Stadium Speaker System Blowing

PA12Tray

Standard Member
Joined
Sep 22, 2021
Messages
9
Reaction score
3
Points
1
Age
53
Location
Mandeville, LA
Hello,

First I'm going to admit I know virtually nothing about sound systems so my terminology may not be accurate, or my description short. I can ask more questions to get additional details if someone here tells me what to ask... My question is related to a new speaker system we had installed at our football stadium.

The stadium system includes a mixer, amp and 4 large speakers. In the input to the mixer we have the wired microphone as well as an input line that we can plug a cell phone into for music.

The day of installation, two of the speakers were damaged / blown and had to be replaced, only the large bass heads, the horns were fine. Last week during halftime at the game we blew out 4 speakers (Bass and Horns) as well as the amp. This was when the dance team was using a cell phone to play music.

During the game the announcer also uses a cell phone to play music between plays when the band is resting.

We are being told that by swapping inputs (Cell Phones), something with the compression rate or downloaded music is causing the amp and speakers to blow. To me this does not sound very feasible, my thoughts are why would many other stadiums systems not be damaged, I'm sure there are multiple cell phones used and inputs swapped. Any other thoughts as to what might be happening or could that actually be the cause? If it is the cause, how can it be prevented knowing that there will be multiple users of the system.

Thank you
 
Why not ask the company that installed the system?
 
We have, he is the one telling us that changing a cell phone from one to another to play music is what caused the amp and speakers to blow out. To us this doesn't make much sense thinking many other systems in stadiums would be experiencing the same thing with the various people using phones to play through the sound system. Also to note the volume was set about half way, we have the system in a case that will only allow a user to turn it on and off and not adjust any of the other settings. Company that installed it was the one that set these settings.
 
More information, we have the 4 speakers with 2 on each channel set up in parallel.

Each speaker is rated for 8 ohms at 2000 watts. From my understanding this would mean that the amp would need to provide at least 2000 watts at 4 ohms per channel. The amp is rated at 1985 watts at 4 ohms per channel.

Google tells me that the amp should provide at least 50% more power than required at the Ohm rating to prevent damage to the speakers.

Could this be our problem with an undersized Amp by it not providing enough power to them?

Again thanks for the help
 
We have one wire coming from each channel of the amp. Then on the back of one of the speakers (Speaker 1) that wire is tied into one positive and one negative. Then we take another wire from Speaker one spare positive and negative and run it to Speaker 2.

We do the same for the other channel for the remaining 2 speakers ( 3 & 4).
 
Ok, crossed posts

Looks from the specifications that you need 2000watts per channel for the 4 speakers at 4Ohm

A rule of thumb is to match the program power (1000Watt per speaker in your case) to the amp output at the correct impedance. Usually ignore the peak power rating
 
Those speakers are rated at 500W RMS, 1000W program, but are not adequately protected if the input gain to the mixer is set too high. The amplifier can produce much higher power than the speakers can withstand long term.

I would suggest you need a limiter between the mixer and the amplifier, so that the level cannot exceed the long term power handling of the speakers. Something like this will work OK and can be set up to hard limit the signal and prevent overload. Behringer Ultradrive DCX2496LE Loudspeaker Management System at Gear4music

4 speakers to cover a football stadium is probably not enough and users are therefore turning the gain up too far to compensate for this. You probably want another 4 speakers and a 2nd amplifier to balance things out a bit.

Most important bit: You need to listen to the sound and when it starts to distort and sound harsh, turn it down! High levels of distortion and too much level are killing your system and you need to ensure that the operator is aware of this and backs the levels off. You cannot rely on any device to provide total protection and some user skill is required.
 
Ok, so looks like the Amp is correct size for the speakers from what I'm gathering however the Input gain to the mixer is most likely to high.

Its a high school stadium and when the system was working we had complaints about it being too loud. But it was the dance team that was using the cell so they might have raised the volume on their phone.

The high input can come from a cell phone is this correct / common?

In order to protect this we need a limiter between the mixer and amplifier and to closely watch the gain and volume during use.

Can't thank yall enough for the help.
 
Yep, it's all too common to turn up the system too loud when the problem is actually a lack of dispersal. Do you have any speakers covering the area where the dancers perform? Some "monitor" speakers might well help in this respect, as they will get good clear audio without it being too loud elsewhere.
 
The speakers are on top of the press box pointing straight at the Field which when you are on the field is pretty loud. I think we will now have someone in the box that knows what they are doing. It could be that in the press box where the coach is controlling the music you don't really hear how loud it is since its projected forward so they are cranking it up thinking its not enough.
 
