travisc Posted August 16, 2005 Share Posted August 16, 2005 someone told me once that you could take the older bose 901's and plug them into the wall and listen to 60hz without hurting them. I dont know if that means anything but I have always remebered it Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 16, 2005 Share Posted August 16, 2005 " clipped wave is not DC for a very long time as it alternates between +DC and -DC (e.g. a square wave). The explanation also doesn't side with tweeters blowing as it hints to the woofer coil burning out. " Exactly, DC won't make it to the tweeters... the crossover wouldn't let it. Yet clipping often kills tweeters.... because of the nature of what a square wave is. Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 16, 2005 Share Posted August 16, 2005 " Now, do I dare bring up Bose? The Bose drivers are pretty tough. They can take a massive beating and keep going so they have minimal warranty claims. " Not so much the drivers as it is the protection Bose adds to their speakers. The few I have looked in have had light bulbs inline with their drivers. They act as limiters to keep from blowing them. When you really start cranking them the bulbs begin to glow (heat up) which increases resistance which lowers the power getting to the driver. If you keep pushing harder the bulbs glow brighter. Shawn Quote Link to comment Share on other sites More sharing options...
psg Posted August 16, 2005 Share Posted August 16, 2005 ---------------- On 8/16/2005 2:04:41 PM travisc wrote: someone told me once that you could take the older bose 901's and plug them into the wall and listen to 60hz without hurting them. I dont know if that means anything but I have always remebered it ---------------- I'd likely blow the breaker. 120V into 8 ohms is 15 amps. I guess that means the Bose has a higher impedence at 60 Hz. Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted August 16, 2005 Share Posted August 16, 2005 ---------------- On 8/16/2005 2:00:46 PM psg wrote: ---------------- On 8/15/2005 9:40:24 PM MrMcGoo wrote: Spkrdctr, Your explanation of clipping is one of the best that I have read. Thanks for the information. Bill ---------------- I'm not sure I agree with that explanation. I always understood clipping in terms of a square wave, representing a lot of harmonic content (think Fourier series if mathematically inclined). A clipped wave is not DC for a very long time as it alternates between +DC and -DC (e.g. a square wave). The explanation also doesn't side with tweeters blowing as it hints to the woofer coil burning out. ---------------- Well, here is more..... You mention you always understood clipping in terms of a square wave which is correct. You then mention that a clipped wave is not DC for very long. This is the entire issue. While the DC is being put out, you must remember that the impedance from lack of voice coil movement is very, very low and creating almost a short. So, you have very large amounts of current being put through the voice coil during that time, so they heat up and fry. Remember how thin a voice coil wire is for the amount of current you are pumping through it. The crossovers/music/driver design and over all cooling you will determine which driver you lose. For example, an extreme bass disk would take out a woofer pretty quick compared to normal music, the tweeter is for the most part just sitting there and if it does see any DC, it is cooling off quickly between the DC bursts. A main woofer on the other hand is still getting thumped hard on each cooling cycle so it really does not get to cool down much. A tweeter will go quickly of course if there is any high frequencies keeping it from cooling in between the DC bursts. Normal music will not allow the tweeter to cool, and they are very fragile compared to a main woofer with better cooling. I hope this helps explain it better. Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted August 16, 2005 Share Posted August 16, 2005 ---------------- On 8/15/2005 9:40:24 PM MrMcGoo wrote: Spkrdctr, Your explanation of clipping is one of the best that I have read. Thanks for the information. Bill ---------------- Bill, Thank you! I think you are very wise...... Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 16, 2005 Share Posted August 16, 2005 "While the DC is being put out, you must remember that the impedance from lack of voice coil movement is very, very low and creating almost a short." Hook a multi-meter to your speakers and measure their DC resistance. Shawn Quote Link to comment Share on other sites More sharing options...
