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  • Refurbishing old speakers

    I recently decided to refurbish some old Sonic speakers. These are the Sonics from the late 70s that everyone says were "white van" speakers, though I bought mine out of a catalog and they were shipped directly from the company to my home. Not having any info from the past to go on, I replaced the two mid-ranges and three tweeters in each speaker with the GRS mid-range and the PE phenolic ring tweeters, only to find the crossover specs for these speakers from on online source. I found out that the tweeter crossover was set at 1500Hz (simple capacitor crossover), necessitating the need to change out the phenolics again because their low frequency response was 6000Hz. However, the new phenolics only go down to 2000Hz. Should i go ahead and replace the capacitors to adjust the crossover to 2000Hz, or will the mid-ranges pick up the slack? Am I going to get significant degradation in sound from the tweeters because there are signals below 2000Hz that are still being routed to them? Also, would i gain anything from putting low pass filters on the woofer and mid-ranges? Another question, all five of the speakers are hooked in parallell which means (if I usnderstand it) that the impedance is now 8/5 or 1.6 ohms for the entire speaker. I have read that it should never be lower than 2 ohms otherwise you might ruin your amp. I get plenty of volume out of these with a 50 watt total amp turned less than half-way up, so it doesn't seem to be straining the amp at all. Am I missing something concerning speaker impedance ratings?

  • #2
    Most speakers have an impedance "profile" that varies w/freq. (JUST like their FR plots vary w/freq.).
    Almost all start off low (about 6ohms for an 8ohm ("nominal" - rated) driver), then have a peak near resonance (which might only be 10ohms for some tweeters, but can be 100ohms or more for some woofers), then drop back down into a "valley" near 6ohms again (could be in the 200-300Hz range for a woofer, and maybe 3k-5kHz for a tweeter), then a constant (but not linear) rise after that. Tweeters might be (again) as low as 10ohms @ 20kHz, but woofers can be 100ohms (or more).

    So it you've got an 8ohm woofer running full range (w/NO crossover filter), up wherre it's overlapping the tweeter (say, above 4kHz), it COULD be running around 30-50 ohms or so. The (single) cap on the tweeter raises that circuit's impedance below a certain freq. - THAT's how it rolls the bottom end of the tweeter off. So . . . the woofer and tweeter aren't both running in parallel (probably) at the XO freq., so the load is NOT 4 ohms (and your speakers are NOT 1.6 ohms).

    BTW, MANY amps (esp. older amps, like 30-40 yrs old) can get in trouble with loads of only 4 ohms, so . . .

    A great book to learn about this stuff is "SpeakerBuilding 201", by Ray Alden.

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    • #3
      Originally posted by Chris Roemer View Post
      Most speakers have an impedance "profile" that varies w/freq. (JUST like their FR plots vary w/freq.).
      Almost all start off low (about 6ohms for an 8ohm ("nominal" - rated) driver), then have a peak near resonance (which might only be 10ohms for some tweeters, but can be 100ohms or more for some woofers), then drop back down into a "valley" near 6ohms again (could be in the 200-300Hz range for a woofer, and maybe 3k-5kHz for a tweeter), then a constant (but not linear) rise after that. Tweeters might be (again) as low as 10ohms @ 20kHz, but woofers can be 100ohms (or more).

      So it you've got an 8ohm woofer running full range (w/NO crossover filter), up wherre it's overlapping the tweeter (say, above 4kHz), it COULD be running around 30-50 ohms or so. The (single) cap on the tweeter raises that circuit's impedance below a certain freq. - THAT's how it rolls the bottom end of the tweeter off. So . . . the woofer and tweeter aren't both running in parallel (probably) at the XO freq., so the load is NOT 4 ohms (and your speakers are NOT 1.6 ohms).

      BTW, MANY amps (esp. older amps, like 30-40 yrs old) can get in trouble with loads of only 4 ohms, so . . .