If you have a situation where your speakers are being blown by your amp and there is no fault present, then the simple fact is you have to much power for your speakers to handle. It is that simple. Gain and volume setting are largely irrelevant.

You have a mismatch between the power your amp can supply and the speakers can handle, and the company you used should know better than to install a system in this configuration. This is quite simply a big NO NO!

Professional systems have various ways of combating this problem but limiting the amplifier or restricting the amount of power it can deliver is rarely usually the best way to go. The easiest solution is to have speakers that can that Safely handle the power delivered by the amplifiers in use.

The power specs for that amp are below
  • 2900W RMS x 1 at 2 ohms
  • 1780W RMS x 1 at 4 ohms
  • 975W RMS x 1 at 8 ohms
  • 2525W RMS x 2 at 2 ohms
  • 1510W RMS x 2 at 4 ohms
  • 890W RMS x 2 at 8 ohms
At high power levels this exceeds the capability of your speakers so it is quite obvious why they are blowing.

@noiseboy72 makes a valid point that 4 speakers are probably not enough for a full stadium and thus the need to overdrive the speakers by turning up the volume to compensate for the inadequate sound level is precipitating the problem.

Personally I would add 2 or 4 more (of the same) speakers to the setup. This will
a.) solve the problem of the speakers not being able to handle the power output of the amp.
b.) Give you the additional speakers (sound output) you clearly need to provide adequate volume levels without overdriving them.
c.) give you a far cleaner and less distorted sound, and prolong speaker life since you won't be pushing them as hard.

I am only surprised the company/individual who has done the installation has not properly spec'd your system.

This is not rocket science.
 
If you have a situation where your speakers are being blown by your amp and there is no fault present, then the simple fact is you have to much power for your speakers to handle. It is that simple. Gain and volume setting are largely irrelevant.

You have a mismatch between the power your amp can supply and the speakers can handle, and the company you used should know better than to install a system in this configuration. This is quite simply a big NO NO!

Professional systems have various ways of combating this problem but limiting the amplifier or restricting the amount of power it can deliver is rarely usually the best way to go. The easiest solution is to have speakers that can that Safely handle the power delivered by the amplifiers in use.

The power specs for that amp are below
  • 2900W RMS x 1 at 2 ohms
  • 1780W RMS x 1 at 4 ohms
  • 975W RMS x 1 at 8 ohms
  • 2525W RMS x 2 at 2 ohms
  • 1510W RMS x 2 at 4 ohms
  • 890W RMS x 2 at 8 ohms
At high power levels this exceeds the capability of your speakers so it is quite obvious why they are blowing.

@noiseboy72 makes a valid point that 4 speakers are probably not enough for a full stadium and thus the need to overdrive the speakers by turning up the volume to compensate for the inadequate sound level is precipitating the problem.

Personally I would add 2 or 4 more (of the same) speakers to the setup. This will
a.) solve the problem of the speakers not being able to handle the power output of the amp.
b.) Give you the additional speakers (sound output) you clearly need to provide adequate volume levels without overdriving them.
c.) give you a far cleaner and less distorted sound, and prolong speaker life since you won't be pushing them as hard.

I am only surprised the company/individual who has done the installation has not properly spec'd your system.

This is not rocket science.
I would suggest that in fact, the amplifier is quite well matched to the speakers, but is being overdriven by the input source, thus creating excess distortion as well as level. Running a lower power amplifier would lead to the distortion starting to appear at lower levels, and it's normally these square waves that kill the speakers, not the heat from pure signal overdriving.

In pro audio, the amplifiers are generally overrated for the speakers they are driving, as it actually protects them from high distortion, allows for more dynamic range and puts less stress on the electronics. Peavy make a version of that amplifier with the protection built in, which might have been the better choice, but as that has not been used, a speaker management system - and as I made clear, competent operation is the way forward.

Using highly compressed music off a phone exacerbates the problem, as the system is essentially running flat out the whole time, with little in the way of dynamic range - which would be present in live music.
 
If the amplifier is blowing the speakers then they are quite simply and most definitely incorrectly matched, and the fact that this has happened more than once makes this abundantly clear.

If that weren't enough, the power ratings the amplifier and those of the speakers remove any remaining doubt.

Input sources are largely irrelevant (without getting very technical) as is the source signal in use, since we are not talking about test conditions with any of the waveforms you mentioned. Dynamic range, music, (signal compression) are also not relevant here. Overdriving (in this circumstance) has nothing to do with input, only the output or power amp stage. That is not how it works.

The speakers cannot safely handle the power being delivered from the amplifier, that is the problem. And! this will continue to happen if you just replace like for like i.e. the speakers with the same number and type in the same configuration with this amplifier..

If you think the speakers are loud enough and quite sufficient for the stadium as is, I suggest you wire them differently to increase the impedance the amplifier sees, thereby reducing the amount of power being delivered by the amplifier.
 
If the amplifier is blowing the speakers then they are quite simply and most definitely incorrectly matched, and the fact that this has happened more than once makes this abundantly clear.
No, not true. It is much safer to run a larger amplifier that will provide clean power than something underpowered that will clip and most definitely kill the speakers. In 25 years of running stadium sized systems, I never damaged a speaker through overdriving it with an amplifier that was too powerful, but I have seen and repaired many a speaker owned by other people killed by a distorting amplifier due to it being underpowered. A 500W / channel amplifier would damage these speakers more easily than a 1KW /channel amplifier will.
If that weren't enough, the power ratings the amplifier and those of the speakers remove any remaining doubt.

Manufacturers lie about power handling as well. You simply cannot match amplifiers and speakers reliably. Much safer to put them into power handling groups - 50-150W, 300-600W etc. and match them to amps that way.

If you think you can simply select a 250W speaker and 250W amplifier and assume it will not be able to damage the speaker, you are sadly very mistaken.

Input sources are largely irrelevant (without getting very technical) as is the source signal in use, since we are not talking about test conditions with any of the waveforms you mentioned. Dynamic range, music, (signal compression) are also not relevant here. Overdriving (in this circumstance) has nothing to do with input, only the output or power amp stage. That is not how it works.
What you are not grasping is that a poor, distorted, compressed input signal is much harder for a speaker to reproduce, as the cone is trying to start and stop almost instantaneously, causing the cone to overshoot, leave the protection of the magnetic flux field and rapidly overheat.

The input signal is of key importance! Amplifiers are rated using a pure sine wave, as this is easy to test for distortion, but it is not representative of real world waveforms. Highly complex, highly distorted signals above the input sensitivity level will cause huge amounts of distortion and will try to drive the amplifier far harder than it was designed for.

Don't forget, you have mobile phones with headphone - not line level outputs, plugged into a mixer with variable gain and level controls - not to mention EQ to boost certain frequencies. You could be looking at an input signal 25db or more over the full power 0db level!
The speakers cannot safely handle the power being delivered from the amplifier, that is the problem. And! this will continue to happen if you just replace like for like i.e. the speakers with the same number and type in the same configuration with this amplifier..
No, not true. Fit a limiter before the amplifier, so that the input signal can never exceed a safe level for more than a fraction of a second. This will protect the speakers and maximise the available level. This is how 99.9% of professional PA systems run, with a speaker controller providing active limiting and control of the signal. On active systems, this is built into the speaker, while passive systems will use a controller and crossover before the amplifier(s)
If you think the speakers are loud enough and quite sufficient for the stadium as is, I suggest you wire them differently to increase the impedance the amplifier sees, thereby reducing the amount of power being delivered by the amplifier.
I think we established in post 14 that more speakers are needed, but without some clever series - parallel connections, they will need a 2nd amplifier to prevent the impedance dropping dangerously low and risking overheating the amplifier and yes, you've guessed it, causing distortion...
 
No, not true. It is much safer to run a larger amplifier that will provide clean power than something underpowered that will clip and most definitely kill the speakers. In 25 years of running stadium sized systems, I never damaged a speaker through overdriving it with an amplifier that was too powerful, but I have seen and repaired many a speaker owned by other people killed by a distorting amplifier due to it being underpowered. A 500W / channel amplifier would damage these speakers more easily than a 1KW /channel amplifier will.
Rubbish. An amplifier's ability to deliver clean sound has nothing to do with being overpowered for the speakers. It is down to its design. Clipping doesn't kill speakers. Clipping is far more likely to kill your amplifer than anything else.

Manufacturers lie about power handling as well. You simply cannot match amplifiers and speakers reliably. Much safer to put them into power handling groups - 50-150W, 300-600W etc. and match them to amps that way.
So your basing the mismatch on the supposition that the company is 'lying about the specifications, seriously? Rather than sensibly following the information given and accepting it as accurate you would do this dance with conjecture? Ridiculous.

