Soledad Posted February 21, 2019 Share Posted February 21, 2019 I know there's a very long thread here re impedance and it may be mentioned somewhere but - I notice Hartke (maybe others) feature switcheable impedance on their single-driver cabs - how? An example is the HD112, single 12", switchable 4/8 ohm. The only way I can think is to build a 4 ohm driver and put a dummy load in series, to turn half the power into heat inside the box. Excellent. Any knowledge please? I Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 (edited) 10 hours ago, Soledad said: I know there's a very long thread here re impedance and it may be mentioned somewhere but - I notice Hartke (maybe others) feature switcheable impedance on their single-driver cabs - how? An example is the HD112, single 12", switchable 4/8 ohm. The only way I can think is to build a 4 ohm driver and put a dummy load in series, to turn half the power into heat inside the box. Excellent. Any knowledge please? I voice coil tap Edited February 21, 2019 by EBS_freak Quote Link to comment Share on other sites More sharing options...
BigRedX Posted February 21, 2019 Share Posted February 21, 2019 I really wouldn't recommend a dummy load with the sort of power the typical modern bass amp puts out. I use a Marshal Power Break as part of my guitar rig which sits between a 50 watt valve amp and the speaker. It's a large and heavy device full of chunky resistors, heatsinks plus a fan for extra cooling. Running the amp at full power with 50% or more attenuation from the Power Break on overdriven sounds will cause the fan to kick in almost continually. I wouldn't like to think what sort of device and cooling would be required dissipate half the power from a 300 Watt plus bass amp. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2019 Share Posted February 21, 2019 Use a dual voice coil driver. One coil 8 ohms, two for four ohms. I don't know if that's what Hartke does, but it's one way to do it. Quote Link to comment Share on other sites More sharing options...
fleabag Posted February 21, 2019 Share Posted February 21, 2019 Didnt another well known cab builder make switchable 4/8 ohm cabs ? Schroeder maybe ? Cannot remember the name Quote Link to comment Share on other sites More sharing options...
chris_b Posted February 21, 2019 Share Posted February 21, 2019 The Barefaced Two10's switch between 4 ohms and 12 ohms. Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 Just now, chris_b said: The Barefaced Two10's switch between 4 ohms and 12 ohms. I think that’s down to the series or parallel wiring of the speakers as opposed to the coils. Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 38 minutes ago, fleabag said: Didnt another well known cab builder make switchable 4/8 ohm cabs ? Schroeder maybe ? Cannot remember the name I seem to recall it was accugroove? Quote Link to comment Share on other sites More sharing options...
chris_b Posted February 21, 2019 Share Posted February 21, 2019 1 minute ago, EBS_freak said: I think that’s down to the series or parallel wiring of the speakers as opposed to the coils. Maybe, but as the thread is about switchable impedance and that's what the BF can do I think it's relevant to give it a mention. Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 7 minutes ago, chris_b said: Maybe, but as the thread is about switchable impedance and that's what the BF can do I think it's relevant to give it a mention. Maybe - the original post did specifically say single driver cabs though. Quote Link to comment Share on other sites More sharing options...
Jack Posted February 21, 2019 Share Posted February 21, 2019 (edited) The Accuswitch on Accugroove cabinets turned out to be snake oil as I recall. Something about switching in a capacitor to fool a multimeter possibly? Not saying that's true of Hartke, but certainly with Accugroove it was a scam. Edited February 21, 2019 by Jack Quote Link to comment Share on other sites More sharing options...
BigRedX Posted February 21, 2019 Share Posted February 21, 2019 (edited) Why would you want to have a switchable impedance speaker anyway? You can't get anything (more volume) for nothing. Guitarists use power soaks in order to get the sound of the power amp valves working hard without having to play at ear-splitting volumes. In the OP's case the power soak (if it was feasible) will simply dissipate all the extra power being delivered by the amp as heat not volume. Putting a coil tap on the speaker will halve its power handling when in low impedance mode which again defeats the object. A dual coil speaker might work, but it seems a rather over-engineered solution, when the easiest way the get more volume out of your rig is to add a second identical speaker. Edited February 21, 2019 by BigRedX Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 33 minutes ago, Jack said: but certainly with Accugroove it was a scam. Indeed it was! Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted February 21, 2019 Share Posted February 21, 2019 17 minutes ago, BigRedX said: Why would you want to have a switchable impedance speaker anyway? Im guess it's for better matching to various amplifiers. Some of Hartke's amps go down to 2 ohm, whereas it's probably fair to say that most amps go down to 4 ohm. By having their cabs switchable to 8 ohm, it makes it more friendly for attaching multiple cabs to 4 ohm stable amps. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2019 Share Posted February 21, 2019 59 minutes ago, EBS_freak said: I seem to recall it was accugroove? It was, and it was a fraud. He put a capacitor in series with one of two paralleled woofers, with a switch that bypassed it. When you measured the DCR with the switch off the cap stopped the DC from the meter from reaching the voice coil of its associated woofer, so the meter only read the DCR of one driver. With the bypass switch on the meter read the DCR of both drivers. One possible explanation of why Accugroove pulled this is that the owner, who's a bit of a loon, didn't know the difference between impedance and resistance. The other is that he was aware that it didn't work, but thought no one would catch him. I lean towards the latter, because the magic component, a capacitor, was encased in epoxy, to prevent anyone from seeing what it was. Interestingly before the AccuSwitch scandal broke someone posted the question on a forum, maybe even this one, if a circuit of this sort would work. I told him why it woulldn't. 2 Quote Link to comment Share on other sites More sharing options...
