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Old 12th April 2009, 01:55 AM   #1
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Default New project underway: Fostex and Pyle Pro

Yes, a very odd combination of quality and quantity with Fostex and Pyle Pro. As many of you know, the Pyle Pro PPA15 has become very popular as an open baffle sub driver. Decided to give it a shot, but crossed over higher. I chose two pairs instead of the goldwood 18 because of increased surface area, reduced footprint, and higher excursion capability. All for roughly the same price (Paid 130 for both pairs, check amazon for great price!).

The full range driver will be a Fostex FF85KeN, from Dave of course. He was gracious enough to sell me a cosmetically challenged pair to fit my budget as a college student. I was originally going to run them passive, but plans have changed and it will be active instead.

Read over MJK's open baffle papers (thank you!) and decided on a U-Baffle with short wings (4-5 inches) to push the ripple well above the crossover point. The FF85K will be crossed over at 250hz-300hz and the PPA15s will be crossed over at around 150hz to combat rising response. Both Linkwitz-Riley 12db/octave.

The top of the front baffle roughly follows the 2.2* Driver diameter rule that has been floating around here. Its about 6.75 inches wide at the centerline of the driver. The FR will be mounted higher than normal of 32 inches to 38 inches (preference). Here are my preliminary drawings. I don't think I will be changing them much. I apologize for the dimension clutter.

Any thoughts or suggestions would be appreciated. I will update this thread once the units have been built!
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File Type: jpg ff85k.ppa15d.jpg (29.3 KB, 1215 views)
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Old 12th April 2009, 01:57 AM   #2
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Here is the back of the baffle, thanks!
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Old 12th April 2009, 07:19 AM   #3
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Quick simulation of this baffle (approximating the U-baffle as a larger, but similarly shaped--flat baffle) in basta using the fostex specs and some PPA15 specs on the web (FWIW) suggests:

--This design will have a 2db hole centered on ~3K and a 3dB peak centered on ~1.5K.
--Extension--without EQ--will be to about 65hz at 3db down.
--Should be Smooth through crossover region (1db dip) --> though this does not include any floor bounce issues in the fostexes output just above XO
--About 6W power handling before the FF85 runs out of excursion at 200hz (PPA15 are only pushing 2.5mm at 20hz)

IMHO, The ripple at 1.5K, if not eq'ed, will be even worse if the rear reflection off the back wall is undamped.

The crossover point appears poorly chosen regarding maximum volume output, a single PPA15 per side would suffice, distortion at in the midrange 300hz-1K will be bad at volumes where the woofers are limping along.

325hz on the fostex and 200 on the woofers doubles the power-handling of the Fostex, but changes un-equed extension to ~75hz. Should be able to eq, reasonably flat to about 30hz if you use a 150w amp on the bottom and 15w on the top.

Sean
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Old 12th April 2009, 08:08 AM   #4
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Quote:
Originally posted by seanzozo
using the fostex specs and some PPA15 specs on the web (FWIW) suggests:
... About 6W power handling before the FF85 runs out of excursion at 200hz (PPA15 are only pushing 2.5mm at 20hz)
An interesting intellectual excercise, but the fostex data isn't that useful ... even for stock drivers -- these FF85KeN aren't stock. My sims show the uFonken show it xMax limited to 1w at 100 Hz... but playing unaided in my big room, i'm pretty sure it has a bit more than that in it. Early measures while i was developing Tysen showed no major dips (in room flat from 25 to 16k +/- 2 dB -- the simplier XO we ended up using is not as flat, but sounds better)

Personally, i think i'd be looking to have a bit more baffle to support the FF85keN as well as some assymmetry.

dave
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Old 12th April 2009, 06:18 PM   #5
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Quote:
Originally posted by seanzozo
Quick simulation of this baffle (approximating the U-baffle as a larger, but similarly shaped--flat baffle) in basta using the fostex specs and some PPA15 specs on the web (FWIW) suggests:

--This design will have a 2db hole centered on ~3K and a 3dB peak centered on ~1.5K.
--Extension--without EQ--will be to about 65hz at 3db down.
--Should be Smooth through crossover region (1db dip) --> though this does not include any floor bounce issues in the fostexes output just above XO
--About 6W power handling before the FF85 runs out of excursion at 200hz (PPA15 are only pushing 2.5mm at 20hz)

IMHO, The ripple at 1.5K, if not eq'ed, will be even worse if the rear reflection off the back wall is undamped.

The crossover point appears poorly chosen regarding maximum volume output, a single PPA15 per side would suffice, distortion at in the midrange 300hz-1K will be bad at volumes where the woofers are limping along.

325hz on the fostex and 200 on the woofers doubles the power-handling of the Fostex, but changes un-equed extension to ~75hz. Should be able to eq, reasonably flat to about 30hz if you use a 150w amp on the bottom and 15w on the top.

Sean
Wow great response! Though I agree with planet10 in that the Fostex should have more headroom when playing music.

Reason I am doing two PPA15s per side is because, frankly I am a bit of a bass head and want to have the headroom.

Regarding te peak at 1.5K, what would you suggest I do? Add damping directly behind the baffle or a diffuser of some sort behind the driver on the back wall?

I will follow your advice on the crossover point though. I have the option to adjust the crossover point all the way up to 400hz for both the woofer and FR, so I can play around with it a lot.

As far as EQ, I will probably only use minimal EQ at the very lowest octaves.

To Dave, what do you suggest on baffle width? I don't want to go too wide, so I am thinking 8 inches wide and change the baffle geometry.
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Old 12th April 2009, 06:32 PM   #6
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dave,

I expect that in a sealed box or a vented cabinet (as opposed to a baffle that provides a nulling effect at the excursion peak) the FF85 would have slightly greater headroom. Additionally, my point was not that a 6W simulated power-handling was too low in the abstract, but that mating that with 2 15-inch speakers was possibly overkill (unless you want to try EQ them flat below 30hz, then you literally cannot get enough woofer excursion ).

I think (agree) that either a greater effective-XO frequency or a wider baffle, would be reasonable. On the MJK OB baffle, adjusting the XO higher to meet the same XO freq, excursion is halved giving 6db additional mechanical headroom, while requiring essentially no EQ.

A wider asymmetric baffle will make the off-axis a little less organized and (0not shockingly) asymmetrical. But, in the narrower baffle the ~1.5K peak moves as you rotate off-axis (at 45 degrees it is centered at 1K) making the EQ less effective

Sean
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Old 12th April 2009, 06:55 PM   #7
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Ill get a modified baffle design done sometime tonight. Yes, I love headroom in the bass region. My pet peeves with loudspeakers is running out of headroom in the bass region when I try to crank it up Granted, these ill not be played very loud. Been there done that with line arrays
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Old 13th April 2009, 04:26 AM   #8
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I changed the dimensions a bit. I played with edge, roughly replicating the listening distance and width to get a ball park figure.

I increased the top edge to 8 inches from 4, and I removed the extreme curvature. I also moved the driver 1 inch up to be slightly offset from the center. The result is a response that closely resembles a rectangular baffle 8 inches with the same height. See attached image.

I still may add some curvature, but it will be very minimal compared to the original rendition. Again, I will raise the crossover point to 300hz+ for the FR.

Any more thoughts? I am usually not the one to spend too much time in the developing stages. I like to build So unless there is something vital I am missing other than the above mentioned, looks like the design is mostly finalized.
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Old 13th April 2009, 05:04 AM   #9
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I've been eyeing those Pyles for helper woofer duty with my Betsys. Ya' can't beat the price! I'll be really curious to see how their LF response turns out in that narrow baffle. MJK has shown the usefulness of the Alpha 15's considerably higher Q when designing OB's, but they ain't as cheap. I'd also be curious to hear about the Pyle's build quality from anybody who has laid hands on one.

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Old 13th April 2009, 05:44 AM   #10
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Ill attempt to provide some notes on build quality, though I am not very experienced with higher quality drivers. Most of my experience stems from my other hobby, which is car audio.
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