iNuke nu3000DSP outputs when in bridged mode

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
I have two 8 ohm subs I'd like to connect to my nu3000DSP as a single 4 ohm load. When running an iNuke nu3000DSP in bridged mode, can I hang one of the subs off each output, or do I need to actually cascade them (in parallel) off a single output?

(In other words; do the outputs become wired in parallel when the amp is running in bridged mode?)

The manual says "The mono output signal isidentical at Outputs A and B, and the amplifier responds to a single combinedspeaker load", which seems to suggest that the loads across each output are in parallel, and my two individual 8 ohm subs would be seen as a single 4 ohm (combined) load. Yeah?

Thanks,
Mitch
 

mackerr

Junior
Jan 29, 2011
374
6
0
Re: iNuke nu3000DSP outputs when in bridged mode

The manual says "The mono output signal isidentical at Outputs A and B, and the amplifier responds to a single combinedspeaker load", which seems to suggest that the loads across each output are in parallel, and my two individual 8 ohm subs would be seen as a single 4 ohm (combined) load. Yeah?

The manual is very unclear, but if you read section 5.2 on output connections you will see that for bridged mono use you need to have a speaker cable where the amp end of the cable is wired Pin 1+ and Pin 2+ while the speaker end needs to be Pin 1+ and Pin 1-. This is a dangerous cable to have sitting around in your cable bin as it won't work with non-bridged outputs. This is a great disadvantage of amps tht have only Speakon outputs.

Mac
 

Attachments

  • Screen Shot 2015-07-12 at 10.30.51 PM.png
    Screen Shot 2015-07-12 at 10.30.51 PM.png
    61.3 KB · Views: 3

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

Oh, nice catch, Mac. I had scanned through that, but must have run right over that one sentence! Ha! I kept looking for a bridged-mode diagram.

I find it interesting it's 1+ and 2+ and not 1+ and 2- (which makes more sense to me in a "two power supplies in serial" thought). This arrangement also kinda precludes one from quickly doing a/b testing since it requires using different cable for running in bridged mode (I had been trying to compare bridged mode against two subs on separate channels).

Thanks again.
 

mackerr

Junior
Jan 29, 2011
374
6
0
Re: iNuke nu3000DSP outputs when in bridged mode

I find it interesting it's 1+ and 2+ and not 1+ and 2- (which makes more sense to me in a "two power supplies in serial" thought).

Bridged mono mode must be between the 2 hot sides of the 2 amp channels, that's how it works. The 2nd channel is polarity reversed so the voltage swing is equal and opposite of the 1st channel. When you use the 2 hots as your speaker drive there is twice the voltage and the load impedance capability is halved. The input sensitivity is also 6dB higher so things immediately sound louder, but in multi-amped systems you need to correct for that.

Mac
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

The 2nd channel is polarity reversed so the voltage swing is equal and opposite of the 1st channel.
Ah hah, that's the part I hadn't considered.

The input sensitivity is also 6dB higher so things immediately sound louder, but in multi-amped systems you need to correct for that.

Oh. Is this because you have half the number of inputs loading down the output from the signal source (assuming the non-bridged alternative is both inputs on a single source, driving both power amps)?
 

mackerr

Junior
Jan 29, 2011
374
6
0
Re: iNuke nu3000DSP outputs when in bridged mode

Oh. Is this because you have half the number of inputs loading down the output from the signal source (assuming the non-bridged alternative is both inputs on a single source, driving both power amps)?

No, it's because you have twice the output voltage for the same input.

Mac
 

Steve Kirby

Freshman
Apr 29, 2015
50
0
0
San Jose, CA
Re: iNuke nu3000DSP outputs when in bridged mode

"and the load impedance capability is halved" This is the critical aspect of Mac's reply. Two 8 ohm cabinets paralleled are a 4 ohm load as the OP recognizes. But when the amp is in bridged mode, each side is effectively seeing a 2 ohm load. While some amps (don't know about the iNuke) are rated down to 2 ohms, running them there isn't necessarily such a good idea. 8 or 4 ohms is just a nominal rating. There will be frequencies where the true load the cabinet presents to the amp will be much lower. There may or may not be published impedance curves for the subs you have, but if you look up some of the better ones you can get an idea of how this looks. The net result is that at some frequency that you're probably trying to get a lot of output, you will be running the amp into a considerably lower load than it is intended for. While there is usually some headroom for this designed into amps, the more cost constrained the amp, the more likely for it to be less tolerant. This also starts to influence the amps "dampening factor" which is a ratio of the load to the amps internal impedance of the output stage. At higher speaker impedances, this is not a factor. But running a cost constrained amp into a 1 ohm load at near rated output will lead to a looser and more distorted sound even if it doesn't shut down in protect mode.
 

Mark Wilkinson

Sophomore
Feb 24, 2015
243
12
18
Re: iNuke nu3000DSP outputs when in bridged mode

......This is a dangerous cable to have sitting around in your cable bin as it won't work with non-bridged outputs. .....

