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Amplifier FAQ - Page 8

post #211 of 227

Hello Michael,

 

I must say this is one of the most refreshing insights I have seen in my 20 or so year on the web (ok, I am a newbie to this site, but was taught my audio background by few co-worker  experts at Bell Labs & HP)...

Your ability to explain the true basics of reality rings true to me. Oh, to have that skill. I ran  by operating with (in the past) having access to the best minds and technical environments that no consumer or (for profit company) could ever wish, and I did it purely as a plaything, as I had to also work to generate real products that turned a profit to the masses once I enter 'reality'. You nailed it on the head. Speaker design, acoustics, power, distortion... all the hype, are measureable, and designs can accommodate those willing to pay. I am not an old-and-moldy designer (40's ain't old), but the equipment we had access to, that no longer exists (practically), though digital equivalents rival it. Advances in R&D will never stop, as I know, and I will continue to be amazed (and want to compete with), but the basic laws of physics won't change anytime soon.

Thank you for such a post.

post #212 of 227
I'm looking for some advice/help. I just picked up some new speakers and they have a much lower sensitivity than my current speakers. I just received them tonight and didn't get a chance to fully set them up but I did plug in my center speaker to my receiver and what I noticed was I regularly watch TV at -40 but with the new speaker I had to turn it up to -30 and it still didn't seem as loud. What do I need to do to get the loudness back? Is that even possible? I am interested in buying a XPA-3 to cover the front stage.

New speakers 87 db NHT Classic 3's and ThreeC (center channel 200w and L/R 150w)

Old speakers 98 db (horn loaded)

My receiver is fairly decent, Denon 3313ci and it drives my old/current speakers with no problem. I'm getting rid of the horn loaded speakers because of ear fatigue. At first they sounded awesome but as time went on, it just got worse.
post #213 of 227
Quote:
Originally Posted by Randall.White View Post

I'm looking for some advice/help. I just picked up some new speakers and they have a much lower sensitivity than my current speakers. I just received them tonight and didn't get a chance to fully set them up but I did plug in my center speaker to my receiver and what I noticed was I regularly watch TV at -40 but with the new speaker I had to turn it up to -30 and it still didn't seem as loud. What do I need to do to get the loudness back? Is that even possible? I am interested in buying a XPA-3 to cover the front stage.

New speakers 87 db NHT Classic 3's and ThreeC (center channel 200w and L/R 150w)

Old speakers 98 db (horn loaded)

My receiver is fairly decent, Denon 3313ci and it drives my old/current speakers with no problem. I'm getting rid of the horn loaded speakers because of ear fatigue. At first they sounded awesome but as time went on, it just got worse.

start by re-running audyssey.
post #214 of 227
Quote:
Originally Posted by 67jason View Post

start by re-running audyssey.

I'll be doing that as soon as my speaker stands arrive. Thanks.
post #215 of 227
Quote:
Originally Posted by Randall.White View Post

Quote:
Originally Posted by 67jason View Post

start by re-running audyssey.

I'll be doing that as soon as my speaker stands arrive. Thanks.

Good. Report back when you do. you may find you have go further up the volume dial to achieve the same/similar loudness levels as you were accustomed to with your old speakers. there is a fairly large sensitivity gap between your old and new speakers. if you cant achieve the desired spl levels with you new speakers the additional amp power may be necessary. If you have no problems getting to your desired loudness then you have all the amp power you need in your denon.
post #216 of 227
Quote:
Originally Posted by 67jason View Post

Quote:
Originally Posted by Randall.White View Post

I'm looking for some advice/help. I just picked up some new speakers and they have a much lower sensitivity than my current speakers. I just received them tonight and didn't get a chance to fully set them up but I did plug in my center speaker to my receiver and what I noticed was I regularly watch TV at -40 but with the new speaker I had to turn it up to -30 and it still didn't seem as loud. What do I need to do to get the loudness back? Is that even possible? I am interested in buying a XPA-3 to cover the front stage.

New speakers 87 db NHT Classic 3's and ThreeC (center channel 200w and L/R 150w)

Old speakers 98 db (horn loaded)

My receiver is fairly decent, Denon 3313ci and it drives my old/current speakers with no problem. I'm getting rid of the horn loaded speakers because of ear fatigue. At first they sounded awesome but as time went on, it just got worse.

start by re-running audyssey.

Excellent advice.

What Audyssey will do is effectively do the same thing as re-adjusting the channel trims so that the AVR's volume control markings approximates either SPL or SPL with respect to 85 dB SPL after the big change in speaker efficiency.

Going from 98 dB/W speakers (way above average) to 87 dB/W speakers (just a tad below average) is really quite a jump - about 10 dB or the perception of "Twice as loud".

Randall, had you run Audyssey on your old speakers?
Edited by arnyk - 12/6/13 at 2:56am
post #217 of 227
Yes, I ran Audyssey with my old speakers. I just didn't do it with my new ones yet because the stands haven't arrived yet. Hoping they'll arrive today but doesn't look like it'll happen.
post #218 of 227
Thank you for the helpful write up. I am going to upgrade everything, and was thinking of buying the AVR I decide on, and dragging it to audition speakers. Now I don't think I will....

Also headed to CES shortly, and will see what I can accomplish there. If anyone has hints on that, please PM me as to not clog this thread. Or if there's a source here on CES, a pointer, please.

Again, Mike, many thanks!
post #219 of 227
Great post, MichaelJHuman! Thanks.

I've heard that for complex stimuli (such as music) the Just Noticeable Difference is about 1 dB, while for a simple stimulus, such as a sine wave, the JND is about 2 dB.

I've also heard that every doubling of distance produces a 6 dB drop in an anechoic chamber, or outside where there are no structures and the mic is elevated. In many rooms the drop with every doubling is more like 3 dB. Paul Klipsch placed a mic 2 feet from a speaker and measured the SPL (using a sweep, I think), then doubled the distance three times, and at 16 feet measured a signal that had dropped between 9 and 10 dB. The room was about 16 x 25 feet, if I remember, probably with an 8 foot ceiling.

Why do you think the Crown/Harmon calculator produces so much higher suggested amplifier power for a given SPL than other calculators? Even after eliminating their 3 dB amplifier head room dictum, I get wattage requirements that are about twice what some other calculators specify.
Edited by garygarrison - 1/3/14 at 6:53pm
post #220 of 227
Thread Starter 
Good point, garygarrison. I believe that's totally correct about the drop in dB in real rooms. If I ever work on this again, I will try to find a link to a calculator and post a range of dB values, rather than the drop under worst case conditions
post #221 of 227
You can try this calculator with room gain:

http://myhometheater.homestead.com/splcalculator.html

- Rich
post #222 of 227

I'm about to pick up an Adcom GFA-7700 used for $425. It's rated at 175wpc x 5. I have a Yamaha Aventage 1030 so I assume with all channels driven with my 5.1 setup would be in the 20WPC range. Is that accurate? The question with the Adcom is, Is 175wpc what I am really going to get or is it something else? Thanks

post #223 of 227
Quote:
Originally Posted by asharris7 View Post

I'm about to pick up an Adcom GFA-7700 used for $425. It's rated at 175wpc x 5. I have a Yamaha Aventage 1030 so I assume with all channels driven with my 5.1 setup would be in the 20WPC range. Is that accurate? The question with the Adcom is, Is 175wpc what I am really going to get or is it something else? Thanks

Look for (Google) reviews of both components by people who TEST them, like Home Theater Magazine. They will (probably) report their results for 2 channels operating AND 5 channels operating. Since the Adcom is a separate power amp, there is a good chance it will meet its specs. I believe Adcom claims that it was rated with all channels operating ... a good thing. I don't think I've ever seen an AVR meet its specs with 5 channels operating, although there may be some. Whoever regulates such things (FTA?) allows fudging in AVR advertisements, as well as with car stereo components. Hopefully the Adcom GFA-7700 not only meets its specs, but is rated in terms of RMS power.
Edited by garygarrison - 1/29/14 at 5:25pm
post #224 of 227
My inherent suspicion is that most modern amplifiers sound the same, similar, or at the very least none is definitely better than the other despite mild sonic differences. Certainly ABX testing I may very well fail.

I specifically have very high efficiency (>105db sensitivity) speakers which will reproduce ANY amplifier hiss or other artifacts while the system is idle or during quiet passages on vocal solos.

I am curious if the amplifier's signal to noise ratio measurements actually mean anything useful. I was looking up some crazy $50000 to $150000 amps and some of them have S/N at 1 watt of about 80-90db. Then other amps like the ATI 2000 series units have A-weighted signal-noise ratio of >123db.

The ATI amps don't describe a first watt signal to noise ratio... are they trying to hide something? Folks say great things about ATI amps and that the same guy designed the amps for Datasat. Also ATI makes amps for all sorts of manufacturers. I am wondering if these would be a great option for high efficiency speakers?

The signal to noise specs are useful in some way or they just more obfuscation? Is 80db s/n at 1 watt a great stat?

Someone look at the Pass Labs XA 30.5 stats and tell me what you think. Stereophile reviewed this amp as a good place to grab the measurements.
post #225 of 227
Quote:
Originally Posted by blazar View Post

I specifically have very high efficiency (>105db sensitivity) speakers which will reproduce ANY amplifier hiss or other artifacts while the system is idle or during quiet passages on vocal solos.

I am curious if the amplifier's signal to noise ratio measurements actually mean anything useful. .

An engineer once told me that a lot depends on the spectral characteristics of the noise. Two components can have identical S/N ratios, but one can sound like it has more hiss than the other, depending on whether there is a peak at a place in which the ear is more sensitive (naturally, hiss is pretty much in the most sensitive part of the spectrum, except for it's upper reaches; hum should be much less of a problem with a decent amp). So, S/N ratios can mean something, but not everything.

Hiss can surely be a problem with efficient speakers. My speakers are almost as efficient as yours (manufacturer claims 105 dB/1w/1M, but others have measured it as slightly less), and most of my problems have been with preamps, one of which hissed (as someone else said) like "a puff adder in heat," and most of the hiss could not be turned down by turning down the volume control. I have had a few power amps with inaudible hiss, unless one got within about 4 feet of the speaker.
post #226 of 227
Quote:
Originally Posted by blazar View Post

My inherent suspicion is that most modern amplifiers sound the same, similar, or at the very least none is definitely better than the other despite mild sonic differences. Certainly ABX testing I may very well fail.

I specifically have very high efficiency (>105db sensitivity) speakers which will reproduce ANY amplifier hiss or other artifacts while the system is idle or during quiet passages on vocal solos.

I am curious if the amplifier's signal to noise ratio measurements actually mean anything useful. I was looking up some crazy $50000 to $150000 amps and some of them have S/N at 1 watt of about 80-90db. Then other amps like the ATI 2000 series units have A-weighted signal-noise ratio of >123db.

The ATI amps don't describe a first watt signal to noise ratio... are they trying to hide something? Folks say great things about ATI amps and that the same guy designed the amps for Datasat. Also ATI makes amps for all sorts of manufacturers. I am wondering if these would be a great option for high efficiency speakers?

The signal to noise specs are useful in some way or they just more obfuscation? Is 80db s/n at 1 watt a great stat?

Someone look at the Pass Labs XA 30.5 stats and tell me what you think. Stereophile reviewed this amp as a good place to grab the measurements.

As has been already mentioned, the ear's sensitivity to noise depends on both its amplitude as indicated by SNR, and also spectral content which is suggested by the weighting technique used to measure the SNR.

The easiest way to obtain an amplifier with low absolute noise output is to get the power as low as you can.

Pass labs specifies output noise in microvolts which ignores the spectrum part of the equation:

https://passlabs.com/images/uploads/manual/xa.5_specs.pdf

BTW they spec the same noise output regardless of power from 30 watts to 200 watts, which seems strange to me. 200 uV is not IME an exceptional number. 200 uV is about 80 dB below 1 watt which while not exceptional is probably good enough unless you stick your head inside the speaker cone in a very quiet room.
post #227 of 227
Quote:
Originally Posted by arnyk View Post

As has been already mentioned, the ear's sensitivity to noise depends on both its amplitude as indicated by SNR, and also spectral content which is suggested by the weighting technique used to measure the SNR.

The easiest way to obtain an amplifier with low absolute noise output is to get the power as low as you can.

Pass labs specifies output noise in microvolts which ignores the spectrum part of the equation:

https://passlabs.com/images/uploads/manual/xa.5_specs.pdf

BTW they spec the same noise output regardless of power from 30 watts to 200 watts, which seems strange to me. 200 uV is not IME an exceptional number. 200 uV is about 80 dB below 1 watt which while not exceptional is probably good enough unless you stick your head inside the speaker cone in a very quiet room.

another point to mention, with preamp disconnected, there is zero hiss from the amp. Clearly my marantz 8801 is a limiting factor and adjusting the volune knob or no source input doesnt help the hiss. The outputs on the preamp are simply noisy.

I'm not sure if upgrading to "ultra high end" like theta digital or datasat would change this problem with high sensitivity speakers. Avantgarde Acoustics makes a pre-amp that is stereo only that works with high efficiency speakers that apparently solves this problem but that is not a good option for my home theater. Theta casablanca also lacks the number if channels i need for home theater. This would literally leave the $20000 datasat as the only contender ... But processors depreciate SO badly that the money is kinda down the toilet once you pony up.

Parasound makes a pre-amp that is stereo (jc2) with home theater bypass inputs for the main channels of your home theater but I am not sure how good it is about hiss, etc.

None of the manufacturers seem to test their gear with high sensitivity speakers.

You would think I was insane and obsessing about this subject and that maybe I should change my speakers... If you heard the avantgarde speakers though you would change your mind... The typical layperson can tell they sound like the "voice of god" and they are clearly the best part of my chain of equipment. These speakers make sound that literally is BLISS... A sound so addicting for almost any type of music that you cant leave the chair. My room is already Very well treated and my overall room response is already beautifully linear.

These silly hiss problems seem to be solved by a -20db xlr pad in-line with the preamp and amp BUT i am not sure this is not in some way affecting the overall signal purity. I think xLr pads maintain the impedance while simply making you turn the preamp vomume up higher to reach desired volume. In the preamp i have the main speakers set to +8db (which is what audyssey did ... In addition to adjusting all other speakers to match). This cut the hiss at idle to near inaudible at sitting position... But is there a "better" way acoustically or is this as good as it gets? I suspect that maybe the avantgarde made preamps made for high sensitivity speakers do exactly what I did: cut the pre-amp's gain at idle by having an in-line resistor network... And then charging the end user $10000 extra... LOL. Maybe i am being cynical.
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