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Old 6th December 2012, 07:15 AM   #11
more10 is offline more10  Sweden
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If you are going to build, or have someone build, JBL 2226 ported something I built from srx boxes. There is one Eighteen Sound and one Faital Pro that can be used instead of the JBL. Trapezoid shape is not essential. It is about 200 liters. With wheels you can handle it self, without you need help.
Interesting as well. I'd obviously go with a different box shape as I don't have any srx boxes, but interesting none the less.
The base for this box is actually an extended bass shelf. The height of the box and the placement of the driver are essential. The quarter wave operation gives some extra spl in the knee of the EBS.

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Tapped horns are difficult to integrate. Ported box is simpler.
Can you expand on this? Are you saying physically? Acoustically?
Any quarter wave tube is going to show phase shifts at 3 times its base frequency. This means high group delay, and often spikes in the spl graph. You want to crossover below these frequencies. Check the grup delay for any tapped horn that is suggested. A group delay of about 10 ms at 100 hz is acceptable, and it should not rise at higher frequencies.

If you decice to use a TH in the region where it is doing fast phase shifts, the filter is going to be tricky to make, since the two boxes are in phase or out of phase very close in frequency.
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Old 7th December 2012, 06:53 PM   #12
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Originally Posted by vhayduk View Post

Very interesting. I haven't seen that thread before. Would a moderate volume increase benefit this design? Say ~25%? The reason I ask is it might work well for me to adapt this into an "L" shape design with the drivers in line rather than staggered. I'll make up a sketch for you to critique.


The one that has really grabbed by attention is the Dual Lab 12. Still reading
Vince,

I measured dozens of actual cabinets before arriving at the WS Lab 2x12, it is pretty well optimized for the low frequency extension chosen.
Larger volume will increase the LF "hump" around Fb, and the speakers will run out of Xmax at less than 400 watts per driver about 1/3 octave up from Fb.

Changing the shape should not be a problem, but you will probably have to experiment with port length to get the same tuning.

Art
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Old 9th January 2013, 03:14 AM   #13
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So I've pondered things over Christmas and have finally made a decision.

Upon reading TONS of pages of info on tapped horns I've decided that front loaded is a better option for me.

I fell in love with the Welter's 2xLAB12. The problem that I have right now is is that I don't really need two 2xLAB12. I don't have the amp power, nor $ to invest in 4 x drivers + another amp. So I started messing around in Bassbox. First I modeled the LAB12 and then started playing around with a single LAB12 box that had the same freq response. Obviously it is 3db down on the the 2xLAB12 output-wize per box, but I managed to get everything else matched up one-for-one with the Welter 2xLAB12. Outside box dims come to 15" high x 24" wide x 19.5" deep (with front baffle @ 18"). Full-height slot port on one size.

Started making sawdust yesterday; I'll post some pictures once I make meaningful progress.

Thanks for all the input and guidance. I"m really looking forward to getting my rig up and running.

Vince
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Old 9th January 2013, 03:20 PM   #14
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Originally Posted by vhayduk View Post
The problem that I have right now is is that I don't really need two 2xLAB12. I don't have the amp power, nor $ to invest in 4 x drivers + another amp.
Obviously it is 3db down on the the 2xLAB12 output-wize per box, but I managed to get everything else matched up one-for-one with the Welter 2xLAB12. Outside box dims come to 15" high x 24" wide x 19.5" deep (with front baffle @ 18"). Full-height slot port on one size.
Vince,

The single 12 box will be 6 dB down in output from a dual 12, -3 dB from loosing half the cone area, -3 from half the power.

Your box is now almost the same size and shape as the DSL CS-30, you might want to consider the port design it uses, similar to the diagram below.

Art
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File Type: png Venturi Port.png (118.5 KB, 83 views)
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Old 9th January 2013, 03:33 PM   #15
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See if you can find the Speaker Builder article on the "show horn" which was a very small very sensible folded horn.

If it was me, I'd get a flat-packed trapeziod cabinet kit and slap in a popular woofer, leaving it sealed. Then you can add more whenever you want, and have something scalable and versatile that you can cross over many different ways as part of a main or monitor system, covering wideband for a small system or narrow-band addition to a high-power system.

Last edited by cyclecamper; 9th January 2013 at 03:36 PM.
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Old 9th January 2013, 03:35 PM   #16
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Art,

Of course it is 6db total... I meant watt-for-watt (so 400W for one box), a single is 3db down on a dual due to cone area.

Can you shed some light on the advantages of a such a port vs a standard slot port? How is such a port tuned? Basically becomes rear-horn loaded?

Thanks!

Vince
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Old 9th January 2013, 03:37 PM   #17
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Originally Posted by cyclecamper View Post
See if you can find the Speaker Builder article on the "show horn" which was a very small very sensible folded horn.

If it was me, I'd get a flat-packed trapeziod cabinet kit and slap in a popular woofer, leaving it sealed.
Too late (by one day)

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Started making sawdust yesterday; I'll post some pictures once I make meaningful progress.
Thanks for the comment though; something to consider for next time.

Vince
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Old 9th January 2013, 04:08 PM   #18
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Originally Posted by vhayduk View Post
Can you shed some light on the advantages of a such a port vs a standard slot port? How is such a port tuned? Basically becomes rear-horn loaded?
Vince,

The port is still a port, but probably behaves a bit better at high excursion.
From the DSL CS-30 specs it looks like it tunes close to what it would if it was as thin as the center of the port.

The inside (right side) upward leg of the port end mimics the front baffle, so the air flow in and out is more similar than a regular slotted port.

Your cabinet is 3" more shallow (and has less cabinet volume) than the CS-30, so unfortunately to tune as low as the CS-30 and still maintain the back distance on the upper leg would require a smaller center area, which may be too small for full excursion without excessive air velocity.

By the way, had you made the dual 12" box and just used one cone, the output at 40 Hz is within a dB of the dual using the same drive voltage.

Art
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File Type: png Dual,Single.png (82.5 KB, 76 views)
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Old 9th January 2013, 04:24 PM   #19
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Ok, that makes sense. I agree that I don't think I can tune quite as low as the CS-30, but it is still an interesting port concept.

In post #14, the drawing shows the narrow portion of the port to be 3.81cm. It APPEARS that this is is an OD measurement (including the cabinet and port wall), however I doubt that. Assuming 18mm plywood, that would mean a port size of 2.1mm??? 3.81 must be the ID measurement...

If so, that is not far off of mine. My port came out to be 13.5" high x 1.9" wide x 22" long. I could work a CS-30 style port into my box... hmmm!

Vince
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Old 9th January 2013, 05:26 PM   #20
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Originally Posted by vhayduk View Post
Ok, that makes sense. I agree that I don't think I can tune quite as low as the CS-30, but it is still an interesting port concept.

In post #14, the drawing shows the narrow portion of the port to be 3.81cm. It APPEARS that this is is an OD measurement (including the cabinet and port wall), however I doubt that. Assuming 18mm plywood, that would mean a port size of 2.1mm??? 3.81 must be the ID measurement...

If so, that is not far off of mine. My port came out to be 13.5" high x 1.9" wide x 22" long. I could work a CS-30 style port into my box... hmmm!

Vince
I assume that with a 22" long port in a 19.5" deep box means you have one bend already, the inside "leg" of a venturi port would be away from the cabinet wall, so it should work about the same as the CS-30.

Your smaller cabinet will need a higher tuning to keep the low end "bump".
Or you can tune it lower and have it flat or slightly dropping off towards Fb.

You can check Patrick Bateman's drawing for accuracy, I pulled the picture from post #7 in this thread:
Featherweight Title Fight

Art
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