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  • What power amplifier do I need?

    Hello Everyone

    I'm John from the UK. I'm normally to be found on the guitar forum on here but I have a PA/Disco related question regarding the speakers I have bought.

    I do mobile discos and have recently bought these:

    https://prolight.co.uk/PRO/item.php?id=508401 Mid/Top Cabs

    https://prolight.co.uk/PRO/item.php?id=508287 Subs



    I demoed them and they sound great for small to medium venues like pubs and Working Mens Clubs. They were demoed with a mixer amp not power amp.



    I run them linked from amplifier to each sub then from sub to top cabinet. The subs have a crossover/filter to send mid/top to the tops.

    I've been powering them with a 12 year old British built Studiomaster 2000e amplifier that is specified at 500 wpc RMS @ 8 ohms and 800 wpc RMS @ 4ohms.

    The amp doesn't quite to be doing the job very well and seems to be running at it's maximum (with no clip lights showing) whilst the speakers seem to be coping comfortably with no distortion at all! They seem to have loads more to give, yet the amp seems to be struggling.

    I'm wondering if the amplifier may have deteriorated over time and it's certainly seen little use in the last 5 years. There are no apparent leaks on capacitors or any other component failure.

    I've spoken to the speaker distributors in the UK and they assure me the speakers can take more than the specified power but I'm reluctant to try it before seeking more advice from places like this where I can get the general concencus of many professionals.



    Having looked at the specifications of the speakers, what would be your thoughts on what power of amplifier to drive them comfortably without having to clip but also taking into account, I don't wish to fry the buggers to death.

    I've had one or two differing viewpoints, so I thought I'd seek a little help on here.

    Please specify amp power per channel using RMS continuous at either 4 or 8 ohms.



    Thank you in advance for any advice you are willing to give me.



    Regards



    John
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    <img src="images/misc/quote_icon.png" alt="Quote" /> Originally Posted by <strong>niceguy</strong>
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    <div class="message">No matter the guitar, a G chord is a G chord. One guitar cannot play notes that another cannot play. They all play the same damn notes.</div>

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    </div>
    </div> <i><b>My Gear:</b></i><br />
    Mania VH 300 (Gibson 335 copy)<br />
    Vox Valvetronix AD15VT<br />
    A strap<br />
    Some picks<br />
    A cheap gig bag<br />
    And a tuner<br />
    <i>Th Th Th That's all folks!</i></div>

  • #2






    Quote Originally Posted by JohnnyLarge
    View Post



    I've spoken to the speaker distributors in the UK and they assure me the speakers can take more than the specified power but I'm reluctant to try it before seeking more advice




    500 wrms is a lot of power!



    So the question is "how much more power can they take"? If you double the avail power to them you will barely make any difference. If you can 4x the power then you'll hear something. Speakers in general will put our 95% of their maximum output level with about 50% of their rated power. It's a quickly diminishing return after that.
    Don Boomer

    Comment


    • #3






      Quote Originally Posted by JohnnyLarge
      View Post

      I run them linked from amplifier to each sub then from sub to top cabinet. The subs have a crossover/filter to send mid/top to the tops.

      I've been powering them with a 12 year old British built Studiomaster 2000e amplifier that is specified at 500 wpc RMS @ 8 ohms and 800 wpc RMS @ 4ohms.




      If I'm reading this correctly you are running one stereo amp and using a passive crossover in the subs to high-pass the tops? The few times I've had to/tried this configuration, I've never been happy with the results. Purely speculating, as I don't know what equipment you're actually using (other than the amp), I would suspect you would be much happier with the results if your were to bi-amp your system. Add a second amp for the subs and use an active crossover as a dividing network. A newer amp may have a crossover built into but I'm guessing the old Studiomaster doesn't, so you'll need a active crossover anyway.
      I love to sing, and I love to drink scotch. Most people would rather hear me drink scotch.

      Comment


      • #4
        Assuming you need to run in stereo, a pair of GX5's or GX7's by QSC one for each side, has a built in crossover as well. One channel on an amp for top one channel on amp for sub. GX7 probably a lil too much juice though, irregardless of what the manufacturer tells you if you over power and have a disco oops you could have a fried speaker oops.



        I tried once what you are doing by paralleling from subs to tops and using subs pass crossover which is fine and will work but better to use crossovered amplifiers, or do what trevcda said, xover then two amps, one for tops one for bottons, if you go that route either two QSC 1450's or two QSC 2450's but the 2450 probably too much juice for your needs.



        I doubt you really need to run any higher than the program rating of the speakers, if anything over I wouldn't exceed 20 % of the RMS rating, it's just not necessary and it breaks stuff like speaker coils.

        Comment


        • #5
          Oh forgot to add if you went with an xover then for sub amp you could also bridge an amp to those two subs i.e., 1450 down to 4 ohms and parallel the two subs that would give you 1400 watts 700 to each box, but your going over the 300 WPC specs, a RMX 850 would probably be better that's @ 830 WPC bridge mono so 415 Watts per sub.



          How do those speakers sound? What do brands of amps do you have access to in the UK? (probably should have asked that first)

          Comment


          • #6






            Quote Originally Posted by JohnnyLarge
            View Post

            Hello Everyone

            I'm John from the UK. I'm normally to be found on the guitar forum on here but I have a PA/Disco related question regarding the speakers I have bought.

            I do mobile discos and have recently bought these:

            https://prolight.co.uk/PRO/item.php?id=508401 Mid/Top Cabs

            https://prolight.co.uk/PRO/item.php?id=508287 Subs



            I demoed them and they sound great for small to medium venues like pubs and Working Mens Clubs. They were demoed with a mixer amp not power amp.



            I run them linked from amplifier to each sub then from sub to top cabinet. The subs have a crossover/filter to send mid/top to the tops.

            I've been powering them with a 12 year old British built Studiomaster 2000e amplifier that is specified at 500 wpc RMS @ 8 ohms and 800 wpc RMS @ 4ohms.

            The amp doesn't quite to be doing the job very well and seems to be running at it's maximum (with no clip lights showing) whilst the speakers seem to be coping comfortably with no distortion at all! They seem to have loads more to give, yet the amp seems to be struggling.

            I'm wondering if the amplifier may have deteriorated over time and it's certainly seen little use in the last 5 years. There are no apparent leaks on capacitors or any other component failure.

            I've spoken to the speaker distributors in the UK and they assure me the speakers can take more than the specified power but I'm reluctant to try it before seeking more advice from places like this where I can get the general concencus of many professionals.



            Having looked at the specifications of the speakers, what would be your thoughts on what power of amplifier to drive them comfortably without having to clip but also taking into account, I don't wish to fry the buggers to death.

            I've had one or two differing viewpoints, so I thought I'd seek a little help on here.

            Please specify amp power per channel using RMS continuous at either 4 or 8 ohms.



            Thank you in advance for any advice you are willing to give me.



            Regards



            John




            Get another amplifier of equal power output at 8ohms. Get a stereo 2-way

            active EQ. Xover @ 100hz-120hz. Use one amp to drive your subs, and the other

            to drive your high pacs. Much better results.

            Comment


            • #7
              I am somewhat familiar with the speakers, IME I wouldn't recommend more then 400 watts (rms) per box. I would also recommend biamping rather then using the subs passive crossover. QSC 's gx-5 would be a good choice in biamp mode.

              Comment


              • #8






                Quote Originally Posted by agedhorse
                View Post

                I would also recommend biamping rather then using the subs passive crossover.




                Yup.



                I don't remember specifically, but I seem to recall that a passive crossover is typically approx. 70% efficient... yes, no, maybe?



                If so, then feeding a passive crossover 500 watts results in approx. 350 watts passing through to the drivers.



                Taking this further: If the sub/mid-high crossover point is 100hz and the spectrum is 40hz - 16Khz (approx. 8 1/2 octaves)... a little quick math suggest that the 350 watts would be split approx. 50/50 between the sub and mid-high cab... resulting in approx. 175 watts per cabinet.



                Yes, no, maybe?



                If so, this begs a question... how big of power amp would = "about right" for a 250w Continuous (RMS) mid-high and 300w cont. sub with passive crossover? I'll suggest 1.5X RMS is probably a safe number for a program rating... so somewhere around 375 - 400 watts per cabinet, times 2, times 1.43 = approx. 1000 watts @ 8 ohms. yes, no, maybe? (it's still fairly early on a Monday morning here).

                Comment


                • #9
                  I would not recommend any more than 1.5 the rated rms rating of the speaker. This will generally give somewhat reasonable margin for the imperfect nature of live loudspeaker applications. I see enough results of overpowering of speakers in my professional day job to be confident in this observation. Program and/or excessively optimistic power ratings serve the marketing folks more than the end user IMO.

                  Comment


                  • #10






                    Quote Originally Posted by W. M. Hellinger
                    View Post

                    Yup.



                    I don't remember specifically, but I seem to recall that a passive crossover is typically approx. 70% efficient... yes, no, maybe?



                    If so, then feeding a passive crossover 500 watts results in approx. 350 watts passing through to the drivers.





                    If so, this begs a question... how big of power amp would = "about right" for a 250w Continuous (RMS) mid-high and 300w cont. sub with passive crossover?




                    Hey Mark



                    The manufacturer's power rating is at the input jack. So although power is lost to the drivers the power rating is in ahead of the insertion losses of that passive crossover.
                    Don Boomer

                    Comment


                    • #11
                      Just to give you an update on this, I contacted the retailer regarding this problem after measuring the combined load of the tops/sub. I got 2.5 ohms!!

                      This is despite both myself and the retailer talking to the manufacturers rep who informed us that the sub was 2 x 10" 16ohm drivers linked together to create a 8 ohm cabinet. I particularly mentioned what loading I wanted when combined (4 ohms) so my currrent amp could drive them.



                      It seems the rep/distributor f**ked up with his information. And guess what? None of their current amplifier range drive their own speakers in the configuration I was told they would.

