Why speakers blow

[tauzero]

The tweeter in one of my Mackie SRM450s has ceased emanating sound. It still shows a resistance of around 8 ohms so I went on a quest to find out whether I should expect it to be open circuit. On that quest, I found a couple of very interesting articles which, while focussed on hi-fi, very much apply in the bass world.

[url="http://sound.westhost.com/articles/speaker-failure.html"]http://sound.westhost.com/articles/speaker-failure.html[/url] - general article on speaker failure

[url="http://sound.westhost.com/tweeters.htm"]http://sound.westhost.com/tweeters.htm[/url] - why tweeters blow, plus interesting bits on the trend to heavy compression in the recording industry and why using a bigger amp isn't the answer.

[discreet]

[quote name='tauzero' timestamp='1437589404' post='2827389']
...why using a bigger amp isn't the answer.
[/quote]

I've often thought this. A bigger amp to 'prevent clipping' due to 'increased headroom' is still more powerful and so likely to blow your speakers anyway, isn't it? And while I'm on, can anyone explain why The Hubble Telescope can't see the geography of Pluto (7.5 billion km away) when it can provide a marvellously sharp image of the Horsehead Nebula (155 light years away)? It is a simple 'Father Ted' explanation, i.e. Pluto is [i]small[/i], whereas the Horsehead Nebula is [i]far away[/i]?

[tauzero]

[quote name='discreet' timestamp='1437590772' post='2827412']
And while I'm on, can anyone explain why The Hubble Telescope can't see the geography of Pluto (7.5 billion km away) when it can provide a marvellously sharp image of the Horsehead Nebula (155 light years away)? It is a simple 'Father Ted' explanation, i.e. Pluto is [i]small[/i], whereas the Horsehead Nebula is [i]far away[/i]?
[/quote]

[url="http://www.planetary.org/blogs/emily-lakdawalla/2013/02141014-hubble-galaxy-pluto.html"]http://www.planetary.org/blogs/emily-lakdawalla/2013/02141014-hubble-galaxy-pluto.html[/url]

[discreet]

[quote name='tauzero' timestamp='1437591158' post='2827419']
[url="http://www.planetary.org/blogs/emily-lakdawalla/2013/02141014-hubble-galaxy-pluto.html"]http://www.planetary...laxy-pluto.html[/url]
[/quote]

Thanks for that! A variation on Father Ted, then - in this case Pluto is small, whereas the Horsehead Nebula is mind-bogglingly huge!

[Woodinblack]

[quote name='tauzero' timestamp='1437591158' post='2827419']
[url="http://www.planetary.org/blogs/emily-lakdawalla/2013/02141014-hubble-galaxy-pluto.html"]http://www.planetary...laxy-pluto.html[/url]
[/quote]

Don't you hate it when your question is so common they made a whole page about it!

[discreet]

[quote name='Woodinblack' timestamp='1437592244' post='2827437']
Don't you hate it when your question is so common they made a whole page about it!
[/quote]

Yes.

[JapanAxe]

[quote name='Woodinblack' timestamp='1437592244' post='2827437']
Don't you hate it when your question is so common they made a whole page about it!
[/quote]
[quote name='discreet' timestamp='1437592681' post='2827442']
Yes.
[/quote]
http://www.youtube.com/watch?v=rX7wtNOkuHo

[Bill Fitzmaurice]

[quote name='tauzero' timestamp='1437589404' post='2827389']
[url="http://sound.westhost.com/tweeters.htm"]http://sound.westhost.com/tweeters.htm[/url] - why tweeters blow, plus interesting bits on the trend to heavy compression in the recording industry and why using a bigger amp isn't the answer.
[/quote]Most of that is correct, but it doesn't really apply to bass amps, and only partly with respect to PA. That's because bass amps and PA systems routinely pass clipped signals, some created in the power amps, but most created much earlier in the signal chain. Those clipped signals result in abnormally high THD, and that does kill tweeters. It's true that a larger power amp usually won't make any difference, because more often than not the clipping takes place in the pre-amp or in the mixing console.

[Dan Dare]

Good point, Bill. Despite the established consensus that one should drive preamps as hard as possible for best signal to noise, I find I get a cleaner sound out of my bass head (EBS 350) by running the output gain high and keeping the preamp gain well down so that the clip light never illuminates. I run my mixing desk channels well below the red, too. I think the advice originates from the time when circuitry was far noisier than it is today - you had to keep the hottest possible signal to mask that noise. As you say, passing an already clipped signal to a hefty power amp is asking to destroy your drive units.

[Bill Fitzmaurice]

[quote name='Dan Dare' timestamp='1437667212' post='2828060']
Good point, Bill. Despite the established consensus that one should drive preamps as hard as possible for best signal to noise, I find I get a cleaner sound out of my bass head (EBS 350) by running the output gain high and keeping the preamp gain well down so that the clip light never illuminates. I run my mixing desk channels well below the red, too. I think the advice originates from the time when circuitry was far noisier than it is today - you had to keep the hottest possible signal to mask that noise. As you say, passing an already clipped signal to a hefty power amp is asking to destroy your drive units.
[/quote]Actually the advice dates to the early days of pro-sound when 100 watts was a huge amp, and instead of using enough of them to do the job sound providers did clip the power amps, resulting in this from JBL:
http://www.jblpro.com/pub/technote/lowpower.pdf

[Phil Starr]

some really interesting stuff here, if you've skipped all or some of the original articles or Bill's JBL article then I'd strongly recommend you have another look.

The two views aren't that different though. Put simply a clipped sine wave can be described mathematically as a sine wave with added harmonics. Hence we talk about harmonic distortion. To be fair this simplification is there mentioned in the JBL piece. Once you start using words rather than maths to explain these issues you inevitably simplify and resort to analogy.

The practical reality is that distorted/clipped sounds contain more energy than u distorted sounds and crucially this will go through the crossovers. As musicians we regularly use distortion, whether by 'overdriving' amps or adding effects and this will imperill tweeters.

The dynamic range/compression thing is informative. Generally the dynamic range of live music is greater than recorded, one of the reasons recorded music rarely sounds like live music. The original articles make it clear they are referring to hi Fi speakers and refer separately to professional high power drivers, the stuff we use. All my articles use a dynamic range of 40dB or a difference between average and peak power of 20dB and this is also the assumption I use in my speaker designs. For the longevity of the speakers I'd advise never using an amp rated for more power than the speaker with your bass. For PA I wouldn't advise anyone to go for more than an extra 3dB of power or double that of the speakers, but only if you are going to run with no clipping, which means knowing exactly how to use your desk and its meters!

The trouble with all advice from techs to musicians is that we are dealing with simplifications of multiple variables, the greatest of which is the slushy organic bit operating the knobs and buttons. That's why the advice that people like Alex and Bill give can't be definitive and sometimes seems contradictory, they don't have the power to see everything you'll do with that advice.

Good articles though, thanks for putting them up.