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Dual 15 inch Corner Bass Bin - Cornscala dbb

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Each woofer cabinet is just over 6 cubic feet. So a total of 12 feet. Infact each woofer cabinet is almost identical in volume to my Cornscalas. It could be off by a few cubic inches. The total volume of the ports is the same as well as total area of the port openings.

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So what you're are saying is the cabinet has twice the interior volume of a single Cornwall. Basically, a single cabinet is like stacking two Cornwalls?

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Yes Dean. That is correct. You would think this thing would be a monster but it isn't. Again, it has the same depth and width of a Khorn. If you look at the below pictures, you can see it is 3-4 inches taller than my KG 5.2s and slightly shorter than the Cornwalls (with risers).

If you were to add an HF section, you could make the height (and the appearance) like a Khorn.

Why did I do this? Well, it all started with that La Scala vs Cornwall debate. That was argued all the time. I think the Cornscala was the answer for that debate.

Now it would be hard to beat the Khorn. I know I can't. If you were to compare the Cornscala to the Khorn, most would laugh at that and I don't blame em. Some love the sound of the Cornwall bass. Raising the Cornscala up 3dB made a big difference. When I have this setup playing "loud", The woofers don't even move to the naked eye. In the mean time there is a lot of bass hittin me.

The Bass bin sounds great with no modification needed there. My big hurdle is the network. So far it is soundin pretty good. The 2uF cap is the Audiocap. I need to upgrade the 13 uF cap. Once, I've done this. I may throw some caps in parallel with the low pass(s). I have an abundance of Solen caps laying around (thanks to Ebay).

Any suggestions are welcome.

jc

combo2.jpg

post-16499-13819267176836_thumb.jpg

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Like your Cornscala, it's really nice work. Did you use any of the online calculators for the cabinet? You know, where you enter in the driver's T/S parameters to get the interior volume correct, and to figure the port sizes? I guess I'm curious if any of them would show you needed to actually double the interior volume. Also, I'm pretty sure that adding a second driver actually adds 6db, not 3db.

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Dean,

JC is using two totally separate Cornwall size enclosures. No connection at all between the two volumes.

Bob

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----------------

On 7/10/2005 8:06:03 PM DeanG wrote:

Like your Cornscala, it's really nice work. Did you use any of the online calculators for the cabinet? You know, where you enter in the driver's T/S parameters to get the interior volume correct, and to figure the port sizes? I guess I'm curious if any of them would show you needed to actually double the interior volume. Also, I'm pretty sure that adding a second driver actually adds 6db, not 3db.

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No online calculators.

Just made the volume and port size IDENTICAL to the Cornwall (x2). Obviously the shape is different.

I did piddle with some software (WinISD) so that I may try to mess around with other woofers. I always ended up coming back to the Cornwall cabinet. The K33 actually requires more volume than most of the 15" woofers I was interested in.

I bought one of those books you mentioned from Parts Express. It was helpful. I reread the part about the increase in 3 dB last night. Could they mean 3 dB per woofer? Maybe so.

I will say, what ever the increase is, it is obvious.

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JC,

If you double the cone area you gain 3 db's in acoustic efficiency. By wiring the speakers in parallel you gain 3 db's in electrically efficiency, yielding the 6 db gain. By wiring the speakers in series you loose 3 db's in electrically efficiency, yielding a 0 db gain. This 6 db's gain is only in theory, but in real life is a little less. Many solid state amp's will double their output going from an 8 ohm to a 4 ohm load, giving you the 3 db's of electrical gain. In your case going from a 4 ohm to a 2 ohm load will put allot of demaind on your amp. Some amps will have a hard time with that low impedance, espically tubes. You'll also notice that the amp will run out of gas at a lower volume setting. You'll hit max volume at 11 o'clock instead of 2 o'clock. I feel using a saparate coil on each woofer is a good move, since the resistance in the coils will raise the total impedance and your 2 ohm load may now be 3 ohms. In any case the cone excursion with half which is a good thing. Nice project!!

