Dampening a cabinet

[Verdinut]

Sealed enclosures can also require damping material. Some plans that I've seen had very specific instructions for it. Others call for damping material and lack any specifics, which can be frustrating. The filler material can be used to tune the bass response, so it's something that you can play with to get the response you want, although having a recommended starting point is helpful.

With a sealed cabinet, there is no possible tuning as opposed to the ported box. As a matter of fact. the sealed box theoritically should not vibrate at any frequency. Damping material just prevents standing waves at certain frequencies.

 

[Eppie]

With a sealed cabinet, there is no possible tuning as opposed to the ported box. As a matter of fact. the sealed box theoritically should not vibrate at any frequency. Damping material just prevents standing waves at certain frequencies.

Would those standing waves still affect the response of the speaker as a whole? I understand what you mean by not being able to tune a sealed box, but would the amount of damping material in a sealed enclosure allow some adjustment at those certain frequencies, or is the goal simply to reduce any standing waves as much as possible?

 

[ryanosaur]

My understanding is that the Damping of a sealed cabinet increases the 'Apparent" volume of the box and will aid in lowering the Fb slightly. Verdi, TLS?

 

[TLS Guy]

My understanding is that the Damping of a sealed cabinet increases the 'Apparent" volume of the box and will aid in lowering the Fb slightly. Verdi, TLS?

You are correct, it increases apparent box volume. A sealed enclosure is tuned. The spring of the air in the box, and driver mass and compliance do create a resonant system. You actually have to manage it very carefully. Sealed speakers tend to have ripple before the 12 db per octave taper. In my experience modelling programs tend to under estimate ripple for some reason.

You have to design a sealed cabinet, with as much, if not more care than a ported one.

 

[Benni777]

Sealed enclosures can also require damping material. Some plans that I've seen had very specific instructions for it. Others call for damping material and lack any specifics, which can be frustrating. The filler material can be used to tune the bass response, so it's something that you can play with to get the response you want, although having a recommended starting point is helpful.

Yeah, no specification for this unfortunately.

 

[Verdinut]

Would those standing waves still affect the response of the speaker as a whole? I understand what you mean by not being able to tune a sealed box, but would the amount of damping material in a sealed enclosure allow some adjustment at those certain frequencies, or is the goal simply to reduce any standing waves as much as possible?

Standing waves affect the response and it's the reason for putting damping material to cancel them between parallel surfaces. There is an optimum box volume for a driver designed to operate in a sealed box. Increasing the volume of the box beyond this optimum volume usually does not provide any extension of the LF response, it will actually raise its LF limit.

 

[Eppie]

Standing waves affect the response and it's the reason for putting damping material to cancel them between parallel surfaces. There is an optimum box volume for a driver designed to operate in a sealed box. Increasing the volume of the box beyond this optimum volume usually does not provide any extension of the LF response, it will actually raise its LF limit.

That has some interesting implications. If the damping material increases the "apparent" volume of the enclosure, would you make the enclosure slightly undersized so that the damping material raises the apparent volume to the optimum?

 

[TLS Guy]

That has some interesting implications. If the damping material increases the "apparent" volume of the enclosure, would you make the enclosure slightly undersized so that the damping material raises the apparent volume to the optimum?

No, because the models take into account that the enclosure will be properly damped. An undamped, or not properly damped speaker rings like a barrel.

 

[highfigh]

With a sealed cabinet, there is no possible tuning as opposed to the ported box. As a matter of fact. the sealed box theoritically should not vibrate at any frequency. Damping material just prevents standing waves at certain frequencies.

Tuning, no, but optimizing for the most usable response, yes. Causing a slight peak is definitely useful in some cases but it's not 'tuning', in by definition.

 

[Verdinut]

Tuning, no, but optimizing for the most usable response, yes. Causing a slight peak is definitely useful in some cases but it's not 'tuning', in by definition.

Putting a loudspeaker driver in a closed box raises its resonance frequency. This new resonance frequency is the system resonance, and the bass cut-off occurs at this same frequency.
In summary, if the box is too large, you get a weak bass and a reduced power handling. If it's too small, you get a boomy bass and a reduced bass range. The optimum box size fits in between and is calculated from the driver's T/S parameters.

 

[Benni777]

Thanks again guys, lots of great info here.

 

[highfigh]

Putting a loudspeaker driver in a closed box raises its resonance frequency. This new resonance frequency is the system resonance, and the bass cut-off occurs at this same frequency.
In summary, if the box is too large, you get a weak bass and a reduced power handling. If it's too small, you get a boomy bass and a reduced bass range. The optimum box size fits in between and is calculated from the driver's T/S parameters.

I have built literally hundreds of subwoofer enclosures and I have never heard a woofer made for a sealed box sound 'boomy' in the same way as a vented box/port that was badly tuned. The Q can't be as high and the resonant peak can't reach the level of the peak from a badly tuned vent/box combo but I agree that your other points are accurate. It's all up to designing the box for the driver and choosing a driver that will do what's needed.