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Thread ID: 58038	2005-05-19 12:30:00	Passive Crossover	george12 (7)	PC World Chat

Post ID	Timestamp	Content	User
356708	2005-05-19 12:30:00	Hi, I'm making a cheap home-made "stereo" with a $7 computer speaker board, and two good speakers and a 120W RMS subwoofer (overkill for a 1W RMS board but....). Anyway, the midrange speakers try to play too low frequency bass, and the subwoofer tries to play the whole range - when they're in parallel. So I need a crossover. If I calcuate it correctly, for an 12dB/Octave order, I need a 22.5uH inductor (for 80Hz crossover) in series with the subwoofer, and a 175.8uF capacitor across it. For the main speaker I will therefore need the opposite with the same values? I don't know too much about this! I couldn't find a 22uH crossover inductor anywhere, but Jaycar has 22uH RF chokes, will they do? I also am more or less guessing the 80Hz crossover frequency. So a little help knowing what I need would be of much help. Don't ask why I'm doing this. But goodness, it's amazing how powerful 1W really is when it's not some made-up rating. I was once tried to sell 800W usb bus-powered speakers... And they expect people to fall for THAT?\ Anyway, thanks in advance.	george12 (7)
356709	2005-05-19 22:01:00	Hi........... Don't ask why I'm doing this. But goodness, it's amazing how powerful 1W really is when it's not some made-up rating.Isn't it though! I'm running a genuine 5,600watt RMS system using largely JBL componets driven by lab.gruppen amplifiers. I wont bore you with all the details. As you probably know every 10 times increase in power/sound pressure level/whatever sounds about twice as loud to the human ear, and is measured as a 10db increase. Assuming that my toys are in use in rooms that are over 100 times the size of where you are, its the equivelant of a 56watt system in a bedroom, which would make it about 17 db louder than your 1 watt, which is almost 4 times as loud. Given that my 5.6Kw has been used with some of the loudest rock, funk and metal bands the country has to offer, and consistantly shakes the stuffing out of each building i wind it up in, then yes 1 watt IS powerful! You should be able to get a cleanish 100db, all other things being equal :D	personthingy (1670)
356710	2005-05-19 22:23:00	........, and two good speakers and a 120W RMS subwoofer (overkill for a 1W RMS board but....).. No, not overkill at all, infact quite the opposite. Translation of "120W RMS subwoofer" is that this speaker is so inefficiant that it takes 120watts to get it moving properly. Because bigger better new improved higher numbered lemon fresh ratings that appear better sell more units than actual quality of product, we consistantly have more and more speakers out there that require huge power input to function properly, which is often less output than speakers that have a lower power rating but greater efficiancy. The more important spec. is sensitivity. A sensitive sub will require very little power to pump. Why people don't apply this with car systems i don't know..... O hang on yes i do.. If the customer spends a few grand on a $2Kw system that requires a bigger alternator to run the thing, they will be able to impress more AND the shop makes more money. Win win. With a less "powerful" system (watts) that actually worked better (db) but cost half as much (unimpressive), theres only half the profit, and Joe Bogan thinks he's only got half the chance of getting laid...... :illogical	personthingy (1670)
356711	2005-05-19 23:24:00	There is an error or typo in the inductance value. Crossover inductance will be around 20 -30 milliHenries not microHenries. If you have access to the wire, say via unwinding old transformers, then you could make your own. If air cored then they will be big and use a lot of wire, that's why 'iron' cored inductors are used these days.	Terry Porritt (14)
356712	2005-05-19 23:51:00	The DSE catalogue catalogue has the calculations. Jaycar have a fair range of chokes for crossovers. They are not too expensive. Chris: There's a dead Sony "sound system" in this morning's auction: According to the front panel sticker it's a 6600W system. (PMPO ... and we know what that means.;)). The power rating by the power entry says 250W. If you could get 6600 W output for 250 W input, every home should have one, and there would be no need for new pylon lines or power stations.	Graham L (2)
356713	2005-05-20 07:37:00	Isn't it though! I'm running a genuine 5,600watt RMS system using largely JBL componets driven by lab.gruppen amplifiers. I wont bore you with all the details. As you probably know every 10 times increase in power/sound pressure level/whatever sounds about twice as loud to the human ear, and is measured as a 10db increase. Assuming that my toys are in use in rooms that are over 100 times the size of where you are, its the equivelant of a 56watt system in a bedroom, which would make it about 17 db louder than your 1 watt, which is almost 4 times as loud. Given that my 5.6Kw has been used with some of the loudest rock, funk and metal bands the country has to offer, and consistantly shakes the stuffing out of each building i wind it up in, then yes 1 watt IS powerful! You should be able to get a cleanish 100db, all other things being equal :D 5,600W? Does it like, connect directly into your power board? Imagine trying to plug it into a normal socket - it's like several ovens... :o.	george12 (7)
356714	2005-05-20 07:42:00	Yep. If someone tells me how I can get 800W out of the USB bus, I'll give them $10. Actually, I won't but.... So this is 1/4 the volume of my 100W RMS/channel stereo which cost $200. And this is worth like $2 :p. Thanks for the useful replies. Personthingy, I haven't found that at all. The little 1W amp can drive my stereos 115W RMS subwoofer really well. My only annoyance is it plays ALL frequencys through it.	george12 (7)
356715	2005-05-20 16:29:00	Personthingy, I haven't found that at all . The little 1W amp can drive my stereos 115W RMS subwoofer really well . My only annoyance is it plays ALL frequencys through it . If your genuine 1 watt rms drives it quite well, which i will define as able to throw the cone to near its limits, then a GENUINE 120watts would rip it to bits in no time at all . There's an awful lot of fiction in the ratings of some components . However it appears that you have a good speaker for your needs . 5,600W? Does it like, connect directly into your power board? Imagine trying to plug it into a normal socket - it's like several ovens . . . . At home it runs fine from a standard 10 amp socket . I don't run it hard, or even with all speakers attached . At work we generally run out of a 32amp 3 phase outlet, often sharing with the stage lighting, and use one phase for the labs, and another for backline, mixer, monitors etc . I have a burnt out 10 amp wall socket which i proudly display to anyone who wont believe what a good concert system can pull . I just got back from using it with D4 (a band) . The sound guy who was also called Chris got it all sounding beautiful!!!!! Chris: There's a dead Sony "sound system" in this morning's auction: According to the front panel sticker it's a 6600W system . (PMPO . . . and we know what that means . ) . PMPO = something about multiplying reality with the last few digits of a randomly chosen phone number?????? So this is 1/4 the volume of my 100W RMS/channel stereo which cost $200 . And this is worth like $2 :pAll other factors being equal, yip, thats how it works!	personthingy (1670)
356716	2005-05-21 02:52:00	It doesn't throw the cone anywhere near its limits. I mean it delivers all the thumping bass I want :p The actual stereo it goes with certainly does, but I don't want it painfully loud. Out of curiosity, I think "DIN" music power is at the peak of the wave, as it is 1.414 times my stereo's RMS. But what is PMPO? How do they figure sometimes up to 300 times the input power?	george12 (7)
356717	2005-05-21 03:22:00	PMPO is largely fictitious. It is the instantaneous current available (even if it is destructive) x the supply voltage. sound.westhost.com	godfather (25)
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