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Old 10th June 2012, 04:21 PM   #1
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Default Painful FE207E

I got a pair of FE207E and built the recommended single bass reflex cabinet. While the bass was decent and the efficiency good, they are unacceptable. Between approximately 2 and 5kHz there are one or more resonant peaks in the output. When a note happens to hit one of those peaks, it positively darts out and stabs the eardrum, making listening tiring and painful.

I tried breaking them in for hours and also lining the cabinets, but neither seemed to have any effect whatsoever on this problem.

Any suggestions? Could different cabinets fix this? Maybe I should upgrade to FF225WK?
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Old 10th June 2012, 04:32 PM   #2
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Have you tried some baffle step compensation?
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Old 10th June 2012, 04:49 PM   #3
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have you got some phase plugs in them, or tried that little trick with stuffing behind the whizzer cone?
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Old 10th June 2012, 06:26 PM   #4
Bigun is offline Bigun  Canada
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I can sympathize with your experience. I built 5 speakers using the Fostex FE127E which has problems with uneven freq. response. They have proven to be too fatiguing for music and currently only one of them is in use and it is to be replaced.

I believe the problem is cone-breakup, resonances in the cone. I tried treating the cone with Plante10's tri-foil pattern and whilst it helped a bit, it was far from what I needed. I don't believe it's possible to fix cone break up without unacceptable trade-offs. I also tried a notch-filter and BSC network, but it didn't fix the problem and they actually made the driver sound a little lifeless. I believe these filters simply reduce the level of signal at the offensive frequencies but they can't proven the cone surface resonances.

My ears have proven to be very sensitive to cone break up resonance. I can even hear it in the CSS EL-70 which few if anybody has complained about - but it's there at around 6kHz. Perhaps you are also sensitive to this issue.

It's not easy. Not everyone (probably nobody except Mark Audio) publishes raw data, the plots you see are all smoothed. I've attached the published spec for the FE207. The bump at around 2.7 kHz is the thing that should set off alarm bells. The off-axis response shows again something unfavourable. I suspect that if the raw data had not been so smoothed this bump would actually look worse and there'd be a sharp dip just before the peak - the classic sign of a cone breakup mode. Large cones seem to suffer more from this.

They will probably improve a bit more with time - these drivers seem to take a long time to break-in so you may need to give it more time. Check that there's some absorptive material on the surface directly behind the driver so h.f. isn't reflecting back through the cone - this is important in my experience. Also make sure the screws holding the driver into the box aren't over-tightened and distorting the frame.

Also see here FE207 -- dustcap removal leads to roughness
Attached Images
File Type: jpg FE207.jpg (64.3 KB, 574 views)
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Last edited by Bigun; 10th June 2012 at 06:30 PM.
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Old 10th June 2012, 06:47 PM   #5
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yea, you have to look closely at the freq responses to get even a start on if they will be unacceptable. I even find the peaks in the 4" bamboo drivers hard to listen to after listening to a smoother setup.

Norman
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Old 10th June 2012, 06:53 PM   #6
tubemax is offline tubemax  Netherlands
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Hi Adipocere,

I had same problems with mine FE207E - after about 9 months I finally give-up ( I had to install BSC filter from MJ King ) - there are better enclosures designed to extract more bass, but I was unhappy with the midband, than 3 years later I finally built for friend of mine FE167E in MLTL design > which was miles better than FE207E but still in need for helper tweeter ( for my ears ) so I decided to say good-by to full-range speakers for now ( until I can hear ready-made example to regain my faith in full-range sound - otherwise I'm not interested in investing my money again just to try-out ).

