Damaging Your Expensive Ported Cab?

[Dan Dare]

[quote name='LukeFRC' timestamp='1482402662' post='3200174']


Part of the problem is that there's a large amount of bass players who think the answer is more bass.
I play at a church, big stone building, modern glass wall at the back and massive resonance down low. We have no backlineand a IEM system and the FOH.
PA folk often end up with a massive mush in the bottom end. Its taken me a year and demonstrating that turning on the desk's HPF on the bass guitar cleans up the sound no end. I only have to suggest they do the same on the acousitic guitars, keys and kick drum and we may one day get it sounding good!
[/quote]

+1 Luke. Relatively few appear to realise that less often equals subjectively more when dealing with low frequencies. Quantity vs quality and all that. And as others say, little point in wasting amp headroom on subsonic mush/rumble.

[Chienmortbb]

I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm) , the point at which the voice coil is in danger, is exceed at 36.7Hz, 5 Hz above low B on a 5 string. Indeed you have to reduce the power at 31Hz to under 200W to avoid exceeding XDamage.
[url="https://flic.kr/p/R8Gr7e"][/url][url="https://flic.kr/p/R8Gr7e"]Kappalite3012HO Cone excursion 400W[/url] by [url="https://www.flickr.com/photos/149986878@N08/"]chienmortbb[/url], on Flickr

Edited January 11, 2017 by Chienmortbb

[lowhand_mike]

ow my head

interesting read though even if i dont understand some of it

[Phil Starr]

[quote name='Chienmortbb' timestamp='1484147758' post='3213040']
I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm) , the point at which the voice coil is in danger, is exceed at 36.7Hz, 5 Hz above low B on a 5 string. Indeed you have to reduce the power at 31Hz to under 200W to avoid exceeding XDamage.
[url="https://flic.kr/p/R8Gr7e"][/url][url="https://flic.kr/p/R8Gr7e"]Kappalite3012HO Cone excursion 400W[/url] by [url="https://www.flickr.com/photos/149986878@N08/"]chienmortbb[/url], on Flickr
[/quote]Thanks for putting this up. The point for those that don't know about all this is that the curve is the same for all speakers in a tuned cab. Excursion rises steadily as the frequency falls but the tuning of the cab dampens the cone movement at the tuning frequency. You can see the dip in excursion at 50hz really clearly on the graph. At this point the port is doing all the work and the cone movement is damped because it is working hard to pump air through the port.

The Kappalite was chosen because it is about as good as a driver gets, and has been recommended by several designers or used in their cabs. There's every chance your speaker wont behave as well unless you use very expensive cabs.

Now moving beyond Xmax/the speakers limiting point doesn't mean instant destruction any more than running a cars revs into the red means the engine will blow up. It does mean you are taking a risk though. What happens next depends upon the exact circumstances but at this point the built in safety designs aren't necessarily going to protect you, and there is no red light on most speakers.

More later, I have to practice

[MoonBassAlpha]

Does anyone know if the Genz Shuttle 3.0 AND 6.0 have h.p. filtering, and if so, at what slope?
Cheers, MBA

[Passinwind]

[quote name='MoonBassAlpha' timestamp='1484229478' post='3213748']
Does anyone know if the Genz Shuttle 3.0 AND 6.0 have h.p. filtering, and if so, at what slope?
Cheers, MBA
[/quote]

They have quite a bit (more than I like TBH) but I've never measured the exact response, which probably changes quite a bit depending on settings, as many amps do.

[Lw.]

Whilst the numbers & that graph look great - I don't understand what any of it means. So - are we damaging our expensive ported cabs or not?

[Bill Fitzmaurice]

[quote name='Lw.' timestamp='1484237779' post='3213865']
So - are we damaging our expensive ported cabs or not?
[/quote]When's the last time you had to replace a driver due to mechanical damage?

[Beer of the Bass]

[quote name='Bill Fitzmaurice' timestamp='1484242936' post='3213940']
When's the last time you had to replace a driver due to mechanical damage?
[/quote]

While I've never had to replace one myself, I've played a lot of rehearsal room or venue house rigs with damaged drivers, presumably from over-excursion. It either shows up as individual dead drivers in a multi-driver cab, or just that distorted voice coil rub kind of sound. Sometimes that's from outright abuse, sometimes it's from simply not having enough rig for the room and running it night after night, but someone out there is doing it.