Mac

To keep from screwing up with this cable, I put a red speak-on connector on the 1 +/ 2+ end.... parts express..

Red speakon.JPG

And here's a hard to find wattage chart for the 3000dsp that shows RMS, in case you haven't seen it...to help you decide if the amp can handle the low per channel impedance Scott and others have talked about..
My guess is bridged 4 ohm is probably ok....but i'd do an impedance sweep before i pounded...

Beh 3000dsp.JPG
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

I like the red cap. In fact here is what I did. The cap, red tape and black connector all have solver sharpie on them proclaiming this the amp end for bridged mode.

uploadfromtaptalk1437009282244.jpg

Incidentally, the subs I have (two of them) have Eminence Sigma Pro 18 drivers in them (Grundorf ST-18 cabs). I can't find specs on the model. Everything seems to be the 18A or 18A-2. According to Frank Grund, these are rated 300 watts RMS.

Currently I have the amp set to limit to 1200 watts (-4.8 dBfs) with defaults of 50ms Hold and 100ms Release.
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

some amps (don't know about the iNuke) are rated down to 2 ohms

As Mark posted, it does specifically have a rating for 2 ohms, when not in bridged mode. When bridged, only gives ratings down to 4 ohms.

There will be frequencies where the true load the cabinet presents to the amp will be much lower.

I've not been able to find specs on this particular driver, but his next of kind seem to hold pretty tight to the 8 ohm min, if I'm reading their chart right. Obviously understanding that the newer model (that I could find specs. for) may perform entirely different than it's older sibling.

And here's a hard to find wattage chart for the 3000dsp that shows RMS, in case you haven't seen it

Heh heh, have definitely seen it. 2000 watts RMS (4 ohm bridged) seems like it'll be quite a bit more than what my cabs can safely consume (~600 RMS as a pair), so it'd seem like there's a fair amount of headroom.
 

Tim McCulloch

Graduate Student
Jan 11, 2011
2,988
41
48
Wichita KS USA
Re: iNuke nu3000DSP outputs when in bridged mode


As Mark posted, it does specifically have a rating for 2 ohms, when not in bridged mode. When bridged, only gives ratings down to 4 ohms.



I've not been able to find specs on this particular driver, but his next of kind seem to hold pretty tight to the 8 ohm min, if I'm reading their chart right. Obviously understanding that the newer model (that I could find specs. for) may perform entirely different than it's older sibling.



Heh heh, have definitely seen it. 2000 watts RMS (4 ohm bridged) seems like it'll be quite a bit more than what my cabs can safely consume (~600 RMS as a pair), so it'd seem like there's a fair amount of headroom.

As per Mac's post, you also pick up 6dB of gain by bridging, so you need to set back your crossover output by 6dB. The illusion of more electrical headroom comes from your subs getting louder, sooner. And in the case of your subs, you're gaining absolutely *nothing* by operating in bridge mode. In stereo there is still enough voltage and current to cook a voice coil or do mechanical damage.
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

And in the case of your subs, you're gaining absolutely *nothing* by operating in bridge mode. In stereo there is still enough voltage and current to cook a voice coil or do mechanical damage.

I might not be understanding the specs. (or the math). From the specs (see Mark's post for reference), as separate channels, into an 8 ohm load, each side can only deliver a max of 440 watts. Since these drivers can handle 300 watts RMS (and without an actual spec. sheet to read from, assuming peak = 4x RMS), these guys should be able to handle the occasional 1200 watt hit.

Run running bridged mono, this amp claims to be able to deliver a max of 3000 (split across two drivers in my config, 1500 watts each).

With the amp's DSP limiter in place at 1200 watts (600 each), it'd seem that I would be gaining from a max of 440 watts (max, per channel, separate channels) to 600 watts peak (limited, bridged mono). Okay, so one could say that going from 440 to 600 watts isn't a hugely significant increase in volume. (However, if I wanted to chance it and set the limiter to 2400 watts, that'd be nearly a 3x increase in power from 440; I honestly don't think I want to apply that much power without an actual spec. sheet for the driver.)

Have I made some bad assumptions or done bad math here?

I really appreciate all the input from you guys.
Thanks again,
Mitch
 

Ron Kimball

Senior
Mar 5, 2011
581
0
16
NE CT
Re: iNuke nu3000DSP outputs when in bridged mode

You haven't said which particular subs you have? I use a non-DSP NU3000 bridged into pair of Danley TH-Mini's no prob but those are rated 700w continuous and 1400w program - and have excellent B&C (?) long throw drivers in them. Plus I'm careful to HPF them as recommended. For connection I have a plastic box with an input connector from the amp via a standard 4 wire speakon cable and there are three speakon outs on it - bridged, "A", and "B" so I can choose to run bridged or not (for smaller rooms or lack of sufficient circuits) without switching the amp out of bridge mode. The "B" output is wired reverse polarity to compensate for what the "bridge" switch does. Note that this amp is somewhat unusual among inexpensive class "D" amps in that most(?) have the bridge output as 1+ 2- not 1+ 2+ like this one (and most all non-class "D" amps).
 
