Sure it will due to VC heating, raising the system Q long before it grenades, something that no box designer I've used can predict. Don't know about current drivers, but a typical prosound driver use to start compressing with as little 1/4 power and be -6 dB at half power. WRT more modern drivers such as the original Avatar/Adire Shiva sub, it could only handle about half its power rating before audibly distorting and why I pay little attention to high power ratings except for fast transient spike capability.
GM
This is for the mains, surround channels, the LFE channel is +10 dB, so 115 dB, which down low of course means lots of air has to be displaced.
GM
Is changing the frequency response the same as adding distortion?
The best power compression figures I've seen were 2dB at 1000W input. That's not bad going when sensitivity was 99dB@1w@1m.
Precision Devices International Limited
That seems mighty good.
Actual 127dB/1kW @ 1m instead of the theoretical 129dB.
Did they specify the power pulse shape and duty and did they specify peak or average? Having a lot of respect for Precision Devices product and ethics, I hope they did the right thing and specify the conditions accurately.
Says "AES Standard (40-400Hz)".
http://www.precision-devices.com/asps/uploads/super/17.pdf
Further research suggests 6dB crest factor pink noise, which is to cover one decade (in this case, 40-400Hz). The speaker should take it for 2 hours, and no "appreciable" damage should occur.
http://www.precision-devices.com/asps/uploads/super/17.pdf
Further research suggests 6dB crest factor pink noise, which is to cover one decade (in this case, 40-400Hz). The speaker should take it for 2 hours, and no "appreciable" damage should occur.
Would heating of the voice coil, providing it's pretty constant in temperature significantly affect the motors linearity though? That's the angle I was coming at when I posted what I did. I don't know how those kind of things behave, I mean if you had a driver capable of working at a theoretical limitless amount of power, putting the driver in a tiny box vs a huge box, it would take a lot more power to reach a given excursion for the tiny box, this would mean that the magnetic field created by the voice coil would be far stronger. Even though the driver is still operating within its xmax would this affect the performance in anyway?
The THX home cinema spec states that the subs should be able to play to 105dB @ 20hz @ 4% THD nothing more nothing less. This is at odds with the rest of the specification for 105dB on the mains with the LFE channel being boosted by 10dB, but this does not mean the spec on the LFE channel changes to require 115dB from the sub.
Apparently 115dB @ 20hz is a requirement for a public cinema installation, but not for a home theatre. Maybe the sub level is relaxed somewhat for a home cinema because actually arriving at 115dB @ 20hz would place unrealistic (and likely unobtainable from a SO acceptance factor) demands on how much of the room is taken over by sub.
If it changes the signal it's distortion, be it mechanical or acoustical, though obviously we don't perceive them the same.
Yes, that's excellent, though its high efficiency is mostly due to its ultra high Vas, so don't see it being relevant. Also, calculated efficiency is ~4.4%, so either the 4.04% is a typo or its related specs aren't quite what they seem to be, but still quite good and my limited experience with some 1550s convinced me they are well worth its high price.
GM
It depends on your listening habits. If you listen at reference levels ( theater level) at home with a flatly calibrated system the LFE channel does indeed require 115db peak capability from the subs at the listening position. If you redirect the bass from the other channels to the subwoofer also this increases the demands even more. With a typical 5 channel setup of 2 fronts, center and 2 surrounds this pushes the theoretical peak output demands from the subwoofer channel to just over 123db at the listening position. This is a highly unlikely signal but peaks of 118-120 db are not unheard of. However most people do not listen at theater reference level as it is really loud. -10 to -20 from that level is more typical so you could de-rate your output needed by an amount corresponding with your listening habits. Many people decide to run the sub channel a bit hot so that should be factored in as well. Also keep in mind that in most theaters there is little if anything reproduced below 30hz.
So my project using the 18PS100 and a 300 watt BASH amp should be pretty good for a medium size room? I'm pretty sure it would be just fine. The cabinet is about 8.5 cu ft including space for the driver and other stuff. Net volume is 7.5 cu ft.
Agreed that it's hardly a "standard" driver.
However, I think we need to specify what constitutues distortion.
Initially, we were talking about raising the Qts because of VC heating. This would in turn change the frequency response (which was unlikely to be optimal initially anyway).
So, does changing the frequency response from one sub-optimal response to another constitute distortion?
Originally Posted by Josh Ricci
It depends on your listening habits. If you listen at reference levels ( theater level) at home with a flatly calibrated system the LFE channel does indeed require 115db peak capability from the subs at the listening position. If you redirect the bass from the other channels to the subwoofer also this increases the demands even more. With a typical 5 channel setup of 2 fronts, center and 2 surrounds this pushes the theoretical peak output demands from the subwoofer channel to just over 123db at the listening position. This is a highly unlikely signal but peaks of 118-120 db are not unheard of. However most people do not listen at theater reference level as it is really loud. -10 to -20 from that level is more typical so you could de-rate your output needed by an amount corresponding with your listening habits. Many people decide to run the sub channel a bit hot so that should be factored in as well. Also keep in mind that in most theaters there is little if anything reproduced below 30hz.
So it should be "just fine" (depending on your listening habits), and if it is not, get an amp with six dB more output
.
Art
It depends on your listening habits. If you listen at reference levels ( theater level) at home with a flatly calibrated system the LFE channel does indeed require 115db peak capability from the subs at the listening position. If you redirect the bass from the other channels to the subwoofer also this increases the demands even more. With a typical 5 channel setup of 2 fronts, center and 2 surrounds this pushes the theoretical peak output demands from the subwoofer channel to just over 123db at the listening position. This is a highly unlikely signal but peaks of 118-120 db are not unheard of. However most people do not listen at theater reference level as it is really loud. -10 to -20 from that level is more typical so you could de-rate your output needed by an amount corresponding with your listening habits. Many people decide to run the sub channel a bit hot so that should be factored in as well. Also keep in mind that in most theaters there is little if anything reproduced below 30hz.
The 18PS100 should be around 95 dB sensitivity, with a 300 watts of power you should achieve 112 dB SPL at 2 meters, more or less depending on room gain.
So it should be "just fine" (depending on your listening habits), and if it is not, get an amp with six dB more output
.Art
THD, total harmonic distortion, consists of sound the speaker makes that are not present in the original signal. The sounds are usually harmonically related to the fundamental tones, but non-harmonic sounds can also be generated by speakers and are part of THD.
Frequency response can be equalized to a desired response, distortion can not be equalized.
Distortion goes up radically above Xmax, frequency response changes relatively little until distortion approaches 100%.
Distortion and frequency response are completely different metrics.
Changing the frequency response from one sub-optimal response to another, ie boosting below Fb can cause a large increase in THD at relatively low power.
That said, most music lives above 30 Hz, I could care less if occasional 15 Hz earthquake noises or T-Rex foot falls are accompanied by more than 4% THD.
Doesn't this contradict what GM has said regarding frequency response and distortion?
GM said:
What I was trying to say is illustrated by comparing the Eminence LAB15 with the B&C 18PS100. The LAB15 is in a 2.5 cu ft vented box and the 18PS100 is in a 7.5 cu ft vented box. Both have -3dB points of about 32 Hz. The LAB15 has a sensitivity of about 88dB and the 18PS100 is about 94dB. In the simulations, both are producing about 108 dB output. The LAB15 requires 100 watts to do this whereas the 18PS100 requires only 18. Cone excursion on the LAB15 is twice that of 18PS100. So, it seems to me that the 18PS100 (together with using the same amplifier as the LAB15) is going to produce a lot less distortion than the LAB15. Distortion in subwoofers is very important in my opinion because of the Fletcher-Munson curve. Our ears are far more sensitive to the higher frequency harmonics of subwoofers than of tweeters, for example.
Attachments
I suppose I should have used another 15" driver for a more clear comparison. All I'm saying is that the lower cone movement and less amplifier power required by highly sensitive drivers means that the subwoofer should produce sound at a lower distortion for the same SPL.
http://www.audioheuristics.org/primers/nonlinear_distortion_testing.htm
"This is the spectrum of distortion products that occur when a loudspeaker based on the 4" Vifa TC11 midwoofer is driven by a 35 Hz signal. When you hear this, you hear a signal that sounds quite different than it should, even though some people would be used to hearing this, and wouldn’t even call it distortion.
What do I mean? Well, first off, the second order harmonic and IM distortion products are around 27 dB down from the fundamental, or, 3-5%. The third order products are only 15 dB down, or greater than 10%. What’s really bad though, is that the ear has a decreasing sensitivity as you go down the spectrum. If you look at the Fletcher-Munson curves you can see that, compared with a 100 Hz signal, our ears’ sensitivity is down 10 dB at 70 and 20 dB at 35 Hz. So, a 70 dB 35 Hz signal sounds subjectively as loud as a 50 dB signal at 100 Hz.
Uh, oh…that’s a major problem. That means that the third order distortion products, which are down 15 dB at 105 Hz, will "sound" 20 dB louder if you look at it in phons. So, the above signal doesn’t really sound like a 35 Hz tone, it sounds like a 105 Hz tone, mixed in with some 35 Hz, and less so 70 Hz tones. There are some higher order products, but not bad.
I know what you’re thinking; a 4" midwoofer can’t be expected to produce 35 Hz bass. That’s not the problem. The problem is, any full range music, reproduced at even modest levels (70 dB at 35 Hz) will be transformed into higher distortion products. It doesn’t sound bad in this case, but it’s clearly not true to the original. It’s "fake" bass that comes out of so many small speakers.
If you didn’t quite follow it, read it again. I don’t mean to club your head with this, but it’s the reason why you will never, ever get accurate bass at virtually any level out of a 4" driver. Even if you doubled or tripled the xmax, you still won’t get there.
Things get better with a larger driver, but it appears generally unappreciated how much bigger you need to go to get undistorted bass, even at moderate levels. Consider the following two graphs. They are both ML TL’s. The first is based on the GR Research M130 5" driver and the other is based on the SS8554 8" driver. Both drive levels are adjusted to get 86 dB at 0.5m. Consider the distortion spectrums with the Fletcher-Munson curves in mind. Make the adjustments in your head and you can see the significant difference in the reproduced signal. Mind you, the M130 does not sound bad, but there is some distortion, audible as "fake" bass, even at this moderate level. The SS8554 isn’t perfect, but it’s measurably and audibly better."
So, maybe an 18" driver is needed to really get rid of all that "fake bass"!
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