Edited January 12, 2017 by Beer of the Bass

[Phil Starr]

[quote name='Lw.' timestamp='1484237779' post='3213865']
Whilst the numbers & that graph look great - I don't understand what any of it means. So - are we damaging our expensive ported cabs or not?
[/quote]

That deserves a serious answer.

This was the whole reason I started this thread. Some people are damaging speakers, usually people who can ill afford it, others are using their gear well within their limits and won't ever have a problem. Some of us probably sail nearer the wind more than is sensible but get away with it. We get quite a few questions on BC about matching amps to cabs and sometimes the advice is better than others. There is an inherent problem with all ported cabs and most bassists will be unaware of it. If you know the problem of subsonic over excursion is there then it's easy enough to avoid. Basschat discussions tend to be pretty measured and by sharing information most people on here get to know their technical side pretty well. As a result the advice newbies get on BC is usually pretty spot on. Simply if there is a point beyond which you shouldn't go it is better to know where it is.

It's also true that an educated customer will ask questions when making purchases and the makes manufacturers cough up more information about the design compromises they inevitably make. I'm sure the whole lightweight movement has been sped up by BassChat and TalkBass. Wouldn't it be great if amp manufacturers published details of any high pass filtering in their manuals and then started making a feature of it. That'll only become a selling point if we all start asking questions.

So, the simple answer is a few people are blowing cabs, but it is easily avoided if you know what you are doing. I'd be pretty happy if I thought even half a dozen people avoided the heartbreak of a blown speaker as a result.

[Lw.]

@Bill Fitzmaurice - never, though if I'm being honest I don't think I've ever pushed any cabs I've owned that hard.

@Phil Starr - thanks for the response & educational posts!

[sratas]

view.....if I knew this info when I purchased my Barefaced Big Baby 2, I sure wouldn't abuse it as I actually did with subsonic material to breaking it in...it seems that I have been lucky and/or Barefaced cabs are idiot proof.
Hit it with wattage and a 20 Hz sine wave (with brief pauses between bursts) for 2 days...

[alexclaber]

[quote name='sratas' timestamp='1484305147' post='3214474']...Barefaced cabs are idiot proof.[/quote]

They pretty much are, for a given value of idiot!

[VTypeV4]

I've done a few (and only a few) drivers (mainly in the PA world) although nearly all have failed thermally - worst case was a succession of 3 Eminence Omega Pro 18s in some folded horns ten years ago - they still looked great but were dead with a black coil on post-mortem.. The other pair of horns still have their original JBLs working in good order..

The only driver I've mechanically broken was a Celestion BG12-100S in a Trace 712 about 15 years ago. It flapped to the point where if I'd have sellotaped a sheet of A4 to the coil the sound would have been cleaner. Not sure if it was a manufacturing fault or it was simply under specified (both I suspect) but Trace changed it under warranty for a Q2025 or it might have been a K12T - can't remember but never had any trouble after that..

As an in-house engineer, I see many an abused bass rig with the driver(s) crying out for a rest!

[Phil Starr]

[quote name='Chienmortbb' timestamp='1484147758' post='3213040']
I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm) , the point at which the voice coil is in danger, is exceed at 36.7Hz, 5 Hz above low B on a 5 string. Indeed you have to reduce the power at 31Hz to under 200W to avoid exceeding XDamage.
[url="https://flic.kr/p/R8Gr7e"][/url][url="https://flic.kr/p/R8Gr7e"]Kappalite3012HO Cone excursion 400W[/url] by [url="https://www.flickr.com/photos/149986878@N08/"]chienmortbb[/url], on Flickr
[/quote]

Apologies to those who got all this already but it seems a few people are struggling to under stand the graph so I thought i'd use a tea break to try and explain what it shows.

The grey line shows how far the speaker cone moves backwards and forwards at different frequencies with 400W of signal passed through it. The speaker itself is rated at 450W so it shouldn't burn out with this sort of power. The horizontal red line is the limits to the excursion of the speaker called Xmax. If you look at 100Hz on the bottom line (kind of mid bass) you can see that the excursion at 400W is 6mm. At this point the speaker cone is going 6mm forward and 6mm backwards a total of 12mm travel.

