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Old 12th May 2010, 03:13 AM   #11
pjanda1 is offline pjanda1  United States
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'Zilla,

What exactly was the "lossy" box? I've been thinking of trying to do something aperiodic for those that want small cabinets. I haven't found a good way to sim them, so it appears they depend entirely on trial and error. I'd be curious to hear any details you can provide.

Paul
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Old 12th May 2010, 11:33 PM   #12
Karl71 is offline Karl71  United States
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Godzilla -

What are the outside dimensions of your sealed 1.3 cu. ft. cabs? Wall thickness? Cabinet Material?

Regards,

Karl
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Old 13th May 2010, 05:12 PM   #13
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>>> What exactly was the "lossy" box? I've been thinking of trying to do something aperiodic for those that want small cabinets.

The 'lossy' box is one that's not perfectly sealed. I have an old pair of nice wooden cabs with a hole for an 8" driver but the tweeter is missing two of its four screws so air escapes. I sim aperiodic boxes in WinISD by tuning to 20hz and making the vent .25" diameter... probably not the best way to sim LOL... and the results are usually the same or similar to a sealed cab. My quick sim of the Betsy this morning indicates a 1.5 cubic ft box sealed works pretty good as does a 2cf... -3 at around 65hz. Anything smaller seems to produce a big bass bump on paper. Listening to Betsy's in smaller sealed 'lossy' boxes sounds good to me in real world listening regardless of the simmed bump. Not sure the sim is indicative of what i hear. I would also like to try a simple 'picture frame' box for the Betsy... a shallow box maybe 16"w x 20"h x 2"d without any back at all and see what i get. My sim shows a smooth gradual slope from 300hz to 150hz... so a simple sub rolled in should provide satisfying bass while the Betsy does the rest. I will post pics of the sims when i can. Certainly not the optimal setup for the Betsy but a real world project that should provide 'good enough' performance while letting the driver do it's thing. I bet the imaging will be to die for (for the small OB anyway) that measurements don't reveal and the sound will be dynamic and detailed.

Godzilla
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Old 13th May 2010, 06:36 PM   #14
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Attached are charts for sealed, vented and small open baffle speaker for Betsy. I left some other drivers in the open baffle sim for comparison. These boxes work well enough. If you like the Betsy's dynamic, detailed sound and don't mind a sub i think the small open baffle might be an interesting idea as a substitute for a bookshelf sized speaker. I should sim the Betsy on a larger open baffle too...

Godzilla
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File Type: jpg betsy-sealed-1.jpg (122.9 KB, 97 views)
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Old 13th May 2010, 08:41 PM   #15
pjanda1 is offline pjanda1  United States
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Just so folks don't get confused: the BetsyK is the ideal choice for nearly all boxes. Though the Betsy can be made to work, the higher Q alignments that usually result won't be for everybody.

'Zilla, I've wondered about the Betsy in something akin to a small open backed cabinet (maybe even down around a half cubic foot), like some vintage stuff. I don't know which would give better bass, the BetsyK in a real aperiodic box or the Betsy in something really lossy, where the back is full of holes.

It is also worth noting that if you are considering a sub with the small cabinet, it may be worth while to use a higher Qts alignment (like your Betsy in a sealed box) in conjunction with a high pass filter (especially line level, but big motor run caps could work too). That would bring the response down and further reduce excursion. Just a thought.

Paul
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Old 13th May 2010, 09:17 PM   #16
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>>> I don't know which would give better bass, the BetsyK in a real aperiodic box or the Betsy in something really lossy, where the back is full of holes.

I wonder too which would be better?

>>> It is also worth noting that if you are considering a sub with the small cabinet, it may be worth while to use a higher Qts alignment (like your Betsy in a sealed box) in conjunction with a high pass filter (especially line level, but big motor run caps could work too). That would bring the response down and further reduce excursion. Just a thought.

That's a good thought! I've only simmed the driver i have with the higher qts... the BetsyK may be better in the sealed or aperiodic boxes for sure. It may be fun to compare Betsy on a small OB to BetsyK in small sealed/aperiodic. I would imagine more base from the BetsyK but the imaging could distinguish itself on the open baffle providing a different advantage (or flavor) over the other. An open back box like the old vintage boxes is probably what i will build for my Betsy in the near future.

Neat stuff to think about.
Godzilla
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Old 13th May 2010, 09:43 PM   #17
freddi is offline freddi  United States
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BetsyK sim I did sometime ago for 3rd order sealed box shows ~350uF "should" flatten the passband and lower F3 but a series capacitor of this value will raise the output and in-band excursion. A leaky box may be good - do nearfield mic and muck with holes/whatever while watching on RTA

Click the image to open in full size.

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Old 13th May 2010, 10:22 PM   #18
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Freddi or anyone...

Can anyone explain or does anyone know, all things being equal, would a driver have greater power handling in a sealed or aperiodic box? I am wondering how allowing the box to breath might change how the speaker lives in that box... is it happier in one box or the other?

I feel like building the Betsy in a small OB just for kicks... will hide a small sub under my office scanner and keep it a secret. Shhhh!

TIA
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Old 13th May 2010, 10:37 PM   #19
freddi is offline freddi  United States
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I'd think it'd burn up at the same rate - a leaky box if used with lps and phono preamp without warp filter ought to be worse.
I'd like to see a discussion of distributive leaky vents - and have seen the cases with small holes or slits produce high air velocity and introduce harmonic distortion below the passband when driven with sine-wave - but does music approach sine-condition?

Last edited by freddi; 13th May 2010 at 10:41 PM.
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Old 13th May 2010, 10:50 PM   #20
pjanda1 is offline pjanda1  United States
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Generally, power handling in it's strictest sense shouldn't be an issue with fullrangers. With most higher efficiency fullrangers, you will exceed Xmax at power levels well below the voice coil's thermal limit. Where excursion isn't controlled by any acoustic means, like an OB, it won't take more than a couple of watts to exceed where the speaker sounds good. And, it will only take a couple more to get the voice coil out of the gap. I can imagine that some BLH's may control excursion enough to allow you to through some serious watts at the speaker, but that isn't what we're talking about here. Even if thermal issues somehow enter consideration, there shouldn't be enough air moving in and out of the aperiodic box to make a difference. Stuffing in the sealed box would limit the speakers ability to shed heat. But, I really don't think that is the primary concern in the vast majority of home fullranger applications. IMO, if you need more than a couple of watts, a single driver isn't for you. Sure, there are drivers with higher excursion, but that doesn't mean using it is a good idea from a distortion standpoint. Thermal concerns are important in pro audio, but that is an entirely different ball game.

What you want is to limit excursion to keep distortion down. Both the sealed and aperiodic boxes should do a decent job of that. With a woofer assisted OB, you'll get better results with some sort of high pass filter. However, in the extreme near field (are you thinking on a desk?), it may not be worth the hassle.

If you are looking for small OB inspiration, how about heavy duty (1/4" wall) aluminum stock pots? They cost a bit of $$ in big sizes (like 40 quarts), but I'd love to put a pair of Betsys in the bottom of some shiny cylinders. Maybe even big roasters on a desk.

Paul
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