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jwc

Dual 15 inch Corner Bass Bin - Cornscala dbb

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I'll try to answer the best I can.

I think I understand your current connection of drivers. You are using a type B to run the mid, tweeter and then the top woofer. Basical a Cornwall raised with an Altec mid horn. Then the lower woofer is running off abother Type B with no tweet or mid connected.

If that is the case, you basically have a two woofers crossed at the same frequency giving you +6 db for that spectrum. If it is running off one amp, you have cut the impedance in half. This would be too bass heavy as now your mid and tweet is somewhere at 99-101dB. The low end is closer to 104-107dB. This would not be what I recommend for crossover purposes.

As far as biamping for the bottom one woofer, you have the same scenario except that you amp is not seeing 1/2 the impedance in the low end spectrum.

Now Biamping both the woofers and using the second amp for the highs. This doesn't accomplish much more as far as the db and frequency. Maybe less strain on amp? Not sure the advantage there.

If you really want to take advantage of that setup, you need to get a hold of at least one Type A network. Use that to run the Top Cornwall and now you are crossing the K55/511b at 400hZ and the tweeter is unattenuated and the squawker is attenuated only 3dB. So the highs are around 104dB. Just use the woofer hookup for the Type B on the bottom woofer and now youv'e got something.

As far as positioning, your setup prevents comb filtering of the low end. I have not listened to my dbb with one of the woofers off and using a Type B network. What I have essentially is a Cornwall at about 104dB with the mid crossed down to 400Hz. This shouldn't be any different than a Cornscala setup except that the dB isn't as high as the dbb cabinets off mine.

I see no need to biamp Unless I was wanting some tubes for the high end and SS for the low end.

To be honest, the cabinet design for each woofer is more optimal in my opinion for the K33 in a reflex ported cabinet. No large panel for resonance, snugs in a corner. The side ports sound good. The bass is the same as the Cornwalls I have owned and like the Cornscala (non dbb) I've built. The dbb design sounds the best....not because there is two woofers there, just luck. This isn't a rectangle or cube/square.

I hope this has helped.

jc

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If that is the case, you basically have a two woofers crossed at the same frequency giving you +6 db for that spectrum. If it is running off one amp, you have cut the impedance in half. This would be too bass heavy as now your mid and tweet is somewhere at 99-101dB. The low end is closer to 104-107dB. This would not be what I recommend for crossover purposes.

Actually as pictured, the top Cornwall is left ch, and the bottom CW (woofer) is right ch on the amp (preamp on mono), so is bi amped already, impedance is normal. I am only guessing here, but it sounds "right" only now the vocals and some instruments sound like they are at the right height, thanks to the higher position of one woofer which crossed over at 600hz , puts out a lot of musical information at the right height( instead of 14" off the floor)

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Progress.

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Al and Dean. I may have lost your interest at this point but I wanted to shed light on what I have done.

I have not RTAed the dbbs with the changes. Against Als recommendations, I was tweaking to satisfy my ear prior to objective measurements. Point well taken. I have lost some of my cables for the RTA setup and will need to purchase more.

Anyway,

I tried several different constant impedance designs with a bandpass. This included your suggested ALK design for this speaker. Now with this, I tried every tap setting combination with the polarity reversed and unreversed. This would work but as you know, the bass was not to my liking. To get any decent bass, I had to turn down the squawker a bunch and then the mids suffered. The tweeter section sounded great. After a couple of weeksI gave up. Yes, maybe a bigger 2.0 mHy inductor would have improved things.

I also want to make note of something that was very dumb on my part. During the above testing, at times I would disconnect the tweeters to compare the dbbs for balance between the woofers and mids. The ALK design kept failing miserably. I then realized that there is no bandpass on the standard Type A and the K55 was playing out to 20k HZ. Yeahthis sounded better than the ALK design w/o the tweeter. No kiddin. I then realized that this was a stupid thing to do. I should have just unhooked the tweeter on the ALK design just to find balance for itself. I hope this isnt confusing. But I learned something there and also could hear the bandpass working.

I then built an ALK Universal A with all Solen stuff as you recommend. I have great praise for this network as I used to have a pair in my late La Scalas and the sound was amazing. As you would expect, it failed miserably in this setup. Pretty much the same as when I tried the Supeer AA with the dbb. However, I took Deans much earlier recommendations and wired the K33s in series as opposed to parallel. This was under the assumption at the time that the reflex/ported K33 was about 3-3.4 ohms and that two in series would be similar in impedance to a horn loaded K33. Doing this I knew I would have to attenuate the JBL 2404 big time. I therefore placed an autoformer with a 10ohm resistor after the tweeter filter to attenuate. Believe it or not, this worked. When comparing the ALK A dbb with the other dbb with the modified Type A with two low pass inductors, there were pluses and minuses of both. It was obvious that the ALK A was playing at a much lower volume since the K33s in series was a less dbb than parallel and the mid and tweet attenuated quite a bit. This earned my faith that something will work if I kept trying. I ditched this setup because my main goal with this speaker build is to have a high db speaker like a Khorn around 104 db.

So then, I put together a bastard design constant impedance network with a Bandpass. For the moment, I will call it Type cs-dbb. I think I took away the diplexer. I DONT have a good understanding of how that is designed but I do understand that the low pass is affected by changes in the tap setting of the squawker. Therefore, the attached schematic is what I did. In objective principle, you may find that this wouldnt be appropriate. Each low pass, squawker, and tweeter are shotgunned right off the input. The JBL tweeter is unattenuated. The squawker is attenuated 3.4dB on the 3619 taps 0 and +4. The result was FANTASTIC by my ears. Now comparing this to the Type A with two 2.5 mH inductors, I can say the following:

The two open up at the same time.

