BASSBOSS Questions

I'm confused. Your zv28 120 volt enclosure & amplifier will do 4000 watts? How is this possible? The largest single pole breaker (120vac) you can legally install is 20 amps. Ohms law states that wattage= volts x amps. 120(volts) x 20(amps)=2400 watts total capability in a 100% efficient amplifier (no amp is 100% efficient.... Most class D amps are around 90%) so 2160 is the approximate rms output (never mind the impedance rise in the enclosure.... But that's a whole nother argument).

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David Lee

Hi, This is a good observation and the calculations are correct. The amp is actually higher than 90% efficient but that still wouldn't get to 4000W. The amplifier is rated to deliver 4000W and theoretically a 20A breaker won't let that happen, right? There are several factors that an audio amplifier can take advantage of that many other devices such as heaters, hair dryers and halogen lamps can't. Breakers are rated to an amp load that's correlated to a time. They are installed to prevent the wires and connectors carrying the electricity from overheating and catching on fire. They will pass much bigger peak current draws for short periods. With audio signals, the demand isn't constant and the breaker reacts to the average current flow. You'll see most amps rated at 1/8 power for current draw, with hard thrashing pushing them closer to 1/5 or 1/4. Since speakers operate over a wide range of impedances, the amplifier only draws a lot of amps over a relatively narrow range of frequencies, so if you hit a looong note at that specific frequency, there is the possibility that the amp could trip the breaker BUT this particular amp also has a built-in safety feature in the form of a current limiter. It will reduce power to ~2400W if the current demand exceeds the limit for longer than one second. In music terms, one second is a long time, and that limit is hit only at those specific frequencies so the odds get pretty slim that you'll hit that limiter. You have to be cranking the right song with the right note at maximum level to hit it, and when you do, the amp will trim 1 or 2 dB from the level to keep the breaker from getting too hot. And while impedance rise in the enclosure does cause in a loss of output SPL, it actually results in a net reduction of current draw from the breaker.

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BASSBOSS Questions

I'm very familiar with dynamic/peak power and the ability of a fuse/circuit breaker to momentarily pass current in excess of its nominal rating. I just wanted to point out that the amp cannot provide 4000 watts rms on a 120 volt AC power source. Now, with any subwoofer system the impedance rating is the static dc resistance of a woofer at rest. The enclosure and environment will dictate the actual impedance at a given frequency and it will be a higher (or equal) impedance as nominal. Of course all vented enclosures are prone to impedance rise at/near the tuning frequency as well, which is fine as typically that is the most efficient part of the bandwidth since you have the cone and the vent working in harmony to maximize output.

I also understand the regulated power supply features of the amp that prevent long term excessive current draw. And I'm a fan of them do thank you for addressing that in your response.

Out of curiosity, what is the expected output (decibels) of this system at, let's say 10 feet (or whatever you've measured it at) in an open environment?

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David Lee

The ZV28 will produce a maximum constant sine wave output of 132dB at 1 meter in a half-space environment. This measurement includes thermal compression. The measurement shows that at maximum power level, including the associated heat, it delivers an average of 129dB +-3dB from 25Hz to 100Hz. 

Since the amplifier has on-board power storage in the form of capacitors, and because it can draw on the breaker for more than 20A for short periods, the amplifier can produce 4000W rms. It isn't 4000WRMS infinitely or indefinitely but it is 4000W RMS for a sufficiently long period of time to garner the 4000W RMS rating for the purpose of driving subwoofers and their associated loads. Most RMS amplifier ratings you see are based on an 8ms measurement of repeating 1kHz tones. This amplifier will deliver its rated power for over 100 times longer at very low frequencies, and that makes a big difference for subwoofer applications. 

For anyone who may not follow what you're talking about, here are a few clarifications: The static DC resistance of a woofer is referred to as DCR. Impedance, by definition, is resistance to alternating current, so an impedance measurement must have a frequency component. Nominal impedance refers to what's expected as an average load to an amplifier. The lowest point in a loudspeaker's impedance curve is referred to as Z-min, and with vented boxes it usually corresponds with the tuned frequency of the enclosure. Z-min is very often the same value as the DCR but it is not the nominal impedance. The Z-min and DCR are usually lower than the nominal impedance. The average (nominally) 8-ohm woofer will have a DCR of between 5 and 6 ohms. The tuning frequency of a vented loudspeaker generally corresponds with its lowest impedance. Sound waves are caused by displacement and, at the vent tuned frequency, the woofer will tend to move very little while the vent causes the displacement. So the tuned frequency is the point at which the vent is providing the majority of the output, while the woofer is providing very little in that range, with the woofer serving to re-energize the port rather than provide output. Electrically, the Z-min or tuning frequency is the least efficient part of the bandwidth because the voice coil is passing the most current. The current flow in that range does tend to create a rise in average impedance due to the heat it produces. The most efficient portion of a loudspeaker's output range from an electrical point of view is around maximum impedance, where the cone is making the displacement but requires very little current to do so since the impedance is high in that range. 

