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Sunday, March 28th, 2010 | Author:

The Jordan JX-92 is a great little driver, but has some raggedness in the upper frequencies.  Below about 4KHz, the driver has a clarity and an uncolored response that is very impressive.  The bass response, while not window-rattling, is really impressive for a 5.5″ driver.  To take the good stuff from the Jordan and not get the bad, I decided to mate it up with a tweeter.  But not any old dome tweeter would do the Jordan justice.  I considered a ribbon, but I kept coming back to the Vifa XT-25 as a great mate for the Jordan.  The crossover point is nice and high, so the XT-25 won’t be stressed.  The character of the XT-25 also matches the Jordan driver quite nicely.  Finally, the deciding factor:  I had a pair of them.

The beginning of this project can be seen here: Where there are pictures of the cabinets being routed, and the drivers mounted.

The jordan is designed to not roll off in the treble, and the Vifa XT-25 doesn’t seem to know it’s tweeter.  So in order to get a reasonable crossover rate and not have a huge upper midrange muddying region where both drivers are contributing, the drivers need to be crossed over pretty hard.  After messing with 2nd order crossovers, it was pretty obvious that it wasn’t rolling the drivers off fast enough.  4th order filters worked pretty well, but the parts count was crazy, and the sound seemed somewhat pinched off and odd sounding in the crossover region.  I settled on a 3rd order crossover (electrical) for both the woofer and tweeter.  The woofer crossover is a butterworth topology, and the tweeter circuit is somewhat of an unknown that compliments the response of the woofer.

I used my computer and an external USB soundcard with my impedance bridge and microphone pre-amplifier, a Panasonic WM-61A electret microphone capsule, and my modified Dyna SCA-35 to drive the speaker as the basis of the measurement hardware to design the crossover.  I used two different software suites to do the driver response measurement.

I used Fuzzmeasure, which uses a swept-sine deconvolution to calculate the impulse response.  I also used software of my own design which uses MLS sequences to calculate the driver impulse response.  Fuzzmeasure is a very slick and easy to use program, but it seems to show a rosy picture of the response.   The drivers are in no way as flat as it makes them out to be, but the crossover region seems to be represented accurately.  Small changes in the crossover show up in the response.  Update:  I was over-driving my Fuzzmeasure measurements and that causes the flat-top readings shown below. My program is also slick and works the way I want it to, and I have control and understanding of the processing the program does.  My code also matches the impulse response of Loudspeaker Lab.

Here is the speaker response as measured with my software.  Note that my  impulse response is “windowed ” to eliminate the room response.  But the windowing process also rolls off the bass response, so anything below about 300Hz is artificially rolled off on the plots below.  The first plot is the impulse response, woofer and tweeter response, and the null from the tweeter polarity reversal.  The second plot shows the port contribution and woofer null with close microphone placement at the driver cone and port exit.  The red woofer trace shows the current port tuning at about 55Hz.  The Jordan is still breaking in, and I’ll lengthen the port to tune it to about 45Hz when the Fs of the Jordan drops.

The output of Fuzzmeasure is shown below.  Note the insane smoothness of the Jordan driver (compare this to every other measurement you’ve ever seen of the Jordan).  But the crossover information looks very similar.  Update:  The smoothness is due to over-driving my input signal, which was not obvious to me.  I’ve since fixed my problem and the Fuzzmeasure readings and my software readings agree very well.  Fuzzmeasure is a great Macintosh program for speaker and audio measurements.

Here’s some pictures of the crossover build-up process:

PCB Layout File:  jordan2way_crossoverPCB

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Monday, March 15th, 2010 | Author:

I’ve had a pair of Jordan JX-92S sitting around for a year or so (part of a DIYAudio group buy).  I built a set of transmission line speakers around these drivers several years ago, and while they are amazing drivers, they do have issues in the treble.   So given that I also have a pair of the very nice Vifa XT-25 tweeters that should mate nicely with the Jordan, these drivers should make a great little speaker.  The JX-92’s really work well in a transmission line or a quarter wave tube, but I was looking for a much smaller speaker.  The Jordan is an amazing driver, but it’s still a small 5 1/2″ driver.

My measurements after a day of break-in show that the JX-92 has the following parameters:

Fs Qms Qes Qts Vas
62.0304 2.4919 0.8639 0.6415 7.8288
Re Mms no (%) Sp So
5.1570 7.2457 0.2076 85.3730 87.2273

The Fs is unusually high, which indicates that the driver is not yet fully broken in.  However the Q of the driver isn’t very far removed from what others are getting from these new “more efficient” JX-92 drivers.  The Q being so high is bad for my hopes of making a small speaker from this driver.  Based on these parameters, I need a 1.3cu-ft box if I was going to used a ported enclosure.  That’s a huge floor-standing box.  A transmission line would also be a slightly smaller floor-standing box.  A sealed enclosure would be small, and completely anemic.

As much as I like the Jordan drivers, A speaker with a 0.5 cu-ft enclosure or larger lends itself to a a whole other class of drivers.  For example in a 0.5 cu-ft vented box, the Zaph SR-71 speaker outclasses the jordan in every way (in the midrange down; with a driver that is 1/3 the cost of a jordan).  A floorstanding speaker lends itself to even more impressive driver and frequency extension.  So in order for the Jordan JX-92 to be a useful driver to me, it HAS to live in a small enclosure.

