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Author Topic: Vented sub port tuning  (Read 6194 times)

Jason Moore

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Vented sub port tuning
« on: August 03, 2013, 03:51:05 am »

Got a couple of Carvin SW1802 dual 18" cabs. Factory loaded with eminence drivers. I want to hot-rod these. Mods will include bracing the cabs (12-ply poplar plywood), possible sound deadening and ports replacement (and of course driver replacement). I would only be using 2 of these dual subs total with 2 3-way mains.

My question is; what's a good port tuning frequency? Car audio guys say low tunings of 30Hz-35Hz is better for sound quality whereas higher tunings are better for SPL. (I realize SPL tunings for them are hitting a single frequency all day long; just wondering how tuning applies in the pro audio world).

I very rarely do EDM or any electronic music for that matter. Mostly jam bands, bluegrass fusion, and occasional rock bands.

Thanks for the help Labsters,
Jason Moore
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Jeff Bankston

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Re: Vented sub port tuning
« Reply #1 on: August 03, 2013, 06:31:46 am »

thats something that needs to be figured out with speaker design software like Eminence Designer. its about 100 dollars from USSpeaker. 1/4" difference in the port can make a difference. theres also port veliocity and other things. i just built one of 4 large rehersal room/drum monitors and have built many other speakers since the 80's and you need to model it if you want it right. heres one i just built using Eminence. i still gotta fill the holes and paint. the 15" woofer is flat to 40 and part of that is the box size. at 4.4 cuft it would be flat to 50 but i want 40 and the box needed to be 6.3 cuft. the port needed to be 1/4" shorter to get the velocity below 35 m/sc/h.

the FB is 37.61HZ , the F3 is 37.77HZ , freq response is -2.9db at 34.7HZ
« Last Edit: August 03, 2013, 06:43:16 am by Jeff Harrell »
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John Halliburton

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Re: Vented sub port tuning
« Reply #2 on: August 03, 2013, 10:18:22 am »

Got a couple of Carvin SW1802 dual 18" cabs. Factory loaded with eminence drivers. I want to hot-rod these. Mods will include bracing the cabs (12-ply poplar plywood), possible sound deadening and ports replacement (and of course driver replacement). I would only be using 2 of these dual subs total with 2 3-way mains.

My question is; what's a good port tuning frequency? Car audio guys say low tunings of 30Hz-35Hz is better for sound quality whereas higher tunings are better for SPL. (I realize SPL tunings for them are hitting a single frequency all day long; just wondering how tuning applies in the pro audio world).

I very rarely do EDM or any electronic music for that matter. Mostly jam bands, bluegrass fusion, and occasional rock bands.

Thanks for the help Labsters,
Jason Moore
You generally don't choose a tuning frequency and put a driver in a preexisting box.

What don't you like about the Eminence loaded Carvin subs now, especially for what sounds like a more than adequate application?

Bracing a marginal cabinet can improve performance some, it will also prolong the lifespan of the cabinet.  What do you mean by "sound deadening" material?



Design will depend on the driver chosen, how well the current box volume matches up for a particular tuning, and if you can change the port to one of adequate size for the design, especially taking note of having enough vent area to minimize air velocity to a point where it won't be noisy when slamming the sub at full power.

If the goal is more output at the current tuning, do you have adequate amplifer for the revamped design?

Best regards,

John

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Paul G. OBrien

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Re: Vented sub port tuning
« Reply #3 on: August 04, 2013, 12:31:00 pm »

Jason you're going about this all wrong. First identify what you don't like about the cabs as they are.. do they not get loud enough, not go low enough, etc. Then you will have to crunch some numbers to see of the boxes you have are suitable to be modified for other drivers. Box tuning is a product of the internal box volume and post dimensions, and you not only need to consider port diameter and length but also how much additional displacement the "new drivers" will can generate as that affects the size of ports needed.. the higher the displacement the larger the ports need to be to avoid port noise, but there is only so much room on the speaker baffle for larger ports so this can become a limitation. So assuming you have determined there is room to grow the boxes, then you need to model different drivers in the box with software like WinISD Pro to see if you can come up with a combination of driver/ports that will physically fit and produce more output and/or extension than the original drivers. And that's not a forgone conclusion, a higher power driver often has a lower sensitivity so even though it may take more power it may not get any louder than what you're starting with.
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Jeff Bankston

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Re: Vented sub port tuning
« Reply #4 on: August 04, 2013, 04:18:18 pm »

another thing is "how many ports" ? it may take more then one port to keep port noise down. my 18" needs 3 ports. the 15" in the foto above only needed one. the 10" in the foto did better with 2 ports. you need to know all the mechanical and electrical specs of the driver you want to mod the box for along with all the deminsions including magnet lenght and diameter. it may take several hours of trying different box and port configurations to get the results you want. do you want a low frequency bump, flat response, the lowest response possible, highes power handling ? how much damping material do you want in the or no damping material. theres a lot to getting it right or the way you want it. also a rectangle or square port is much better than a round port. it also helps to have a tone generator and an spl meter at the very minimum.
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Jason Moore

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Re: Vented sub port tuning
« Reply #5 on: August 05, 2013, 01:14:05 am »

These cabs currently have 2x800w drivers. I'm pushing them with 2000w. They also have 4x6"dia.x6"long ports. Pulling these and modifying to a rectangular wood port would be no problem. I'm looking for more output and "snap" from these cabs. I'm happy with the low extension.

I completely understand all of the number crunching and modeling ill have to do to modify these cabs.
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duane massey

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Re: Vented sub port tuning
« Reply #6 on: August 05, 2013, 01:36:37 am »

You won't get more output and "snap" from that cabinet, no matter what you do. Carvin boxes are generally fairly well-built, but a little more structural bracing certainly wouldn't hurt. If these are the cabinets that have the Omega Pro18's, they are decent speakers. I would suspect power compression will be an issue that would negate anything you can do.
If you truly want to DIY, build a new design, preferably a horn.
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Duane Massey
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Paul G. OBrien

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Re: Vented sub port tuning
« Reply #7 on: August 05, 2013, 10:26:49 am »

I'm looking for more output and "snap" from these cabs. I'm happy with the low extension.

Kick drum snap extends up in the low khz range so time alignment of subs to mains is a primary requirement and if using aux fed subs a high passed version of the kick signal needs to be fed to the mains as well.
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Jason Moore

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Re: Vented sub port tuning
« Reply #8 on: August 05, 2013, 11:21:03 pm »

Thanks for all the input guys. I've decided for $69 I'm just going to recone the one blown woofer and sell off these cabs to upgrade to higher power units.
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Re: Vented sub port tuning
« Reply #8 on: August 05, 2013, 11:21:03 pm »


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