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Topic: Knowing when an amp isn't providing enough power (Read 10566 times) previous topic - next topic
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Knowing when an amp isn't providing enough power

I recently posted about matching an amp with some B&W Nautilus 804s (rated at 8 Ohms, but with min impedance 3 Ohms), and ended up getting a Denon AVR-X3200W (105 WPC at 8 Ohms; 135 WPC at 6 Ohms, 2 ch driven). The speakers feel a little light on low frequencies to me - for example, the deep bass that kicks in around 0:47 in this track is barely audible:
https://www.youtube.com/watch?v=qSXzMrcpAks

How likely is it that the amp is struggling to power the speakers? I can dial up the graphic EQ settings and get more than enough bass, but the manual also says that the speakers should ideally be paired with an amp that provides twice the wattage at 4 Ohms than at 8 Ohms, which I'm not sure this one does.

Does it sound like this speaker/amp combination is OK? Apologies if this is a noob question, but would appreciate your help!

Re: Knowing when an amp isn't providing enough power

Reply #1 –
If the amp isn't distorting, it's probably not an issue.

Consider acquiring a measurement mic + software so you can see what's happening to the frequency response of those speakers in your room: It's a lot cheaper than buying a new amp, and more effective too.

Re: Knowing when an amp isn't providing enough power

Reply #2 –
At normal listening levels an amp is supplying a tiny fraction of its full power, so unless your neighbors were calling the cops, the amplifier was not limiting the bass.

Re: Knowing when an amp isn't providing enough power

Reply #3 –
Quote from: sirdavidoff on
I can dial up the graphic EQ settings and get more than enough bass
Here is your first clue that your amp is absolutely, positively, not the problem.

Re: Knowing when an amp isn't providing enough power

Reply #4 –
Wow, those speakers better come with marital favors at that price. I would venture to suggest you've spent a lot of money on mediocre speakers. Looking at the specs I walk away underwhelmed. Oooh, a kevlar speaker cone. I have a professional bass cab with 8 of those and that cab brand new cost one quarter what those do.

Does the amp sound fine with another reasonable pair of speakers? I seriously doubt this is a power issue unless the power amp is faulty and, as Greynol suggested, if you can EQ it to sound OK then it's not the power amp.  Either there is a problem in the preamp or DSP section (config?) of the AVR, the speakers aren't very well designed, or it's the room acoustics.

Re: Knowing when an amp isn't providing enough power

Reply #6 –
I'm going to guess you, OP:
A) Don't use a sub and
B) are using the receiver in Pure Direct mode.  [no Audyssey].

"Because my big speakers don't need those things."

Both of these, A and B, are mistakes. Also when you do get a sub you are probably going to be inclined to set the output for the front speakers to "large" instead of "small". That's also a mistake, however a very understandable one. This very poor wording the receiver uses really should be "Do you want to use bass management so I can redirect the low bass to your sub(s), optimally placed for bass response rather than simply soundstage direction , using a dedicated channel I focus 8X the resources towards to adjust?"

Re: Knowing when an amp isn't providing enough power

Reply #7 –
Note the woofers in these"big speakers" are 165mm, roughly 6.5 inches.

Re: Knowing when an amp isn't providing enough power

Reply #8 –
Quote from: sirdavidoff on
The speakers feel a little light on low frequencies to me - for example, the deep bass that kicks in around 0:47 in this track is barely audible:
What other amp did you use, where the same speakers, in the same position, in the same room, at equal volume, didn't sound a little light on that track?
Loudspeaker manufacturer

Re: Knowing when an amp isn't providing enough power

Reply #9 –
OK guys, thanks for assuaging my paranoia. I did warn you it was a noob question, after all :)

Re: Knowing when an amp isn't providing enough power

Reply #10 –
BTW, I played that clip last night at a reasonable volume on a 90W per channel AVR in direct mode driving a pair of $150 KLH 3 way floor speakers (12", 4" and tweeter). It made the walls rattle.

Re: Knowing when an amp isn't providing enough power

Reply #11 –
Quote from: yourlord on
12"
...and the room can make all the difference for a track that has deep bass and essentially zero mid bass.  That track has very silly instrumentation (if you can call it that) and mixing, IMO.  You can sub the word gimmicky if you find silly too offensive.

Fear over wattage, blind reverence to "upper-mid-tier" models, and/or non-elite name brands aren't going to help matters.  The same might be said regarding fear over minimum impedance requirements (the speaker drops below 4 ohms, OMG!), depending on the usage. Too much money was likely spent on this system as it is.