Lar

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I built some JBL 4570 clones (dual 15" + 2" HF) with the K43E instead of the JBL woofer.

http://www.jblpro.com/pub/cinema/4670d.pdf

With a B6 tuning they are -3dB at 28hz with only 8 cu ft net for both drivers, as opposed to -3dB at 40hz for the JBL woofers. They really growl on the low end, and the 2" throat HF driver really sounds great (it ought to for how much they cost).

They are mounted flush in the living room wall, as is the big screen TV.

They are about 101dB/W from 100hz~500hz, or 107dB/2.83V with a solid state amp because of the 2 ohm load.

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Great input.

Right now it is running from a Carver m1.0t which is 200 watts per channel at 8 ohms. It will run at 4 and 2 ohms w/o a problem.

This amp, in my opinion, and from others is that it can be a little harsh. It however, will run 1000 watts mono at 8,4,2 ohms. I have done this and it doesn't get hot.

Eventually, I will run it through the McIntosh setup. The Amp is a powerhouse 100lb amp. The MC252. This will run down to 2 ohms w/o a hiccup (I hope).

djk....Did you get a PM from me a couple of weeks ago. I may have messed it up. Let me know if you didn't get it. I had a question regarding these dual woofer setups before I started the project.

You made some statements regarding Colterphotos AL network double bass bin La Scalas. Your suggestion was one of two:

1. Just add an addition 8-10mH ERSE inductor for the second woofer (kinda like I did here)

2. Reduce the inductor from 2.5mH to 1.25mH. Increase the tap of the mid cap from 13uF to 50uF. Change the sqwuaker tap to #4. Add a swamping resistor in parallel(?) with the sqwauker.

Do you think those suggestions apply here?

Thanks in advance

jc

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JC-

I LIKE IT!

I've liked your idea for this design since the 'sneak peek' you gave me a few weeks back. The design philosophy totally makes sense. Like the CornScala, it combines the best of LaScala with the direct radiator/vented bass of Cornwall. You've gone a couple of steps further by doubling the bass section, essentially halving cone movement and therefor lowering the already infitessimal distortion. Keeping the exact cabinet and port volumes of the Cornwall eliminates extra engineering/tinkering. The 'corner' design gives easy placement in most rooms, 'hiding' the massive cabinet volume in unused space, yet allowing the user to tweak the toe-in, since it's not corner loaded.

I don't know enough about crossover design to be of any help, sound like you and Bob have the fine-tuning.

One question though. I have a set of Bag-End PA cabinets that utilize two EVM-12L for mid bass. Each cone is in a separate sub-enclosure, and I always thought that this was a protection measure in case one unit failed- the other could continue playing without having a 'drone' cone in the same enclosure. Now I'm wondering, is there something to gain in terms of backpressure/distortion by putting each woofer in it's own enclosure, or could construction of your design be simplified by building a single double-sized Cornwall enclosure?

Good going, now I'm going to have to buy a better table saw!

Michael

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Awesome! I was envisioning someone building almost exactly what you have built, actually I was talking to Dr.Who about this a couple of weeks ago!

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On 7/11/2005 9:12:33 AM colterphoto1 wrote:

JC-

I LIKE IT!

I've liked your idea for this design since the 'sneak peek' you gave me a few weeks back. The design philosophy totally makes sense. Like the CornScala, it combines the best of LaScala with the direct radiator/vented bass of Cornwall. You've gone a couple of steps further by doubling the bass section, essentially halving cone movement and therefor lowering the already infitessimal distortion. Keeping the exact cabinet and port volumes of the Cornwall eliminates extra engineering/tinkering. The 'corner' design gives easy placement in most rooms, 'hiding' the massive cabinet volume in unused space, yet allowing the user to tweak the toe-in, since it's not corner loaded.

I don't know enough about crossover design to be of any help, sound like you and Bob have the fine-tuning.

One question though. I have a set of Bag-End PA cabinets that utilize two EVM-12L for mid bass. Each cone is in a separate sub-enclosure, and I always thought that this was a protection measure in case one unit failed- the other could continue playing without having a 'drone' cone in the same enclosure. Now I'm wondering, is there something to gain in terms of backpressure/distortion by putting each woofer in it's own enclosure, or could construction of your design be simplified by building a single double-sized Cornwall enclosure?

Good going, now I'm going to have to buy a better table saw!

Michael

----------------

Micheal C.

Your first paragraph hit the idea right on the head.

I wouldn't think that your PA cabinet would have seperate cabinets for failure purposes.

I think the seperate cabinets does provide more of an assurance that the volume will be just right for each woofer. I bet a ~12 foot cabinet would do. However, Would this effect porting? Not sure. Text books would tell you it wouldn't

Basically, I've got this Cornwall size and port thing down to an art and I didnt feel it was mich more of a burden to make the cabinets seperate.

AS YOU KNOW, resonance could be a big issue in a 12 cubic foot cabinet. The mid horizontal panel of wood between the two bass bins is a good way to prevent resonance. If you look into each enclosure, there is no large panel to resonate like the Cornscala or the Cornwall. Therefore, this is a better bass bin in that regards. The downside is that the ports aren't coupeled(sp) to the floor. However, the ports are closer to the two side walls of the room. This could be a good thing. Not sure.

jc

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Jc is correct that having two cabinets is better from a bracing standpoint, as smaller panels are less likely to need bracing, which quicly eats up internal volume.

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How's the polar response in the upper regions that the woofers play in? I just wonder if that's not part of the reason you feel a need for some tinkering with the crossover. Stacking two woofers like that will of course narrow the verticle dispersion while the horizontal remains the same, which often times can sound wierd. Whether or not this is a good thing will of course depend on the room (though I can see it possibly being a good thing as it starts to match the dispersion coming out of the horns).

Have you toyed at all with the idea of a 2.5 way crossover, or we trying to stick to the simpler is better approach?

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----------------

On 7/11/2005 2:16:16 PM DrWho wrote:

How's the polar response in the upper regions that the woofers play in? I just wonder if that's not part of the reason you feel a need for some tinkering with the crossover. Stacking two woofers like that will of course narrow the verticle dispersion while the horizontal remains the same, which often times can sound wierd. Whether or not this is a good thing will of course depend on the room (though I can see it possibly being a good thing as it starts to match the dispersion coming out of the horns).

Have you toyed at all with the idea of a 2.5 way crossover, or we trying to stick to the simpler is better approach?

----------------

Guess I am missing it. Why does the verticle narrow? Are the upper waves(for lack of better words) from the top woofer interrupted by the lower woofer?

Thanks,

Terry

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I would think that you'd want the woofers stacked verticaly as they are in the prototype- to eliminate timing differences if anything.

Agree with the double bin, stiffer box theory. Works for me.

Michael

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----------------

On 7/11/2005 5:22:56 PM IB Slammin wrote:

Guess I am missing it. Why does the verticle narrow? Are the upper waves(for lack of better words) from the top woofer interrupted by the lower woofer?

Thanks,

----------------

Well I don't fully understand the smaller details, but the basic idea is that you're introducing comb-filtering in the higher frequencies as you move off-axis. In the horizontal plane, you can move around and you're always the same distance from each driver. But in the vertical plane, as you move up and down you are now introducing different distances between each driver:

Fig1.gif

-http://www.prosoundweb.com/live/articles/jbrusi/pa.php

So basically, the different path distances will cause cancellation at frequencies that get shifted a distance of 1/2 wavelength. Frequencies that get shifted slightly less and slightly more also experience this cancellation.

This picture does a good job of showing a 3-D model:

Figure6.jpg

-http://www.prosoundweb.com/studyhall/am/lobes/lobes2.php

(Note that each balloon plot is for ONE SINGLE frequency and there are two plots shown. Notice that the points of cancellation aren't always the same for different frequencies).

When you look at every graph at the same time, the end result of all the summations and whatnot is a polar response that has narrowed...because everything closer to on-axis tends to remain in phase. The following picture is a bit of an extreme example, but it gets the idea across. Notice the narrow beam going right down the middle.

Fig10sm.jpg

(Click For Larger Picture)

Here are some array guidelines:

1. For most venues, sub arrays should be stacked vertically to narrow vertical coverage and maintain horizontal coverage.

