3-way Aurum Cantus, PR170M0 w/measurements

[tiroth]

I've made some progress on my active 3-way project using Aurum Cantus G2, PR170M0, and 2xHM170Z0.

The PR170M0 is in a 12L stuffed box with aperiodic vent. The two HM170Z0 share a sealed 40L stuffed box, final Q was 0.67 (lower than predicted).

Crossover points: (all 2nd order)
Low: 320Hz, Q=0.8
Mid: 400Hz, Q=0.5; 4000Hz, Q=0.7
Hi: 4000Hz, Q=0.7

Here is the magazine pic of the on-axis response, 1/10 octave smoothed. I'm not including the nearfield measurement, because there isn't anything too exiting. F3 is 56Hz.



I promise I won't include any more such useless pics. Here is an expanded scale, still smoothed 1/10 octave. The response looks pretty good to me, +-3dB from the nominal 1dB level.



Looking at negative vertical angles also doesn't ruin the party. The picture shows the -5 and -10 degree measurements; the ribbon is fine up to -10 degrees but really starts to go at that point.



But looking at the positive angles reveals comb filtering. The +2.5 trace is fine, but there is a progressively deeper dip at higher angles. I didn't show the +12.5 degree measurement but it is even worse: -20dB.



Bold blue: 0
Purple: +2.5
Dark blue: +5
Green: +7.5
Gray: +10

[tiroth]

My first band-aid attempt was to move the PR170M0 upper XO frequency to 6300Hz. This did actually improve the dip significantly at higher angles; the dip at +12.5 is now about on par with the old +5 dip.



There isn't significant improvement at +5; the dip has been pushed out to 6kHz but the magnitude is the same. There is also a new peak in the response at 4700Hz, but that could be notched.

[tiroth]

I'm not really sure where to go from here; it seems as though it could be a decent response with a 5 degree baffle tip but my bandaid is not going to fix the response for a standing listener. Any of the experts have a suggestion on where to go from here?

I'll also post a pic of the pulse response, since that might help.

[BDP]

Tiroth,

I'm very interested in your results because I also am working with the PR170M0 and G2, but open baffle. Currently everything is passive until I complete the MOX active x-over. The lower end mid bass driver is the PR330M0, they were a good buy from Zalytron, about half the price of other similar drivers and it integrates well with the midrange. When I go active it will be between the midbass and midrange.

I have been listening and measuring different x-over points. At this point I like the 4-5K range. Any lower and the tweeter starts sounding harsh, but I'm only using 2nd order filters on the G2. Any higher in frequency and the off axis response gets bad with large dips. Even though the measurements are better at frequencies below 4-5K I don't think they sound as good. This is still early on in the project and things could change. There are many combinations to try. Are you using a passive capacitor on the G2 tweeter for protection and then using an active 6dB filter to make the 12dB combined output slope?

I'm using the IMP audio analyzer to test the driver responses. I would be glad to share any info here on the forum or through e-mail, though I don't know how to post the IMP graphs on the forum (maybe someone can help !).

Which amps are you using?

BDP

[tiroth]

Originally posted by BDP
[B]I'm very interested in your results because I also am working with the PR170M0 and G2, but open baffle.

Is just the mid OB? PR330M0 has very low qts...

I have been listening and measuring different x-over points. At this point I like the 4-5K range. Any lower and the tweeter starts sounding harsh, but I'm only using 2nd order filters on the G2. Any higher in frequency and the off axis response gets bad with large dips.

Not surprising. If you look at the G2 and PR responses separately the 4-5kHz region looks like an ideal place to cross.

Are you using a passive capacitor on the G2 tweeter for protection and then using an active 6dB filter to make the 12dB combined output slope?

No, I currently have a large (22uF) film cap so I can do everything actively. I'm using a little test kit I built up that has 3 channels of LM3875 along with the MOX boards, PSU, and level pots.

I'm using the IMP audio analyzer to test the driver responses. I would be glad to share any info here on the forum or through e-mail, though I don't know how to post the IMP graphs on the forum (maybe someone can help !).

I'd definitely be interested. I think Saurav is also working with PR170M0 and a ribbon now, so if we all get our heads together it might speed things up. I think the easiest way to post graphs is just take a screen shot (CTRL-PrtScrn) and paste it into Paint or an imaging program.