Below this frequency the speaker just exceeds it's Xmax limit, a teensy bit. At this point the speaker coil will just be leaving the magnetic field and distortion will start to rise. If the coil is outside the magnet for any length of time it will also start to heat up excessively because the magnet conducts a lot of the heat away. Going over Xmax isn't good, though it is not going to instantly destroy your speaker.

Now if you look at the grey line at 50Hz you can see it has dipped down. That's the effect of the port, the air in the port is resonating and making most of the sound the energy to do this is damping down the movement of the cone which is now only moving just under 2mm

Now if you go and look at 40Hz (roughly bottom E) the movement is 9mm well outside the magnetic field and at 30Hz (roughly bottom B on a fiver) it is 19.5mm which is beyond the mechanical limits of the speaker. At this point I couldn't tell you what is happening without dissecting the speaker. Some of them are mechanically limited by the suspension and some of them hammer the coil on the back of the magnet, Some of the experts will tell you that going beyond Xmax (6mm in this speaker) is dangerous to the speaker some will tell you Xlim (12.5mm) is where the damage happens.. I'm going to sit on the fence a little, you might get away with 10mm for a short while and don't mind a bit of distortion but don't go near 12.5 if you want your speaker to last.

Now most people who play bottom E won't be playing it at 400W even if the rest of the sound of their bass in total is 400W. Most of their sound is made of higher harmonics but the damaging deep bass will be greater if they use the neck pickup, much greater if they use and octaver or they use a lot of bass boost. All of these are the booby traps which cause some people to blow speakers when most of us don't. Protecting us in the other direction is the natural bass filtering caused by the positioning of the pups and any filtering built into our amps.

Playing 400w bottom B into the speaker and you can see you are asking a 6mm limited speaker to travel 19mm. Put another way at this frequency it can only handle 6/19ths of 400Watts, about 125W.

There's another little booby trap here too. If you are pushing 400W through your speaker then it will get very hot, heating the coil will increase it's resistance and make it quieter, if you are struggling then you might be tempted to turn it up to compete with the rest of the band, which in turn heats it a little more. If you'd brought a second speaker you'd be pushing less than half the power (because two identical speakers are more efficient than one) and you wouldn't be getting any of this thermal compression.

Anyway tea break over and I hope the graph makes a little more sense now.

[markstuk]

I was looking at driver spec sheets (3012ho) and noted that the impedance appears to go into tens of ohms at low frequencies. Does this not limit the amount of power your amp delivers at low frequencies ?

[Bill Fitzmaurice]

[quote name='markstuk' timestamp='1484582603' post='3216481']
I was looking at driver spec sheets (3012ho) and noted that the impedance appears to go into tens of ohms at low frequencies. Does this not limit the amount of power your amp delivers at low frequencies ?
[/quote]Speakers are voltage driven devices, not power driven devices. An amp will deliver a constant voltage into any load.

[Phil Starr]

[quote name='Chienmortbb' timestamp='1484147758' post='3213040']
I have just done a plot of the cone excursion of a well known, well loved driver the Eminence Kappalite 3012HO. The box is 50L and the tuning frequency is 50Hz

The power is 400 watts, the stated power of the 3012HO. The red line is Xmax, the maximum excursion at which the voice coil is under the influence of the magnet. It is not dangerous to exceed XMax by a small amount. However the Xlim or XDamage (12.5mm)
[url="https://flic.kr/p/R8Gr7e"][/url][url="https://flic.kr/p/R8Gr7e"]Kappalite3012HO Cone excursion 400W[/url] by [url="https://www.flickr.com/photos/149986878@N08/"]chienmortbb[/url], on Flickr
[/quote]

OK Tea break again

So.... our computer model shows a typical curve which pretty much applies to any ported cab. Which isn't saying sealed cabs have no problems by the way. Cone movement increases as the frequencies go lower but the port controls any over excursion at the tuning frequency and gives you an extra 3db of bass. The problem for the cab is that there then isn't much to control the cone's movement below the port's area of operation. Below 40Hz or bottom E in this cab and at this power the speaker is at risk. +/- 9.5mm or 19mm of travel doesn't leave a lot of room for error. You won't destroy your speaker instantly but unless your the sort of wierdo like me that does calculations in your head during a gig it's a worry you don't want. So, what can you do about it?

