My freshly reconed JBL 2240s showed up today. They look good. If all goes as planned I will be measuring them in the cab this weekend.
________________
Best Regards,
Carl huff
My freshly reconed JBL 2240s showed up today. They look good. If all goes as planned I will be measuring them in the cab this weekend.
________________
Best Regards,
Carl huff
Drum rolls.................
My Saturday progress to report:
Once the last bit of glue dries, the cab will be ready to receive it's baffle board and JBL 2240 drivers. Tomorrow (assuming the weather holds) is test sweeps day.
The measurements will all be IGM (In Garage Measurements) I wonder what my neighbors will think? Ha, ha ...
_____________
Best Regards,
Carl Huff
.That your watching Star Wars! My wife calls our garage "Chirp Labs"The measurements will all be IGM (In Garage Measurements) I wonder what my neighbors will think? Ha, ha ...
If we knew what the hell we were doing, we wouldn't call it research would we.
It's almost there. One more day. Before gluing the front baffle, make sure that you have the same distance between the rear of the baffle and the throat, as the throat is high. It should be 3.25". Horizontally and vertically.
Sorry fellas ...
Measurements are put off for a week. It was a rainy and windy day in (usually sunny) Bakersfield.
_____________
Best Regards,
Carl Huff
Pictures. Pictures. Pictures
That beautiful horn most definitely needs a better supportOriginally Posted by hjames
Good work!!
Yeah - that's an old picture from when I first set I up ...That beautiful horn most definitely needs a better support
- I have a wooden support underneath it these days -
its much better, but it still deserves more ...
2ch: WiiM Pro; Topping E30 II DAC; Oppo, Acurus RL-11, Acurus A200, JBL Dynamics Project - Offline: L212-TwinStack, VonSchweikert VR-4
7: TIVO, Oppo BDP103D, B&K, 2pr UREI 809A, TF600, JBL B460
There is only one place where these drivers can go! If they are exactly centered over the buckets there is roughly 1/4 inch clearance on all sides.It's almost there. One more day. Before gluing the front baffle, make sure that you have the same distance between the rear of the baffle and the throat, as the throat is high. It should be 3.25". Horizontally and vertically.
If the weather holds tomorrow (Sunday) is test day!
______________
Best Regards,
Carl Huff
I finally found some free time when the wind wasn't blowing! My first round of measurements.
Notice the JBL active monitor setting on the cabinet for prospective. This cabinet is huge, even by my standards!
Two JBL 2240s each enclosed in their own bucket. There are no holes in the dividing partition between the drivers or in the board that separates each driver from the chamber below it. I used Dirac Live software to do the testing. Altho Dirac Live is a product that optimizes your loudspeakers for use within a listening room, it can be used to plot nearfield loudspeaker response. Here is my test setup.
Dirac Live runs as an application on the laptop, a USB Pre is the measurement microphone preamplifier. I use an Earthworks M30 with a calibration file for the measurements. The amplifier in use is of my creation. It is in fact a Hypex class D amplifier module and linear power supply. Dirac Live works by taking a series of measurements (9 in this case) and averaging the results for view. I wanted an accurate (worst case??) set of measurements. To accomplish that I placed the microphone at a one meter distance from the loudspeaker and took 3 measurements moving the microphone from left to right, first at a high position (inline with the center of the cones), low (one foot off of the ground in front of the scoop) and then midway between where cross coupling between the out of phase signals should be the worst.
3 measurements at the 'high' position ...
3 measurements at the 'Low' position ...
And finally 3 measurements midway between
And here are the results!
They are shown normalized to 1/12th octave. You can clearly see the 'phase funnies' at 120 and 300 Hz. All scoop cabinets have them. It is just the nature of the beast. The notches amount to about 6dB each.
I then used the Dirac Live editor to create an EQ target curve that could result in a filter set being generated. The red line that is superimposed is my idea of a target curve. It is a typical home theater kind of curve that includes the usual subwoofer bump. The 'pull tabs' left and right are cutoff high pass and low pass filters.
And here is how close Dirac Live thought that it could come to my ideal curve. Not bad!
In my experience Dirac Live is quite good at predicting the end results when confirmed by taking another round of measurements.
As you can see the phase funnies are gone! Only the ripples at 35Hz remain. With reasonable EQ applied the cabinet is down 3dB at 28Hz. Only another round of measurements in a real setting will tell if the results are in fact as projected. These measurements were taken out of doors. If I had taken these measurements indoors room gain and room modes would have played into the equation and the results would have undoubtedly been different. However I am quite pleased with the results. Altho it has taken me much longer than I had expected, I am glad that I built this cabinet and have a clear incentive to continue the experiment.
Thanks again to Lee for sharing this design. More to come.
_______________
Best Regards,
Carl Huff
And here is my experiment #2 in preparation.
I've removed one of the JBL 2240 drivers and attached a baffle board to hold a UREI variant of the classic Altec 604 duplex driver.
Hopefully I will have results that I can post late tomorrow.
________________
Best Regards,
Carl Huff
Hi Carl;
Will Dirac show you the phase response of your SPL measurements?
Barry.
If we knew what the hell we were doing, we wouldn't call it research would we.
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote