Hello follow DIY'ers
I was pondering the various ways a driver can fail depending on real world operating conditions, meaning input power, bandwidth and enclosure design (loading) and how this may differ from what is specified for the driver itself depending on method used.
Thermal failure is input power related but the time it takes for this failure to occur will also be influenced by ambient temperature and driver ventilation aspects as granted by the enclosure and driver excursion profile.
Mechanical failure could mean several things depending on how the driver is designed, and as before time is a factor here as well since there are different thermal masses that makes up a driver mechanically, the metal and ceramic parts of the motor structure will take a bit longer to reach critical temperatures compared to the voice coil (for example).
So how does one arrive at what the power rating is for a certain driver in a specific design? Testing and measuring is a given, but this may not be an option for most DIY'ers since it requires specific equipment, climate chambers etc.
The reason I ask is that I believe that matching an amplifier to the driver specifications without taking the enclosure into consideration (which seems to be a fairly common practice) could be risky, or am I wrong about all this?
I was pondering the various ways a driver can fail depending on real world operating conditions, meaning input power, bandwidth and enclosure design (loading) and how this may differ from what is specified for the driver itself depending on method used.
Thermal failure is input power related but the time it takes for this failure to occur will also be influenced by ambient temperature and driver ventilation aspects as granted by the enclosure and driver excursion profile.
Mechanical failure could mean several things depending on how the driver is designed, and as before time is a factor here as well since there are different thermal masses that makes up a driver mechanically, the metal and ceramic parts of the motor structure will take a bit longer to reach critical temperatures compared to the voice coil (for example).
So how does one arrive at what the power rating is for a certain driver in a specific design? Testing and measuring is a given, but this may not be an option for most DIY'ers since it requires specific equipment, climate chambers etc.
The reason I ask is that I believe that matching an amplifier to the driver specifications without taking the enclosure into consideration (which seems to be a fairly common practice) could be risky, or am I wrong about all this?
Some thoughts:
- Mechanical failures happen instantly. The voice coil getting smashed on the back plate, cone folding/shredding, moving parts disconnecting from each other... I'd say it's usually because the speaker has been driven hard below tuning, although it would be possible to damage a speaker with an in-band signal and a large amplifier.
- Yep, the cabinet design will influence things. For instance, anything in a small sealed box will have trouble with long-term power handling, since the hot air has nowhere to go. Tapped horns should be pretty good in that regard: the entire bandwidth has air moving directly over the motor.
- I tend to find that drivers will tell you when they're struggling, and then you can pull the faders down accordingly. Helmholtz-based bandpass designs are troublesome here, since the acoustic lowpass of the ports means the distortion is filtered out. Only really gross distortion is obvious, and by then it's usually too late.
- Calibrating the limiters to make sure you'll never ever destroy the driver will unfortunately mean you have to melt a few drivers to find the outer limits. Part of the cost of R&D, I suppose.
Chris
- Mechanical failures happen instantly. The voice coil getting smashed on the back plate, cone folding/shredding, moving parts disconnecting from each other... I'd say it's usually because the speaker has been driven hard below tuning, although it would be possible to damage a speaker with an in-band signal and a large amplifier.
- Yep, the cabinet design will influence things. For instance, anything in a small sealed box will have trouble with long-term power handling, since the hot air has nowhere to go. Tapped horns should be pretty good in that regard: the entire bandwidth has air moving directly over the motor.
- I tend to find that drivers will tell you when they're struggling, and then you can pull the faders down accordingly. Helmholtz-based bandpass designs are troublesome here, since the acoustic lowpass of the ports means the distortion is filtered out. Only really gross distortion is obvious, and by then it's usually too late.
- Calibrating the limiters to make sure you'll never ever destroy the driver will unfortunately mean you have to melt a few drivers to find the outer limits. Part of the cost of R&D, I suppose.
Chris
B&C drivers are tested by slowly (like 24hrs) ramping up the power in free air to the point where the magnet heats up to 100c as the power handling figure. Beyond this point there are adhesive failures. You can repeat the same experiment in a cab to determine the thermal power handling but you will be running at full output for a long period of time so you may struggle to find somewhere to do this!
