Will a BFD eliminate port resonance problems?

[Leonardo]

These are my port options.

8" x 24.6" - 277 Hz
10" x 40" - 168 Hz

Is there a reason I can't use my BFD to roll off everything above, say 140Hz? My x-over will be at 80 or 100 depending on how it measures in-room.

[Ricci]

You can use it to roll off the higher freq's but it is not a brick wall and there will still be some info coming through at a low level.

What is your project? You could make your tune higher or increase your volume to make the 10"er a little shorter. Alternatively you could split the difference and go with 2 6" ports or a slot port.

[brent_s]

As Josh says, Xovers are not brickwalls. The slope of the lowpass crossover is complementary to the highpass rolloff. If you use EQ filters to artificially increase the lowpass rolloff above 80-100hz, your main speakers are likely to sound thin in the first octave or so above the Xover point as they are only reproducing half of the intended signal in this range, with the other half being filled in by the subwoofer.

-Brent

[Leonardo]

Ricci wrote:

What is your project? You could make your tune higher or increase your volume to make the 10"er a little shorter. Alternatively you could split the difference and go with 2 6" ports or a slot port.

It's a 585 l 14.5 Hz Sonotube. It's the largest volume I could fit in an 8' ceiling x 24" tube. I'm using an RL-P18 D4.

2 6" will not fit in the 24" endcap and give full port diameter clearance on all sides.

9" is what i would really like to use (32", 213 Hz)

Is there any 9" diameter cylindrical material I could use? 3/4 MDF would take up a lot of volume if I built a slot.

Maybe I'm just being too picky about the port noise from the 8? If I understand correctly, the max velocity represents a full power sine wave just below the tuning freq.

[collo]

An 8 inch port with a 1" rollover routed flare is good for around 25m/sec below 20hz

[Ricci]

I don't think that you would encounter any problems if you couldn't get 2 6"ers more than 6" away from everything.

[SteveCallas]

18" driver LLT owners have just about all been using 8" diameter ports with no problems. If you really want to worry yourself about it though, just go overboard on the flare.

[shr-t]

One could apply a narrow bandstop filter on the BFD, right? 1/60 octave around 200 would mean a few Hz wide filter, dropping the gain to the minimum will essentially silence that frequency.

And then there's the more elaborate possibility of using a tuned Helmholtz resonator at the middle of the port

Correct me if I'm wrong, though.

[shr-t]

Effects on the listening band (up to 100Hz) are essentially zero: