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2K views 7 replies 4 participants last post by  Wayne A. Pflughaupt 
#1 · (Edited)
Hello Everyone.
I have been searching and using this forum for a few weeks now, and I'm a new user of REW with a ECM 8000 (your calibration file) mic. I am a musician and producer, and I am using this to analyze my home studio. I am quite thankful for this site and the REW software and the knowledge I have found in these forum Q&A's. I have thoroughly read the REW manual, but I have a few questions.. The most basic, and forgive me if this sounds stupid, but when I measure at, say 80 or 75 db, after calibrating and using the SPL, how do I interpret the frequency response graph? I see the response, measured with different smoothing applied, but does it reflect the source level of 80 or 75db? (like an imaginary line at that level in the graph)?
I have measured my speakers 3.75" from the cones and the room with each speaker an added speakers to get the "master measurement" to see how things are affecting each other. I see a good mountain at 70 hz, for instance, but I am trying to accurately read the graph.
I am also ingnorant about the phase graph. Are there more threads that can tell me how to better interpret these graphs? The waterfall and decay time graphs are easier to understand.
Thanks
 
#3 ·
Here is one of the measurements. Before I can get into what to do for corrections, I need to fully understand this graph, which I smoothed at 1/3 to simplify. Taking one item: I read a peak around 70hz. My SPL db was about 80 or 81, so am I correct that I have a +9 db or so peak at 70hz? Then there is the matter of the phase graph. Does it look right? I have other smoothing settings to show more detail, but I wanted to make sure I can read this graph correctly, and I'd like to know what I'm trying to make this graph look like (which I assume is rather flat response thru the frequency bands).
Also, you can see the mic calibration file (which I downloaded from this site) is this correct? I've measured this with both Rad Shack Old style SPL meter and the ECM 8000 mike and I get that same 70hz bump (of course I also calculated the room dimensions to have an axial mode at 70.8 and a tangential mode at 67.8hz) Room dims are 11.67f x 11.92f x ceiling 7.98f
Thanks
 

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#4 ·

The most basic, and forgive me if this sounds stupid, but when I measure at, say 80 or 75 db, after calibrating and using the SPL, how do I interpret the frequency response graph? I see the response, measured with different smoothing applied, but does it reflect the source level of 80 or 75db? (like an imaginary line at that level in the graph)?
You don’t have to be concerned about the “source level of 75 or 80 dB.” It has no affect on the response reading or what it tells you. If you measured with the mic at the listening position, and pointed at the speaker, the response graph basically shows what you’re hearing (assuming an accurate mic calibration, which in this case you don’t quite have since you’e using a generic calibration). For instance, your graph in Post #3 shows a big peak at 70 Hz and a trough at 150 Hz. They are severe enough that they should be audible, and you would certainly notice a difference if they were eliminated.


I have measured my speakers 3.75" from the cones and the room with each speaker an added speakers to get the "master measurement" to see how things are affecting each other. I see a good mountain at 70 hz, for instance, but I am trying to accurately read the graph.
You basically have the right idea: Measure each speaker independently and then both together. The only other thing I’d recommend is to measure and the listening position, with the mic located where your head would be, with the mic pointed at the speaker and oriented slightly upward, perhaps 20°.


I am also ingnorant about the phase graph. Are there more threads that can tell me how to better interpret these graphs?
I can’t think of anything useful for the phase graphs. Perhaps John can comment. :)


Here is one of the measurements. Before I can get into what to do for corrections, I need to fully understand this graph, which I smoothed at 1/3 to simplify. Taking one item: I read a peak around 70hz. My SPL db was about 80 or 81, so am I correct that I have a +9 db or so peak at 70hz?
Yes, and a 9 dB trough at 150 Hz. Your graph scaling actually makes response look better than it really is – see here: Getting Graphs Ready to Post

Good call on the 1/3-octave smoothing – it’s a good representation of what you’re hearing. Lesser smoothing shows all the scary comb filtering, which gives an indication of how “live” your room is but isn’t necessarily audible.


... I'd like to know what I'm trying to make this graph look like (which I assume is rather flat response thru the frequency bands).
Yes, reasonably flat response, perhaps with an upward house curve tilt towards the lower end. Assuming you’re using near-field monitors, you’d probably want something of a downward tilt for the upper frequencies. Flat response when you’re up close to the speakers often sounds unnaturally harsh.

Regards,
Wayne
 
#5 ·
Thanks Wayne!
I did read your articles on "Room Curve" and also the "Waterfall" threads and I will start with acoustic treatment to try to tame the modes, before touching eq.
I am pleased that different measurements, different speaker settings and even open/closed door measurements all yield pretty much the same peaks and valleys.
Do you have any particular bass trap products (either D.I.Y or off the shelf) that you like?
The room is both small and filled with stuff and there is not a lot of wall space left for treatment, although I think I have some axial modes from the ceiling to deal with here.
Also, if treatment doesn't cut it, do you have any particular pro-audio (as opposed to home theater) stereo eq's you recommend?
Thanks
 
#6 ·

Hi Brad,

I personally have never used any bass traps. Their main function is to reduce low-frequency signal decay times, which serves to audibly “tighten up” bass. They can also serve to reduce peaks and nulls in bass response, although I expect traps alone would not be enough to fix your 70 and 150 Hz issues. The Waterfalls thread has some good info, but you can see here for some recent thoughts of mine about them.

For an equalizer, I recommend the discontinued Yamaha YDP2006 parametric or its cousin the YDG2030 if you prefer a third-octave EQ. Here’s a link to a quasi-review I did on the YDP that you might find helpful.

Regards,
Wayne
 
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