In terms of real-world use, if you assume a Z-min of 30Hz and you hit a note at 30Hz, the output of the loudspeaker will be 129dB. If the note sustains unchanged for more than 1 second, the output level would be gradually attenuated from 129dB to 126dB. As soon as the note changes or there is a pulse to the beat, the timer resets and you get back to your 129dB for approximately another second. Bear in mind that an RMS rating of 4000W also provides for a peak rating that's higher than 4000W, so peak demands, such as drum hits, can exceed the 129dB average. Thus the hits can be 132 to 135dB and the sustains would be no lower than 126dB.

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BASSBOSS Questions

You clearly post a 4000 watt rms rating that is clearly not RMS by most standards. RMS over a few seconds is hardly a true statement of usable power over a period of time. It's closer to a WLS (when lightning strikes) rating and not something that is sustainable over a the long haul. Yes, it might be able to produce 4000 watts occasionally during dynamic playback, but in no way could it sustain a 45Hz bass note for 30 seconds at 4000 watts. It would either trip the circuit breaker or drop well below 4000 watts. That is a fact, and that is the definition of you cooking your stats.

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David Lee

RMS over a few seconds is a very true statement of usable power over a period of time, especially considering the context is audio. Most amplifier specifications quote RMS power in milliseconds, often from 8 to 32 milliseconds. Just one second of RMS output would equate to 30 TIMES the output duration of the average amplifier's specification, or what you may call "most standards". By that math, our specifications are WAY above the standard. 

We routinely see that our amplifiers deliver four times (aka 400%) the continuous output of amplifiers with the same or even higher output ratings. You do the math for yourself. 89V into 2 ohms is 4000W. We run 30 second AND LONGER sine wave tests on these amps and they maintain 90V output into 2 ohms using static dummy load or 2 ohm nominal reactive loads throughout multiple tests at frequencies from 20 Hz to 150 Hz. And we test with swept frequency and single tone. If you want visual confirmation of this, watch this video. Thanks!

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BASSBOSS Questions

How many do I build that will sustain a 4000 watt 30 second burp? Many. Considering some of the amps we use are 20,000 WRMS and we have built several systems using multiple 20k amplifiers. The limiting factor is fold:

1. Having enough current reserve to keep up with amplifier demand
2. Impedance rise in the enclosure

Now, RMS can be best described as the "average" power an amplifier can do over a period of time (or more accurately a continuous time waveform), not how much it can do dynamically in bursts. 

It would be like saying I can pedal a single speed bmx bike at 25 mph (which I can in bursts) and claiming that is the RMS speed of the bicycle, when in reality the average speed that I ride over a period of time is 10-12 mph. Down hill I can even hit faster speeds..... dynamically. Now, no-one would ever argue that my average speed is my top speed, right?

So yes, 4000 watts RMS is a BS claim on a 20 amp circuit breaker. I'm not saying that you are the only company using the burst method to get your RMS output claim, just that everyone that is using it is full of crap and that you , like them, are "cooking your specs".

I'm also not saying you build a bad product. Just pointing out the hypocrisy in your statements.

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David Lee

There is, in fact, no hypocrisy in our statements. An elegant, practical and balanced design is undermined by inaccurate representations of its performance. These specifications are numerical representations of measured performance and our specification methods are - verifiably - the most conservative in the industry. 

Our products are intended for intense usage, and that’s what they get. Ultimately specs are not going to tell the consumer much about the depth, power, physicality, sonic character or reliability of the loudspeaker. That said, I have some comments regarding your assertions. 

