List of Reference Level, High Sensitivity & SPL Speakers - Page 13 - AVS Forum
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post #361 of 824 Old 11-29-2012, 12:53 PM
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Quote:
Originally Posted by popalock 
Question: Does speaker sensitivity have anything to do with dynamic capability? If one was to have ample power to push any speaker of their choosing, would sensitivity matter?

There should be no difference in performance between a hypothetical 90db efficient 100w speaker and a hypothetical 80db efficient 1000w speaker and a hypothetical 100db efficient 10W speaker; assuming you have enough power to drive them all.
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post #362 of 824 Old 11-29-2012, 12:54 PM
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Quote:
Originally Posted by JerryLove View Post

There should be no difference in performance between a hypothetical 90db efficient 100w speaker and a hypothetical 80db efficient 1000w speaker and a hypothetical 100db efficient 10W speaker; assuming you have enough power to drive them all.

In reality there is, it has to do with how each speaker stays linear, no compression, etc... near it's limits.
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post #363 of 824 Old 11-29-2012, 01:17 PM
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Originally Posted by MKtheater View Post

In reality there is, it has to do with how each speaker stays linear, no compression, etc... near it's limits.

You don't seem to have finished your post; which makes it look entirely unsubstantiated.

What is the formula for sensitivity - vs - percentage of power at which distortion occurs?

I'll wait while you find either the statistics or the physics.
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post #364 of 824 Old 11-29-2012, 01:26 PM
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Originally Posted by JerryLove View Post

You don't seem to have finished your post; which makes it look entirely unsubstantiated.
What is the formula for sensitivity - vs - percentage of power at which distortion occurs?
I'll wait while you find either the statistics or the physics.

I am just going on what I have measured in my room.
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post #365 of 824 Old 11-29-2012, 01:34 PM
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it is often said that the difference between HE and LE speakers only comes to play at high volume levels. But I almost never listen at full ref. levels, yet at -10dBFS or even -15dBFS the difference is unmistakable. the same goes both for music and movies. I do not know why that is.

I am a relatively recent convert. I got a taste of it with SHO-10s but I still missed the refinement and precise imaging I got accustomed to with Ascend Sierras they replaced. Now with 4Pi's I have the best of both words.
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post #366 of 824 Old 11-29-2012, 01:36 PM
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Originally Posted by MKtheater View Post

I am just going on what I have measured in my room.
Well, unless you've plotted a couple score at random it's anecdotal.

"this" 90db speaker had better/worse distortion at 75% power than "that" 92db speaker therefore it's true for all lower and higher efficiency speakers.

Even given that: what's the formula? For every 3db of efficiency the point of distortion drops 5%? What do your measurements indicate and what is your sample-set (and actually: I'm a little curious to methodology; but that's less important)

Actually: I think someone mentioned JBL professional publishing their distortion numbers? I wonder what I would get if I gathered those up and ran some analysis on them comparing point of arbitrary distortion as a percentage of overall power and graphing that along a sensitivity line. Do you think it would confirm your answer to the above?
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post #367 of 824 Old 11-29-2012, 01:55 PM
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Quote:
Originally Posted by JerryLove View Post

There should be no difference in performance between a hypothetical 90db efficient 100w speaker and a hypothetical 80db efficient 1000w speaker and a hypothetical 100db efficient 10W speaker; assuming you have enough power to drive them all.
Distortion is proportional to excursion, so yes, there's a big difference. High sensitivity systems require less excursion to reach the same output levels, so they also have less distortion.
Quote:
Well, unless you've plotted a couple score at random it's anecdotal.
Hardly, this is well known acoustical engineering fact dating to the 1960s.
Quote:
Even given that: what's the formula? For every 3db of efficiency the point of distortion drops 5%? What do your measurements indicate and what is your sample-set (and actually: I'm a little curious to methodology; but that's less important
Read this, and parts 2 & 3, plenty of math there be:

http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_1.pdf

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post #368 of 824 Old 11-29-2012, 02:06 PM
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Originally Posted by Bill Fitzmaurice View Post

Distortion is proportional to excursion, so yes, there's a big difference. High sensitivity systems require less excursion to reach the same output levels, so they also have less distortion.

So then ribbon tweeters never ever distort and my JL 10W7 runs in constant distortion (since it has a common excursion orders of magnitude higher)?

