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jwc

Dual 15 inch Corner Bass Bin - Cornscala dbb

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I finished up the ALK for the dbb today.

The best sound came from the least attenuated at -2.6dB. This taps 5 and X.

Noted more detail than the Type A. Also more "open" than I expected. The tweeter is a little hotter on the ALK than the Type A. Can't explain that one.

The big bummer right now is the bass on the ALK. Seems as it want to be tight but very weak. Very noticeable difference between it and the Type A.

Any suggestions? Is there a way to make the low pass 1st order and still integrate well? The bass no longer has that "Cornwall" bass. If I could get the low end improved, this would be the way to go.

thanks in advance. jc

The pic is the way the Type A is modified.

post-16499-13819278253404_thumb.jpg

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jc,

The reason you have no bass is because of the transformer settings! x-5 is WAY too hot on the midrange. That is casuing the bass to drop in proportion. You need to align the midrange to the woofer, then and ONLY then, you cut the tweeter down with an attenuator if you need to, and I'm sure you WILL need to.

Al K.

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JC,

Grab a spare autoformer and see if you can mount it on the board close to the left side of the barrier strip.

Strap a 20 ohm resistor (or two 10's in series) across taps 0 and 5.

Run a wire from tap 0 to common on the barrier strip.

Disconnect the lead from the 7uF capacitor going to tweeter positive and connect it to tap 5.

Run a wire from tap 4 to tweeter positive.

Set the squawker using taps 5 (neg) and 2 (pos).

post-3205-13819278256474_thumb.jpg

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Thanks guys. Will do this tonight. I can't thank you enough.

Dean, I follow you. I just need to know this. There isn't any problem having both transformers grounded to the same common ground...right?

jc

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Nope -- common is common no matter where it is -- it all leads back home.

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Well if you want to be uber technical, all the wires have their own electrical properties so it's best to keep all the runs as short as possible...I don't think it makes an audible difference - so I'm just being a pain really (though it does become an issue with amplifier design). [:D]

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Jc,

I second what Dean just suggest you do, but I think you may need to go further with it. I am going to suggest X-4 or even 0-3 on the squawker and you may even need to cut the tweeter down more too. BTW: I am assuming you are using the K55 squawker driver and 3619 transformers.

Also, you may want to "float" your tweeter if you need intermediate settings. Just as with the squawker, the tweeter need not be connected to the common on one side. It can use the exact same attenuation tap setting table as the squawker.

I also suggest that you try inverting the woofer. The delay is now in the squawker compared to the woofer in a Khorn or LaScala. It may need inverted polarity.

Al K.

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Jc,

I second what Dean just suggest you do, but I think you may need to go further with it. I am going to suggest X-4 or even 0-3 on the squawker and you may even need to cut the tweeter down more too. BTW: I am assuming you are using the K55 squawker driver and 3619 transformers.

Also, you may want to "float" your tweeter if you need intermediate settings. Just as with the squawker, the tweeter need not be connected to the common on one side. It can use the exact same attenuation tap setting table as the squawker.

I also suggest that you try inverting the woofer. The delay is now in the squawker compared to the woofer in a Khorn or LaScala. It may need inverted polarity.

Al K.

OK. Al and Dean. I've got the stuff kinda evened out. The squawker is at -6.2dB (4 and X) and the JBL 2404 is -3dB. The bass is better. Yes Al, you were right on the settings.

Now the JBL is attenuated with a T2A and I was wondering if I wanted to "float" the tweeter any, what are my options with this autoformer. Is it only -3,-6,etc.

Now I am more pleased but I am not completely satisfied with the Bass. It is "caught up" now but the sound is too thin. It could be that I like it a little more "rumbly"...not sure. My wife overall agreed that the bass was a little disapointing. If in the end this ends up being the case after I have tweaked as much as I could, is there an option to change the low pass to a first order like you guys have on your Super AA andf ALK A. Would this be possible or make a difference?

I have not yet reversed the polarity of the woofer. For simplistic sake, can I just change the driver inputs around? I know this is probably a dumb question.

Thanks as always.

jc

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Ok. This was a duoble post...had to delete this entry.

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jc,

Your choices on the tap setting for the T2a are the same as for the 3619 except that the "x" tap is not available. All of the other setting involving taps 0 through 5 work the same.

As to going 1st order on the filter, I think you will be going backward. 2nd order can give you a 3 dB boost at the crossover under the right conditions (if the drivers are in phase) but 1st order sums flat at best. I would try reversing the polarity before doing anything drastic. It should be simply a mater of reversing the wires that connect the two woofers to the network right at the network barrier block woofer terminals.

I really think you should invest in some simple test equipment for testing speakers. You have done a lot of good things and I think you are into it enough that you should think about going the next step. Maybe a laptop computer with RTA software and a calibrated mike. You won't regret it. It will open a new world to you of actually knowing what is going on with your speakers!

Al K.

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Al, I do have an RTA setup with the TrueRTA software on the computer with a Behringer UB802 mixer (phantom power) and the Behringer ECM8000 MIC.