I was pretty pleased with the off-axis response of the PR170M0; I was worried it would be beaming to heck but here is the 0-15-30-45-60 degree horizontal polar measurements with the mid crossing at 6300 (still 4000 on the tweet).

[ThorstenL]

Konnichiwa,

Originally posted by tiroth
I'm not really sure where to go from here; it seems as though it could be a decent response with a 5 degree baffle tip but my bandaid is not going to fix the response for a standing listener. Any of the experts have a suggestion on where to go from here?

Hmm. first by having one midrange and one ribbon (or other tweeter) there is always going to be a response problem in the vertical. TYou can invert the Arrangement of the driver to place the problems on the downward axis, but they are practically impossible to eliminate. Going MTM with a sufficient low crossover point and the correct crossover order can fix this, as Mr. D'Appolito showed ages ago.

As a concolation price, narrow dips are not very audible, my guess your standing listener will be bothered more by having a rather narrow vertical dispersion from the ribbon.

Sayonara

[RussianBlue]

I am also using the PR17MO, currently with a GR-6 tweeter, a 10inch low mid and a 15" JBL 2125, in an 4-way active configuration. I am driving them with two Yamaha 2201 and two Yamaha 2100. The mid+highs are in a sealed box and yes, I have them inverted on the baffle. I have had good experiences taking them all the way up to around 6K without adverse effects. I tend to like this midrange running with a 6dB/slope crossover on both "ends," although right now I am rather enjoying the system with the midrange using 12 dB/oct Bessel filters crossed over at 385Hz and 3850Hz. The tweeter also comes in with a Bessel 12dB, the lowmid with a Bessel 12 on the high end and a Butterworth 6 at 65Hz on the low end. The JBL comes in at 125Hz.
I am still not 100% convinced about the quality of the AUDAX mid. It sounds a bit brittle to me, for the lack of better description, dampening the chassis with mortite helped a bit. I am thinking of trying the MOREL MDT 33 as a tweeter next. Help me dispel my worry that there are substantially better midranges out there.


Many greetings

[BDP]

Tiroth,

Yes, the mid range is the only one OB. My plan is to make a box for the PR330M0 large enough for BR but use it sealed with a little boost to help out on the bass. It will also give the flexibility to try a bass reflex configuration if need be. From there I will see if the in room bass will be satisfactory. The driver doesn't go very low, but I wanted a driver that was good into the midrange. If not I will expand the MOX x-over to accomodate a sub ( Another amp!!).

The test OB measures 15 x 24 and reaches down to about -3dB at about 300Hz. I need to offset and/or change the dimensions some because there is a dip in the 1100-1300Hz region that I want to eliminate. The x-over from bass to mid is going to be 400-500Hz.

So far I like the sound of these drivers (and the prices). I have MTM scan-speak 8546 and I prefer the Audax, but then again it is a three way and with a much more acceptable impedance. Higher impedance and sensitivity is what I'm after to mate better with some of the low power low feedback Pass amps. Once I get these speakers completed I want to try a Zen light. I think I have gone full circle from a few years back of low power amps on Altec A-7 horns. Here we go again.

BDP

[ThorstenL]

Konnichiwa,

Originally posted by RussianBlue
I am still not 100% convinced about the quality of the AUDAX mid. It sounds a bit brittle to me, for the lack of better description, dampening the chassis with mortite helped a bit.

Try painting the cone. I would STRONGLY advise to use C37, but you can try Dammar or other natural resin varnishes.

Originally posted by RussianBlue
Help me dispel my worry that there are substantially better midranges out there.

Sorry, I can't. THERE ARE substantially better midranges out there. But they usally cost tons more and tend to be much larger and are harder to apply. As a 6.5" Cone midrange the AUdax is stock excellent and with some mods exceptional.

Of course it will never give the smooth tone of "damped polypropylene" Cone, the "smoothness" is simply the removal of low level information due to the damping in the cone itself.

Sayonara

[RussianBlue]

Thank you for the input, KWY!

Would you help me with your advice, what do you mean by C37?
It sounds dangerous.

RB.