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Old project redux? Dayton PT2C planar and Peerless PPB 6.5"
This was my first real build, 5 or so years ago... I barely knew what I was doing. Just messing with the factory response graphs in PCD. I remember I snagged the PT2C-8 when they first released it for $25ea and held onto them for a while. I later picked up the Peerless 830874 6.5" on sale for $35ea. The result was..ok. I could hear the potential in the drivers atleast. Eventually I got a measurement mic and that confirmed the crossover needs a complete overhaul. Box is a little over .5cf, ported F3 around 50hz.
I have debated just parting it out and use the woofers with a second pair of 830874s in a tower with other tweeters. But it seems PE says the planars can be crossed as low as 2.5k (3rd order electrical), And I checked out Ben's old Nephila project, which gave me some hope this combo could still work out. Then I could save the other 830874s for the second pair of beastmode tweets I have.
What would you guys do?
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Sell me the planars for $25/ea... Lol!
Seriously, I would revisit the XO. Should be pretty nice if you get it dialed in.
I like how the width of the tweeter is almost exactly the same width of the woofer's truncated flat. I haven't looked at either of those drivers... could the sensitivity of that planar keep up with two of those woofers wired in parallel (i.e. a killar tower MTM)?
830874 is rated 88.5db/1w. Seems accurate based on their graph.
PT2C rated 94db/1w but the factory graph starts just under 90db around 2.5k and peaks over 95db past 9k then rolls down from there.
So probably could handle 2x woofers after some BSC.
Though now that I think of it. Just redoing the crossover could give me something to do for the PE SDC. Been aspiring to enter something for years. Would be rather fitting to enter these.
Psh. I don't wanna hear it Mr-"$1 ea plus shipping"
I've used the PT2a, and it was good to about 3k, so I feel yours should be too. The poly cone will be minimal breakup, so you should be successful.
The RT5002 in the Nephila is only good to 3.4kHz, and a very different animal.
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There you go Andrew. Sounds like that MTM could work!
Drew - I bought those same drivers when I first saw the pics you posted of that alignment on PETT. LOL.
Still on the shelf unused so I am very interested in what you do with them in a passive XO.
My desires for that combo would be XO'd to a sub so the 830874 could be pushed harder with less distortion and in a smaller box . . .
I vote for redoing the XO.
The 874 is my favorite Peerless driver.
https://www.jfcomponents.com/
Regarding the Nephila, I was thinking generally about the driver size/form factor with a somewhat high crossover point. Much of the dogma I have soaked up over the years tells me that might not be such a favorable setup. But it flies anyway, and well apparently.
For MTM, I don't think I'm to that point yet. I would rather do more research and probably experiment with that config on a smaller scale first. I really need to start shrinking the size of my builds anyway.. Running low on space. [pushes a stack of buyout 15"s out of view]
If I were to do a multi woofer tower I'd probably try 2.5way. That config always piqued my interest for some reason.
Opened one up today and pulled the old crossovers out. I originally lined em with self stick vinyl floor tile and adhesive carpet squares that had a thin layer of dense foam rubber underneath. Seemed like a good idea at the time, but It didn't work out so well. The vinyl tile adhesive would come unstuck from the plywood. So I pulled all that out and put some 1" acoustic foam back in.
The woofers had an RC (zobel) on em that I hot glued to the magnet so I opted just to leave em on. Took measurements and messed around in WinPCD for a while. Was a little interesting getting the combined measurement for figuring out acoustic offset. I had to invert polarity for the tweeter to get them to "add up" properly. I was pretty mindful when I was attaching the leads, but I'll need to be sure to check when the drivers come out again. Z offset came to about 1.2" with the tweeter recessed and woofer flush mount. Got some sim results that seem decent with only 5 components +2 resistors, not including the RC on the woofer.
Oops, chopped off the frequency legends. Shows crossing just under 3k.
Sorry if the pics are loading slow. imgur is probably a bit under siege right now with all the reddit stuff going on.
Do you guys do minimum phase on both woofer and tweeter? I really haven't messed with minimum phase much. Maybe that is the problem I've had all along.
