bass extenzion for jim griffin minimonitor

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Hi all the guys out there.
I've built the Jim Griffin Minimonitor (thanks Jim) made out from the AC g2Si+Jordan jx92s, and have to say that compared to my
Monitor Audio Studio 20 they have a richer vocal presentation and an incredible soundstage reconstruction.
IMHO totally the result achieved is astounding. If you have such drivers laying around is mandatory to build them.
If you don't have such drivers, go and pick them up immediately.;) ;)
Now it happens that I have 2 Jordan jx125 that are waiting for an application, and to me sounds good to try building a bass extension cabinet for the minimonitors.
The problem is that if i can understand almost anything in amplifiers, I'm a newbie with loudspeakers. Never tried to design one. Therefore If some of you have experienced in building an extension cabinet tailored on the Jim Griffin minimonitor, I will be
very happy to have indications on how to go on.

thanks.

Paolo
 
WinLSD says...

...that with a JX92 you should get F3 of 29 Hz with a 1.76 cubic foot box tuned to 32.2 Hz. A JX125 will have an F3 of 27.5 Hz in a 2.48 cubic foot box tuned to 29.5Hz. A sealed box with Qt of .701 and volume of 1.18 cubic feet will have an F3 of 52Hz with a JX125. You can download this and other T/S box calculators from the web and play with the box volume and tuning frequency to your hearts content. Others on this site can probably comment on the accuracy (or lack thereof) of the various models.
 
Paolo,

I'm glad to hear that you are enjoying the mini-monitors. They do provide an awesome sound.

I'll assume that you can work through the enclosure design for the JX125 and you will have to decide if you build two separate boxes (for stereo) or just use a single enclosure with both drivers in one box.

While I have not used the JX125 driver, let me make a suggestion or two on integration with the JX92S/G2si. First, I would not suggest that you use a passive crossover between the mini-monitor and the JX125s. The best way to proceed would be to use an active crossover to separate the signal for the JX125s and the minimonitors. It would be easy to use a plate amplifer (typically used for sub woofers) for the active crossover. This amplifier would provide the power to drive the JX125s while incorporating the crossover. One plate amplifier would be capable of driving both Jx125 drivers as these amps typically can drive a 4 ohms load (the JX125s wired in parallel). If you have stereo enclosures, then you can run an external cable from the Jx125 with the amp to the driver on the other side.

My suggestion would be to use the line level inputs on the plate amp (this assumes that you have access to the outputs between your preamp and power amplifier in your system. Just connect the outputs for the preamp to the plate amp's inputs. Then run the outputs from the plate amp back to the inputs of the power amp. If you don't have access to the preamp outputs, then use the high level (speaker terminals) connections on the plate amp.

Finally, you could also stuff a piece of foam or a sock in the port tube of your mini-monitors to effectively seal these enclosures when you use them with the JX125 drivers as subs. You can adjust the crossover frequency and the amplitude of the plate amp to suit your taste.

Some examples of plate amplifiers from the www.partsexpress.com site include their part numbers 300-802, 300-804, 300-792, and 300-794. Plate amplifiers like these examples are available from many suppliers and I'm sure that you can locate such amps in Europe.

Good luck!

Jim
 

GM

Member
Joined 2003
Greets!

FWIW I designed a ~2.76ft^3 net T/S max flat ML-TL some time ago for myself, but to date I haven't built it so if you're willing to gamble some time/wood............

L = 57.28"
CSA = 83.258"^2
driver down 20"
vent near/at the bottom
rp = 1.5"
Lp = 6.25"
density = ~0.2lbs/ft^3

Since it's aneochoically flat to ~25Hz it may have too much gain down low so you may need to experiment with vent damping and/or length and/or worst case, plugging the vent, which in a sim yields an aneochoic IB response to ~30Hz, then down only ~3dB/10Hz referenced to it.

GM
 
thanks guys

Thanks everyone of you for your suggestions.
I was planning to use an active xover as Jim was suggesting, just because, probably (hope so!!) it's an easier task to set up the whole thing.
My plan was to build two separate cabinets that are supposed to accomodate on top the minimonitors.
I'll think on your suggestions, and probably will ask for your opnion, as i will focus how to proceed.
Thanks again guys.

Ciao

Paolo
 
what about non oversampling DAC ?

Hi guys/ Dr Jim,

On a side note but relating to this speaker, has anyone tried using a non oversampling DAC as a source ? Will the AC tweeter still be ok due to the ultrasonic noise that these type of DAC outputs ? I definately don't want to learn it the hard way.


regards,
Will.
 
Will,

With this speaker I have used various CD players--from an early one without oversampling to a more recent one with oversampling and several between these. I have not experienced any issues with the DACs in these various players. The ribbon in this design is well padded to match the sensitivity of the Jordan driver so I doubt that you could endanger the ribbons. On the other hand your dog may not like it.

Jim
 
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