I have eq my sub now what about the front channels?

Discussion in 'Archived Threads 2001-2004' started by Doug_M_Fraser, Feb 13, 2003.

  1. Doug_M_Fraser

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    I would like to know if anyone has had any experience in EQing the three front speakers in their HT set up.

    What is driving me is that I have EQ my sub (Stryke 15.2) with a BFD and I am very very pleased with the results. I had a 24db peak that resulted in true one note bass. With the EQ in I can now here all the bass notes.

    In the Feb edition of Audio Express there is a review of the Behringer DSP 8024. More info can be found here:

    http://www.behringer.com/02_products...P8024&lang=eng

    From the Behringer web site it has a US list price of $230.

    This is 31 band stereo digital graphic equalizer. It has a cool feature that allows the unit to auto equalize a room. This is done by connecting a calibrated mic to the unit and then let it do its thing. The reviewer claims that there is a significant difference with the EQ in vs EQ out.

    Now here are some of my thoughts/issues....

    My Integra 9.1 receiver provides access to the LCR signal after the pre amp and before the power amps in the unit. This is where I would connect the EQ for the 3 front channels.

    Is the best solution a 1/3 octave graphic EQ or a parametric?

    I have been considering the analog RANE EQ's. They seem to have good specs and a good reputation. Are there any issues with analog eq such as raised noise floors while EQing higher frequencies?

    While the Behringer DSP 8024 looks good and has gotten a favorable review, it operates in the digital domain. It samples the signal at 48khz with a 24 bit word, applies the EQ and then D to A converts the signal and outputs an analog signal. (Rane has a new product that operates similarly in the digital domain). The issue is that with DVD A at 96Khz sampling (and 192KHz sampling) putting a signal through another A to D then back to A conversion would negate the value of the higher speed format?

    Any thought or experiences in EQ front channels would be appreciated.

    regards,
    Doug
     
  2. Wayne A. Pflughaupt

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    I’m running three AudioControl 1/3-octave EQs in my system for the front three channels. I have passive subs with an electronic crossover and related amps after the equalizers, so the L/R EQs are able to do the subs as well as the mains.

    I like the improvements the center EQ gave me. I have the center speaker in the upper shelf of the entertainment center, so it definitely needed some equalizing.

    My speakers had a spike in the 5kHz range of something like 4-5dB. They sounded much better after equalizing. And since one main is near a corner and the other near a door opening, there were some differences between the two in the upper bass/lower midrange that I was able to somewhat compensate for. However, the subs could have been better equalized with a parametric like you’re using; there were frequencies the 1/3-octave filters just couldn’t get to.

     
  3. Stephen Dodds

    Stephen Dodds Second Unit

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    Full range EQ is indeed a good thing if done properly. I've owned the Behringer 8024 and it does a good job, although not as good as units such as the Tact ones. But you can get an 8024 from www.zzounds.com for well under $200, so there is a massive price difference.

    The problem with the 8024, as Wayne mentioned, is in the A/D conversion. At low volume levels you can sometimes hear quantization errors, usually with bass notes.

    The solution is to keep the volume from the preamp as high as possible. You can do this by tweaking levels within the 8024, or by attenuating the signal to your power amps.

    The question is, I guess, does the 8024 improve the sound even with these proviso? In my system, the answer was yes, but I am a big believer in room EQ.

    I replaced the 8024 with a dbx Driverack ($500), which does not have audible quantization problems. Behringer also has a replacement for the 8024 (DCX 2496) that may be better in this regard and costs $350.

    The Auto EQ feature is very handy and works as advertised, although you will need to tweak the final results.

    Cheers

    Steve
     
  4. Doug_M_Fraser

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    Wayne/Stephen:

    Thanks for the great replies.

    Wayne, I like your idea of examining the in room response before deciding on either a parametric or graphic equalizer. This is clearly the way to proceed! I have a licensed version of Doug Plumb's ETF software so I am able to pre test the in room response. In fact, I could utilize the unused channel from my BFD to experiment.

    Thanks also for pointing me in the direction of Audio Control equipment. I have looked at their web site, but for some reason never really considered their products. I will have another look. The noise floor issues also makes sense to me. I will have to dig out the specs of my receiver and compare them to the EQ candidates.

    I too am concerned about all the conversions from digital and back to analog. I wish receivers had a processing loop out of the digital section that would allow a signal to stay in the digital domain for further processing. Then one could send the processed digital signal back to the receiver for conversion back to analog (yea, I know, keep dreaming !). This will probably drive me to an analog EQ.

    Stephen, the review in Audio Express of the 8024 measured the THD as a fruition of input signal level and the amount of gain provided by the EQ. The curves show a dramatic rise in THD when the input signal lowered and this situation is worse when the EQ inserts less gain. With unity gain in the 8024, THD is .1% with an input level of .2v. What I can gather from your post is that EQ works well however there are better units than the 8024 (especially at low volume levels).

    I have another question....

    Rane has traditionally advertised constant Q EQ's. With their digital version they are now promoting perfect Q EQ's with the claim that one band will not effect adjacent bands. In you estimation how important is it to have "constant Q" design or for that matter a "perfect Q" designed EQ.

    Finally, do you think I should get separate EQ for the L, C and R channels or would a stereo EQ work for the L, R and a separate EQ for the center?

    Thanks,
    Doug
     
  5. Stephen Dodds

    Stephen Dodds Second Unit

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    The problem with any graphic EQ is that the frequencies in the EQ may not match the frequencies you need to fix. That's a good reason to RTA your room first. That said, even the 1/3 EQ of the Behringer did improve my sound.

    The Behringer has a digital input option. The problem is finding a signal to feed it with, especially if you are using it for HT. The only units that will convert all sources to PCM are the Meridians, some models of Theta, and the MSB decoder.

    I'd like to see a combined DVD-A/SACD player with built-in parametric EQ so everything can be done at the source, but I don't fancy my chances.

    What I'd suggest you do is do your measurements with ETF and see where problems lie, then try fixing them with your BFD. It will give you an idea of both the effects of removing room problems, and the effect of inserting an extra A/D stage into your mains.

    The channel question would depend on your budget and the type of EQ you choose. I would choose the same device for all channels though, just to make life easier.

    Steve
     
  6. Wayne A. Pflughaupt

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    Doug,

     
  7. Kevin C Brown

    Kevin C Brown Producer

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    I just went through the exercise of trying to eq my mains with a Behringer Ultra-Q T1951. Tubed, analog, parametric eq. Using ETF too. (Same idea, I liked the effect with a BFD on my sub enough that I wanted to do something for my mains.)

    I had some different "guidelines" though:

    1) I only went after room induced peaks: < 200 Hz.
    2) Had to be analog. Didn't want any (crappy) digital eq messing with my system's 2 channel performance.

    I spent a few hours on it. My conclusion? Wasn't worth it. The BFD is fantastic because of the extreme resolution you can get: center freq, bandwidth, attenuation. All digital. With an analog eq, you have knobs, and even with ETF, it was a long laborious process.

    I could get only *some* improvement in my mains by themselves, but when I graphed mains + sub, it was still better without the eq for the mains.

    But of course, my room is different, my system is different, and ymmv! [​IMG]

    But personally, I had to try it before I could believe that it wasn't worth it. But that's what makes all this fun. The learning.

    I do like Wayne's idea of (just doing) the center. (I listen to 80% 2 channel music, so I wasn't even thinking about the center, surrounds, or rears.)
     
  8. RussKon

    RussKon Stunt Coordinator

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    concerning the behringer dsp 8024.....there have been some serious quality control problems with this unit...

    for one of my customers i have had to replace the unit three times!!!!...number 1 was a bad power switch...numbers 2 AND 3 were dead out of the box.....

    behringer makes a line of products that have alot of features for the dollar....but not a great reputation in the professional sound world....i have quite a few dealers and sound contractors that won't touch behringer with a ten foot pole!

    i would recommend the rane anyday over a behringer product!!!!

    russ
     
  9. Doug_M_Fraser

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    Guys, thanks for the great replies.

    My next step will be to measure the in room response of the fronts and then experiment using the unused channel in the BFD.

    I'll try and post the results when I get them.

    Thanks

    Doug
     

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