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Applying JBL Spkr Tunings to DR260 and PLX Amps

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  • Applying JBL Spkr Tunings to DR260 and PLX Amps

    I am trying to understand whether different amps will require a change to the DR260 "factory" tunings.  Specifically I am thinking the input sensitivity of the amp must be accounted for.

    The situation is Bi-amping an SRX722.  Using the JBL suggested DR260  tunings if we ignore all the EQ settings and actual crossover frequency, and just look at the crossover Gain, they suggest the mids be at 0db and the high be at -10db.  Presumably this is because the horn is more effecient.

    But I am using two different amps for the mids and the highs.  The amps are both 40x (32db) gain and I run them wide open, but the input sensitivity is different.

    Mids - PLX3402  input sensitivity 1.7Vrms @ 4ohm  (6.8dBu)

    High - PLX1202 input sensitivity 1.0Vrms @ 8ohm (2.2dBu)

    So don't I have to compensate for this difference in input sensitivity when programming the DR260?  That is  6.8dBu - 2.2dBu = 4.6dBu.    Should I subtract this additional 4.6dBu from the High crossover Gain making it -14.6dB?



    --Mike<br><b>&quot;</b><i>If your not confused, you don't know what is going on</i><b>!&quot;</b><br><br>Live Sound for the Mt. Shasta area<br><a href="http://www.shastalivesound.com">ShastaLiveSound.com</a><br>

  • #2

     I can't answer your question but I've wondered about the same thing. I guess you can set it up and use a measurement mic to balance the levels. The DRPA has a wizard. Does the 260?


    • agedhorse
      agedhorse commented
      Editing a comment

      Yes, you need to account for the different sensitivity. This is one reason why I recommend sticking with one line of amps, and accounting for sensitivity off of the data sheets if all the models are fixed gain. That way, at least you are dealing with identical measurement methods and overload points (only an issue on some amp lines, and when operating at less than full sensitivity).

  • #3

    Did you ever get specific recommendations or figure how to calculate the difference you asked about?


    • #4
      Note that in this case sensitivity is input voltage for rated output. What's really importan is the 40x gain which is the same across the line of amps so it doesn't matter... the amps will al be of identical loudness at the same drive voltage, the smaller one will limit first then the next, then the next. This is the reason for fixed gain rather than fixed sensitivity.


      • #5
        Aged clarified this nicely in this last post.
        IF you have amps that are the same gain (eg 32dB or 40X)
        and IF you have the attenuators set the same (WFO in my case),
        THEN the input sensitivity does not matter.

        Below is alongwinded description of one way I get my head around the whole situation . Simple as it is, it has taken me a few years to grasp the basic principles. Apologies in advance if this is too rudimentary or contains technical errors.

        I think of the mixer output as a varying voltage signal that is well balanced across the frequency spectrum with respect to the music it represents. So for example if you plugged in some imaginary perfect full range head phones, it would sound great. Next the DR260 gets the signal and breaks it up into the high and low pass bands and also applies gains and EQ that have been derived by the Harmon engineers to take into account the sonic characteristics of the specific speakers. Those are the "tunings" that modify the electrical signal and are supposed to result in a well balanced "acoustic" signal from the speakers.

        So the DR260 LF and HF outputs are voltage signals that should work great to bi-amp those specific speakers. Of course the voltage is too low to drive the speakers and so the amps must increase this voltage to a level that will drive the speakers to usable volumes. If both LF and HF amps have the same fixed gain (eg 40x), then the amp output will still represent the signals intended by the DR260, just at a higher voltage.

        The input sensitivity of the amp is not directly of concern. As long as we are within the linear operating range of the amp, the DR260 output signal should be faithfully multiplied 40x. If the PLX1202 gets a 0.1V signal it should output a 4.0V signal. If the PLX3402 gets the same 0.1V signal it should output the same 4.0V signal. So, given the fixed situation described, you would NOT want to start changing the crossover gains just because the input sensitivity is different on the two amps.

