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Question on Port placement ...Again!


jwc

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No, don't fill the dog house. In fact, don't put stuffing on any of the

vertical portions (I just noticed that's pretty much what it comes down

to). Stuffing at the bottom of the bass bin is probably not needed

either. You don't want stuffing inside the dog-house because the shape

and acoustical space acts as an acoustic spring which affects the

behavior of the driver through the horn. The reason the ported mod

works so well is because it does not affect the behavior of the spring.

The end purpose of damping in the cabinet is to reduce the magnitude of

standing waves (so that they don't inadvertantly get amplified and then

make their way out of the ports). And standing waves are only going to

happen between parallel surfaces.

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Nice to have stiff competition with a Mississippi boy. I know all about STIFF competition....right Todd.

Looks like your cabinets and mine will have a bunch of BEC stuff.

jc

Isn't it interesting that a couple of Mississippi boys are taking on the most DIY projects, flanked and supported by a dude from Arkansas. Where's Terry? JC, wendja add teeth to your Mac avatar?

BS

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Ahh, the big Mac just gets happier and happier hooked to the dbb's. Still haven't build anything to top those mammoth speakers.

Yes the Southern folks doing lots of tinkering. Bob's shipping items are at my doorsteps in two days from the order. Unlike ordering from Solen. Hell, that takes weeks and the packing job is always terrible. Packing materials are hanging out of the box when I get them.

Terry is still floatin me emails. I'm just waitin for him to build his own dbb's and for you to build the Bass Cannon![:P]

jc

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Well, Guys I fired these puppys up last night and I am less than satisfied. I ran them without any port tubes to see what they sound like. (crap) I notice that the mids and highs are not as prevelant, I hooked up the factory one and one of the project ones together and switch back and forth between the two to listen to the difference.The bass on mine did not have a solid punch like the factory so I decide to seal off the top in mine to mimic the factory to try and achive a factory sound to start with. The factory LS had a more solid punch. As someone once said the snare had a kick to it. Standing in front of each one of them, the factory LS diffanatly had a more solid punch then the project speaker this is even after I sealed the top of the project speaker to mimic the factory one. The next thing I was going to do tonight is try to complete one of the project speakers with the ports (7") and isulate (per Dr Who) and leave the other one like the stock set up with top sealed off.

What bothers me is that when I sealed the top off the project speaker I was expecting it to sound like the factory one. But still no kick! So another experiment I was going to try was take the factory crossover and put it on the project speaker to see if I get factory results. I have no fancy meters just my ears and my chest to feel. The bass lows seem to be the same but no soild kick from the project one. I do have the woofer wire between the board that seals the top on the project one passing through. Could that little bit of air leak cause the bass to be flat and not soild (punchy)?

I guess I am trying to achive a starting point. Get it to sound like factory and modify from there...

Any feed back would be great.

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"I guess I am trying to achive a starting point. Get it to sound like factory and modify from there..."

That's the approach I would take. How about inverting the factory unit on top of the project? Then use only the bass bin (sealed at the top of the doghouse and connected to the factory network) of the project to see if the bass sounds like the factory units. If it doesn't, then figure out how and why the project bass bin differs from the factory. If the project bass sounds the same, then change variables, e.g., ports, networks, Crites tweeters, etc., one at a time to evaluate each change.

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Neil,

You know, it's not just the bass sound on the project speaker that differers. The mid and highs are not as prevalent ether... Just has a flatter sound in comparason. I guess it would have been ok if I had not set them side by side and did a sound check. That is why I was going to switch the crossovers to see if the sound changes. That will help me narrow down the possible couse of the problem whether it be crossovers or drivers that differers.

I thought the Crites tweeter puts out more highs? Not hearing the cymbals as well in the project ones. The mids and the highs I can live with but that dull bass is not going to cut it.

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What woofer are you using in your project speaker? Try inverting its polarity.

Btw, you are doing the listening comparisons between one speaker

playing at a time, right? And you are are doing so with the exact same

source material? (one of them isn't L and the other R).

Another thing you might try would be to swap the drivers between the

factory and your custom cabinets...and see if the problem follows the

driver or the cabinet.

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What bothers me is that when I sealed the top off the project speaker I was expecting it to sound like the factory one. But still no kick! So another experiment I was going to try was take the factory crossover and put it on the project speaker to see if I get factory results. I have no fancy meters just my ears and my chest to feel. The bass lows seem to be the same but no soild kick from the project one. I do have the woofer wire between the board that seals the top on the project one passing through. Could that little bit of air leak cause the bass to be flat and not soild (punchy)?

I guess I am trying to achive a starting point. Get it to sound like factory and modify from there...

Any feed back would be great.

Positively! That back chamber (doghouse) must be sealed well.

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Bruce,

I was wondering if that little bit of leak might change things. By just putting that top cover on last night was a quick patch mode. I will try to pass the wire through better before I start my runs tonight. The rest of the dog house is sealed with glue & silicone.

Santa

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Santa,

If you just cover the hole to the bass bin, you will still have a volume difference between the back chamber volumes. Don't know how significant that would be.

Also, you can power the woofers directly from an amp to more easily compare bass output.

Bob

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Roto. Not that this will make a difference but your driver from bob is the CW1526. The one in your La Scala is a K33....what year is the scala.

I too would be scared of the right and left comparison. I would keep everything the same and switch the each speaker to the "other" listening position....and do the same comparison again.

I got burned with this once recently.

jc

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JW,

The year the LS was purchase early 80's

I am doing the comparason on the left channel on both speakers. just switching a to b.

I understand that the CW1526 is eqivalent to the K33?

I think I will try to reduce the dog house close as i can back to stock and make a better seal. The dog house volume increase when I raised the top section. Also make a better air tight seal on the make shift top. Hope for a better report tomorrow.

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After many nights of playing with the ports, this is what I have settled with. Ports cut to about 7 1/2". That is where it seems to sound the best. I got the punch back. But the bass seems to roll out a little longer. I have to give up for a while because my hearing is demishing!

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