Even more to the point:
"The ear’s decreasing sensitivity at low frequencies is a significant problem and lead to the need for quite low distortion at the low end. To reiterate, if xmax is defined by a manufacturer as 10% harmonic distortion, then say, at 20 Hz, when the 10% figure is reached, the amplitude of the 40 Hz 2nd harmonic may be down only 20 dB. The problem is, the relative sensitivity of the ear has increased by 20 dB from 20 to 40 Hz. So what are heard are two tones, 20 and 40 Hz of equal magnitude. So, even though the driver is still operating in its linear range, obvious audible distortion is occurring. And this doesn’t take into account problems with the 3rd order product or higher. The 3rd order product has to be down almost 40dB just to be perceived as equal in magnitude to the 20 Hz fundamental. Wow!
It’s hard not to draw the conclusion that, even for moderate levels in moderate sized rooms, the smallest driver needed for undistorted low frequency extension is an 8" driver. 10-12" drivers are required for true low distortion bass at realistic levels. In addition, transient levels can be 15-20 dB higher than the average SPL level. If this weren’t taken into account, while the average levels would be relatively undistorted, distortion would occur at the peaks.
You can see why the xmax/excursion-limited prediction by modeling software that use xmax provided by the manufacturer could be poor. The builder who thinks that he can get undistorted bass from a 7" driver at 105 dBSPL half space because that’s what Unibox says may very likely be wrong, and by a significant margin. (I’m not picking on Unibox-I think it works well. But distortion and SPL predictions should always be tested-all modeling software has limitations.) Remember, higher order products can be very audibly offensive and these generally will not be accounted for in these simple xmax limited excursion predictions.
Higher order products are bad, even at levels of –40 dB and lower. IM distortion is bad. The higher the order, or the more numerous the products, the worse the perceived distortion."
from the same website...
"The ear’s decreasing sensitivity at low frequencies is a significant problem and lead to the need for quite low distortion at the low end. To reiterate, if xmax is defined by a manufacturer as 10% harmonic distortion, then say, at 20 Hz, when the 10% figure is reached, the amplitude of the 40 Hz 2nd harmonic may be down only 20 dB. The problem is, the relative sensitivity of the ear has increased by 20 dB from 20 to 40 Hz. So what are heard are two tones, 20 and 40 Hz of equal magnitude. So, even though the driver is still operating in its linear range, obvious audible distortion is occurring. And this doesn’t take into account problems with the 3rd order product or higher. The 3rd order product has to be down almost 40dB just to be perceived as equal in magnitude to the 20 Hz fundamental. Wow!
It’s hard not to draw the conclusion that, even for moderate levels in moderate sized rooms, the smallest driver needed for undistorted low frequency extension is an 8" driver. 10-12" drivers are required for true low distortion bass at realistic levels. In addition, transient levels can be 15-20 dB higher than the average SPL level. If this weren’t taken into account, while the average levels would be relatively undistorted, distortion would occur at the peaks.
You can see why the xmax/excursion-limited prediction by modeling software that use xmax provided by the manufacturer could be poor. The builder who thinks that he can get undistorted bass from a 7" driver at 105 dBSPL half space because that’s what Unibox says may very likely be wrong, and by a significant margin. (I’m not picking on Unibox-I think it works well. But distortion and SPL predictions should always be tested-all modeling software has limitations.) Remember, higher order products can be very audibly offensive and these generally will not be accounted for in these simple xmax limited excursion predictions.
Higher order products are bad, even at levels of –40 dB and lower. IM distortion is bad. The higher the order, or the more numerous the products, the worse the perceived distortion."
from the same website...
Not necessarily, it depends on the driver's design/construction, ie. at what point thermal power compression [part of AMD] sets in and where the VC is on its BL curve. Unfortunately, historically, few manufacturers publish this data, so this kind of simmed comparison is pretty much worthless for high power apps without it.
FWIW, the historical rule-of-thumb was to design based on 20-25% of rated power for the BW below its mass corner if its 10% distortion rating wasn't known.
GM
So, if one woofer is being driven at 100watts and the other at 18, and they are both fairly substantial professional drivers with adequate VC ventilation, which do you think is going to heat up faster and may experience thermal power compression? Also, don't forget the amplifier, which typically produces more distortion at 100watts than at 18.
The one driven at higher power will, obviously, heat up quicker.
Power compression shouldn't be an issue until the voice coil is properly hot - assuming a fairly substatial professional driver with adequate VC ventilation, 100w simply won't be a problem.
