60 Degree DIY Mid Hi - AKA PM60

Matteo Gagliardi

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Hi, i was wondering what you all think of a hypothetical version with only one 12" and maybe not 3-way but with a compression driver.
Does it make sense to modify it like this, to make it even more portable?

I did not find the parameters for hornresp anywhere, are they available?

Thank you
Matteo
 

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Don J Davis

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Not sure what you would gain with this over using a conventional 12" point and shoot box. Peter's brilliant dipole design allows the 2 twelves to combine nicely while creating a powerful 3-way pole mountable box.
 

Adrian Patino

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Hi,
I intend to build a pair of those speakers soon. I read both threads about the design and still have a few questions. B&C released their new HF Coax the DCX354. Its lighter and a bit smaller than the DCX464 but they claim that it will have nearly the same output. Is it suitable for the PM90/60? I wanted to go with the DCX464 but saving weight is always good. :)

To my knowledge there is no passive crossover for the DCX354 at the moment which is a not an option for me because I use a six-way DSP and Subwoofers need to be controlled as well. Therefore, I can only Biamp the Speakers now. Maybe someone knows what B&C is planning in the future?

I will post build pics when im done making sawdust. :)

Thank You
Adrian
 

Art Welter

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Adrian,

The B&C DCX354 spec sheet lists the FB354 passive crossover as "also available", so it probably will be soon ;^).

As Peter mentioned in post #878, the high output of the horn loaded 2x12" and the low crossover of around 700/650Hz for the PM90/60 with a relatively small HF horn with limited low frequency loading demands a lot from the mid driver.
Although the DCX354 has "nearly the same output" in the upper range as the DCX464, there is no replacement for displacement, smaller diaphragms simply can't put out as much SPL before running out of excursion at the lower end of their pass bands. The DCX464 is rated for another 1/3 octave lower output than the DCX354.
DCX354 vs DCX464.png

The reduction in diaphragm area between the 100mm of the DCX464 vs the DCX354 76mm voice coil is apparent in the above comparison.

Art
 
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Rhys Edwards

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I've also been closely watching the DCX464 vs DCX354 situation, while i will take B&C's word for it that the 354's MF plays a smaller range, the response graph on the website between the two is extremely similar. Output wise the 354 has the same or better sensitivity with a small sacrifice in total power handling ending up with roughly a max output reduction of .5dB on both the MF and HF sections compared to the 464, seems like a reasonable compromise overall for improved distortion i think (i do wonder how much?). From the postings/updates, it's mentioned there have been several improvements on the design and manufacturing process since the 464 release so i suspect the 354 may be even better than it initially appears.

I know graphs don't always tell the full story but you would think they are almost interchangeable seeing this (manually overlapped images from B&C site):
DCX464 in blue, red
DCX354 in green, purple
464-354-2.jpg

Unrelated, for those who don't know Australia now has a B&C distributor at surgesound.com.au and from my correspondence with them, the prices are very reasonable compared to previous import options.
 
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Joris Wijgerde

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I've also been closely watching the DCX464 vs DCX354 situation, while i will take B&C's word for it that the 354's MF plays a smaller range, the response graph on the website between the two is extremely similar. Output wise the 354 has the same or better sensitivity with a small sacrifice in total power handling ending up with roughly a max output reduction of .5dB on both the MF and HF sections compared to the 464, seems like a reasonable compromise overall for improved distortion i think (i do wonder how much?). From the postings/updates, it's mentioned there have been several improvements on the design and manufacturing process since the 464 release so i suspect the 354 may be even better than it initially appears.

I know graphs don't always tell the full story but you would think they are almost interchangeable seeing this (manually overlapped images from B&C site):
DCX464 in blue, red
DCX354 in green, purple
View attachment 209679

Unrelated, for those who don't know Australia now has a B&C distributor at surgesound.com.au and from my correspondence with them, the prices are very reasonable compared to previous import options.
That's sensitivity though, seeing the 464 has a higher SD and larger voice coil, and midrange will probably be limited by it's excursion won't the DCX354 bottom out way before the 464 when crossed as low? I guess that's why the recommended crossover frequencies for both drivers differ, since otherwise there'd be no way for it to play at the rated power.

