else settling in.
- I started messing around with speaker placement and listening position and measuring the changes with REW. Moving them closer to the front wall has made a significant difference in the low end response of the speakers. They come in strong at slightly below 30Hz and because of the width of the baffle they sound anchored in the lower mids which I really like. Mid bass is very satisfactory, too, however I feel like this can be improved upon with room treatment.
- Subjectively some soundstage width and imaging clarity was lost when moving the speakers against the front wall and closer into the corners. I feel the resulting improvement in tonal balance is definitely worth it in my case.
- The fact that it sounded rather dull and somewhat lifeless at first puzzled me. Not very Altec/GPA like from what I've read. Placement has made a lot of positive difference in this area and simply getting some hours on the system definitely improved things furthers. I'm very happy with how things are right now.
- I feel like I've might have over damped the enclosure and driver slightly so experiments are in order. Starting with an empty cabinet to hear its effects and then slowly building up an optimal compromise. As I've read this might help the mid-bass fequencies too. I'm also thinking the 24 feet loop runs of 16 AWG wire from crossover to LF driver might impose some unwanted series resistance. I will experiment with shorter cabling and perhaps doubling the runs, too. The above experiments might bring improvement and will post my findings with the changes.
- This might sound like a negative first impression but that's not the case. I'm simply trying to understand its minor flaws and figuring out ways of optimizing the performance. On an absolutely positive note; I'm in love with these drivers! Driven by the DHT 2a3 Stereomour II amp the sound is so eerily real at times, it's startling. They sound absolutely coherent, as if you're listening to just one driver. Very cohesive and non fatiguing, no horn shout to speak of. In short: they put a smile on my face!
Well, this is about it for now. Hope I didn't bore you to death. Will keep listening and enjoying for now!
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