Sorry to pile on, I'm just annoyed that the OP didn't get (or heed) rational advice before spending his money.

Thankfully no one is blaming youtube compression for the apparent lack of bass. ;)

Re: Knowing when an amp isn't providing enough power

Reply #12 –
Before you 'piled on', greynol, you might have asked yourself how much I paid for those speakers, and indeed whether I paid anything at all.

As for getting (or heeding) advice, that's exactly what I'm trying to do by posting on this forum.

The questions may be naive, and I don't mind being reminded of my ignorance in a constructive way. But I'm not sure what I've done to warrant ad hominem references to 'blind reverence', 'gimmicky songs', 'OMG', etc.

I sincerely hope you don't treat people like that outside of Internet forums.

Re: Knowing when an amp isn't providing enough power

Reply #13 –
I have been so negatively seasoned by fear based threads, that have undoubtedly been fueled by $$$-driven placebo-based nonsense that I've grown completely calloused to the whole thing.

AFAIC, save for a tiny and perpetually dwindling fraction, the audiophile community is a complete joke.

I'm far more annoyed at what I imagine led you to this point than I am at your initial question, I assure you.

Re: Knowing when an amp isn't providing enough power

Reply #14 –
To put it another way, you can have all the current in the world, but without voltage you have no watts.

Low impedance speakers and headphones lean toward needing more current, while high impedance speakers and headphones lean toward needing more voltage. It's a matter of matching the characteristics of the amplifier to the characteristics of the speaker/headphone, i.e. matching their impedances for greatest efficiency.

Re: Knowing when an amp isn't providing enough power

Reply #15 –
Most people don't know how much wattage they even need. Some erroneously assume more than they need will always be better.

Re: Knowing when an amp isn't providing enough power

Reply #16 –
Although they weren't terribly accurate, there was a time in audio when power output meters were so common in stereo receivers that some brands even had them on their entry level units. As I understand it, this photo shows how Pioneer's SX line-up, c. 1979,  had them on every single model, at least in this pic, even the baby!

I suspect the manufacturers at one point realized keeping people in the dark was to their advantage and that marketing inconsequential power gains, like 100 w/ch vs. 120  w/ch was the better way to go, hence power meters pretty much disappeared from the scene.

New topic. Since it seems built-in to the new forum's software, and I use this exact method to post images in other forums without any objection, I assume it is O.K.. If not, I'll be glad to modify the post.

Re: Knowing when an amp isn't providing enough power

Reply #17 –
One of these replaced our RCA console in the late-'70s:

The two lights are for power and fm stereo reception the analog needles are for signal strength and fine tuning stations.  There is no indicator for clipping.

Re: Knowing when an amp isn't providing enough power

Reply #18 –
Amp clipping is quite audible. It will plainly sound like crap : distortion, loss of dynamics. Also, if you're daft enough to keep turning the volume up, you'll notice the volume isn't getting any louder.
If you ever turn the volume up enough to encounter clipping, you've got to turn it down fast as the amp will start outputting signals closer to a square wave than a sin wave (ie : music), and that can severely damage your speakers, beginning by your tweeters. But you'd have to turn up the volume pretty high to be able to hear that on most decent quality regular consumer amps, frankly. I would probably flee the room before reaching that point.
If it's not broken, don't fix it.
 

Re: Knowing when an amp isn't providing enough power

Reply #20 –
Maybe others could hear the same song that you've linked to. Have you tried it on another setup?
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Re: Knowing when an amp isn't providing enough power

Reply #21 –
If you have access to a good AC volt meter then you can measure either the average or the RMS voltage out of the amplifier during the loudest parts of a song. Divide the square of this voltage by the impedance of your speakers to get a value in watts. If this value is more than one sixth of the rated output power of your amplifier then you are probably clipping.

Re: Knowing when an amp isn't providing enough power

Reply #22 –
Quote from: pdq on
If you have access to a good AC volt meter then you can measure either the average or the RMS voltage out of the amplifier during the loudest parts of a song. Divide the square of this voltage by the impedance of your speakers to get a value in watts. If this value is more than one sixth of the rated output power of your amplifier then you are probably clipping.

why one sixth?

Re: Knowing when an amp isn't providing enough power

Reply #23 –
Six to one is the typical crest factor for audio.

Re: Knowing when an amp isn't providing enough power

Reply #24 –
oh right, i seem to forget we're in AC world here  :D