Axiom Audio EP500 VS SVS PB12-Plus/2

[Steve42]

Craig,

I would think THD would be harder to hear in the lower frequencies anyway, especially around 20Hz. Is that not true?

I would think that with "subwoofer" freq. THD would be pretty much be a non-issue.

 

[craigsub]

I guess one could take the Klippel test and see for themselves just how audible THD when using their own ears. I'm going to try it tonight, sounds cool.

Edit: You beat me to the suggestion Craig. I guess I should have used the "quote" function

P.S. I'm guessing that the test signals do not go extremely low either if they suggest using headphones which usually do not produce lower frequencies very well. And correct me if I'm wrong, but isn't THD usually harder to "hear" the lower the frequency is? At least I would think it would be harder to hear around 20Hz in the case of "subwoofer frequencies".

Yes ... THD levels are harder to hear as frequencies get lower. I would think -30 dB would not be too difficult with some excellent headphones. Hard to say for sure, though ...

 

[Manic Miner]

Steve: In theory it's just the opposite the ear's lack of sensitivity in the lowest frequencies as illustrated by the equal loudness curve makes HD even at lower amplitudes, but higher frequecies 'louder' then the original signal even tough THD doesn't exceed 100%. Now that is theory, I would love to have someone explain me why this isn't the case

 

[Steve42]

Yes ... THD levels are harder to hear as frequencies get lower. I would think -30 dB would not be too difficult with some excellent headphones. Hard to say for sure, though ...

Yeah headphones are one thing, I have an expensive pair of Sony CD3000's at home, so I'll see. But with a subwoofer for playing back music/HT selections I would think it would be even harder to hear the THD.

 

[Steve42]

Steve: In theory it's just the opposite the ear's lack of sensitivity in the lowest frequencies as illustrated by the equal loudness curve makes HD even at lower amplitudes, but higher frequecies 'louder' then the original signal even tough THD doesn't exceed 100%. Now that is theory, I would love to have someone explain me why this isn't the case

Interesting, but most subs are crossed over at around 60-80Hz anyway. So how much louder (and detectable) are those "higher" HD low frequencies going to be as far as being able to differentiate them from the original lower bass note. I know a common 24dB cross-over slope is not a "brick-wall", but anything under 80hz or so is going to be pretty hard for the ear to detect I would think.
I doubt I could tell much of a difference if the HD is around 50-60Hz from a 20-30Hz signal with say 10-30% THD. Especially if the program material is near 100dB to begin with.

 

[Manic Miner]

Took the test with a pair of crappy Sony headphones connected to my IBM laptop. My first mistake came at -36db, up til then it was semi-easy to pick out the distorted sample. The guitar sounded a little bit thicker, and the voice was not as distinct. But at -36 I could tell that there was a small difference, but I could not tell wich one was distorted

 

[Manic Miner]

Steve, jakeman posted a link were there was a paragraph on THD, and the equal loudness curve

http://www.linkwitzlab.com/thor-measmt.htm

 

[craigsub]

Let's take the 20 Hz Fundamental. Yes, at 70 dB, the 20 Hz fundamental is barely audible, while 70 dB @ 80 Hz is quite audible. But, for the intended use of a subwoofer, it needs to hit 110 dB in room peaks @ 20 Hz in order to be a solid performer. As you get higher SPL's, the detectible difference between, say, 20 and 40 Hz, shrinks considerably.

You might have the subwoofer producing a 110 dB fundamental @ 20 Hz, a 93 dB 40 Hz harmonic, an 87 dB 60 Hz signal, and an 80 dB 80 Hz signal. This subwoofer "flunks" the 10% THD+N test, yet I doubt the THD+N is audible.

I HAVE heard subwoofers, on the other hand, deliver terrible noises, while being under the 10% THD level ... the Tumult based Denali subwoofer was a great example of that. The Passive radiators would bottom long before 10% THD was met.

Looking forward to guys taking the Klippel test. It should be informative. Anyone doing so by tonight will have their % threshold published ...

 

[Steve42]

Manic,

I was busy editing my last post to be more clear on what I was trying to say. When I was finally finished, I noticed Craig put it much better than I did with his example here (which in the end, is the point I was trying to make):

But, for the intended use of a subwoofer, it needs to hit 110 dB in room peaks @ 20 Hz in order to be a solid performer. As you get higher SPL's, the detectible difference between, say, 20 and 40 Hz, shrinks considerably.

You might have the subwoofer producing a 110 dB fundamental @ 20 Hz, a 93 dB 40 Hz harmonic, an 87 dB 60 Hz signal, and an 80 dB 80 Hz signal. This subwoofer "flunks" the 10% THD+N test, yet I doubt the THD+N is audible.

