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Old 19th April 2010, 06:25 PM   #21
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Haha. I'm about 30 miles out of Philly. I don't know dubstep. If I were into pro sound professionally I'd probably take the time to view some track files in an audio signal processing software. You can plot the power for the entire track, and then go back and see what frequency the big peaks center around. You can also look at the waveform envelope too, to get an idea of what sort of transient performance you need. Overall, though, you want all the performance you can get. Lots of dance music has mild transients in midbass with lots of heavy tones. You have to wonder what the musicians and DJs would to, however, if the sound systems available would do it.
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Old 19th April 2010, 06:25 PM   #22
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Originally Posted by Xoc1 View Post
OK Asbestos scare over!
From the dimensions you gave in your first post you seem to have a speaker box of about 500 litres or maybe a bit less internal capacity.
This is about the right size for a pair of 18" drivers
There are 2 off, 6" ports they seem to be quite short, so they are probably tuned to give a bass peak around 50hz .
I think that at least another 2 off 6" diameter ports would help.
The 4 off, 6" ports would need to be longer to compensate for the larger area.
Or maybe you could cut out the baffle between the speaker holes and make a rectangular port like the G sub design.
What is that port made of , would I fit it to the scale of the g sub design . I think it might be easier just to cut 2 more ports , would I put them opposite the other 2 ports in a square formation ? I'm definitely new to wood working and would have to get a buddy to help me out . I don't mind drilling stuff .... but I am definitely trying to get into speaker building .

I really appreciate the help , you guys are freakin geniuses

btw I live in San Diego , California , not far from LA
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Old 19th April 2010, 06:39 PM   #23
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Originally Posted by Andrew Eckhardt View Post

An "easy" way to beef that box would be to make posts or vented tube for the magnets to press against, and use T nuts to seat the driver, essentially pre-loading the largest faces. Of course you need to be sure the rest of the cabinet construction can withstand this or you will blow it right apart. By immediate looks, it wouldn't take it.
This sounds good but its really hard for me to visualize . So what your saying is drill or hot glue some posts into the box that are touching the speaker magnet , supporting it from below or just up against the back ??? I don't know what a T nut is , so how would I go about "seating" the drivers on them ???
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Old 19th April 2010, 06:42 PM   #24
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btw what exactly are transients ?
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Old 19th April 2010, 07:00 PM   #25
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In order to pull off pre-stressing a cabinet you need to be sure that the gluing job is superbe. In a jobbie like what you have, unless you can see that it's been rabbeted and the joints are tight and filled with glue, it's probably not glued well enough. You'd have to pull all the damping material out and glue blocks/strips or gussets all away around the edges. Hot glue doesn't enter into the picture, you need a wood to wood bond with aliphatic resin wood glue or better. Paint and dust/contamination wont work either. Doing the rear support can get technical. You need a perfect length, so that the driver protrudes from hard seated when placed by hand by about 1/4 of an inch to 3/8 in a cabinet that size. It works best for cubic cabinet sections so that the stress around the panels is most even. Some hard rubber or something at the contact points behind the magnet structure, which have to handle whatever profile is there, which changes from one driver design to another. If you don't get it just right it will buzz and carry on and cause more trouble than it solves. I guess it's "easy" if you've done it a few times. Permanently stressed wood eventually takes a set, faster in higher heat and humidity, so it wont last unadjusted forever, but you can make a comparatively light cabinet very strong this way. You can see what T nuts are by looking for them on the web. They're good for pro cabinets since you never know how many drivers a cab will see in its life.

Last edited by Andrew Eckhardt; 19th April 2010 at 07:13 PM.
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Old 19th April 2010, 07:01 PM   #26
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Transients are how quickly a signal reaches peak and diminishes.
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Old 20th April 2010, 04:03 AM   #27
danielm is offline danielm  United States
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[QUOTE=droberts;2157588]that's all you got for me ? thanx . So should I go back to the guy that sold them to me . I gave him $100... QUOTE]

We need to talk. I usually bust up and burn old cabinets.

