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FlaCharlie 23rd December 2005 03:18 AM

FE103 - What Port Size?
I posted this in the speaker area but just realized that full range might be more appropriate. Please forgive the double post . . . I've got some cabinets that are 10 1/8" x 13 1/4" x 7 1/2" internal. They originally came with a 5 or 6" full range driver and were sealed. I've got a few versions of the Fostex FE103 . . . one pair of the alnico 10F3, a couple pairs of the RS 1197 versions as well as some similar drivers from vintage KLHs - the 3" that they used fullrange in table radios and as mids in the KLH 5 and even tweeters in some models I think. Anyway, I want to use these cabinets and add a port to the rear. I know these cabinets are a bit larger than the BR cabinets I've seen recommended for these but I want to put something together with them. What size port (diameter? length?) would work well? I'd like to get decent bass, given the limitations. Or would something other than BR work better with these cabinets and drivers?? Thanks . . . Charlie

Godzilla 23rd December 2005 02:57 PM

That’s a .58 cubic foot cabinet so…. According to WinISD the port should be

4” diameter x 4” length… which gives you a giant peak at about 90hz. Sealed starts rolling off at 200hz. Either way doesn’t look to good.

My suggestion is to go aperiodic with this driver in that cabinet for best sound.

Either make one like I did or buy this part:

Much like the way Omega does it but I would use only one ‘vent’ on the back with the 1197.

I would stuff the cabinet loosly with acoustastuff or wool also and bet the speaker will sound very nice.


FlaCharlie 23rd December 2005 03:48 PM

What About a Smaller Cabinet?
I guess I should have mentioned that the alnico 10F3s are currently in sealed cabs that measure about 5" x 8.75" x 5.75" internally. A bit smaller actually since there is some internal bracing. Would I be better off just leaving them alone? Or maybe adding a port to these cabinets? What about just removing the backs - kind of mini open baffle?? I don't really have the tools/skills to build anything from scratch but I have a few small cabinets lying around. I've got another pair that are 7.5" x 9" x 5.75" which don't have backs at the moment but I could add some and make them sealed, ported or aperiodic. Would any of these options work better? Thanks . . . Charlie

Godzilla 23rd December 2005 04:08 PM

They will all work about the same 'sonically'... they may measure slightly different but should sound very similar.

I like these drivers very much. No tweeter needed either. But i would add a powered sub later on if you can accomodate one.


sreten 4th January 2006 10:09 AM

2 Attachment(s)


I suggest you put 2 drivers in each cabinet with one rolled
off to give you baffle step compensation, obviously roll-off
the driver with the poorest treble.

I presume you'd run an alnico Fe103 full range with a RS1137 rolled off.

The port tuning is in the range 60 to 80Hz.

For a 40mm dia port :
80Hz - 70mm
70Hz - 180mm
60Hz - 350mm

Tuning of one driver in the cabinets is very poor.

How Is Rolloff Accomplished? Post #3
That's an interesting possibility. Are the graphs you attached for two drivers in the cabinet? I'm a novice at speaker building . . . how is rolloff accomplished? What type of part/circuit and what value(s)? This sounds somewhat like a pair of vintage KLH speakers I picked up at a thrift for a couple of bucks. They have two of the ubiquitous KLH 3" drivers in each cab and are ported but they're very thin (13.25" x 17.5" x 2.75") and were made to be hung on a wall. They supposedly have some kind of "compenstation" network or something - not a simple crossover. They're called the Model 14.
Yes the graphs are for two drivers per cabinet.

One driver has a series inductor - usually in the range 2mH to 5mH.
Suggest you wind the inductor yourself and set by ear.


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