Of course not. While you may be referencing something valid, what you are actually saying (in the context of what you are responding to) is that we can measure the distortion of speaker X if we know it's excursion and nothing else. That's simply not true.

Also worth noting: the person you are agreeing with tied distortion to sensitivity. You are now tying distortion to excursion.

So unless excursion can be derived from sensitivity; you are contradicting one another.

I will after dinner.
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post #369 of 824 Old 11-29-2012, 03:29 PM
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OK. Your article discusses two distortions.

FM distortion occurs when a driver is putting out two different frequencies and a Doppler shift is caused on the higher frequency by the movement of the other.

I would have thought that this was already dealt with via the combined waveform, but regardless it is not effected by speaker efficiency nor excursion and so does not interact with either of those claims and so must not be what you are talking about.

AM distortion: your author says that it's long known and never proven that higher efficiency = lower AM distortion; but then your author goes to great pains to say is "unfinished" and "tentative" don't bear out your claim either.

Then we get to Table 1, where is 10" and 15" drivers have the same SPL (since that's not a constant of the table, I can only assume it's the result of sensitivity), but significantly different distortions.

None of which even beings to touch on cone breakup causing distortion. http://www.diyaudio.com/forums/multi-way/58817-cone-breakup.html

It's also possible that the understanding has improved in the 45 years since Mr.Klipsh wrote this paper which concluded that horns were superior to other speaker types.
It's not likely coincidence that he made is living selling horns.

Others in the same industry (like say, Dr.Toole) failed to reach the same conclusion in their own designs.
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post #370 of 824 Old 11-29-2012, 03:53 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Distortion is proportional to excursion, so yes, there's a big difference. High sensitivity systems require less excursion to reach the same output levels, so they also have less distortion.
Hardly, this is well known acoustical engineering fact dating to the 1960s.
Read this, and parts 2 & 3, plenty of math there be:
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_1.pdf
You may wish to reconsider the significance of that article. Richard Pierce wrote in Google groups (https://groups.google.com/forum/m/?fromgroups#!search/Pierce$20Klipsch$20distortion$20modulation/rec.audio.tech/zAv6xhT-MfU) the following.
Quote:
In article <4qhbk5$3...@ase.ase.com>, Tim Brown wrote:
>In article <31C87A...@bmts.com>, "L. Van Wormer" wrote:
>>I've been building speakers for a while now, and listening to many others. A
>>question I thought I'd post here: why does it seem to be that the larger a
>>speaker is, the louder it will play cleanly?
>>
>>I suspect, but certainly don't know, that the drivers start to distort with
>>very little displacement, well within the range that is supposedly linear.
>>If so, does anyone have data on which makes of drivers are best in this
>>respect? (I have certainly heard most of the conventional types, but none of
>>the "short voice-coil, long-gap" types, are they better in this respect?)
>>
>>Has anyone conducted experiments, or seen any records of such, that address
>>this point?
Yes, LOTS of people have conducted experiments.

>Larger speakers have more radiating area and suffer less displacement for a
>given acoustic power output. Displacement produces modulation distortion, even
>if the voice coil "motor" and suspension are perfect. Speaker manufacturers
>and reviewers talk little about modulation distortion because the picture is
>not pretty and there is only two solutions: a bigger radiating area and
>breaking the spectrum into smaller segments (multi way system). This is where
>electrostatic and horn loaded speakers excel. Check AES articles from the '60s
>and '70s by Paul Klipsch.
To balance the issues, I would also recommend checking out articles from
the AES journal in the 80's by Allison and Villchur which do a fairly
good job of debunking Klipsch's claims. Klipsch demonstrably used a set
of completely unrealistic criteria for his claims. For example, from one
of Allison's articles ("Magnitude and Audibility of FM Distortion ni
Loudspeakers," JAES 1982 Oct), we read:

   "Pure tone and square-wave signals at 1026 Hz were used by Klipsch
   on a tape machine with an offset capstan to produce what Vilchur and
   Allison calculated as 0.7% rms unweighted flutter (Klipsch stated that
   the flutter was 0.35% rms, but this appears to us to have been the
   result of miscalculation) at rates of 10, 20, and 40 Hz. Klipsch
   reported that the flutter modulated tone was unpleasant at the 20 Hz
   flutter rate and extremely irritating at 40 Hz. To produce the same
   amount of FM sideband distortion in the reverberent field of a
   listening room, a loudspeaker would have to execute very large peak-
   to-peak cone excursions: 3.8 in. (96.6 mm) at 20 Hz or 1.9 in (48.3
   mm) at 40 Hz, and masking by the low-frequency tone would make the
   flutter less audible than that produced by the eccentric tape cap-
   stan.

