Amplifier Question

[ChazHS]

Hi guys,

 

I've got a couple of questions which I'd like to ask the people who are a little more knowledeable than myself. :)

 

Firstly, this is a question about powering a subwoofer, specificially a Nexo LS-600 sub with it's appropriate controller.

 

I'm using Crown Macrotech-I series amps, specifically the 5000i. This will output 1250W into 8R, 2500w into 4R, and about 4000W into 2R in stereo mode. It will also output 5000W into 8R bridged, which is all we need to know for this.

 

Nexo say that the reccomended amp power to use for the LS-600 is 1000-2000W into 8R. Not 4R like they specify for their smaller LS-400 sub.

 

My question is this, I want to get the maximum power out of these subs without cooking them. I know the controller should protect the subs, but is it really going to be ok with me putting 5kW through each one? Will it be able to effectively limit this much power to the 2kW it wants? I know that this isnt the best use of these Macrotechs as I'm effectively wasting 3kW on each one (gives headroom for transients I guess? ;)) but I have 3 of them so I'm not too worried about that.

 

Thanks in advance.

[arobinsonaudio]

Whilst Nexo are very good subs and the Macrotech amps are awesome as well I would personally not risk pushing an extra 3kW of power in to them. I would say either buy the LS-600 like they recommend or just run it on a single channel and give them the 1250W.

[Cupboard]

Either run them in single channel or just turn the amps down when bridged?

 

They've got built in doodahs for doing exactly what you want:

http://www.crownaudio.com/pdf/amps/137327.pdf

See section 3:

 

"The Average Power Limiter allows you to regulate the long term output of the amplifier by setting an average power limit that corresponds with the speaker’s long-term power rating. All three limiters can be accessed from the front panel display as shown in Figure 3.2, and from IQwic software."

 

edit: arobinsonaudio: The LS-600 isn't an amplifier :)

[arobinsonaudio]

Cupboard. Yeah I realised this about an hour ago when I woke up properly. :)

[Simon Lewis]

Power wise, 5kW is only ~4dB more than 2kW, so if used judiciously you can have the extra headroom and transient response without damaging the loudspeakers. Of course, if clipped or used at full power with heavily compressed or small peak to mean ratio material, there's a chance that even the protection mechanism may not save them. Most amp manufacturers rate their bridge mode power figures at a higher %THD. Crown's spec sheet suggests 8R bridged might be 4kW at 1kHz, with THD at 0.35%.

[ChazHS]

They've got built in doodahs for doing exactly what you want:

http://www.crownaudio.com/pdf/amps/137327.pdf

See section 3:

 

That's for an iTech I'm afraid, these are MacroTech-I series amplifiers which have no limiting features built in. Hence I'm concerned the amp may be allowed to simply run away and put a full 5kW into a sub.

[Matt Riley]

With the Nexo kit you don't really want to be adding other limiters after the NX/ PS(X)TD processor, as it can really confuse the sense circuitry.

 

In reply to the OP, I would say you've got clever nexo controllers to stop the speakers from getting fried, as long as the sense lines as wired right, and so I would just go with it with the assurance you're very unlikely to fry anything. That said, I'm not convinced that you're going to get the kind of improvement you are anticipating - I used to use an LS 1200 / PS15 rig and even that wasn't particularly pokey on the subs, and you would probably only get the kind of benefit you're anticipating if you either got another sub, or selling the LS600 and getting something like the RS-15

 

Maybe it's just something about 90s french sub designs? *ahem* SB218...

[ChazHS]

In reply to the OP, I would say you've got clever nexo controllers to stop the speakers from getting fried, as long as the sense lines as wired right, and so I would just go with it with the assurance you're very unlikely to fry anything. That said, I'm not convinced that you're going to get the kind of improvement you are anticipating - I used to use an LS 1200 / PS15 rig and even that wasn't particularly pokey on the subs, and you would probably only get the kind of benefit you're anticipating if you either got another sub, or selling the LS600 and getting something like the RS-15

 

Firstly thanks for your input. I've come to the conclusion I'm probably best bridging 1 MacroTech 5000i and running both subs from it.

 

It does state 1000-2000W into 8R on the datasheet for the LS-600. So that says to me it's a 8 ohm woofer inside each one? Therfore it would be 4kW (I dont know why the Macrotech is 4kW into 4 ohm and 5kW into 8 ohm when bridged?) so thats perfect for the 1000-2000W it asks for. :)

 

Oh and on a side note the LS-600 is quoted as having a max dB of 138, whereas the old LS-1200 is quoted as only having a max dB of 135. :)

[jamesperrett]

It does state 1000-2000W into 8R on the datasheet for the LS-600. So that says to me it's a 8 ohm woofer inside each one? Therfore it would be 4kW (I dont know why the Macrotech is 4kW into 4 ohm and 5kW into 8 ohm when bridged?) so thats perfect for the 1000-2000W it asks for. :)

 

 

If I understand this correctly you've got 4kW into 2 ohms when the channels are driven separately. In bridged mode I would expect 8kW into 4 ohms given that 2 ohm spec for the individual channels.

 

James.

[ChazHS]

It does state 1000-2000W into 8R on the datasheet for the LS-600. So that says to me it's a 8 ohm woofer inside each one? Therfore it would be 4kW (I dont know why the Macrotech is 4kW into 4 ohm and 5kW into 8 ohm when bridged?) so thats perfect for the 1000-2000W it asks for. :)

 

 

If I understand this correctly you've got 4kW into 2 ohms when the channels are driven separately. In bridged mode I would expect 8kW into 4 ohms given that 2 ohm spec for the individual channels.

 

James.

 

Yes thats the norm, but if you look at the datasheet thats what it says!

[jamesperrett]

Ah - I've had a look at the Crown website and it looks like there's some kind of current limiting going on when working at 2 ohms. While the 4kW into 4 ohms bridged looks to be a perfect match to your subs, I'd be a little worried that the current limiting might be doing strange things to the sound.

 

James.

[ChazHS]

Ah - I've had a look at the Crown website and it looks like there's some kind of current limiting going on when working at 2 ohms. While the 4kW into 4 ohms bridged looks to be a perfect match to your subs, I'd be a little worried that the current limiting might be doing strange things to the sound.

 

James.

 

Well hopefully the Nexo controller would be limiting before too much of that happened. I can't imagine a single 15" sub can handle a full 2kW for a sustained period of time. Not to mention it is a Crown amplifier, and they do kind of have a rough idea of what they are doing. ;)

[dbuckley]

... I'd be a little worried that the current limiting might be doing strange things to the sound.

There was a big discussion on the BR about this a while back. The manufacturer said current limiting wasn't an issue with normal programme material. However, I fail to see how it couldn't be an issue with certain types of music which effectively test the sine wave handling of your bottom end.