Well, it was 1974 a mere 38 years ago. I didn't remember the 2 and 4 woofer options. wow!
Well, it was 1974 a mere 38 years ago. I didn't remember the 2 and 4 woofer options. wow!
Wow! Those are some old plans! The bracing is interesting and very much along the lines of what I would add to my cabinets. The tuning of the enclosures in your plans is interesting too. The cabinets are tuned lower than I expected and, if I'm reading this correctly, the resonance that you are supposed to perceive is higher. Did you put the 2405's off center? I remember reading that high frequency drivers are often placed to maximize separation between channels. I am planning the right and left cabinets to be mirror images.
I should clarify that my need to keep the cabinet size limited is not driven by floor space, but rather, my spouse's concern that the speakers will become the focal point of the room. I have a Sunn 215BH bass cabinet (JBL loaded) in the garage and she doesn't want anything that size, or even close, in the house. I think she's OK with the 4647 size, if its veneered and looks like a home speaker. To keep everyone happy I'll have one-off cabinets based on the the 4647. I knew there would be compromises, for engineering and domestic reasons.
I'm hoping to post some drawings soon.
The isobaric concept lost favor when the need for a second set of 2225's came up. This project started because I needed to clean the garage. No new speakers!
I'm now looking at the cabinet materials. Plywood with with cherry veneer is available and I'm wondering if that is better than particle board. Baltic birch would be preferable. Does anyone know if plywood is an acceptable alternative to the particle board?
Birch plywood is probably the best material you can find.
Check out Some photos of my 4345 clones. If you need inspiration :-). You can come quite close with an ordinary router.
If your spouse has opinions about the size of your speakers, you can get deeper bass with the same box size. Since the 2225 is a pro driver with strong motor and high VAS you will need a big cabinet to get deep bass.
I did mirror the baffles (left/right) so the mid-range driver locations furthest apart for separation. The 2405 slot tweeters send the high frequencies evenly around the room and could go on the inside.
Since all speakers are installed from the front with tee-nuts, I dado'd a groove in all four sides to receive the baffle and back. Leave a 1/4" reveal at the back and 1/2" recess at the front for the grille cloth fame. The 3/4" front and rear exposed edges need to be veneered in birch unless you want to showoff the lock-miter joint or veneer everything. I did straight (45 deg.) miters with 2x2 pine glue-blocks front to rear.
The thing I liked was the baffle to back bracing on all midpoints of the sides (and the 1x3 pine braces across the back). Maybe the Sun had more bracing than the Showman cabinets I copied (6" o.c. screws). The front to back braces really made the baffle, weakened by the speaker cut-outs, rigid. The ribs across the rear panel were effectively making 3- 1'x2' panels instead of 1- 2'x3'.
For sound reinforcement I think the idea was to get the most speaker surface area in the smallest cabinet and lowest weight. Increasing to 18" deep would be better for bass, but so would a bass reflex cabinet.
I've finally got some plans and graphs to share. The graphs are from WinISD and show the SPL and gain for components in a 5 cubic foot box.
I've added K130's to the list of possible components, as I have one and a D130F reconed with a K130 kit. I understand the specification follows the cone if the motor is the same. Originally, I didn't include these because I thought the E130 would be smoother. Not so! My initial intent is to use the 2225's, but perhaps later add a sub and install the K130 or E130.
I got curious what enclosures the 2403 was used in and searched. That brought me to the EN5 low frequency enclosure. http://www.jblpro.com/pub/obsolete/l...nclosures2.pdf The recommended components are what I've got, although no specific mid driver was recommended. I believe the 2205 was a predecessor of the 2225 and the response curve is close to what I'm getting out of WinISD for my cabinet. Because I want to put the smith horn on top, I'll continue developing my box design. At least I'm pretty sure I'm on the right track!
Here's the preliminary plans. I'm still working out details on the joints, as I want walnut on all the corners and also to round them over on a 1/4" or 3/8" radius. The port and 076 locations could still change, but the 4 inch ports will allow for higher or lower tunings. I'll initially tune to 40hz.
The bracing where the panels meet will probably be 1X1 hardwood and has not been added to the drawings. The 1X3 side bracing will continue to the back which will have the same overall dimensions as the baffle. I think the top/bottom will have a single 1X3 brace in the center from front to back. There will also be a brace from the baffle to the back panel.
More to come soon.
I'd offset the 15 to one side of the box (to help with standing waves), use 2x4 (old school) bracing.
Good point Maxwedge. Standing waves, those pesky constant zones of high and low pressure when the length of a sound wave is a whole or fraction of the distance from the reflective surface (back panel or walls in the room). I've been thinking of using R19 to help dampen the effect and add virtual volume, but yes, off-setting the woofer can help. I've redrawn the baffle so many times that I've finally made paper cutouts of the drivers and ports!
If I use 2X4's, I'm a little concerned about the volume consumed and whether the virtual volume from the insulation will be enough to compensate. A 2X4 is really solid though. In the past, 2X2 and 2X4 were the stock choice for bracing my cabinet builds. But, those were bigger cabinets. I may have to see if there's meaningful comparison of 2 by stock versus a smaller unit of dense hardwood. The goal is making the panels rigid and joints solid.
Designing from the ground up really makes one appreciate the efforts the folks at JBL put into their products and the efforts of other DIYer's.
Remember 2x4, 2x2 1x3 ect isn't really spec, it's less. I'm sure if the cab is smaller, less bracing is in order. Real 2x4 = 1 3/4 x 3 3/4. Regardless, I like to use a 2x4 T brace at the top of the woofer across the baffle to the back wall of the cab. Where the leg of the T hits the back, I put an approx 12" square piece of 3/4" ply to spread the load on the back panel. This really stiffens up the cabinet.
You are absolutely right that the bracing from the baffle to the back should be substantial and well supported. 1 X 3 would be less than adequate for this. The 4647 cabinets also had a brace from side to side, but no braces across the sides. I think bracing the sides like the EN5 will be the way I go. The goal is to make them rigid. If they have any give, I can add a cross brace later.
I've been thinking about standing waves since your post. They can cause a woofer to sound muddy and poorly defined. I've finally decided that my box's internal dimensions are based on the 4647 and the JBL engineers probably dealt with the issue. I really won't know until I fire them up.
I've revised the baffle design, offsetting the drivers and ports. The attached image shows the approximate measurements. I'll layout the baffle and check it in full size before cutting any wood. All panels will fit on two 5' X 5' baltic birch plywood sheets. They are $55 locally. The JBL 2410's and 'Smith' horns will sit on top of these cabinets.
I've begun cutting the walnut for the horns. The upper and lower panels will be made up of glued up panels to reduce the chance of warping and cupping over time. The vanes will either be walnut or cherry. Hope to have pictures soon.
There's an article in a thread that discusses the horn design and has some useful information. http://www.audioheritage.org/vbullet...-me-design-one! Bob Smith's article is embedded. I notice in his article that there is no vertical tapering of the horn at the mouth as in the 2397. Additionally, Bob states the vane shape/dimension is not critical except at the low frequency of the horn. I'm considering altering the vanes and the mouth based on this information. Does anyone have strong opinions on the shape of these horns at the mouth? How would keeping the top and bottom flat all the way to the mouth affect the sound? Westlake puts a straight angle on the mouth, close to a 45 degree taper. Is this better for a diffraction horn? I have a few days before these decisions have to be made. Any input will be appreciated.
I've cut the parts for the 2397 clones and will work on the final shaping and assembly this weekend. Finally building something! I'm working on a mounting assembly for the 2410's. This should be a single unit and will be made from the claro walnut.
I've attached pictures to show the progress.
Now that looks cool!
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