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Old 15th January 2009, 02:19 PM   #1
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Default Please check this out

Hi there,

I was having a discussion concerning ported design and a guy claims to have designed a sealed 1.5 cu ft box with a single 12" woofer cone (27mm p-p) that can reach down to 12 Hz.

Now I don't think that 27mm is nearly enough to get anywhere close to achieve output at 12 Hz that is perceptible. The design is servo-controlled. Now correct me if I'm wrong here but don't servo's necessarily limit dynamic range as a byproduct of reducing distortion ?

I mean, in a size enclosure that small, I can't even begin to imagine how much EQ will be required.

A guy then chimed in the discussion and posted a graph on WinISD showing the Shiva driver (modified with 27mm x-max) as an argument to show that a 12" cone (with 27mm x-max) is beefy enough to achieve it.

Now I don't know about you about does that graph look correct ? Considering that it doesn't factor in room gain apparently. Tell me what you think.

Regards,
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Old 15th January 2009, 06:28 PM   #2
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Anyone ?

Regards,
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Old 15th January 2009, 06:51 PM   #3
jbell is offline jbell  United States
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servo -- you mean rhythmic audio? where they have a feedback coil to their amp, where they can modify speaker T/S params? (similiar to acebass)
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Old 15th January 2009, 06:59 PM   #4
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Yes the design uses a servo-mechanism. My question is really two fold; how on earth can a 12" woofer even one with 27mm p-p in a 1.5 cu ft box (servo or no servo) reproduce a 12 Hz note that one can perceive ?

Second is that a member threw a graph in WinISD showing that a cone with 27mm p-p (used the Adire Shiva which is 14 mm but modified the results to reflect 27mm) can indeed reproduce down that low. Now the graph shows the cone pushing down to 10 Hz at 90 dB's and the member claims that this is done without room gain whatsoever.

So I'm really skeptical of the results. I mean, take those values and put them in a room where room gain might add 8-12 dB's to those figures and it really doesn't look right.

If a servo mechanism limits ultimate output in order to maintain exceedingly low distortion and if the box size is that small then surely the driver will need tons of EQ to shape the response down that low ?

Alright, that's 3 questions. Thanks.

Regards,
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Old 15th January 2009, 08:05 PM   #5
jbell is offline jbell  United States
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http://www.rythmikaudio.com/technology.html

ask the guys who do it. Although some of the links at the bottom of the page may answer some of your questions...
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Old 15th January 2009, 08:29 PM   #6
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What about the graph ? Anything look strange ?

Regards,
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Old 16th January 2009, 12:38 AM   #7
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Well if you're putting 650w into it like it says I can believe that. This computer putting out 47 watts I can hear 10 hz coming out of a 5.25" driver in a bass reflex plastic enclosure.
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Old 16th January 2009, 11:05 AM   #8
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Is that sarcasm or are you being serious ?

Regards,
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Old 16th January 2009, 12:36 PM   #9
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You can use this graph to look up whether the xmax * sd (vd ) is enough to produce the claimed spl at the claimed frequency.

Rob.
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Old 16th January 2009, 01:13 PM   #10
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Vp will be roughly 1400cm^2.

Using linkwitz spreadsheet this is good for about 89dB @12Hz

I think actually achieving this could be a different story. You'd probably fry the VC first
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