Power Handling Deep Dive - YouTube
for excursion measurement in a cab to find out voltage limiting to prevent mechanical over excursion you can use a cheap sharp IR infrared sensor and many averages on a scope to plot the excursion at a test frequency:
measuring excursion - Bass Gear - Data-Bass Forums
I have never bothered doing this for a finished cab though because its far easier to sweep at ever increasing levels until you start to see compression. The sweep that gives you 3dB compression is a good point to voltage limit the cab as at that point any increase in voltage is only increasing stress on the driver not giving more output. If you look at the sub design in my sig you will see that the final ~90v sweep is showing compression (before the amp itself starts to limit and compresses far more) the maximum compression is observed where hornresp also predicts maximum excursion from the driver.
It is possible to fully protect a driver and get full output using a mixture of peak voltage limiting, high pass filters and either voice coil DCR sensing limiter (voice coil temp) or 'true power limiters' however you need an amp that measures driver voltage and current for the last two.
Power Handling Deep Dive - YouTube
for excursion measurement in a cab to find out voltage limiting to prevent mechanical over excursion you can use a cheap sharp IR infrared sensor and many averages on a scope to plot the excursion at a test frequency:
measuring excursion - Bass Gear - Data-Bass Forums
I have never bothered doing this for a finished cab though because its far easier to sweep at ever increasing levels until you start to see compression. The sweep that gives you 3dB compression is a good point to voltage limit the cab as at that point any increase in voltage is only increasing stress on the driver not giving more output. If you look at the sub design in my sig you will see that the final ~90v sweep is showing compression (before the amp itself starts to limit and compresses far more) the maximum compression is observed where hornresp also predicts maximum excursion from the driver.
It is possible to fully protect a driver and get full output using a mixture of peak voltage limiting, high pass filters and either voice coil DCR sensing limiter (voice coil temp) or 'true power limiters' however you need an amp that measures driver voltage and current for the last two.
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All good points Kipman725, very helpful and useful information.
For the more common design principles I assume there is a pretty well charted map for thermal and mechanical limitation behaviours even though there are specific variations on the theme from design to design.
But if we look at the more recent higher order quarterwave designs (paraflex, roar) and the way these load (lacking a better word for it) the drivers in combination with the more recent high power drivers and the availability of power amps in the multi key range, is this really that well understood?
The approach you show for determining the onset of power compression or more instantaneous output limitation should still be just as valid, but something tells me that even if the cone load is decent but the excursion is reduced due to loading, won't the cooling suffer? Perhaps even to the point of seeing premature powercompression or excessive temperatures pretty early on, or at least quicker, than what could otherwise be expected?
Could it even be so that it may reduce the expected service or lifetime of the drive units due to increased thermal fatigue, if one is not careful that is?
I believe that the drivers are tested to failure several times over in order to obtain, form and or verify the FMEA and balance the driver the design to have a predictable failure structure, but most often these test are done in standardized open baffle arrangements, allowing the forced air cooling to operate as intended based on the rather inhibited excursion.
For the more common design principles I assume there is a pretty well charted map for thermal and mechanical limitation behaviours even though there are specific variations on the theme from design to design.
But if we look at the more recent higher order quarterwave designs (paraflex, roar) and the way these load (lacking a better word for it) the drivers in combination with the more recent high power drivers and the availability of power amps in the multi key range, is this really that well understood?
The approach you show for determining the onset of power compression or more instantaneous output limitation should still be just as valid, but something tells me that even if the cone load is decent but the excursion is reduced due to loading, won't the cooling suffer? Perhaps even to the point of seeing premature powercompression or excessive temperatures pretty early on, or at least quicker, than what could otherwise be expected?
Could it even be so that it may reduce the expected service or lifetime of the drive units due to increased thermal fatigue, if one is not careful that is?
I believe that the drivers are tested to failure several times over in order to obtain, form and or verify the FMEA and balance the driver the design to have a predictable failure structure, but most often these test are done in standardized open baffle arrangements, allowing the forced air cooling to operate as intended based on the rather inhibited excursion.
I think what your getting at is that in a high order box design you have many impedance minimums that also correspond to frequencies where the cone is close to stationary (no cooling effect). If you run sine waves at these frequencies you very quickly can overheat the driver (fortunately this is unlikely with music). In the free air test the driver manufacturers do the driver has a single self resonant impedance peak and only a minima at DC. So yes the manufacturer free air measurement is a best case number for power handling.