Max
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File Type: jpg Fostex FE207E left copy.jpg (73.6 KB, 565 views)
File Type: jpg FE167E MLTL 5 copy.jpg (71.1 KB, 560 views)
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Old 10th June 2012, 10:29 PM   #7
Bigun is offline Bigun  Canada
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Let's not give up altogether - just need to find the 'right' driver. I believe there is enough knowledge on this forum to help point the way....
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Old 11th June 2012, 12:24 AM   #8
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AS Gareth mentioned, it's the cone resonance that produces the peaks in the response that is so annoying and using the trefoil treatment + paper coating does reduce the magnitude of the peak(s), it also changes the response/sound of the driver quite a bit.

Every cone driver made has cone resonance peaks but the heavier cone,softer material, etc, drivers just dampen the peaks out - and the smaller the diameter means the peaks are at a higher freq, hence the upper limits placed on high efficiency midrange drivers, and so on. (very broad statements here, plenty of exceptions - no flames please!)

One thing that's often ignored is the effect of the amplifier on speaker performance, and that's why many people prefer the combination of valve amps and high efficiency drivers, whether they're multiway or FR.

Over the years, there have been many and varied ways of reducing the effects of cone resonance peaks and the 'enable' method is one that has been extensively investigated and there are many variations of the technique still undergoing development.

I got a fully 'modded' Fe167 from Peter Daniels awhile back and it was a dramatic change to the original and I ended up adding a tweeter to it and it functioned very well indeed - on another Fe167, I tried adding small dots of water soluble 'paint" to the cone in a series of spirals in an attempt to duplicate the smooth response of the Scan 'W' series drivers and it was also quite reasonably successful and sound was again quite different to the original ('better' to me, IMO naturally!) - there are many other ways to do this.

The addition of a thing called a "tapered resistance tube" at the back of the speaker chamber is of great benefit to light cone high efficiency drivers - more info available on the "pro-audio" sites and the reference still seems to be the B&W Nautilus design 'white paper' from their site - you do have to do your homework.

I have found the use of "high impedance, current output" amplifiers suits high efficiency driver very well - again, some homework required.

... my 2 cents
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Old 11th June 2012, 02:06 AM   #9
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Adipocere View Post
Any suggestions? Could different cabinets fix this? Maybe I should upgrade to FF225WK?
I took a peak at the data sheet for the FF225WK (attached); unfortunately it still looks to have the tell-tale cone break up peaks in there.

The FE208EZ is another Fostex 8" but it has a peak around 3kHz that people (e.g. Mr. Brines) says needs to be notched and it has rolled off treble.

Seems the best choice is to try modifying the driver - beyond my experience but you could try contacting Dave at Planet10 - he knows a lot about this, many years of experience with full-range drivers.

http://www.planet10-hifi.com/pp-info.html

Perhaps last ditch option is to turn it into a full-range-assisted-by-a-tweeter kind of speaker. Use a low-pass filter on the FE207 and add a tweeter to handle the treble without the peakiness issues. You can readily add a tweeter to the enclosure you have built already.

Tweeter to suit Fostex FE207
Attached Images
File Type: jpg FF225.jpg (66.0 KB, 492 views)
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 11th June 2012 at 02:15 AM.
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Old 11th June 2012, 01:50 PM   #10
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Quote:
I took a peak at the data sheet for the FF225WK (attached); unfortunately it still looks to have the tell-tale cone break
Actually I was able to listen to the FF225WK twice over the last week. it does not suffer from irritating aspects, in fact it is remarkably smooth and unfatigueing and in short quite a bit better in tonality than its x06E and x07e ancestors.
But, you need a tweeter, the driver has good bass but, as you can guess from the frequency plot, it lacks air in the higher frequencies.
By the way, the metal dustcap of the WK series isnt a sphere but has a ridge. I first thought: wtf? Then i read in the leaflet that came with the FF125wk that I bought that the ridge is there to prevent resonance effects.
In any case this is a good series, they were quite obviously better and more refined than comparable FEx06En in their japanese BK series horn boxes with which I could immediately compare them.
I recommend to check out the driver, and add an affordable ribbon or magnetostat tweeter. Since the 225 is so smooth I would first try to only put a filter on the tweeter.
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