FR88Ex based micro-Onken ? - diyAudio
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Old 14th September 2010, 03:56 AM   #1
Bigun is offline Bigun  Canada
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Default FR88Ex based micro-Onken ?

Until the Alpair6 (paper cone) shows up I'm thinking of using the Fountek FR88Ex. Compared to the now obsolete FF85k the Fountek has the same Qts (although half the Qms), similar Vas and a lower Fs. It may not be of the same ilk but perhaps the Fountek could be used to make some kind of micro-Onken (aka planet10 uFonken) ?

Going on the premise that the Onken is an EBS alignment (enhanced bass shelf) the best information I could find was here [Calculating an EBS alignment where GM gives some guidelines that I've followed using the Fountek FR88Ex data:

Where Qt is the total Q of the system = roughly 0.6

Vb = 7.95*Vas*Qt^2.21 = 3.3L

Fb = 0.471*Vas*Qt^-0.677 [Fs instead of Vas?] = 63Hz

F3 = 0.33*Fs*Qt^-1.01 = 52.5Hz

Using the box simulation here []Loudspeaker enclosure calculating with Thiele Small parameter] I explored this alignment, at least very simplified. Using Vb 3.3L, port diameter of 3.5cm and port length of 20cm gives me something that looks like an EBS. It seems to indicate a lower group delay around Fs at the expense of worse delay below Fs. I Used a low QL in this simulation (if I understand properly what this means) to represent the lossy nature of the resistive ports.

Feels like I'm just scratching the surface here, the simulation doesn't know it's an Onken, so what else do I need to know ?
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Old 14th September 2010, 04:30 AM   #2
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That driver models really nice for a uFonken. And since Fountek starts with an F we can call it a uFonken... to avoid confusion i dub it uFonkenEX. More bass extension (at the expense of efficiency).

Take one uFonken and adjust the slot height & width to meet the specs in the attachment. Adjust cutout & holey brace.

Damn... just had a shipment leave from Madisound today. A pair of those will need to wait till next time, but well worth a try i'd say.

dave
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Old 14th September 2010, 04:38 AM   #3
GM is offline GM  United States
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Qa = box losses due to absorption (stuffing, etc.)
Ql = box losses dues to leakage (poor construction, etc.)
Qp = port losses due to friction (too small, too high aspect ratio, damping in the port, etc.)

So a combination of Qa, Qp will show the response change trend, though no easy way to tell how much of what matches the sim without measurements, so usually whatever amounts sounds OK as a balance between driver protection and sounding over-damped.

GM
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Old 14th September 2010, 08:22 PM   #4
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by planet10 View Post
That driver models really nice for a uFonken. And since Fountek starts with an F we can call it a uFonken... to avoid confusion i dub it uFonkenEX. More bass extension (at the expense of efficiency).

Take one uFonken and adjust the slot height & width to meet the specs in the attachment. Adjust cutout & holey brace.

Damn... just had a shipment leave from Madisound today. A pair of those will need to wait till next time, but well worth a try i'd say.

dave
I ended up getting my drivers from Solen, by the time I cover shipping from the US the price difference was negligible but I guess the volume of stuff you normally buy makes it worthwhile to get the better US prices.

Your suggested port dimensions are not what I understood to be an Onken alignment, it has no extended bass, if anything the extension is reduced, falling somewhere between a sealed box and optimally flat vented enclosure.

Why do you choose this approach instead of the EBS approach ?
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Old 14th September 2010, 08:31 PM   #5
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My miniOnkens only share the high aspect ratio ports with an "official' Onken.

I'm not a big fan of EBS alignments. I use my approach because it has proven in practise to work REALLY well. At least 10 successful basic designs (+ lots of variants)

dave
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Old 14th September 2010, 09:00 PM   #6
Bigun is offline Bigun  Canada
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Thanks Dave. I'll go with your wisdom on this.

I may already have some wood for the uFonkenEX, just need to watch Postie for the drivers.

If we did not already have a 2L box design, would there be any advantage in a bigger box for the Fountek driver - perhaps bringing the driver closer to ear height ?
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Old 14th September 2010, 09:37 PM   #7
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Quote:
Originally Posted by Bigun View Post
If we did not already have a 2L box design, would there be any advantage in a bigger box for the Fountek driver - perhaps bringing the driver closer to ear height ?
It worked so well in 2 litres i didn't bother playing with anything else. Put a tilt on the baffle (or prop up the front) if you need to fire it at your head -- or as i will eventually try, i'm going to hang a set of milli or micro size off of some surplus legs off flat screen iMacs.

dave
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Old 14th September 2010, 09:55 PM   #8
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I just got in those big buck ScanSpeak 3" (nicely made but nothing in the build that justifies them costing as much as FE126En). I'll be angling towards some sort of miniOnken for these too.

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Old 15th September 2010, 12:27 AM   #9
Bigun is offline Bigun  Canada
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Glad to hear that the (F)Onken series will have a life beyond Fostex and you will widen the net to consider some other drivers. I think a lot of newbies like me look to you and Chris and Scott for advice and we tend to follow your lead towards the kinds of drivers we consider. For awhile it seems that Fostex was king and now it's Mark Audio. But a bit more variety would be welcome - although I recognize that it's a bit more work for you guys.
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Old 22nd September 2010, 12:55 AM   #10
Bigun is offline Bigun  Canada
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The Fountek drivers turned up from Solen. They were well packed. And the drivers look very nice indeed
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