        With a fixed gain amp family (eg PLX series) the input sensitivity is sort of another way to describe the maximum power of that amp. The input sensitivity is supposed to be the signal that will drive the amp to its full rated output if the attenuator is WFO. So for example the PLX3402 sensitivity is 1.9V at 8 Ohms. If it is a 40x amp and we put 1.9V in we should get 76V out into a 8 Ohm load without clipping. That is about 700 watts of power and will drive the low speaker in an SRX722 very loud. On the other hand if you use the PLX1202 it has an input sensitivity of 1.0V at 8 Ohms. So at 40x the maximum voltage it will deliver to an 8 Ohm load is 40V. That is about 200 watts and well under what the LF driver on the SRX722 can handle. But as long as you are running your rig at a low volume, the PLX1202 would work fine for both the LF driver and the HF driver in the SRX722. It would be "linear" and sound just the same as if you used the PLX3402 on the low frequency driver. BUT the PLX1202 runs out of gas as soon as the input signal hits 1V. The PLX3402 will keep going all the way up to an input signal of 1.9V which allows the PLX3402 to deliver more voltage to the speaker when you want to crank the volume up. By the same token you could use th PLX3402 on both the LF and HF driver in the SRX722. It would be "linear" and sound the same as if you used the PLX1202 on the HF driver. One catch is that it would be easy to destroy the HF driver if you had an "oops" moment. Not because the 3402 input sensitivity is different, but because it won't run out of gas at 1.0V input and instead will keep putting out higher voltage to the speaker as the input climbs above 1.0V. But really the main catch is that power is expensive. An amp that will produce 700w at 8 Ohms is usually more expensive than an amp that will produce 200w at 8 Ohms. If the SRX722 HF driver can only handle 75w rms, why pay for an amp that can delivery 700w? So manufacturers typically have a line of amps with different power ratings but with the same fixed gain.

        Another "cool" thing about most amps is that the fixed gain (eg 40x) stays the same whether you drive an 8 ohm load or a 4 ohm load. You can even bridge the amp and the gain stays the same. The amp is just capable of delivering different amounts of maximum power. This makes it easy to set up your system with "conservative" power or "High" power without having to change the DR260 program. For example say you were doing a small show that didn't need much power and a single speaker stack would work coverage wise. You could use one PLX3402 and drive an SRX722 (not bi-amp mode) off one stereo channel and one SRX728 off the other stereo channel. You scale the system up, keeping the same ratio of tops to subs, to 4 SRX722 and 4 SRX728's and run them all off multiple four PLX3402's using stereo channels. If you had source material with wide dynamic range and a wanted maximum ability to handle transients, you could use eight PLX3402's and bridge them all, one per speaker. All this could use the same DR260 program.

        Back to the Gain Offset issue, we said if you are using amps with the same fixed gain (eg 40x) you normally would not have to make any changes to the factory specified crossover gains to achieve the factory supplied results. However there are a number of situations where additional factors come into play and you may want to make an adjustment to the crossover gain.

        -You might not like the "flat" response given by the factory tunings so you make an additional crossover gain adjustment to change the balance.

        - You are NOT using amps with the same gain on all channels. For example if the HF amp was 40x (32dB) and the LF amp was 50x (34dB), then to achieve the same results you should adjust the LF crossover gain down -2dB.

        - If you find, like me, the HF amp run WFO produces objectionable levels of hiss with no input signal. In this case you might want to turn the attenuator on the HF amp down 3dB or so to mitigate the hiss. Then to achieve the same response when there is a signal, the HF crossover gain would be adjusted up +3dB.

        One final note, if you use the DR260 Wizard, all bets are off! The wizard sets crossover gains by taking into account the specific amp model's gain (eg 40x) and where the attenuator is set. It also may apply some overall crossover gain reductions to set up limiting. In the end it might produce good results if you have the specific amps and speakers in the tables. But figuring out how it arrived at the final settings is not easy. And if your gear is not in the list, then you won't know what adjustments need to be made.

        --Mike<br><b>&quot;</b><i>If your not confused, you don't know what is going on</i><b>!&quot;</b><br><br>Live Sound for the Mt. Shasta area<br><a href="http://www.shastalivesound.com">ShastaLiveSound.com</a><br>


        • #6
          Note that in most cases, bridging changes the gain to 46dB from 40dB.


          • #7
            Originally posted by agedhorse View Post
            Note that in most cases, bridging changes the gain to 46dB from 40dB.
            Thanks for catching that. The gain on the PLX series amps does change when bridged. It goes from 32dB (40X) to 38dB (79x). So that part about the amp gain staying the same when it is bridged was totally wrong.

            What I was doing was taking all my amps and either running them all stereo (conservative power) or bringing twice as many and bridging all of them (aggressive power). It just happened to work out that this resulted in the same relative increase across the board so the same DR260 program still works for either case.
            --Mike<br><b>&quot;</b><i>If your not confused, you don't know what is going on</i><b>!&quot;</b><br><br>Live Sound for the Mt. Shasta area<br><a href="http://www.shastalivesound.com">ShastaLiveSound.com</a><br>


            • #8
              I wasthinking the base gain was 40dB. In any case there's a 6dB increase in net sensitivity.