How to properly calibrate my EQ using my SPL meter?

[FuzzyReets]

Hi everyone. This weekend I did what I think to maybe be the proper way to calibrate the EQ of my receiver. My receiver has the ability to lower or raise levels by -6.0db to 0db to 6.0db in .5db increments. I have the ability to do this at 63hz, 160hz, 400hz, 1kHz, 2.5kHz, 6.3kHz, and 16kHz. So I downloaded this program called NCH which creates test tones and used the headphones out of my laptop and connected to my receiver to generate the tones through the speaker. I disconnected all but the speaker I was setting and went through the tones for each and adjusted according the level on the SPL meter.

I'm not sure if this is right. I didn't really know where the starting volume of the tone should be. I originally use 80 level on my SPL as the starting point for the standard test tones to level out the sound. For this EQ setup, I played the first test tone out of the first speaker at the 0.0 db level on my receiver then set each hz level up and down until it matched 80 as well.

I'm questioning all this now because today I downloaded the tones from the RealTraps website and when I played them they were much louder than the tones coming out of my laptop so I don't know if the level that I used as a base level coming out of my laptop was correct now or how to really get that base level for the tones to be played.

I know this is probably confusing to follow but I don't know the exact correct procedure for doing this. I just figured this was correct based on things I have read. Can anyone confirm or tell me how this should be done correctly? Thanks.

 

[WaynePflughaupt]

The first thing you have to keep in mind is that the level of one set of test tones vs. the next that you use has no bearing on what EQ settings you may or may not need.

The second thing is that the receiver’s equalizer does not have the capability to accomplish what you’re attempting to do. You’re trying to fine tune the response of your system with an equalizer that’s merely a sophisticated tone control. You’d need a much more powerful and precise equalizer to accomplish an accurate system equalization.

Not that you can’t accomplish some improvement in sound quality with the EQ provisions you do have, but you need to first determine where in the frequency spectrum EQ might be needed, then weigh that against your equalizer’s capabilities – i.e., can the equalizer make an effective change where (and in the way) that it’s needed, or not.

To determine where equalization might be needed, you’ll need 1/6-octave test tones from about 30-20 kHz, preferably sine wave tones. There are various websites where you can find these. Also needed will be some graph paper to plot your readings, or even better, download the Excel Workbook from the BFD Guide website. It’s mainly for measuring subwoofers, but it’s easy to modify for full-range measurements.

To make your measurements, first establish a baseline volume level. A good way to do this is to use the pink noise calibration tone the receiver has for adjusting the speaker levels of the various channels. Something between 75-80 dB is good.

Once that is done, play the test tones one by one, measure them with your SPL meter, and enter them on your graph paper or the Excel program.

After that, connect the dots to see what your frequency response looks like.

The thing to consider at this point is the equalizer’s capabilities. Keep in mind that this equalizer by its nature will cut a very broad path. In other words, it won’t just boost or cut specifically at say, 2.5 kHz. No, everything around 2.5 kHz, both above and below, will be raised or diminished with the EQ adjustment.

So, look at the graph you’ve made and the EQ adjustments you have available. Basically, what you’re looking for is rather broad (wide) depressions or peaks that are near one of the EQ adjustments you have available. You’re looking for an overall [/i]trend,[/i] even if there are small “ripples” present “inside” the broader peak or dip.

For instance, the graph below shows a broad dip between 1200-45 kHz, even though there are smaller dips and peaks in between.

If you see issues like this, that are centered at or near one of the EQ adjustments you have available, then you can make an improvement. This particular wide depression “bottoms out” at about 3 kHz. That’s pretty close to the 2.5 kHz EQ filter you have available, so if this was your response graph you’d be able to make an adjustment there. However, probably no more than 3-4 dB at most, because your filters are so wide that getting too aggressive would end up pushing the peaks at 1200 Hz and 4.5 kHz even higher. Just keep in mind that the objective is an improvement in sound quality, not a picture-perfect graph. Improvements in sound quality can be accomplished with moderate eqaulzation.

Something like the peak at 1200 Hz in the graph above is an example of what you wouldn’t be able to adjust, because it’s fairly narrow. Equalizing it down with the EQ you have would also pull down the substantial dips at 800 Hz and 2.5 kHz even lower.

Anyway – hope this helps. Good luck.

Regards,
Wayne A. Pflughaupt

 

[FuzzyReets]

I have a question about setting up levels. Let’s say I’m starting from scratch with my SLM using the test tones coming from the receiver. All the speakers have their own level setting from -10 to +10 in .5db steps. So they all start directly in the middle. My goal would be to have them all even at 75 on the SLM. When I play the test tones, should the receiver main volume be at 0.0db to start and then adjust all the other speaker levels from there or does the main receiver volume not matter when I start as long as they are all even at the end?

 

[WaynePflughaupt]

In the end, all speakers should be at the same relevant level.

Assuming that with your receiver the other speakers are adjusted in reference to the mains (i.e., the other speakers have trim adjustments, but the L/R do not), run the main volume control up so that the L/R mains are 75 dB. Then adjust the rest so that they also read 75 dB.

Regards,
Wayne A. Pflughaupt

 

[FuzzyReets]

Right I hear you guys. I think a huge problem I have is sound bouncing in the corners of where my big 15" speakers are. They are super boomy and throw all my manual frequency adjustments all over the place. I really have to look into getting some kind of cheap dampening material. I think someone recommended something in one of these threads I've been on.