Compare the 21 IPAL in free air:
Data-Bass: Subwoofer Measurements
to the 21 IPAL (x2) in a 6th order box:
Data-Bass: Subwoofer Measurements
In the real world unless your already running hard against your peak limiters thermal failure doesn't seem to be a significant issue except perhaps sealed rear chamber horn subs. There is a trick to cooling those though where you port the rear chamber but with a very low tune so air still circulates but it has not affect on the acoustic output of the horn. If you want to run your subs at the absolute limit you require limiting linked to the real power input and or voice coil temperature sensing, both of which don't care about the type of box your using.
Compare the 21 IPAL in free air:
Data-Bass: Subwoofer Measurements
to the 21 IPAL (x2) in a 6th order box:
Data-Bass: Subwoofer Measurements
In the real world unless your already running hard against your peak limiters thermal failure doesn't seem to be a significant issue except perhaps sealed rear chamber horn subs. There is a trick to cooling those though where you port the rear chamber but with a very low tune so air still circulates but it has not affect on the acoustic output of the horn. If you want to run your subs at the absolute limit you require limiting linked to the real power input and or voice coil temperature sensing, both of which don't care about the type of box your using.
I suspect temperature sensing is the only way to do it. The real power input method will still allow the driver to fail if the driver itself is thermally compromised.
ie, we should derate drivers, and then limit the input power accordingly.
It's tricky stuff to do, without burning a few drivers in the process.
FWIW, where possible I design any high-power speakers to have their bass reflex ports passing air directly over the magnet. It probably helps a bit with long-term thermal buildup.
Chris
It would need testing possibly burning drivers in the process but if its heat buildup over the course of hours that's problematic then measuring magnet temp (easy to do) would work.
If you are making your own amps adding voice coil temp sensing would be relatively easy:
Voice Coil Temperature
the problem I see with adding this to an existing system is that many amps won't pass a 1-4Hz signal very effectively and even if they do it may trigger DC protection circuits. A higher frequency tone could be used at a tuning frequency or fitting to an impedance model of the driver without an explicit test tone but this then requires a more information about the cab.
Have you ever lost a driver in your subs Chris? I haven't damaged any drivers since changing to vented boxes from sealed.
If you are making your own amps adding voice coil temp sensing would be relatively easy:
Voice Coil Temperature
the problem I see with adding this to an existing system is that many amps won't pass a 1-4Hz signal very effectively and even if they do it may trigger DC protection circuits. A higher frequency tone could be used at a tuning frequency or fitting to an impedance model of the driver without an explicit test tone but this then requires a more information about the cab.
Have you ever lost a driver in your subs Chris? I haven't damaged any drivers since changing to vented boxes from sealed.
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Well, how about making it a 20kHz tone? The big cone isn't going to reproduce that anyway, but Le(x) might become an issue. Some averaging would solve that, though.
The only time I've lost a driver was when I did a 500w sweep 0-200Hz, with no highpass engaged. Folded the cone on a Beyma 15P1200Nd.
Apart from that, I've taken a Crown MA12000i to clipping into 1x cab/ch, and that was fine. I've also bridged a T602 into 2x cabs (about 3KW/driver), and the cones hit the grilles. Backed it off a touch and kept it there for the evening. No worries.
Modern sub drivers are tough cookies!
Chris
PS - I wouldn't want to bridge that Crown amp into a single driver. I'd say that's asking for trouble.
The only time I've lost a driver was when I did a 500w sweep 0-200Hz, with no highpass engaged. Folded the cone on a Beyma 15P1200Nd.
Apart from that, I've taken a Crown MA12000i to clipping into 1x cab/ch, and that was fine. I've also bridged a T602 into 2x cabs (about 3KW/driver), and the cones hit the grilles. Backed it off a touch and kept it there for the evening. No worries.
Modern sub drivers are tough cookies!
Chris
PS - I wouldn't want to bridge that Crown amp into a single driver. I'd say that's asking for trouble.
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High frequency wouldn't work as we are looking for the DC resistance. At higher frequencies you have the skin effect and losses due to the high frequency currents induced in the magnet structure so the resistance measured will be different. Also your attempting to find a small resistance in the presence of a large reactance which means you have to determine a small phase angle difference between voltage and current. I'm inclined to think from B&Cs comments and your comments that thermal failure isn't a big issue for modern sub drivers unless you have the most powerful amps available (and possibly bridge them one per driver which is not a cost effective configuration). You must have been totally beating it to get the cone to the grill!
Well, it was a party in an old barn with a pair of 15"s covering <100Hz. Had "feel the bass" levels on the dancefloor down to 40Hz, which was enough to keep the customers happy.
