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In Reply to: Re: I'm just not sure about one thing posted by morricab on November 23, 2006 at 09:43:31:
The old Kef 104 was pretty flat in the listening window but with the 8" woofer crossed over to a 3/4 tweeter at 3 kHz the off axis response suffered between about 1000 and 2500 Hz, which would affect the total power response. You can't really fix that with an equalizer, though it can help things to a degree, as it won't improve the dispersion. It was quite a good speaker in the right set up, but not really room friendly. Compared with the Quad ESL-63, it really didn't sound bad at all, but not as detailed.The ear is less sensitive to both low frequencies and high frequencies. This has nothing to do with the deficiencies of stereo systems. It's easy to look up on the net.
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"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
Follow Ups:
"The ear is less sensitive to both low frequencies and high frequencies. This has nothing to do with the deficiencies of stereo systems. It's easy to look up on the net."THat's my point! In real life with real live instruments your hear sensitivity also drops at high and low frequencies with decreasing level. When we hear the highs and lows dropping out with a stereo at low levels its because there is EXCESS loss over and above our normal lack of sensitivity in these ranges. THis loss is coming from the stereo itself. If it were to maintain the same FR and dynamic envelope at 50db as it has at 80 db then the softness would sound natural as when an instrument gets softer from 80 to 50db. Since most stereos don't sound natural at low levels this is a clear indicator of excess loss from the stereo not because of the change in hearing sensitivity. Loudness contours were designed to overcome the limitations of the gear not the listener. Your brain knows what sounds natural at low levels and so the hearing curve is irrelevant for live sounds. If the response of the stereo system is constant regardless of level then the sounds on the recordings will soften in a natural sounding way but most systems are not constant thus the loss of realism at low levels (and high levels).
Well, just from a layperson's point of view, I think it's a little more complicated than that. First of all, we have your idea of "natural" sound, which has not been verified. Second, in real life, sounds farther off are often softer but have more reflected sound. Third, turning the volume down often makes the stereo image seem to move back some. Fourth, like it or not, at lower volumes, the ear is less sensitive to low and high frequencies.Many posters here besides my self have suggested that speakers which sound good at low volumes tend to approximate the Fletcher-Munson curves (or someone else's equal loudness curve).
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
"First of all, we have your idea of "natural" sound, which has not been verified"True and the same can be said for when you say your system sounds fine as well. However; are you a regular goer of live classical and/or other music that is unamplified? Are you a musician or have you lived with someone who is a professional musician? Do you now or have you ever been involved in the making of recordings in natural spaces (ie. a concert hall)? If you answer yes to these then I perhaps we are coming from the same background.
"Second, in real life, sounds farther off are often softer but have more reflected sound."
Yes this is correct; however, we are discussing the systems effects on sounds that were recorded from farther away or that are soft but close. You don't want the system to impose the same effect as a live sound from far away. It is like a double negative, its a no no!
"Third, turning the volume down often makes the stereo image seem to move back some."
Why should this be? Is this simply your observation in your system or do you have some physical explanation? If the system is properly preserving the harmonic content of the instruments when you decrease the volume then it shouldn't happen. With a real instrument, like a sax or trumpet, the sound recedes more inside the instrument at lower volumes than when it is played full blast. This has a lot to do with how the harmonic content of the instrument changes with the volume level its played at.
If I understand you correctly you are saying that a loud trumpet (as it is on the recording) played back softly (as in the volume control turned down) will sound farther away than it would if the volume control was set to give a realistic SPL level. IMO, this is a clear sign that your system has a different set of harmonic components that it adds at the low level vs. the high level or the speakers FR balance is different at low spl level vs. high spl level. Either way this would seem to indicate a problem with that system. I don't disagree that this receding of the sound with decreasing level could happen just that it should not happen.
"Fourth, like it or not, at lower volumes, the ear is less sensitive to low and high frequencies."