OK, maybe that was a really dumb question?
Had to get MS office installed on the new PC and extracted minimum phase from FRD blender. Did for both woofer and tweeter.
Though I seem to get much closer results on the WinPCD acoustic offset by not using the min phase graphs. The instructions explicitly say to use min phase on both, but not on the combined measurement. So still a bit confused about how I should do it to be correct.
Next attempt, same part count:
IIRC here's what Jeff said about min-phase and non min-phase measurements:
You can use non min-phase measurements, but the result will apply only to that single point and distance where the measurement was made. If you want to adjust the distance and/or off axis angles use min-phase measurements.
The acoustic offset will be different for min-phase and non min-phase measurements. So if using min-phase measurements use them when doing the 3 measurement (woofer, tweeter & combined) approach to determine the acoustic offset. You don't need to make the combined measurement min-phase (although it wouldn't affect anything) since you are just trying to match the combined measurement magnitude.
The above assumes you are using a single channel measurement program. If you're using a dual channel system you shouldn't need min-phase at all.
I can get the min-phase measurements to line up above about 3khz at the same z offset as the non min-phase measurements. And that is about the best I can get the min-phase measurement to match up to the combined measurement.
However one big oddity is the non min-phase measurements match up almost perfectly to the reverse polarity (tweeter) wired combined measurement. The min-phase measurements are a closer match to the combined measurement when the drivers are wired up in normal polarity.
Non min-phase (tweeter reverse polarity):
min-phase (tweeter normal polarity)
Both above were about as close as I could get each one. And that is at pretty much the same Z offset result for both.
I believe I took all the other measurements involving the tweeter in reverse polarity also after seeing all the cancelation in the normal polarity combined measurement.
So either I just roll with that Z offset result and hope it is correct or I guess I do a bunch more measuring to try and figure it out without confusing myself.
Why does your data just stop at 500 Hz on the top graph and continue as a horizontal line on the bottom graph? Did you extend the response tails before you extracted minimum phase? It makes a difference.
I didn't want to go below that on the tweeter so I just did all those measurements above 500hz. I've been living under a rock for quite a while just reading what I can find on forums and sites up until more recently joining the forums. So I always felt like I didn't quite know what I was doing, just trying to figure stuff out as I go. I think I've come a long way, but still lightyears behind you guys.
So no I did not extend the tails because I was not aware that was necessary.
See screen shot below of FRD Blender 2.0:
Step 2: change the lower and upper limits to 5 and 40000 Hz.
Step 3: don't care because you aren't blending near and far field responses. For a tweeter just go to the LF_FRD_Data tap and hit "Clear Data" button
Step 4: enter where you want the tails to begin and adjust the slopes to match the naturally occurring slopes
You can see everything below about 200 Hz is just the noise floor of my room
Thank you for the info! Do you think I should measure lower anyway? Just a little leery of blowing the planar.
No, 500 Hz is plenty low. Just add the tail below that and it will make your minimum phase more accurate.
Finally picked this back up. Got some measurements that matched up well to the acoustic offset graph. Woofer comes in 3/4" behind the tweeter which makes a bit more sense. So maybe I can finally get a sim to reasonably match up to reality.
Unfortunately there is a hefty woofer dip. The dip in tweeter response doesn't completely line up, so my best guess is stacking natural woofer FR with baffle interaction. I get the feeling the beastmode would be a better match.. Use it's grunt to cross below 2k. Maybe a future possibility with the second pair of woofers.
Does the dip stay there in off access measurements? Also remember in audio a dip is better than a hill.
I try to get off axis measurements more often now. Though it is tough to change the angle of the tray table accurately without moving off center so those measurements are always a bit suspect for me.
I stared at this for a while as my mind wandered. Had a bit of a "duh" moment.
The woofer is nearly the same distance from the bottom as the sides (potentially getting a triple whammy). I did the measurements with the speaker on a folding tray table that has almost nothing of substance underneath. I could see about propping up a board underneath to see if it makes much difference.
Time for a simple turntable and dedicated measurement stand?