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Old 17th August 2004, 09:46 PM   #21
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Default Re: FF85 ?!

Quote:
Originally posted by jim
Suppose I combine the 88dB/w/m Fostex FF85 with a 13cm or 17cm woofer with the same sensitivity, will placement near the rear wall of the room compensate for baffle step ?

Thanks,
Jim
It might do the trick, but you would kind of back yourself into the corner as far as room placement. It shouldn't be too difficult to find a woofer around 92dB that would fit your bill. Why not try the Emenince Alpha 10"? I imagine that would do the trick pretty well. I would go to the PI speakers site and get the box info for the PI 2 tower (I think that is what it is called) this uses the Alpha 10" in a BR cabinet, and get some pretty good bass from what I hear. That might take a lot of the guess work out of it. Then all you would have to do is find your crossover point and mess around with that and an L-pad....
If you use a woofer with the same effecincy as the fostex you might find that you have to put an L-pad on the fostex to keep things even, which would be to bad.
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Old 18th August 2004, 06:18 AM   #22
navin is offline navin  India
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to fully compensate for baffle step you'd have to place the drivers in the wall.

baffle step is a function of baffle size/dimensions/shape. to some extent baffle step can be compensated by placing the speaker on a wall or very very near one. this compensation is NOT accurate and might make the freq. resp. ragged and placing a speaker near a wall might also adversely affect imaging and excite room nodes (usually low frequency).

the 85k is not a fullrange but a wide range working best above 200-500hz depending on your SPL requirements. it requires a 1st or 2nd order XO.

the easiest way to compensate for baffle step using a single 85k. is to use a woofer that is about 91db/1w and let it run to about the baffle step freq (usually between 300-500Hz). so in effect what you will get is a 2 way (maybe 1st order) XOed at 300-500Hz.

right now one option for me is to use a FF125K and 85K and do this. however this option does not fulfill my power / SPL requirements. to fulfill my requirements I would need the 88k to be about 91db or handle about 10W rms (twice it's current rating of 5W rms). I'd prefer the latter because finding a woofer that is 94db (3 db more sens than 91db) and acoustically similar to the 85k is quite diffcult.


my object is to make a small speaker (under 12 liters) that can operate from 60Hz+ and create 95db/20W/2m. above 100Hz.
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Old 18th August 2004, 11:37 AM   #23
jim is offline jim  Belgium
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Talking Back to the Alpha10

Hi all,

I think the best approach for me is going for the Alpha10 combined with the Fostex fe127.
That way I can still have a reasonable sensitivity for my tube amps.
I can also borrow an active crossover to test some crossoverpoints before building my own.
Do you think the qaulity will be better by going active ?

Jim
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Old 19th August 2004, 06:11 AM   #24
navin is offline navin  India
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Default Re: Back to the Alpha10

Quote:
Originally posted by jim
Hi all,

I think the best approach for me is going for the Alpha10 combined with the Fostex fe127....Do you think the qaulity will be better by going active ?Jim
there are 2 advantages of going active. both are related to having a dedicated amp for most of the music.

1. the energy hungry bass freq. can quickly sap a small amp's resources and this is affects the behavior of the small amp deteriorating the system's sound. by redirecting the bass freq to a seperate amp the main amp does not get overloaded and the whole system sounds cleaner. any distortions in the bass amp stay away from the rest of the music and since the ear is less sensitive to bass than to midrange these distortions are not as noticebale. hence you can get away with a cheap bass amp like a $100-150 plate amp and a good fullrange amp like a SE tube (I hear that the El84, 34, KT88 and 300B are best for this purpose depending on power requirements, parts availability and safety).

2. adjusting for driver sensiivity becomes easy esp with an active XO. even with a line level passive XO it is quite easy to adjust sensitivity.

BTW do you have specs for th alpha 10? any link?

my fear is that i might not mate as well with the FF85 as say a paper cone 8" (SEAS P21 for example).
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Old 20th August 2004, 10:49 AM   #25
jim is offline jim  Belgium
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Default Alpha 10

Hi Navin,

Here's a link to the Eminence Alpha 10

Alpha

I would combine this with a FE127 as it has a higher sensitivity compared to the FF85.

Greetings,
Jim
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Old 21st August 2004, 06:53 AM   #26
navin is offline navin  India
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ofcourse the 127 is a bigger driver. it does not have the top end response of teh 85 but is still a very good unit (from what i have heard).

some others have been very happy with it's smaller brother the 107.
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