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Old 10th June 2004, 04:27 AM   #31
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Quote:
Originally posted by phase_accurate

It is perfectly possible to make low-end EQs that don't have the restrictions of LT (not possible to make dynamically tuneable) and ELF (intrinsic LPF).

Could you rephrase that? I can't figger it out. What is "LT"?
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Old 10th June 2004, 07:13 AM   #32
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Hi Dave

LT= Linkwitz transform

Advantage of LTF:

Very wide range of possible driver/tuning combinations. No intrinsic HF rolloff.

Disadvantages:

Hard to make tuneable (the implementation via state-variable filter is a possible workaround) let alone dynamically tuneable for overexcursion protection. Needs 6 fairly accurate capacitor values.

ELF (extended low frequency)

Advantages:

Simple. Lower cutoff easily made tuneable, even electronically for dynamic excursion/amp-overdrive control. Basically only two capacitors needed.

Disadvantage:

Intrinsic lowpass function, depending on driver fc.


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Charles
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Old 10th June 2004, 08:31 AM   #33
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phase_accurate asked:

Quote:
What is its working principle ?
I'm not sure. The page you referenced mentions Dr Leach's name, but IIRC he followed his original publication with another in the 80's.
When I read about the LT on Linkwitz' site, it really sounded like them principle Leach used in the paper I read. However, I don't know if their implementation is equivalent.

I guess it's time to dredge up the old, faded thermal copy and see if I can still read it...

Tim
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Old 13th June 2004, 05:10 PM   #34
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Hi Pafi!

...was on holidays since June 4th....
Great, really nice to see that my sub inspired you
The link to the DataSheet of that MosFet-modules is:
http://www.semikron.com/databook/05mosfet/m120b020.pdf

I also feel that they are oversize and their high gate charge pushed me think about that heavy FET-drivers UC3710T from TI/Unitrode.
http://focus.ti.com/docs/prod/folders/print/uc3710.html
I have received the two SADHARA drivers and since had them in my hands in real life, I decided to make two subwoofer with one drive each. One driver already has a weigth of approx. 20kg.
A box with two drivers would result in about 60kg....
To heavy, to difficult to find a proper position....
Alright, so the required power reduces.
Also I am now planning to integrate the amp into the box, so I will not need a short circuit protection anymore. This will also relax the power requirements for the MOSFETs.

Which types would you recommend?
If I will keep the possibility to go for a rail voltage of about 130V, then I will need at least 150V types, better 200V.
If I calculate the max. value of the sine wave current by dividing the
rail by the DC resistance of the speaker (2.3 Ohms) I will end up short above 50A .
As the frequency is vey low and the speakers are driven much below the resonance frequency, they will show an impedance close to their DC-value. And as the frequencies are very low the SOA of the MOSFETS will not allow much more current than their DC-rating...

I don't think that I have to much money, I simply optimized my financial range:
Which thing is sucking really a lot of a man's money, but in fact is not really necessary? -- NO! It is not his wife!!!
It's the car.



@ Yuri:
Why should 80Hz be the definite limit?
I see to major reasons for distorsions:
1. ..speakers cone may bend or break up into partial modes....
2. ..non linearity of the air suspension...
(Air suspension of a sealed box is stiffer for compreshion and less
stiffer for decompression)
Point 1 is related to the selected speakers.
Due to this I decided to pick that crazy expensive ESOTECs, which
drive a 110mm cone with a 75mm voice coil.
Point 2 is important if the ratio volume of enclosure / volume displacement is getting small (for my taste: less than 20 at full excursion). You overcome Point 2 by an active excursion
regulation and skip the LT. I think some of the VELODYNE's top level Subs are also UnderResonancePrincipleSubwoofers (URPS) with active excursion regulation...
Of course I agree: The higher you choose the resonance frequency the more power you require. A hell of lot of more power, because the speakers output transfer function drops with second order....
On the other hand your subwoofer should not have a resonance frequency which matches to one of your 3 major resonances of the
room were you want to listen to music.
In normal rooms the highest main resonance is about 71 Hz, which corelates to the commeon 2.4m height of the room....
So I would prefer to stay above that.

Cheers to all
Markus

P.S.
I started that subwoofer in 1999 and I use it since 2000.
...have no idea, if URPS was new at that time or not.
I simply had the idea, tried it, and it was working really fine.
..didn't care about patenting it, because I don't like our completely derailed patent system...
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Old 14th June 2004, 03:10 PM   #35
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Default pic of my cost optimized car

<void>



no car, no financial trouble...
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Old 14th June 2004, 03:27 PM   #36
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Default Re: pic of my cost optimized car

Quote:
Originally posted by ChocoHolic
<void>



no car, no financial trouble...

have no loudspeaker - have not loud in your sweethome
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Old 14th June 2004, 06:00 PM   #37
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Hi Yuri!
...also quite promising your proposal for optimization..

@Pafi:
I looked around for some less bulky MosFets and this
IRF type seems to match perfectly to my new requirements:
IRFB52N15D:
150V / 60A / 32 mOhms
Cgate: 60nC at Vgs=75V / Vds=10V / Id=36A


....time will tell....

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Old 14th June 2004, 06:05 PM   #38
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correction: Cgate should be Qgate....
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