Unfortunately, there is no specification of the xover values in the docs, so it is hard to say what the combined C value of C4+C6 really is. But I agree that the caps will cause a short at high frequencies, which is not nice for the amp.
Eric, can you check the values of C4A, C4B, C6A and C6B in your xover?
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I am pretty sure there is a problem with DATS - I've been struggling over the past few days to make it work at all with my work-issued notebook computer. I'm thinking some new admin-imposed group policy is causing problems of one sort or another. I haven't yet tried hooking DATS to my desktop computer. I used my DATS box years ago with a few of my speakers (on a different computer) and it produced smooth-looking impedance plots that matched my expectations. Something seems screwy now and I haven't figured it out yet...
According to DATS (still suspect), the impedance peak near 1kHz is at 44ohms. I was also expecting the impedance low point to be closer to 35Hz instead of at 73Hz as DATS indicates. The tuning of this speaker/cabinet combination is CEARLY lower than 73Hz. I'm a total noob with these types of measurements, so another thought is maybe the drivers still need to break in before measurements like this settle in?? I didn't enter any data into DATS, I just hooked up the speaker to the test leads and ran a "Measure Free Air Parameters" so I've probably done something wrong as well...
I'm not going to reveal specifics of Tony's design, but the value of C4 in series with C6 is small, less than 0.1uF.
According to DATS (still suspect), the impedance peak near 1kHz is at 44ohms. I was also expecting the impedance low point to be closer to 35Hz instead of at 73Hz as DATS indicates. The tuning of this speaker/cabinet combination is CEARLY lower than 73Hz. I'm a total noob with these types of measurements, so another thought is maybe the drivers still need to break in before measurements like this settle in?? I didn't enter any data into DATS, I just hooked up the speaker to the test leads and ran a "Measure Free Air Parameters" so I've probably done something wrong as well...
I'm not going to reveal specifics of Tony's design, but the value of C4 in series with C6 is small, less than 0.1uF.
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I've been using DATS V2 for some years now and it has worked a treat for me.
I regularly do have a problem with measurements because I've not found a way to stop "Enable audio enhancements" from being on by default each time I plug the unit into my computer.
Un-ticking this box fixes my measurements every time. Might be worth a look on your system.....
I regularly do have a problem with measurements because I've not found a way to stop "Enable audio enhancements" from being on by default each time I plug the unit into my computer.
Un-ticking this box fixes my measurements every time. Might be worth a look on your system.....
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Thanks, Mazza! I’ll check those settings on my portable computer to see if that’s the problem. I just connected my DATS to my desktop computer and got much better measurement performance with no calibration issues at all. So, there is clearly some interfacing issue with DATS and my portable computer that I need to sort out.
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After a great deal of playing around with Win10 settings, I managed to get DATS to interface with my portable computer. What a PITA! Of course, I won't rule out the possibility of operator error along the way 
Anyhow, here is an updated impedance graph of my Calpamos speaker. It just might be an easier to drive speaker than I first thought with a low point of 6ohms at 80Hz. Have to give it a try with my 300B amps at some point soon. It matches fairly closely with what Tony published in his documentation. There are a few small differences: the impedance spike at 20Hz is lower by about 9 ohms in my cabinet and the cabinet tuning seems about 5Hz higher.
Not sure what these differences mean, especially the cabinet tuning - I built the cabinets to within +/- 1mm of Tony's specifications...
Anyhow, here is an updated impedance graph of my Calpamos speaker. It just might be an easier to drive speaker than I first thought with a low point of 6ohms at 80Hz. Have to give it a try with my 300B amps at some point soon. It matches fairly closely with what Tony published in his documentation. There are a few small differences: the impedance spike at 20Hz is lower by about 9 ohms in my cabinet and the cabinet tuning seems about 5Hz higher.
Not sure what these differences mean, especially the cabinet tuning - I built the cabinets to within +/- 1mm of Tony's specifications...
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Great!
The small differences are well within the tolerances of the driver(s). Also these PA woofers take a looooong time to break in, and their suspension parts (and to some extent also the magnet) are sensitive to temperature. It would be sheer coincidence if you'd get the exact same tuning.