fleabag Posted February 21, 2019 Share Posted February 21, 2019 2 hours ago, EBS_freak said: I seem to recall it was accugroove? Thanks - thats them Quote Link to comment Share on other sites More sharing options...
Jack Posted February 21, 2019 Share Posted February 21, 2019 It seems as though Hartke don't get the same vitriol, so I've always assumed that their speakers do actually switch (unlike the Accugroove). Is this true? If so, how do they accomplish what Accugroove couldn't? Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2019 Share Posted February 21, 2019 OK, once more, but this time with feeling: Use a dual voice coil driver. One coil 8 ohms, two for four ohms. I don't know if that's what Hartke does, but it's one way to do it. 3 Quote Link to comment Share on other sites More sharing options...
Soledad Posted February 21, 2019 Author Share Posted February 21, 2019 9 hours ago, EBS_freak said: voice coil tap Got it, I'd forgotten about that. Seems neat but I suspect efficiency would drop a bit when one coil (or half total whichever) is bypassed, half the copper in the flux gap doing nowt. Thanks for sorting that for me anyway - i'd been browsing 15" cabs and it came up. Quote Link to comment Share on other sites More sharing options...
stevie Posted February 21, 2019 Share Posted February 21, 2019 Just now, Bill Fitzmaurice said: OK, once more, but this time with feeling: Use a dual voice coil driver. One coil 8 ohms, two for four ohms. I don't know if that's what Hartke does, but it's one way to do it. Dual voice coils are particularly popular with the car audio people, but even they would never suggest using just one coil of a dual coil driver. Sure, it's physically possible, but nobody does it because it halves the driver's power handling, halves its xmax, reduces its efficiency, increases its distortion and alters its TS parameters so much that it drastically changes the sound of the cab. Dual voice coil drivers are normally wired either in series of parallel. They give you a choice of, for example, 8 or 2 ohms. If I had to choose, I'd take the Accugroove solution. Quote Link to comment Share on other sites More sharing options...
stevie Posted February 21, 2019 Share Posted February 21, 2019 Just now, fleabag said: Didnt another well known cab builder make switchable 4/8 ohm cabs ? Schroeder maybe ? Cannot remember the name I think it was Duke le Jeune. He offers the option of switching in a high power resistor on his 4-ohm cabs to turn them into 8 ohms. I think it just takes a one- or two-ohm resistor to take his cab from nominal 4 to nominal 8 ohms because the impedance of his 4-ohm cab is already on the high side. Quote Link to comment Share on other sites More sharing options...
Jono Bolton Posted February 21, 2019 Share Posted February 21, 2019 (edited) EDIT: I just re-read the thread and realised that the OP refers to single-speaker cabs. I really should read things properly. Edited February 22, 2019 by Jono Bolton Quote Link to comment Share on other sites More sharing options...
Dan Dare Posted February 21, 2019 Share Posted February 21, 2019 Bill, would there be any point in using a dual voice coil driver, apart from being able to vary the impedance? Would it affect the performance of the driver in any helpful/useful way? Quote Link to comment Share on other sites More sharing options...
BigRedX Posted February 21, 2019 Share Posted February 21, 2019 25 minutes ago, stevie said: I think it was Duke le Jeune. He offers the option of switching in a high power resistor on his 4-ohm cabs to turn them into 8 ohms. I think it just takes a one- or two-ohm resistor to take his cab from nominal 4 to nominal 8 ohms because the impedance of his 4-ohm cab is already on the high side. I wouldn't fancy that considering the amount of heat my Marshall Powerbreak generates with just a 50W amp driving it. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted February 21, 2019 Share Posted February 21, 2019 1 hour ago, Dan Dare said: Bill, would there be any point in using a dual voice coil driver, apart from being able to vary the impedance? Not that I can think of. The original reason some sub drivers used dual coils was to sum the L/R channel low frequency content, back in the days before receivers had LFE outputs and subs went from being mainly passive to being mainly self powered. They're becoming less and less common as there's no real need for them anymore. Quote Link to comment Share on other sites More sharing options...
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