Is this a fault or normal, sub bottoming out when at max?

[mikay786]

Hi guys, just finished working on a monitor audio BXW10 subwoofer, repaired amp section.

Anyhow when testing when at maximum volume it makes a metallic clapping sound, perhaps bottoming out. Ive made a video to show this

Is this a fault with the driver or is this normal and perhaps just too much gain on my phone? On my PC connected same way as below is fine, when connected to my amp again can make the clunk when at max.

(yes using phone via 3.5mm jack to RCA inputs on sub)

https://youtu.be/vMmEa9WBxVc

[stj]

Re: Is this a fault or normal, sub bottoming out when at max?

is the speaker o.k.?
maybe the magnet assembly is loose.

i cant see how you could get a metalic sound from the "normal" moving parts!

[mikay786]

Re: Is this a fault or normal, sub bottoming out when at max?

Not sure , its definitely coming from the speaker / driver itself as have removed from case and isolated it by picking the speaker up so its in free air and still makes the sound at max.

the cone is metallic aluminium material, it sound like that is hitting something. For example I can replicate the sound by putting something hard in front of the cone when its on for example a pen and when the cone hits it make the same kind of noise.

[budm]

Re: Is this a fault or normal, sub bottoming out when at max?

That is the sound of Voice coil bottoming out, I get the same sound on my JBL Sub when I drive it really hard, overexcursion.
Just search for 'Voice coil bottoming out', and yes you can damage the speaker.
I.E.
http://www.data-bass.com/myths
https://www.youtube.com/watch?v=hbo73j9fqRU

[mikay786]

Re: Is this a fault or normal, sub bottoming out when at max?

Cool so the sub is ok then, just turn it down a bit?

So even with a new driver it would bottom out too?

[budm]

Re: Is this a fault or normal, sub bottoming out when at max?

Cool so the sub is ok then, just turn it down a bit?

So even with a new driver it would bottom out too?

If you overdrive the speaker that would happen to new or old speaker.
You want the long excursion speakers (Long throw subwoofer drivers) to help reduce the chance of over excursion.
Good sub woofer should have built-in limiter circuit.

http://www.tobyspeakers.com/modern-subwoofers.html
http://sound.westhost.com/articles/speaker-failure.html

[mikay786]

Re: Is this a fault or normal, sub bottoming out when at max?

Its an entry level model so guess it doesn't have a limiter.

You would think the amp would not let you overdrive the driver, given they would be rated at similar watts?

[Khron]

Re: Is this a fault or normal, sub bottoming out when at max?

Watts and excursion (or limiting it) don't really have much to do with one another.

Underpowering a speaker is the worst thing you can do - when the amp clips, it's basically sending DC to the driver, which can / will toast the voice coil.

Overpowering is better (or best), but only in the sense that the amp should be capable of delivering at least the power the speaker's rated for. Limiters can only help so much, before they actually end up clipping the signal in the first place.

The only thing you can do is be a bit more sensible with the volume control Or if you REALLY want / need more SPL, just get more speakers

[diif]

Re: Is this a fault or normal, sub bottoming out when at max?

It's a sub designed for home cinema rather than music.
It's got a crossover in, so if it's on it's own you're missing the middle and high frequencies.

[kaboom]

Re: Is this a fault or normal, sub bottoming out when at max?

Underpowering a speaker is the worst thing you can do - when the amp clips, it's basically sending DC to the driver, which can / will toast the voice coil.

No it isn't. At worst, it's square wave with higher average power.

This old wives' tale needs to die.

http://billfitzmaurice.info/forum/viewtopic.php?t=1886

DC in Clipping

One of the most famous myths regarding clipping is that it produces DC. The assumption is made because of the flat tops and bottoms to a square wave. It's incorrect to think of a squarewave as made up of positive and negative dc components. The only way for a it to be DC would be if there was a non-zero average value over long periods of time. If the polarity changes at all within the time frame that you are looking at, it is simply not DC. What are these flat portions of the signal? It is simply a combination of the fundamental frequency and all of it's higher order harmonics in sine wave form. For example, if you were to play a 20hz tone while clipping, there would be the fundamental frequency (ie. 20hz) and the second (40hz), third (80hz), and 4th (160hz) order harmonics. The sum of these frequencies creates what appears as a squarewave. There are two ways to test this for yourself; one is quite easy, the other is a little more advanced. The first way is simple if you have a variable crossover and an oscilloscope handy. Pass a low frequency square wave. You will notice the square shape on the oscilloscope. Now turn your crossover's low pass filter on. Slowly lower the setting as you approach the fundamental frequency. You will notice the waveform on your oscilloscope slowly rounding off into a typical sinewave. Once you have reached the fundamental frequency, your oscilloscope will show a perfect sinewave. The second way is for your math guys (or for those who like to use Matlab). If you look in the frequency domain using a Fast Fourier Transform, you will see the fundamental frequency and its higher order harmonics only. There will be absolutely no DC present.

This is BCN; let's not stoop to spreading misinformation and outright lies, as if it were "antecrep's" playground.

http://forum.qscservice.com/viewtopic.php?f=29&t=2736
http://www.proaudiospace.com/forum/t...-damage-a-myth

The classic reality-check:

If it were true that clipped signal blew speakers, people would be blowing up there guitar rigs constantly since modern rock guitars are constantly driving clipped waveforms through their drivers both from overdriven preamp stages as well as output stages

[smc]

Re: Is this a fault or normal, sub bottoming out when at max?

Over excursion. Lower the level on the sub, it should never be past 50%, especially on entry-level equipment. It almost seems like that isn't the proper cabinet for the driver too. I would suggest building a ported enclosure, but it might not be worth it; it might be more cost-efficient to just buy a better sub and build a proper enclosure for it for what your needs/tastes demand.

I'd be happy to help, as I have a hardcore aversion to bad bass and terrible-sounding audio "systems." I design audiophile-grade speakers and crossover networks. I specialize in making low-cost speakers sound GOOD.

Props to kaboom for the hand-slapping!

[Khron]

Re: Is this a fault or normal, sub bottoming out when at max?

In light of new evidence, i stand corrected. My bad...

[charis]

Re: Is this a fault or normal, sub bottoming out when at max?

My friend the sub seems to lost some freq responce(OVER 60 Hz) maybe is your smart phone that dont match the input specs .
If you have low crosover pass inside check the caps usualy are 2 3.3 or 4 μf about 65 v or more (usualy for 100w output)
The good units have Mylar capasitors that very difficult to fail.
Sometime the freq adjustment in this units get rust and that can destroy the responce.