Members Guitarist4life Posted November 23, 2009 Members Share Posted November 23, 2009 Hello, I'm trying to do the wiring on a cab I made with a 15"speaker and 2 motorola piezo tweeters and 1 horn driver. They are all 8ohm.I was wondering what type of capacitor value should I use with the piezos and the horn driver and how should I wire everything them so the amp sees an 8ohm cab.As you can see I don't know much about this and would really appreciate some help. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Hello, I'm trying to do the wiring on a cab I made with a 15"speaker and 2 motorola piezo tweeters and 1 horn driver. They are all 8ohm. I was wondering what type of capacitor value should I use with the piezos and the horn driver and how should I wire everything them so the amp sees an 8ohm cab. As you can see I don't know much about this and would really appreciate some help.I "improved" some similar cabs a few years back. What I used for crossovers: 15" speaker:Input minus -> speaker minus.Input plus -> 1mH coil -> speaker plus Horn:Input minus -> horn plus.Input plus -> 8uF 100V non-polarized capacitor -> 8 ohm 20 watt resistor -> horn minus. Piezos:Input minus -> both piezo pluses.Input plus -> 1uf 100v non-polarized capacitor -> 33 ohm 10 watt resistor -> both piezo minuses.Input minus -> 33 ohm 10 watt resistor -> junction of 1uf cap and other 33 ohm resistor. This gives you crossovers at about 1250hz and 4800hz. The piezos sound a WHOLE lot better crossed over higher than their natural (with no crossover) point! You should be able to get the parts at:http://www.parts-express.com/home.cfm8uf 100V http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=027-3381uf 100V http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=027-3201mH coil http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-5508ohm 20w http://www.parts-express.com/pe/showdetl.cfm?Partnumber=017-833ohm 10w http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=016-33 Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 You need to know the specs for the horn to know what value cap and coil to use. While the piezo can handle any frequency, if the horn driver is driven with too low a frequency it can be damaged. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 You need to know the specs for the horn to know what value cap and coil to use. While the piezo can handle any frequency, if the horn driver is driven with too low a frequency it can be damaged.His description is of some crappy DJ speaker. Chances of finding out the specs of that horn are close to zero. The Gemini's I modded sounded a whole lot better afterwards and have survived a few DJ gigs powered at 200w (RMX850). Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 His description is of some crappy DJ speaker. Chances of finding out the specs of that horn are close to zero. Where'd you get "crappy DJ speaker"? The OP specifically stated he built this speaker (a cab I made ). So let's not assume anything, and see if he can provide the specs so a good match can be found. 1.2kHz is very low if he happens to be using a budget horn driver. Either way the point is to make him aware of the situation so he can decide how to deal with it. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Where'd you get "crappy DJ speaker"?"2 motorola piezo tweeters" - 'nuff said? OTOH if he actually made the cab you're right - he may have used decent stuff in which case he should tell us the make and models of the drivers - as much as we love it when folks come on here and ask questions without giving us all the info . Oh, and he was just planning on using caps to HP the horn (sort of OK) and piezos (not OK). BTW to the OP: Piezos are NOT 8 ohms - they act mostly like capacitors so a simple capacitor in series just reduces their output at all frequencies. You need to put that 33 ohm resistor in parallel with them to be able to use a capacitor in series with them for a crossover. The additional 33 ohm resistor (value not critical) in series with them I mentioned is to prevent them from looking like a capacitor to the amp at high frequencies which may freak out the amp. Some piezos already have a series resistor internally. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 "2 motorola piezo tweeters" - 'nuff said? OTOH if he actually made the cab you're right - he may have used decent stuff in which case he should tell us the make and models of the drivers. Yup, that's why I added his "a cab I made" quote. I'd be a little cheesed if some internet dude called my hard work "crappy DJ". Oh wait, didn't all the BF choir accuse me of hacking the Tuba??? Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 23, 2009 Members Share Posted November 23, 2009 Roadranger... you need to recalculate your crossover frequencies based on the new load due to the added resistors in series with the drivers. Those will cause an upward shift in additon to lower amplitde. You are off by probably an octave or more on your horn, but good try. The piezo frequency is a complete crapshoot because the piezos themselves are capacitors. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 I'd be a little cheesed if some internet dude called my hard work "crappy DJ".As he was planning on just a cap or two as crossovers that's exactly what he'd end up with. At least with the coil on the 15" it would be a step up from the bottom of the pit . Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 The piezo frequency is a complete crapshoot because the piezos themselves are capacitors.The 33 ohm resistor in parallel pretty much swamps out the high impedance of the piezo at the crossover frequency. Ive got the white paper from CTS somewhere around here... Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 Is "swamps out" a technical, or clinical, term? Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Roadranger... you need to recalculate your crossover frequencies based on the new load due to the added resistors in series with the drivers. Those will cause an upward shift in additon to lower amplitde.I use 159000/(R*C) = F for about the 3db point (forget where I got that from). So since the 8ohm horn plus the 8ohm resistor = 16 ohms - 159000/(16*8) = 1242 hz. As for the resistor in series with the piezos it increases the impedance of the drivers which makes that even less of an effect on the resistor in parallel with all that. Just in case it wasn't clear: amp to piezos: plus -> 1uf -> 33 ohms -> minus---------- ^------- 33 ohms---------- ^minus -> ------------- -> plus Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Is "swamps out" a technical, or clinical, term?Technical actually - the impedance of the drive at the crossover frequency is so much higher than the 33 ohm that it doesn't effect the total impedance much. For instance if the driver's impedance was 3300 ohms at 4800hz it would only change the net impedance to 1/(1/33+1/3300) = 32.67 ohms. Even if it was 330 ohms the net would be 30 ohms which is only a 10% difference = the tolerance of the capacitor I mentioned. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 Technical actually - the impedance of the drive at the crossover frequency is so much higher than the 33 ohm that it doesn't effect the total impedance much. For instance if the driver's impedance was 3300 ohms at 4800hz it would only change the net impedance to 1/(1/33+1/3300) = 32.67 ohms. Even if it was 330 ohms the net would be 30 ohms which is only a 10% difference = the tolerance of the capacitor I mentioned. [Foghorn Leghorn] That was a joke, son. [/Foghorn] Link to comment Share on other sites More sharing options...
Members guitarharv52 Posted November 23, 2009 Members Share Posted November 23, 2009 One of the classics:thu: Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Haven't seen that ol' rooster in years - and I just don't get the joke I'm afraid . In any case was a good excuse to show the math . Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted November 23, 2009 CMS Author Share Posted November 23, 2009 Haven't seen that ol' rooster in years - and I just don't get the joke I'm afraid . [Foghorn] Oh c'mon son, it was humor, you know; a funny. Somma mah best stuff! Nuthin' Ahh say son! you're just built too low; the fast ones go right over your head! I'm pitchin', but you ain't catchin'! [/Foghorn] Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 23, 2009 Members Share Posted November 23, 2009 Yup, shore did . Link to comment Share on other sites More sharing options...
Members Guitarist4life Posted November 25, 2009 Author Members Share Posted November 25, 2009 I "improved" some similar cabs a few years back. What I used for crossovers:15" speaker:Input minus -> speaker minus.Input plus -> 1mH coil -> speaker plusHorn:Input minus -> horn plus.Input plus -> 8uF 100V non-polarized capacitor -> 8 ohm 20 watt resistor -> horn minus.Piezos:Input minus -> both piezo minuses.Input plus -> 1uf 100v non-polarized capacitor -> 33 ohm 10 watt resistor -> both piezo pluses.Input minus -> 33 ohm 10 watt resistor -> junction of 1uf cap and other 33 ohm resistor.This gives you crossovers at about 1250hz and 4800hz. The piezos sound a WHOLE lot better crossed over higher than their natural (with no crossover) point!You should be able to get the parts at:http://www.parts-express.com/home.cfm8uf 100V http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=027-3381uf 100V http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=027-3201mH coil http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-5508ohm 20w http://www.parts-express.com/pe/showdetl.cfm?Partnumber=017-833ohm 10w http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=016-33 Thanks! I need these cabs wired by this weekend, so I went to radioshack to see if they have any of the components you mention. For the horn driver, they do have an 8ohm (20 watt) resistor, but no 8uF (100v) cap. Instead they have a 10uF 50v one, can I use those instead? As for the piezos, they only have 1uF 250v caps, not the 100v.And 50ohm 10watt resistors, not 33ohm. Im ordering the list from parts-express, but I need to get the cabs working by this comming saturday using whatever is available locally:facepalm: Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 