[vasyachkin]

1 - what is the rate of high frequency roll off - 12db/oct ? 24db/oct ?


2 - is the boost proportional to volume of front chamber ?


assuming the answer to 2 is yes then effective rolloff rate close to tuning frequency will be higher with larger front chamber volume ?


is there any good read on how to tune bandpass boxes ? i don't really feel like playing with software - i feel lazy

 

[Ricci]

Strangely the roll off both above and below tune appears to be about 14db octave.


#2 is yes. Boost is proportional to vented chamber volume and gets increasingly peaky. Roll off close to tune gets more rapid but still ends up at 14db octave.

 

[tvrgeek]

Model shows 12 dB on the HP, about 16 on the LP. WinISL Alpha maximally flat 4th order BP for the Dayton 280. Just a model. From this model, I might conclude the front chamber, IF the tuning frequency was high enough, does not effect the sealed chamber tuning. A bit odd on the 16 dB, where we might expect 18. Just a model. I have not built one.

 

[vasyachkin]



Quote:
Originally Posted by tvrgeek /forum/post/16864154


Model shows 12 dB on the HP, about 16 on the LP. WinISL Alpha maximally flat 4th order BP for the Dayton 280. Just a model. From this model, I might conclude the front chamber, IF the tuning frequency was high enough, does not effect the sealed chamber tuning. A bit odd on the 16 dB, where we might expect 18. Just a model. I have not built one.

why would we expect 18 and not 12 ?

 

[tvrgeek]

Assuming the LP frequency is high enough that the driver is no longer being influenced by the sealed chamber, it should behave like any other single ported chamber. My understanding, but as WinISL shows different and those who have built and measured report otherwise, there is something here I do not understand. Let's hope someone can enlighten us. I found no discussion in Bullock. If I get a chance, I will search through the old issues of Speaker Builder and see if I can find some explanations. I never paid much attention until recently.

 

[Vinculum]



Quote:
Originally Posted by vasyachkin /forum/post/16864832


why would we expect 18 and not 12 ?

Because you are adding another filter (port) to the front of a sealed box, which adds 6dB per "pole" or filter element. 12+6=18.

 

[vasyachkin]



Quote:
Originally Posted by Vinculum /forum/post/16872028


Because you are adding another filter (port) to the front of a sealed box, which adds 6dB per "pole" or filter element. 12+6=18.

we were talking about low pass. where do you get 12+6 from ?