Well all the trouble is caused by too much power, so turning down is an option, turning down 3dB will halve your excursion but only be a little quieter.

Better still add an extra speaker. With a solid state amp that will give you an extra 6db or thereabouts, that reduces your excursion to a quarter. Actually if the speakers run cooler you won't have that thermal compression effect either and your amp won't have to work so hard.

Looking at the graph it's plain to see that all the nastiness is below 40Hz, If you don't know the frequency response of your amp it may not be filtering that out so get a high pass filter. We don't really hear most of the subsonic stuff so it won't make as much difference as you expect.

Watch your tone controls. If you have a traditional bass/middle/treble set up then they usually give you about 12dB of boost. Just turning it up a notch to 2 o'clock will probably double your excursion below 40Hz. fine if you are bubbling along at 100W, not so good if you are already caning it. If you turn down by a notch of course you will halve your excursion. If I turn up to a venue with justone speaker and it needs a lot more volume than I expected that's what I'll do. Watch any octavers too, they may have subsonic filters in but you really don't want to boost the output down there without complete confidence in your rig.

Push your rig into a corner or at least against the back wall, the reinforcement from each surface will give you an extra 3db in the bottom octave and you can then cut bass but retain as much of your tone as possible.

Tea break over, I'm bound to have forgotten something so I'll wait and see what people add and then update that second post to save anyone from having to read the whole thread through.

[alexclaber]

Some things to point out:

1. Few amps have flat response below 50Hz - there's usually some kind of high pass filtering, even if it's just the side effect of capacitors in the signal chain.
2. Although some basses can have relatively high output in those super low frequencies that isn't part of the inherent sound of bass guitar - too much super deep low content and it doesn't sound musical.
3. Speakers do not behave linearly beyond Xmax - the motor strength drops and with good designs the suspension compliance decreases, which means you have to put a lot more power in to get the excursion that oversimplified graph suggests.

Bear in mind that plenty of bass cabs with low excursion (<3mm) drivers are tuned to ~60Hz and used with amps in the 300W+ range - if they were behaving as suggested by these graphs people would be replacing all the drivers after their first loud gig. Woofers get blown a fair bit in some cabs but not that often!

[Bill Fitzmaurice]

[quote name='alexclaber' timestamp='1484656628' post='3217193']
Bear in mind that plenty of bass cabs with low excursion (<3mm) drivers are tuned to ~60Hz and used with amps in the 300W+ range - if they were behaving as suggested by these graphs people would be replacing all the drivers after their first loud gig.
[/quote]Even if they did there's another consideration. Going beyond xmax doesn't cause damage, reaching xlim/xmech does. The Beta 10 has 3mm xmax, with 8.6mm xlim, so there's a lot of room for overshoot. The BP102 with 6.2mm xmax will go a lot louder than the Beta 10, but with 10mm xlim there's a lot less overshoot capability, so despite the higher output capabilty of the BP102 you're far more likely to see them creased than Beta 10s. A minimum 2:1 xlim to xmax ratio is prudent. If that much is not available then it's wise to not only high pass but to limit the maximum voltage applied to the driver as well. That's seldom seen with electric bass rigs, but in high end PA it's SOP.

[alexclaber]

[quote name='Bill Fitzmaurice' timestamp='1484658293' post='3217213']Even if they did there's another consideration. Going beyond xmax doesn't cause damage, reaching xlim/xmech does.
[/quote]

Yes, that's what I was implying but failed to make clear - if Xlim is twice Xmax then this simplistic model would tell you it takes four times as much power to reach Xlim as Xmax at a given frequency but thankfully the reality is much less worrying. The Xmax to Xlim ratio is a critical thing - before my Barefaced days I creased four woofers due to their low Xlim to Xmax ratio, low efficiency (needed a really powerful amp to get loud) and their low tuning. And I was using a 30Hz high pass filter on the amp!

