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Question on the ports [message #14194]

Sat, 07 August 2010 04:58

kbass20
Messages: 14
Registered: April 2010
Location: Danville, In.

Junior Member

So I had this sound guy ask me about the ports on my k200 2x15 cab and being something that I wouldn't have really thought of I didn't have an answer for it, so here it goes!

Are the ports just there for looks, to vent the air, or are they tunned? If they are tunned what is the tunning? Could changing the length or adding a flare to the inside improve the tunning?

Thanks
Noah

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Re: Question on the ports [message #14209 is a reply to message #14194]

Wed, 11 August 2010 15:14

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

Here`s somewhat of a anwser for you.
I will have to say that its my belief that the port size that Kustom used was a average of what was need by the drivers the cabinets could be sold/fitted with to tune the cabinet for the best low frenquency responce and not un-load a given driver which could lead to a blown driver.

These days each given model of speaker made is tested and rated for its VAS spec which is a rating of how much air volume is needed to be moved by the driver to achive its other rated spec`s.

As with any ported cabinet the lenght of the port, its diameter and its inlet and outlet flare/radius will affect the tuning.
Their are many computer programs you can get that will help you to tune a cabinet better, the problem will be getting the needed spec`s on some of the vintage drivers used in Kustom`s, as only the spec`s for the Altec and JBL vintage drivers can be found, the CTS and Jensen spec`s are a mystery to this day, although some educated guesses could be made.

One thing I can tell you for sure is the 3-15" cabinets when fitted even with the standard CTS model bass drivers, no less the up greaded drivers could use two more larger ports for a total of four.

The thing to understand is for the most part in regards to bass guitar these stock cabinets reproduce the needed bass tones very well with out being boomy and bottom heavy, and I find that they even carry a 5 string bass pretty good.
So far I have not found a stock drivered 4-10" cabinet for bass that can stand up to one of these cabinets when fitted with JBL,Altec or a good EV or Eminence driver.

The easyest mod to make on these cabinets to tune them to the larger VAS needs of better drivers is to pull out the baffle a board and shorten the bottom end and then pick up some scrap plywood and paint it black to make a slot type baffle of the area you figure you need.
So yes to make a long story short, they are tuned somewhat!

[Updated on: Wed, 11 August 2010 15:21]

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Re: Question on the ports [message #14241 is a reply to message #14209]

Mon, 30 August 2010 18:00

BC
Messages: 583
Registered: March 2000
Location: Kentucky

Senior Member

Good info Steve! I have wondered how to add port without making the cabinets look like a hack job.....I like your idea. I would imagine the same can be said for the 2x15s. I have a 200 series 2x15 that sounds choked on the pair of E-140 JBLs that are in it. Do you have any feel for the size of a slot port in a 2x15 or a 3x15 and is there any proper way to estimate it? Many thanks for your sharing of knowledge. I wish you could make Chanute! BC Cool

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Re: Question on the ports [message #14245 is a reply to message #14194]

Tue, 31 August 2010 14:20

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

BC in regrds to the tuning info you ask of, you will need to get a software program or book which will let you input the info on the E140 specs that you can pick up off the JBL site and then figure out the needed area and depth of the port for your cabinet.

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