I do agree that the "burst method" is not an appropriate way to represent RMS output power and I say again that we do not use the "burst method" to measure, calculate nor specify the amplifiers' output. Your argument is based upon an incorrect assumption that many people share about 20A circuit breakers. This assumption is based upon a lack of understanding of the function of circuit breakers. Allow me to explain: 

4000W at 120V represents a current draw of 33.33A. Assuming 90% efficiency of the amplifier, which is realistic and reasonable for the amplifiers we use, the current draw required to produce 4000W of continuous sine-wave output would be approximately 36A. For the sake of your argument, I will increase that to 40A as a worst-case scenario. 40A is also a simple doubling of the rated current of a standard 20A breaker. 

Based on NEC design parameters and manufacturer specifications of electrical breakers, the standard 20A circuit breaker will pass 40A, effectively double the rated current, for a minimum of 25 seconds and not more than 80 seconds. It will trip instantly, that is to say in 0.02 seconds, at 9X rated current and will trip in approximately 3.5 seconds at 5X rated current. Thus it's entirely reasonable to assume that an amplifier putting out 4000W and consuming 36.3A will be able to do so for 30 seconds without tripping a standard 120V, 20A breaker. I've attached an image below that illustrates this.

RMS stands for Root Mean Squared. Calculating RMS power requires only one full cycle. There is no absolute time required to determine RMS power. Amplifier power ratings are based upon how much power is available, not how much power you are likely to use to get the SPL you require. A 4000W amplifier isn't producing 4000W the moment you turn it on. It's CAPABLE of producing 4000W upon demand. 

Thus the 4000 W rating is the equivalent to your CLAIM that you can PEDAL your bike fast enough to achieve a top speed of 25 MPH. It similarly equates to the horsepower claim of any automobile. It's not disputed that it CAN generate the horsepower, but it can't do it for an unlimited period because something will run out. On a test bench it could be engine overheating that limits the time duration. 

In the real world you might run out of road, or fuel, or overheat your tires. No-one ever looks at a horsepower claim on a car and says, yes, but for how long can I continuously maintain peak horsepower? Saying that it CAN produce 500HP is cooking its specs because I couldn't drive it from Barstow to Vegas and be producing 500HP all the way! If that's the way you're thinking, you've misunderstood the purpose and intention of that specification. BTW, 500 Horsepower is the equivalent of 373 Kilowatts, which would require 93.25 x 4000W amplifiers.

Your speed at 25 MPH is better equated to the SPL you would be able to produce using 4000W than the power you're using to achieve the speed. The speed is limited by the efficiency of the bicycle, a fixed gear ratio single speed bike. If you put the same effort into a bike with a different gear ratio, your top speed would change. No one would argue that your top speed was your average speed but would you accept that you can only expend a maximum amount of effort for a given duration? 

What you are suggesting is that your maximum speed is a lie and that your top speed should be specified as your average speed, in other words because you can't sustain the effort required to do 25MPH forever, your maximum effort should be specified as only sufficient to sustain 10-12 MPH. How long must you be able to maintain 25 MPH before you're allowed to state that it is your maximum speed? It's not forever, and it's not for 0.001 seconds, so how long is long enough? Is 30 seconds at 25 MPH long enough? You won't get very far in 30 seconds at 25 MPH, about 2/10 of a mile, but it will feel like a long time! And you will need a cool-down period. And when you were done, no-one would say it didn't count because you couldn't go on for 10 miles. 

An amplifier that can produce 4000W for .001, 1, 10, 20, 30 or 100 seconds is producing 4000W RMS. The question is, how long is long enough to count? To qualify for use in a BASSBOSS subwoofer, we require a reasonable time duration, long enough to sustain long low-frequency notes. The problem with burst power numbers on subwoofer amps is that they are so short that they don't even allow for the completion of one cycle of the frequency being reproduced. An 8ms burst allows for the completion of one cycle at 125 Hz. This time duration is too short for relevance at frequencies below 1 kHz. It's only long enough to complete 8 cycles at 1 kHz. 

The point is, it's so short that it doesn't require current pass-through from the power supply. The burst output can be achieved from the energy stored in the power supply capacitors and the time is too brief to cause the output devices to heat up. Increasing the duration to just one second allows for the completion of 20 cycles at 20 Hz and 40 cycles at 40 Hz. This is sufficient to test the power envelope of the amplifier, particularly because these test frequencies are below the 60 Hz line voltage frequency. We run our power tests for extended periods, as long as several minutes at full power. 

The amplifiers do have protection systems that will reduce output power when temperatures rise, in order to prevent damage. How long it takes for those protections to engage varies with ambient temperature and load and signal content but until those protections engage, the amplifier will always be able to deliver 90V into 2 or more ohms from a 120V source, thus it is a 4000W RMS amplifier. 

