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help with FAST setup
help with FAST setup
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Old 12th April 2017, 02:46 PM   #21
scottjoplin is offline scottjoplin  Wales
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The other potential problem which is touched upon there is the low load impedance to the source with the high pass filter which can cause roll off at high frequencies, most modern sources won't have a problem with that but if you are adding a pot for level matching then it would be best to use a buffer after the pot. Then you are halfway to an active filter........
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Old 12th April 2017, 03:04 PM   #22
twoNibbles is offline twoNibbles  United States
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I had thought about an active filter. I am not a fan of op amps though. They are... finicky. "Close enough" engineering doesn't really work with them as they tend to amplify the difference. Also I don't really want to mess with making a PCB. Nasty chemical process I'm not a fan of or an expensive long wait from a contract MFR. Big passive components are nice and easy.
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Old 12th April 2017, 03:13 PM   #23
Boden is offline Boden  Netherlands
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Dear twoNibbles,

Before worrying about opamps, there is is whole Universe in other priorities to right first. The first priority is trying to get your filtering in order, be it passive or active, which will require in-box measuring the drivers SPL curves plus impedance curves, and then using these in a simulation tool such as XSim.

Before, or rather without that, the whole thread will lead to a lot of handwaving. Not to a solidly designed system. There is no short cut, I am afraid.

Good Luck,
Eelco
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Old 12th April 2017, 03:15 PM   #24
scottjoplin is offline scottjoplin  Wales
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Any level matching will effect the filter, but this can be taken into account in the design and so long as its something which is not adjusted later you can find a work around.

As an aside, I've just finished building Doug Self's preamp with adjustable tone controls. It uses 15 dual op amps and a multitude of electrolytic capacitors in the signal path.... the kind of thing that gives some people here nightmares
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Old 12th April 2017, 04:23 PM   #25
twoNibbles is offline twoNibbles  United States
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Quote:
Before worrying about opamps, there is is whole Universe in other priorities to right first. The first priority is trying to get your filtering in order, be it passive or active, which will require in-box measuring the drivers SPL curves plus impedance curves, and then using these in a simulation tool such as XSim.

Before, or rather without that, the whole thread will lead to a lot of handwaving. Not to a solidly designed system. There is no short cut, I am afraid.
Is this really necessary? Is it impossible to arrive at a decent system without a mic and a simulation software? My gut tells me that something of reasonably high quality can be achieved via a mixture of research, listening, and tuning. I have no doubt that the way you are suggesting is the correct way but this is just my first speaker project. I am starting from nowhere. With nothing. As I build projects I will gain tools and education that will aid me in operating to your level of exactness but for now I want a reasonably successful speaker system that I can listen to and enjoy while I work on making another one to do an even better job with somewhat more educated approach from the beginning. Is this such a terrible approach?

edit: My intention is not to whine at you but honestly ask. You truly don't believe that I can attain something satisfactory in this way?

Last edited by twoNibbles; 12th April 2017 at 04:24 PM. Reason: clarification
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Old 12th April 2017, 06:09 PM   #26
Boden is offline Boden  Netherlands
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Yes, I am convinced (and so do Vance Dickason, Joe DÁppolito. John Kreskovsky Siefried Linkwitz and many many other serious designers) , although many here seem to think otherwise.
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Old 12th April 2017, 06:15 PM   #27
twoNibbles is offline twoNibbles  United States
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I suppose I will have to find out on my own as I am not convinced.
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Old 12th April 2017, 07:15 PM   #28
scottjoplin is offline scottjoplin  Wales
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If you were designing a system from scratch, and particularly if you were using a high level crossover and multiple drive units, then I would agree with Boden, but that is not the case. For what you want to do ie, add a subwoofer to a full range speaker (FAST) that approach is not necessary in order to achieve the improvement you're after.
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Old 12th April 2017, 07:21 PM   #29
twoNibbles is offline twoNibbles  United States
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That is what I thought. I'm not doing anything overly complicated here. Maybe I'll take on some ridiculousness in the next iteration but this seems overly exacting for my purposes at the moment.
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Old 12th April 2017, 07:23 PM   #30
chrisb is offline chrisb
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I think there's room in this sandbox for us to agree that both methodologies - the scientifically rigorous and the iterative "let's see if this works" - can yield results that will ( at least temporarily) satisfy the ears and pride of the builder.
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