tuning a fr125

[catsby]

Hi all, long time lurker here... Just wondering if any of the gurus on this site can help me out with a strange problem I've been having.

I am finishing up a simple css fr125 build using a 4L box (3/4" MDF) and a front mounted 4x1" port from parts express. It sounds good as-built, but curiously, when I reverse the port so that it sticks out of the box (see below), the bass response shoots through the roof! (in a good way)

I was wondering why this happens and what can i do to keep this killer bass? Is it just a function of internal volume? or is it because i've extended the port by an extra 3/4"?

here's what i mean:


appreciate any help!

[LineArray]

Hi,

there may be 2 reasons:

1. By increasing the volume you changed the BR
alignment. Adding length to the port lowers fb too ...

2. Maybe the inside mouth of your vent is not free enough.

To investigate 1. you can increase the volume and/or make your
vent longer.

To investigate 2. you can replace the port by a slightly
curved one or place the vent in a diagonal manner into the
cabinet, to get the vent's mouth more free.

As a rule of thumb, 2xdiameter of the vent is the
minimum distance to the next cabinet wall ...


BTW: How did you find your alignment ?

4 Liters seem pretty small for that driver.



Kind regards

[69stingray]

Download Unibox and compare the two responses.

1. Use the net internal volume and port length with the port inside the box.

2. The new internal volume and new port length with the port outside the cabinet.

http://home20.inet.tele.dk/kou/ubmodel.html