Hello,
I am about to start building a pair of loudspeakers using Seas A26 drivers. I will be constructing the cabinet out of Birch ply and was planning on making the port out of a drilled stack of plywood. The entire cabinet will have a 20mm radius roundoff milled on all the edges and I was planning on doing the same around the edge of the port hole.
My question is, should the length of the port include the 20mm roundoff or not?
Thanks!
I am about to start building a pair of loudspeakers using Seas A26 drivers. I will be constructing the cabinet out of Birch ply and was planning on making the port out of a drilled stack of plywood. The entire cabinet will have a 20mm radius roundoff milled on all the edges and I was planning on doing the same around the edge of the port hole.
My question is, should the length of the port include the 20mm roundoff or not?
Thanks!
You will have to account for the roundoff, there is already a lot of info at diyaudio.com about how to calculate when using a flared port.
That would be a perfect opportunity for an even more flared port, using my port optimizer tool: https://www.diyaudio.com/community/...rbers-and-port-geometries.388264/post-7943524
And then again, don't focus too much on the exact alignment. You won't hear the difference if it's 5Hz off.
Depends on the frequency, the 5 Hz between 20 to 25 Hz is 1/3 octave, same as the difference between 50-60Hz.
Below Fb (box tuning) output drops at ~24dB per octave as the port output transitions from in phase to 180 degrees out of phase, 8dB in 1/3 octave. That is a big change, less than half as loud sounding in 5 Hz.
It is a good idea to verify what the actual Fb is..
I typically have to iterate once to get my port tuning dead on anyway. Yall hit yours on the first go?
Not so far (in the last 50 years..), unless copying a design.
And zero to five Hz is all or nothing… I was relating to real world situations. Few of us have tuned to 25Hz (I did once and was spot on, accidentally, with a slot port, but I wasn’t that lucky when I tuned a 160 liter enclosure to 21Hz…) and most of us aren’t in the business of multisub systems or open air listening. So the room shall and will mess things up.
Do an impedance measurement.
Impedance minimum between the two peaks is at tuning frequency.
First try to evaluate if the incorrect tuning is a real problem (usually if a too high tuning creates one-note-bass peak).
Then try to minimize the problem by moving the speakers.
You can shorten the port(s) for higher tuning and much easier: narrow the port with play dough or similar for lower tuning.
Or increase tuning frequency by reducing enclosure volume by filling it with bricks, sand, wood ...