O.T: How do you correlate the SPL with db?

[jasminphotography]

This is not about the altec component, but I think this forum may be the appropriate place to ask this question. I am new to graphic equalizers and recently I bought a digital equalizer, Behringer DEQ2496, for my system. One of the function in this unit is the RTA. I tried this function, but the scale is in SPL. When I try to compensate the RTA result to the graphic equalizer, I realized that the scale of the eq. is in db. My question is that how do you convert SPL of RTA to the db of graphic eq? How do you determine the reference point from the RTA so that it's equivalent to the 0db (flat or non deviated ) of the graphic eq?. Also, how do you determine how many SPL db equals to one graphic eq db? I understand that many of you are using graphic qualizers for your altec system, and please tell me in a simple sentence, how to interpret the result of the RTA scale so that I can apply it to the graphic equalizer. I hope you can understand what I am trying to convey.
Thanks

[bowtie427ss]

Decibels(db) are the standard unit for measuring sound pressure level(SPL).

I suspect your issue here is a simple matter of the RTA's display resolution being set different from the resolution of the EQ display which should be switchable(usually 1, 3 or 6 db). I'm sorry i'm not intimately familiar with the DEQ, so i cannot tell you how to change the resolution, but that should be clearly covered in the user manual as it's a rather basic and important function. Without knowing the current resolution setting, the display could be showing anywhere from 1db to 6db per display unit. It's important to get a handle on the basic functions and parameters, once you do, i think you'll find the DEQ a very useful tool.

If you didn't receive a hard copy of the manual with your unit, it's downloadable from the Behringer website.

Just my .02.................

[Panomaniac]

Mr. Bowtie is quite correct - it's a matter of scale. You can twist a knob and change the scale of the RTA. But no matter what the scale, the number will be the same.
If you need more details, let me know, I have one of these beasties.

Have you tried the "Auto EQ" function? It's pretty good to get you started. I rarely use it as the definitive setting, but it's nice to know what the DEQ thinks is correct.

If it still leaves you baffled, send me a PM thru the forum, we can work thru it on the phone.

[jasminphotography]

Thanks for the reply, unfortunately, the RTA of my unit has no switchable function to change the SPL value into db. Perhaps, I didn't make myself very clear. I will try to explain it again. You see, the RTA scale on the Behringer has two scales, one at the bottom from left to right and has the frequency range, in this case, from 20-20KHz. On the left side, there is a vertical column which has the output range, in SPL. The range of SPL level can be alter from 15db to 90db, and by doing so, you can widen or narrow the range of the volume of sound, for example, from -70 to -10db. When the RTA is done analyzing the frequency spectrum, it displace, as you know, in "wave" form of frequency response from 20-20KHz. Now, I can't tell from the RTA spectrum which one is equivalent to the GEQ 0db, or the flat spot. In another word, how can I tell which is the reference point based on the RTA scale? And how do I convert the value from the SPL to the db of the GEQ? The simple example is that if the RTA scale of 1000Hz is at-25db, how do I calculate that value to know just how much db should I attenuate on the GEQ? Is there an equation to solve this problem? I hope you guys can understand me this time.
Thanks,

[Old Guy]

I'm missing something. the questions aren't making sense to me? The spl value is in dB already.

You don't really need to know how to reference that. Lowering or raising the measurement window only allows you to center the measurement.

What you do with an RTA is look at the response. If there is a 6 db peak at 4 kHz, just drop 4 kHz on the EQ by 4 dB.

And the same for a dip. only you boost it.

Why do you need to reference anything? All you are trying to do is eliminate peaks and dips.

FWIW many systems aren't set flat but exhibit a gentle HF rolloff.

If we don't understand keep asking, text is hard to communicate with, but we will get what you want to know sooner or later.

But I sort of get the feeling you are worried things are more complicated than they need to be. You do not need to measure absolute spl, only relative spl.

[jasminphotography]

Yes, the SPL is in db, but it demonstrates how loud a particular frequency is. Let's say that at it measured -30db at 1000Hz and -20 at 1200Hz. If I want to eq these two values so that they will be flat (the neutral point on the graph )on the graphic eq, how would I know how much to increase or decrease? Also, how will I know which of these two values is closer to 0db on the eq, assuming there are deviations on these two values? I hope my topic won't boring you guys, I am trying to figure out how to interpret the RTA scale so that I know how to apply it onto the eq. Thanks again.