What drivers came out of them?
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Old 23rd April 2010, 11:02 PM   #28
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I would rip out the lining wearing a good dust mask and gorilla glue the corners, add braces, and cover the ports. Then put these in there: Sigma Pro-18A-2 18" Cast Frame Driver | sigma pro-18a subwoofer 18" subwoofer pa subwoofer 18" driver This will kick hard down to 40Hz and make like 126dB at 40Hz. Forget those small ports, small ports don't work anyway and just let midbass out the hole in the cabinet and mess up the midbass quality you are looking for. Oh yah, add some modern lining before closing up.
What the other guy said----Standing on the shoulders of giants.
New avatar- no more little array
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Old 2nd May 2010, 04:00 AM   #29
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We can talk until we turn blue . I just got back to my thread today , and I could use all of the advice I can get . finally I said **** the drivers and saved up for a used srx 728 , I'm pretty happy about that . My next venture is probably a qsc 5050 or 2 crown xti 4000 's , then hopefully another 728 or some drivers for the dual 18's and maybe some drivers for my sound factor 15's

something i've noticed going out to alot of electronic shows lately is that the subs will kick all night but eventually , either the dj's get deaf , or equally likely is that the horns in the mains start to overheat to the point where all you hear are scratchy highs. This is one of the main issues I am hoping to combat , maybe by upgrading my mains or taking backups so I can rotate the mains out ????????
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Old 2nd May 2010, 06:09 PM   #30
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Default sumsoundguy's mega-cab repair breakdown

Porduct 1 or product 2 is fine. Use more in the mid cabinet.

I have not tested that woofer personally but it on the next order from part-express. When tested will post it. The design is based on published specs which sometimes are good and often off some.

40Hz is really low in a PA system, lower than almost anyone has heard. People hear 80Hz and believe they have 40Hz. In a sealed box 40 Hz can be very real compared to a box with a port that is way to small to work.

To get the sound you want I would strongly suggest using a DSP such as the Behringer DCX2496 or to upscale a Peavey Digitool. I use both. For live there must be compression to have good sound. I typically set the threshold at -30dB and 2 to 1 so the signal is always compressed. Having the signal go into and out of compression sounds really awful. Also the use of a correctly set limiter to protect speakers and amplifiers will prevent the system from ever being damaged. A big plus!!

As for bracing, I would brace from front to back between the drivers. Then from side to side behind the drivers more or less. The brace between the drivers if possible should be a square doughnut if possible. DO NOT place braces exactly at the same distance from the ends. Asymmetry is the rule. Having equal distance anything is always bad.

Cut like 3/4 inch plywood and glue that over the ports. Use screws to hold in place until the glue dries. Make sure the covers do not interfere with other things in the cabinet or driver installation.

Gluing the corners means placing the cabinet so that runny gorilla glue will sit in the corners until it set up. Then turn or rotate the cabinet and do another corner. A tiny amount of water can be misted into the corner to speed this process. I mean tiny amount as the goal is to keep the cabinet from coming apart. With two 18s in there making real bass down to 40Hz if the cabinet is not well glued and braced soon you will have a bunch of cabinet parts. Real bass requires a very sturdy cabinet. Fake bass does not and as most woofers make fake bass fake cabinets are fine. I have blown apart more cabinets than I wish to ever recall making real bass.

One more thing, using that DSP to EQ the woofer for max flatness use a Q of 1 set to about 44Hz high pass 12dB per octave filter. This will limit out of band signals lowering distortion and protect the driver from over excursion by those out of band signals.

Feel free to put this on a post on your thread if you like. I see the cabinets are made from floor underlay plywood which should be alright. Use T-nut or now called hurricane nuts to hold in the drivers. Also some large rubber feet could be helpful. MCM electronics and maybe parts-express has cabinet corner protectors which are also nice.

As for the existing brace I cannot see it clearly so cannot respond to that part of the question.

Hope this helps - SUM
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