Jonah M.

asked • 05/22/19

Home-made speaker cracks when bass is played loudly

I made this "boombox" type speaker about a year ago and it always crackles at loud volumes during bassy parts of the song. The boombox consists of 2 JBL CLUB6520 6.5" 300W Club Series 2-Way Coaxial Car Speakers. And one JBL Stage 810 8" 200-Watt Subwoofer. It is powered by a Dual channel amplifier of 50W+50W power output, and a 100W subwoofer output and a input voltage range from 12V to 26V DC. I am using a 12v battery to power the amp.


Any solutions on how to make the bass not crackle. Is it possible I need a more powerful amplifier?



2 Answers By Expert Tutors

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James R. answered • 05/26/19

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MIT & Harvard graduate | NYS certified math teacher | 30+ yrs tech exp
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Based on the incomplete information you have provided (it would have been useful to see the construction and more details on the equipment and battery specifications.), I think the "crackle" that you described could be caused (at least) by one or more of the following:


(1) mechanical vibration in the speaker cabinet or mounting structure

(2) distortion caused by overloading the amplifier inputs, over driving the outputs, or speaker impedance mismatch

(3) loose or corroded connections

(4) defective or under powered battery

(5) defective amplifier

(6) tears or other damage in the speaker cone


To solve the problem, you should systematically eliminate the possible reasons that I stated above, or any others you think of. Start with the simplest first, such as verifying that the unwanted noise is not mechanical. After that, examine all wires and connections and the condition of the speaker assembly. If you are good up to this point, I would start at a low volume level and gradually increase the volume until the problem starts. At this point, check to see whether the input specifications for the amplifier have been exceeded (your voltage numbers seem suspect). If you can achieve the loudness you desire without distortion, then you might explore building a simple attenuating circuits (e.g. a voltage divider) to limit the input voltage to the amplifier to avoid distortion.

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Jonah M.

Ok, thank you for the answer. I am already sure that it is not mechanical vibration or tears to the speaker cone. I just got a 12v step up to 24v. So now I have 24v going into the amp. The problem still occurs. I think the problem lies in the amplifier. I just ordered a more powerful amplifier that will hopefully not distort the bass at loud volumes.
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05/29/19

James R.

tutor
Well it is good that we can eliminate a couple of variables. But without knowing more about the details of your setup and equipment, I am at a loss to confidently give you further advice. For example, what prompted you to use the 12V to 24V step-up? Is the amplifier rated for a 24V power supply? What is the power output rating of the amplifier? What is the power rating of the speakers? Are the speakers and power amp impedance matched? What is the length and gauge (AWG) of the power cables and speaker cables you are using? Every mismatch wastes power and has the potential to lead to distortion. And remember, the step-up device does not manufacture power. (Power out) = (Power in) - losses, where Power = voltage x current. For a given amount of power, the step-up device delivers approximately half the current at twice the voltage. So, if your battery and cables are not capable of delivering the power required by your system, then stepping up the voltage will not solve that.
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05/29/19

James R.

tutor
Ah, and the other thing I mentioned - over-driving the amplifier inputs: what is the source for the input to the amplifier? Is the output of the source matched to the input specification of the power amp (voltage range, impedance)? To be clear, the input voltage of the amp is to be distinguished from the amplifier power supply. I'm sure you know this, but I make this point for the benefit of other readers who might not. For example, a high-impedance "line-level" input might distort given an input signal greater than 1 or 2 volts, whereas a low-impedance "speaker-level" input might be capable of taking several volts of audio input because it was designed to be driven from the headphones output of an audio device.
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05/29/19

Jonah M.

The boombox consists of 2 JBL CLUB6520 6.5" 300W Club Series 2-Way Coaxial Car Speakers. And one JBL Stage 810 8" 200-Watt Subwoofer. It is powered by a Dual channel amplifier of 50W+50W power output, and a 100W subwoofer output and an input voltage range from 12V to 26V DC. I am now using a 24v to power the amp. I am going to check the speaker connections. The impedance of the speakers is matched to the amp. To be more specific, Everything sounds great until I get to around 75% volume. Then if there is a bass drop it crackles. And 75% is louder than you probably think it is.
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05/29/19

James R.

tutor
Thanks for that info. Please see my comments about the difference between input voltage and power supply voltage. By "input voltage", I mean the voltage range of the audio source - NOT the voltage of the power supply that is powering the equipment. Your system should be designed such that at 100%, you get no objectionable sounds from the type of music that you listen to, at the volume level you want. This means that if the system is loud enough for you at less than 100%, then you need to attenuate the input signal. On the other hand, if at 70% (say), the system has no distortion, and it is still not loud enough for you, then I would agree that you need a more powerful amplifier. You car speakers claim to be rated for 300W. I am suspect, But if they really are, then your amp should certainly be sized below that. Also, I hope you are using a CROSSOVER. If you are feeding a lot of bass energy into the speakers, or non-bass energy into the subwoofer, you might be getting distortion that way as well, because the speaker cones for each type of speaker are designed to handle only a certain range of frequencies at their rated power level.
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05/29/19

Jonah M.

thank you for the advice. I will check to see if it is in crossover.
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05/30/19

James R.

tutor
Not what I meant. I just wanted to make sure you were using one. I doubt if the problem is in the crossover. It could be a problem if you were NOT using one.
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05/31/19

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