The small differences are well within the tolerances of the driver(s). Also these PA woofers take a looooong time to break in, and their suspension parts (and to some extent also the magnet) are sensitive to temperature. It would be sheer coincidence if you'd get the exact same tuning.
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you have a little wrinkle in the impedance curve at about 260 Hz. It could be a resonance, maybe acoustical resonance (i.e. standing wave), or it could be a structural resonance. Maybe it is a cone resonance, but I doubt it. Or it could be a phantom artifact of the measurement process.
If you feel curious about it, you could slowly sweep a modest signal ( ~1 V) from 200 to 300 Hz, and see if you can energize the resonance. Once energized, it will be easy to identify the source. if it is coming from the driver cone, it is most likely an acoustic resonance or a cone resonance. If it is coming from one of the cabinet panels, it is a structural resonance. Maybe you find nothing, which would be the best outcome.
If it is an acoustical source, you may be able to mitigate it with more stuffing or rearranged stuffing. If it is a structural resonance, you may be able to lessen its impact with some bracing, although your options for bracing at this point are somewhat limited... the nice thing about your cabinet is that huge woofer hole makes getting hands and tools inside the cabinet rather easy.
Hopefully the impedance wrinkle is nothing.
j.
If you feel curious about it, you could slowly sweep a modest signal ( ~1 V) from 200 to 300 Hz, and see if you can energize the resonance. Once energized, it will be easy to identify the source. if it is coming from the driver cone, it is most likely an acoustic resonance or a cone resonance. If it is coming from one of the cabinet panels, it is a structural resonance. Maybe you find nothing, which would be the best outcome.
If it is an acoustical source, you may be able to mitigate it with more stuffing or rearranged stuffing. If it is a structural resonance, you may be able to lessen its impact with some bracing, although your options for bracing at this point are somewhat limited... the nice thing about your cabinet is that huge woofer hole makes getting hands and tools inside the cabinet rather easy.
Hopefully the impedance wrinkle is nothing.
j.
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I also discovered that I have an intermittent problem with the crossover in the first speaker that I built. I was "exercising" the drivers a bit today and from time to time (seemed to correlate with drum hits) the tweeter all of a sudden became very loud compared to its usual level. It would last a few seconds then go back to behaving better.
I'm wondering if there is a broken/intermittently connected solder joint somewhere in the crossover as a result of either shipping or installation. This sounds rather like it did when I commented that I didn't like this speaker with the Vfet lottery amp. This is making me think it's not the amp, it was the crossover. Have to pull it out to inspect/reflow the joints.
I always get irritated when I have to re-do something that I just did - it's never so easy to fiddle around afterwards...
I'm wondering if there is a broken/intermittently connected solder joint somewhere in the crossover as a result of either shipping or installation. This sounds rather like it did when I commented that I didn't like this speaker with the Vfet lottery amp. This is making me think it's not the amp, it was the crossover. Have to pull it out to inspect/reflow the joints.
I always get irritated when I have to re-do something that I just did - it's never so easy to fiddle around afterwards...
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I've examined the crossover and all that I can find with close visual inspection is this resistor leg that looks like the copper has corroded to some extent. I'll reflow all of the solder joints anyhow.
Does anyone have any commentary of the appearance of this leg of the resistor?
Does anyone have any commentary of the appearance of this leg of the resistor?
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Found it! The crossover is mounted on top of the dampening material. The dampening material has a heavy sheet of tin foil on the top that is coated with paint. The solder joints on the bottom of the crossover are poking through the paint and shorting on the foil, thus “removing” a few components from the crossover circuit.
With the crossover mounted in the cabinet, pressing down in a particular location created the problem. With the crossover removed from the cabinet, I am unable to duplicate the problem. I’ll add a layer of cardboard or thin plywood under the crossovers in both cabinets.
Problem solved!
With the crossover mounted in the cabinet, pressing down in a particular location created the problem. With the crossover removed from the cabinet, I am unable to duplicate the problem. I’ll add a layer of cardboard or thin plywood under the crossovers in both cabinets.
Problem solved!