What you are not grasping is that a poor, distorted, compressed input signal is much harder for a speaker to reproduce, as the cone is trying to start and stop almost instantaneously, causing the cone to overshoot, leave the protection of the magnetic flux field and rapidly overheat.

Irrelevant.
If you put a distorted compressed signal in, you will get a compressed distorted signal being reproduced. it doesn't affect the power handling capability of the drivers. The power handing (for the most part) is independent of the signal and not the cause of the speaker being blown. I think 'You' need to grasp this, put aside what you know, and instead deal with what is happening in this situation instead of trying to confuse the it with irrelevant technicalities that are not at play.

The input signal is of key importance! Amplifiers are rated using a pure sine wave, as this is easy to test for distortion, but it is not representative of real world waveforms. Highly complex, highly distorted signals above the input sensitivity level will cause huge amounts of distortion and will try to drive the amplifier far harder than it was designed for.
The input signal is not relevant here. it is a standard reference used to determine the output capability of the amplifier not to determine accurate reproduction. An amplifier will start to distort once it is pushing past it's rated capability, and since this amplifier is blowing the speakers (repeatedly) before this, why do you think this is relevant? You seem to be more interested in parading your knowledge of audio amplification than dealing with what is the issue here.

Don't forget, you have mobile phones with headphone - not line level outputs, plugged into a mixer with variable gain and level controls - not to mention EQ to boost certain frequencies. You could be looking at an input signal 25db or more over the full power 0db level!
Why are you taking issues into consideration which are not at play. Again, irrelevant

No, not true. Fit a limiter before the amplifier, so that the input signal can never exceed a safe level for more than a fraction of a second. This will protect the speakers and maximise the available level. This is how 99.9% of professional PA systems run, with a speaker controller providing active limiting and control of the signal. On active systems, this is built into the speaker, while passive systems will use a controller and crossover before the amplifier(s)
This response is the most baffling. I say
"The speakers cannot handle the output of the amplifier which is why they are being blown, and you say
"no not true fit a limiter before the amp"
This is totally ridiculous. Your using a your hypothetical solution as justification that his system isn't mismatched... that is just nonsense. Deal wit the situation as is.

That's like putting 100kg person on a scale with a max weight of 50kg, having it break then saying no no, its fine you just need to loose weight.

I think we established in post 14 that more speakers are needed, but without some clever series - parallel connections, they will need a 2nd amplifier to prevent the impedance dropping dangerously low and risking overheating the amplifier and yes, you've guessed it, causing distortion...
I have guessed nothing.

He doesn't necessarily need more speakers. As I have said, wiring the speakers in a simple series - parallel configuration will drop the impedance down to 8 ohms which is quite within the spec of the amplifier in a single channel configuration and will safely keep him within power limits. It is not what I would personally do but it is a easy option which he can at least try without any additional purchases.

I really don't understand you responses in this thread. You seem intent on complicating a simple issue and using it as a platform to display your audio knowledge. That isn't cool. At any rate this is my last post since I don't want to 'get into it' with you, and the moderators tend to look dimply on such disputes.
 
@jimscreechy It sounds like you need some schooling in basic audio electronics to have any form of valid contribution to this thread. Your advice is just plain wrong.

Here's a couple of articles that explain it and reinforce the facts. If you have an alternative view, please support it with similar evidence.


These articles directly contradict your statement that "Clipping doesn't kill speakers. Clipping is far more likely to kill your amplifer than anything else"

I am struggling as to why you fail to understand the importance of the input signal, both in terms of content and level. I'll do my best to explain that, along with what an amplifier rating means.

TLDR: Clipping is what kills speakers quickest. Excessive input level needs to be controlled either electronically or by a competent operator. Simply putting in a smaller amplifier will not stop failures unless other methods are employed.

Putting in more speakers will help with overall dispersal but may not necessarily prevent speaker damage.

OK, so the facts.

Amplifier Power:
Amplifier power output is generally referred to as Watts. This is made up of 2 components - voltage and current. The output voltage is derived from the input signal - as it follows what the input voltage does, while the current will depend upon the impedance of the speaker or load being driven. Watts therefore, equals voltage x current, where current (in a simplified model) = voltage divided by resistance.

