Mini Fostex OB

kctess5 · 26th August 2012, 06:52 AM

I am going to college in about a year, so I need to start thinking about what I will bring with me. I need something really good so that I am not depressed about being away from my main system.

I have a pair of Fostex FW168HR's and a pair of B&G Neo3W (non PDR) to use. My budget for the rest of this project is quite low, I would normally go for a miniDSP and a couple of amps but right now I can't afford it. I had to buy a new macbook after my old one unexpectedly died so I'm low on cash.

What I am thinking is a small open baffle, about 8" wide and 13" tall. I would have a non OB sub. I need to get the Fostex drivers down to about 80Hz, I know that that's a lot to ask from a driver with such low xmax, but I figure it doesn't have to go very loud. listening position will be 2-3' from the speakers and it won't ever really be asked to play loud. I want to use a passive crossover, that way I don't need the miniDSP or any new amplifiers, I can use my Gainclone to drive it. The sub will be taken care of.

I can't seem to find much about the crossover design for this kind of thing, I read MJK's Open baffle design paper, but I'm having trouble applying it to this situation.

I need to figure out how to do the crossover. It seems like I need to put a low order low pass at 80 Hz, in addition to a 2nd order high pass at the same point. The low pass would flatten the rising response while the high pass would prevent over excursion. This seems like it would work but as soon as I got out of the bass range, and the baffle became large compared to the wavelengths the response would no longer be rising and the low pass would roll the response off. I feel like I must be approaching this the wrong way...

Here's the question:
How do I use passive components to flatten out the woofers response between 80Hz and at least 2000Hz?

Sorry for the noob question, I've never done anything but active crossovers before.

Thanks all

chris661 · 26th August 2012, 11:08 AM

What's going to be the signal source?

If its a computer, I'd throw together a reasonably simple crossover (you might need to Zobel the woofer) at, say, 2kHz, and then eq the lower mids into line using something like Foobar2000.

Saves wasting power in the crossover - efficiency suffers massively on small OBs.

Chris

kctess5 · 26th August 2012, 04:31 PM

Thanks for the reply. The source is a macbook. The only problem with that plan is that I use spotify a lot.

26th August 2012, 06:52 AM	#1
kctess5 diyAudio Member Join Date: Dec 2011 Location: California	Mini Fostex OB I am going to college in about a year, so I need to start thinking about what I will bring with me. I need something really good so that I am not depressed about being away from my main system. I have a pair of Fostex FW168HR's and a pair of B&G Neo3W (non PDR) to use. My budget for the rest of this project is quite low, I would normally go for a miniDSP and a couple of amps but right now I can't afford it. I had to buy a new macbook after my old one unexpectedly died so I'm low on cash. What I am thinking is a small open baffle, about 8" wide and 13" tall. I would have a non OB sub. I need to get the Fostex drivers down to about 80Hz, I know that that's a lot to ask from a driver with such low xmax, but I figure it doesn't have to go very loud. listening position will be 2-3' from the speakers and it won't ever really be asked to play loud. I want to use a passive crossover, that way I don't need the miniDSP or any new amplifiers, I can use my Gainclone to drive it. The sub will be taken care of. I can't seem to find much about the crossover design for this kind of thing, I read MJK's Open baffle design paper, but I'm having trouble applying it to this situation. I need to figure out how to do the crossover. It seems like I need to put a low order low pass at 80 Hz, in addition to a 2nd order high pass at the same point. The low pass would flatten the rising response while the high pass would prevent over excursion. This seems like it would work but as soon as I got out of the bass range, and the baffle became large compared to the wavelengths the response would no longer be rising and the low pass would roll the response off. I feel like I must be approaching this the wrong way... Here's the question: How do I use passive components to flatten out the woofers response between 80Hz and at least 2000Hz? Sorry for the noob question, I've never done anything but active crossovers before. Thanks all

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26th August 2012, 11:08 AM	#2
chris661 diyAudio Member Join Date: Feb 2008 Location: Sheffield Blog Entries: 8	What's going to be the signal source? If its a computer, I'd throw together a reasonably simple crossover (you might need to Zobel the woofer) at, say, 2kHz, and then eq the lower mids into line using something like Foobar2000. Saves wasting power in the crossover - efficiency suffers massively on small OBs. Chris

26th August 2012, 04:31 PM	#3
kctess5 diyAudio Member Join Date: Dec 2011 Location: California	Thanks for the reply. The source is a macbook. The only problem with that plan is that I use spotify a lot.