PA Speakers - moving to a passive crossover

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Hi Chris,

Passive? No way, my friend.

TD is a ******** genius at visualizing the entire electrical and acoustic interrelationship between passbands, driver selection, box construction, port locations in horn etc....

You gonna duplicate that without digging deep, starting over, all the way down?

And if you do design from ground zero, remember...you still have limiting to lay on top of the individual passbands....otherwise you're left simply triggering off the time interval implied by highest freq you need to protect, ....for the whole dang box ! ...

Seriously, screw passive....

I think the crossover sim on the first page looks pretty good. With this particular driver complement, a crossover in the 800-1kHz range gets a nice smooth off-axis as the 10"s are just starting to narrow their directivity there.

Good point on the limiting, though. It's something that would be a problem for this application, and has got me re-thinking the whole thing.

I wonder how Jeff does it with the JTR 3TX...


If you can tame the DJ - IF you can! - , plus the system is way overdesigned for the location, you don't need limiting.

You always need limiting.
This is for live sound as well as DJs. If someone goes up to a mic and screams, I'd rather some red lights flicker on than the HF voice coils become magic smoke.

Chris
 
I wonder how Jeff does it with the JTR 3TX...

Chris

Here you go below....taken from Limiters - JTR Speakers Inc.

How does that compare with what you'd set for the double 10"s, if you were setting them on their own via biamp?
Seems like a pretty fast attack to me...???
Voltages seem right though...


Noesis 3TX, Noesis 2TX, Noesis 2AX-

RMS (0.050s attack with 0.50s release):
8 ohm - 80v (800w)
4 ohm - 56v (800w)

Peak (0.010s attack with 0.10s release):
8 ohm - 160v (3200w)
4 ohm - 113v (3200w)
 
I use different drivers to Jeff, so I'd be looking for 600w continuous to each 10". They're rated with the AES standard test signal, so I guess in theory they'd be fine with 2400w instantaneous peaks per driver.

If there's a passive crossover in play, there are losses to account for so I might set the RMS limiting in the 1500w region.

Though if you go back to the first page, you'll see I currently only have the limiters offered by the DCX2496. ie, peak limiting only. The amplifiers I use would be able to cook the drivers eventually, so it's up to me to keep them out of constant clip:

HF:
NU4-6000 - 300w/ch into 8ohm.
ND1460 - 100w continuous.

MF:
NU6000 - ~2000w/ch into 4ohm
10FH520 - 600w continuous each, so 1200w combined.

Having gone over Jeff's limiter settings, I'm wondering if there's much to be gained by using a lot more power for the midrange drivers. 2400w peaks each would be 4800w per cab, which is a touch more than the MA12000i will put out.
The extra 3.5dB of theoretical output would be nice, but using an amp that big to drive 4x 10" midrange drivers really feels like overkill.
... and I'd end up needing a really big sub amp.

Chris
 
Having gone over Jeff's limiter settings, I'm wondering if there's much to be gained by using a lot more power for the midrange drivers. 2400w peaks each would be 4800w per cab, which is a touch more than the MA12000i will put out.
The extra 3.5dB of theoretical output would be nice, but using an amp that big to drive 4x 10" midrange drivers really feels like overkill.
... and I'd end up needing a really big sub amp.

Chris

Diminishing returns for sure....maybe it's time to upgrade to bigger cabs, line arrays, mid-bass horns, etc.

Or put fans on your drivers :eek:
 
Diminishing returns for sure....maybe it's time to upgrade to bigger cabs, line arrays, mid-bass horns, etc.

Or put fans on your drivers :eek:

I won't be going to line arrays. Too many compromises there, the big one being that tonal balance changes with distance. I find that unacceptable.

I'm rather tempted to put the drivers in a Synergy-style horn, but that's another thread entirely.


Limiting each way in separately is still possible even with a passive X-over: For decades, light bulbs have been used. You just need to factor in a small cold state ohmic series resistance, when you design the crossover network.

Finding the correct lightbulb would be an expensive game of trial and error. New diaphragms are £100 each.
Plus, I'd have to get the crossover to behave correctly with a wide range of impedances, which would be really difficult without almost shorting the whole thing out with a huge 4ohm resistor.


I've got a house move coming up soon, but a quick test with the home HiFi reveals the MA12000i is noticeably nicer-sounding than an NU3000DSP. Less "hash". I don't really have the words to describe it, but I do wonder if I can measure it.

Cheers, all.
Chris
 
Finding the correct lightbulb would be an expensive game of trial and error. New diaphragms are £100 each.
Chris

The way to find the right bulb is first to find out what current the voice coil can withstand. Apply DC voltage to the speaker, start at very low levels, like 1V. Measure the initial current and the lower current after it has warmed up. If no difference, increase the DC voltage. Be sure to start again in cold condition. At a certain voltage, the hot state current will be approx. 0.7 times the cold state current. The voice coil is heated up and you do not want to exceed that temperature. This hot state current level is your target for the light bulb. Choose the light bulb in a way that it should should be at full rated power at that current and it should be consuming a significant portion of the voltage in that state, so no 5V rated bulb, maybe 2 x 24 V bulbs in series. In case the amp voltage goes even higher, the lower voltage bulb bulb will open circuit immediately while the higher voltage ones will still have some room to tame /limit the voice coil current.
 

Yes and no.

The "yes" is that I picked up a Powersoft T604 to run the main speakers bi-amped.

No passive crossover, though. I did a bit of playing around, and found that the low-pass inductors would need to stand exceptionally large currents. Easier to just use 4-core SpeakOn. Add in the arguments for individual band limiting, and staying active made more sense for this system.

Thanks for the interest.

Chris
 
Are you happy with the T604? I am also interested in buying one...

Yep, it's an excellent amp. My only complaint would be that it's not great for stage monitor use, as there are only 2x SpeakOn (NL4) outputs - you'll need some kind of splitter to get to 4x NL2 to run to different monitors.

The T604 sees infrequent use in my home stereo, as I use it to prototype 2-way designs. It's very easy to get things sounding good when you have that amount of DSP (and power) available.

I did more of a write-up here: Powersoft T-series

Long-term, I'm thinking of picking up a couple of T304s for stage monitor use, and another T602 for more power into the subs.

Chris
 
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