      A great book to learn about this stuff is "SpeakerBuilding 201", by Ray Alden.

      Thanks.
      Have any thoughts on the crossover issues I mentioned?

      Comment


      • #4
        Why not draw up a schematic of your XO. OR take a pic of it and tell us the component values. If you've already dropped in new drivers (from PE?), give us the ir part numbers? Was the orig. tweeter like a 3" or 4" cone tweeter?

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        • #5
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          Originally posted by Chris Roemer View Post
          Why not draw up a schematic of your XO. OR take a pic of it and tell us the component values. If you've already dropped in new drivers (from PE?), give us the ir part numbers? Was the orig. tweeter like a 3" or 4" cone tweeter?
          Well, let me see if I can describe this. 12" woofer, 2-5" paper cone mid-ranges, 3-phenolic ring tweeters which are angled for dispersion. Each driver has its own crossover capacitor, and the drivers are connected in parallel off of the terminals on the woofer. I can't see the values of the capacitors as they are coated over with an insulating plastic. The crossovers are set at 600 and 1500 (according to the spec on the original box they came in). The Mid-ranges from PE are the GRS 5SBM-8 Sealed Back Midrange and the tweeters are the GRS Phenolic Ring Tweeter Marantz replacement and two equivalent phenolic ring tweeters with almost identical specs (Dynavox brand). The original tweeters were phenolic ring also.

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          • #6
            Anybody else have thoughts on this?

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            • #7
              The multiple mids/tweets really make a (potential) mess out of this. If your specs are correct, a pr. of 89dB mids in parallel will net 95dB, and a triplet of 90dB tweets all parallelled will net 100dB. Hard to believe the mids & tweets aren't pretty "hot" (w/out any attenuation resistors).

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              • #8
                Originally posted by Chris Roemer View Post
                The multiple mids/tweets really make a (potential) mess out of this. If your specs are correct, a pr. of 89dB mids in parallel will net 95dB, and a triplet of 90dB tweets all parallelled will net 100dB. Hard to believe the mids & tweets aren't pretty "hot" (w/out any attenuation resistors).

                I've always liked they way these speakers sounded. Great clarity without harshness They were far better than the Kenwoods, Cerwin Vegas, and Realistic speakers i had over the years (in my opiniion). And i'm not very big on bass in my music. I prefer hearing the instruments and voices that are going to carry the melody as opposed to thumping bass that drowns out everything else. Beyond that, do you think I need to raise the crossover point to 2000Hz to accommodate the higher lower limits of the tweeters? And what about low pass filters on the woofer and mids?

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                • #9
                  Originally posted by mccalljd View Post
                  Anybody else have thoughts on this?
                  Respectfully suggest you build an inexpensive modern 2 way DIY kit and listen for a while to get some perspective on your old speakers.

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                  • #10
                    Originally posted by djg View Post

                    Respectfully suggest you build an inexpensive modern 2 way DIY kit and listen for a while to get some perspective on your old speakers.

                    Thumb your nose at them if you must, but I spent many hours in the listening rooms back in the day when they had designated audio stores that dealt only with home stereo equipment, and I never heard anything much better than these speakers. The definition and clarity were among the best I ever came across, and as I mentioned, they beat the Cerwin Vega and Kenwood three-ways I had all to hell. Listening to classical music on these is as good as being in a live concert hall. I haven't heard anything lately,, either, that was much of an improvement over these and over the years I've had people comment on how great they sounded. The original speakers as shown in the photo may have looked like cheap drivers and the crossover situation may appear like a mess, but if I could have purchased new versions of the same drivers, I would have done that and been quite happy. As it is, I have had to replace the drivers my kids poked holes in over the years with drivers from PE and other sources, which don't have the same frequency response as the original drivers, hence the question about whether I should adjust the crossover capacitors on the tweeters and add some low pass filters. I'm pleased with the way these sound now, but I wonder if doing those things would get even more out of these new replacement drivers. I could use some constructive advice on that, rather than passing judgement on speakers you've probably never listened to.

