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Old 28th June 2004, 06:02 PM   #1
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Default Notch filter for full range driver.

This is my first adventure into speaker building.

I have been playing around with the Fostex FE127E drivers. I built the simple BR box recommended for them on the Fostex web site. When I plopped the drivers in, they sounded pretty good, but with what I would characterize as a bit of "edge" to them. Some of the middle high range sounds a bit agressive to me. Other than that I really like them.

There is a subwoofer in the system, so I do not really need a lot of bass extension, but I was wondering what to do about this little bump they seem to have. If you look at the Fostex advertised response for these, there is indeed a bump at about 6kHz.

I was thinking about letting these speakers run in for another week or two, and then trying some sort of notch filter tuned to 6kHZ. It may also be that after the run-in time, some of this harshness will mitigate.

Thoughts or suggestions appreciated.

Overall I am pleasantly surprised at how well these inexpensive units perform for me in a simple vented enclosure.

I do not consider myself an audiophile, or member of the "Golden Ear" crowd, but I am definitely having fun with this little experiment.

Thanks in advance.
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Old 28th June 2004, 10:36 PM   #2
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Try here:http://www.lalena.com/audio/calculator/seriesNotch/
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Old 29th June 2004, 12:41 AM   #3
MarkMcK is offline MarkMcK  United States
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Hi Steve,

I am glad to hear you are having fun. Fun is a very good thing (I am absolutely serious about this).

Just a couple of things about notch filters. The "Q" of a notch filter will not always match up with the "spike" in driver output. If is does not match, you can introduce other errors into the response. Always best to measure what you use.

Bill's link to the resonant filter calculator is a good link (Thanks Bill). I will have to bookmark this myself. Just substitute the frequency you want to notch for the "resonant frequency" variable.

Also, as a rule of thumb, if you want a high "Q" filter, use larger inductors and smaller capacitors. Get too far apart, however, and the circuit will no longer resonate.

Standard values will not produce an exactly 6 KHz resonance, but .25 mH with either a 2.7 microfarad cap or a 3.0 microfarad cap will res at 6125 and 5811. Either is pretty close. Using a .25 mH inductor should provide a fairly deep notch in case you need it. If you need less, just degrade with a resistor.

Best wishes, and measure if you can,

Mark
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Old 29th June 2004, 02:49 AM   #4
sreten is offline sreten  United Kingdom
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Also consider some form of Baffle step Compensation.

sreten.
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Old 30th June 2004, 03:03 PM   #5
MarkMcK is offline MarkMcK  United States
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Just one little (but important) point about the link to the series res filter calculator. This shows a series res filter wired in parallel to the driver. This is fine for smoothing impedance, but will not impact driver output when driven by a constant voltage amplifier (99 percent of all amps are constant voltage).

What you want is a parallel res filter wired in series with the driver. Reactive component values will not change, but the resistor values will invert.

Best wishes on your project,

Mark
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Old 30th June 2004, 03:56 PM   #6
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Default Thanks for the advice.

I appreciate the info. I am going to do a couple of things on this.

First, I am going to give the drivers a little more time to break in.

Second I am going to try some rough and ready measurements, to see if there is indeed a correlation between what I think I hear, and what is really happening. (At my age, I have some doubts!)

I honestly think that my old speakers were so bad, that I am just not used to the sound of something better.

I ordered one of those Stereophile Test CDs from Parts Express today, and found the correction values for my old Radio Shack SPL meter.

Hopefully room effects won't me much of a factor in measuring the high middle range of frequency response on these units.

Thanks again for the help.
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Old 30th June 2004, 04:21 PM   #7
Lusso5 is offline Lusso5  United States
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Default Re: Thanks for the advice.

Quote:
Originally posted by SteveGoTex

I ordered one of those Stereophile Test CDs from Parts Express today, and found the correction values for my old Radio Shack SPL meter.
FYI -
RS SPL Meter Mods to increase the frequency response.
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Old 11th July 2004, 08:57 PM   #8
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Default Well, The Fostex's Smoothed Out

Either these little guys have smoothed out, or I have adapted to their sounds. I decdied against the notch filter. But thanks for the help.

I got the Stereophile CD. Good News and Bad News came from that. I also got my little RS SPL meter out and measured things.

The Good News is that these little drivers are really full range. The Bad News is that I cannot even hear half of it

The SPL meter showed lovely even levels from the drivers from 12.5 Khz to 20Khz. My ear canals however, were not in the game at that range. I heard nothing...

The bump at 4 or 5 khz seems to have smoothed out. I also put the units on some small stands and off the shelf, which help much more than I expected.

My hearing seems to cut out at about 12.5 KHz. This can probably be completely attributed to the '70's, the Rolling Stones, Steve Miller, and milddle age, not to mention the various experimental self medications and related activities tried by Yours Truly in those Wonder Years. (In retrospect, I would do them again.)

The other down side is that the test CD had some really neat music tracks on it. I just spent another $100 on CD's that were represented on the test CD, because the tracks sounded so good to me.

Oh well, still havin fun. If you have a modest size room, and want a simple full range project, I can recommend these drivers. Not bad at all.
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Old 12th July 2004, 02:29 PM   #9
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I have a similar high frequency roll-off, probably caused by the same things, and helped along by cronic ear/nose infection. The good news for both of us is that there is as much noise as music up there on most recordings, so we're not missing much.

Dave
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Old 13th July 2011, 05:57 AM   #10
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Is there any reason why I would want to play around with a notch filter in my mMar-Kel70 millis with EL70 drivers? The frequency response is actually fairly smooth except about a 5db peak around 430hz.
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