Avoid blowing speakers!

[garyod7]

There's a great pinned topic on impedance etc already but its still hard to grasp - I had a GK MBE410 800w 4ohm cab with a GK MB800 800w head and by running the head master volume and gain just above 12 o'clock a speaker blew in the cab. If both are 800w and cab is 4ohms I don't see how it blew when I consider that the volume and gain both went to about 5pm on the dial! I was nowhere near topping it out to my mind.

I'm now using markbass 151 traveler and 102 traveler with tube 500 (actually it says 600w on back instead of 500w though which is less common?!) and its a much bigger sound and I'm very happy with it, but how do I know if I'm pushing cabs too hard to the point that they blow and avoid a repeat?! The GK stuff didnt sounded strained then boof, night ruined!

[Bill Fitzmaurice]

Nothing lasts forever. I'd only suspect a problem if you'd blown all four drivers. But don't assume that the knob positions have any relationship with the amp output. All that 12:00 indicates is that it's more gain than 11:00 and less than 1:00.

[hubrad]

Did you get sparks? I once had a speaker blow, well within power, and I was alerted to it by one of the guitarists pointing and laughing! Sparks , smoke, the works. :-D

[JTUK]

It happens...but hopefully you'd hear some sort of distress through the cab.. but that isn't always easy when
things are loud and doubley complicated if running FX.

Chassis are much better these days but I'd never line up a 500w amp with a 500w cab by choice...I'd always
want more 'cab'.
I think it would be quite easy to break any speaker if you were a) being stupid enough, or unlucky enough
and I don't mean it the wrong way...

[garyod7]

The stuff was 2 months old by the way just when you mention how long stuff lasts or doesn't!

Didn't sound distressed at all but yeah in the heat of the mix maybe its just harder to detect that.

My immediate conclusion is that it definitely WAS something I've done in error so no offence taken lol I can operate a bass guitar but less skilled in the tech areas of heads and cabs as you can all tell, my worry is that the 500/600w head I have now is powering 2 400w 8 ohm cabs and when you mention having more 'cab' - i still have more head power which leaves me open to over running at this point

[garyod7]

No sparks haha!! Just farty noises and I took all bottom end out to limp to the end of the gig! Guitarist was laughing though 😂

[Bill Fitzmaurice]

[quote name='garyod7' timestamp='1446500800' post='2899920']
The stuff was 2 months old by the way just when you mention how long stuff lasts or doesn't!
[/quote]At 2 months old it should be under warranty.

[garyod7]

Yeah it was all covered but was a bit of a rigmarole resulting in me now having the markbass gear, I know what you mean by the way about the dials not really affecting it like I'm thinking, just makes it trickier to know where I stand when judging how hard gear is being worked though i guess, bit of a minefield!

[Guest bassman7755]

You must have been playing ridiculously loud to blow a 4x10 800w cab, or ... have huge amounts of low frequency boost dialled in. I've never blown a speaker and honestly don't think I've ever been close to it even when I've powering a 750 watt cab with a 1.6K PA amp (a setup I used for about 10 years).

As mentioned above the master volume position means nothing, you could have been kicking out full power (especially if you have a load of bass EQed in).

Edited November 2, 2015 by bassman7755

[garyod7]

It didn't sound particularly loud, not as loud as the markbass 151 traveler or standard both 400w which was the odd thing, id expect serious volume from the 800w stuff even though I see from reading here that decibels and wattage aren't linked

[xgsjx]

I'd be inclined to suspect there was already a fault with the driver (going on what you've said so far).
Though if you had the lows boosted quite a bit, then that could cause an issue.

[KingBollock]

The only speaker I ever "blew" was a PA bass cab. We were doing a party for a mate's birthday and were doing it for free (even though it was a 320 mile round trip...). My mate was helping lift the gear in and dropped the cab. Not hard, it only fell a few inches and didn't damage the cab itself, just killed the speaker.

(Carrying all the gear so far also took out one of the suspension leaf springs in our van. That damned party cost us a fortune!)

[Guest bassman7755]

[quote name='garyod7' timestamp='1446504423' post='2899955']
It didn't sound particularly loud, not as loud as the markbass 151 traveler or standard both 400w which was the odd thing
[/quote]

Id expect to never get anywhere close to needing to run a properly functioning decent quality 800 watt bass rig at full capacity, something was wrong somewhere.

