# Is it a good idea to EQ above 250hz ??



## randyc1 (Jul 20, 2011)

Is it a good idea to EQ above 250hz ??

Iv'e read that above 250hz the FR cannot be corrected with EQ

Do any AV recievers do Auto correction just below 250hz ??


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## robbo266317 (Sep 22, 2008)

The room interactions make it unlikely that you can achieve any meaningful result over 250 Hz.
The only situation would be if your speakers had a problem. I would however address the speakers first and not the EQ.


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## randyc1 (Jul 20, 2011)

So what do EQ's like audessey XT32 do above 250hz ??


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## robbo266317 (Sep 22, 2008)

randyc1 said:


> So what do EQ's like audessey XT32 do above 250hz ??


I will have to look into that. I suspect though it may be more broadband to account for slopes in the overall response. 

Quote from http://www.audyssey.com/audio-technology/multeq

MultEQ XT32
Our newest and most accurate room correction solution with more than ten thousand individual control points allowing finer details of the room’s problems to be captured and corrected. The ultra high resolution filters are applied to all channels including the subwoofers, with the most obvious benefit being heard in the low frequency range where correction is needed the most.

Edit:- It seems it looks at all 8 microphone positions and does 100's of points across the range and then tries to get the flattest response for all positions using EQ as well as delays. Quite an interesting article actually.


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## hjones4841 (Jan 21, 2009)

My experience with Audyssey is that it indeed deals with general problems above 250Hz or so. The problem with those frequencies is that the wavelengths are small, meaning that small changes in position will make significant changes in amplitude due to room interactions (modes or resonances.) Regardless and however Audyssey does it, it does make a significant improvement in overall sound.


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## sdurani (Oct 28, 2010)

randyc1 said:


> So what do EQ's like audessey XT32 do above 250hz ??


Closer to tone control than correcting each peak & dip. From the measurements I've seen, in the mid to higher frequencies XT32 seems to smoothen broad humps and adjust the overall tilt of the response, but not address individual peaks & dips (like the lesser versions of MultEQ do). Pointless to pull down a peak at a frequency that has a one inch wavelength.


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## jtalden (Mar 12, 2009)

randyc1,
You may find this interesting:
All this is based on my experience as a hobbyist. 
I did some investigation using measurements of a 5.1 full range EQ setup (DCX2496 used for EQ). 

> Below is a measurement of each of the 5 main speakers (plus 2 SWs) using an RTA average over a 24 x 48 inch vertical window surrounding the LP. These 5 plots closely follow my intended house curve (also shown). The EQ was adjusted in each channel to achieve this result.








> Below is a measurement of the same setup using a single sweep with mic at the LP. 








Observations:
> The results in the SW range are very close and thus it is not necessary to average various mic positions to EQ the SW.
> The response at higher frequencies is much more variable with mic position at LP. The midrange being significantly more variable than the range above 1500 Hz.

It’s reasonable to construe that if EQ was instead adjusted to a target using a single measurement with mic positioned at LP, then there would be greater deviation of the average of the listening window around the LP. If we agree that people detect sound differently than a single small mic capsule and that they also move around a bit then using an average of the listening window to do EQ seems more reasonable. Done this way, the results are also very repeatable at all frequencies. 

I have also compared the averaged RTA measurement to a near field single sweep measurement of a speaker. The near field, in-room measurements are limited to frequencies over about 600 Hz as the room influence imposes itself too much below that. See below one main speaker measured at about 0.4 m distance (RTA averaged over maybe a ±8° window Vs a single sweep on the listening Axis Vs a house curve (one that is not quite corrected properly for the near field situation). It does appear that a near field or free field measurement will agree closely with an average measurement near the LP. There is good agreement between these methods so that does suggest that the higher frequencies can be adjusted to a house curve using a single near field measurement.








I have found that it’s the mid frequencies (maybe 100 - 600 Hz) that can be improved the most by EQ by using an averaged response around the LP to compensate for room effects. I have only indirect evidence of this since I don’t have specific free field measurements of these DIY speakers. I do know it takes significantly different EQ settings for each channel in this range and have found that there is improved sound uniformity between channels when doing so. My space is not symmetric and that probably accounts for most of the EQ differences needed between channels.


My overall experience is:
> Using an averaged response around the LP is the best way for full range EQ, but is more difficult to implement manually.
> EQ of the SW range can also be done very well with a single mic positioned at the LP.
> EQ of the high frequency range can also be done very well with a single sweep near field measurement. To the extent that the as-designed response meets a desired house curve (as adjusted for the near field measurement) there is no need for EQ.
> The mid range frequencies can be significantly improved with EQ, but only by using an averaging measurements in a window around the LP. Using a single mic position is very unlikely to improve the sound uniformity.
> My experiments with the older Audyssey XT showed that it did a very good job of matching each speakers response to the Audyssey target curve based on the average of the measurements taken. There was some concern in the XO and LF area, but that was no doubt improved with XT32. Below is an old measurement after running Audyssey XT. The measurement methodology used was my current averaged RTA method. The shape of the Audyssey default house curve is well defined for frequencies > 200 Hz suggesting that the 8 mic positions used by Audyssey (they were selected to be in the same window around the LP) agree closely with the averaged RTA method that I use manually.









The final thought is that it will be difficult for most novices to improve on the results that Audyssey normally provides assuming a good selection of measurement positions. As with any automated system, I suspect that certain conditions of room positions or speaker types may be more problematic. Also, the Audyssey XT32 house curves may not be ideal for some situations.


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## tonyvdb (Sep 5, 2007)

hjones4841 said:


> My experience with Audyssey is that it indeed deals with general problems above 250Hz or so. The problem with those frequencies is that the wavelengths are small, meaning that small changes in position will make significant changes in amplitude due to room interactions (modes or resonances.) Regardless and however Audyssey does it, it does make a significant improvement in overall sound.


Agreed, EQ above 250Hz is doable and beneficial but you need a 1/3 octave EQ at minimum. Otherwise the filters are to far apart and too wide to achieve any meaningful adjustments.


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## randyc1 (Jul 20, 2011)

hjones4841 said:


> My experience with Audyssey is that it indeed deals with general problems above 250Hz or so. The problem with those frequencies is that the wavelengths are small, meaning that small changes in position will make significant changes in amplitude due to room interactions (modes or resonances.) Regardless and however Audyssey does it, it does make a significant improvement in overall sound.



Where you using XT or XT32 ??


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