[Chienmortbb]

[quote name='Bill Fitzmaurice' timestamp='1484658293' post='3217213']
Even if they did there's another consideration. Going beyond xmax doesn't cause damage, reaching xlim/xmech does. The Beta 10 has 3mm xmax, with 8.6mm xlim, so there's a lot of room for overshoot. The BP102 with 6.2mm xmax will go a lot louder than the Beta 10, but with 10mm xlim there's a lot less overshoot capability, so despite the higher output capabilty of the BP102 you're far more likely to see them creased than Beta 10s. A minimum 2:1 xlim to xmax ratio is prudent. If that much is not available then it's wise to not only high pass but to limit the maximum voltage applied to the driver as well. That's seldom seen with electric bass rigs, but in high end PA it's SOP.
[/quote]Bill the drivers in the example were chosen at random and I quite agree that exceeding Xmax is not a problem. XLim is the damaging area. However once you exceed XMax your driver is operating outside of the control of your amplifier and in a very non linear fashion, under only the the control exerted by the suspension of the driver and the "spring" in the cabinet.

[alexclaber]

[quote name='Chienmortbb' timestamp='1484667643' post='3217320']...once you exceed XMax your driver is operating outside of the control of your amplifier and in a very non linear fashion, under only the the control exerted by the suspension of the driver and the "spring" in the cabinet.[/quote]

Yes but that works both ways. Once you exceed Xmax the amp cannot drive the cone with the same motive force because BL (magnetic field strength multiplied by metres of coil in the magnetic field) drops as more coil leaves the gap.

[Bill Fitzmaurice]

[quote name='alexclaber' timestamp='1484669867' post='3217350']
Yes but that works both ways. Once you exceed Xmax the amp cannot drive the cone with the same motive force because BL (magnetic field strength multiplied by metres of coil in the magnetic field) drops as more coil leaves the gap.
[/quote]+1. By far the main issue with providing more voltage swing than the xmax can make use of is heat build up. When you factor in thermal compression as well it becomes obvious why thermal failures predominate

[Phil Starr]

Many thanks to Alex and Bill for their contributions. To be fair the choice of the Kappalite as our example driver wasn't completely accidental, it's one of the best drivers widely available and both of them have either used it in their designs or recommended it, for good reasons.

Ironically when we were developing our own 12" design I was the one gung ho about Xlim being the limit and drivers being designed so that the suspension would prevent the coil hitting the back of the magnet. Stevie has always argued that operating a speaker with the coil outside the Xmax limit isn't a good thing to do. He also pointed out that whilst I asserted that any driver designer worth their pay would put a suspension designed to progressively soft limit excursion into their speakers I didn't have any actual data as this isn't freely available on any of the published data sheets.

This thread wasn't really aimed at those who already understand all this, though I'm really genuinely grateful to have everyone's input. So I'm going to try to sum up this little bit. I've also tried to be very careful in my language, apart from my over the top headline for the thread (sorry ) I hope that in any statement where I've been summing up complex data I have qualified them with words like sometimes, often, possibly and so on. I'm a science teacher (now retired) so I ought to have got that right.

So, the summary so far

Speakers fail, not often but they do. Bass players, by the nature of low frequencies push their speakers harder than most people. Most speakers when they fail do so by overheating, a few by physically exceeding the limits of travel. Whilst the coil is working within the speakers magnetic field the way it is designed to do it is pretty unlikely that you will damage the speaker. If you try to go beyond the limits where the manufacturer says you will damage the speaker you will damage the speaker. In the nether regions between Xmax and Xlim the speaker will heat up more quickly and depending upon how long it stays in this region and the chances of failure increase.

Different models of speaker will all have slightly different characteristics and their reliability and the details of their failure modes will vary, though you are unlikely to know the details before they fail. However all ported cabs will exhibit a curve broadly like the one here (with two hills and one valley) the danger areas are the hills where excursion is highest and the biggest danger, unless the speaker is really poorly designed, is in the subsonic area, where all you would hear is unwanted crap. In the hilly areas of the curve your speaker won't be able to continuously handle it's rated power and will start to overheat.

Finally if you know this you can avoid going near the limits of your speakers with a few simple steps. Knowledge is power (handling) If you want more reading then this is worth a look [url="http://sound.whsites.net/articles/speaker-failure.html"]http://sound.whsites...er-failure.html[/url]

Edited January 19, 2017 by Phil Starr