 

[Manic Miner]

I know that the equal loudness curve flattens somewhat as the SPL increases, but still at 120db we are less sensitive to lower frequencies then higher.

But going from there to that THD is inaudible is a huge step, and it doesn't jive with common sense. Now, I do not know at what level THD becomes audible, 5, 10 or 20%? My listening for THD has been subjective, and at first even unintenional so I don't have any measurements to back them up.

For THD to be inaudible the brain would somehow have to know what the original signal was so that it could discard all other information, that is common sense. That is a task that my brain isn't up to, maybe it was a factory option that my parents were to cheap to spring for

 

[craigsub]

I know that the equal loudness curve flattens somewhat as the SPL increases, but still at 120db we are less sensitive to lower frequencies then higher.

But going from there to that THD is inaudible is a huge step, and it doesn't jive with common sense. Now, I do not know at what level THD becomes audible, 5, 10 or 20%? My listening for THD has been subjective, and at first even unintenional so I don't have any measurements to back them up.

For THD to be inaudible the brain would somehow have to know what the original signal was so that it could discard all other information, that is common sense. That is a task that my brain isn't up to, maybe it was a factory option that my parents were to cheap to spring for

The issue is not whether THD is inaudible ... the issue is WHEN does THD become audible ? This whole 10% THD + N "brick wall" makes no sense, unless your subwoofers happen to be built to that spec.

For now ... just take the Klippel test, and let us know how you do. I think it will start you understanding your own ears, rather than a bunch of graphs.

 

[silversurfer]

Quick question:

What is more objectional to the ear, IMD or HD?

 

[craigsub]

Quick question:

What is more objectional to the ear, IMD or HD?

I would say IMD, as a general rule - though not necessarily always. What do you think ?

 

[Manic Miner]

Craig: I have taken the test, and posted about it already.

Took the test with a pair of crappy Sony headphones connected to my IBM laptop. My first mistake came at -36db, up til then it was semi-easy to pick out the distorted sample. The guitar sounded a little bit thicker, and the voice was not as distinct. But at -36 I could tell that there was a small difference, but I could not tell wich one was distorted

 

[craigsub]

Manic ... Here is the scale of relative THD numbers ...

-5 dB 56.2 %
-10 dB 31.6 %
-15 dB 17.8 %
-20 dB 10.0 %
-25 dB 5.62 %
-30 dB 3.16 %
-35 dB 1.78 %
-40 dB 1.00 %
-45 dB .562 %

Try the test again on some speaker, would you please ?

 

[silversurfer]

I would say IMD, as a general rule - though not necessarily always. What do you think ?

That is what I am thinking as well, but I don't know for sure. Looking at the graphs/numbers, it seems that the IMD and the HD of the SVS box are of the same order, whereas the Axiom box the difference between the two is much greater.

Just thinking out loud here, but since HD is a product of fundamentals, and in some studies show to be more pleasing to the ear, is it possible that in some cases it will mask the IMD? If so, maybe with the SVS's IMD and HD being on the same magnitude, there is less of a mask?

I may be be thinking way over my head here, but maybe I am on a roll?

 

[Manic Miner]

I'm in the midst of moving, so I have no speakers here with me, will do once I'm settled

 

[craigsub]

I'm in the midst of moving, so I have no speakers here with me, will do once I'm settled

Cool ... Headphones are so much more revealing than are speakers, for the obvious reasons. Even the headphones that came with my IPOD allow things to be heard that speakers miss. Of course, headphones have other drawbacks.

 

[craigsub]

That is what I am thinking as well, but I don't know for sure. Looking at the graphs/numbers, it seems that the IMD and the HD of the SVS box are of the same order, whereas the Axiom box the difference between the two is much greater.

Just thinking out loud here, but since HD is a product of fundamentals, and in some studies show to be more pleasing to the ear, is it possible that in some cases it will mask the IMD? If so, maybe with the SVS's IMD and HD being on the same magnitude, there is less of a mask?

I may be be thinking way over my head here, but maybe I am on a roll?

LOL ... A roll like Belushi (Bluto) at the end of Animal House ...

Bluto ... "Did we quit when the Germans bombed Pearl Harbor ?" ...

Seriously - I don't know if HD will mask IMD ... I DO know a lot of conclusions guys make by staring at a graph are just plain unproveable in a listening test.

 

[jakeman]

Craig: I have taken the test, and posted about it already.

Hmm...-36db on crappy headphones? That would put you in the top 5% of everyone taking the test. GoldenEar territory. You might want to take the test several times to get a range and try using a good set of headphones for greater fidelity. Not saying you don't have golden ears.

The test does show that different people have varying levels of audibility of THD. I'm probably typical as I can't tell audible THD below -18db.