Open Source Monkey Box

Ok I will apply 4.5 cm horizontal offset on both tweeter and midrange.

Can you also move the drivers up by 2mm (90mm tweeter center to baffle top)? That's very little, and it will probably have almost no effect on the acoustics, but it would be nice to get the golden ratio in there. ;)

Also, the 22mm baffle will require some extra machining to mount the Volt dome flush with the front. 19mm would be easier. But again, this will have zero effect on the Leap model.
 

Attachments

  • Audio Express measurement Volt VM752 SPL off axis .JPG
    Audio Express measurement Volt VM752 SPL off axis .JPG
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The Faital is available almost worldwide, the DAS is available only in Europe?
Should we take availability into account?

First thing this morning I received an email with a quote for the DAS driver from the Swiss distributor. These guys are quick! If there is a dedicated distributor in Switzerland, they might as well have distributors in other, larger countries. I will ask them, but I guess availability is not as much an issue as one might think.

Oh, the price in the quote was CHF 180.- for one unit, including VAT and shipping. That is slightly more than what I have seen in some online shops outside of Switzerland, but I believe it's still a little bit less than the Faital (not that I would care, though).
 
As an information, the horizontal off axis responses on infinite baffle of the tweeter Satori TW29BN and the ATC SM75 3 inch midrange. The responses are normalized to the on axis response.

In both plots the measured data and the Leap simulations to compare. The datasheet curves for the Satori and Troels' measurements of the ATC (post #85). The Leap curves are the more solid curves.

For the Satori tweeter the 30 and 60 deg data is shown and for the ATC midrange the 20 and 40 deg responses.

You can see that for the tweeter the Leap model is matching, for the ATC there is some difference with the Leap 3 inch model, maybe because of the missing waveguide in the Leap model.

We will see what we can be done about it, also with own Volt measurements. To do a first study now, I will use these current Leap models.
 

Attachments

  • Satori TW29BN off axis normalized 30 60deg.JPG
    Satori TW29BN off axis normalized 30 60deg.JPG
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  • ATC SM75 off axis normalized 20 40deg.JPG
    ATC SM75 off axis normalized 20 40deg.JPG
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Very useful again!

I attached a plot of my own measurements of the ATC SM75-150 (centered on a 23cm wide baffle, and also with 13cm baffle extensions on both sides). The measurements were made with an electronic high pass filter (24 dB/oct, 360 Hz). Looks like the waveguide achieves constant directivity up to about 3 kHz. Maybe that's useful.
 

Attachments

  • ATC-SM75-FARFIELD-diffraction.pdf
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Yes it is constant directivity up to 3 kHz, I also see in Leap by comparing the SPL on axis and power response of the Volt VM752 in the Monkey Box. In attach the plot, SPL in red and power in blue. Technically this is a real top driver.

Looking to your ATC measurements, I understand now why the SPL off axis is lower below 1 kHz in the AudioXpress measurements. It is because it is placed in an enclosure and not on a large baffle. I see the same in the Leap simulation.
 

Attachments

  • SPL and power Volt VM752 in Monkey Box.JPG
    SPL and power Volt VM752 in Monkey Box.JPG
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Matthias used 23cm baffle, this project will be something like 43cm...
AudioXpress mounted the driver in an enclosure with a baflle of 28 x 43 cm, I suppose 28 cm wide.

In attach, the SPL on and off axis 0 30 60 degrees of the Volt VM752 in the Monkey Box simulated in Leap.
 

Attachments

  • Volt VM752 SPL off axis 0 30 60 in Monkey Box.JPG
    Volt VM752 SPL off axis 0 30 60 in Monkey Box.JPG
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I was calculating with 35cm internal width. So ca. 38,7cm with 18mm material.

Edit:
What did you go with in your sim Paul?

In Leap the internal volume can be chosen independent of the external dimensions of the cabinet. I have chosen 70 L now.

I did choose the dimensions of the front 38 x 78 cm as a function of the driver dimensions. And did a rough estimation of the depth for a netto internal volume of 70 - 80 L.
I have not calculated yet excatly. I used 22mm for the walls and 30mm for the front as a first shot :).

I will do a simulation with the final dimensions later, that is no problem.
The final dimensions, we have to do together of course...

Looking at your plot I'd say that an x-over to the tweeter at about 2.5 kHz would make sense -- what do you guys think?

Yes that is exactly what I thought also :). And probably you don't need a tweeter waveguide, looking to the polar diagram.

Polar diagram of Volt in Monkey in attach. Remark: with the current Volt VM752 Leap model, which is not 100% correct off axis, see previous posts... The driver responses in the cabinet are ready, so X-over can be designed. What should it be?
 

Attachments

  • Horizontal polar diagram Volt VM752 in Monkey Box.JPG
    Horizontal polar diagram Volt VM752 in Monkey Box.JPG
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The driver responses in the cabinet are ready, so X-over can be designed. What must it be?

I'd suggest trying a 1st order filters between mid and tweeter because they behave very well in the time domain and sound good if the drivers are clean enough in the x-over range (at least to my ears). See also here.

The woofer/mid x-over should not be lower than 400 Hz, maybe a little bit higher to avoid loading the mid too much (500 Hz?). The filter slopes should be a bit steeper (2nd order?) to avoid the woofer from doing too much in the midrange.

In general I'd suggest to apply full impedance compensation so that the filters see a flatish impedance. For sure, the huge impedance peak of the Volt dome will need compensation to make the high-pass for the Volt dome work. But I guess going all the way by compensating also the tweeter resonance peak and the (upper) woofer resonance peak is a good thing. Same goes for the impedance rise due to the voice coil impedance. This means a bunch of extra parts, but they are a good investment in my experience (and they don't need to be expensive super-duper parts).
 
Does anyone have the voice coil inductance of the DAS 12P?

Paul:
Was that internal or external dimensions? Including vent?

For the simulation I have chosen 70 L netto exclusive the vent.

With the current dimensions of the cabinet model, and taken 22mm for walls and 30mm for front panel, the netto internal volume is 86 L now, exclusive vent, inclusive optional bracing and inclusive volume occupied by drivers.
The cabinet can be made smaller (less deep maybe). Or some more volume than 70 L can be used.
 
Here are the simulation results of the drivers in the cabinet.
I have added also the frd files for X-over experimenting.
As an information, to realize a F3 = 45 Hz the SPL should be designed at 91.2 dB (full space).
 

Attachments

  • Leap Monkey Box Volt VM752 FS 1m 283 FR.txt
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  • Leap Monkey Box Faital 12PR320 283 Imp.txt
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  • Leap Monkey Box Faital 12PR320 FS 1m 283 FR.txt
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  • Impedance drivers in cabinet Monkey box simulation.JPG
    Impedance drivers in cabinet Monkey box simulation.JPG
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  • SPL drivers in cabinet Monkey box simulation.JPG
    SPL drivers in cabinet Monkey box simulation.JPG
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  • Leap Monkey Box Volt VM752 283 Imp.txt
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  • Leap Monkey Box Satori TW29BN FS 1m 283 FR.txt
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  • Leap Monkey Box Satori TW29BN 283 Imp.txt
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