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Subwoofers 80hz and Down under!

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  #11  
Old 04-01-2019, 09:10 PM
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W9TR W9TR is online now
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You know, I think itís more about the implementation than if the sub is sealed or ported. There are great examples of both. The trend is clearly toward sealed subs driven by high power amps and lots of eq.

If you want to do a ported sub that plumbs the depths it will be very big - like 5 cu ft. The WAF will be lower than the frequencies it can reproduce!

Thatís why most commercial subs are sealed in small enclosures.

Passive radiator subs can be made very small as well, and can go very low. Size for size I donít see a huge improvement and the cost will be higher for the passive radiator sub.

You bring up a good point - it is definitely way more difficult to match any sub with ported mains. The phase/amplitude response varies with the position of the mains and is hard to predict.

One sub manufacturer even tells you to stuff the ports of your mains before attempting to integrate the two.
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  #12  
Old 04-02-2019, 09:54 PM
Clark2 Clark2 is offline
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Quote:
Originally Posted by W9TR View Post
...it is definitely way more difficult to match any sub with ported mains. The phase/amplitude response varies with the position of the mains and is hard to predict...
Thanks again for the good information. I'll certainly report where I end up... -- Clark2
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  #13  
Old 04-09-2019, 10:29 PM
Clark2 Clark2 is offline
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Well I now have a KIN Sub on approval, and I'm working to "integrate" it into my system. A few results and stumbling blocks already:

1) The KIN does appear capable of producing enough low bass in my room to fill in where my mains (Beovox M 70's from the 1970s) give up -- around 80 HZ at 8 dB/octave -- although I could probably benefit from a larger sub or a corner placement (which I don't have). Frequencies at about 40 Hz and below seem thin in this preliminary evaluation.

2) It has a non-DSP cross-over that is low-pass only to the sub at 12 dB/octave -- although it does have speaker-level pass-through terminals in addition to line inputs, they would have no effect on the mains. Therefore it should not introduce any time delay relative to the mains other than that from the presumed greater mechanical inertia to get the sub's cone moving.

3) Right off I found that the KIN is close to out of phase with my mains, for whatever reason. This led to some concern that the mains (hookup is via DIN connectors and spliced leads, so non-transparent) might both be wired in inverted polarity. I went down a rabbit hole with absolute speaker polarity, as follows:

4) I installed the free "Polarity Checker" app on my Android phone, downloaded its MP3 band-filtered impulse files to my computer, burned them onto a CD-R, and played them through my system from the CD player. This app is pretty good as far as I can tell. I tested it by thumping on opposites sides of a door and a window -- it gets the polarity of these ad hoc impulses right. Bottom line is that the mains are in correct polarity and the sub (at 0 deg "phase shift") is (approximately) opposite. I "solved" this problem in a first cut by wiring the sub to the amp via speaker-level connections (in parallel to the mains). This had no noticeable effect on the sound from the mains but allowed me to invert the polarity going to the sub. Now the sub is close to in phase with to the mains (at the first-guess 80 Hz cross-over frequency) at 0 deg of "phase shift."

5) I finally found what appears to my untrained eye to be an outstanding step-by-step description by Bob Katz of how to integrate a simple sub like the KIN with mains driven by an ordinary (not home-theater) amplifier like my Yamaha A-S501 -- search the Web on "70-how-to-accurately-set-up-a-subwoofer". Unfortunately the 1/3-octave pink-noise samples needed to carry this out properly are only available on Bob's site in archaic formats that I have been unable to convert to ISO for burning to another test CD. I have yet to locate similar files anywhere online. Bob says he will try to find the original files for me "when he has time." Meanwhile does anyone have such files to share (or maybe they are in a library here somewhere)?

I'll post more of the saga after I find suitable files and can complete the recommended setup procedure. Meanwhile any comments or suggestions would be most welcome. -- Clark2
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