[chris_b]

I bought a brand new Mesa Boogie 400+ that failed as soon as we switched it on in the shop.

Stuff happens. That's why there are warranty arrangements, and good people who will stand behind their products.

[Jazzjames]

Without having looked at the back of a Markbass tube 500, perhaps the 600w rating is the watts it will use when plugged in, and not the amount of watts that it will deliver to the speakers?

Stuff breaks...it sounds like the speaker was defective. In future, just listen to your rig if you're playing loud, it will start to fart out before you blow a speaker. If it's farting out, take some of the low end out, and/or turn down the volume.

[garyod7]

Without having looked at the back of a Markbass tube 500, perhaps the 600w rating is the watts it will use when plugged in, and not the amount of watts that it will deliver to the speakers?

Ah cool, that's probably it!

Appreciate the replies folks by the way, usually I'm just a 'watcher' on the forums but thought I should take advantage of some knowledgeable people 👍

I thought there might have been an issue with the head somehow cos the replacement cab did the exact same thing after about 2 gigs lol when the distributed took the first cab away they said they didn't note any fault, but the guys in the music shop heard it same as in did, id have thought when a speaker went, that's it, but this seemed more intermittent. I ran the head with mids and highs boosted a bit but bass at 12oclock or cut at times, or I got a rubbish boomy tone.

[garyod7]

King Bollock - the perils of doing favours 😂

[Guest bassman7755]

[quote name='garyod7' timestamp='1446560175' post='2900294']
King Bollock - the perils of doing favours
[/quote]

No good deed goes unpunished

[barkin]

[quote name='garyod7' timestamp='1446500800' post='2899920']
...my worry is that the 500/600w head I have now is powering 2 400w 8 ohm cabs and when you mention having more 'cab' - i still have more head power which leaves me open to over running at this point
[/quote]

500W into 2 x 8Ohm cabs, the power will be split equally - 250W into each.

[garyod7]

Ah, great cheers barkin 👍

[Phil Starr]

If you want some practical advice, with a bit of explanation? Understanding why speakers blow helps and there are essentially two reasons why they blow early. One is that they overheat and the other is that you push the sound levels up so high that the speaker moves so far the coil comes out of the magnet. The problem is that speakers are most likely to be damaged by the second problem of over-excursion but they are rated for the first problem by their ability to handle heat.

So your 400W cabs should be able to handle a 400W amp all day, so long as you don't put bass through them. Sing as loud as you want or play a skinny string or anything above 7th fret on the A string you'll be fine.

The problem comes when you go down an octave, making bass sounds needs you to shift a lot of air so you need more power and the speaker has to pump backwards and forwards more to shift all that air. Eventually it moves so far two things happen, either the delicate coil hits the back of the magnet or it moves out of the magnet gap, either way it gets damaged. Once the coil leaves the gap the cooling fails and the rating of the speaker goes right down. Your 400W speaker becomes maybe a 100W speaker. That's usually why they fail.

So apart from using much more speaker than amplifier how do you stop it? You limit excursion.

1. Get a filter that stops the deepest bass (like a Thumpinator)
2. use eq wisely. A tweak on the bass boost (say 2 o'clock) will make your speaker work twice as hard. (10 o'clock half as hard) Never go to full bass boost unless you are absolutely confident you have enough capacity in the speaker.
3. watch the effects, an octaver means you need twice the power handling if you are going to play anything lower than 7th fret E. Amp modelling and quite a lot of effects boost the bass, using two in line can push this to unexpected levels.
4. If you want a bassier sound it is often better to cut treble and mids and then turn the volume up.
5. think about keeping the deepest bass out of your rig and putting it through the PA bins.

If you really have to have that trouser flapping, deep bass, distorted sound then you are going to have to have more power and more speakers but the Thumpinator or similar will help a lot and they are far less audible than you might expect.

BTW I think BFM was spot on, this failure was down to a faulty component and should have been sorted under warranty.

Edited November 4, 2015 by Phil Starr

[garyod7]

Nice one Phil thanks for the advice there 👍

[alexclaber]

It's extremely rare to blow a woofer with bass guitar without it sounding pretty distorted first. If something does go pop without any warning overdrive, especially something fairly new, then it's most likely to be a manufacturing fault.

Phil, I'd say you've got things the wrong way around in terms of excursion for most half-decent modern bass guitar woofers. Older designs which don't have vented motors do indeed rely on the magnetic gap removing heat from the coil via radiation but most modern drivers have vented motors so getting the woofer pumping back and forth, even if the coil is moving out of the gap, will remove more heat via convection. Also, most decent modern MI/PA drivers use the suspension to limit excursion to reduce the chance of bottoming out or jumping out of the gap and have a decent margin between Xmax (where distortion tends to rise significantly) and Xlim or Xmech (where permanent damage occurs).

Bass boost does tend to cause problems though, because most cabs are quite a lot less sensitive at 50Hz than at 100Hz, so you can put a lot more power in without getting a lot more sound out. Also, most cabs are tuned to the 40-60Hz region, which means the impedance is low so much more power actually flows in that region that at 80-120Hz, so you have a double whammy of it taking more volts to create the sound and more current flowing for the volts, so more true power hitting the voice coil. And at that low impedance region the woofer is moving much less because it's operating against the high pressure load of the tuned port, and the port is creating most of the acoustic output, so there's less voice coil movement to pump the hot air out of the motor.

[Phil Starr]

[quote name='alexclaber' timestamp='1446649486' post='2901137']
It's extremely rare to blow a woofer with bass guitar without it sounding pretty distorted first. If something does go pop without any warning overdrive, especially something fairly new, then it's most likely to be a manufacturing fault.

Phil, I'd say you've got things the wrong way around in terms of excursion for most half-decent modern bass guitar woofers. Older designs which don't have vented motors do indeed rely on the magnetic gap removing heat from the coil via radiation but most modern drivers have vented motors so getting the woofer pumping back and forth, even if the coil is moving out of the gap, will remove more heat via convection. Also, most decent modern MI/PA drivers use the suspension to limit excursion to reduce the chance of bottoming out or jumping out of the gap and have a decent margin between Xmax (where distortion tends to rise significantly) and Xlim or Xmech (where permanent damage occurs).

Bass boost does tend to cause problems though, because most cabs are quite a lot less sensitive at 50Hz than at 100Hz, so you can put a lot more power in without getting a lot more sound out. Also, most cabs are tuned to the 40-60Hz region, which means the impedance is low so much more power actually flows in that region that at 80-120Hz, so you have a double whammy of it taking more volts to create the sound and more current flowing for the volts, so more true power hitting the voice coil. And at that low impedance region the woofer is moving much less because it's operating against the high pressure load of the tuned port, and the port is creating most of the acoustic output, so there's less voice coil movement to pump the hot air out of the motor.
[/quote]

I was trying to keep it simple Alex, and I'm making the assumption that an 800W 4x10 isn't using the same drivers you use. There are still a lot of ceramic magnet speakers out there that don't have vented motors, though you'd expect it with neo drivers at least. Even so I doubt that the cooling is improved by the coil leaving the magnetic gap. There's also the behaviour of the speaker below the tuning of the port to consider. Surely you aren't saying the speaker runs cooler when the excursion is pushed up by increased power?

The OP asked about how to avoid blowing speakers and the best way is surely to avoid Xlim. I wanted to give a few practical tips which anyone reading could take to avoid having to replace speakers.

I'm also not sure most bassists would recognise rising distortion in a gig situation with a set of cymbals by their ear, two guitarists going flat out and all sorts of pedals in their sound chain. I'd want the safety of my rig designed in and not dependant upon my noticing at the climax of a gig.

[Dad3353]

All precious stuff so far, with the different spotlights on the subject adding to the usefulness. If I may, I'd like to have some expert opinions on the rather modern tendency to use, not simple distortion, but outright fuzz on bass, giving a waveform much closer to square wave than sine. Does this not have a bearing on the cone behaviour, as it is effectively receiving almost a DC element for a good deal of its cycle. Would that increase the heat dispersion problems..? Is this negligible, or something worth considering when estimating power handling requirements for speakers..? Please ignore if too far off topic.

Edited November 5, 2015 by Dad3353