Last edited:

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

Guess I mentioned the drivers, but not the actual subs. I have a pair of older Grundorf ST-18's. They have Eminence Sigma 18 Pros in them.

I'm doing the crossover (80Hz, and low cut at 25Hz) in my X32's matrix section and the limiter in the nu3000 (since I have the DSP version).
 

Ron Kimball

Senior
Mar 5, 2011
581
0
16
NE CT
Re: iNuke nu3000DSP outputs when in bridged mode

Guess I mentioned the drivers, but not the actual subs. I have a pair of older Grundorf ST-18's. They have Eminence Sigma 18 Pros in them. I'm doing the crossover (80Hz, and low cut at 25Hz) in my X32's matrix section and the limiter in the nu3000 (since I have the DSP version).
25 is WAY too low - it should be about 35-40. But they're yours so "smoke 'em if you got 'em" LOL. The xlim on those is only 18mm so I'd raise the HPF even further if you're going past RMS on them...
 

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

25 is WAY too low - it should be about 35-40. But they're yours so "smoke 'em if you got 'em" LOL. The xlim on those is only 18mm so I'd raise the HPF even further if you're going past RMS on them...
Thanks for the input. And new term. Now I need to go research xlim.'s relationship to the HPF. Is that a straight up wavelength thing? (I love the math side of this stuff.)
 

Ron Kimball

Senior
Mar 5, 2011
581
0
16
NE CT
Re: iNuke nu3000DSP outputs when in bridged mode

Xlim is how far the voicecoil can move before bottoming out and smashing the heck out of it (or in some cases just how far before suspension/cone damage occurs). And (very roughly) halving the frequency doubles the motion at a given power level. And if the cab isn't tuned to the particular driver all hell can break loose at it's Fs (AKA resonance frequency which is 28Hz on those drivers).

[video=youtube;j-zczJXSxnw]https://www.youtube.com/watch?v=j-zczJXSxnw[/video]
 
Last edited:

Mitch Miller

Sophomore
Oct 30, 2012
121
1
16
Re: iNuke nu3000DSP outputs when in bridged mode

Xlim is how far the voicecoil can move before bottoming out and smashing the heck out of it (or in some cases just how far before suspension/cone damage occurs).
That's pretty much what I expected.

And (very roughly) halving the frequency doubles the motion at a given power level.
This I didn't know. Thanks.

And if the cab isn't tuned to the particular driver all hell can break loose at it's Fs (AKA resonance frequency which is 28Hz on those drivers).

Didn't know it was 28Hz on those boys (thanks for that). Saw that spec. on some others (while trying to find specs. on the Sigma 18 Pros), but didn't make the correlation to why that's important. but that totally makes sense. And here I was just trying to prevent low-end sub-sonic rumble from overheating the voicecoils.

Incidentally, that's the second time today I saw video of that bridge -- someone is trying to crowd-fund a propless wind powered electric generator and used the same event as part of their promo piece.

Much appreciated.

So, since the amp has the DSP, and it's not as easy to accidentally change, and that amp will be sticking with these subs for a while, I think I'll move the HPF over to the amp instead of the board. Kinda less chance of accidentally changing (or removing altogether).

Still a little uncertain where'd be a good level for the power limiter. I currently have it set to 1200 watts (as I understand, it has only a peak limiter), which is likely a little hot for those drivers. And I suppose, if I bring it down to under 880 (2x440), then I might as well unbridge the thing and not have to worry about special cables, etc. (since each side can deliver 440 watts max into 8 ohms).
 

Ron Kimball

Senior
Mar 5, 2011
581
0
16
NE CT
Re: iNuke nu3000DSP outputs when in bridged mode

From German magazine tests of the NU3000:

Peak power 20ms/1000Hz
8 Ohm 2x465
4 Ohm 2x870
2 Ohm 2x1700

RMS (sine wave)
8 Ohm 2x312
4 Ohm 2x600 (2x375 after 3 seconds)
2 Ohm 2x1176 (2x750 after 1 second, protect after 5 seconds)

So - bridged into two 8 ohm cabs the real spec is:
1176wrms each (limited to 750wrms each after 1 second, protect after 5 seconds)
which is why I'm not particularly concerned with the amp frying my 700wrms rated TH-Mini's. I've never had it go into protect or even limit back AFAIK. As I implied the biggest concern is overexcursion and a HPF set properly (and not overridden by bass boost in the EQ's) will protect against that. If bridging in your case I'd set the HPF to 40 as steep as possible (24db/oct?) and limit at 800w. I'd then not push it past 3-6dB of limiting.

In the past I've run PV118's (300wrms drivers) on an unbridged RMX2450 (500w/driver) into 3-6dB of limiting no prob. Same voicecoil diameter as the Sigma's - not sure I really believe their 650w rating - YMMV ;) .
 
Last edited: