Is tonality and volume related?
Do you believe speakers change their tone/performance/sound, between very low volume and maximum volume?
and if 'yes'
at what percentage of max volume do they sound/perform *best* ?
fullrange, subwoofers, tweeters and midranges.
and do you use/buy/build speakers to run in the 'ideal' range,
or are you using speakers at volumes that are not ideal?
Our ears change a lot. See Equal Loudness Curves.
Some drivers go into cone break-up when pushed (ie, electric guitar solos become unlistenable - very piercing sound). Mine just become forward in the treble (planning on an active BSC for that).
The changes in the drivers (provided there's no obvious cone break-up) are, I suspect, negligible compared to the changes our ears undergo according to volume. This is provided Xmax isn't exceeded.
A system able to go loud (and I mean PA levels - 98dB speakers driven by 100w/ch) will always sound better than one thats struggling to keep up. Following this, design a system capable of the listening levels you desire. Plus a bit, in case you need music while you hoover.
Well if by "tone" you mean frequency response balance then yes, all speakers will have some change in their frequency response between low volumes and very high volumes due to dynamic range compression, which is usually frequency dependent in nature. This means that a speaker with a flat response at low levels would become progressively less flat at high volume levels (certain frequency ranges would start to sag in relation to others) in a manner which is dependent on the design of the speaker.
The primary causes of compression are increasing cone excursion, heating of the voice coils, heating of passive crossover components, (particularly coils and resistors) and port turbulence in bass reflex designs. Of those, cone excursion is probably the biggest culprit, especially in woofers, but the others are important too.
Cone excursion - a woofer can only move so far before it reaches Xmax, and typically even before this point is reached the excursion is already not increasing as much as the drive signal - compression is starting to occur, and increases very rapidly beyond Xmax. Because excursion generally increases as frequency goes down (with the exception of the saddle near the port tuning in a bass reflex) this means that woofers (and drivers in general) have more compression at the bottom end of their range.
If you model a woofer/cabinet in something like WinISD and look at the cone excursion graph and flip it upside down in your head, you'll get a pretty good idea of how the excursion will alter the frequency response at high levels - frequencies where excursion is highest will have the worst compression, and the most deviation from the small signal response.
Excursion related frequency dependent compression in the bass is very common if not unavoidable with smaller speakers. The only solution is to design the speaker such that it can produce the highest SPL peaks in the music + 10dB or so headroom without reaching Xmax, which requires a lot larger speaker than many people might think. A lesser speaker might play the average level ok but chop off / compress the peaks.
Voice coil heating - at higher power levels the voice coil in a driver will heat up, resistance goes up causing SPL to go down and Qes to go up. In a woofer this change in Qes will alter the bass alignment and thus change the frequency response of the bass roll-off, as well as causing an overall drop in sensitivity.
In a multiway design if one driver is heating up and losing sensitivity but the others aren't, you'll get a shift in frequency response balance after some period of time of playing loud music. (Seconds to minutes depending on which driver, due to different thermal time constants)
Again, the answer is to choose drivers that won't be stressed by your expected SPL levels to the point where there is a significant resistance change. Higher sensitivity drivers can help a lot too - because provided they don't have flimsy voice coils, heating is much less of a problem on a driver that doesn't need nearly as much power for a given SPL. (A sub woofer in a small closed box that's 82dB/w/m sensitive needs 10x the power of a 92dB/w/m woofer in a larger bass reflex cabinet for the same SPL for example - with the more sensitive configuration having less thermal compression, provided the woofer is of a similar size.
Resistance of coils and resistors - series coils for woofers in particular can get hot at high power levels, resistance increases, and the effect is the same as the voice coil heating up in the woofer. The answer is to keep the resistance of the coil as low as possible and wind it from heavy wire. Again, a higher sensitivity driver helps since the power handling requirements of the coil are reduced.
Resistors in L-Pads - more of an issue with midrange crossovers. (and maybe tweeters to a lesser degree) If they heat up their resistance will increase, and depending on the relative heating of series and shut resistor the drive level may actually increase or decrease. This is bad because it's introducing a relative change in level between this driver and the other drivers, affecting frequency response. The solution here is to over-rate the resistors and maybe mount them on a heatsink.
Even if you can get away with a couple of air cooled 5 watt resistors in the L-Pad of a midrange without any risk of them burning out, they may get hot enough to affect their attenuation at high volumes - if you make them larger 20 watt resistors (and maybe heatsink them) they will hardly heat up at all. This is especially important if you're using a high sensitivity driver that needs a lot of attenuation - most of the power is being dissipated in the L-Pad.
Ports - an ideal port reduces excursion dramatically at and around the tuned frequency of the box, which as well as reducing distortion and increasing maximum possible SPL, also reduces dynamic range compression.
If the ports are undersized (in area) so that the air becomes too turbulent at higher volume levels their effectiveness is reduced and dynamic range compression occurs in that frequency range. (As well as increased distortion and cone movement) Answer - make sure peak port air velocity is well below 17m/s at maximum driver excursion. If in doubt, make the ports a bit larger than you think they need to be - the only drawback is they need to be longer.
In multiway speakers you have an additional potential source of problems - using drivers with mismatched dynamic capabilities. If you had a midrange driver that could cleanly produce 105dB SPL but a woofer that could only manage 95dB SPL before reaching excursion or thermal limits then as the level increases the woofer will reach it's limits first - further increases in level will keep increasing the midrange but the woofer has no more to give - the frequency response balance will shift dramatically. (Distortion will be high too...) The opposite can happen too - a huge woofer coupled with an inadequate midrange driver, where midrange is going to compress before the bass.
It's important to note that the maximum SPL of the drivers in a mutiway system don't need to be matched to the same absolute level, (like all reaching 105dB for example) they need to be matched in relation to the spectral content of music. Specifically, most music typically has a lot less energy in the treble, something of the order of 10dB less than lower midrange, so a tweeter doesn't need to (and usually can't) produce the same maximum SPL level's as the midrange driver or woofer. The important point is on typical music spectra you want the different drivers all reaching their limits at about the same playback volume so that no one driver is unnecessarily holding back the rest.
So yes, there are a lot of ways that frequency response will change with signal level, particularly in multi-way designs where choosing suitably matched drivers is important and sometimes difficult.
In answer to your question - at what volume level do speakers perform best, the answer is obviously at the lowest levels. As levels go up, frequency response shifts (due to all the above) and distortion increases. At some point the increasing distortion and increasing playback volume will cause the distortion products to become obvious and obnoxious. (Generally a speaker that has lower distortion at high SPL's can be listened to louder before discomfort than one that has high distortion)
At what volume level do speakers sound best, that's an entirely different question, and depends not only on the speakers, but also the type of music, listeners preferences, and the way the recording is mastered. Because of the fletcher munsen curves, technically there is only one "correct" playback level for any given recording, play it too softly or too loud and the response will sound different even if the speakers are perfect and don't change characteristics with level. (Also I would argue certain types of music require a minimum volume level to be fully enjoyed - especially those with a strong beat or bass line)
If a given pair of speakers can't play loud enough without significant distortion and/or dynamic range compression, but the music doesn't sound good at a lower volume level, there may be no volume level at which they sound good, at least on some kinds of music that need a minimum volume level to enjoy.
Personally, I believe in having plenty of headroom in the design - a large speaker with good dynamic performance doesn't mean you have to play it really loud - it also means that distortion and compression at moderate volume levels will be much lower than a smaller speaker, as it is just "ticking over" at moderate playback levels instead of being pushed hard all the time. Chances of damage occurring from a slip of the volume control are greatly reduced too.
If a speaker can play louder than you can comfortably tolerate in the room without it breaking a sweat, it essentially becomes indestructible because you'll always have to turn it down before it reaches its safe limits...whereas a small speaker that can only just manage your desired playback level is always one step away from disaster...
The differences in sound pressure traces of the dBA and dBC sound measurement curves, show the perceived increase in loudness at the extremes of the spectrum, IIRC. Perhaps a reason why high efficiency FRs can sound good at volume, since the volume is generally higher than that of a lower efficiency 2 way, and the ears compression of the middle frequencies in comparison to the high and low extremes, can balance the sound out somewhat better than at low volumes.
