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Old 14th September 2008, 02:00 PM   #21
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Quote:
Originally posted by otto88
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snip
> best to have a single bass line. Otherwise, maintaining two (or more) woofer channels, you are creating separate bass pseudo-phases, and pseudo-sounds where none existed before. All this and many more reasons are real good persuasion to mix your base below, say 100-140 Hz. I think you should do so even if you choose to use two independent woofers for some odd reason.

Not sure what you meant by “a single bass line”. Being an 0.1 for HT, it’s a single channel, only for LFE, below 120 Lz. Maybe you’re referring to eg a two way + sub(?)

Cheers
I meant just add together any L and R channels there might be and certainly not creating new channel divergences by imprecise filters. 'Fraid I am mired in the old world of acoustical music reproduction (using the term loosely). In acoustic music, while you can put mics anywhere you want in a hall and pick up very LF stuff differing in phase, etc., it really isn't meaningful differences and choosing just one of those mics is probably better than feeding both to a CD.

I suppose there are serious electronic composers (Vangelis' thundering Mission to Mars) as well as pop producers of disaster movies who diddle with the knobs to make synthetic special effects based on differing waves in two LF channels.

But all things considered, I'd just wrap them together anyway. By "but all things..." I am also thinking of the cost of making two seriously profound subwoofers, not just intra-music issues. Not sure I wouldn't extend that argument to favouring one fine speaker instead of two so-so stereo speakers. Or even one fine narrow-band full-range driver instead of....
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Old 15th September 2008, 09:20 AM   #22
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Thanks for the input guys
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Old 15th September 2008, 10:46 AM   #23
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The effect of a 12dB 15hz Q=.9 filter on an arbitrary speaker design ported to 20hz.

Click the image to open in full size.

Note that the combined response of the system with and without the filter is essentially the same to about 15hz~17hz, and then begins to reduce both response amplitude and cone excursion. By 13hz the cone excursion is reduced by 30%, by 10hz it is reduced by 50%, by 5hz it is reduced by over 85%.
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Old 15th September 2008, 09:20 PM   #24
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Thanks for the curves, theoretical though they may be.

If I am reading the colours correctly, I'd say they are a good argument for not using anti-resonant boxes for low frequencies because they go wonky in the subsonic range... dealing with which is what this thread is about.

You get wild, undesirable, uncontrollable cone flaps but none of the sound down there. Unlike sealed boxes or Klipschorns (that also have sealed boxes deep inside them).
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Old 15th September 2008, 09:37 PM   #25
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K horns aren't going to be any better at cone control at 10 hz. Sealed boxes might have more control, but not much spl. Pick your poison.
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Old 16th September 2008, 09:43 AM   #26
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>By 13 hz the cone excursion is reduced by 30%, by 10hz it is reduced by 50%


> Thanks for the curves, theoretical though they may be

A theory that needs to be applied for EBS

> a good argument for not using anti-resonant boxes for low frequencies because they go wonky in the subsonic range

wonky?

You get wild, undesirable, uncontrollable cone flaps but none of the sound down there

They wont be uncontrollable with an appropriate filter. And why would they *not reproduce the sound down there - soundtracks?
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Old 16th September 2008, 10:43 AM   #27
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Same as before, but upped the power 3dB and added a sealed box for grins and giggles.

Click the image to open in full size.

(note: if you apply EQ to the sealed to get some bass, the excursion will climb through the roof)
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Old 16th September 2008, 03:15 PM   #28
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I'm over my head here, so I hope a tech-inclined person will correct me (well, correct all of us).

The Klipschorn cone is well controlled at all frequencies by the small sealed box behind the cone and even at frequencies below which the front horn-air-load is no longer much.

Watching cones flap about, that's what I mean by wonky behaviour. You don't want the cone to be loose in light of many mechanical and electrical reasons, and sonic reasons include Doppler (I'm not sure the status of Doppler effects esp. now-a-days that small woofer cones are in style). Adding electric LF filtering helps only to a point because you really need the acoustic control of flapping downstream (except for motional feedback, ahem ahem, sadly there's no feedback from the cone... and none ever possible from resonant boxes). Flapping bad, even if some deranged mixer added it to your movie soundtrack. Best to use a very sharp LF cutoff that removes as much signal as you can below the useful range of the woofer.

When djk cheerily points out that sealed boxes with dramatic amounts of LF EQ have big excursions "that will climb through the roof" - a very comic image indeed seeing a large woofer enclosure climbing my cluttered walls to reach the roof - it is just a matter of what EQ he chooses to plot (esp. if that's a 5 inch woofer plotted there). Big and growing EQ leads to big and growing excursions. It would be nice to see the curves/assumptions described and the colours identified too.
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Old 17th September 2008, 02:38 AM   #29
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Ben

> now-a-days that small woofer cones are in style

Im intending to use a driver a got a coupla years ago, the Peerless XLS, 12” with 12 mm Xmax. Though much bigger Xmax drivers are available now.

> Best to use a very sharp LF cutoff that removes as much signal as you can below the useful range of the woofer.

Yes, that’s my intent.

What do you mean by “the *acoustic control* of flapping downstream”?
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Old 17th September 2008, 02:16 PM   #30
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Quote:
Originally posted by otto88
Ben
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What do you mean by “the *acoustic control* of flapping downstream”?
You suggested (electronic) filtering to control flapping. That only controls the electric input and only stuff upstream of the filter, not in the amp, turn-on transients, etc. Moreover, the frequency range where flapping gets going falls right square in the music range. In other words, you can cut the real low freqencies but not higher.

For resonant boxes, TLs, and baffles (and unlike sealed boxes), as I poorly understand these things, there is no brake on the cone motion below the anti-resonant or unloading frequency (often the same as the speaker resonance) and the cone is just a floppy mass except as limited by the restoring mechanisms (spider and maybe the surround). So any nudge, electric or mechanical, can set the cone in motion at those low frequencies.

Aside from Doppler, you just don't want your cone shifting about in the magnetic gap, reacting to a rhythms besides your source, or otherwise misbehaving.
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