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Old 10th August 2006, 02:11 AM   #1
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Default Has anyone tried this!

Has anyone tried this to get the most out of the low frequency of a driver in a box that's too small.
I tried it and it definatly makes the driver go an octave or two lower, but what I would like to know is what happens to the Qtc of the spearker in the box, does it go up or down or stay the same?
I've seen this done on Infinity Speakers, all the high end ones from years ago RS1, RS1b, RS4.5, RS Betas and such, when Infinty were highly regarded with their Emmits and Emmins mids and highs and had great bass from 12ins drivers that were capacitor coupled with huge caps as well.

Read at the bottom ( A Third Octave Sealed System)

http://www.subwoofers.cc/HomeAud/HDr...alignments.htm

Cheers George
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Old 10th August 2006, 06:33 PM   #2
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yes, and interesting enough did it with the SV12 in an ACI design subwoofer. It worked, but the bass while extended missed something.

Kept the cabinets, changed the drivers, lost the caps... went to active eq... much happier

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Old 10th August 2006, 11:35 PM   #3
Ron E is offline Ron E  United States
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Qtc is not defined for a 3rd order system.

If you are gonna throw your transient response away, why not just go vented? While you can get deeper bass with a 3O sealed, make sure you model excursion - it may alarm you.
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Old 10th August 2006, 11:50 PM   #4
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Greetings fellow "Digger". If I've understood it correctly then I think the first example I saw was a KEF 105 Series I (in mid 70's) where they used a 600uF cap in series with a sealed (second order) box. Auditioned very well from all reports. I gather it depends on starting with an underdamped response in the first place.
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Old 11th August 2006, 12:20 AM   #5
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Can Ron or anyone give a fix to this, I'm almost there.
I'm not using the capacitor coupling, it was just an experiment.

All working perfect SV12 in 85lt fully stuffed laid in but not squeezed in 75%wool 25%dacron batts, with my low pass now modded to only 5mh (instead of 10mh) and 470uf, Unibox gives me -3@35hz and Qtc of .708 and it sounds great.
But, there's always a but, the bass is just a little too loud around the peak of 60-80hz, is there any way of reducing it 2-3db without introducing a series resistance and blowing my Qtc to hell, or increasing the feedback on my bass amp? (pig of a job)

Below is the circuit of my xover I bridged out the 2ohm and bridged out the first 5mh choke, with 10mh I had not enough ooph around the 200hz with the 5mh it's just right but the total level is just a bit loud.

Thanks for the help George
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File Type: pdf monolith 3 passive crossover schematic.pdf (9.4 KB, 49 views)
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Old 11th August 2006, 01:50 AM   #6
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Is it at all possible to move the crossover down? My sealed Assassin sub sounded bloated in the 60-80 hz region also, so i moved the crossover down from 80 hz to 50 hz and it took away all the bloat but left me with the extension. What mains are you using? Are they capable of a lower crossover?
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Old 11th August 2006, 02:21 AM   #7
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Quote:
Originally posted by LightwaveDude
Is it at all possible to move the crossover down? My sealed Assassin sub sounded bloated in the 60-80 hz region also, so i moved the crossover down from 80 hz to 50 hz and it took away all the bloat but left me with the extension. What mains are you using? Are they capable of a lower crossover?
They are Martin Logan Monolith III, electrostaic above the 125hz xover, they won't go down any further, guess it's the upping of the feedback on the bass amp to reduce bass a couple of db did'nt want to go that route, as both amps are pefect gain match at the moment.
I'll wait a few weeks, maybe the bass units and all the fresh stuffing will change for the better, (less) bass, or worse get more efficient and become even louder.

Cheers George
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Old 11th August 2006, 04:51 PM   #8
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Quote:
“the bass is just a little too loud around the peak of 60-80hz, is there any way of reducing it 2-3db without introducing a series resistance and blowing my Qtc to hell”
Have you tried this proposed method to control the Qtc (Qts):


Enclosure for high Q driver


A picture showing voltage readings only considering the driver at the filter drive point, and if lowering Qms:

B
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Old 11th August 2006, 05:04 PM   #9
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edit picture
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File Type: gif aci_sv12x.gif (79.4 KB, 584 views)
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Old 11th August 2006, 09:40 PM   #10
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Thanks Bjorno, I will study this, as this is my first venture into speaker design, and i'm learning slowly, been building amps too long and never dabbled in the blak art of speaker design.

I have mange to flatten the response down a little by just the right amount and the 80hz mark, and it is sounding very good with studio recordings, nice and tight and dry, but with big orchestral pieces I actually prefer the way I thought it was too loud.
What I did was put an LCR network across the back of the SV12 which was 18mh-900uf-5.6ohm and that is perfect for studio done recordings closely miked double bass and such, but for big orchestral work that is distant miked I perfer it off.
Can you simulate what the LCR network is doing on your program? With the 5mh then 470uf to ground and the LCR across the SV12.

Cheers thanks for you intrest and help
Cheers George
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