I am rather impatient, and once I decided I wanted a new amp, I want it today. The Fosi V3 Mono is not scheduled to ship until August 28, and I know that the probability of a new product being launched on-schedule is 50:50 at best.
The IcePower 50ASX2 is available, but the necessary wire harness is out of stock. For an additional $100, I can get the 125ASX2 with wire harness. It meets my needs, 100 W x2, it has a very flat frequency response to 20k with 2, 4 or 8 ohm load, and excellent THD and IM distortion, and excellent SNR. I already have the necessary connectors, fuse holders, switch, and power cord. I can zip together a case in about 45 minutes. Another advantage is that someday I may use IcePower in an active speaker, so it is nice to get some experience with it.
AINOgradient amps use 50 and 125 ASX modules in same box per speaker. Power connector has a 10A fuse, 230V, separate power button. Speaker connectors are Speakon 2ch. At start this sucks surprisingly much power. The box is closed and power is on 24/7 (10 years now) without problems, place vertically and box surface temp is between 35-40C. Well one channel of a 50ASX2 got silent and was changed, don't know why and it looks ok.
Last edited:
I added fuses on my 200as2 and first one burned just some days ago, noticed it yesterday, but those are quite small ones I had in hand when I boxed the thing. There is fuse on board, which is not replaceable and means the module is busted if that one goes. Anyway, very handy to have PSU on the same board with the amp, greatly simplifies things.
Hello,
Linkwitz is one of my go to sources: take a look at this link.
https://www.linkwitzlab.com/faq.htm#Q29
Q29 - How do you measure cone excursion of a driver?
A29 - A simple wedge micrometer that is cut out of paper can be used on larger drivers to measure their peak-to-peak cone excursion. It is a rectangular triangle with 2:1 sides and a scale at its base line. Attached to the dust cap of a driver cone it moves back and forth. The eye cannot follow the movement, but sees a diagonal line that intersect the scale graticule. The axial movement is translated to a sideways displacement of the diagonal intersection and gives a twofold magnification of the excursion. While this is not a precise measurement instrument it is still very useful in relating acoustic distortion data to cone displacement.
Top
I am surprised that there is not some cheap and easy device on the market for diy use. I will keep an eye out.
I did look at the AES2.org site for AES papers that discuss measurement of driver cone excursion. There are papers that discuss distortion measurement and calculation of cone excursion. This seems roundabout to me.
I do not wish to clutter up @hifijim thread any more with this. I will look into it a little more and perhaps open another thread.
Thanks DT
The midrange driver performance is a bit of a mystery. Back in post #75, I built a prototype box to test this driver as well as the SB12MNRX, and determined that this driver was well suited. Now that I have it installed in the real cabinets, the response is different than I was expecting.
https://www.diyaudio.com/community/...ivers-a-new-3-way-project.413182/post-7706642
Here is the polar response of of the SB15CRC30-8, installed in my cabinet. This is gated far field scans merged with the near field response.
Here is the same driver in the prototype cabinet.
Here is a comparison of the current on-axis response and the foam-board prototype response I measured back a few months ago. Dashed is the prototype response.
When I selected this driver based on the prototype testing, I considered the 2 dB wiggle in the response between 1.5k – 3k to be minor. Now looking at the response in the full cabinet, it is a 3 dB wiggle, and to me it seems no longer minor. It now seems like something I will have to design around.
This is the same driver. The prototype box is the same width as the cabinet, with the same edge bevel. The prototype baffle is not as tall as the real cabinet, and the driver is positioned lower down than in the real cabinet. I have photos in the link above. Baffle simulations indicate that these differences would have a small effect, and virtually no effect in the 1.5k – 3k region.
The impedance sweeps of the driver in the two different cabinets are identical above 200 Hz, although below 200 there is some difference because the enclosed volume is larger in the real cabinet. Both sweeps show a small wrinkle at about 2.2k. That same wrinkle is present in the free-air impedance sweep of the raw driver.
I am trying to come up with a rational explanation for this difference. In the past I have had very good agreement between foamboard prototypes and final cabinets.
edit: My theory is that the 2.2k resonance is not the cone, but the rubber surround. I will post some spectral decay plots later which will show that the 2.2k resonance damps out very quickly. Many 5-6" drivers have a surround "bobble" in this region.
Thoughts?
j.
https://www.diyaudio.com/community/...ivers-a-new-3-way-project.413182/post-7706642
Here is the polar response of of the SB15CRC30-8, installed in my cabinet. This is gated far field scans merged with the near field response.
Here is the same driver in the prototype cabinet.
Here is a comparison of the current on-axis response and the foam-board prototype response I measured back a few months ago. Dashed is the prototype response.
When I selected this driver based on the prototype testing, I considered the 2 dB wiggle in the response between 1.5k – 3k to be minor. Now looking at the response in the full cabinet, it is a 3 dB wiggle, and to me it seems no longer minor. It now seems like something I will have to design around.
This is the same driver. The prototype box is the same width as the cabinet, with the same edge bevel. The prototype baffle is not as tall as the real cabinet, and the driver is positioned lower down than in the real cabinet. I have photos in the link above. Baffle simulations indicate that these differences would have a small effect, and virtually no effect in the 1.5k – 3k region.
The impedance sweeps of the driver in the two different cabinets are identical above 200 Hz, although below 200 there is some difference because the enclosed volume is larger in the real cabinet. Both sweeps show a small wrinkle at about 2.2k. That same wrinkle is present in the free-air impedance sweep of the raw driver.
I am trying to come up with a rational explanation for this difference. In the past I have had very good agreement between foamboard prototypes and final cabinets.
edit: My theory is that the 2.2k resonance is not the cone, but the rubber surround. I will post some spectral decay plots later which will show that the 2.2k resonance damps out very quickly. Many 5-6" drivers have a surround "bobble" in this region.
Thoughts?
j.
Are you measuring the real cabinet with the tweeter in place? That could account for some diffraction difference. The real cabinet looks as if it is the on axis that is more problematic with the off axis actually looking more even than the prototype. If you hide the on axis and look at the listening window it might not look quite so bad.
Yes, in the real cabinet, all drivers are installed. In the prototype cabinet, the tweeter was not installed and the hole was packed with foam. The day after I made the polar scans and was surprised, I thought of this issue. I taped a thick piece of foam over the tweeter waveguide and ran an on-axis scan. It did have an effect, but I soon realized that a big block of foam over the tweeter was not going to be representative of anything... The fact that I observed an effect does not prove it is the tweeter waveguide, nor does it prove it is not the waveguide.
It is a good theory though 🙂.
Solid line is with foam plug over tweeter. blue dashed is real cabinet. crimson dashed is the prototype foam cabinet.
I don't want to make too much out of this 2 khz bobble. It is certainly manageable, and I have two different crossover designs in work that handle it fine. But mysteries are interesting...
They certainly are. Your foam experiment shows that there are diffraction differeces below 1.5K from the interaction of the physical drivers in the real cabinet. The 2KHz peak is there in the foam board but is more damped. You could try a more compliant mounting scheme for the mid driver to see if that changes anything.
The factory data on the SB15CRC30-8 shows a solid 3-4 db hump at ~2khz. Seems clear to me that the foam test box was damping a resonance in some way. Enough perhaps to justify exploring a damped mounting method for the SB15? Decoupled or braced in some way, which being best I cannot say...
Hello @hifijim and All,
My insight in the FR wobble at ~ 2000Hz to 2300Hz goes like this.
If the curves including the factory data were due to only a solid cone or dome piston the FR and Directivity Index curves would be flat and smooth, there would be no wobble.
I suspect what we are seeing is a resonant / unstable wobble in the wide and tall 1/2 round roll suspension. Perhaps a mid range driver does not require the long 11mm excursion of this driver.
Thanks DT
I agree with @DualTriode, I saw something similar with the SB12MNRX25-4 and ultimately attributed it to the large surround. This is why I recommended a mid range driver with an accordion style surround, if one still exists.
May be resonances in the foam proto over a larger range looking at the spl responses, but may be also in the final version yet they are different, not only at the 2k bump. Sort of makes me think of a not stiff mounting, difficult to put it into words.
Pretty sure the midrange was decided 100-200 posts ago.
...
If you continue to try to determine the blip, maybe jsut use a piece of notebook paper over the tweeter AND WOOFER rather than the rather large protruding piece of foam over the tweeter, which may be closer to the prototype baffle.
...
If you continue to try to determine the blip, maybe jsut use a piece of notebook paper over the tweeter AND WOOFER rather than the rather large protruding piece of foam over the tweeter, which may be closer to the prototype baffle.