Considering a DIY cab from Eminence website

[gregoire1]

Most of these designs are single driver cabs, if I choose 2 drivers, can I just double the box volume and number of ports?

[MNAirHead]

Trust me.. start reading.. or consider one of the tested and proven designs.

I built 5 cabs to find one that I liked... I did it for the personal challenge.. it is NOT a way to save money

[gregoire1]

I've followed the fEarfuls but the drivers are kinda pricey, (I need 4ohm), and I've built an Omni10, but sometimes I miss the harmonic distortion. The Eminence designs allow "budget" drivers, in cabs designed by someone who (I hope!) knows what they're doing. There are just very few multi-driver cabs for bass guitar.

sorry if this is a dumb question.

[DukeLeJeune]

Yes, if you double up on the drivers, go ahead and double up on the box volume and number of ports. Like if the Eminence design calls for 1 cubic foot and one 4" port that's 6" long, use 2 cubic feet and two 4" ports, both 6" long.

Note that the Eminence designs usually call for a protective high-pass filter to prevent fartout. If you don't have a protective highpass filter similar to what they recommend, use a lower tuning frequency to better protect the driver. Typically mid to upper 40's works well.

What driver are you looking at?

[gregoire1]

Thanks Duke, I'm thinking about a 2x12 (or 2x10) based on the baslites s2012 (or s2010). I have noticed the HPF warning, but am told my head (GK Bl600) already has one which I hope is sufficient.

[billfitzmaurice]

Originally Posted by DukeLeJeune

Note that the Eminence designs usually call for a protective high-pass filter to prevent fartout. If you don't have a protective highpass filter similar to what they recommend, use a lower tuning frequency to better protect the driver.

They don't need filtering any more than any other designs do, though no less either. Jerry specifies them as a CYA measure, following on the heels of the LAB12/LabHorn fiasco that led to this missive:
http://eminence.com/faqs/faq5.asp

In standard alignments you'll hear the driver fart out well below the thermal power limit, with the exception of the Kappalite LFs. The downside to having the displacement limited power so close to the thermal rated power is that the driver won't fart out before failing. That's something owners of Kappalite LF drivers should be aware of.

[DukeLeJeune]

Originally Posted by billfitzmaurice

They don't need filtering any more than any other designs do, though no less either. Jerry specifies them as a CYA measure, following on the heels of the LAB12/LabHorn fiasco that led to this missive:
http://eminence.com/faqs/faq5.asp

In standard alignments you'll hear the driver fart out well below the thermal power limit, with the exception of the Kappalite LFs. The downside to having the displacement limited power so close to the thermal rated power is that the driver won't fart out before failing. That's something owners of Kappalite LF drivers should be aware of.

Thanks for the information, Bill. Yeah I've thought about undersizing the ports a bit on boxes with Kappalites just so there's some audible sign of distress to let you know you're pushing 'em close to their limits, but I don't know whether that would work.

[billfitzmaurice]

Originally Posted by DukeLeJeune

I've thought about undersizing the ports a bit on boxes with Kappalites just so there's some audible sign of distress to let you know you're pushing 'em close to their limits, but I don't know whether that would work.

It would work to some extent, you could size them so that they start chuffing at a pre-determined input level. Since chuffing occurs over a relatively narrow bandwidth near Fb it wouldn't be a perfect solution, but better than nothing.

[bgavin]

Reducing the vent area compromises the design.

Vent output is directly affected by the vent area.
Doing the math for the 3015LF in a Flat alignment, the vent areas are 45.6 and 33.7 square inches for Mach 0.045 and 0.100 respectively.

The 0.100 Mach value is the upper limit for acceptable non-chuffing.
The formula 20log(VentArea / Sd) produces the dB correction factor for the difference in vent vs. woofer radiating area.

At Mach 0.045 this is 20log(45.6/136.57) = -9.52dB
At Mach 0.100 this is 20log(45.6/136.57) = -12.15dB

Reducing the vent area from ideal to minimal incurs a -2.63dB penalty in vent radiation.
Bigger is better.

Link to Vent vs. Woofer Nearfield

[greenboy]

There's no stopping the deaf and the dull from blowing drivers. Certainly chuffing won't deter them... chuffing is a "feature" in a lot of bass cabs anyway so people think it belongs there ; }

Maybe put some pressure-specific whistles on the baffle ; }

[bgavin]

Originally Posted by greenboy

Maybe put some pressure-specific whistles on the baffle ; }

I can sure agree with that... compromising the design to function as a wake-up call is a bad idea.