Fostex FF85wk and Mark Audio Alpair 6p tested against each other - Page 2 - diyAudio
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Old 23rd September 2013, 04:17 AM   #11
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I know what it does to the sound, but not measurements.

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Old 23rd September 2013, 03:15 PM   #12
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Fair enough. I do see the center of the break up peak in my measurement is at 9khz where fostex shows it at 10khz. I'm totally speculating, but wonder if the treatment doesn't lower the amplitude and frequency of the breakup. More likely just a sample to sample variation thing though.
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Old 23rd September 2013, 03:26 PM   #13
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Quote:
Originally Posted by blumenco View Post

It looks like you just stuck the driver in the middle of a baffle that is clearly a bit wide for the driver considering what it'd be put in in normal home use. This is bound to cause problems in the response so its hard to take the data for that driver entirely seriously.
I already responded to you, but I just re-read your post and noticed this. Are you kidding? It's 7" wide... The driver is not centered vertically, on purpose, but it is centered horizontally, on purpose. It's a crappy phone picture of a crappy test box.

Cause WHAT problems? It's hard to take you seriously. Please clarify what problems this would cause.
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Old 23rd September 2013, 03:28 PM   #14
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Note that not only does the test enclosure for A6P have a much larger baffle overall than the Fostex enclosure, but it appear to be almost square, indeed the box looks to be close to a cube. On the other hand, the baffle dimensions and shape of the FonkenSET enclosure is rather carefully calculated to mitigate diffraction effects.

Could that have some impact on measurements, particularly depending on mike distance, which I don't think was indicated?

A more valid direct comparison of the drivers would be in boxes as close to identical baffle dimensions as the Alpair's frames would allow, or on an IEC open baffle.

FWIW, I've heard both drivers in stock and modified form (the Fostex extensively), and would certainly not ascribe shouty-ness to the Alpair. If anything the Fostex might be considered a bit bright and forward - as seen as the approx 6-8(?) dB difference in the 8-9K region where enclosure would have less effect I think.

As for the sonic effects of the cone treatment, without devolving into the same old polemics, let's just say that we're as eager as anyone to see a simple and easily repeatable measurement technique that can pinpoint how/why it changes what we hear "deep in the mix" . The absence of proof isn't proof of absence.
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Old 23rd September 2013, 03:37 PM   #15
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Ok, I see the baffle is really causing some concern. Here's the modelled diffraction character of the alpair in the enclosure I built. The enclosure was thought out to achieve golden ratio characteristics, even the depth. The only thing I didn't shoot for golden ratio was the horizontal placement, cause nobody does that.

Here it is.

Click the image to open in full size.

See, no diffraction except the diffraction hump from baffle step. The fostex will have the exact same shape except a little higher up (maybe 1800hz or so). Diffraction is a much smaller problem than people think. Most of the testing people point to is with dome tweeters which diffract off baffle edges like crazy. This isn't that.
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Old 23rd September 2013, 05:13 PM   #16
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Ryan - if you look closely at Dave's GR Fonken / Marken drawings as far back as 2007, you'll see that achieving close to GR in all three dimensions was considered in the design.

modelling is one thing, but such a strongly voiced conviction should probably be verified by testing under identical conditions - such as mentioned in my earlier post
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Last edited by chrisb; 23rd September 2013 at 05:16 PM.
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Old 23rd September 2013, 05:35 PM   #17
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Chris, I suppose what's being misunderstood is that I'm just showing two measurements. The alpair 6p in my 7x11" box. And the FF85wk in the P10 box (not sure what it's called). I think it's perfectly ok to make a comparison between the two. I think I made the thread title to strong of wording. I wasn't looking to pick a winner or something. Just show the measurements against each other for reference. Without a reference they're less useful.

My strong conviction does come with verified testing... I've tested all kinds of box sizes and shapes with various types of drivers. The model is only posted to show how minor it really is and because blumenco suggested it. For the hundreds of models posted in the FR forum and the scant few actual measurements made, I'm puzzled by the criticism. All you have to do is look at the measurements I posted and the Fostex spec sheet, and you can easily see there's hardly any box influence other than a baffle step tail below 1khz.

I'm very comfortable with criticism and welcome it. I'm just a bit baffled by this one. I expected questions like, how did you deal with reflections? How did you check the off axis angles? Why doesn't it match the MA spec sheet? Etc.
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Old 23rd September 2013, 05:44 PM   #18
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Sorry if I sound wound up. I am a little bit. Comments like

this

Quote:
Originally Posted by blumenco View Post
its hard to take the data for that driver entirely seriously.
and this

Quote:
Originally Posted by gafhenderson View Post
need to do this again
aren't appreciated. If people think the data is useless, I welcome their measurement data, which tends to not exist on this forum. I don't claim to be some expert, or suggest that a frequency response plot will tell someone if they like the driver. But if the critics wanna be critics without basis, I welcome them to put their words into actions.

And that's definitely not directed at you Chris, as it was you that suggested I nab this pair to test. So I appreciate you seeking the data. Your ears obviously already confirmed the FF85wk sounds great. This only backs up your claim. And it sounds like you like the alpair 6p as well. So this backs that up also.
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Old 23rd September 2013, 06:13 PM   #19
chrisb is offline chrisb  Canada
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oh, we're all entitled to get exercised when misconstrued, intentionally or otherwise.

Not to belabor the point, when I said earlier "nearly as identical" baffle dimensions as possible, that's exactly what I meant - in other words your measures so far, as rigorous as they might be, do not represent identical operating environment for the drivers under test. Data is seldom useless, but not always meaningful for direct comparisons - I think you have at least 3 variables at play here.

- drivers
- baffle dimensions
- enclosure volumes
- venting vs sealed(?)


It could be an entirely separate discussion as to whether / how much the cone treatment might affect the specific measurements shown here.

and yes, I quite like both drivers, but if pressed to make a choice between the two, it'd probably be the Fostex in this case

BTW, the oak enclosures of Dave's design are uFonkenSET - I'm not sure if drawings have been released for public consumption, but I'm sure it's much smaller cubic volume than your quick test boxes for the Alpairs - which I rather suspect would contribute somewhat to perceived and measured differences. The only way to prove that of course would be to cut another baffle for the FF85WKs on your test boxes- 95mm hole saw, IIRC, and which could take less time than the next few posts in this thread .
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Last edited by chrisb; 23rd September 2013 at 06:22 PM.
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Old 23rd September 2013, 06:21 PM   #20
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That is fair. I'd say the enclosure size and type are irrelevant and the dimensions are minor and should be considered when evaluating the results. Otherwise, ya, that's it. When you consider that, I think the comparison is valid.
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