# Room Response - comments, please!



## jaypeecee (Mar 31, 2008)

Hi Folks,

I am re-visiting some REW room response plots I did a while ago and would appreciate any comments.

Please take a look at the attached plot. This is a stereo pair of Fostex FE167E full-range drivers each supplemented with an HiVi TN28 supertweeter. The response was measured using the Behringer ECM8000 microphone, which was located in the listener position. The room is 5.5m (L) x 3.5m (W) x 2.5m (H). The plot shows the LH channel (purple), RH channel (blue) and the averaged response (green). One-third octave smoothing has been used.

Despite the use of the TN28 supertweeters, HF roll-off is apparent beyond 3.5kHz. It is 3dB down at 6kHz and almost 8dB at 10kHz. I am also curious about the dip between 100Hz and 700Hz reaching a trough at 200Hz.

Would anyone care to shed light on these observations?

Thanks in advance.

JPC


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## AudiocRaver (Jun 6, 2012)

Is there a calibration curve in use for the mic? The HF rolloff looks like what one might find from the mic's natural response.


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## tonyvdb (Sep 5, 2007)

My understanding is that gentle falloff is natural. If you were to have a flat even line that stays even with the rest in those frequencies your ears would hurt particularly at higher volumes.


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## jaypeecee (Mar 31, 2008)

AudiocRaver said:


> Is there a calibration curve in use for the mic? The HF rolloff looks like what one might find from the mic's natural response.


Hi AudiocRaver,

Thanks for your reply.

Yes, I used the calibration file that is available on this site.

Perhaps tonyvdb is correct? It just seems like a significant loss in HF but I'm really not sure. What kind of response is to be expected in the listening position? And what about that 200Hz trough?

JPC


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## jaypeecee (Mar 31, 2008)

tonyvdb said:


> My understanding is that gentle falloff is natural. If you were to have a flat even line that stays even with the rest in those frequencies your ears would hurt particularly at higher volumes.


Hi tonyvdb,

Thanks for the reply.

Your point that "gentle falloff is natural" makes sense but is this a case of _gentle_ falloff? As I said above, the response is 3dB down at 6kHz and almost 8dB at 10kHz. That seems a lot. Presumably, it would be different with headphones in that the HF would be at much the same level as the rest of the response?

JPC


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## tonyvdb (Sep 5, 2007)

It seems a little bit much however even my EV 500 studio monitors exhibit the same roll off above 10k using the same mic your using. They are flat 35-18,000Hz


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## jaypeecee (Mar 31, 2008)

tonyvdb said:


> It seems a little bit much however even my EV 500 studio monitors exhibit the same roll off above 10k using the same mic your using. They are flat 35-18,000Hz


Hi tonyvdb,

Thanks again.

When you say "They are flat 35-18,000Hz", is that in the listening position? If so, then what I'm seeing with my setup is very different. At 18kHz, the response is 16dB down at the listening position with my setup.

JPC


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## tonyvdb (Sep 5, 2007)

Sorry, I meant to say the Specifications on the speakers are flat. My measured response with the sub is below.


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## Wayne A. Pflughaupt (Apr 13, 2006)

jaypeecee said:


> Yes, I used the calibration file that is available on this site.


Our calibration file is generic; you can’t be absolutely certain that your measured response is accurate without a custom calibration file. Mic orientation can make a difference too, whether or not you measured with it pointing at the speaker.

Regards, 
Wayne


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## AudiocRaver (Jun 6, 2012)

As Wayne P. says, using the generic cal file could easily leave you with that amount of error.

As far as how flat you want it to be, it depends on your room. In a fairly live typical home theater or music listening room, the high-frequency buildup due to reflections will indeed seem harsh with a flat response. The rolloff you see is not too far from some suggested "target curves" for rooms like that, the intent being to help tame that harshness. A studio control room or mixing room, with well-damped acoustics, is generally tuned for flat response and it seems "just right" because of those acoustics.


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## jaypeecee (Mar 31, 2008)

Wayne A. Pflughaupt said:


> Our calibration file is generic; you can’t be absolutely certain that your measured response is accurate without a custom calibration file. Mic orientation can make a difference too, whether or not you measured with it pointing at the speaker.
> 
> Regards,
> Wayne


Hello Wayne,

Thanks for your reply.

I'm unclear about the custom calibration file - where would I get that? When you say that your cal file is generic, perhaps you could elaborate? How accurate can I expect my ECM8000 to be using the HTS cal file?

Mic orientation was in the listener position, pointing upwards and angled forward approx. 20 degrees.

JPC


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## jaypeecee (Mar 31, 2008)

AudiocRaver said:


> In a fairly live typical home theater or music listening room, the high-frequency buildup due to reflections will indeed seem harsh with a flat response. The rolloff you see is not too far from some suggested "target curves" for rooms like that, the intent being to help tame that harshness. A studio control room or mixing room, with well-damped acoustics, is generally tuned for flat response and it seems "just right" because of those acoustics.


Hi AudiocRaver,

OK, thanks again.

You've made some very interesting points that I would like to fully understand.

You point out that the HF buildup in a typical listening room will seem harsh with a flat response. So, if a studio control room is tuned for a flat response, why does it sound "just right"? I guess what you are saying is that the flat response in itself does not prevent the HF buildup due to reflections - is that correct? When you referred to "target curves" for listening rooms, where could I get hold of these?

JPC


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hey John,



jaypeecee said:


> I'm unclear about the custom calibration file - where would I get that?
> 
> Read more: http://www.hometheatershack.com/for...response-comments-please-2.html#ixzz2PiFqul6N


The mic has to be calibrated by a lab, which compares its response against a reference mic and creates a calibration file to compensate for the former’s deviations from flat response. Sounds expensive, but you can buy calibrated mics from Cross Spectrum for less than $100.



> How accurate can I expect my ECM8000 to be using the HTS cal file?
> 
> Read more: http://www.hometheatershack.com/for...response-comments-please-2.html#ixzz2PiEisd00


 Here’s a graph from Cross Spectrum showing response deviations among a number of samples: 












> Mic orientation was in the listener position, pointing upwards and angled forward approx. 20 degrees.


That alone would account for the high-end droop you’re seeing. Our generic calibration file is 0-degree, meaning it was generated with the mic in a horizontal position. With such a file, the mic should be pointed at the speaker and tilted up 20-degrees or so. The orientation you used, straight up and angled forward 20-degrees, requires a 90-degree calibration file.

Regards, 
Wayne


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## tonyvdb (Sep 5, 2007)

jaypeecee said:


> Hi AudiocRaver,
> 
> OK, thanks again.
> 
> ...


Nearfield listening in the studio VS normal listening positions in a home environment are very different.


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## jaypeecee (Mar 31, 2008)

Wayne A. Pflughaupt said:


> Hey John,
> 
> The mic has to be calibrated by a lab, which compares its response against a reference mic and creates a calibration file to compensate for the former’s deviations from flat response. Sounds expensive, but you can buy calibrated mics from Cross Spectrum for less than $100.
> 
> ...


Hi Wayne,

Many thanks.

For some reason, the links you have provided above take me back to this post.

With reference to the Cross-Spectrum graph showing response deviations for the Behringer ECM8000, it is apparent that this microphone has a rising response at the HF end of the audio range. That being the case, my room response at the listener position will be even further down at the top end than I had originally thought - to the tune (!) of a further 4dB or thereabouts. Your last comment above is therefore of particular relevance. The orientation for my test microphone was based on something I had read on the HTS forums but perhaps I got it wrong. It did seem odd pointing the microphone upwards. Looks like I need to repeat all my measurements with the ECM8000 tilted upwards 20 degrees from horizontal and pointing towards the loudspeakers.