Stated Power Output
The RMS (Root Mean Square) of the power was hit upon many years ago as a simple method to illustrate the average maximum power of an amplifier and is usually defined as 0.707 of the peak undistorted signal. So to work out the RMS Power of an amplifier, we would input an undistorted signal at a known frequency, connect a known impedance load (Probably a simple resistance, as impedance is just a frequency dependant resistance) and monitor the output while increasing the amplifier gain until clipping just starts to occur. At that point, we would measure the voltage being produced and the current demanded by the load and calculate the peak power. Multiply this number by 0.707 and we have a reasonable approximation of the RMS power. Because this is not a true representation of what a musical waveform looks like, this figure can only ever be used as a guide. A 500W amplifier is not necessarily suited to a speaker rated at 500W, other factors need to be considered.

Clipping and speaker killing distortion:
Clipping happens in amplifiers for 2 reasons. The first that the input signal is driving the amplifier so hard (loud) that the output is attempting to exceed the power supply rails, so the signal is "squared" off when it hits this limit. The second is when the current demand exceeds that available by the power supply, so the voltage rails sag and clipping results. The first is most common in poorly controlled systems - such as referred to by the OP, the second where an underpowered amplifier is used.

Clipping is basically distortion, containing lots of high frequency harmonics. If you look at the image below, you can clearly see the difference between an undistorted signal and the severely distorted clipped signal. What is evident is that the clipped signal generates significantly more energy for the speaker to try to reproduce compared to the undistorted signal, leading to a greater likelihood of speaker failure - even though the peak power output remains virtually unchanged.

main-qimg-daa955add1637ef634eee93328334ee3


Speaker Damage
Speaker drivers - excluding any crossover have 4 main failure modes, many of which are interlinked:

1. Mechanical / Shock - Dropping the speaker causing damage to the basket and suspension. Generally, the voice coil will jam or rub against the magnet assembly, causing a distorted sound, even at low volumes. Common in hifi speakers if poorly handled during delivery or setup.

2. Short term high voltage failure - the input signal is so large that the coil will fail in the same way as a fuse. Common in tweeters when over driven due to clipping, where huge amounts of HF energy is generated due to high order harmonic distortion.

3. Long term heat failure - the input signal is large enough to cause a build up of heat, which eventually causes the voice coil to become damaged and to jam in the gap. This leads to the mechanical failure mentioned above. Common in bass units, where very high currents are called for. Can lead to fires in extreme cases!!

4. Over excursion of the cone, causing the voice coil to change from being part of a motor to being a simple coil as it leaves the safety of the magnetic field. This can lead to either mode 2 or 3 failure, depending upon the severity of the overload.

So, bearing all this in mind, our ideal amplifier would be one that would never clip or distort, and would never output more power than the speaker was designed to handle. This is achieved in practical terms by using an amplifier that won't run out of power, so has a higher rating than the speaker, but has electronics or a competent operator that limit the input signal so that it will never overdrive the amplifier or speaker. This is common practice for large scale PA systems and an electronic solution is normally built into active speakers and systems designed for unattended operation.

System design and distribution:
My experience is that many problems with sound systems are due to poor design regarding speaker distribution and dispersal. Covering large areas but still controlling spill and ensuring equal coverage is an art that takes years to perfect. The end requirement for the audio must also be considered. Is it simply to make announcements - so clear, band limited audio is required, to provide chest thumping music beats to incite excitement in the crowd - so more power, particularly in the low bass is needed, or is it, as is most common to try and do all these things on a small budget??

For simple, predominantly speech systems, set up on a temporary basis, grouping speakers as a point source makes perfect sense. It reduces unwanted echo, delay and poor intelligibility, but it will mean that the sound level between the back and front of the listening area will vary considerably. For music systems, distributed systems might be preferred, but the design needs to ensure that electronic delays are used to time align the audio throughout the area, so that the focus remains to the intended point. In a stadium, it's quite usual for the speakers to be nearer the crowd than the pitch, so dancers and anyone on the pitch needing to hear the system will probably complain it's too quiet while the the audience complain that it's blasting their ears off.

Therefore, a local monitoring system with additional speakers with separate control could be deployed pitch side, pointing at the performers. These will provide them with the sound level they require, while keeping levels for the crowd at reasonable levels.

Conclusion
Hopefully if you have read and understood this, you can contribute to the discussion. There's nothing simple about high power audio systems and making broad sweeping and factually incorrect statements helps nobody.

School over.
 
So much (i.e. nearly all) of this is over my head but its fascinating reading what the two of you are saying, I find myself definitely agreeing with one, until the other posts, then definitely agreeing with them etc etc !
Ay further update on this?
 

The latest video from AVForums

TV Buying Guide - Which TV Is Best For You?
Subscribe to our YouTube channel
Back
Top Bottom