Questions about massloading/tuning

1581 Views 9 Replies 6 Participants Last post by FoxPro5, Apr 4, 2009

WhiteFiver

Discussion Starter · Apr 4, 2009

I'm looking for some help on basic sound principals & tuning. I've done a bunch of reading on here, but I'm not sure I fully understand how everything works.
This is how my system is set up:
Car is a 2008 Pontiac G5 with base stereo (not factory upgrade).
I have an LOC spliced into my front speakers. Each channel is going to the correct output channel on the LOC, to retain Balance features. I'm using a stock head-unit.
RCA's are connected to this amp:
Audio System - Products - F2 190
Amp is connected to Kaption CLX-602 6" 2-way (iirc) speakers.

My questions are this:
What should I have the cutoff frequency for the speakers set to? I don't have a sub ATM (the last one got a screwdriver through it), but I will be adding one or two in the near future.

Next question:
I've read a little bit on here about massloading. Does that basically mean stuffing the empty space behind panelling with foam? If so, does it matter what type of foam it is?

TIA
Nathaniel.

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Xander

· #2 · Apr 4, 2009

Start around 80 hz. If you hear distortion at higher volumes or when there is bass, raise the crossover frequency.

Mass loading is just that...applying mass to a surface. This is done with products based on asphalt, rubber, concrete, etc. Heavy stuff. These materials lower the resonant frequency of the material by increasing the mass of the object. So it rings less and does not flex as much.

Foam serves a different purpose. It absorbs, diffuses, or deflects sound waves. This helps to keep sound waves from bouncing back to the cone of the speaker and introducing distortion. Foam is also used between panels to stop vibrations.

Optimally you want to mass load all metal panels (even some plastic ones) in the vehicle interior. Then apply foam on top of the mass loading material behind the speakers to reduce reflections back to the speaker cones.

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Rudeboy

· #3 · Apr 4, 2009

Mass loading is really the wrong term. You would need to add much more mass than is practical to lower a panels resonance enough to be inaudible. Adding mass also increases the amplitude of a panel's resonance at its natural frequency which actually makes it more effective at propagating sound - exactly what you don't want. It's almost impossible to add mass without stiffening the panel and since adding mass and stiffening move the panel's resonant frequency in opposite directions you can easily end up with no net change.

What you do want to with resonant panels is apply vibration damper on the center of the panel. This will minimize the resonance.

Put foam between any two components that are in intermittent contact. Door card/door skin, etc.

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Brian Steele

· #4 · Apr 4, 2009

Rudeboy said:
Mass loading is really the wrong term. You would need to add much more mass than is practical to lower a panels resonance enough to be inaudible. Adding mass also increases the amplitude of a panel's resonance at its natural frequency which actually makes it more effective at propagating sound - exactly what you don't want. It's almost impossible to add mass without stiffening the panel and since adding mass and stiffening move the panel's resonant frequency in opposite directions you can easily end up with no net change.

What you do want to with resonant panels is apply vibration damper on the center of the panel. This will minimize the resonance.

Excellent points.

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Oliver

· #5 · Apr 4, 2009

WhiteFiver look for pics in the build logs

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WhiteFiver

Discussion Starter · #6 · Apr 4, 2009

Xander said:
Start around 80 hz. If you hear distortion at higher volumes or when there is bass, raise the crossover frequency.

Mass loading is just that...applying mass to a surface. This is done with products based on asphalt, rubber, concrete, etc. Heavy stuff. These materials lower the resonant frequency of the material by increasing the mass of the object. So it rings less and does not flex as much.

Foam serves a different purpose. It absorbs, diffuses, or deflects sound waves. This helps to keep sound waves from bouncing back to the cone of the speaker and introducing distortion. Foam is also used between panels to stop vibrations.

Optimally you want to mass load all metal panels (even some plastic ones) in the vehicle interior. Then apply foam on top of the mass loading material behind the speakers to reduce reflections back to the speaker cones.

So by lowering the resonant frequency of panelling, does it also contribute to lowering the overall resonant frequency of the car?

Rudeboy said:
Mass loading is really the wrong term. You would need to add much more mass than is practical to lower a panels resonance enough to be inaudible. Adding mass also increases the amplitude of a panel's resonance at its natural frequency which actually makes it more effective at propagating sound - exactly what you don't want. It's almost impossible to add mass without stiffening the panel and since adding mass and stiffening move the panel's resonant frequency in opposite directions you can easily end up with no net change.

What you do want to with resonant panels is apply vibration damper on the center of the panel. This will minimize the resonance.

Put foam between any two components that are in intermittent contact. Door card/door skin, etc.

So there would be a benefit to stuffing my interior door panel full of foam?

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Rudeboy

· #7 · Apr 4, 2009

WhiteFiver said:
So there would be a benefit to stuffing my interior door panel full of foam?

That depends on what you are trying to accomplish. If your plastic trim panel is buzzing, putting a resilient closed cell foam between it and the metal skin so it is exerting force on both the plastic panel and the sheet metal skin will probably help. it will also eliminate some resonance and if it covers the entire surface it will block some high frequency noise. In terms of just making the the door mounted speaker sound better, it won't make much difference.

The general steps for making a door into a better speaker enclosure are to treat the inside surface of the exterior skin with a vibration damper. If you want to reduce noise coming through the door, line it with a barrier like mass loaded vinyl. To improve low frequency attenuation, add a layer of closed cell foam between the sheet metal and the barrier. This also decouples the barrier from the substrate.

Moving to the inner skin - the one the door card attaches to, use some vibration damper on the flimsiest areas. Next you want to close off the access holes in the door with something stiff and as non-resonant as possible. This gets you closer to a sealed enclosure. It's important that the speaker be mounted to a solid surface, so if you haven't done so already, consider making something out of a high density material for that purpose. If you want even more noise reduction, apply a barrier over the entire surface.

Before reattaching the door card, it is a good idea to make a gasket from closed cell foam that fits between the card and the sheet metal wherever the two make contact. This should eliminated buzzing and rattles between the two surfaces.

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FoxPro5

· #8 · Apr 4, 2009

WhiteFiver said:
So by lowering the resonant frequency of panelling, does it also contribute to lowering the overall resonant frequency of the car?

Yes, it can. This is one of the main reasons for applying vibration damper to the roof. Not in all vehicles, but the roof is usually a large, flat transmission line that can distribute resonance all over the car. For ex, when I "killed" my roof, my rearview mirror became nice and still due to me damping the transmission line vibration between the subwoofer in the hatch and the mirror with damping material.

Keep in mind the mass added was about .4 lbs sqft. Like Rudboy said, there's effective vibration damping with effective vibration dampers and there's mass loading - they are not one in the same, never have been and never will be. If you want to mass load, IMHO, use some MASS and do it!

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WhiteFiver

Discussion Starter · #9 · Apr 4, 2009

Allright, thanks for your help! Next time my door panels come off, I'm definately doing some work to them.

The other question I have is this:
Is it possible to wire the speakers with a switch and possibly some relays, so that I can switch the speakers signal from the amp to the headunit, semi-on-the-fly, so that if I ever need to do work on the speaker system or amp system, I can still have something to listen to?

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FoxPro5

· #10 · Apr 4, 2009

WhiteFiver said:
Is it possible to wire the speakers with a switch and possibly some relays, so that I can switch the speakers signal from the amp to the headunit, semi-on-the-fly, so that if I ever need to do work on the speaker system or amp system, I can still have something to listen to?

You'd have to have have two separate speaker runs; one from the deck and one from the amps. Sounds like a mess.

Keep an AM/FM radio handy and put it on your dash. :laugh:

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