Now, what about the 100Hz to 700Hz dip on my room response? Any thoughts?

Thanks again.

John


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## jaypeecee (Mar 31, 2008)

tonyvdb said:


> Nearfield listening in the studio VS normal listening positions in a home environment are very different.


Hi Tony,

OK, many thanks.

John


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## AudiocRaver (Jun 6, 2012)

jaypeecee said:


> ...the HF buildup in a typical listening room will seem harsh with a flat response. So, if a studio control room is tuned for a flat response, why does it sound "just right"?


Here is how I understand it: In your home environment there is a lot more LF energy than HF energy, relative to them being pretty equal in a "dead" studio control room, for 2 reasons - 1) speaker directivity being broader at LF, more total energy being dispersed into the room, not being soaked up by room treatment, and 2) almost all untreated rooms have longer reverb times at LF, getting shorter and shorter as frequency increases. So when you equalize for flat response in your home environment, the sound is more & more direct as frequency increases, and seems more and more "beamed at you." It is a relative perception issue, the more direct at HF vs. the more diffused at LF, that makes the HF seem harsh in contrast, needing to be ramped down to compensate. In the studio control room, all the sound is "beamed at you" and does not seem harsh with a flat response setting.

How much HF attenuation is called for to compensate? The effect in your lively home environment depends on many factors, the speakers, placement, the room, personal taste, & humidity are all significant, so no 1 target curve fits all. Some of the target curves out there compensate with 10 db attenuation at 10 KHz. I think that is way too much. I run my own speakers down only 2 db at 10 KHz, and that works great for me. It is known that we tolerate (do not notice) dips or attenuations in frequency response much more easily than peaks or increases, so maybe it is partly untrained listeners quickly selecting target curves that are super-easy on the ears and not noticing all the detail they are missing out on. No insult intended to those who have tried target curves and like them. It seems like a lot of listeners grab target curves out of convenience rather than letting their ears guide them.

I think target curves are overrated, do not see any 1 generic curve fitting all speakers in all rooms. Start out flat, listen a bunch, if it is too harsh, hinge it at 1 KHz and drop the top end 2 db and see how that works for awhile, go 2 db at a time and stop when you like it. Probably no one on the planet will agree with me, so if another explanation makes more sense to you, go with it.

Harmon, B&K, JBL all have published target curves. I don't have any bookmarked, but they shouldn't be hard to find with a web search. There was some lively discussion at this thread awhile back, you might find some of it interesting.


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## jaypeecee (Mar 31, 2008)

Hi AudiocRaver,

Many thanks for your comprehensive reply - it is greatly appreciated.

You have provided much food for thought. I must check out the effect of humidity on sound reproduction. It also occurs to me that, if humidity plays a part, then what about temperature and barometric pressure?

Once again, thanks.

John


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## jaypeecee (Mar 31, 2008)

Hi Folks,

In view of Wayne's comment "That alone would account for the high-end droop you’re seeing" in response to the ECM8000 orientation that I had used for all my REW measurements to date (red plot), I repeated my measurements with the ECM8000 pointing to the mid point between the speakers and tilted upwards 18 degrees (black plot). See below. It is clear that there is virtually no difference in HF response as a result of changing the mic orientation _in the listener position_.

As a result of the above comparison, I once again repeated the measurements for each individual speaker at a distance of 0.5 metres with the ECM 8000 horizontal, on axis and pointing half way between the two drivers. This is shown in the green plot. At 10kHz, the SPL is 9dB higher than at the listener position.

For simplicity, all plots are for the RH channel only.

JPC


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## AudiocRaver (Jun 6, 2012)

jaypeecee said:


> It is clear that there is virtually no difference in HF response as a result of changing the mic orientation _in the listener position_.


