# Please comment on my REW measurements



## inter_voice (Oct 18, 2010)

I have taken my room measurement using REW 5 and generated a number of plots.

With my limited knowledge on REW they look quite allright but I need some expertise views on any areas that I need to be aware of.

Advise and comments are welcomed.

Thanks in advance.


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## SAC (Dec 3, 2009)

_Post the mdat file please!_
This allows us to open and display the data as appropriate.



And then describe in detail HOW you are taking the measurements. 

Are you driving one or more speakers (it looks like you are driving multiple speakers as it appears to be a comb filtering lab in the first FR.). Sub or full range, etc... and information about the environment ( a diagram would be useful).

Drive one speaker for frequency response and ETC measurements.

And for the record, 1/3 octave smoothing and RTxx calculations are of little use.)


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

inter_voice said:


> I have taken my room measurement using REW 5 and generated a number of plots.
> 
> With my limited knowledge on REW they look quite allright but I need some expertise views on any areas that I need to be aware of.
> 
> Advise and comments are welcomed.


If you’re asking if your graphs are okay from a technical standpoint – i.e. if you “have a handle” on REW and are doing the measurements right – the answer is yes. :T

Now that you’re clear on that - for your “serious” measurements, it’s best to take full range measurements one speaker at a time, measured from the primary listening position. Smoothing eliminates the comb filtering caused by all the room reflections and lets you see the overall trend in response. However, for subwoofer-specific measurements we generally recommend that no smoothing be used.

Regards,
Wayne


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## inter_voice (Oct 18, 2010)

SAC said:


> _Post the mdat file please!_
> This allows us to open and display the data as appropriate.
> 
> 
> ...


Thanks SAC for your reply.

I have uploaded my mdat file as suggested.

I took the measurement using the left speaker (I believe it was the case as I only choose one channel in REW for measurement) and the omi mic was at my listening position at about 7 ft from the speaker.

Yes I took the measurement of both the book shelf speaker and the subwoofer at the same time. The speaker is at about one foot from the wall and my listening position (my sofa) is 2 ft from the back wall. The room is about 6m X 4m X 2.5m high. The speaker is about 6 ft apart. The sofa is on the longer side of the room.

Your expertise view are most welcomed :wave:


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## inter_voice (Oct 18, 2010)

Wayne A. Pflughaupt said:


> If you’re asking if your graphs are okay from a technical standpoint – i.e. if you “have a handle” on REW and are doing the measurements right – the answer is yes. :T
> 
> Now that you’re clear on that - for your “serious” measurements, it’s best to take full range measurements one speaker at a time, measured from the primary listening position. Smoothing eliminates the comb filtering caused by all the room reflections and lets you see the overall trend in response. However, for subwoofer-specific measurements we generally recommend that no smoothing be used.
> 
> ...


Thank you Wayne. I have made my reply to SAC and uploaded my mdat file.

It is nice to know that my initial measurement seems to be "okay". What I need to know is how should I make my listening environment better


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## SAC (Dec 3, 2009)

Attached are 2 convolved plots for modal issues at the listening/measurement position as well as an ETC regarding specular reflections. 

Ignoring for a moment possible effects of SBIR,(reflections off the walls perpendicular to the speakers), the water fall and spectrogram show 2 differing views of the same data. You will note to rather prominent modal peaks/resonances at ~29 and ~58 Hz. 

This can be variously explored by mapping the modal distribution in the listening area and perhaps moving the seating forward or back to avoid the peak and null regional distribution. Also, you might consider installing large porous corner bass traps with _a minimum_ 6 mil plastic covering in order to absorb the low frequency energy and to retain the mid freq and up energy. 6mill will reflect above ~600 Hz. Thicker is better...)

(For possible SBIR issues, you can move each speaker out or closer to the front wall (not changing the distance from the side) and see how any comb filtering notches change. Likewise, you can repeat this by moving the speaker closer and further from the side wall - keeping the other distance to the front wall constant- and determining any differences. Then you can adjust them appropriately to minimize such effects. But do each adjustment with respect to one separation distance at a time to minimize the variables and make it easier to determine exactly what is responsible for what...)

I am guessing that both the sub and full range speaker is being driven, which can very easily account for the irregularities in the estimated crossover region. Addressing the synchronization of the time arrival of each source will help minimize problems caused by the superposition of two out of sync signals. The impulse or ETC response can be generated for each source and they can be adjusted for coincidence either physically or by precision electronic delay.

