Calculate port length for JBL K110 in a small box

[deathness]

Hey gang,

Been a minute since I've been around these parts. I have a quick question I'm hoping someone can help me with. I have a small combo amp that I'd like to throw a JBL K110 in. It's 0.89 cu ft in internal volume (17" w x 14" h x 6.5" d). There is a 3 in round port hole in the baffle. I'd like to know how long of port would be needed for the JBL. Here are the relevant specs for the K110.

Fs - 65 Hz
Qts - 0.36
Qms - 4
Qes - 0.4
Vas - 45.3 litres
Re - 6 ohms

I don't have any modeling software at my disposal. Primarily, I'm using the combo for guitar (it's a 70s Ampeg bass practice amp) but I'd like to use it for low-volume bass practice, too. Essentially, the type of performance I'm looking for: optimized for clean guitar but also good for bass. So I'm not sure exactly what it should be tuned to... 40 Hz? 50 Hz? 60 Hz? I don't play any lower than Eb on a 4-string bass. Also, I tune half a step down on 6-string guitar.

Any help is appreciated.

 

[micguy]

In that size box, Win ISD gives you an optimal tuning with about a 75 Hz port tuning. -3dB is 80 Hz - the whole lowest octave of your bass will be unloaded (below the box tuning) , with the driver flappin' around. It might work OK for guitar, but for bass, I'd suggest it isn't a great combination.

This is the kind of result that happens when you try to force a driver and box size together without regard to if they'll work well together or not.

Win ISD is a free program - i suggest anyone who wants to build their own speakers get a copy and learn how to use it before you go buying parts that may or may not work well together.

 

[agedhorse]

No port length beyond the 3/4" baffle thickness is needed for just about as good tuning as you can get... BUT this is really a mid bass driver and you will run out of mechanical power handling at 100 watts RMS between 100 and 150Hz. I would certainly recommend using a 24dB/octave HPF set to at least 80Hz for survival.

Sensitivity will be in the high 90's (dB/1W/1M) with an F3 of 81Hz, an F6 of 70Hz and an F10 of 60Hz.

I am very familiar with this driver, it makes an outstanding companion to an 18" sub box in a biamped rig, I built several custom high dollar rigs for players back in the day based on these drivers plus the 2241 or 2242. Biamped at 100Hz or so makes for a really articulate sounding rig at good volume levels. Just beware that these are not very high power handling drivers, I typically used 2 of the 10's to 1 of the 18's.

 

[deathness]

Thanks for replies, dudes. Just to be clear, the amp tops out at 15 watts. For bass, I'm only want to have a box I can plug into quickly for practice without having to drag out my 40 lbs Sunn tube amp (Sorado) and 65 lbs Ampeg 1x15. I'm an NYC apartment dweller so space is an issue. I'm looking to get good performance with guitar (I've somehow become a tele player and go for clean clean clean) and not blow it up when practicing bass. For any live shows or recording on bass, I've got the Sunn and Ampeg.

The HPF is a nice idea! So if I leave the round port as is and chuck an HPF for a steep roll-off below 80 Hz, I should be good?

 

[deathness]

I suppose asking a bass players forum for optimal guitar performance on a drive is a kinda dick move.. just was worried that any guitar-centric advice wouldn't take into account that I would like to use this for low-volume bass and not damage the driver.

 

[agedhorse]

I suppose asking a bass players forum for optimal guitar performance on a drive is a kinda dick move.. just was worried that any guitar-centric advice wouldn't take into account that I would like to use this for low-volume bass and not damage the driver.

I missed the guitar part, but that's not going to be the challenge. At 15 watts, you are going to be plenty fine but an active 24dB/octave HPF will greatly improve your success.

 

[JimChjones]

Only thing I'd add is reckon to spend a good bit of time experimenting with damping material in the cab. My experience is there will be a big effect on tone. I fear though whats nice for bass will suck brightness out of the Tele.
Is there any chance you can run to a second cabinet? My gut feeling is that you'll be happier if you tune the cab for bass and plug a little 1*6 or 1*8 in for the guitar. My practice setup is a baby Blackstar combo that has a switched external speaker socket and it sits on and plugs into a ported 1*10 wedge for bass.

 

[agedhorse]

The K-110 is a very extended range driver without much coloration, good well past 5kHz -3dB. Some internal dampening of the cabinet shouldn't hurt for guitar and will help for bass.

I just looked at my data, it's rated for 75 watts RMS, so to others who may be contemplating using this driver in the future, respect these limits.