I bought a set of the Parts Express 0.25 cu-ft enclosures and have cut them into a set of ported enclosures.   I’ve got the port tuned for about 55 Hz at this point, but it should actually be a bit lower.  I’m considering trying an extended bass shelf design in this little enclosure.

The problem with this driver selection is that the woofer really is trying to be a tweeter, and the tweeter thinks it’s a woofer.  So I’m slapping both drivers down with third order crossovers.  It’s a good first cut, but not perfect.  Coming up will be the final crossover design and my Labview speaker measurement software in action.  I’m using Fuzzmeasure and my own software in a MacBook Pro with an M-Audio Transit USB soundcard.

Below are some pictures of  the fabrication and some of the crossover design.

Monday, December 08th, 2008 | Author:

The original plan was to add a 5 volt regulator in the Dension cradle cable. I was planning to add it about 6 inches from the connector and heat shrink it when I was done like some sort of cable goiter. As I was checking out the back cavity of the cradle I realized that the regulator would damn near fit inside it. However, with the metal attachment bracket it wouldn’t quite fit. I ground down the metal bracket and sanded down the regulator a bit and everything fit perfectly. I added filter caps before and after the regulator to suppress noise and called it as day. The cradle is working well and is ready to install. As usual, pictures are below.

Monday, December 08th, 2008 | Author:

Last night I installed the voltage divider assembly into the Dension cradle.  I thought I had some fine soldering tools but my smallest Metcal iron tip looks like a Louisville Slugger next to the 30 pin cock connector pins.  It took some steady hands (which apparently I don’t have either), and some good diffuse light to make these connections.  I used a strand of silver plated copper wire to make the connections, and a piece of the full stranded wire to make the power connection to the voltage divider assembly.

It would have been a little less kludgy to make a new circuit board with the proper resistor divider traces on the board, but I’m not sure that I can make a boar with traces fine enough to reliably fit the connector.  I am also concerned that I couldn’t get the connector off the existing board without damaging it.  So this is the result.  It seems to work quite well at this point.

The next step is to step down the power coming into the cradle from 12(ish) volts to 5 volts.  A linear regulator doing this job would be dumping more power into heat than it provides to the iPhone for charging, which not only may overload the factory head unit, also requires the linear regulator be heat sunk somewhere.  V-Infinity has a really snazzy switching regulator that has an efficiency of about 92%. This means that during full charging, the regulator will only dissipate about 0.2 watts and will not need a heat sink.


Wednesday, December 03rd, 2008 | Author:

This resistor divider kludge marks the official start of modifying a pair of Dension Ice Link iPod cradles for use with 3G iPhones.  The Dension Ice Link is a cradle that fits a variety of Apple iPod models (and iPhones).  It plays audio out from the iPod through an OEM car stereo, and charges the iPod unless you have a 3rd gen nano, 2nd gen iTouch, or iPhone 3G.  These new models charge via USB only, and these old Ice Link systems only charge via FireWire.  With a little kludging, that problem is easily solved, and for $7 on ebay, these systems are a steal. 




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Sunday, November 23rd, 2008 | Author:

Several years ago I bought a Dension Ice Link to charge my iPod and play it through my Toyota stereo. This system has served me well though a 3rd generation iPod, a 5.5th generation iPod, and a 1st generation iPhone. A friend of mine went out and got himself a sweet 3G iPhone only to find out that many of the older accessories do not work with it. To date, there are no car cradle systems that both play the iPhone through the stereo and also charge the unit.

It appears that the newest generation of iPods (4th gen nano, 2nd gen touch, 3G iPhone) do not charge through the firewire pins of the dock connector anymore. They are USB only, and not just any USB either. So many USB chargers are blissfully ignored by the iPhone.

My friend’s desire to get a car integration system for his 3G iPhone and m desire to understand what had changed with the dock connector has led me to try to understand the changes in the newest generation charging circuit.

Information is pretty scant out on the interwebs, but I did find this:
which talks about what appears to have changed in the charging circuit, and why any old USB charger won’t charge a 3G iPhone. Cutting to the chase, the issue is that the USB dock pins are in fact used for charging, but having 5 volts present on the 5 volt pin of the USB plug of the sync isn’t enough (and ground obviously). The Data+ and Data- lines need to be held at a certain voltage for the phone to recognize that it should charge.  The Data+ pin needs to be held at 2.8 volts, the Data- pin needs to be held at 2.0 volts.

I have a craptastic generic USB car charger that would not charge my first generation iPhone.  This charger like every generic USB charger I’ve measured leaves the data pins floating.  This strikes me as a very wise decision, but makes it a non-starter to charge the iPhones.  I cracked my generic charger open and added a pair of voltage dividers form the 5volt pin to the ground pin.  I chose resistor values I had laying around to produce the 2.0 and 2.8 volts.  The link suggested different values for the divider resistors, the absolute choice seems to not be critical.  Shown blow is some pictures of the process.  

This is the first step in modifying my Dension Ice Link for charging 3G iPhones.  My friend bought an Ice Link from ebay for $30 and we are going to mod the cradle for charging 3G iPhones.  Stay tuned for that later.  

Category: Audio, Computers, iPhone, Tacoma  | Tags: , , , ,  | 4 Comments