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Bass Reflex Enclosure & Port Tuning
Bass Reflex Enclosure & Port Tuning
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Old 2nd December 2004, 07:23 PM   #1
D_GR8_1 is offline D_GR8_1  Australia
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Default Bass Reflex Enclosure & Port Tuning

I have two bookshelf speakers in a D'Appolito configuration using Visaton 2xW130S & DT72 drivers.

The woofers are stated as having 49Hz Fs. My enclosure size is around 40L with a 50mm/150mm port. The box is tuned around 25~30Hz.

My question is, does it matter that the box is tuned much lower than the resonating frequency?

How does this affect the sound?
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Old 2nd December 2004, 08:20 PM   #2
Hornlover is offline Hornlover  United States
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Tuning a ported box needs to take into consideration several parameters. Go to the HEL site and download the article on Alignment Calculations.

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Old 2nd December 2004, 09:11 PM   #3
aaroncgi is offline aaroncgi  United States
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Default Depends on many variables, as Hornlover mentions.

I personally like to tune much lower than Fs, often very close to the 50% of Fs that you mention. My reasons are that doing so keeps the group delay in the audible frequencies much closer to that of a sealed box, while stile increasing the power handling and achieving lower extension than the sealed box provides. Also, tuning lower will allow you to use a somewhat unusual slope, say a slope that falls off at 4-6 dB per octave down to Fb, as opposed to a flat line down to Fb then dropping at 24 dB per octave. I find that the slow rolloff starting higher, down to a quite low Fb, leads to a better match with the gain inherent in most rooms.

Whether this option is really viable though, will depend greatly on the size of the box. If it's too small, the advantage to tuning so low vanishes and there's little difference from the sealed box. A larger box really helps when you want to extract more extension tuning 50% below Fs.

Tuning lower also has the benefit of reducing the frequency below which the woofers will unload. Contrary to what I hear rather often, tuning so far below Fs does not make the power handling lower than it would be in a sealed box, because a vented box operates more and more like a sealed box as you increase frequency above Fb.

Aaron Gilbert
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