2. If subs are to be split horizontally, they should be as far apart as possible (>5 wavelengths).

3. If subs MUST be arrayed horizontally, con sider the Bessel array.

4. Cardioid subwoofers can be useful for control ling rear radiation.

5. Remember that the polars are frequency dependent, and a good polar at one frequency will produce the opposite effect at twice (or half) that frequency. For this reason, it may be necessary to use multi-way subwoofer systems with each passband optimized for the desired polar.

6. The rooms response will interact with the subwoofer array response, and can nullify the ben efits of the array.

7. A ridgid boundary near a subwoofer (floor, wall, ceiling or combination) will produce a reflection that can be treated as another low frequency source. The princip of subwoofer spacing apply, and the best coupling takes place within 1/8 wavelength of the sur face, producing a mirror image that couples with the sound source as though separated by 1/4 wavelength.

One thing not explicitly stated is that keeping the speakers within a 1/4 wavelength of the highest frequency to be reproduced exhibit no comb-filtering issues. If you think about it, two sources have the biggest discrepancy when you are 180 degrees off axis (off to the side or up above in this situation). If the most out of phase they can get is 90 degrees (1/4 wavelength) then the most cancellation you get is -3dB at the highest frequency...all the other frequencies will "couple" and approach that 3dB gain you get from using two drivers.

So here are a bunch of links for anyone interested:

-http://www.prosoundweb.com/install/synaudcon/tt26_3/tt26_3.php

-http://www.prosoundweb.com/studyhall/am/lobes/lobes.php

-http://www.prosoundweb.com/live/articles/jbrusi/pa.php

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----------------

On 7/11/2005 2:16:16 PM DrWho wrote:

How's the polar response in the upper regions that the woofers play in? I just wonder if that's not part of the reason you feel a need for some tinkering with the crossover. Stacking two woofers like that will of course narrow the verticle dispersion while the horizontal remains the same, which often times can sound wierd. Whether or not this is a good thing will of course depend on the room (though I can see it possibly being a good thing as it starts to match the dispersion coming out of the horns).

Have you toyed at all with the idea of a 2.5 way crossover, or we trying to stick to the simpler is better approach?

----------------

Doc,

I somewhat understand your point but I don't think I can answer your question.

I have no equipment to measure anything.

I haven't seen woofers placed horizontal. However, I did consider such a cabinet. It would be very wide at least 37-38 inches. I even calculated some cabinets where they weren't horizontal or vertical but more oblique from each other. This concept made it hard to build two different enclosures in one cabinet.

I don't know if this helps but there are "dead" places in this room. Remember, this is a mono speaker. The bass really sounds no different than the Cornwall I have. The Cornwall has the same "dead" places as well. For instance....when I sit on the couch in which I am about 8 feet in front of the cabinet, the bass impact is not as strong as when I walk around the room. The most bass is behind the cabinet itself. My Cornwall works the same way. When I am standing (I'm 6 foot 2 inches) about 10 feet away, the speaker sounds awesome. Punchy musical bass. Not boomy. I think I need a larger room.

Now, the only need I thought I need to tweak the crossover is that originally, I had only one inductor. the addition of the second inductor filled the gap of my problem which was a loss of some mid bass. The woofers were crossed to low. It was like a thin midrange with a subwoofer.

Right now there is no gap in sound. The drivers are balanced. The bass is perfect. I am just assuming there are more possibilities for tweaking this setup. This is a Type A network with another inductor. Maybe this is all that is needed. I was just hoping for more suggestion on what I could do to make a network fit this situation. Right now, it seems that the AK-3 with a second low pass maybe the thing that makes this really sing.

Honestly though, it sounds real good right now. I bet with the better type a 13 uF cap, it will sing more.

I haven't considered the 2.5 crossover. Please feel free to explain some advantages there.

Just remember. I'm looking to keep this a "Klipsch Heritage" sounding speaker. I could have easily bought some JBL woofers and build a bass bin that would rattle the neighbors doors. My main goal was to keep the "Cornwall Bass" and then secondly preserve the Sound of the La Scala midrange. The JBL tweeters were for my experimenting. I have not yet been able to see a huge advantage yet of the different tweeter. My gut feeling is that I will like the JBL 2404H.

jc

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