SirReal63
Active Member
Hello AK, I thought I would do a little documentation of my current speaker build.
I have always been an admirer of the JBL 250 series, the shape, elegant lines and size has always made me appreciate the style and art of Greg Timbers. I have lusted after these for a long time, but other financial responsibilities and the gypsy like atmosphere of my career made it impractical to buy a set of them, complete with the sub. I had a hard enough time moving my 1983 Genesis 210's which I faithfully did until 2007, and regret letting them go every day since.
I do not really want to deal with getting an older set of 250's and having to rebuild them back to better than new condition, which I would insist on. So I examined what I liked the most about them, it was the elegant shape. I decided to go way beyond my abilities and design my own. I thought I had a clue on how to do this, then I figured out that the more I learned the less I understood, and the more I must learn. I have changed my design several times now, and hopefully I have it figured out. (I bet I have to change things again before I am happy)
Lansing Heritage (audioheritage.org) is an amazing place with more information than I would have thought possible. I was able to get the exact dimensions, drivers specs, crossover specs, internal bracing and everything I did not need, but without them I doubt I would have started this.
With the help of many resources on the web, I made my design.
The base is 24" wide and the top is 12.5" wide, the short leg is 48" and the long leg is 49.25 giving a 48" tall speaker that is 12" deep. Originally I had designed it to be 53" tall instead of 48" but it meant a lot of wasted veneer and added nothing to the acoustics.
I did not take any pictures of building the box, there are plenty of those out there.
After the box was built and partially braced, I noticed an issue, the base had a sharp transition on the sloped side. I made it the way I did to help prevent the issue the 250 had, the veneer coming off the bottom.
Veneer does not like sharp transitions, so after a lot of thinking I decided to sand it off to remove the sharp transition and allow the veneer to follow the contour.
I ended up with this, my veneer guru approved it.
A shot of the woofer area and the bracing. This cavity is 2.5 cu. ft. with two 2" ports, one facing forward and facing back and tuned to 30 hz. I hope I do not need to add any more bracing, but I know it is possible. I was able to stand on it with my 190 lbs and had no deflection.
The upper part of the cabinet.
The cabinets after filling, sanding, shellac and finish sanding, ready for veneer.
The veneer is flat cut Teak from Veneer Factory Outlet, Bob is a great guy, he answered my questions and took more time with me than I expected.
The drivers are not JBL or even high quality drivers, but the specs indicate they should work well together.
The tweeters are Eminence APT 200 horn loaded drivers, they will be crossed to 3500 hz and above. There will be an L-Pad to attenuate as needed.
The mids are Faital Pro 6FE100 limited to 3500 hz on the high end and 100 hz on the low end. This should work well as the faital's get peaky above 3500. There will also be an L-Pad to attenuate as needed.
The high and mid will be wired in parallel to get to a 4 ohm load.
The woofers were a challenge and they get replaced. They are GRS 12SW-4 and are really a subwoofer but do reach 700 hz, they will be crossed to 500 hz and below, these are 4 ohm. I chose them because they were a perfect fit for 2.5 cu. ft. and 30 hz. They were inexpensive so if I have to change them I can. I suspect I will not have to.
The parts layout.
The rear panels are in two parts and will be held in place with 1/4-20 SS bolts and insert nuts to allow easy removal.
The crossovers are cheap Dayton parts, which is ok, the long term goal is to use an active crossover. I have this set up for a bi-amp system but with the bridges it can play with a single amp at 8 ohms.
The amps I chose are simple and inexpensive, the mids and tweets will run off a Sonance 260x3 at 4 ohms which will send about 50 watts to each speaker. The subwoofer will be run off a Sonance 275x3 at 4 ohms which will send about 120 watts to each. I really like these amps, they are bulletproof and over built. They are designed to sit in a closet and be forgotten, the auto on feature is great and they are stable down to 2.7 ohms. After hours of use they are barely warm.
The pre-amp is an Outlaw Model 950 which was not my first choice but I am happy with it and the price was unbeatable.
