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Help selecting tweeter for 1961 console

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  • Help selecting tweeter for 1961 console

    I am restoring a 1961 Motorola 3 channel console. Source is a tube amp with 15-20w per channel. The bass channel is a big 15" woofer in the center and left and right are 8" whizzer and a 5" both 8ohm. The standard crossovers on the side channels are 5mf but I have a 4.7 in there because the 5mf have been sold out for a while. I would like to add a small tweeter on the right and left channel to bring out some more airy highs and clarity. I know very little about speakers and wiring, and although I have been reading for weeks, I am in kind of a state of parallelization. I have read that I need to be looking for something with high QTS because of the open back nature. of the console. The space in the right and left is approx 15" square. The baffle board has the whizzer up high and the 5" down low and is only about 14.5 x 13", so I need something small.

    I believe they are currently wired in parallel?

    Click image for larger version

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    Can anyone recommend a small tweeter that I could use to accomplish my wish on this unit as well as suggestions on how to wire it in? I'm not even sure what OHM to be looking for, and if I should add it in parallel or series to the existing setup. I have to have the crossover inline to it because of the complicated nature of other wiring happening on these to accomplish another task - which is the channel verifier that allows you to turn each channel on and off with a switch. Both existing speakers have two terminals per pole and the whizzers are all taken, so I have to come off that negative that's left on the 5".

    I have been considering the Dayton AMT mini 8 for its size and potential, but then think maybe I should go with a paper cone, or a silk dome....but how would the open back nature affect this....Im really at a loss here. I don't need the highs to dominate, just smoothly blend in and add some clarity.

    This is all I could come up with for wiring
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    Thanks in advance for any help or insight!

    - Andrea



  • #2
    Swapping out drivers and adding a tweeter will require a completely different crossover. I recommend gutting the cabinet, find a kit that will fit into the space, and call it a day. Re-using those old drivers is not going to get you good sound quality.

    Comment


    • #3
      Hi Buggers, Im not really interested in gutting it. It actually sounds quite good just missing some highs for clarity. Can hear some old Herb Alpert on it here just after I finished the amp and changer

      Can you assist with wiring and tweeter selection?

      Comment


      • #4
        GenTso - Have you selected your replacement 8" and 5" drivers yet or are you reusing the existing ones?

        As it stands it appears that you already have a tweeter in your system and it is the 5" driver - is it a sealed back driver or open back driver?



        Comment


        • #5
          You are basically adding a super tweeter. It is fairly common to use a single small cap for a super tweeter and connect it in parallel with the other drivers. The Dayton Mini-8 seems like it could work fine, as long as it is efficient enough to keep up with the existing drivers. The Qts of the tweeter is not very important in this case. It is the woofer that might benefit from a high Qts, 0.5 or higher.

          You could also order a small selection of metalized polypropylene capacitors, maybe a 1 uF, 1.5 uF and the 2 uF that you have suggested. Since you are putting the 2 uF in series with the 5uF, that works out to ~ 1.4 uF. That seems like it should be OK, but it may require some experimentation for best sound. You probably don't want the super tweeter to be too loud.

          Comment


          • General Tso
            General Tso commented
            Editing a comment
            hey Billet - what is the mathematical formula to calculate the caps like you did here? "2 uF in series with the 5uF, that works out to ~ 1.4 uF"

        • #6
          Originally posted by Steve Lee View Post
          GenTso - Have you selected your replacement 8" and 5" drivers yet or are you reusing the existing ones?

          As it stands it appears that you already have a tweeter in your system and it is the 5" driver - is it a sealed back driver or open back driver?
          Both drivers are open back, I would like to keep them, mostly because the 8" whizzer is involved in a complicated wiring for the channel verifier switches. Yes its SORT OF a tweeter but lacks the highs, so I guess Billet is spot on that Im looking for something to use as a super tweeter up around 6500 to 8500
          Click image for larger version  Name:	Mtj7cjP.jpg Views:	0 Size:	201.3 KB ID:	1460352
          Last edited by General Tso; 12-30-2020, 07:56 PM. Reason: better pic

          Comment


          • Steve Lee
            Steve Lee commented
            Editing a comment
            GenTso - Here is what I would do as an experiment.

            1. Grab a pair of these because they are also paper which will keep the sound similar to the existing speakers --> https://www.parts-express.com/goldwo...eeter--270-018

            2. Get some capacitors as suggested by Billet and also get some 8 and 4 ohm resistors.

            3. Using some alligator clip-leads attach the tweeter in #1 above in parallel with the existing 5" speaker.

            4. Place the tweeter on top of the console facing the listening position.

            5. Listen to the results and change/EXPERIMENT with the capacitor and resistor values in SERIES with the new tweeter speaker to get the desired effect/result.

            The impedance of these two drivers in parallel (5" & paper tweeter) should stay high enough to prevent any issue with the amplifier.

        • #7
          Originally posted by Billet View Post
          You are basically adding a super tweeter. It is fairly common to use a single small cap for a super tweeter and connect it in parallel with the other drivers. The Dayton Mini-8 seems like it could work fine, as long as it is efficient enough to keep up with the existing drivers. The Qts of the tweeter is not very important in this case. It is the woofer that might benefit from a high Qts, 0.5 or higher.