25, 2009 Members Share Posted November 25, 2009 Thanks! I need these cabs wired by this weekend, so I went to radioshack to see if they have any of the components you mention. For the horn driver, they do have an 8ohm (20 watt) resistor, but no 8uF (100v) cap. Instead they have a 10uF 50v one, can I use those instead?Assuming you're not going to have a coil in series with the 15" use their 4.7uf 50v for now: http://www.radioshack.com/product/index.jsp?productId=2102480 Also un-reverse the polarity of the horn driver until you get the coil (horn minus to input minus, horn plus to 8 ohm to 4.7uf to input plus). As for the piezos, they only have 1uF 250v caps, not the 100v. And 50ohm 10watt resistors, not 33ohm.Just wire both piezos together with the minus to the input minus and the plus to a 10 ohm 10 watt resistor to the input plus. You can keep that resistor in place of the first 33 ohm (the one connected to the piezo plus terminals) as that value isn't critical. Piezos don't really need crossovers unless you want them to sound better than "normal". Their response right above their "natural" crossover point is quite peaky and if you cross them over a bit higher you avoid the worst of their nastiness . The cabs will sound a bunch better with all the "right" parts but they'll work for a few hours. Hopefully your amp is under 200w into 8 ohms - otherwise the 4.7uf 50v cap won't last long. They usually make a nice "bang!" when they blow . Hmm... BTW I just edited the original instructions to reverse the polarity of the piezos to match the polarity of the horns. Looks like way back when I did the mod to my cabs I forgot that there was no coil in series with the horns so no need to reverse the phase of the piezos in relationship to the horns . Link to comment Share on other sites More sharing options...
Members trevcda Posted November 25, 2009 Members Share Posted November 25, 2009 [Foghorn] Ah say, ah say there's just somethin' a little yahoo! about a kid that doesn't build his own crossovers! [/Foghorn] Link to comment Share on other sites More sharing options...
Members Guitarist4life Posted November 26, 2009 Author Members Share Posted November 26, 2009 Assuming you're not going to have a coil in series with the 15" use their 4.7uf 50v for now: http://www.radioshack.com/product/index.jsp?productId=2102480 Also un-reverse the polarity of the horn driver until you get the coil (horn minus to input minus, horn plus to 8 ohm to 4.7uf to input plus).Just wire both piezos together with the minus to the input minus and the plus to a 10 ohm 10 watt resistor to the input plus. You can keep that resistor in place of the first 33 ohm (the one connected to the piezo plus terminals) as that value isn't critical. Piezos don't really need crossovers unless you want them to sound better than "normal". Their response right above their "natural" crossover point is quite peaky and if you cross them over a bit higher you avoid the worst of their nastiness . The cabs will sound a bunch better with all the "right" parts but they'll work for a few hours. Hopefully your amp is under 200w into 8 ohms - otherwise the 4.7uf 50v cap won't last long. They usually make a nice "bang!" when they blow . Hmm... BTW I just edited the original instructions to reverse the polarity of the piezos to match the polarity of the horns. Looks like way back when I did the mod to my cabs I forgot that there was no coil in series with the horns so no need to reverse the phase of the piezos in relationship to the horns . ok, So I won't use any caps for the piezos, just the 10ohm resistor, right? And what about the horn driver, should I use 8ohm 20watt resistor and radiochack's 10uF 50v cap? they don't carry 8ohm 100v caps. thanks again! Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 26, 2009 Members Share Posted November 26, 2009 ok, So I won't use any caps for the piezos, just the 10ohm resistor, right?"wire both piezos together with the minus to the input minus and the plus to a 10 ohm 10 watt resistor to the input plus" - yes, no caps (for now) And what about the horn driver, should I use 8ohm 20watt resistor and radiochack's 10uF 50v cap? they don't carry 8ohm 100v caps."use their 4.7uf 50v for now: http://www.radioshack.com/product/in...ductId=2102480 " - use this 4.7uf cap instead of their 10uf 50V cap. "(horn minus to input minus, horn plus to 8 ohm to 4.7uf to input plus)" . Oh, and the 15" - input plus to plus, input minus to minus. Link to comment Share on other sites More sharing options...
Members agedhorse Posted November 26, 2009 Members Share Posted November 26, 2009 What an abortion. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted November 26, 2009 Members Share Posted November 26, 2009 What an abortion. Yah, definitely gonna have that "$100 DJ cab sound" thing goin' on. Too bad RadShack only has 50V non-pol caps - hopefully they'll fail open . Don't know why he couldn't wait for the mailorder parts but he might luck out and get a gig out of them . Link to comment Share on other sites More sharing options...
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