Question about port length for FE207E's

[2litre]

I finally picked up my first pair of Fostex drivers, some FE207E's.

I had enough scrap ply to get close to the Fostex recommended simple bass reflex cabinet size of 35L for immediate listening and break-in.
I got my cabinet in at 31L.

In the 35L drawing Fostex shows 18mm for the port length on the 80mm port. I've never built a ported speaker before but that just looks like a misprint. I have some 3" PVC cut to a 2" length in them right now but wondering what length I should be using.

Any help would be appreciated.

R/
Jim

[rjbond3rd]

180mm. That was a gotcha for me too!

[GM]

18 mm is a common material thickness, so the vent is just a hole in an 18 mm thick baffle. Scaling vents to fit readily available pipe stock: FE126E enclosure question

GM

[borispm]

A 35L cab with a 18mm means a tuning frequency of 75Hz! I think it's a misprint as well. FE207E can get much lower in a large cab! I would say 150mm with a tuning frequency of 45Hz.

[Bob Brines]

I use a 3"dia x 5" port on my 35L BR's. They probably net more like 32L and are stuffed back to 35L. I much prefer EBS alignments, so I tend to tune low. This can give better bass extension and avoid boomyness.

Bob

[Godzilla]

I simmed the 207e a while back in WinISD. Here is what i came up with.

http://www.zillaaudio.com/fostex207e-box-plots.htm

35L box with a 4" x 4.25" port.

Doesn't mean it's correct, only what i would try and then work from there. Please double check my sims bc i can't remember if i used a round or square shaped ports!!! Regardless, if you tune the 207e too low a deeper dip appears between 100hz and 200hz. I was uncomfortable with this bc i would not want the speaker sounding too thin thru this range. The older style Fostex 168s produces similar charts and is a balancing act to get right imo. With this driver i prefer not to tax it too much in the bass only bc i want to retain its midrange accuracy. Using a 45L box you can go lower but at the expense of a balanced frequency response. I never used or heard this driver so buyer beware... but offer this as food for thought.

Godzilla

[borispm]

It's just a trade off. Smaller and higher tuning frequency for more controlled bass, larger and lower tuning frequency for less controlled bass. If you're going to add a BSC, you can tune it a bit lower. That's just my personal opinion.

[GM]

Originally Posted by rjbond3rd

180mm. That was a gotcha for me too!

Missed this when I posted. Japanese audiophiles are mostly 'old school' design wise, so tend to use high output impedance systems which require cabs be tuned to around/at driver Fs as this one seems to be, so add BSC as required for PP tube or SS to get a similar frequency response.

GM

[GM]

Originally Posted by borispm

It's just a trade off. Smaller and higher tuning frequency for more controlled bass, larger and lower tuning frequency for less controlled bass. If you're going to add a BSC, you can tune it a bit lower. That's just my personal opinion.

This is backwards, lower tunings have a lower Q (slower) roll off, ergo more controlled.

GM

[Bob Brines]

Well, I've posted this graph before. This is real measured data. 207E in a 35L box with a 3"dia x5" port. This is the EBS type alignment I favor. Note F3~50Hz, F10~30Hz. I hate to see this driver go, because the 207E + FT17H make one fine speaker.

Bob