scriven Posted August 16, 2005 Share Posted August 16, 2005 901s as nightlights? The Fourier series for a square wave of frequency f is the summation of: (1/(2i-1)) * sin (2i-1) f for i=1 to infinity. So the series looks like: sin f + 1/3 sin 3f + 1/5 sin 5f + 1/7 sin 7f + The series has frequencies from the base frequency through the high end of the audio spectrum. Assuming a base frequency that would normally go to the woofer the crossover will send the incoming signal to all the drivers. That signal is now the full power supply voltage swinging between + and -. The tweeter usually fails because it is the most delicate of the drivers but they are all in harms way. Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted August 16, 2005 Share Posted August 16, 2005 ---------------- On 8/16/2005 2:45:34 PM sfogg wrote: "While the DC is being put out, you must remember that the impedance from lack of voice coil movement is very, very low and creating almost a short." Hook a multi-meter to your speakers and measure their DC resistance. Shawn ---------------- Thank you for the correction. I got a little carried away with my explanation. So, we end up with 60 volt rails divided by the 4 ohms (I picked out of the air) of DC resistance to give us 15 amps of current through a hair thin voice coil wire. That should create plenty of heat..... Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted August 16, 2005 Share Posted August 16, 2005 Mark, you did a great job. Especially in your summation of the delicate tweeter. Gee, you guys come up with the most interesting bits of math.......... Quote Link to comment Share on other sites More sharing options...
scriven Posted August 16, 2005 Share Posted August 16, 2005 Thanks, I happened to say awake in physics class that day! Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 16, 2005 Share Posted August 16, 2005 And for a visual this is a FFT of an amp that is starting to clip. The signal feeding the amp was just a 50hz sine wave. But because the amp is clipping it is producing many many harmonics of that sine wave. Shawn Quote Link to comment Share on other sites More sharing options...
seti Posted August 17, 2005 Share Posted August 17, 2005 I've been told that clipping on an 8wpc system was harder to differentiate than clipping on higher watt amplifiers. How can I tell if or when I am clipping? Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 17, 2005 Share Posted August 17, 2005 "I've been told that clipping on an 8wpc system was harder to differentiate than clipping on higher watt amplifiers." There is really no reason for that to be the case just based on available power. Other then a lower powered amp will obviously clip sooner then a higher powered amp. Different amps 'clip' in different manors so that can make a difference in the resulting sound. FWIW the amp in the photo above is clipping at around 10w. "How can I tell if or when I am clipping?" With instruments it is fairly easy. By ear it is harder to notice occasional clipping on peaks if it is very brief. But if you push it too far and start clipping pretty badly the music will start to get congested then distorted and just downright nasty sounding. If you start noticing your speakers are sounding lousy after turning up the volume back the volume down. Shawn Quote Link to comment Share on other sites More sharing options...
seti Posted August 17, 2005 Share Posted August 17, 2005 Well thats easy enough. Thanks Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 17, 2005 Share Posted August 17, 2005 Thanks for the nice picture. This shows my argument that Fourier harmonics probably are not as big a factor as people say. The vertical scale is logarithmic. We see the 10 volt level. The next marker down is 1.0 volt, the next is 0.1, then 0.01 volt. Look at how little power is getting into the mid and tweeter freqs. We could probably get some conditions more dangerous to a tweeter. E.g. higher freq of square wave, harder clipping, and a more powerful amp. So I'm not saying it is impossible. Just that the conditions shown on the scope show clipping is not causing harmonics at a level strong enough to fry a tweeter. i do think clipping is one part of a train wreck in the making. Gil Quote Link to comment Share on other sites More sharing options...
sfogg Posted August 17, 2005 Share Posted August 17, 2005 "This shows my argument that Fourier harmonics probably are not as big a factor as people say." That is at 10w of output on an amp that is rated for 25w of output. At that clipping level on a 'scope you probably won't even see any distortion of the waveform but it shows up on a FFT. Also note that it was a 50hz sine input. If I did the same thing at 100hz the distortion products would end up covering 2x the frequency range. Clip at 1000hz and the harmonics are in the tweeters range very very quickly. And that is clipping on single tones, clip on noise/music and you get a huge number of harmonics. If I push the amp harder (so that a 'scope shows visible clipping) the percentage/level of distortion jumps up dramatically. Unfortunatly I know longer have the amp that test is from or I'd show that condition as well. Shawn Quote Link to comment Share on other sites More sharing options...
Cleve Posted August 17, 2005 Share Posted August 17, 2005 The best defense against accidental speaker damage is either a new or used McIntosh amp with the Power Assurance system (Sentry Monitor and Power Guard). Not to mention the fact that such amps usually have highly accurate meter systems which allow the user to monitor how much power is actually delivered to the speakers. Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted August 17, 2005 Share Posted August 17, 2005 JBL Tech Note regarding the dangers of underpowering a loudspeakerTechnicalNoteLowPower.pdf Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted August 17, 2005 Share Posted August 17, 2005 JBL Tech Note for Speaker Power Requirments and sources of failure.JBLTechNoteSpkrPwrReq.pdf Quote Link to comment Share on other sites More sharing options...
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