waveguide with a little fostex

mrkramer · 9th February 2010, 05:15 PM

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

planet10 · 9th February 2010, 05:45 PM

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

mrkramer · 9th February 2010, 06:11 PM

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.

MrKramer

planet10 · 9th February 2010, 06:17 PM

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

badman · 9th February 2010, 07:13 PM

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.

planet10 · 9th February 2010, 08:22 PM

Quote:

Originally Posted by badman

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

mrkramer · 9th February 2010, 09:51 PM

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

badman · 06:20 PM

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.

ultrakaz · 10th February 2010, 08:54 PM

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.

maxro · 11th February 2010, 03:46 AM

Quote:

Originally Posted by mrkramer

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.

9th February 2010, 05:15 PM	#1
mrkramer diyAudio Member Join Date: Mar 2008 Location: San Francisco bay area	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

9th February 2010, 05:45 PM	#2
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	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 __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

9th February 2010, 06:17 PM	#4
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	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 __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

9th February 2010, 07:13 PM	#5
badman Custom Title diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	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. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

10th February 2010, 06:11 PM	#8
badman Custom Title diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	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. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned! Last edited by badman; 10th February 2010 at 06:20 PM.


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9th February 2010, 06:11 PM	#3
mrkramer diyAudio Member Join Date: Mar 2008 Location: San Francisco bay area	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. MrKramer

9th February 2010, 09:51 PM	#7
mrkramer diyAudio Member Join Date: Mar 2008 Location: San Francisco bay area	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

10th February 2010, 08:54 PM	#9
ultrakaz diyAudio Member Join Date: Oct 2004	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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