1670318684420.png
 

Art Welter

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That's sensitivity though, seeing the 464 has a higher SD and larger voice coil, and midrange will probably be limited by it's excursion won't the DCX354 bottom out way before the 464 when crossed as low?
Yes, the diaphragm would hammer the phase plug with about 5dB less output at 650Hz in the DCX464 than the DCX354, so the DCX354 may sound distressed while the 12" are still clean.
 
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Robin Fredsson

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Yes, the diaphragm would hammer the phase plug with about 5dB less output at 650Hz in the DCX464 than the DCX354, so the DCX354 may sound distressed while the 12" are still clean.
At how strong of a signal do you bash the DCX464's diaphragm into the phase plug in the first place? With a recommended lowest highpass of 300hz for the 464, I assume that you have a whole lot of displacement left if you cross if over at 650hz instead. So much so that you could probably go for a smaller diaphragm and still not bash it. After all, B&C do recommend a lowermost highpass at 400hz for the 354, so there is likely quite a bit of displacement left if you cross over at 650hz.

The way I see it, the 354 is likely the new go-to for the PM90/60, given its smaller size, lower weight, (smoother top end?), practically identical output, improved design and most likely lower price than the 464.
 
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Art Welter

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At how strong of a signal do you bash the DCX464's diaphragm into the phase plug in the first place?
I'd guess a little more than what is required to "keep up" with the dual 12" at 650Hz ;^).

The difference between displacement between the DCX464 and the DCX354 is about the same as between a 4" and 3" diaphragm, Peter Morris has stated previously in this thread that a 4" diaphragm driver is required to "keep up" with the 12" at 650Hz.
Compression drivers don't have "a whole lot of displacement", the lower annular ring probably has around 0.8mm.
Four times the displacement (excursion) is required for each halving of frequency to maintain the same level.
The DCX464 and DCX354 charts are for the "Driver mounted on 320 Hz exponential horn".
A 320Hz horn loads the diaphragm to a much lower frequency than the smaller horn used in the PM60.

The Eighteen Sound XT1464 horn "Usable Frequency Range" is specified as "above 500 Hz", with a recommended crossover frequency of 800Hz or above, but the response of the 12" requires a crossover in the 650Hz range.

Anyway, if you think the smaller diaphragms in the DCX354 will keep up to the 2x12" in the 650Hz range on the XT1464 horn, go ahead, and report back how they compare when the 12" are reaching 135+dB.

Art
 
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Rhys Edwards

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Anyway, if you think the smaller diaphragms in the DCX354 will keep up to the 2x12" in the 650Hz range on the XT1464 horn, go ahead, and report back how they compare when the 12" are reaching 135+dB.

The official wording from B&C themselves on the news release say:

Continuing the family started by our DCX464 coaxial compression driver, the DCX354 features a similar design with smaller dimensions. 76mm (3”) MF coil and 51mm (2”) HF coil ring radiator diaphragms allow the DCX354 to provide very high sound pressure levels above 500Hz, with even lower distortion than its big brother.

And in this other thread NEW B&C coaxial MF/HF Bennett also says:

It’s going to be about 80% the cost, 80% the diameter, and 80% the weight of the DCX464. Surprisingly not much less output, except <500Hz. Smaller diaphragms are a little better behaved!

I'm pretty tempted to believe it really does perform the same at 650hz; just because it hasn't been possible in the past on a smaller diaphragm doesn't mean it will always be that way. I'd like to believe as the technology matures it's possible to squeeze out more performance over time. It seems reasonable to believe that the 464 was intentionally designed as a direct competitor and drop in replacement for the BMS 4594ND (now 11 year old design) and that with careful assessment and overhaul the optimised 354 can now do the same with close to no compromises.
 

Art Welter

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I'm pretty tempted to believe it really does perform the same at 650hz; just because it hasn't been possible in the past on a smaller diaphragm doesn't mean it will always be that way.
It is possible to allow a smaller diaphragm have more displacement by increasing the diaphragm to phase plug distance.
A larger diaphragm to phase plug distance creates an acoustic bandpass, rolling off the high frequency response as can be seen in the response of the DCX464.
As can easily be seen In the overlay #1007 the DCX354 response extends higher than the DCX464, which would indicate that diaphragm to phase plug distance has not been increased.
 

Robin Fredsson

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FWIW, the 4594 has a 3" diaphragm and is speced as being good for 1kw peak power above 500hz. The DCX354 does have a higher sensitivity and a more extended MF response than the 4594, indicating a lighter moving mass or a smaller chambre or both, but I'd be surprised if it couldn't handle at least it's program power over 500hz, and more than that above 650hz, excursion wise.
 

Art Welter

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FWIW, the 4594 has a 3" diaphragm and is speced as being good for 1kw peak power above 500hz. The DCX354 does have a higher sensitivity and a more extended MF response than the 4594, indicating a lighter moving mass or a smaller chambre or both, but I'd be surprised if it couldn't handle at least it's program power over 500hz, and more than that above 650hz, excursion wise.
The BMS 4594 has a 90mm (3.5") voice coil, the diaphragm is slightly wider than the DCX464's.
At 400Hz, the rating drops from 1kw peak to 150W RMS.
DCX354 vsDCX464vsBMS4594.png

The reduction in diaphragm area between the 100mm of the B&C DCX464 vs the B&C DCX354 76mm voice coil is significant, the smaller being about half the Sd (diaphragm surface piston area) of the larger. Assuming the same Xmech, there should be just under 6dB difference in displacement limited output.
The difference in Sd is similar to that between an 18” and a 12”.

The hole in the center of an annular diaphragm reduces the Sd in comparison to a dome diaphragm, but larger diaphragm to phase plug spacing is possible with reduced high frequency.

The 100mm diaphragm appears about 14mm wide, an Sd of 3.4 square inches (22 square cm).
The 76mm diaphragm appears about 10mm wide, an Sd 1.84 square inches (11.94 square cm), just over half the displacement assuming the same excursion.
The above computations assume a flat Sd, while the annular diaphragms have a “V” shaped diaphragm cross section, so the Sd would be larger than indicated, but by the same ratio assuming similar “V” angles.

The BMS 4594 drops at around 6.8kHz, slightly higher than the B&C DCX464.
The DCX464 may have more excursion than the BMS 4594’s +/-0.8mm, so could still have more displacement.

Art
2/26/23 edit-the Sd of the B&C DCX354 is larger than the estimations above, so displacement assumptions made are incorrect, sorry for the errors!
 
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Nelson Chen

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Just wondering what you guys think about this newer 12" woofer (Precision Devices PD.123C001)? Suitable for PM60? It has a high BL of 24.5 T/M. Frequency response graph looks smooth. Price is reasonable. I am concerned about that dip at 500Hz. But, Ciare 12NDH-4 also has a dip there. 12NDH-3 does not. Slightly lower Mms than Ciare. Higher EBP than Ciare. Fs and Qts are both lower than Ciare.

 
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Robin Fredsson

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The BMS 4594 has a 90mm (3.5") voice coil, the diaphragm is slightly wider than the DCX464's.
At 400Hz, the rating drops from 1kw peak to 150W RMS.
View attachment 209681

The reduction in diaphragm area between the 100mm of the B&C DCX464 vs the B&C DCX354 76mm voice coil is significant, the smaller being about half the Sd (diaphragm surface piston area) of the larger. Assuming the same Xmech, there should be just under 6dB difference in displacement limited output.
The difference in Sd is similar to that between an 18” and a 12”.

The hole in the center of an annular diaphragm reduces the Sd in comparison to a dome diaphragm, but larger diaphragm to phase plug spacing is possible with reduced high frequency.

The 100mm diaphragm appears about 14mm wide, an Sd of 3.4 square inches (22 square cm).
The 76mm diaphragm appears about 10mm wide, an Sd 1.84 square inches (11.94 square cm), just over half the displacement assuming the same excursion.
The above computations assume a flat Sd, while the annular diaphragms have a “V” shaped diaphragm cross section, so the Sd would be larger than indicated, but by the same ratio assuming similar “V” angles.

The BMS 4594 drops at around 6.8kHz, slightly higher than the B&C DCX464.
The DCX464 may have more excursion than the BMS 4594’s +/-0.8mm, so could still have more displacement.

Art
Good input, Art!

So, what we have figured so far is that the MF for the 4594 and the DCX464 likely have very similar output when displacement, sensitivity, and power handling are all accounted for.

The 4594 is specified to be good for 1kw above 500hz, but only 150w above 400hz. That equals about a 8.5db input difference. How much power should the displacement be good for at 650 hz then? Another 3-6db? That equals 2-4kw then. Now lets say that the DCX354 has half the displacement of the other two, which equals a 6db difference in displacement capability. In terms of power, we're now at 0,5-1kw. I don't know where others would like to set their peak limiters, but twice the nominal power handling of the DCX354 could be a good place to start, which equals 180w, which is less than half of the lower range in the example.

Now, testing is what it all comes down to in the end, and this sort of voodoo comparison can only give us rough estimations at best, but even if the rough estimations are off by an order of 3-6db, we should still be good with the DCX354 when crossed at 650hz.

Bennett has written that it leaves no compromises over 500hz when compared to the 464, which goes well along the lines of my very rough estimations.

Like I wrote earlier, I believe that the 354 is likely the new go-to for the PM90/60.
 

Art Welter

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Good input, Art!

So, what we have figured so far is that the MF for the 4594 and the DCX464 likely have very similar output when displacement, sensitivity, and power handling are all accounted for.
If mounted on the same 320Hz exponential horn, yes. The 18 Sound XT1464 cutoff is >500Hz, it's sensitivity
The 4594 is specified to be good for 1kw above 500hz, but only 150w above 400hz. That equals about a 8.5db input difference. How much power should the displacement be good for at 650 hz then? Another 3-6db?
I'd only be guessing at an answer, and it would depend on the horn.

Now lets say that the DCX354 has half the displacement of the other two, which equals a 6db difference in displacement capability.
Without knowing the DCX464 and DCX354 Xmax/Xmech, we really don't know the displacement capability.

AES power ratings are a 2 hours test made with continuous pink noise signal (6 dB crest factor) within the specified frequency range, with power calculated at rated minimum impedance. The driver must survive the test, but lack of distortion is not a requirement.
On the 320Hz exponential test horn, at around 320Hz, the DCX354 reaches around 50 Ohms.
Using 27 Volts (90 watts AES power rating) it would be using under 15 watts at 320Hz, but nearly full power at 400Hz (11ohms), it's lower specified frequency range .
At around 320Hz, the DCX464 is 10 Ohms. Using 30 Volts (110 watts nominal AES power rating) would be using around 90watts.
Below it's lower specified frequency range of 300Hz, impedance rises to near 50 ohms.

Now, testing is what it all comes down to in the end, and this sort of voodoo comparison can only give us rough estimations at best, but even if the rough estimations are off by an order of 3-6db, we should still be good with the DCX354 when crossed at 650hz.
"Good" is a relative term.
At any rate, compression driver sound when driven to the low frequency limitations are a different issue than surviving RMS and peak voltage swings.
I believe many won't notice the difference as long as the driver continues working ;^).

Art
 
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Derick Phan

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If you are using the BMS with a passive crossover then an NL4 will work fine. If you are using the BMS 2- way you will need an NL8 ... BMS VHF pins 4,4, BMS HF pins 3,3, mid 12NDL76 pins 2,2, Sub pins 1,1.
Peter,

Thank you for all the help as its been greatly useful for beginners as the thread is still active throughout the past 8 years. I am attempting to build my first PA system having just about completed my first TH18 build based off of one of Brian Steele's sheets and wanted to find a suitable mid high top to pair with it. Trying to get as much value/performance as possible, I have DCX2496 for active crossover which it seems the IIR filters will be able to handle for the PM60, and for the amps a NX6000d and the FP14000 clone I plan to purchase.

As I've gone through this and the pm90 thread, I still have some (rudimentary) questions regarding the wiring, if you could please correct me on these. The three crossover points needed will be at around 120hz for the subs, around 650hz for the BMS horn, and around 6.3khz for the BMS or other compression driver used between its two drivers.

-With the passive crossover, does this mean I would have the mid (2 12" in parallel) on one output NLX connector and the high (BMS) on another output NLX connector and crossover the channels within the DCX2496?
-Am I correct in saying that if the BMS passive crossover is not used, it then requires an additional output connector and amp channel to crossover at 6.3khz for the VHF range?
-How is it possible to filter out all these frequencies on a single NL4 or NL8 connector even though they are on separate poles? It seems that on the DCX2496 the crossover point is between each output channel, do other DSP units have a different method to crossover within the poles?
From the DCX2496 manual
rynNn3w.png


Thank you again for any reply and help; I work in a completely different area of Electrical Engineering (and admittedly did not have great grades in DSP), but this has been lots of fun :)

Derick