No one is disputing this. However; the microphone doesn't suffer from this problem, which means that soft sounds are captured with close to the original harmonic content and freqeuency balance. The reproduction will then sound natural (ie. you will hear the same content on the recording that you would have heard live if you were there) IF the system is not further altering the harmonic content and FR with level. If it is, namely losing bass and HF response at low levels, then the sound will lose life at low levels and no longer sound realistic. As long as these are preserved at low levels it will sound like a natural softening not the usual lifelessness most systems exhibit.
For example, whenever a reviewer says a speaker needs some juice to "wake up" this is a clear sign to me that this speaker cannot perform naturally with low level signals, this means either when played at low volumes or when there are soft sounds (like ambient information) in the louder matrix of the music.
"Many posters here besides my self have suggested that speakers which sound good at low volumes tend to approximate the Fletcher-Munson curves (or someone else's equal loudness curve)."
Maybe they are purposely designed this way to compensate for the losses that typical speakers show at low levels (the losses are always there just more noticeable at low levels where the percentage of error is larger). However; now this speaker will not sound correct at higher volumes because the bass and treble are tipped up. Manipulating frequency response is not really the answer to what is really a loss of dynamics. The only way I can think to do this in the frequency domain is with DSP where the DSP monitors the current to drivers and then applies a sliding scale equalization curve dependent on the signal level. It can be fast enough but I don't know anyone making a level dependent equalizer. Maybe a bright idea though.
It is the same problem with Class AB amps. They have zero crossing distortion that makes itself most known at low levels and is a major reason why these amps don't sound good at low levels because the distortion to signal ratio is much greater than at full power. The zero distoriton is always the same in absolute level terms.
Of course, my idea of natural sound has not been verified, either.Musician? Well, I've been a choral singer most of my life and have been capable of baritone solos for some decades. I've done some recordings. Just heard the dress rehearsal for Messiah last night (I have laryngitis, so couldn't participate). Maybe I'll be able to do some of the performances . . .
Yep. Speaker with a depressed midrange will sound that way played louder too, but that can be quite pleasant on a lot of material. But it doesn't prevent them from sounding great at low levels.
Walking away from a live performance is not the same as turning the volume down.
You'd better look at those equal loudness curves again. Sensitivity in the bass drops quite a bit as the level goes down.
When you get around to measuring the behavior of speakers at low levels I'll give your theories more credence. Perception of the distance of the sound source seems to be a controverted area with natural sounds and the sound image from a stereo system lacks many of the clues we can have with natural sounds.
Oh, I just looked on the Stereophile site and there is an interesting article by Keith Howard on voice coil heating and changes in impedance. He thinks it's likely to be a negligible factor in normal listening.
http://www.stereophile.com/reference/1106hot/
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
http://www.rythmikaudio.com/servo_tech.htm
http://www.jblpro.com/pages/general_faq.htm#What is "power compression"?
http://www.nearfieldacoustics.com/whiteppr.pdf (read the section on dynamics where they state that even small compression effects in the bass can have big effects on perceived loudness).
http://www.klippel.de/download/bin\AN12 - Amplitude Compression.pdf"Don’t Make a Bad First “Compression”
All these SPL ratings are 1w/1m ratings. “But what type of performance can I expect if I apply more than 1w of input electrical power to my subwoofer?”Well, it’s quite simple: you suffer from compression. There are two types of compression to be concerned with:
1. Thermal/Power
2. BLAs electrical power is applied to a voice coil, the voice coil heats up. This causes an increase in the Resistance of the voice coil, also known as Re. This is referred to as thermal or power compression.
As the voice coil moves out of the gap, motor strength (also known as BL) begins to drop. The further the voice coil moves out of the gap, the lower BL drops. As BL decreases, output drops as well. A 30% decrease in BL will cause a 3dB decrease in acoustical output.
