Subwoofer depth vs volume - AVS Forum
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Old 10-21-2011, 06:56 AM - Thread Starter
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Discussion for designing subs mostly speak of ideal volumes.

Is there a minimum depth component for this discussion?

Or could a sub be shallow, but tall and wide and sound as good as a cube?

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Old 10-21-2011, 07:23 AM
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It can be any dimension as long as you can fit the driver (possible plate amp in the box).

I have always wondered about a minimum distance for the rear wave of a woofer but I have never found any info, I think it wouldnt matter anyways but could not validate that opinion.

There are issues with standing waves when any one dimension gets longer then a 1/4 wavelength of a frequency within an octave of the design.

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Old 10-21-2011, 06:01 PM
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Some drivers with vents in the magnet structure will require some distance to allow air to flow through them without impediment, but 5cm or so should be enough unless the manufacturer recommends more. I doubt it will ever be critical for home use with the exception of some subs.
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Old 10-21-2011, 08:02 PM
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"Or could a sub be shallow, but tall and wide and sound as good as a cube?"

yes. if the reflection off the rear wall is properly damped.

otherwise the reflection off the rear wall comes back right through the driver and muddies things up.

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Old 10-22-2011, 01:16 AM
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Quote:
Originally Posted by LTD02 View Post

"Or could a sub be shallow, but tall and wide and sound as good as a cube?"

yes. if the reflection off the rear wall is properly damped.

otherwise the reflection off the rear wall comes back right through the driver and muddies things up.

It's not relevant for a sub, and for a shallow enclosure there are no acoustic materials available in thin sections that will be effective at LF.

For midbass and up I agree though.
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Old 10-22-2011, 08:33 AM
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Originally Posted by A9X-308 View Post

It's not relevant for a sub, .

It is, because the movement of the cone creates above bandwidth harmonics. Most of those will be heard from the front wave, which is unavoidable, but having them reflect off the rear wall will make matters worse. BTW, acoustically filtering said harmonics is a benefit of rear and down firing cones.

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Old 10-22-2011, 01:17 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It is, because the movement of the cone creates above bandwidth harmonics. Most of those will be heard from the front wave, which is unavoidable, but having them reflect off the rear wall will make matters worse. BTW, acoustically filtering said harmonics is a benefit of rear and down firing cones.

I might be havig a slow morning, but you're going to need to explain that in more detail please. I have never heard the term 'bandwidth harmonics' so references or appropriate math would help.
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Old 10-22-2011, 02:03 PM
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Quote:
Originally Posted by LTD02 View Post

"Or could a sub be shallow, but tall and wide and sound as good as a cube?"

yes. if the reflection off the rear wall is properly damped.

otherwise the reflection off the rear wall comes back right through the driver and muddies things up.

can someone show me how a 80Hz down to 10Hz soundwave can be dampened enough in any box? Aren't they just a little too large to be dampened?

Also considering the material used in our subwoofers (most are not paper!!) really is there enough "Bleed through" the woofer itself still??


Mid range is definitely a different story.

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Old 10-22-2011, 02:27 PM
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"can someone show me how a 80Hz down to 10Hz soundwave can be dampened enough in any box? Aren't they just a little too large to be dampened?"

big spikes up around 100-120hz have been measured in subs. knocked down with pillows. can't recall the links at the moment.

both you and alpha niner are right for low bass frequencies. the wavelengths are just too long.

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Old 10-22-2011, 02:31 PM
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Quote:
Originally Posted by A9X-308 View Post

I might be havig a slow morning, but you're going to need to explain that in more detail please. I have never heard the term 'bandwidth harmonics' so references or appropriate math would help.

Even if the input signal is low passed by a crossover the driver will create harmonics that extend well above the low pass frequency. The longer the excursion the greater the THD.
http://www.readresearch.co.uk/loudsp..._article_1.pdf
http://www.readresearch.co.uk/loudsp..._article_2.pdf
http://www.readresearch.co.uk/loudsp..._article_3.pdf

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Old 10-22-2011, 02:55 PM
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I was looking for your explanation as to why a shallow enclosure will make a difference. For example, as we are discussing subs, if a 20Hz signal is applied to a speaker which due to the driver's inherent non-linear behaviour, creates a 2H at 40Hz and the enclosure is of a suitable volume for the driver, please explain why the shallow depth will be of concern, say an enclosure just deep enough to contain the driver.



Quote:
Originally Posted by Bill Fitzmaurice View Post

Even if the input signal is low passed by a crossover the driver will create harmonics that extend well above the low pass frequency. The longer the excursion the greater the THD.
http://www.readresearch.co.uk/loudsp..._article_1.pdf
http://www.readresearch.co.uk/loudsp..._article_2.pdf
http://www.readresearch.co.uk/loudsp..._article_3.pdf

Well that's obvious and nothing I didn't already know - I misread earlier, neglecting the 'above'. I've had the papers for years - but I will re-read them later to ensure there is not something relevant I have forgotten directly related to the enclosure depth issue.
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