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2 like speakers don't sound the same???

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  • 2 like speakers don't sound the same???

    I've noticed recently that my main L+R towers don't sound alike. One has a pronounced midrange, not always noticable but it's definitely there when playing back pink/white noise. All the drivers are functional and placing my ear directly in front of each one they all sound fine. The speakers in question are Dahlquist DQ-20's with ScanSpeak mids and tweets, early-mid eighties vintage.

    Is there something in the crossover that could have gone or is on it's way out that would cause a change in sound but continue playing?

  • #2
    Re: 2 like speakers don't sound the same???

    One has a pronounced midrange, not always noticable but it's definitely there when playing back pink/white noise.
    Have you tried a frequency sweep to help isolate better?.
    A failure in shut leg or a device that Shunts ( goes to ground ) would allow operation but would alter the circuit response.
    "Not a Speaker Designer - Not even on the Internet"
    “Pride is your greatest enemy, humility is your greatest friend.”
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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    • #3
      Re: 2 like speakers don't sound the same???

      Could be as simple as reversed polarity on one of the drivers.

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      • #4
        Re: 2 like speakers don't sound the same???

        Could be lots of things . . . have you swapped them to see if it's as simple as room position? Is one of them close to a window with direct light exposure (even if through a grill cloth)? Over time sunlight can (does) severely degrade surrounds. Humidity will also change the properties of paper cones . . . is one of them near a regularly watered indoor plant? Another possibility of course is aging caps in the crossover . . . it's worth checking to see if any electrolytics were used, and replacing thim (preferably with film, and on both sides) if they were.
        "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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        • #5
          Re: 2 like speakers don't sound the same???

          These are all interesting thoughts. I did swap them left to right and the "problem" followed, so it isn't a room issue and it's in the speaker, not anywhere else in the signal chain.

          I think I do recall removing a mid at one time to "take a look at what's inside", maybe I messed up and reversed polarity on one when putting the mids back in...I will check that.

          I was thinking caps might be due for replacement, as they are nearly 30 years old.

          What are some good, cost effective replacement caps these days? I'm not interested in super duper high dollar parts but I don't mind paying a few bucks more for something a little better.

          Comment


          • #6
            Re: 2 like speakers don't sound the same???

            Originally posted by emilime75 View Post
            These are all interesting thoughts. I did swap them left to right and the "problem" followed, so it isn't a room issue and it's in the speaker, not anywhere else in the signal chain.

            I think I do recall removing a mid at one time to "take a look at what's inside", maybe I messed up and reversed polarity on one when putting the mids back in...I will check that.

            I was thinking caps might be due for replacement, as they are nearly 30 years old.

            What are some good, cost effective replacement caps these days? I'm not interested in super duper high dollar parts but I don't mind paying a few bucks more for something a little better.
            Erse Audio PulseX caps are just fine.
            Don't listen to me - I have not sold any $150,000 speakers.

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            • #7
              Re: 2 like speakers don't sound the same???

              More than likely, your crossover caps are NOT the problem. Don't waste money fixing things that aren't broken. The only way you could damage a cap would be to send more than its rated voltage through it, and by that point you're way beyond smoking drivers.

              If you want to find out what's going on with your speakers, one thing that can help is an impedance sweep, which the Woofer Tester 3 makes very easy. Sweep one speaker, then save that response curve to memory and sweep the other speaker, then look for differences of more than 0.5 ohms.

              Before doing this, however, swap the midrange driver polarity in the speaker that sounds abnormal. If it sounds normal then this was the problem.

              If the caps really have dried out (swapping midrange polarity doesn't do anything and the two impedance sweeps show the peaks and dips in different places through the midrange and treble frequencies), don't waste a bunch of money on their replacements, either. Dayton metallized polypropylene caps will work just fine and be trouble-free for the rest of the life of the speaker. (The only thing about older caps that might cause a problem is if the electrolyte in an electrolytic-type capacitor has dried up.)
              Best Regards,

              Rory Buszka

              Taterworks Audio

              "The work of the individual still remains the spark which moves mankind ahead, even more than teamwork." - Igor I. Sikorsky

              If it works, but you don't know why it works, then you haven't done any engineering.

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              • #8
                Re: 2 like speakers don't sound the same???

                Originally posted by emilime75 View Post
                I was thinking caps might be due for replacement, as they are nearly 30 years old.
                I you're going to dig in that much, then why not simply swap the existing XO's to opposite cabinets? Then you can narrow it down to a possible driver problem.
                Bryan K.

                Midwest Audio Club

                Speedster | | The Wildeman | Sean's NLA Towers | , COUGAR II and | Triton | Lithium | J-Boom | Trym MLTL | Docere MLTL

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                • #9
                  Re: 2 like speakers don't sound the same???

                  Originally posted by emilime75 View Post
                  I think I do recall removing a mid at one time to "take a look at what's inside", maybe I messed up and reversed polarity on one when putting the mids back in...I will check that. ...
                  Did the problem arise shortly after?
                  "Not a Speaker Designer - Not even on the Internet"
                  “Pride is your greatest enemy, humility is your greatest friend.”
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                  Comment


                  • #10
                    Re: 2 like speakers don't sound the same???

                    Originally posted by Sydney View Post
                    Did the problem arise shortly after?
                    I check (and recheck) polarity with a 1.5 volt battery.

                    Comment


                    • #11
                      Re: 2 like speakers don't sound the same???

                      Process of elimination...
                      What events ( if any ) proceeded the "change".
                      Is it something that was done inadvertently; a result of deterioration due to age or environmental conditions ( as mentioned prior by Deward).
                      "Not a Speaker Designer - Not even on the Internet"
                      “Pride is your greatest enemy, humility is your greatest friend.”
                      "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                      Comment


                      • #12
                        Re: 2 like speakers don't sound the same???

                        Originally posted by Theresa View Post
                        I check (and recheck) polarity with a 1.5 volt battery.
                        Then, if they're not the same, there's the issue of figuring out which one is right...

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