Now which is worse? I guess you could say that depends. Thermal/Power compression is typically a slower process. Because music is very dynamic, it does take a few seconds for the voice coil to increase in heat, and therefore, a few seconds for the voice coil’s resistance to increase. Once this voice coil is hot, it takes 10-30 seconds to cool back down. As you can see, once the voice coil has become hot, the effects of Thermal/Power compression are fairly constant.
On the other hand, BL compression is a "quicker" issue. A voice coil can move right out of the gap and back into the gap in a single second. As excursion increases, it only gets worse. It is quite obvious that BL compression is the more serious issue of the two.
Don’t Make a Bad First “Compression”
All these SPL ratings are 1w/1m ratings. “But what type of performance can I expect if I apply more than 1w of input electrical power to my subwoofer?”Well, it’s quite simple: you suffer from compression. There are two types of compression to be concerned with:
1. Thermal/Power
2. BLAs electrical power is applied to a voice coil, the voice coil heats up. This causes an increase in the Resistance of the voice coil, also known as Re. This is referred to as thermal or power compression.
As the voice coil moves out of the gap, motor strength (also known as BL) begins to drop. The further the voice coil moves out of the gap, the lower BL drops. As BL decreases, output drops as well. A 30% decrease in BL will cause a 3dB decrease in acoustical output.
Now which is worse? I guess you could say that depends. Thermal/Power compression is typically a slower process. Because music is very dynamic, it does take a few seconds for the voice coil to increase in heat, and therefore, a few seconds for the voice coil’s resistance to increase. Once this voice coil is hot, it takes 10-30 seconds to cool back down. As you can see, once the voice coil has become hot, the effects of Thermal/Power compression are fairly constant.
On the other hand, BL compression is a "quicker" issue. A voice coil can move right out of the gap and back into the gap in a single second. As excursion increases, it only gets worse. It is quite obvious that BL compression is the more serious issue of the two."
A well designed voice coil system shouldn't move out of the gap unless very long excursions are happening so thermal is the bigger problem at realistic volume levels.
Almost every speaker maker in audio is concerned with the effects and not many mention FR at all. Could it be because compression affects realism in sound more than FR abberations, perhaps?
"Yep. Speaker with a depressed midrange will sound that way played louder too, but that can be quite pleasant on a lot of material. But it doesn't prevent them from sounding great at low levels."I disagree, a depressed midrange most certainly affects things from sounding correct at any level. Speech intelligibility for one thing suffers. I have heard this with a number of speakers that have a dip in the presence region. Also, when the level gets lower that 3-5 db or so dip may now drop the response in that region below the level where the speaker performs correctly thus further reducing the clarity of sounds in that frequency range.
"You'd better look at those equal loudness curves again. Sensitivity in the bass drops quite a bit as the level goes down"Not sure what point you are trying to make here. It would be helpful if you completed the full thought rather than give a one liner and expect me to interpret what you mean. I try to be as explicit as possible so as not to be misunderstood. I frankly have now idea what you want to make of this obvious factoid. It seems like a non-sequitor.
"Oh, I just looked on the Stereophile site and there is an interesting article by Keith Howard on voice coil heating and changes in impedance. He thinks it's likely to be a negligible factor in normal listening."
I read this but I question his methodology a bit. Here is another test done with small hifi and pro monitors (not very different from the kind of speaker Howard used) and they show quite demonstrable differences in the performance due to thermal compression.
http://www.soundonsound.com/sos/jul02/articles/monitors2.asp
If you do, the least of your worries is thermal compression.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
No the average levels are that loud but the peaks could be because I often listen to wide dynamic range recordings (like 20+ db over the average level). So if it takes only a few ms to heat the coil up (one large peak) and 10-30 sec to cool it down then it is clear that thermal compression can be a problem for the music following the peak(s). The point is that the response of the system is not constant but instead constantly changing subtly. This can affect imaging stability also (for instance if the woofer in the left speaker has sublty different dynamic behavior than the right speaker woofer).
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