Message Boards

8040:closing the port (closed system)

ilikesound, modified 10 Years ago.

8040:closing the port (closed system)

Youngling Posts: 9 Join Date: 2/24/11 Recent Posts
Hello Genelec,

the 8040 is a (good) ported design for a reason, but personally I don't need the ultra deep low end (40 hz at -3db) and the very high SPL from my 8040. I generally prefer a fast impulse response to a extended low frequency cut off so I ask myself how the 8040 behave when I close the port (with a closed cell foam plug or something). I think the impulse response is great in the high and mid frequencies, but (of course this is the case for most ported speaker of that size!) it could be better in the low end.

Theoretical speaking when I close the port I would expect a higher cut off frequency, less possible SPL and a better impulse response in the low end. Any negative effect? Or em I complete wrong?

best regards and I'm very interested in a professional opinion on this. :-)
ilkka-rissanen, modified 10 Years ago.

Re: 8040:closing the port (closed system)

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
Hello,

In general you are right, but the better impulse response part is a little bit difficult. In theory a 2nd order system exhibits less ringing and group delay around the low frequency corner than a 4th order system. Any additional electronic filtering of course comes on top of that. So in that sense there is a slight difference. But usually the problem is not the impulse response of the speaker but the listening space instead. So if you want to clearly improve the sound quality of your speakers, you should look at the whole system (room + speakers). Typical rooms have a lot of acoustic problems in the bass range which makes the speakers sound heavy/slow/boomy etc. The reason for this isn't the impulse response of the speaker but the speaker + room instead where the room contributes maybe 90% of the total amount. So that's what you have to concentrate in.

When talking about improving the low frequency reproduction quality of your sound system, of course traditional acoustic treatment is the best way to go, but it requires thick damping materials, and lots of them! Another way to deal with the room modes is electronic filtering of the actual signal. In a way closing the port of a reflex speaker is a very basic acoustic filtering because it reduces the acoustic output of the speaker within a certain frequency range. But it's not the best method because it also reduces maximum SPL, raises the cut off frequency and increases distortion. Better do it electronically because then you are not touching the acoustic performance of the speaker but instead shaping the input signal. So if you feel that there is too much bass in your speakers, they sound heavy/slow/boomy, try engaging the bass roll-off DIP switches on the speakers. For example a -6 dB bass-roll will shape the low frequency corner similarly to blocking the reflex port, but doesn't reduce the maximum SPL or increase distortion. For even more sophisticated room response equalization, you should look at our range of DSP speakers.
ilikesound, modified 10 Years ago.

Re: 8040:closing the port (closed system)

Youngling Posts: 9 Join Date: 2/24/11 Recent Posts
Sorry for the late reply, but thanks. I really appreciate this forum with feedback from Genelec-professionals.