I have performed similar tests in the past and come to the same conclusion. Pointing the mic 180 degrees away from the speaker causes HF droop of several db. Anything less than 90 degrees off axis, the measurement difference was less than 1 db and that was all above 10 KHz where no EQing is done anyway. There is a lot said about mic orientation and it does no harm to follow the common guidelines so I don't argue about it, but if someone asks how much difference it really makes, this is my answer: At 90 deg or less off axis - for all practical purposes - none.


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## Wayne A. Pflughaupt (Apr 13, 2006)

We’ve certainly seen cases here in the past where an upright vs. horizontal orientation using the 0-degree calibration file showed drooping high-end response with the former – really distressed the fellow when his response looked worse than he felt it sounded. My AudioControl RTA shows a sag in high-end response above 2 kHz when I point the mic off-axis. 

I suspect a room’s acoustics can make a difference in these situations, but that’s a hard thing to quantify from one case to the next on a Forum like this. It never hurts to try legitimate measurements with both mic orientations (“legitimate” meaning that the proper calibration for the orientation is in place). However, if the two measurements come out different, I have more confidence in the accuracy of the horizontal orientation w/ a 0-degree calibration file measurement. :T

Regards, 
Wayne


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## jaypeecee (Mar 31, 2008)

AudiocRaver said:


> I have performed similar tests in the past and come to the same conclusion. Pointing the mic 180 degrees away from the speaker causes HF droop of several db. Anything less than 90 degrees off axis, the measurement difference was less than 1 db and that was all above 10 KHz where no EQing is done anyway. There is a lot said about mic orientation and it does no harm to follow the common guidelines so I don't argue about it, but if someone asks how much difference it really makes, this is my answer: At 90 deg or less off axis - for all practical purposes - none.


Hi AudiocRaver,

Many thanks for your reply.

It is good to know that you had come to the same conclusion based on your experiments.

JPC


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## jaypeecee (Mar 31, 2008)

Wayne A. Pflughaupt said:


> We’ve certainly seen cases here in the past where an upright vs. horizontal orientation using the 0-degree calibration file showed drooping high-end response with the former – really distressed the fellow when his response looked worse than he felt it sounded. My AudioControl RTA shows a sag in high-end response above 2 kHz when I point the mic off-axis.
> 
> I suspect a room’s acoustics can make a difference in these situations, but that’s a hard thing to quantify from one case to the next on a Forum like this. It never hurts to try legitimate measurements with both mic orientations (“legitimate” meaning that the proper calibration for the orientation is in place). However, if the two measurements come out different, I have more confidence in the accuracy of the horizontal orientation w/ a 0-degree calibration file measurement. :T
> 
> ...


Hi Wayne,

Thanks for your reply.

I think you've hit the nail on the head when you say "I suspect a room’s acoustics can make a difference in these situations". Clearly, the room's acoustics _will_ make a difference. I can well appreciate that HF signals will be attenuated/absorbed along the length of the room. My room is carpeted and has a thick rug placed on top of it. One of the walls along the length of the room has cabinets and cupboards on it thus reducing reflections.

For me, this is a very useful observation. On the face of it, I may need to increase the upper end output from my speakers to compensate for the room's acoustics. I was already planning to replace the TN28 tweeters anyway!

John


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## JohnM (Apr 11, 2006)

jaypeecee said:


> On the face of it, I may need to increase the upper end output from my speakers to compensate for the room's acoustics.


There's a good chance they will sound worse if you do that. Our ears/brain are very good at distinguishing the direct signal from the speakers from the sound that is reflected from the surfaces of the room (much better than our measurement equipment).


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## AudiocRaver (Jun 6, 2012)

I don't think we have seen any RT60 numbers for your room yet. If it is truly pretty dead, RT60 below .3 sec or so and minimal early reflections, then a slight HF boost might sound OK. But as John says, it can easily do more harm than good. Can you show us an RT60 plot or post your measurement file?

Reiterating, I am not suggesting you ignore accepted mic orientation guidelines, only sharing my observations since you asked about it specifically.


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