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speaker cabinet resonance?
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sammi84
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#1
25th December 2010
Old 25th December 2010
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speaker cabinet resonance?

Hello slutz, long time reader first time poster .

I am a relative noob.

I have some krk rp5's, just hooked them up and on ultrabeat with some kick drum bass my speaker cabinet appears to be resonating , ive many diy bass traps and the speakers themselves are on sand filled stands which are on conrete.

Is this normal? or are my speakers faulty? or is it the amp inside or something?

do all speaker cabinets resonate to some degree? this is the first time ive used monitors usually use headphones.

Ive gone around the studio and it really does sound like its coming from the speaker cabinet it self .

thanks

sammi
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26th December 2010
Old 26th December 2010
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Sadly, a lot of expensive monitors do have cabinet resonances and rattles. It's the nature of economics: these things are built cheaply and lightly for the mass market. If they were built first and foremost for sound quality, they would use heavy solid woods and dovetail joints and the shipping costs alone would make them uncompetitive.

Maybe you can repair them with some glue and bracing. Sometimes all you need is a bit of absorbant (e.g. foam or felt) jammed between the speaker terminals - it can act like a shock absorber.

Room position may affect rattles - it might be situated in a nasty low frequency node. Try not to send unnecessary sub frequencies to them - maybe keep a limiter with a high pass filter on the master bus.
sammi84
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26th December 2010
Old 26th December 2010
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Ok thanks a lot for your reply, knowing that it is something even expensive monitors suffer from makes me feel a little better, yet a little annoyed with the price of serious monitors that could still have this problem.

I found the resonance was subject to some psychological affect, when i first heard it - it was all i could here - very distracting, when i read that it is a problem with a few speakers i didnt notice it so much...

could u answer me another few questions?

When using a bass kick drum like an 808 that last for about a second before serious decay, then u play a bass note of a similar pitch is it normal for the speakers to cut in volume slightly almost like its overloaded?

it is a stupid question as i dont tend to use more than one instrument for low pitch noises but was surprised the speakers couldn't handle it - yes 5 inch speakers i know but still....

And to follow on would a sub (eg krk rp10) ;

1) cut the resonance from the rp5 cabinet (as i will use filter any frequency below 80hz) with out replacing it with its own.

2) be able to handle a sub bass kick drum and more of a tuned sub bass at the same time?


And finally you mentioned room nodes, i have read about them when acoustically treating my studio/shed. Are you saying that these nodes can affect the resonance coming from the speaker cabinet?? Is that not dictated by the cabinet itself? or can these horrible nodes also be causing the resonance from the rp5s?

Apologies for the lack of knowledge and many questions.

Thanks

Sammi

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26th December 2010
Old 26th December 2010
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Have you ever played a bass guitar or synth bass in a room, and noticed that on certain notes the windows rattled? Basically, all structures have a resonant frequency based on physical dimensions and the speed of sound. If you excite a structure at it's resonant frequency, you can induce a sympathetic vibration. The transfer of energy is very efficient at this exact frequency, and the longer the impulse is applied, the stronger the amplitude of the vibration grows - possibly to the point of structural damage.

Bass notes have long wavelengths, measured in metres. If you imagine a full sine wave (positive and negative peaks) of several metres in length, there are the zero crossing points, and there are the two peaks. The zero crossing points are where the air velocity is zero, and the peaks are where the velocity is at maximum. This is why 1/4 wavelength is very important: 1/2 wavelength is just a zero crossing, but 1/4 and 3/4 wavelength are the two peaks where velocity is maximum. Whether you are trying to dampen/absorb bass notes, or whether you are trying to excite them - 1/4 wavelength is the best place.

So if you have a bass frequency that is causing your cabinet to rattle - it will be worse if the cabinet is located 1/4 or 3/4 of that wavelength from the wall (a wall being an obvious zero crossing). This is roughly how 'nodes' work.

Is that a real analog 808? Analog synths can generate sub harmonics and voltage transients that can be hard on a speaker. Digital is sort of self-limited by the converters. But if you are layering sounds, it's also possible to create 'beat' frequencies that are sub audio. For example: if you play two sinewaves together, one a 100 hz and the other at 107 Hz, you are going to get two 'sideband' frequencies of 7 Hz and 207 Hz. Even if your converters and speakers can't reproduce 7 Hz, the combined signals will mix in the air and recreate these additional frequencies.

That's basically why i'm suggesting you try moving the speakers - and consider using a limiter and high pass filter. (I use Voxengo Elephant).

I've often found with pairs of speakers that one will rattle and the other won't. A lot of monitors are built with chipboard to keep the cost down, which is a dodgy material. Construction methods are probably a bit rushed, and some will be better than others. Frustrating I know. And none of the makers or agents or pimps would ever admit that these products are compromised - but that's the nature of living in a market driven "economy" which forces makers to make things as cheap as they can get away with ...

Very often, if you want real quality, you have to build it yourself. Concrete or marble with plenty of rubber and foam would be a good material for monitor speakers ...
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