Next build*, I'm giving the cones more clearance. Mechanical damage can happen quickly.
* I think it'll be the monster 2x18" with the Faital Pro 18XL1800. Flat to 30Hz, and enough excursion to get loud doing it.
Chris
Next build*, I'm giving the cones more clearance. Mechanical damage can happen quickly.
* I think it'll be the monster 2x18" with the Faital Pro 18XL1800. Flat to 30Hz, and enough excursion to get loud doing it.
Chris
In my case I'm running B&C 15SW115 (8 Ohms) in a higher order quarter wave design (ROAR15) and I have newer had the chance to feed them any real power, real that is when compared to what is specified for the driver, but the output compared to the excursion (only observed not measured) is rather impressive and this made me wonder if the published power handling is still valid when the driver resides in an enclosure that loads the driver to a greater extent (I assume) then the more common designs principles do.
As an example, right now I'm trying to understand, lacking the tools to measure either coil temp or input power, if a bridged LAB.gruppen LAB1600 that acc. to spec. delivers 1560W FTC / 1680W EIA / 1700W IHF into an 8 Ohm load when bridged is safe given that the drivers are specified to handle 1700W nominally / 3400W continuous.
Normally this would be just fine I guess going by 1560W FTC being fed into an 1700W driver, but when the driver excursion is potentially somewhat limited compared to closed or reflex, is this still ok? I understand you cannot answer this correctly without doing actual testing and measurements, but do you have a gut feel answer or any thoughts.
As an example, right now I'm trying to understand, lacking the tools to measure either coil temp or input power, if a bridged LAB.gruppen LAB1600 that acc. to spec. delivers 1560W FTC / 1680W EIA / 1700W IHF into an 8 Ohm load when bridged is safe given that the drivers are specified to handle 1700W nominally / 3400W continuous.
Normally this would be just fine I guess going by 1560W FTC being fed into an 1700W driver, but when the driver excursion is potentially somewhat limited compared to closed or reflex, is this still ok? I understand you cannot answer this correctly without doing actual testing and measurements, but do you have a gut feel answer or any thoughts.
The only time I'd worry would be if you're playing dubstep with continuous tones, and still hitting the peak limiters on the amplifier.
For non-dubstep stuff, I'd look for something in the 2.5-3KW range per driver.
Remember, the ROAR designs have the driver's motor in the air flow, and that air flow is exchanged with the outside world. Pretty favourable conditions.
Chris
For non-dubstep stuff, I'd look for something in the 2.5-3KW range per driver.
Remember, the ROAR designs have the driver's motor in the air flow, and that air flow is exchanged with the outside world. Pretty favourable conditions.
Chris
The manufacturer's "Continuous Program" rating of 3400 watts is OK for peak limiting, using short time constants of a few wavelengths duration.
Long term "RMS" limiting with a time constant of longer than 500 ms (milliseconds) should be no more than half the rating of 1700 watts (850 watts), as AES ratings are conducted in free air (the actual power dissipated is less than 1/2 the nominal "wattage"), while driver's voice coils heat up far more when loaded in higher order quarter wave or tapped horn designs due to the far lower average impedance than the free air test rating. If operators tend to get "heavy handed" playing low crest factor music, use 425 watts for long term "RMS" limiting.
As a reference point I used my Keystone BC18SW115-4 tapped horns for several years driven with bridged mono Crest CA-9 capable of 80volts (1600 watts continuous, possibly near double that short term peak) into 4 ohms with no apparent power compression.
After I sold the system, the new operator cooked one of the drivers on the second gig (live rock music), likely from accidentally panning kick/bass hard to one side. Hard panning adds +4.5 to +6dB (depending on the mixer), but using only one sub reduces potential output by -6dB, so one sub trying to do the work of two didn't ;^).
Had the system employed properly set separate peak and RMS limiters, there would have been no loss from the mistake.
Art
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Thanks for the input and examples, much aprichiated, so if lacking the tools and facilities to properly study the impact of a higher than normal acoustical loading, meaning less excursion at a given amount of input power, then it's "simply" a matter of applying a bit of caution in the process of determining the drivers power handling once deployed in a cabinet exhibiting these traits?
The important takeaway so far, if I understand you correctly, is that the published powerhandling specs are only valid under such conditions as where present during the tests, and that these are to some extent valid for the more common design approaches (I would assume), and they are important for comparison purposes as long as one can be sure that the tests are all performed according to the standards between different manufacturers.