The louder its played, the more you hear of the frequency extremes.
Its difficult to compare between loudspeakers until you've given them their most likely amplifiers.
For a HE single driver, a low-wattage valve amp will probably be used.
For a low efficiency multi-way system, there's likely to be several solid state amplifiers of much higher power.
They'd both hit roughly the same SPLs, but a cranked valve amp will overload much more gracefully than a SS amp running under similar conditions. Is this why we like to turn such a system up? Very mild valve overdrive gives an attractive sound, with lots of low-order harmonics (of course, depending on the amplifier, topology and feedback used), whereas I'm yet to find a SS amp overload "nicely".
Another point to consider is...
IIRC, a thread on the subwoofer section was about drive level of a woofer vs Fs. As drive level increased (to a point), Fs decreased: the suspension became more compliant.
Is that a contributing factor to why we like to turn things up? You get the cone moving more than a tiny bit, and there's an increase in bass, as the cone is more willing to move.
Just a thought.
There have been studies showing that below 20Hz or so not only do you not perceive the sound as a discernible tone, the bulk of your perception of those low frequencies actually comes from the pressure wave physically vibrating your body, rather than movement of the eardrum.
Given that in-ear earphones will only stimulate the eardrum and <20Hz doesn't sound like a tone, if you're hearing a tone when you drive it with 17Hz then you've got to be listening to the harmonics...
One is a typical 12" woofer with butyl rubber surround where the small signal Fs was 29Hz, dropping to around 24Hz at higher excursions, the other was an 8" full range driver with cloth surround whose Fs is 48Hz at very low levels and drops all the way to 34.5Hz at high levels.
While the cloth surround seems more excursion sensitive the butyl rubber surround also has a memory effect due (presumably) to the plasticity of the rubber - after large excursions the Fs would remain at 24Hz even for small excursions for a period of several seconds - over about 10 seconds the Fs would "creep" back up to it's no signal value of 29Hz.
(This would mean bass with high crest factors such as a big kick drum every couple of seconds would tend to keep the woofer's surround more compliant even when average levels were low, at least with a rubber surround)
So there is definitely a volume level dependent change in a woofers characteristics, but I think it's a bit oversimplifying things to say that more drive (below Xmax) = softer suspension = more bass.
What happens to the bass response when the surround becomes dynamically softer from excursion depends on the bass alignment. In some alignments like a closed box with a high tuning ratio (large Vas, small Vb) even a large change in the free air Fs will have negligible change on the in-box response, since the Cms wasn't much of a determining factor in the first place.
Open baffle and bass reflex are more likely to see a significant change, and in the case of a bass reflex although softer compliance generally means more lower end bass, with many alignments it will reduce the mid bass, since the Qms will drop when Cms drops.
The way I've approached the issue is to measure the parameters for the driver at both very low ("small signal") levels, and also near but below Xmax, (typically 1/2 Xmax) save the two sets of values as two different drivers and model both responses in the same size box / port tuning to see the difference in response - now you know what the response would be at low and high levels due to changes in Cms, and you know that intermediate levels will lie somewhere in between...
I would just add this to the long list of reasons why a speakers frequency response does change somewhat between low and high volumes... :)
That is part of it, I have always held the point of view that our skin is an extention of the ear at low frequencies, in that it captures the vibration and append it to the audiable range through a type of synesthesisa, kind of the way smells and tastes have a very blurry line between two senses. Strange no one tried makeing a speaker with an integrated peltier cooler yet.
One reason why we used to test FR testing @ 1 /10/20/30 watt and then compare curves . Ideally you will not see a change and for the most part we never did when tested as all spkr where shipped out in matched Prs to within +/- 1db of each other...
I can see this being an issue with FRange speaker systems and most high efficiency system that are not multi- driver setups, they will have tonal changes with increased db levels and dynamic growth is never linear IME...
|All times are GMT. The time now is 06:22 AM.|
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio