SX,
Given the same voltage, two cabinets net a 6 dB gain over one. Two cabinets with smaller frontal dimensions will have less forward output than two cabinets with larger frontal area.
The difference is probably only a dB or so, and a slight change in the overall frequency response, requiring a new optimization of the Keystone exit shape for best results. If the cabinet depth is more important to you than the last bit of output, go for the change.
Art
So..having built 4 boxes using Oliver's dimensions of 9.5" and 7.15" instead of the correct 10" and 6.125"...........what might you expect the impact to be on the performance other than driver clearence ?
I'd expect the difference to be measurable, but room response differences would have far more effect.
Have you measured the output of your cabinets?
The first two I built and measured extensivly. Recall I used the Peavey LR 18 in these - so already limited output and response. Power compression at 34v, 3db dip at 70hz, 3db down at 40hz......however they still outperform the dual 18 box the drivers were in. I plan at some later point to swap out to B&C TBW100.
The second pair recently finished I have only done impedance sweep with Dayton WT3.
Interestingly, the first 2 boxes show nearly identical sweeps. The 2nd two boxes also are nearly identical impedance sweeps --yet different from the first ??
All dimensions are within 1/8", drivers are from same age and random batch. Construction is nearly the same except for two things. On second ones the interior surface is oak veneer instead of luan... and the cleat that holds the keystone face at the top is full width on first boxes but is 2" short on each side for second boxes.
Were the second impedance sweeps taken with the cabinets in identical surroundings to the first?
Good question. The first pair were measured outdoors and the second pair in my basement. However, knowing that the test is pretty sensitive to boundaries interfering...I had them positioned w/o any thing close. Still, I plan to retest outside when weather gets better here.
Thanks again for sharing your great design.
At 35 Hz, 8 feet is within 1/4 wavelength, most basements will have a ceiling boundary that is quite "close" to the floor boundary.
Art,
Besides myself, I know at least one other member is interested in the Keystone but would prefer the cabinet internals turned 90 degrees so it would be a deeper but narrower cabinet. I am willing to pay for your first hour of time to rework the internal panels. I realize the Keystone opening might not have the exact same effect but we could do our own experimenting on rhe mouth if needed. Maybe there is enough interest from other members (donations to Art) that we could persuade you to mod the cabinet for us?
Besides myself, I know at least one other member is interested in the Keystone but would prefer the cabinet internals turned 90 degrees so it would be a deeper but narrower cabinet. I am willing to pay for your first hour of time to rework the internal panels. I realize the Keystone opening might not have the exact same effect but we could do our own experimenting on rhe mouth if needed. Maybe there is enough interest from other members (donations to Art) that we could persuade you to mod the cabinet for us?
Realistically, it would take me a couple hours to rework the cabinet.
By keeping the cross sectional horn area the same, the output in general would also be the same, but to keep cross sectional area the same at the top bend with a narrower dimension will require shortening the two internal panels, which will shorten the path length and slightly raise the low frequency cut off, not good, bass fans.
The cut off could be lowered back by reducing the Keystone exit, but arriving at the proper size and shape took a lot of experimentation, and reducing the exit size (and the frontal area) will reduce overall output, again not good, bass fans.
You may be better off just widening mRgSr's PAL12 sub design to fit an 18" instead of the Lab 12.
http://www.diyaudio.com/forums/subwoofers/232219-325-lab-12-based-pa-tapped-horn-35hz-extension.html
Art
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I think there would be more takers encouraging Art to expand development of the extended version but deeper instead of wider. I'd be in. Something like, 46x26.5x30. No doubt this will take it to 2 full 4x8 sheets instead of 1.5 but curious if Art could get close to 100db 30hz 1w/1m out of it with such a simple fold...
there are many people that can*draw* up cabinet
The magic with Arts original Keystone design is that he put in the real work by building, testing, and measuring (more work than just about any design here on diyaudio).
While I would appreciate a redrawn version of the cabinet in the event I run into a pile of bc sw115's and a couple pallets of 3/4 ply, it wont be as attractive as the original version because (afaik) it will lack WelterSys's expert revisions.
The magic with Arts original Keystone design is that he put in the real work by building, testing, and measuring (more work than just about any design here on diyaudio).
While I would appreciate a redrawn version of the cabinet in the event I run into a pile of bc sw115's and a couple pallets of 3/4 ply, it wont be as attractive as the original version because (afaik) it will lack WelterSys's expert revisions.
No arguments here, I just was making the point that if I were paying to change the cabinet I would be looking to improve upon it. That said, could an argument be made since Art's testing was so exhaustive proving the design that slight variations could be extrapolated successfully?
To further illustrate your point that anyone make draw up a cabinet. Here's is my cobbled together sim for the KS 4" taller and 5" wider as suggested in the thread. This was obtained by adding 20% to throat area and 10% to length purely done for giggles and learning more about HR. (flame suit on)
To further illustrate your point that anyone make draw up a cabinet. Here's is my cobbled together sim for the KS 4" taller and 5" wider as suggested in the thread. This was obtained by adding 20% to throat area and 10% to length purely done for giggles and learning more about HR. (flame suit on)
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Hi Art and Neo Dan,
It's amazing how long it takes until one of these projects is finalized.
I noticed the dimensional update in Post #451. Has that been updated in Dan's drawing(s) as shown in Post #450/451 (nice work!)? Also, I did not see a notice to where the latest greates drawings can be found in Post #1.
As a further question/suggestion: how about making a laminated driver baffle board, e.g.: from 2ea. 3/8" or 1/2" plywood? The driver can then be inserted into the outside layer, and secured to the inside layer. This would add a little room in the front chamber w/o changing the geometry more than most people will change it through their woodworking tolerances.
Regards,
It's amazing how long it takes until one of these projects is finalized.
I noticed the dimensional update in Post #451. Has that been updated in Dan's drawing(s) as shown in Post #450/451 (nice work!)? Also, I did not see a notice to where the latest greates drawings can be found in Post #1.
As a further question/suggestion: how about making a laminated driver baffle board, e.g.: from 2ea. 3/8" or 1/2" plywood? The driver can then be inserted into the outside layer, and secured to the inside layer. This would add a little room in the front chamber w/o changing the geometry more than most people will change it through their woodworking tolerances.
Regards,
Oliver,
I screwed up the dimensional update in Post #451, when measuring my actual build template I accidentally measured the distance between the driver flange to the front panel rather than the baffle. As anyone who can add the dimensions could tell, they don't add to 22.5", but I neglected to "do the math" before posting.
Dan's updated drawings were again going off my incorrect posting, so he could not identify which dimensions were wrong.
There is plenty of driver clearance with the proper 10.5" front panel to baffle dimension, so no recess using a laminated baffle as you suggest is needed.
Art
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Hi Art,
There still seem to be some minor problems w/ the dimensions. The 10.5 and 6.125 @ the top turn-around will give you a duct height @ S1 of 3.024 instead of 2.875.
At the bottom 180° the length in the middle of the turn is the longest of the turn dimensions.
I just started to draw on this for my reference, and thought I better let you know about this. I'll attach my interim work.
Regards,
There still seem to be some minor problems w/ the dimensions. The 10.5 and 6.125 @ the top turn-around will give you a duct height @ S1 of 3.024 instead of 2.875.
At the bottom 180° the length in the middle of the turn is the longest of the turn dimensions.
I just started to draw on this for my reference, and thought I better let you know about this. I'll attach my interim work.
Regards,
Oliver,
That looks good, but the 2.875" and 6.125" dimensions are correct, reduce the 10.5" dimension slightly to make the overall depth 22.5".
Art