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In room response

Hello, Lately I have noticed more talk of in room freq response measurements. It has been mentioned in regards to room treatment, subwoofers and their intergration, speaker placement, room size, crossover points, listening volume levels, speaker choices in regards to the type of music you listen to and a myriad of other reasons. I for one fell it is quite important and others seem to disagree to its importance in playback of recorded music.

This thread would be a great place for members to discuss its importance, ramifications, reason for being and to discuss results.

I have seen a few members who allready have posted results of the measurements under their "systems page". I just recently posted my freq response and waterfall graph on my "system" link.

I am quite sure that there are members who have allready done in room measurements of freq response, waterfall and RT60 or other measurements. If you are new to this, a program can be downloaded for FREE at the Home Theatre Shack, it is called the Room EQ Wizard. See link below. It would be used for mesurment only for our purposes, although it can be used with equalizers such as Behringer if you so desire.

http://www.hometheatershack.com/roomeq/

The only thing you need to provide is a sound level meter, which everyone should own, even if you don't use this program. A very inexpensive one is available from Radio Shack and is a welcome addition to any audiophiles toolbox.

I will start off with my freq response from 15-200 hz at 74db reference level posted here;
http://cgim.audiogon.com/i/vs/i/f/1208699468.jpg

Waterfall response 20-116hz posted here;
http://cgim.audiogon.com/i/vs/i/f/1208644826.jpg

Waterfall response 116-210hz posted here;
http://cgim.audiogon.com/i/vs/i/f/1208645085.jpg

Anyone else?

Bob
acoustat6
goatwuss
877 posts
 
Hi Bob and others,

To see my room response, click the following link:

http://cgim.audiogon.com/i/vs/i/f/1209579742.jpg

That was measured with JDFT which is free RTA software. That was actually measured from my turntable(Vpi scoutmaster, jmw9sig, shelter 901), with a pink noise vinyl test track. I was in the process of testing the response of some phono pre's. (comparing the sim LP5.3 to the one built in my Supratek.)

Using the microphone and mic pre found on the ETF (now rplusD) site.

The speakers are Merlins vsm mxe's, and you'll see that I'm getting down to 30hz or so maybe -4db. Not bad for a 2 way with a single 6.5 mid/bass driver! This is an all tube system, with the Supratek Syrah pre, and Cary sixpac EL34 triode amps.

The scale on the left is not accurate as I didn't set a reference DB, but I did the measurements at about 75db on the SPL meter.

The room is 13ft by 14.5 ft, the speakers on the 14.5 wall, pulled about 3 feet out. There is no right side wall as it opens to the kitchen. I have GIK corner traps in the left corners, and fiberglass acoustic panels on the front and back walls.

There is a 50" plasma TV, and the left wall is a sliding glass door, and I've got nothing to address the 1st order reflections on the glass wall at this point, other than some shades.
acoustat6 OP
357 posts
 
Hi Goatwus, Nice of you to post. Which test record LP are you using? While I think it is very important to use a test LP, I think you need to go to a more accurate analyzer. A -4db at 30hz would be a very good in room response for those speakers and perhaps you can get a better response with more bass trapping and speaker placement if they are not yet optimized. You should try to use the REW, though there are other free software this one is very good. It will give you much better detail than the current software you are using and it is free.

I don,t believe you will "see" much comparing preamps at least in regard to their freq response in room. For that you would need specialized equipment to measure freq response, distortion etc right from the preamp. But one could very well sound better to your ears!

Bob
goatwuss
877 posts
 
Hi Bob,

Thanks for your reply. I was using the Hifi news test LP.

Can you explain how exactly REW is a more accurate analyzer? I'm not challenging your assertion in the least, I just don't know.

I have used REW before, and I'm familiar with it. When I get a chance, I'll take another measurement with REW and post it on this thread. What type of smoothing should I use in REW? 1/3 smoothing still gives me quite a bit of comb filtering. Do you find 1/1 smoothing still gives accurate enough results?

Regarding comparing the phono preamps - Actually I did see quite a big difference. My supratek phono had some major response problems in the bass. I heard weak bass from it, and that is why I borrowed the Sim piece from my dealer, to run comparative RTA tests. Supratek has acknowledged that there is a problem with my preamp, and there are some parts now in transit to me that I will install in the phono circuit to hopefully fix the bass response problem.
acoustat6 OP
357 posts
 
Hi Goatwuss, I believe the REW would be higher resolution than what you are using , but I am not familiar with it just the one graph you posted. You need finer resolution than that.
I like to look at the graphs in several ways. No smoothing shows the most accurate response and therefore the real story of comb filtering, just how severe peaks or dip are within very narrow freq bands. 1/12 smoothing for general viewing and posting graps is preferred. 1 octave smoothing shows the energy levels loss or peaks over the octave levels.

Regarding the testing of preamps, I would not have assumed too much of a variation between preamps, unless one was broken, or so "colored" by design. And Iwold still have assumed that the in room response would overshadow that.

Bob
jpv
23 posts
 
Chad,
Did you ever get the 40Hz dip figured out?
John
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