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Multi-Way Conventional loudspeakers with crossovers

waveguide with a little fostex
waveguide with a little fostex
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Old 9th February 2010, 06:15 PM   #1
mrkramer is offline mrkramer  United States
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Default waveguide with a little fostex

Hi all,

Ive been playing around with 2 drivers on an open baffle. A little Fostex ff85k fullrange and a JBL 123a 12" woofer. I think they sound really great together. Having said that it seems I can never leave well enough alone...

I was thinking about mounting the ff85k in a shallow waveguide roughly the same diameter as the JBL (12") and finding a good crossover point that integrates them directivity wise. Figured this would help in time alignment and stands a chance of making things sound better....ha!

I should say this isnt a "FAST" system. The ff85k is only handling upper mids and higher.

Any experiences/thoughts out there on using a midtweet/fullranger this way?

MrKramer
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Old 9th February 2010, 06:45 PM   #2
planet10 is offline planet10  Canada
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waveguide with a little fostex
It should work fine. We 1st listed to the FF85 rear mounted in a short waveguide the thickness of the oprn baffle.

Where is your XO?

dave
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Old 9th February 2010, 07:11 PM   #3
mrkramer is offline mrkramer  United States
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Thats good to hear. How did it effect the sound? Did you notice any difference?

As for the x-over, I guess it depends on whether or not a waveguide thats 3" deep ( distance to align them) can actually control the dispersion. If so, Ill cross it right around where the JBL begins to beam. In the neighborhood of 900-1200hz.

Up till now, Ive been crossing it from 300-750hz. Sounds good no matter where it crosses but I do notice issues with excursion when I cross it lower and play louder.

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Old 9th February 2010, 07:17 PM   #4
planet10 is offline planet10  Canada
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waveguide with a little fostex
The little FF85 quite stunned us, the waveguide certainly did not detract.

You must play pretty loud. We were able to get Tysen going pretty good (droppy PLLXO at 333 Hz).

dave
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Old 9th February 2010, 08:13 PM   #5
badman is offline badman  United States
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Default 123A ff85k

I designed an OB around this combo. Try using 10uF highpass and a heavy duty woofer grille with a 4x4 square of absorbent material (I used 1/4" F11 felt) centered on the grille to absorb highs from the woofer. The result is a near perfect 2k first order crossover. To get some directivity (less than you may think is required) around the edges of the ff85k I built up a few layers of felt for absorbtion. Tilt in the baffle was used for time alignment. There may be a writeup on enjoythemusic's DIY section soonish.
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Old 9th February 2010, 09:22 PM   #6
planet10 is offline planet10  Canada
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waveguide with a little fostex
Quote:
Originally Posted by badman View Post
There may be a writeup on enjoythemusic's DIY section soonish.
I'm eagerly waiting a review of the FF85KeN in the same section of ETM.

dave
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Old 9th February 2010, 10:51 PM   #7
mrkramer is offline mrkramer  United States
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Thats pretty interesting.
So you are using the felt as a mechanical low pass then? Is that the only 'filter' on the woofer?
How does it sound?

MrKramer
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Old 10th February 2010, 07:11 PM   #8
badman is offline badman  United States
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Yes. The felt is the only lowpass. One of many nice parts about it is that it makes the filter act as a 1st order electrical AND acoustical, so a textbook highpass on the fostex aligns nicely with the .6mH Le to create a near-perfect first order filter. The distortion products in high freqs are filtered by the felt as well as the top end of the response, which is an added benefit. It also seems to counteract lobing somewhat by interfering with opposite edge cancellations.

Sound is superb. They are the best speaker I've made, and amongst the very best I've heard. They're not without their limitations and are not very attractive, however. Being dipoles, they're definitely sweet-spot oriented.

The 123A, within its limited Xmax, makes some very serious deep sounds.
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Last edited by badman; 10th February 2010 at 07:20 PM.
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Old 10th February 2010, 09:54 PM   #9
ultrakaz is offline ultrakaz  United States
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Hello Badman,

Thanks for sharing your good work. A few questions if I may ask....

What is the size of your open baffle? And did you experiment on the 123a by varying the thickness(es) of the felt to achieve a lower crossover point. Perhaps, going down to 1kHz would be better for the 12" and get a little bit more of goodness from the FF85.
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Old 11th February 2010, 04:46 AM   #10
maxro is offline maxro  Canada
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Quote:
Originally Posted by mrkramer View Post
As for the x-over, I guess it depends on whether or not a waveguide thats 3" deep ( distance to align them) can actually control the dispersion.
Considering the JBLs are about 4" overall depth from front face to back of magnet, I doubt that you'll need 3" of offset.
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