I am planning on building a cabinet around the JBL 322c. The cabinet will be 15.5" W X 25" H X 13.5" D (roughly heresy iv size) with an internal volume of 3948 cubic inches, just a hair under the 2.4 cubic feet of the enclosures JBL sells. I'd like to get down as close as possible to the 30hz measurement in the JBL specs. I am not sure how to go about calculating port dimensions, and was hoping someone here could help. My intention is to build this cabinet entirely out of 3/4" ply. Any help would be greatly appreciated!
I know nothing, but the drivers I see already have 2 ports?
Also you would want something like WinISD to tune the enclosure, and determine port dimensions, though this will be complicated since the driver comes with 2 ports already on it. If you've found a version of the driver without ports, ignore what I said and plug it into winisd.
Also you would want something like WinISD to tune the enclosure, and determine port dimensions, though this will be complicated since the driver comes with 2 ports already on it. If you've found a version of the driver without ports, ignore what I said and plug it into winisd.
Without TS values (or the ability to measure the driver), you're kind of dead in the water. Given that this is a ceiling speaker, getting it to go down to 30Hz may be a tall order, but that's just a guess.
jeff
https://jblpro.com/products/mtc-300bb12https://jblpro.com/products/control-322c#specificationsShould be all the info you'd need.
My plan is to take it out of the pre installed baffle and mount it in a wooden box.
If my box is the same size internally could I combine the width of the two ports on the baffle it comes on into one and match the depth?
It doesn't work that way exactly. Typically, when you enlarge a port diameter you also enlarge it's length. You're going to have to experiment with that if you have a specific vent tuning in mind. I noticed that JBL recommended 35hz as a DSP cutoff frequency. Port tuning was higher no doubt.
I'd knock together a box like the JBL blackbox and measure the driver w/port tuning. Then you can make what you like and abandon their baffle/ports. Remeasure in the new enclosure with your single port and adjust the port length to get a good match with the old setup.
Ahh, got it. I don’t have measurement software or microphones, just an iPhone, is it possible to take measurements with the phones mic?
OK, since you don't per se need actual specs to design the box/vent and assuming a ~ 35 Hz tuning like is shown for the 3 ft^3 box @ 400 W max will require a 'Sd'/2 = ~240.72"^2 (i.d.) vent duct to ensure a low vent mach in your smaller box.
Using Hornresp or similar quality accuracy soft/freeware and the default/whatever 8 ohm, ~20-40 Hz Fs driver specs, input the vent area and 1"/whatever long vent length to see where the driver's excursion tuning dip is and lengthen the vent dim. till it's in the 32-35 Hz range.
You will notice the vent is quite large and will need to fit outside your undersized box, so either recalculate for a bigger box or keep reducing the max power and/or its tuning as required to get the vent smaller/shorter with the understanding that 'Sd'/4 is the normal minimum for exceptable reflex performance.
If you set up the driver like I posted, using the existing baffle/ports first, a guy could lay some raw rice in the cone and run some low frequency test tones through the woofer. Rice will stop moving around the tuning frequency of the old ports. I'd expect the tuning to be around 60hz ... so don't start too low with the test tones. Start at 100hz and work your way down.
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Oh, that's the fun part. 😉
Have a look thru this thread: https://www.diyaudio.com/community/threads/what-is-your-method-for-measuring-t-s-parameters.243435/
jeff
Have a look thru this thread: https://www.diyaudio.com/community/threads/what-is-your-method-for-measuring-t-s-parameters.243435/
jeff
Any number of ways to do it, so Google is your friend 😉, but based on JBL's published specs and your stated desired performance tuning, you don't need to, i.e. look at the 3 ft^3 's measured frequency/impedance response plot pdf down low where it shows two peaks in the impedance, so its box tuning (Fb) is a little bit offset to the right from center of the dip, hence my ~32-35 Hz assumption, and if the peaks were equal amplitude, driver resonance = ~35-40 Hz Fs.
The big peak around ~105-110 Hz implies the system is DSP'd and/or the box is still much too small for its specs, implying a typical ceiling driver's high Qts (low effective motor strength), low compliance (Vas), so if the latter is true, the peak will be higher with decreasing box size (Vb).
All that said, always nice to know any driver's (after break-in) specs, so looking forward to what you measured for each driver.
The big peak around ~105-110 Hz implies the system is DSP'd and/or the box is still much too small for its specs, implying a typical ceiling driver's high Qts (low effective motor strength), low compliance (Vas), so if the latter is true, the peak will be higher with decreasing box size (Vb).
All that said, always nice to know any driver's (after break-in) specs, so looking forward to what you measured for each driver.
Thanks everyone for all the information. I need to get some software and play around a bit before pulling the trigger. I still feel like a fish out of water though.
what determines if a speaker is a good candidate for a sloped horn. Could building something similar to a jbl c34 help this guys low end?
what determines if a speaker is a good candidate for a sloped horn. Could building something similar to a jbl c34 help this guys low end?
You're welcome!
In short, yes you could, but not normally worth the high total cost, effort since as a general rule a horn wants to 'feel' a powerful enough motor to cover the desired BW, so let's assume we want to boost/fill in the BW between ~ 35 - 100 Hz based on the driver's vented box response, so at a glance the C34 seems the obvious choice horn-wise, ergo we want a motor with a ~ 2*35/100 = ~ 0.7 Qts', which is very weak from a box loading POV, though could be dialed in with a pot and insert a fixed resistor, wasting a lot of power, so historically a high output impedance tube amp would be the way to go.
But the trade-off is a huge sized horn is required since driver wants to 'feel' an infinite baffle's super weak air mass 'spring' (acoustic) loading.
[Qts']: [Qts] + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html
[Rs] = 0.5 ohm minimum for wiring, so may be higher if a super small gauge is used as a series resistor plus any added resistance from an XO/whatever.
In short, yes you could, but not normally worth the high total cost, effort since as a general rule a horn wants to 'feel' a powerful enough motor to cover the desired BW, so let's assume we want to boost/fill in the BW between ~ 35 - 100 Hz based on the driver's vented box response, so at a glance the C34 seems the obvious choice horn-wise, ergo we want a motor with a ~ 2*35/100 = ~ 0.7 Qts', which is very weak from a box loading POV, though could be dialed in with a pot and insert a fixed resistor, wasting a lot of power, so historically a high output impedance tube amp would be the way to go.
But the trade-off is a huge sized horn is required since driver wants to 'feel' an infinite baffle's super weak air mass 'spring' (acoustic) loading.
[Qts']: [Qts] + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html
[Rs] = 0.5 ohm minimum for wiring, so may be higher if a super small gauge is used as a series resistor plus any added resistance from an XO/whatever.
Hi, sorry for ressurrecting this old thread. I've just come into possession of two JBL C322 drivers. I want to build the optimum cabinet for them. But there are no TS parameters available, but JBL recommends the MTC-300BB12 backbox with an internal volume of 2,4 cubic feet.
The easy approach is to copy that cabinet.
But then I looked at JBL's recommended third-party boxes and they vary wildly, from 2,4 cubic feet to 6 cubic feet. So what to do?
Thank you,
Mads
The easy approach is to copy that cabinet.
But then I looked at JBL's recommended third-party boxes and they vary wildly, from 2,4 cubic feet to 6 cubic feet. So what to do?
- How do I calculate the best size cabinet for the drivers if I don't have the TS parameters?
- Will a bigger cabinet than the 2,4 cubic feet, say for instance 4 cubic feet, allow the drivers to go deeper?
Thank you,
Mads