port lengths, Tuning my Box

I have two Kole Audio KMMX-15''s in a custom box. Kole Audio suggest that I should tune the box to 40 Hz. Suggestions include to have two ports, per driver, at 11'' with a diameter of 4''. Which would mean I need four ports, but I only have two.

Right now, the box is 6 cu ft, and the subs are in one chamber. The port diameter is 4'' right now and the port length is 11'', but I only have two ports in all instead of four(the suggested number from Kole Audio). Right now I calculated that my box is tuned to about 29 Hz.

Am I hurting my subs by having it tuned so much lower than the suggested tuning of 40Hz? I tested the box by putting two ports that were 6.25'' (35Hz) in and I didn't like the output. The punchy beats were somewhat better but I lost soo much of my low end bass, and I listen to mostly rap, Three 6 Mafia with low deep bass.

Last Question..lol. I used a port calculator, and I found out that I could simply tune my box to 40Hz by making the port lengths 4'' with my existing two ports. What are the advantages of drillng two more holes in the box and added two more ports so I would have the suggested number of ports for my drivers. Basically im asking why have four ports at 11 inches that makes 40Hz, when I could just have two ports at 4 inches that makes 40Hz also.

Thanks in advance

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

Need help guys. I'm about to leave here in a few to pick up some more PVC pipe so it would be appreciated before I leave

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

You can build an enclosure tuned to any frequency you want to, however you don't want to go below what the woofer is capable of.  But what's the Fs, Qts and Vas of the woofer?  Are you using a subsonic filter?

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KMX-15
• 2000 Watts MAX Power
• 1000 Watts RMS Power
• 270oz. Magnet
• 4-inch 18 AWG Voice Coil
• Fs: 29.6 Hz
• Vas: 1.79 Ft3
• Qms: 4.685 • Qes: 0.484 • Qts: 0.439
• Xmax: 0.748"
• SPL: 92 dB
• Recommended Enclosure: 3.0 Ft3 Ported
• Port Size: 4" x 11.25"
• # of Ports:

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

and no, i am not using a subsonic filter.

Is it better for me to tune the box to 40Hz by using two ports with lengths of 4'' OR four ports with lengths of 11''...thats my main question

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

The formula are Vb = 20*Qts^3.3*Vas, Fb = (Vas/Vb)^0.31*Fs.  Vb = volume of the ported enclosure, Fb = best tuning frequency.  Volumes for those equations must be in liters. 

Since your enclosure is already built at 4 cuft, you're stuck with that even though it is not optimal for those woofers.  So using 4 cuft (113.25 liters) your ideal Fb would be about 28 Hz.

To answer your question about what ports to use, @ 4" diameter, 40Hz tuning in a 4 cuft enclosure with 2 ports each needs to be 7.6" long.  With 4 ports each needs to be 18.25" long.  With your woofers I'd say 4 will be better than 2 to minimize port noise.

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ok thanks...ima replug in a few figures cause the box is at 6cu ft, not 4cu ft...but again thanks

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

Oh, and if you plan to use an amplifier anywhere near the RMS rating of those woofers, you'll need a subsonic filter of at least 24 db/octave set at or just below Fb.

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At 6 cuft 4X 4" ports @ 40Hz = 11.18" each.

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Ok, one more question, sorry if im a bother. What exactly is a subsonic filter? I alway hear of it but still am not exactly sure what it does.

This is the amp I have hooked up to the drivers.

Power Acoustik A2400DB

# Ultra-Efficient Class D Circuitry
# Fully Regulated PWM Mosfet Power Supply
# 1 Ohm Stable - 1800 Watts RMS Into A 1 Ohm Load!
# Variable 50-150 Hz Low-Pass Crossover
# Variable 15-40 Hz Subsonic Filter
# 0-180 Degree Phase Control
# Variable Bass EQ at 45 Hz
# Remote Level Control Included
# 4-Way Protection Circuit
# Gold-Plated Input and Speaker Terminals
# 1 Ohm Stable
# RCA Outputs

# Amplifier Type: Mono
# RMS Power: 900W x 1 @ 4 Ohms
# THD at 4-Ohm RMS Power: 0.5 %
# RMS Power: 1400W x 1 @ 2 Ohms
# Speaker Level Inputs: No
# Preamp Outputs: Yes
# Built-In Crossovers: LP
# Bass Boost: 0 - 18 dB
# Frequency Response: 15-150 Hz
# Signal to Noise Ratio: 100 dB

I know there is a small knob on the amp that says subsonic filter but i've never messed wit it because I didn't want to mess anything up

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

and i have the subwoofers hooked up series if that helps

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Subwoofer(s): Two(2) 15'' Kole Audio KMX-15's
Amplifier: One(1) Power Acoustik Digital Series 2400A
Headunit: Pioneer 860DEH
Speakers:Factory
Yellow Top Battery

A subsonic filter is a high-pass electronic crossover designed to protect the woofer from over-excursion.  In your case if you're tuning to 40Hz, set the amp's subsonic to just below 40Hz.  Woofers become "unloaded" below the enclosure port tuning frequency and can be destroyed very easily if they see too much power while unloaded.  A subsonic helps prevent that.

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