Note, any modifications you make to the speaker positioning and/or the seating positions will also necessitate the re-measuring of the ETC with regard to reflections, so all comments are based upon the current scenario.

...Hope that gives you a hint at the process and helps get you started...


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## inter_voice (Oct 18, 2010)

SAC, you are GREAT.

I will spend some time to digest your comments and see what I can do.

Thank you very much :T


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## inter_voice (Oct 18, 2010)

Hi SAC,

I have moved the 2 speakers and the sub away from the wall and moved my listening position further away from the back wall as well.
I took a set of new readings again and made some plots with parameters similar to yours. Do you think the situation is now a bit better than before ? My limited knowledge on REW's plots could not give me a clue :sad:

I observe that you mainly focus on improving the LF region, does it mean the mid to HF range is okay and requires no treatment ?

Pete


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## inter_voice (Oct 18, 2010)

Hi SAC,
Hope you have seen my plots and can offer some comments.
Thanks
Pete


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## SAC (Dec 3, 2009)

You have reduced the degree of the modal peaks - somewhat.

The difficulty I have is in determining exactly what effects specific changes have had.
The process I alluded to is iterative - meaning that you make one specific change at a time and measure and determine precisely what (if any) effect it has on the response.

Thus, for instance, in order to explore SBIR (and also to observe the effect on modal distribution) you move one speaker forward from the wall (maintaining its spacing with respect to the side wall) and see what effect it might have on a notch frequency - if it is related, then the frequency will move based upon the spacing. Similarly, you would explore the effect of moving it farther from the side wall, maintaining its spacing with respect to the front wall and again observing the change on notch frequency.

Each of the said variations will also provide the opportunity to also determine the overall modal response at the listening position.

Additionally you might also explore the effect of subwoofer position on the modal response. This can be done is in several complimentary ways...by leaving the sub in the same position and mapping the areas forward and behind the listening position to see if you can locate a region 'between the identified peaks and nulls such that by location you can minimize the effect, or by doing the infamous 'sub crawl' by literally positioning the sub at the listening position (securely!!!! - on a stool, or other secure support) and then crawling around to listen for and locate a floor position where the response is most even - and placing the sub there.

Once you find the best locations such that the modal response is stimulated the least at the listening position, you may want to employ frequency specific LF bass trapping (using a minimum of a 6mil plastic front facing affixed to an asymmetrical 'Superchucnk' style corner trap filled with the 'cheap(er) pink fluffy stuff' to reflect the mid -high energy back into the room.

Once the modal issues are minimized, you can then move to address the effects of the high gain specular reflections that adversely effect the imaging, localization and intelligibility of the signal above the modal regions from ~250-300 Hz and up.

This is done via an ETC response made for each individual full range speaker. From this each high gain early reflection can be identified and its specific path and point of boundary incidence determined - and appropriate treatment material (absorption, reflection-redirection, or diffusion) surgically applied and its effects with regard to the total room response model verified.

Again, this is a 30,000ft view of the iterative process. And I realize that reading this as opposed to my telling you to specifically 'do this or that' is a bit frustrating - just as it is for me without having more detailed information provided by a more iterative process...
Its not difficult, but it is not a simple 'move everything around and expect every issue to magically resolve itself' process.:bigsmile:
But done properly, I can assure you that it will take less time, effort and money to do right, what the usual serendipitous path requires - and with much better confirmed results!

I think you are well on your way to optimizing the space. You just need to break things down a bit more systematically and to make changes one step at a time designed to isolate individual variables. The problem with changing 'many things' is that you may very welt observe a change, positive or n4egative, but you have too many variables at play in order to determine which factor is primarily responsible for the noted change. Thus a more systematic iterative approach will actually save you some time and effort by allowing you to 'zoom in' and identify the particular relationship that has a direct effect on the response aspect you are trying to optimize.

If you like, you can PM me and I can, as time permits, using IM (Skype or Yahoo Messenger) _and voice _provide a bit more detail as you progress through the process with the benefit of more detailed information.


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## inter_voice (Oct 18, 2010)

Thanks SAC for your very comprenhensive comments and "how to do it". 
Now I have some idea as to how I should move my speakers, sub and my listening position and take the mesaurements.

Thanks again SAC :T


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