There is no universally established method for rating the output of amplifiers to which all manufacturers subscribe but, for the sake of a better understanding of the specifications, consider this. Most companies publish the nominal current draw of their amplifiers at 1/8 power. This is because the average power consumed and delivered by an audio amplifier when in use for music reproduction is actually about 1/8 the rated output, due to the dynamic nature of music. 

The average density of music is about 12.5%, with the peaks at about maximum output and the valleys close to minimum output. This phenomenon can be called Duty Cycle. Normal use equates to about 12.5% duty cycle. Heavy use equates to about 25% duty cycle. This involves the use of compression to reduce the difference between the maximum and minimum signal levels. Continuous sine-wave output at full power would equate to 100% duty cycle.

14570411_1258473874197325_8055617595525509345_n.png

 

This is not a condition that occurs in music reproduction. It can be caused by feedback or can be created for test purposes but it's not something you will find in music recordings or live performances. Should anyone desire to produce very long-duration sine-wave output, it's recommended to have an amplifier and loudspeakers that have some excess capacity or you risk failure. Amplifier ratings are indications of their maximum capacity for their intended purpose, which, for the vast majority of amplifiers, is music reproduction. 

The distortion contributed by loudspeakers during normal use is orders of magnitude higher than the distortion contributed by amplifiers, provided the amplifiers are used within their limits, so it is very good practice to use amplifiers within their limits. If your demand exceeds the amplifier's output capabilities, many orders of magnitude more distortion will result, with the source being the amplifier. 

Loudspeakers are inefficient transducers that convert more of the amplifier's power into waste heat than into acoustical energy. They are far less accurate and far less efficient than amplifiers. Impedance rise occurs in the voice coils and is a function of heat, which is the result of an amplifier's output energy being wasted! Impedance rise will actually reduce the current demand of the amplifier because it reduces the current the amplifier can deliver to the load. Amplifiers are voltage amplifiers and the current they draw is determined in large part by the current they can pass through the loudspeaker load. The higher the loudspeaker impedance rises, the lower the demand for current from the power source. 

You may have heard the term "Headroom". Headroom can be described as capacity beyond your expected demand. Dynamic headroom is recommended to ensure that the waveform you are attempting to amplify is reproduced without clipping or other distortions. Using any device beyond its maximum capacity will result in distortion. When you look at the specifications for an amplifier, what you want to determine is that it can deliver sufficient power to drive the attached loudspeakers to their limits without reaching its limits. The idea is to have some excess power capacity in order to accommodate some over-drive without causing damage to the loudspeaker(s) connected to the outputs. 

In conclusion, how well the loudspeaker's transducers convert electrical energy into acoustical energy is far more important to the end result than how much electrical energy is available. That said, it is critically important that sufficient energy is available to achieve the design potential of the loudspeaker. Loudspeakers don't work without amplifiers and amplifiers are very quiet without loudspeakers. How much power you have available is irrelevant if the loudspeaker can't take full advantage of it. 

BASSBOSS systems are completely balanced packages, with the amplifiers matched to the transducers. In the ZV28, the transducers are rated to handle 3400W of power RMS and 6800W of dynamic program power. A 4000W RMS amp provides enough continuous power and enough dynamic headroom to achieve maximum utilization without causing damage. There is no requirement and no benefit to having more power, and no advantage to having less power. There is no reason to cook specs because more power would simply cook voice coils. We wouldn't want that because our warranty fully covers the voice coils against getting cooked for 2 years! 


Thanks for your comments,

best,

David Lee

 

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Tatnall
Damnmnmnmnmnnnn Mr Bassboss Questions, any more inquiries for sir David Lee?? Son you got handed to in that marvelous electrical engineering smack down. Best pick up your pocket protector and volt meter off the floor and head out....... Damnmnmnmnmnnnn that sh%t was hot.

Actually all joking aside that was a really interesting read probably the best explanation of speaker impedance, usable wattage, supplied wattage, RMS, and just I guess basic knowledge of speaker electrical engineering. And the winner of that forum fight
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AdubsDJService
I have to concur with Tatnall. That was an excellent read probably the best thorough explanation of speaker impedance, usable wattage, supplied wattage, RMS, and knowledge of speaker electrical engineering.

I would say an the level of a "deep dive" [smile]


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