Patrick Sun
Senior HTF Member
- Joined
- Jun 30, 1999
- Messages
- 39,670
Well, for some reason, my current Sunosub's placment seems to be the best spot in my room. The SVS sub is on the other side of the TV, and at my main listening spot, it's sounds like it's in a bit of a null. I say this because I get closer to the SVS sub, I feel the null going away and it thumps just dandy. I'm not going to swap out the 2 subs because Sunosub II has a bit of a weak leg at the moment. And as expected Sunosub II has a bit more low end extension.
I took some quick-n-dirty measurements, and you'll see what happens when you over-port an enclosure (I'm using 1/3 octave sine waves and a Radio Shack SPL meter, and the readings have been adjust per generic correction table):
Graph 1:
The light blue line is a near field measurement of the sub, and as you can tell, the low end isn't extended too far, with a F3 around 28Hz (using a Shiva to model the enclosure size and porting, LspCAD predicted a F3 around 27Hz, so this jives). Also, my snake-like porting gives me a Fb around 20Hz (I did the Helen Keller method of determining Fb by playing low frequency test tones and when I got the test tone that moved the driver cone the least, I called that Fb). LspCAD told me that the FB would be 21Hz, so the reality was very close to the simulation. My room tends to boost 45-60Hz, so there's a slight adjustment to smooth out the curve.
The fuscia curve is a 1m measurement of the sub. As you can tell over-porting the enclosure does cause a nice dip below 36Hz, and that was also expected.
Given the size of the enclosure (2.75 ft^3), I could shoot for Fb=25Hz and moving the F3 down a little to around 25Hz. This will involve just taking out one of the two 90 degree PVC bends in the porting. This should give me a little pop while lessening the driver protection for low end material at high volumes. Basically it would mimic the 25-31 SVS model if I changed the porting to a tune of 25Hz. Since I'm enclosure-size-limited, this might be the best configuration for this application. But I haven't decided if I want to do it or not.
Graph 2:
Just for laughs, I wanted to see how the response was affected when I sealed up the port with a nerf football. The thin light blue line is the sealed frequency response. As expected, there is a more gradual fall-off in output under 40Hz. This may be what I use for music (the bass is a little tighter in the seal configuration), and then unplug it for DVDs. The fuscia line is the ported frequency response (I will admit to moving the sub around to another spot in front of my current Sunosub, but the response is pretty similar to the initial measurement).
Anyhow, just thought some of you wanted to see "theory" in action (w/r/t predicted simulations and real world measurements).
I took some quick-n-dirty measurements, and you'll see what happens when you over-port an enclosure (I'm using 1/3 octave sine waves and a Radio Shack SPL meter, and the readings have been adjust per generic correction table):
Graph 1:
The light blue line is a near field measurement of the sub, and as you can tell, the low end isn't extended too far, with a F3 around 28Hz (using a Shiva to model the enclosure size and porting, LspCAD predicted a F3 around 27Hz, so this jives). Also, my snake-like porting gives me a Fb around 20Hz (I did the Helen Keller method of determining Fb by playing low frequency test tones and when I got the test tone that moved the driver cone the least, I called that Fb). LspCAD told me that the FB would be 21Hz, so the reality was very close to the simulation. My room tends to boost 45-60Hz, so there's a slight adjustment to smooth out the curve.
The fuscia curve is a 1m measurement of the sub. As you can tell over-porting the enclosure does cause a nice dip below 36Hz, and that was also expected.
Given the size of the enclosure (2.75 ft^3), I could shoot for Fb=25Hz and moving the F3 down a little to around 25Hz. This will involve just taking out one of the two 90 degree PVC bends in the porting. This should give me a little pop while lessening the driver protection for low end material at high volumes. Basically it would mimic the 25-31 SVS model if I changed the porting to a tune of 25Hz. Since I'm enclosure-size-limited, this might be the best configuration for this application. But I haven't decided if I want to do it or not.
Graph 2:
Just for laughs, I wanted to see how the response was affected when I sealed up the port with a nerf football. The thin light blue line is the sealed frequency response. As expected, there is a more gradual fall-off in output under 40Hz. This may be what I use for music (the bass is a little tighter in the seal configuration), and then unplug it for DVDs. The fuscia line is the ported frequency response (I will admit to moving the sub around to another spot in front of my current Sunosub, but the response is pretty similar to the initial measurement).
Anyhow, just thought some of you wanted to see "theory" in action (w/r/t predicted simulations and real world measurements).