Once the driver is deployed in a cabinet these specifications will change, the power handling specifications for the system (driver+cabinet) will be different and this needs to be investigated and tested in order to obtain the safe conditions with regards to power handling for that particular speaker.
Am I getting this right?
As for my example using the 15sw115 in the ROAR15, there are considerations that's needs to be taken into account in this regard depending on what material is being reproduced and the level of compression that is applied, for now I will try the bridged option and be very careful, meaning 1,5kW or rated output power per driver, with clip limiters engaged on the amp this should be "safe" for most types of music.
The important takeaway so far, if I understand you correctly, is that the published powerhandling specs are only valid under such conditions as where present during the tests, and that these are to some extent valid for the more common design approaches (I would assume), and they are important for comparison purposes as long as one can be sure that the tests are all performed according to the standards between different manufacturers.
Once the driver is deployed in a cabinet these specifications will change, the power handling specifications for the system (driver+cabinet) will be different and this needs to be investigated and tested in order to obtain the safe conditions with regards to power handling for that particular speaker.
Am I getting this right?
As for my example using the 15sw115 in the ROAR15, there are considerations that's needs to be taken into account in this regard depending on what material is being reproduced and the level of compression that is applied, for now I will try the bridged option and be very careful, meaning 1,5kW or rated output power per driver, with clip limiters engaged on the amp this should be "safe" for most types of music.
Art's suggestions make a lot of sense.
I'm guessing that you can probably work out the best RMS limiting level by running bandwidth-limited pink noise through the speaker at different levels for about 5 minutes or so and immediately measuring DC resistance right afterwards. As the driver's coil heats up, its resistance will rise, and from that you can not only estimate the voice coil temperature, but track the driver's ability to dissipate heat from the coil at higher voltages.
Pink noise at high levels can be annoying, so it might be best to do this with two of the systems located next to each other, with one connected out of phase.
Or you could be really geeky and figure out a way to have a circuit included in the speaker that trips in 1~3dB of attenuation if the driver's magnet or tinsel leads reach a certain temperature
.
I'm guessing that you can probably work out the best RMS limiting level by running bandwidth-limited pink noise through the speaker at different levels for about 5 minutes or so and immediately measuring DC resistance right afterwards. As the driver's coil heats up, its resistance will rise, and from that you can not only estimate the voice coil temperature, but track the driver's ability to dissipate heat from the coil at higher voltages.
Pink noise at high levels can be annoying, so it might be best to do this with two of the systems located next to each other, with one connected out of phase.
Or you could be really geeky and figure out a way to have a circuit included in the speaker that trips in 1~3dB of attenuation if the driver's magnet or tinsel leads reach a certain temperature
.
1)One tool at your disposal is Hornresp, you can compare the power dissipated under the conditions of the AES test procedure to the design under consideration.
The AES2-1984 (r2003) power rating has the LF driver mounted in free air.
Power is determined as the square of applied rms voltage, divided by Zmin. The driver is driven with pink noise extending one decade upward from the manufacturer’s stated LF limit of the device. The noise is bandpass filtered at 12dB per octave and the peak-to-rms voltage ratio of the noise signal is limited to 2:1 (6 dB crest factor).
The problem with the rating is Zmin (the minimum impedance) is generally much lower than the average impedance over that range, so the power generated by the voltage may only be a fraction of the rated “power”.
As an example, in free air, an “8 ohm” speaker may be over 80 ohms at Fs (30 Hz), dropping to 6.5 ohms at 150 Hz, then rising to around 9 ohms at 300 Hz.
The AES nominal power rating of “1700 watts” would use around 105 volts (105 x105=11,025/6.5=1696), while the impedance average is nearly double that, so actual power absorbed is only around 850 watts.
In a cabinet, the impedance curve is different- at Fb (box tuning) the impedance is now the lowest. When a droning bass line concentrates it’s power in a range of low impedance, the power absorbed can easily be double what the AES rating would indicate to be safe. To make matters worse, at Fb, the cone/voice coil excursion (movement) is at minimum, so heat is not pumped out as effectively as in free air, where the opposite occurs- maximum excursion at maximum impedance.
2) Correct, but as noted in #1, you can approximate the difference by comparing the impedance curve of the speaker's free air simulation compared to your particular design and determine the actual power difference on average.
3) So far, so good.