I have always been an admirer of the JBL 250 series, the shape, elegant lines and size has always made me appreciate the style and art of Greg Timbers. I have lusted after these for a long time, but other financial responsibilities and the gypsy like atmosphere of my career made it impractical to buy a set of them, complete with the sub. I had a hard enough time moving my 1983 Genesis 210's which I faithfully did until 2007, and regret letting them go every day since.
I do not really want to deal with getting an older set of 250's and having to rebuild them back to better than new condition, which I would insist on. So I examined what I liked the most about them, it was the elegant shape. I decided to go way beyond my abilities and design my own. I thought I had a clue on how to do this, then I figured out that the more I learned the less I understood, and the more I must learn. I have changed my design several times now, and hopefully I have it figured out. (I bet I have to change things again before I am happy)
Lansing Heritage (audioheritage.org) is an amazing place with more information than I would have thought possible. I was able to get the exact dimensions, drivers specs, crossover specs, internal bracing and everything I did not need, but without them I doubt I would have started this.
With the help of many resources on the web, I made my design.
The base is 24" wide and the top is 12.5" wide, the short leg is 48" and the long leg is 49.25 giving a 48" tall speaker that is 12" deep. Originally I had designed it to be 53" tall instead of 48" but it meant a lot of wasted veneer and added nothing to the acoustics.
I did not take any pictures of building the box, there are plenty of those out there.
After the box was built and partially braced, I noticed an issue, the base had a sharp transition on the sloped side. I made it the way I did to help prevent the issue the 250 had, the veneer coming off the bottom.
Veneer does not like sharp transitions, so after a lot of thinking I decided to sand it off to remove the sharp transition and allow the veneer to follow the contour.
I ended up with this, my veneer guru approved it.
A shot of the woofer area and the bracing. This cavity is 2.5 cu. ft. with two 2" ports, one facing forward and facing back and tuned to 30 hz. I hope I do not need to add any more bracing, but I know it is possible. I was able to stand on it with my 190 lbs and had no deflection.
The upper part of the cabinet.
The cabinets after filling, sanding, shellac and finish sanding, ready for veneer.
The veneer is flat cut Teak from Veneer Factory Outlet, Bob is a great guy, he answered my questions and took more time with me than I expected.
The drivers are not JBL or even high quality drivers, but the specs indicate they should work well together.
The tweeters are Eminence APT 200 horn loaded drivers, they will be crossed to 3500 hz and above. There will be an L-Pad to attenuate as needed.
The mids are Faital Pro 6FE100 limited to 3500 hz on the high end and 100 hz on the low end. This should work well as the faital's get peaky above 3500. There will also be an L-Pad to attenuate as needed.
The high and mid will be wired in parallel to get to a 4 ohm load.
The woofers were a challenge and they get replaced. They are GRS 12SW-4 and are really a subwoofer but do reach 700 hz, they will be crossed to 500 hz and below, these are 4 ohm. I chose them because they were a perfect fit for 2.5 cu. ft. and 30 hz. They were inexpensive so if I have to change them I can. I suspect I will not have to.
The parts layout.
The rear panels are in two parts and will be held in place with 1/4-20 SS bolts and insert nuts to allow easy removal.
The crossovers are cheap Dayton parts, which is ok, the long term goal is to use an active crossover. I have this set up for a bi-amp system but with the bridges it can play with a single amp at 8 ohms.
The amps I chose are simple and inexpensive, the mids and tweets will run off a Sonance 260x3 at 4 ohms which will send about 50 watts to each speaker. The subwoofer will be run off a Sonance 275x3 at 4 ohms which will send about 120 watts to each. I really like these amps, they are bulletproof and over built. They are designed to sit in a closet and be forgotten, the auto on feature is great and they are stable down to 2.7 ohms. After hours of use they are barely warm.
The pre-amp is an Outlaw Model 950 which was not my first choice but I am happy with it and the price was unbeatable.
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