I have done this with the dbb with the Type A modded network. I thought I posted it here already in this thread somewhere but it looks loke I didn't. I'll find the file. I am gonna get to that after the holidays because I swore to my wife that I wouldn't pull all that crap out until after our company has come and left.

You are exactly right. That is needed. I was just trying to get it right to the ear first. I also owe that to you and Dean for helping me out. Much appreciated for sure.

I'll switch the polarity of the woofer tonight.

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"Also, you may want to "float" your tweeter if you need intermediate settings. Just as with the squawker, the tweeter need not be connected to the common on one side. It can use the exact same attenuation tap setting table as the squawker."

10 ohm resistor if you decide to do it this way. The 20 ohm resistor I suggested using input tap 5 and output tap 4 was a fixed setting of -3dB.

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Thank you Dean. Still need to do the woofer thingy first. But I will probably use that trick if needed.

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Where we at JC? No one can do anything with this until you figure it all out.:)

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Hey Dean. Sorry. I've been given a list of chores to wrap presents and assemble my sons toys for xmas.

Well this is what I have done so far.

I have inverted the polarity of the woofer. Yes this made a slight improvement but still doesn't carry the bass "quality" of the modified Type A.

After inverting, I went through squawker tap settings from about -2 dB to -7dB. This was done with the JBL tweeter at both -3dB and -6dB. This took awhile. Listened to about 5 songs of different variety at each setting.

There is no doubt that the ALK design has a good seperation of the tweeter and squawker. There are times the ALK sounds a lttle recessed and that the Type A is too forward or "boxy" or "in a tunnel" sounding. The variable options on the ALK really allow a lot of flexibility for what your tastes are and what kinda music you listen to. So with that, I am pleased.

It's just the Bass that is mainly my concern. I do need to RTA the thing before I draw a final conclusion by all means. It's almost like I'm missing part of the low end. It sounds nothing like the "cornwall" bass would sound.

I will have to hold off a few days before I run through that much of a listening trial. However, if you guys have any other suggestions that can be modified on the network and such, I am mre than willing to try it.

I hope you aren't burn out on helping me. I still am very thankfull for the help. I have no doubt that there is an ALK "like" design that will work for me since I have heard the ALK B and the ALK A and they have proven to be good quality to my ears.

jc

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Jc,

I think you were using a seperate inductor to each of the two K33 woofer drivers. This may be the reason for the better deep end. I think maybe you need to use a woofer inductor wound of thicker wire to reduce the DCR since my design only uses one inductor for both. If you are willing to spend some money go with #12 wire air-wound.

Al K.

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You know, I actually had thought of that. I may do that. I will probably whip out the RTA setup first to make sure I am getting the entire low end spectrum of sound.

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jwcullison,

Would like to start with nice workmanship on the

cabinets, very professional looking. I understand that you are

after the same "Cornwall" bass sound with more db and in a smaller

appearing package, looking for more bass here also, though we are going

down different paths, looking for the same results. To start, I have

1977 Cornwalls, with the cabinets inverted (180 degrees) with

511B's/K55's on top (ports and woofers are now top) and k77 between the

511's and woofer's, goal-- to get sound off the ground, voices and

instruments more at a live performance level, works good, actually

raised the cabinets 12" further off ground, sounds just right IMO

except the "Cornwall" bass level went down for obvious reason

(ports/woofers over 3' off ground), still sounds good but lacking.

My path, cruder than yours, is to stack

existing Cornwalls onto another pair of Cornwalls as bass bins ( may

fabricate them for the purpose) only, I see others have double stacked

here on the forum, though was thinking of laying them sideways with

woofers aligned to same side, and 511's/K77 aligned also. A bit big,

but not much more than a dresser or other furniture, so here at least

the look will be ok.

Was wondering, since I have'nt seen it posted

here, are you planning to try bi-amping the woofers? I only have the

two Cornwalls right now, double stacked and drove the top woofer,K55,

and K77 with stock type B crossover as a stock speaker, then powered

the lower ( using type B crossover) and the "Cornwall" bass was back

plus. Wondering also ( anyone can jump in) if the lower woofer bi

-amped would be better crossed over, maybe with a type A? another

question is can you run just the woofer with these crossovers minus the

mid/high outs hooked to anything, no bare wires to terminals of course,

(they don't need a dummy load or anything?)

JW, was also wondering if you tested the

lower woofer only with stock crossover and the k55/k77 on top of your

cabinet to see/ hear if the "Cornwall" sound is there? in other words

as close as you can configure to see where your baseline is? I know you

have the same volume and port size, though the shape and motorboard

area can also have an "effect" on sound and despersion as well. I find

the woofer height raised is getting to be more of a lower midrange,

which is why I did it in the first place, a lot of vocal information

coming from them,

and I want that information more at a live performance level (

height wise, seems floor speaker systems leave out the Z axis, have the

imaging but..), actually trying to get the "big" open sound similar to

Magnaplaners I once had, though with more bass, db level, 100's of

watts less power consumption, and wider sweet spot, think I am already

there! Again, nice work on the cabinets!

note: mid/high horns in cabinets are non-functional

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