cheap room curve adjustment?

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chopperguy99 · #1 Post by **chopperguy99** » Tue May 29, 2007 12:07 pm

Burn a cd of test tones the same freq. as the eq sliders, then play them through the system with the outboard eq flat. Get a rough idea of the average db, then do it again, adjusting each slider till you get that db on your spl meter placed in the listening position. Would this make a fairly flat room curve?

AntonZ · #2 Post by **AntonZ** » Tue May 29, 2007 5:31 pm

I like the idea, think it could make a good start, but needs a pair of well trained ears. Perhaps better to do this outside with no walls nearby so you have a reference point to start from when going inside. You might want to add a few slow tone sweeps to your test cd to bring out narrow peaks (room resonance freq's), you will miss those with the graphic sliders and single frequencies. Dial those out with a simple one or two band parametric eq. That can be found very cheap these days since everyone is going digital - and analogue parametric is both very powerful and easy to operate if you understand what it does.

DAVID_L_PERRY · #3 Post by **DAVID_L_PERRY** » Wed May 30, 2007 2:12 am

I think he is looking at using a SPL meter to see what level each freq is putting out and then adjust the graphic to balance it out, not use ears..

It will work, but it is a slow and horrid process, and will wind up the punters unless you have an empty room. I have used this very method when I was doing lots of trials on my first DR cabs. I only did it to satisfy my own curiosity.

Pink noise is your winner for this one.

Look out for second hand Behringer Ultracurve 8024 RTA:-
http://www.behringer.com/DSP8024/index.cfm?lang=eng
They are very cheap on ebay and even if you only use it for its RTA function its a good tool to have.

The best option is the new Behringer Ultracurve DEQ2496. Its one unit in size and works very well as a dual RTA/EQ:-
http://www.behringer.com/DEQ2496/index.cfm?lang=eng

Possibly one of the best bits of kit I have purchased
Dave

chopperguy99 · #4 Post by **chopperguy99** » Wed May 30, 2007 6:13 am

It does sound pretty time consuming. I just thought it would get me in the ball park without spending any dough. I would eventually like to get the behringer unit, but its SWMBO turn to spend some dough on the HT room. She will have more cash in 1 couch than I have in the whole audio system! I may give it a try on a rainy saturday and see what happens until I can get some proper gear. Thanks.

Dave Non-Zero · #5 Post by **Dave Non-Zero** » Sat Jun 02, 2007 5:43 am

Yeah you think you are spending so much money on audio gear till you see the price of a 3 piece suite.

Sydney · #6 Post by **Sydney** » Sat Jun 02, 2007 7:40 am

The Stereophile Test CD series have a variety of test tones and tracks.
Including 31 frequency tracks of modulated pink noise. These warble tones are ( in theory ) better than non-modulated pink noise.
The suggested test procedure ( circa 1992 ) is to use a microphone on cassette deck, with a mic. input, and observe the VU meter, Or use a SPL meter.

Ancient History - In the 70's I built a DeltaGraph 10 band eq. and used a SoundCraftman test record with a Radio Shack SPL meter.
The results revealed some problems but was somewhat disappointing, in that I didn't like what I tuned to be flat response.
Granted - My system was not SOTA and testing and EQ was crude by today's standards ( 12 band eq is not fine enough - 31 is better )
AudioXpress June 2007 tested the new RS sound level meter. It is not a highly accurate device.
Unless a microphone is calibrated, I would expect a certain level of inaccuracy, especially at low frequency extremes.