The bass is very similar.

The mid is more open and more real on the Type cs-dbb.

The tweeter is more dynamic? and not as hot on the Type cs-dbb. Blends well vs the JBL on the Type A at a few times only is noticed to be hot.

This is all the conclusions for now. Will listen to this a few more weeks to make sure I continue to like it.

Again, thanks for the help.

jc

post-16499-13819281119372_thumb.jpg

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Please excuse the dirt and extra drill holes. This wasn't for looks. Testing only

post-16499-13819281120062_thumb.jpg

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The mad scientist that you are.......[:D]

I can't wait to read the comments.

It looks like your schematic still shows the woofers in parallel.

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Yes they are in parallel. I don't plan on utilizing the series wiring anymore. Right now the woofers in parallel easily keep up with the JBL tweeter rated at 105dB. The JBL is running wide open with no attenuation. I just adjusted the K55 with the taps to match.

Listened more tonight and more satisfied.

The only other option I thought I would try is Bob's latest idea of placing a .5mH in series with the mid cap on the type A. Also crossing the tweeter lower say 5000Hz by placing a higher value cap on the first order tweeter filter. Now there would be a bandpass on the Type A to see if there is an improvement. I am tempted however, just to go ahead and make another constant impedance network like the schematic above. I think I will listen for a few more weeks to make sure what I am hearing is to my liking.

jc

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I thought I would update this post as I have done a few things with my dbbs. There are some out there who are considering or currently building something like these.

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I have tried a few networks over the last several months. I had to take a break from it as my own opinions of stuff was getting tough to make with so many different sounds. I aqlso needed time to build my TallCorns.

I need to admit to a mistake during my testing. I later discovered a problem with one channels input that made a slight difference in sound. This unfortunately led me down a wrong path on a few things. Because of this, I will need to try out AL and Deans suggestion of their crossover again sometime in the future. Therefore, dont weigh in my above opinions strongly just yet.

For now, I have settled on a network that I will stick with at least temporarily. For a reminder, the Type A network with a duplicated lowpass filter with a 2.5mHy inductor does a great job for those wanting as simple start.

The network now is basically similar to Deans ALK Jr. This is like it except for a tweeter attenuation mod and a duplicated filter. I also dont have the tweeter filter running through the mid cap. The 2.5mHy inductor (duplicated) as a first order low pass filter does so well. I have discovered another way for first order as I have tried out on Terry Cruses Alcorns. This is a lower value that he seems to like. He can give his vote of confidence here if he wants. For now, I will stick with the 2.5mHy.

One thing I noticed on the 6000Hz third order tweeter filter that the combo 2.2 cap, .20 inductor, and 7uF cap will work unattenuated in this setup. When changed to the 2.2 cap, .15 inductor, and 4uf cap, there needs to be a slight attenuation of the JBL 2404 tweeter. It unattenuated plays a tad bit too hot.

The mid cap was upgraded to the dual 20uf Sonicaps that has received some attention here recently. Each woofer has its own filter that is Solens 12 AWG air core inductors. These are big. I got tired of having two sets of boards to move in and out of the back of the top hat so I made a castle that has all the components on it. I put these together in 3 days so the finishing look on them wont be perfect. Since the below picture was taken, I changed out the (white) Dayton resistor and placed a Mills. I didnt really notice a difference.

So now, I have one network that I can slide in and out of the speaker and the squawker and tweeter can be attenuated separately. Right now, the tweeter is attenuated 2.6 and the squawker 6.8.

I also changed out the mid driver to the Altec 902-8B. My bandpass is first order and I got too caught up in the whole possible glitch at 9000Hz and the rumor/reality of the K55 poor quality after 6000Hz.

Interesting, the change of attenuation wasnt needed at all for the 902. Nice sounding driver. Very big too.

If you are coming to Hope, you will get to see the dbbs and the networks. I am tired of jamming here all alone and not have the opinion of other audio lovers what these things sound like. It will be a big hassle to move all this stuff but it will be worth it. If you love Cornwall bass to its fullest, I would like you all to listen to these and tell me what you think.

jc

post-16499-13819298570712_thumb.jpg

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Awesome, I've been dying to hear something similar - I can't wait [H]

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I love it everytime this thread comes back up. I have read it from the beginning about 4 times. I'm thinking about a DIY project in the near future, and i'm torn between the Cornscala dbb, and something like Wardsweb is currently using. This is great stuff. BTW the two tier networks look awesome.

Jeremy

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Thanks for the compliments. The networks are beasts. I actually have a more "reasonable" network that will probably work and be a constant 4 ohm load to the amp. Won't have time to build those before Hope.

Where is a link to Wardweb speaker?

jc

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This is what I would like to try in the future

jc

post-16499-13819298587442_thumb.jpg

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I dug this up. I need to add some things.

More on that later.

jc

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"All the caps are Solen except for the 30+27 uF in the high channel. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

They can be Sonicaps or any quality brand. The sum should be 56 to 57 uF.

The inductors should be #14 solid wire. You might want to go to #12 for

the 1.3 mHy at the input of the low channel.

The swamping resistor comes to 3.6 Ohms, 10 Watt for using with the Altec 902-8"

I currently am using the Klipsch K69/510 combo at the top end. A parametric EQ is used.

post-16499-13819334949866_thumb.jpg

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