It's interesting to see horn-loaded 4th order BP designs are scoring the top marks here. I'm wondering though how much gain the "horn" section is actually providing. 1/4 wavelength @ 300 Hz is around 27.5 cm, so the path of the horn would have to be at least that long and the mouth would have to a bit larger than given in that design. What that "horn" might be actually doing is amplifying any harmonic distortion related to the fundamentals that the driver is trying to produce within the passband being tested. A slot-loaded bandpass design might actually produce better results (a lot less amplification of any distortion). An offset-driver slot-loaded bandpass design (to null out the first harmonic resonance) might perform even better.
Oh, concerning the impedance curves, I've found DATS isn't so great at giving a detailed view of the impedance - I think the data loses a bit of detail due to the amount of sample points DATS uses. I did get the DATS hardware to work with REW at one point, and REW's impedance measurement routines can provide a lot more detail (those little bumps you're seeing at 600 Hz and above will become a lot more visible). I'll see if I can get it working again, then provide the details here.
Another thing I'd like to have seen in the tests is the response of the D.U.T. to a sine sweep done at various levels until the THD exceeded a known amount, e.g. 20%. All well and nice that the designs can provide high output levels, but if they sound like a** when doing so... 🙂.
Well, it turned out to be easier than I thought. Here are the steps.
1. Connect the DATS v3 device to the PC
2. Open REW,select the "Preferences" menu option, and set the I/O Preferences as follows:
3. Select "Measure" and then the "Imedance" option, and then set Rsense to 100 Ohms and proceed through the calibration procedures. When performing the "Reference Cal", set RREF to 1000 Ohms.
...and that's it! You can now use REW to do impedance measurements with the DATS v3 software.
As per the author, DATS uses the impedance curve to guess the parameters instead of directly measuring the 3 relavant points. Thusly has a large margin of error.
dave
I don't think the approach used by the DATS software would necessarily lead to a large margin of error. Quite likely it's just using a software model of the driver and then doing a curve fit to see what parameters give the closest match between a computed impedance curve and the measured impedance curve. I've compared the DATS results to those computed by the semi-inductance parameter workbook shared by Stephen Bolser, and there's usually pretty good agreement, unless Le/Re is REALLY high...
BPs are 2 for 2! I'm surprised of the arch throat. I would have kept it the height of the horn path.
The adjustable compression chamber reminds me of a trombone...hence, bandpass HORN!
The adjustable compression chamber reminds me of a trombone...hence, bandpass HORN!
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What microphone are you using for the SPL reading? And are you using calibration?
Typical measurement microphones are only good for 130ish dB. In the first video you mention in passing that high dB levels could be an issue with the microphone, but I couldn't find any other info about that aspect.
And readings when you're talking seem to be in the high 90 dB range? Is something going on with SPL that you haven't described in the first couple videos?
Thanks
That was probably due to the drive voltage. The DATS v3 drive voltage is a bit low. For use with large pro audio drivers, or if you just want to get a better idea of what the t/s params would look like if a higher drive voltage is used, it might be better to use something like the DIYMA Eazy Z Interface, along with an external USB sound card and amplifier.
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It's called TRANSFER FUNCTION or CABIN GAIN when dealing with vehicles.
https://www.caraudiohelp.com/newsletter/cabin_gain.html
One of the best sounding subwoofer systems I ever heard was an 80's Saab 900 turbo with two 15's in a BR enclosure in 1991. The setup was EXACTLY like this pic with four 4" ports firing up between the rear of the enclosure and the drivers.
Love that car… “O Lord, won’t you buy me a Saab SPG, my friends all have Porches”. Apologies to Janis Joplin
dave
dave
Yeah, no.
Let's assume a 23 cm^2 Sd, 5 mm of one way travel: SPL = 93 dB at 150 Hz. He got "145 dB" with a simple ported enclosure. So you need to come up with 52 dB of gain through some means, assuming the microphone is reading correctly and no kind of other scaling is going on.
Typical cabin gain is 20-25 dB at 20 Hz. So we're still missing about 25 dB of gain.
And cabin gain surely isn't going to make a microphone that's only capable of 130 dB somehow read accurately at 145 dB.
Which is why I asked the guy running the tests to confirm what is going on. I was trying to do it politely and not assume I knew all the details.
https://www.diymobileaudio.com/threads/does-anyone-understand-cabin-gain.120190/
"This is JBL's measurement of cabin gain"
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The "cabin" he's using is a LOT smaller, so the gain starts a lot earlier 🙂.
Also, the responses of the designs that he's tested so far are noticeably non-flat. The driver has a fairly high Qts, so there's going to be a fairly large peak in the response around the resonance frequency of any of the vented or high order designs.
Also, the responses of the designs that he's tested so far are noticeably non-flat. The driver has a fairly high Qts, so there's going to be a fairly large peak in the response around the resonance frequency of any of the vented or high order designs.
He stated the HWO sounded good. That arch throat is causing the EXTRA sound. Like I said before, make the throat the same height as the horn path, no EXTRA sound.
Plus, NONE of the other enclosures match the BP's in with the 33, 45, & 60hz tones in SPL. A giant peak at 25hz is going to give you that ONE NOTE bass.
If BP's sound so bad, then why are Tom Danley, Klipsch, etc. making $ from BP4 and BP6S enclosures???
All compression horn tweeters are BP4s with the waveguide attached.
All FLHs are BP4's with a positive flare port.
All THs are BP6S's where the whole enclosure is the port.
You can model a straight flare single fold TH with the BP6S function in HR.
You can do the same for a stepped straight flare single fold TH.
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I suspect the "extra sound" is being caused by the horn amplifying any distortion being generated by the driver, so it's not necessarily being caused by the restriction at the throat. That driver has a fairly low Xmax, and it's behaviour during high excursion suggests an asymmetric BL curve or a spider that's not progressive in nature.
I should mention that this is with version G of the hardware. I haven't tested it with version H. Switching between version G and version H settings in the DATS software produces different impedance measurement results (it's a small difference, but still). I suspect that the sense resistor might be of a different value. It might be possible to identify if this is the case using the REW "open leads" calibration, but I really haven't tested this.