4)Here is where you seem to miss the main point- most "clip limiters" limits peak, not average power. You may not know whether you are playing "safe" music until after the driver lets out the magic smoke, so protection requires limiting the average power with a slow attack RMS limiter in addition to HP filters and peak limiters.
Brian's suggestion of using pink noise to track the driver's ability to dissipate heat from the coil at higher voltages also misses the "elephant in the room", standard pink noise has a 12dB peak to average ratio, while there are music tracks with low frequency signals even less than the 3dB peak to average of sine waves.
Art
The greatest risk you run overloading a driver long term thermally is in any small heavily pressurized type of enclosure such as a small sealed box, front loaded horn or a 4th order bandpass cab, especially when running 2 drivers in push pull configuration ( inside driver is virtually unventilated ). The lack of VC movement at higher power levels really loads the driver and reduces impedance in a broader range, allowing the amp to feed lots of current into the VC.
The other extreme situation is when the driver is pushed hard and over EQed in a small sealed box, forcing the driver to play lower than Fc. This both heavily loads the driver physically and electrically. A common issue is when the mechanical limits of cone adhesives are exceeded, tearing the cone from the VC, ripping or folding the cone itself, or any other part of the suspension. The most vulnerable of enclosures types are front loaded horns. You must have a good sense of how hard you push these types of enclosures if you want decent driver life and reliability.
Much of this trickles down from live sound reinforcement and can be applied as basic rule of thumb -
- Limit cutoff Fc to just above lowest impedance peak of enclosure where it unloads acoustically. This avoids wasted power, increases system headroom and reliability. When arraying subs, you often can achieve lower system rolloff frequencies, but understand that in most cases with most genres of music, its not necessary to push the low end much past 40 Hz. With electronic music (EDM, hip hop, etc), things change but more than likely you won't need more than 30 Hz low end extension. In these situations it helps to use dynamic EQ and side chaining, so you still have the more extended low end at moderate levels and the higher rolled off material can still hit hard.
- Never allow amps to hard clip and introduce excessive distortion into the driver. Amps should be sized so that driver can be guaranteed +3dB power headroom of realistic continuous driver rating (derated by type of driver enclosure). Soft clip limiters work very well, but there is no way to avoid excess distortion from improper gain structure i.e. heavy handed DJs who push their mixer output into clipping.
- Hard limit the main input level to the system DSP or crossover and avoid post EQing of crossover/DSP outputs. Lock out main EQ/DSP/xover from unauthorized fingers. This also includes gain settings on amps.
Use your common sense to determine if something sounds bad. 99% of the time you will hear bad things long before they cause a failure. Know your equipments limitations and don't let so called "friends" borrow your stuff unless you're ok with knowing it will likely be damaged.
The other extreme situation is when the driver is pushed hard and over EQed in a small sealed box, forcing the driver to play lower than Fc. This both heavily loads the driver physically and electrically. A common issue is when the mechanical limits of cone adhesives are exceeded, tearing the cone from the VC, ripping or folding the cone itself, or any other part of the suspension. The most vulnerable of enclosures types are front loaded horns. You must have a good sense of how hard you push these types of enclosures if you want decent driver life and reliability.
Much of this trickles down from live sound reinforcement and can be applied as basic rule of thumb -
- Limit cutoff Fc to just above lowest impedance peak of enclosure where it unloads acoustically. This avoids wasted power, increases system headroom and reliability. When arraying subs, you often can achieve lower system rolloff frequencies, but understand that in most cases with most genres of music, its not necessary to push the low end much past 40 Hz. With electronic music (EDM, hip hop, etc), things change but more than likely you won't need more than 30 Hz low end extension. In these situations it helps to use dynamic EQ and side chaining, so you still have the more extended low end at moderate levels and the higher rolled off material can still hit hard.
- Never allow amps to hard clip and introduce excessive distortion into the driver. Amps should be sized so that driver can be guaranteed +3dB power headroom of realistic continuous driver rating (derated by type of driver enclosure). Soft clip limiters work very well, but there is no way to avoid excess distortion from improper gain structure i.e. heavy handed DJs who push their mixer output into clipping.
- Hard limit the main input level to the system DSP or crossover and avoid post EQing of crossover/DSP outputs. Lock out main EQ/DSP/xover from unauthorized fingers. This also includes gain settings on amps.
Use your common sense to determine if something sounds bad. 99% of the time you will hear bad things long before they cause a failure. Know your equipments limitations and don't let so called "friends" borrow your stuff unless you're ok with knowing it will likely be damaged.
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