Chris
Again, as presented, no way to tell for sure. WRT amp distortion, ignoring high output impedance ones, if you choose one that's appropriate for the app, it's a non-issue as far as audibility is concerned.
GM
So, you are disagreeing with the person who wrote the web page I posted earlier? You're saying that the Fletcher-Munson curve is not a concern when it comes to subwoofers? Because everything I'm writing is supported by that website.
Since most woofers have distortion components that are about 20-30dB down at best (given the standard AES 10% drive level), then I don't see how you can disagree that subwoofer distortion is an extremely important concern. The second and third harmonics produced by subwoofers are far more easily heard by our ears than the fundamental frequency, as per that website.
To me, the bottom line to reducing distortion is to reduce cone movement and to reduce the required amplifier power for a given SPL. Horn loudspeakers do just that, but large high sensitivity direct radiators can be similar, though probably not as good.
OK, here they are producing 116dB each. The LAB15 requires 600 watts and the 18PS100 requires about 100. The 18PS100 is still barely breathing and the LAB15 is out of breath. This is a simple simulation so maybe the LAB15 requires even more power to achieve 116dB, I don't really know. Anyway, cone excursion is exceeded in the LAB15 at subsonic frequencies, and is over twice that of the 18PS100 at other frequencies. Certainly, I'd think the LAB15 is getting a bit warm now, don't you think? Distortion products must be very high at this point as well, but still fairly low in the 18PS100.
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All other things (ability to remove heat from the motor structure being one) being equal, if you have two drivers of different sensitivity playing the same tone at the same level, the less efficient driver will be receiving more power. As >90% of the power fed into a loudspeaker is dissipated as heat, the lower sensitivity driver will be trying to get rid of more heat than the higher sensitivity driver.
Of course, things are never so simple in the real world - VC ventilation, thermal mass of the coil, magnet, and everything else that sees any heat will all have an effect, so comparing one driver to another won't be so easy.
Chris
No, you're 'putting words in my mouth' rather than 'hearing' what I'm saying. Quite the contrary, if you'd been on the various forums as long as me you'd know that I've been 'preaching the gospel' of horns/high efficiency since day one [my system at the time was ~112 dB efficient down to ~40 Hz in-room], which actually got me banned from several early so-called 'HIFI' audio BBs where inefficient 'monkey coffins' were touted as the most accurate/revealing, ad nauseum.
No, my responses are based on your 'one size fits all' dictum without consideration of driver, amp, design used, etc.. Just because it's true sometimes doesn't de facto make it a rule.
Down low, there's 'no replacement for displacement', but how you get it at low distortion isn't necessarily only by horn loading now that materials and manufacturing technology has advanced to the point where high power and drivers able to handle it at low distortion are available and relatively inexpensive. Frankly, I no longer tout horns for true sub systems, only multiple driver IBs or TLs and enough power to keep the amp linear, which as I noted renders amp distortion moot.
Of course using these drivers in horns is 'icing on the cake' for prosound apps and complete overkill in all but the most extreme HIFI/HT apps.
GM
Greets!
Long time no see! Did you ever get that tapped pipe sealed up and working properly? I don't recall ever seeing any posts beyond the first measurement.
GM
True, but that doesn't necessarily mean it has higher distortion, just able to 'sink' more current.
Right, isn't that what I've been saying?
GM
I'm trying to understand your point, not putting words in your mouth. All you've said is "it depends", as far as I can tell. You haven't given any real reasons that I can see. I am not attacking you personally.
I really don't care how long you've been on message boards. That is not relevant to me. If you disagree with what the author of that web site has to say, then I'd like to hear your reasons why. His is just one example that I found through a simple search.
I'm not looking for a dictum so much as just a general guide. If you know of ways to minimize subwoofer distortion, then why don't you talk about that? What would you do to minimize it? My solution is to use a high quality driver with high sensitivity and low enough Fs. This usually means going big.
I'm not horn loading these drivers. They are both sim'd in 4th order vented boxes. Folded bass horns are acoustical low pass filters which are basically impossible to model, so I stick with straight horns when I can.
I disagree that amplifier distortion is not important. With subwoofers, we're usually dealing with a lot of power, and that often leads to a lot of distortion also.
True, but that doesn't necessarily mean it has higher distortion, just able to 'sink' more current.
Right, isn't that what I've been saying?
GM
Assuming that both have similar THD @ 10% of their rated power, then the more sensitive driver would produce lower distortion at the same SPL.
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