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Paul S
San Diego, California, USA
Posts 2,664
Joined on 10-12-2006
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1
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Post ID:
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27105
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Reply to:
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27105
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The Loudspeaker (Troels Gravesen project); Finally!
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The Loudspeaker (Troels Gravesen project); a report started "too soon" because they've taken sooo long to build, and they fired right up (first try), and they already do Music!
For some time (at least a decade) I thought about
building a very large center speaker, in order to add power and Musical presence
to my stereo system. I played with many vintage drivers, trying to improve the
sound and increase the amount and range of Musical sounds I got from them. Fair
to say, I learned a lot, including sobering up with regards to my own
manufacturing capabilities. As it turns out, I just don’t have the chops to
make my own drivers. During this time I listened to and kept track of many stock
speakers and drivers that interested me, including re-built and classic-type direct,
horn, and hybrid speakers. I ran across Troels Gravesen’s website a couple of years
ago, and I liked the way he went about things and what he said about vintage
drivers and open baffle speakers that I already knew something about. When
Troels came up with The Loudspeaker, I was hypnotized, and I saved up and
bought the Jantzen kit (which includes full specs), then I back-ordered the
drivers from US-based pro sound distributors. I used Visaton horn UHF drivers. My hopes/expectations were fueled
by “classic” JBL speakers I have heard over many years. Generally speaking, I
was hoping to wind up with speakers that were very immediate and lifelike
without being too shout-y or pushy. Due to the pandemic and personal health
issues, it’s taken me a long time to finish this complex and difficult project. Anyone interested in what Troels has to say about it can go here: http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm
Troels’ original The Loudspeaker is either based on or
it’s coincidentally very similar to the fairly short-lived JBL 4345 studio playback
monitor, a Greg Timbers design/model I’d heard about but never actually heard. For
better or for worse, Troels’ version uses selected and mated modern/contemporary
“pro” divers rather than re-built or new JBL “tribute” drivers, along with Troels’
proprietary crossovers and his own cabinet design, which is very similar to but
not the same as the JBL 4345.
Please note: IMO, The Loudspeaker is not a good first (or
second…) DIY project. It’s just too big, heavy (over 200#/ea.) and complicated
for a rooky to handle. This was a very difficult project for me despite I am a
Master Carpenter with over 50 years of experience and lots of tools. Basically, these cabinets are a job for a fully-equipped (and properly staffed) cabinet
shop with full scale panel saws, etc. In fact, CNC would be nice! My approach
was to “circumvent” the fixed equipment with very basic “work-arounds”,
including dead flat cutting tables on the garage floor, a special blade for my
Skilsaw, and several straight edges. I can’t in good conscience “recommend” any
of my work-arounds; there’s just too much margin for error, especially given
the cost of the Baltic Birch plywood, which is very “unforgiving” and difficult
to process under the best conditions. Further, glue-up of sub and main
assemblies also requires flat tables, and 3-D controls. There are lots of
pieces, and assembly is very complicated and nearly impossible without a lot of
pre-engineering and pre-fitting, and, preferably, another pair of experienced hands,
not to mention loads of clamps and well-thought-out control measures to get and
keep everything in line for clamping before the glue sets up. Regarding construction details, I will tell more on Troels’ Builder Response board only.
Here at GSC I’ll try to stick to conceptual and construction basics and focus
on the sound. I do want to want to mention that I spent a lot of extra time messing with
glues and sound deadening/dampening ideas as I went along. Also, I bi-wired
(and internally wired) my Loudspeakers with 12 gauge Speltz Anti-Cable speaker
wire. One pair of speaker wires goes from the amp to the woofer X/O, and the
second pair of wires goes from the amp to the X/Os for the rest of the drivers.
I should also say that my X/Os are all passive, at speaker level. My amps are
Marantz MA9-S2 monoblocks that are literally made for bi-wiring, and these amps
put out a lot of power, including a whole lot of current. I have already posted
plenty about these amps on this board, and they are an integral part of my speakers in my
system.
Per Troels, The Loudspeaker is a 95 dB efficient, 4-way
design that uses an 18” treated paper woofer in a big reflex cabinet from about
25 Hz up to ~160 Hz; a 10” paper cone midrange unit in a sealed box up to
~1,300 Hz; a compression driver and a short horn for upper-mids and treble to
~9k Hz; and I use a compression horn for UHF above 9k Hz, for anyone who can hear
it. Again, look at Troels’ site if you
want full specs. Please understand that I am not offering any specs as “proof”
of anything, in any case. I will repeat,
because I like this quote, what the original designer of the JBL 4350, Greg
Timbers, said of that speaker, that “It does not know it is not supposed to
sound as good as it does.” When it comes to designing a loudspeaker, I agree
with Troels that any loudspeaker is a pile of compromises, so it’s basically a
matter of Pick Your Poison.
Like I said, too soon to say much. So far, I've only listened to 3 LPs: Kind of Blue; Sketches of Spain; Solti/Chicago Symphony Orchestra, Bruckner 7. I actually built them to try to further explore Bruckner and other "difficult" Music, and indeed, new Musical doors are already opening.
Paul S
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