          You could also order a small selection of metalized polypropylene capacitors, maybe a 1 uF, 1.5 uF and the 2 uF that you have suggested. Since you are putting the 2 uF in series with the 5uF, that works out to ~ 1.4 uF. That seems like it should be OK, but it may require some experimentation for best sound. You probably don't want the super tweeter to be too loud.
          Hi, thank you for clarifying a bit for me - the point you are making about the the caps being in series - did not dawn on me. There are two terminal for each pole. This is a potentially dumb question but....coming off a different pole STILL makes the caps in series? power in at 5" and then cap in line with one negative pole to 8".

          Secondly, if they are currently wired up in parallel (I think they are?) then we are at 4ohm now, right, so do I switch them to series and parallel the 8ohm super off the 5" to stay close to the same load? Im having a hard time calculating this because I cant find any examples that match my setup. I have roughly calculated this as 5.3 with an 8ohm super tweeter in this scenario...how much would this affect output? And if that math is correct then I guess scavenging for a 6ohm super tweeter somewhere gets me closer at 4.3?

          I agree about picking up several different values, thanks.

          Comment


          • #8
            GenTso/Billet - see comment in post # 6.1

            Thoughts?

            Comment


            • General Tso
              General Tso commented
              Editing a comment
              Thanks Steve.

            • General Tso
              General Tso commented
              Editing a comment
              oops I forgot to ask - wire wound or non inductive resistors, or try both? and watts or try several?

            • Steve Lee
              Steve Lee commented
              Editing a comment
              Non-Inductive resistors, GenTso.
              Use 10 Watt.

          • #9
            It is a wise idea to calculate the impedance load to the amplifier. If it is too low or too high, you could have problems. In this case, you already have two drivers in parallel. Adding a third driver in parallel could cause problems.

            Moving coil speaker drivers are generally not purely resistive loads, they usually have an impedance curve that varies with frequency. Steve's suggestions seem helpful, the paper cone driver appears to have a rising impedance at high frequencies, plus a resistor in series with the additional tweeter may help to minimize the change in impedance.

            Given that the current setup sounds good and was designed as a system by the manufacturer, maybe it would be best to simply enjoy it as it was designed.

            Comment


            • #10
              Many of the older consoles used 4 ohm two inch cone tweeters with alnico magnets. They're efficient and have high spl. Keep it simple.

              Comment


              • #11
                PE has several paper cone tweeters described as appropriate for vintage designs, dirt cheap. Minimize your risk.

                https://www.parts-express.com/cat/tw...%5D&PortalID=1

                Comment


                • #12
                  IMO (for best results) you'd NOT rewire all your stuff, you'd just add a tweeter in parallel w/the others (or, paralleled off the 5").
                  That 3" GW has a nasty peak near 1.5kHz (look at its FR graph). A 2uF cap (in series w/it) won't roll it off near 7k, but a 1uF will.
                  It will end up running around 87dB in it's passband (the "top" octave, or 1-1/2 octaves).
                  The mini-8 won't roll off low enough w/a 2uF cap either. A 1uF will roll it near 7k, BUT - it's sensitivity (crossed that way) is a LOT lower than the 3", only around 76dB or so. I don't think that will be loud enough for you.

                  Either way, adding the 'tweeter" (using a 1uF cap) shouldn't trouble your amplifier. It'll be equivalent to paralleling a 3rd "load" in the 12-14ohm range, above about 8k, or higher. Shouldn't be a problem.

                  I'd recommend using Dayton's DC28-8 dome (275-070) w/a 1.5uF cap in series w/it. A "cheap" ($1) npe would probably be fine, but a poly (in that small of a value) wouldn't break the bank either. Configured that way, it'd be like adding a 12ohm load in parallel (w/ the others) @ 8k, dropping to 8ohms @ 20k. I think that would be alright as well (it would probably be as sensitive as the 3" cone).

                  Comment


                  • #13
                    Originally posted by Chris Roemer View Post
                    That 3" GW has a nasty peak near 1.5kHz (look at its FR graph).
                    The Goldwood cone tweeter actually sounds pretty good to me, at least with a first order filter. I have found that the 1.5 kHz peak is not objectionable when listening. Maybe paper cone tweeters damp their resonances pretty well.
                    Last edited by Billet; 01-02-2021, 10:30 AM.

                    Comment


                    • #14
                      off topic but...I have been trying to get to the crossover caps and regular electrolytic caps page for 2 days and the website continuously times out. I can get to the upper level page but using any of the links to filter and refine results on the left ie select category, brand etc - its a no go. Even the contact us page I can reach. Is it me?

                      Comment


                      • Billet
                        Billet commented
                        Editing a comment
                        I have the same problem...

                      • General Tso
                        General Tso commented
                        Editing a comment
                        thanks for confirming.

                      • djg
                        djg commented
                        Editing a comment
                        It's working fine for me, just now, and two orders earlier this week. Firefox on windows 10.

                        Edit: crossover components stalled just now.

                    • #15
                      If you're familiar w/Ohm's Law, SERIES capacitance is figured the same as PARALLEL resistance.
                      You add the "inverse" of the capacitance values (so, 1/2 + 1/5, or 0.5+0.2 = 0.7), then take the inverse (reciprocal) of that. 1/0.7 = 1.43.
                      (FYI, inductance is similar to resistance.)

                      Comment


                      • Steve Lee
                        Steve Lee commented
                        Editing a comment
                        Following Chris's tutelage the calculation can also be identified by calculating the "product over the sum" for capacitors in series as is done with resistors in parallel.

                      • General Tso
                        General Tso commented
                        Editing a comment
                        thank you both. To clarify for my wee brain, the end result of the value in series is the value used at crossover? so if we are at 1.43 then we are crossing over a wee above 12k?
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