Amplifier freq response specs question...

madmatt

Okay, I need a little primer here. I've been looking at specs for various receivers/amps and it occurred to me that I don't understand something that I think should be quite fundamental.

For example, here are some specs for an old Kenwood stereo receiver (make and model don't really matter for this discussion, I think):

Power output: 80 watts per channel into 8Ω (stereo)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.02%

So, let's say I'm running this amp to watch a movie with significant sound effects dipping below 20 Hz (whether or not I have speakers/subwoofer that can reproduce it or not). Here's my question, will this amp be able to produce those sub 20 Hz signals to send to the drivers? If so, which is my guess, is that the distortion levels increase? I have seen older vintage receivers that claim 5-20,000 Hz freq response.

Thanks in advance for any insight.

FestYboy

I have yet to see an amp that can't dip into the single digits. The specs you see are a little suspect without a +/- dB spec, but still, there's no reason any amp can't get lower than 20, though they might not have the amperage capacity to get a speaker to do any real work down that low. Also, as power requirements go up, so does THD. So in your example, at 80w, the THD is 0.02%, but at say, 110w it might be at 0.15%, and snowball from there. The Kenwood may be good for 200w peaks @ 1%, but that doesn't look good for HiFi.

daddyjt

Those specs are fine, and that amp will easily produce sound below 20hz, and I would suspect at reasonable distortion levels.

Specs are just a marketing game. For example, an amp may have ALL of the following real world performance numbers:

50wpc, 5hz-25khz, .005% thd
100wpc, 20hz-20khz, .05% thd
200wpc, 20hz-20khz, .1% thd
450wpc, 1khz, 1% thd

Now the question the marketing department has to decide is, “who are we marketing this amp to”?

An audiophile will be most interested in the first set of specs, a home theater buff the second or third, and bubba will like the fourth.

It’s easy to get caught up in the numbers in this hobby - don’t forget to enjoy the sound

madmatt

Thanks for the replys. I don't have that Kenwood nor plan on getting it. This has been more of a theoretical muse. From the pure electrical engineering perspective of your average audiophile amp (however you define that), what is the limiting factor to providing the "oomph" to push a driver in that deep freq range (that FestYboy referred to)? What does a high power amp with lots of overhead have that a low end "wimpy" amp doesn't?

Which leads to ask , if shopping for an amp and maybe more specifically a sub-amp, what numbers ARE important?

Perhaps I'm overthinking this, which is entirely possible. My father is an engineer, so his engineer brain rubbed off on me. We like to understand how things work.

afterburnt

Better to be rubbed off than rubbed out is what always say.

FestYboy

Capacitance and peak short term current capacity <100ms with a good damping factor is what you want for any good amp, but especially for one dedicated to a sub. Also it's ideal that the amp is stable to 4 ohms or LOWER. You'll note that most big boy amps are good for at least 35A and 4ohm stable.

madmatt

Well, me and my Carver M1.5T should be okay on that front.

daddyjt

madmatt wrote: »

...what is the limiting factor to providing the "oomph" to push a driver in that deep freq range (that FestYboy referred to)? What does a high power amp with lots of overhead have that a low end "wimpy" amp doesn't?....

That's a very complicated question, and involves more than just your amp selection. What your amp will do (or NOT do) is as much a factor of the speaker its driving, as it is of the amp itself.

Your 1.5t is a great voltage source amp (as are most Carver amps). It will perform admirably into 8 or 4 ohm loads, but will protest going below 4ohms consistently. It also has a very spartan (read "not warm") sound signature. Not an ideal pairing for Klipsch:-)

Current source amps tend to have LARGE transformers, and A LOT of filter capacitance (>40,000uf). 2 ohm stability (and by that I mean ALL DAY stability) is a prerequisite to any amplifier considering itself a current source.

pitdogg2

some lite reading. Marketing will determine how they rate many things in audio. back in the 70's they played fast and loose in the ratings.

http://soundandsong.com/Issue004/004_PowerAmpRatings.html



https://en.wikipedia.org/wiki/Audio_power

pkquat

madmatt wrote: »

what is the limiting factor to providing the "oomph" to push a driver in that deep freq range (that FestYboy referred to)? What does a high power amp with lots of overhead have that a low end "wimpy" amp doesn't?

Which leads to ask , if shopping for an amp and maybe more specifically a sub-amp, what numbers ARE important?

daddyjt wrote: »

That's a very complicated question, and involves more than just your amp selection. What your amp will do (or NOT do) is as much a factor of the speaker its driving, as it is of the amp itself.

Your 1.5t is a great voltage source amp (as are most Carver amps). It will perform admirably into 8 or 4 ohm loads, but will protest going below 4ohms consistently. It also has a very spartan (read "not warm") sound signature. Not an ideal pairing for Klipsch:-)

Current source amps tend to have LARGE transformers, and A LOT of filter capacitance (>40,000uf). 2 ohm stability (and by that I mean ALL DAY stability) is a prerequisite to any amplifier considering itself a current source.

The speakers impedance curve also plays a part. The impedance of an "8 ohm" speaker can vary greatly depending on the frequency. Some speakers don't vary much, and others can dip heavily into the 2 ohm and/or 16 ohm range, or extend beyond 32 ohm.

For sub woofer amps, thoughts vary. Many are going to a Class-D SS amp. They provide lots of economical power. Their main issue is inconsistencies as it switches from positive to negative. This is much less noticeable at lower frequencies, and not considered that big of an issue for sub woofers (generally speaking).