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Which Amp for 8 Ohm, 1000 watt RMS 18" Sub

#21
Zooberwerx said:
Yes, the clip limiter is designed to attenuate and illuminate below a given threshold...that's protection, do not defeat. You may also want to consider inserting a compressor / limiter in the kick drum channel to handle the transient spike you referenced. I can see upgrading the power amp but doing so with the intent of adding a second 18" enclosure. I'm as frugal as the next guy but this would be money well-spent.

Still at work...

Riis
Click to expand...
I tried using defeating the limiter this afternoon. Of course, I wasn't trying to see if I could push it harder, but there was no difference.

Putting a compressor/limiter in the kick channel will only bring down the signal before the amp, which is like turning down the volume of the kick, which is the exact opposite of what I want to do.
 
#22
Zooberwerx said:
The 1400i has a high pass filter on the reverse. 12:00 = 35 hz. I'd recommend a bit higher @ ~50 hz. The manual has a rather convoluted (or so it seems at first) procedure for running subs exclusively but that ties in the use of the onboard crossover...or is it a low pass filter?...to process a full range signal.

To the OP: what are you using for a crossover, if anything?

Riis
Click to expand...
The Mackie 1400 does indeed have a subwoofer option, and while it might be good for smaller subs, I don't think it works as well for power hungry subs the likes of mine. For example:

In Subwoofer mode, the limiter is bypassed, and you are presented with two low-pass options, 125hz and 63hz. I have spoken to Mackie and they say this filter affects the input sensitivity. I believe them because I compared their internal filter against a passive 125hz low-pass filter at the speaker. When I set the Mackie filter to 125hz, and connect directly to the speaker, I get significantly less volume than when I run the Mackie in Full Range mode and place the 125hz passive low-pass filter inline to the speaker.

Now, the Mackie manual also advises that the variable low-cut filter you mentioned above be set to OFF, but that is mentioned in the manual in the Subwoofer mode section, so maybe they mean to do this when in Subwoofer mode.

I run 15" mains, and I prefer my low-pass be closer to 100hz. Because I saw a significant difference between Mackie's internal low-pass filter and the passive low-pass filter I put inline, I decided to forego Mackie's internal low-pass filter and inserted a Rane AC22B active crossover in the chain instead, which if I recall correctly, also has a 6db boost, so I can set the Mackie to Full Range mode, which as I mentioned above, outputs more power than Subwoofer mode (go figure).

BUT, now that you mentioned it, I think I still have the variable low-cut set at OFF (which I set when I used to run the amp in Subwoofer mode). If I recall correctly, the low end of the response range of the subwoofer is either 35hz or 45hz, so I should probably set the variable low-cut on the amp to match. Thanks for bringing that up. I've heard that some amp power gets wasted when you send frequencies too low to "heard" by a speaker, but could that really make that much of a difference? I guess I will find out tomorrow.

But, as you can see, I am doing all I can to milk as much out of this amp as possible, and while it is all well and good, I think at the end of the day I would be better off with so much headroom that little tweaks like this should only be of minor significance, wouldn't you agree?

BTW, have you run a kick drum through your XLS1500 at all, or do you just run bass guitar?
 
#23
MrLeadFoot said:
I tried using defeating the limiter this afternoon. Of course, I wasn't trying to see if I could push it harder, but there was no difference.

Putting a compressor/limiter in the kick channel will only bring down the signal before the amp, which is like turning down the volume of the kick, which is the exact opposite of what I want to do.
Click to expand...

In a sense, yes, but that's why compressors have post-compression gain controls. Once you've tamed the transient, you compensate by bringing the level back up to the original volume. A compressor dedicated to a single channel such as the kick drum can be quite effective when adjusted correctly. I run everything through the board and use a DriveRack set at 100 hz crossover. The 2500 runs the mains, the 1500 lights up the subs.

Dialing the HPF back up to 50 hz may you some addt'l relief. After glancing through the manual, I have to agree that your best bet is to run the 1400 in bridged mono fed w/ a <110 hz signal from your external crossover.

There's a whole science / practice behind percussion reinforcement....we're just skimming the surface.

Riis
 
#24
I tried turning the low-cut filter up to 35 hz. While the speaker spec says 45 hz, I feel less of the kick with the filter up that high, and experienced no appreciable difference in volume. But, then again, it's not easy to maintain perspective when I am sitting behind the drums when I step on the kick pedal, because I still get the ambient sound of the kick somewhat. I will try it again later this evening when the full band is coming to rehearse.

I will then try the compressor I already have. Not a great one, just a Nady, but it's just sitting unused in another rack.
 
#25
MrLeadFoot said:
I tried turning the low-cut filter up to 35 hz. While the speaker spec says 45 hz, I feel less of the kick with the filter up that high, and experienced no appreciable difference in volume. But, then again, it's not easy to maintain perspective when I am sitting behind the drums when I step on the kick pedal, because I still get the ambient sound of the kick somewhat. I will try it again later this evening when the full band is coming to rehearse.

I will then try the compressor I already have. Not a great one, just a Nady, but it's just sitting unused in another rack.
Click to expand...

Rolling off the <50 hz won't increase volume but, in theory, it should provide some addt'l headroom which can be applied elsewhere. We're looking for the "thonk" here, not the boom. I'm sitting here reading a Presonus EQ manual which address EQing the kick drum. In a nutshell: cut 80 hz and below (eliminates boom), cut 400 hz (muddy), boost somewhere between 60-125 hz (accentuates bottom end), boost 2-5 khz (sharpens attack). I'm not citing this as gospel but rather as one manufacturer's perspective. I've always heard that the "kick in the chest" resides ~80 hz; my ancient Aphex Aural whatever's "Big Bottom" is preset at 110 hz. A parametric EQ is great for this sort of thing: a boost and sweep will reveal the low-end sweet spot.

BTW, did you notice that the Presonus reference addresses 400hz and 2-5 khz, two frequency ranges that aren't even covered by the subwoofer?

One more thing: I just stumbled across this thread which pretty much parrots what I've mentioned re: EQing the kick drum.

http://www.talkbass.com/forum/f203/kick-drum-eq-972796/

Riis
 
#26
Just an update:

I happened across a used QSC PLX3402 in very nice condition at a Guitar Center near me for $400. Darned cheap, given the market value for these used seems to be $600-$700.

I am running the sub on one channel at 700 watts, and it is quite happy (as am I). In fact, I haven't even tried bridging it. I did, however, hook up my bass player's 4-Ohm sub to the same channel, and even with the mix-match of impedances with my 8-Ohm sub, the amp rocks. I tested both the single and dual setup outdoors, and either way you're thumped in the chest with the kick.

DMUSIC148: Interestingly, the manual says "When driving subwoofers, some users let the amplifier clip without limiting because it gives extra &#8220;punch&#8221; to kick drums and similar sounds".

Looks like you were right. I don't think QSC would even mention that in their manual if they thought it was dangerous for the kick to clip. In hindsight, I could've just kept running my Mackie in Bridge mode and let the kick clip it, but I am glad I got the QSC PLX 3402. Even though the Mackie ran 850watts bridged, it really seems like the QSC pushing only 700 watts to that sub gives a fatter sound. And, I have plenty of juice so I can still run 4 mains or monitors on the other channel!
 
#27
I wrote the manual.

The only reason to not use a clip limiter is if you actually want audible distortion when the amp clips. If you're using the amp and sub primarily for kick drum, that distortion might improve the kick's sound--maybe not. It's subjective.
 
#28
Hi Bob, and thanks for the clarification.

On another note, can the internal limiter even respond fast enough to a kick drum strike? In fact, I don't hear any distortion at all even when the clip light illuminates, with or without the limiter on. Does that mean that even though the clip light comes on that I may not necessarily be clipping, and/or that it's OK to run this way, as someone alluded to in an above post? FWIW, I run the kick, and toms to a lesser degree, to the amp and sub, as well as the bass guitar. Out of all of them, the kick drum level is much higher going to the amp, and the kick is the ONLY signal that is hot enough for the clip light to come on. In fact, the bass guitar and toms don't even come close.

Thanks again.
 

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