Hello folks.
Large signal differences in compression, distortion, and port noise in bass reflex speakers have been exhaustingly documented in the longstanding literature (such as). The following research of mine, which originally was published in 2020 in German, and only recently translated to English, addresses large signal behavior of bassreflexes as well, but the main point / focus lies on small signal sensitivity differences of different vent sizes, which I am not aware have ever been discovered & empirically documented before.
Multiple port sizes and shapes on multiple enclosures each were compared, and diagnosed thoroughly. I'd say it goes quite in-depth. Enjoy.
Regarding the method of publication, I realize a PDF or forum post would have been preferred, but I am not a commercial entity, and you're getting the benefit of my countless hours of work for free, so I get to choose how & where
I recommend viewing the video on a desktop or laptop, pausing it, and using the left and right arrow keys on your keyboard to move through the text at your own pace.
For completeness' sake, some minor attempts at theoretical explanation. An empirical observation like the one made within this research stands on its own and doesn't require a theory behind it. However, it can be satisfying, and also often useful/helpful, to be able to explain what you're observing - so it is valid to also put some effort into the theoretical background.
In a German webforum discussion about the paper, a former Elac engineer offered Small's loss model (Qb, Ql, Qa, Qp) as a possible explanation. He offered no proof, and even Small's model itself is a purely theoretical one that has never seen an empirical verification. Still, I'll throw this possible explanation in the ring.
If the cause was related to Small's model however, it would have to purely be differences in Qp (friction within the port), since Qa (absorption losses) and Ql (leakage losses) do not apply to a sturdy, sealed enclosure; and Qp alone causing such a huge difference at very small signals (-> very low vent air movement) does not seem plausible.
Another, or perhaps rather an additional possible explanation might be the differences in air mass within the vent. In the first test subject, the 1/8 sd port has 0,65g (500cm³), the 1/4 sd port 2,9g (2250cm³), and the 1/2 sd port 11,9g (9150cm³) air mass. Relative to the woofer's 104g moving mass (mms), these values might already be entering significant territory. I doubt this scale of air mass changes is responsible for dBs of measured difference, but, perhaps combined with some minor friction loss differences in accordance with Small's theory (Qp), the combined effect could be large enough to account for the measured SPL differences.
These are two theoretical explanation attempts. Make of them what you will, feel free to entertain your own, or, again, also feel perfectly comfortable entertaining none and just concentrating on the observation.
- Stoneeh
Large signal differences in compression, distortion, and port noise in bass reflex speakers have been exhaustingly documented in the longstanding literature (such as). The following research of mine, which originally was published in 2020 in German, and only recently translated to English, addresses large signal behavior of bassreflexes as well, but the main point / focus lies on small signal sensitivity differences of different vent sizes, which I am not aware have ever been discovered & empirically documented before.
Multiple port sizes and shapes on multiple enclosures each were compared, and diagnosed thoroughly. I'd say it goes quite in-depth. Enjoy.
Regarding the method of publication, I realize a PDF or forum post would have been preferred, but I am not a commercial entity, and you're getting the benefit of my countless hours of work for free, so I get to choose how & where
I recommend viewing the video on a desktop or laptop, pausing it, and using the left and right arrow keys on your keyboard to move through the text at your own pace.
For completeness' sake, some minor attempts at theoretical explanation. An empirical observation like the one made within this research stands on its own and doesn't require a theory behind it. However, it can be satisfying, and also often useful/helpful, to be able to explain what you're observing - so it is valid to also put some effort into the theoretical background.
In a German webforum discussion about the paper, a former Elac engineer offered Small's loss model (Qb, Ql, Qa, Qp) as a possible explanation. He offered no proof, and even Small's model itself is a purely theoretical one that has never seen an empirical verification. Still, I'll throw this possible explanation in the ring.
If the cause was related to Small's model however, it would have to purely be differences in Qp (friction within the port), since Qa (absorption losses) and Ql (leakage losses) do not apply to a sturdy, sealed enclosure; and Qp alone causing such a huge difference at very small signals (-> very low vent air movement) does not seem plausible.
Another, or perhaps rather an additional possible explanation might be the differences in air mass within the vent. In the first test subject, the 1/8 sd port has 0,65g (500cm³), the 1/4 sd port 2,9g (2250cm³), and the 1/2 sd port 11,9g (9150cm³) air mass. Relative to the woofer's 104g moving mass (mms), these values might already be entering significant territory. I doubt this scale of air mass changes is responsible for dBs of measured difference, but, perhaps combined with some minor friction loss differences in accordance with Small's theory (Qp), the combined effect could be large enough to account for the measured SPL differences.
These are two theoretical explanation attempts. Make of them what you will, feel free to entertain your own, or, again, also feel perfectly comfortable entertaining none and just concentrating on the observation.
- Stoneeh