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                    • #11
                      If the mids REALLY are wired in parallel, EAch w/their own cap . . . you COULD get the same effect by just using a single cap w/the parallel pr. hanging off of it.
                      Same w/the tweeters. You should be able to use a single cap, with the 3 (paralleled) tweeters hanging off of it.

                      How would you raise the cross pt. of the tweeters to 2000Hz (as opposed to 1500)?

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                      • #12
                        Do you have any way of doing an Impedance sweep of the entire speaker?

                        Also, any chance of actual pictures of the ones you own, including the interior and back of woofer, just curious.

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                        • #13
                          I don't really think DJG was 'thumbing his nose' at your speakers, seems like he was trying to be helpful and respectful.

                          I realize you want to work with these, understandable. I remember hearing and even owning a few sets of speakers when I was younger that sounded amazing to me at the time and probably did sound pretty good or I wouldn't have liked them so much. It's just that it's possible these days to get amazing sound out of a decent woofer/tweeter combo in a box 1/3 to 1/4 the size of those speakers. I would have never known how good a speaker could sound unless I had built a smaller, but much better equipped modern speaker; D-3's in my case. Some folks just want to fix one set, or build one set and that's it.... but lots of folks continue on, and it's hard to know who will do what from a few posts.

                          Anyway, I'd refurb them too, they're super cool looking and there is something to be said for multiple drivers and lowering distortion considerably, best of luck!

                          TomZ
                          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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                          • #14
                            Originally posted by kevintomb View Post
                            Do you have any way of doing an Impedance sweep of the entire speaker?

                            Also, any chance of actual pictures of the ones you own, including the interior and back of woofer, just curious.

                            I'll try to post a pic in a few days. I will have to take the woofer out to get a shot,

                            Comment


                            • #15
                              Originally posted by tomzarbo View Post
                              I don't really think DJG was 'thumbing his nose' at your speakers, seems like he was trying to be helpful and respectful.

                              I realize you want to work with these, understandable. I remember hearing and even owning a few sets of speakers when I was younger that sounded amazing to me at the time and probably did sound pretty good or I wouldn't have liked them so much. It's just that it's possible these days to get amazing sound out of a decent woofer/tweeter combo in a box 1/3 to 1/4 the size of those speakers. I would have never known how good a speaker could sound unless I had built a smaller, but much better equipped modern speaker; D-3's in my case. Some folks just want to fix one set, or build one set and that's it.... but lots of folks continue on, and it's hard to know who will do what from a few posts.

                              Anyway, I'd refurb them too, they're super cool looking and there is something to be said for multiple drivers and lowering distortion considerably, best of luck!

                              TomZ

                              Thanks for the reply. You are right, they are making much smaller speakers with impressive sound than was ever possible before. I'm ok with the size as they are, though, because I really don't have anyplace but the floor to set another pair of smaller speakers where they wouldn't get kicked around by the people in my house or my dogs. Like I said, even the new speaker systems I've heard don't seem any more impressive except for the bass end. I concede these are a bit weak on the bass without adjusting the equalizer to boost it, but the bass is very clear and un-muddied, and I am not one of those who enjoys the bass portion of my music simply because you can feel it vibrate the floor like these guys who put sub-woofers in the car and turn them up to the point the car's body panels are vibrating and dropping off in the street, lol. I would probably enjoy building my own speakers, but I fear it might turn into an obsession and would end up being a hobby I couldn't afford to indulge in to the extent I would like. My big question was just if I should tweak the crossover since the replacement drivers don't have exactly the same specs on the frequency response as the originals. It sounds pretty good to my ear now, but am I getting all that I could out of it without making those modifications? Anyway, I appreciate you taking the time to reply. Eventually, I would like to add a pair of smaller speakers to utilize the synthesized quad effect on my amp. Any suggestions for a decent inexpensive speaker kit?

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