[S. Stogel]

I've got a DIY (that I didn't do-it-myself) sub.  It's a Tempest driver in a 270L ported box (two 4" flared ports tuned somewhere in the neighborhood of 16-18Hz).  Well, that's neither here nor there, so on with the question.

I currently have a 150w amp pushing the Tempest (quite well, I might add), but I'd like a little extra oomph and a little more headroom.  I've considered the PE 272w plate amp for $120, but the Tempest can handle quite a bit more.  I'd like around 500+ watts, and here are the two amps I've been considering.

1)  QSC RMX850.  It puts out something like 830w when bridged into four ohms.  I can get it for right around $300 shipped, but there are fan noise issues with this amp.

2) Crown XLS202.  Puts out 500w when bridged into four ohms.  Can be purchased for just shy of $250 shipped.  I have no idea if this one has any fan noise issues.

3) nOrh's Le Amp II.  400w into four ohms.  $300 shipped (I believe).

To me, the clear leader of the bunch is probably the Crown on a price/performance basis.  The extra 300w of the QSC will only yield a couple dB bump, and that will be when the Tempest is most "stressed" anyway.  I'm only curious about the nOrh because I like the looks quite a bit, and it's monoblock, so I won't be bridging a stereo amp (not that that necessarily matters).  But being as it's just a sub amp I'm looking for, would I be just wasting $50 (and losing 1dB in the process)?  Or is it possible that even subs could benefit from (admittedly unfounded at this point) a higher quality amp?

Mark (the sub's creator) said that he used the PE plate amp and it was very good, but that he thought the sound noticeably improved when he stepped up to an Adcom GFA 555II.  Similar power (I don't think he bridged it), but he liked the sound better with the Adcom.

Now, as far as Crown vs. QSC vs. nOrh, that's kind of where my curiousity lies.  Any help would be appreciated, and sorry for my rambling post.

BTW, I bought marble 4.0s for my fronts and 4.1s for my R&L surround from a guy on this forum (thanks again GCS), and I've been very pleased with the quality/sound of these speakers.  Huge step-up from what I had, but what I had was pretty weak.  I do hear things in movies that I seem to have missed with my other speakers.  Okay, okay, I'll shut up now.

Steve

[Rob Babcock]

Well, are you in a hurry?   Some of us have been waiting for our LA II's since May or so, and I'm not sure if we're any closer than we were back then.

One advantage of the Crown or QSC over the nOhr (for a sub) is the inclusion of a volume control.  That alone would probably do it for me.  However, if you were using an external X-over w/a volume knob (eg an Outlaw ICBM) it wouldn't matter; in fact cascading volume controls probably wouldn't help any.  The Crown has a great warranty.  If you're looking at Parts Express for your Crown, you've probably noticed the free shipping offer on that amp.

[rkapadia@ROOP]

Steve,

If you haven't already, I'd suggest looking beyond just the watt rating of the amplifier.  I'm in complete agreement that a high watt amplifier is necessary for a Tempest application, but you might also want to consider the specification of "damping factor" when looking for a proper amplifier.

Damping factor can loosely be defined as an amplfiier's ability to control the woofer, and an amplifier with a high damping factor will add quite a bit of tightness and musical satisfaction to a subwoofer.  I'd suggest not to have a damping factor below 200 when measured at near full output and at the nominal impedence of your subwoofer.

Kind Regards,

Rup

[James Tg]

Steve,

If you haven't already, I'd suggest looking beyond just the watt rating of the amplifier.  I'm in complete agreement that a high watt amplifier is necessary for a Tempest application, but you might also want to consider the specification of "damping factor" when looking for a proper amplifier.

Damping factor can loosely be defined as an amplfiier's ability to control the woofer, and an amplifier with a high damping factor will add quite a bit of tightness and musical satisfaction to a subwoofer ...

rkapadia, Mike posted the specs of LA II at another thread.  The damping factor is "Greater Than 100."  Comparing to other amps, damping factor 100 is not impressive to me.  Actually it is kind of low.  It brings my concerns if the LA II is suitable for subwoofer use because I am going to use it to drive HSU TN1220 subwoofer.   What is your opinion on this matters?  I appreciate your comments.

Mike, can you also offer your comments?  Thanks.

James

[Rob Babcock]

I've used several different amps to drive my TN 1220's, and while they do appreciate a lot of power, they don't really seem that difficult to drive.  The Carver amp I used to use to drive them for a while didn't have a terribly high damping factor yet worked magnificently.  I'm guessing the LA II won't have any problem, either.  Again, the lack of a volume knob to trim the level could be an issue, depending on your setup.

I agree, though, that you don't want an amp that's too "loose" in the bottom end.  And certainly make sure any amp you use to drive them can sustain a high power output at low impedance for long periods of time.  Especially for HT; a flick like LotR will warm you sub amp up pretty well.

[andrewbee]

This "figure" is caluclated by dividing the load on an amplifier by the amps output impedence. So if you have a 8 ohm speaker and the amps output impedence is 0.1ohms it would be 8 /0.1 which is 80.
The thing is speakers are not purely resistive loads but rather they rise and fall at different frequencies so while your speaker may nominally be a 8 ohm speaker it could go from 2 ohms to over 50 ohms depending on frequency. I would not buy an amp based on its damping factor, it is  essentially meaningless in the real world, simply because you have no idea what figure you would have with your speakers at what frequency
These things are just numbers that manufacturers throw out to try to impress the unaware. More important would be output impedence but rarely do you see this spec mentioned.
I see no reason why the LEAmp 2 would not be able to drive your sub if you can get one
In any case if all you want is to drive a sub then why not buy a plate amp? I have one with a damping factor of >1000 according to the manufacturers literature if I remember correctly

[James Tg]

I've used several different amps to drive my TN 1220's, and while they do appreciate a lot of power, they don't really seem that difficult to drive.  The Carver amp I used to use to drive them for a while didn't have a terribly high damping factor yet worked magnificently.  I'm guessing the LA II won't have any problem, either.  Again, the lack of a volume knob to trim the level could be an issue, depending on your setup.

I agree, though, that you don't want an amp that's too "loose" in the bottom end.   ...

I have a 150W amp from HSU to drive TN1220 but I find the amp can not drive the bottom end frequency very well.  TN1220 can take 250W.  So, I would like to try LA II.  I do not need a volume knob because I have a parametric EQ.  Also, I can control volume from my pre/pro.  Your advise is appreciated.

James

[S. Stogel]

Thanks for the input, guys.  I do like the looks of the nOrh, but I'll probably go with a Crown XLS202 for $240-$250 and save myself $50 (and get an extra 100w to boot).  I just was curious if anyone thought the sub would have a better sound with a LEII as opposed to a bottom-of-the-line Crown or QSC.  Of course, if I want to spend $300, the QSC will give me 830 watts  .

James, I believe those Hsu's need quite a bit of EQ down low to stay flat, so even though it's the Hsu amp, it still needs 3 or 6 (can't remember whic) dB of boost down low to stay linear.  Pretty sure it's 6dB, so down low (way low), that 150w will act more like a 37.5w amp.  At least I think that's how it works with the 6dB of bass boost.

Again, thanks all for your input.  As I'll be waiting for a while before I buy, I can wait and see what kind of reviews the LEII gets and (if they're not steller) perhaps pick up a used one for $200ish anyway.  After all, it's just a sub .

Steve

[Andrikos]

I would think that a 6dB boost "down low" (I'm assuming low 20's of Hz) would actually need QUADRUPLE the power (600W)... Am I missing something here?

[S. Stogel]

That's the point.  The way I think it works, Hsu's 150w amp has the EQ boost in there.  So, in theory, a 60Hz signal to the sub could get a full 150w, but a 20Hz signal would need 600w to stay linear.  So, if you're really cranking it, the 50-60Hz stuff might be gettting a full 150w, but the 20Hz stuff will sound 6dB down.  So when the amp is pushed to around 40w, it's all good and linear, but after that, the low stuff is going to start to roll off because of the 6dB boost.  I've explained myself poorly (it was that dang 37.5w statement), but I think it's correct to say that you'd need 600w at 20Hz to stay linear with a 60Hz signal and 150w into the Hsu tubes.  I'm probably not making any sense, so someone please chime in and explain what I'm babbling about.

Steve

[NealH]

Probably a good move going with the Crown.   I would not recommend the LeNorh for two reasons, one is that you are not going to get it anytime soon, and secondly, the transformer has been replaced with a smaller continuous VA rating to bring the cost down.  A subwoofer needs a strong continuously rated amplifier which requires robust output devices, storage capacitors and supply transformer.  The peak figures don't hold up under a lot of strain.

[rkapadia@ROOP]

The thing is speakers are not purely resistive loads but rather they rise and fall at different frequencies so while your speaker may nominally be a 8 ohm speaker it could go from 2 ohms to over 50 ohms depending on frequency. I would not buy an amp based on its damping factor, it is  essentially meaningless in ...

Given the context of the application and original question; being a Tempest subwoofer, we know the nominal impedance of the speaker within the range of 20Hz to 60Hz, as Adire does disclose the nominal impedance graph if I'm not mistaken.

For example, if a damping factor of an amplifier is published to be >200 measured at full power, @50Hz into a 4 ohm load, then we can correlate this to the impedance curve of the Tempest.  

While I agree that most speaker amplifiers should not be purchased solely on damping factor, subwoofers are a specialty application in which woofer control does have relation to bass quality, and the frequency range is very limited.   I also agree with you that if the damping factor is published without the measured frequency and impedance specification, then it's not very useful.

Kind Regards,

Rup

[andrewbee]

I hear you Rup,

let me ask you this.

You have three amplifiers with identical specifications for this application with the exception of the damping factors, one is >100, another >200 and the other >1000.
In your experience, do you think that you would actually be able to hear the difference between them ?

Thanks,

Andrew

[Marbles]

Let me try to anwser it this way....I have the nOrh mark II subs with 8" vifa drivers.  They sound woolly..you know fuzzy and not clear.  I also have some 12" SVS Ultra's driven by a Crown K2.  These are very clean woofers.

I would bet I could make the 8" drivers in the nOrh subs sound very clean too if I used the Crown on them.  The K2 has some amazing dampening facter..something like >2000.

I think you could probably tell the difference between the amps with how clean the sound is.

BTW, I only use my nOrh subs as stands for my 9.0's.