                      The speakers really do sound nice but are proving a bugger to drive. I specifically went away from a two-amplifier/crossover setup to save weight and space in my transport and hoped I had found a good solution with these compact speakers driven with one amp.



                      I'll keep you posted on developments as I am going back to the retailer today to try and resolve this. Both he and I feel we were given poor information and the speakers are not fit for purpose as intended and particularly specified by me prior to purchase.



                      Thank You for all your help so far.



                      John
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                      <div class="bbcode_postedby">
                      <img src="images/misc/quote_icon.png" alt="Quote" /> Originally Posted by <strong>Ratae Coritanorum</strong>
                      <a href="showthread.php?p=31997937#post31997937" rel="nofollow"><img class="inlineimg" src="images/buttons/viewpost-right.png" alt="View Post" /></a>
                      </div>
                      <div class="message">You are one dumb cünt and you seriously need to ****************ing shut up, go away and reconsider your existence</div>

                      </div>
                      </div>
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                      <div class="bbcode_quote">
                      <div class="quote_container">
                      <div class="bbcode_quote_container"></div>

                      <div class="bbcode_postedby">
                      <img src="images/misc/quote_icon.png" alt="Quote" /> Originally Posted by <strong>niceguy</strong>
                      <a href="showthread.php?p=38808980#post38808980" rel="nofollow"><img class="inlineimg" src="images/buttons/viewpost-right.png" alt="View Post" /></a>
                      </div>
                      <div class="message">No matter the guitar, a G chord is a G chord. One guitar cannot play notes that another cannot play. They all play the same damn notes.</div>

                      </div>
                      </div>
                      </div> <i><b>My Gear:</b></i><br />
                      Mania VH 300 (Gibson 335 copy)<br />
                      Vox Valvetronix AD15VT<br />
                      A strap<br />
                      Some picks<br />
                      A cheap gig bag<br />
                      And a tuner<br />
                      <i>Th Th Th That's all folks!</i></div>

                      Comment


                      • #12






                        Quote Originally Posted by JohnnyLarge
                        View Post

                        Just to give you an update on this, I contacted the retailer regarding this problem after measuring the combined load of the tops/sub. I got 2.5 ohms!!

                        This is despite both myself and the retailer talking to the manufacturers rep who informed us that the sub was 2 x 10" 16ohm drivers linked together to create a 8 ohm cabinet. I particularly mentioned what loading I wanted when combined (4 ohms) so my currrent amp could drive them.



                        It seems the rep/distributor f**ked up with his information. And guess what? None of their current amplifier range drive their own speakers in the configuration I was told they would.

                        The speakers really do sound nice but are proving a bugger to drive. I specifically went away from a two-amplifier/crossover setup to save weight and space in my transport and hoped I had found a good solution with these compact speakers driven with one amp.



                        I'll keep you posted on developments as I am going back to the retailer today to try and resolve this. Both he and I feel we were given poor information and the speakers are not fit for purpose as intended and particularly specified by me prior to purchase.



                        Thank You for all your help so far.



                        John




                        How are you measuring?



                        Impedance is not the same as DC resistance. In fact, I am quite sure many 4 ohm nominal loads will measure near 2.5 ohms of DC resistance.
                        <div class="signaturecontainer">-</div>

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                        • #13
                          Unless I'm missing something, a Peavey IPR1600DSP seems like a perfect fit to me. It does everything you want.



                          - Subs on one side = 450W per sub (2 ohms)

                          - tops on one side = 285W per top (4 ohms)

                          - built in crossover, eq, HPF, and delay

                          - the crossover is adjustable (the GX-5 is fixed)

                          - 1 rack space

                          - ridiculously light (7 lbs / 3.2 Kg)

                          - Inexpensive

                          - Easy to find
                          www.nextexitrocks.com

                          Comment


                          • #14






                            Quote Originally Posted by abzurd
                            View Post

                            Unless I'm missing something, a Peavey IPR1600DSP seems like a perfect fit to me.




                            A non-DSP model would be fine too, or the previously-mentioned GX-5 (I'm still pretty sure the subs are in the 8 ohm class and JohnnyLarge is just looking at a multimeter reading for them).
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                            • #15






                              Quote Originally Posted by soul-x
                              View Post

                              A non-DSP model would be fine too, or the previously-mentioned GX-5 (I'm still pretty sure the subs are in the 8 ohm class and JohnnyLarge is just looking at a multimeter reading for them).




                              Except he doesn't want an external crossover and the passive crossover solution is not a good one, especially if buying a new amp anyway where a real crossover can be onboard. Frankly, even is the GX-5 would be a good choice, I think the IPR may be a better option. If "smalling it up" is the main objective here, it's 20 lbs saved over the GX5. It also has more robust DSP. The delay isn't so useful, but the EQ could be. I could see it used to flatten the system outside then saving it to a baseline. Then use the mixer/eq to fine tune to a venue.



                              Also the IPR has an adjustable crossover whereas the GX is fixed. The adjustable HPF on the IPR is also very useful and absent in the GX and most other dedicated rack mount crossovers.
                              www.nextexitrocks.com

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