[ISLAND1000]

Mike,
I consider your experiments and build an important revelation. Your enclosure, the usual sonotube, proves to have identifiable resonance issues with the ( open space surrounding the PORT ). Just as interesting is that the cure for the resonance is to stuff the open area surrounding the port with poly pillows. Simple.
But wait, does this resonance issue apply to ALL sonotube enclosures? If so, will the poly pillows cure any resonance issues in any sonotube?
It makes me wonder if square and/or rectangular ported enclosures also have a similar resonance issue surrounding the port tube as in the sonotube design?
I had always assumed that any resonances created within the enclosures would usually be below the hearing threshold. Obviously they are not as your charting shows and you also noticed immediately upon firing the units up.
This is interesting stuff.
Oh, by the way the tubes and drivers look neat. Are you gonna use them as rolls on the floor or install them vertically?

 

[ISLAND1000]

Well then, is it possible what you've accomplished by the poly pillows is created another but shorter reflective acoustic surface including the rounded mouth of the port? A shorter reflective length would raise the HZ past the pass band ending up somewhere in the 175hz range?

 

[ISLAND1000]

ISLAND, no, that shouldn't be what is happening. The pillows aren't dense enough to reflect a wave, rather, they are significantly reducing the magnitude of the wave from endcap to endcap through absorption. This is why we line the walls and ports of ported enclosures with absorption.

Normally, if the end cap was completely exposed without the intrusion of the port and flare that's what I would expect. But in Mike's project there is so little space between edge of flare and wall of the sonotube as to be a possible toss up as to what is actually reflecting a wave, the end cap or the port end and pillows or even a combination of all three? Thereby the shorter wave length causing any reflected wave to be above the pass band and not noticeable on the chart.

 

[ISLAND1000]

did some experiments as to the number of pillows and their orientation in the enclosure. A single pilow in the center of the enclosure was enough to completely kill the end to end reflection, and was MORE effective than 4 pillows in the one endcap.

Hmmm . . . . . . . very interesting.
Mike, you're pillows may give me nightmares. :foottap:

Now I wonder if centering (ALL) sound absorbent material in an enclosure rather than applying it to the outside wall, is a more efficient way to do this "interior reflection cancellation" stuff.

I'll go read the other stuff on AVS.

 

[ISLAND1000]

I like 4 in the end cap.
That sure is a nice response curve and the waterfall plot is very good. The driver, tube length, and tune add up to an excellent measured sub.
Subjectively, how does it perform?

 

[ISLAND1000]

I just KNEW they would. There's an example of a project that measures well and predicts the ultimate result . . . . . audio pleasure.