In other words, to reach his conclusions, Klipsch first miscalculated the
amount of flutter present in his tests by a factor of two, then chose a
flutter condition that simulated the "modulation distortion" occuring when
the cone was being asked to move a factor of TEN greater than any cone in
the history of loudspeakers was ever asked to do, then further skewed the
results by selecting a test signal that would be impossible to produce in
ANY loudspeaker: he only played a 1 kHz tone: without the huge amounts of
low frequency present to "modulate" the high frequency, no high frequency
modulation could take place. If it WAS there, the low frequency tone
required to produce his results would have so overwhelmed the high
frequency sidebands as to render them inaudible, indeed, those low
frequency tone that Klipsch was simulating would possibly be loud enough
to render the listening panel deaf.

Allison's and Villchur's listening experiments are far more revealing than
Klipsch's, since Klipsch spent little effort in eliminating the hug biases
due to experimental error, such as those described above. His
comp[arisons, for example, between HIS commercial horn systems and other
speakers were done with little or no effort expended to correct the fact
that the sound of these systems is fundamentally different for reasons far
more significant than modulation distortion, such as gross frequency
response, bandwidth and dispersion differences. It's further interesting
to note that in listening performed where modulation distortion was
simulated using an electronic delay line where the clock frequency was
varied by taking a low-passed control signal from the audio signal itself
(which is a far more realistic test than the flawed and imple-minded test
Klipsch used), the horn system was simply NOT revealing of huge amounts
of such distortion that was readily audible on other systems, suggesting
that the horn systems have significant distortions of their own that were
effectively masking large amounts of sideband distortion.

--
|                Dick Pierce                |
|     Loudspeaker and Software Consulting   |
| 17 Sartelle Street   Pepperell, MA  01463 |
|       (508) 433-9183 (Voice and FAX)      |
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post #371 of 824 Old 11-29-2012, 04:36 PM
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Quote:
Originally Posted by Chu Gai View Post

You may wish to reconsider the significance of that article.
No need, as I confirmed for myself its accuracy by measuring the distortion of every speaker I've designed/built for the last twelve years or so. That number is well over one hundred.

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post #372 of 824 Old 11-29-2012, 04:50 PM
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Originally Posted by Bill Fitzmaurice View Post

No need, as I confirmed for myself its accuracy by measuring the distortion of every speaker I've designed/built for the last twelve years or so. That number is well over one hundred.
And you confirmed Klipsh's claim that less sensitive always equals greater AM distortion, or you confirmed Table I which showed two speakers with the same sensitivity and different distortion.

How did almost the entirety of the audio world miss this; going so far as to move *away* from high sensitivities like horns? Revel, Focal, HK, McIntosh, B&W, Paradigm, Pioneer, Sony, Kenwood, Yamaha, Onkyo, Walsh, Kef, PSB, SVS, EMP, Emotiva, Lexicon, Mark Leavinson, Magipan, Martin Logan, ad nauseum?

For that matter: how have the major recording studios not cared all this time?
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post #373 of 824 Old 11-29-2012, 04:51 PM
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How do you reconcile Allison and Vilchur's findings which call into question Klipsh's paper as well as Pierce's findings that when distortion products were intentionally introduced, the horn based system was found not to be as audible revealing compared to other speakers. Perhaps you're overlooking something. Certainly, to my mind, it would be poor science to hold up Klipsh's paper as definitive when subsequent research calls its findings and calculations into question. I can probably get a hold of that paper if you don't have it.
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post #374 of 824 Old 11-29-2012, 04:54 PM
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Wow, some of you guys really are sensitive. I am not proving anything. I don't trust specs, I measure and see what is actually happening. When a speaker says It can handle 1000 watts and play a certain level and instead it reaches a peak and never gets louder. You then measure what is going on and the response it just compressing. Then you measure the THD and that is what is getting higher. I am not tying anything with anything. Just because in theory they should be the same the higher sensitivity speaker still gets louder and does not compress. Of course not every 1000 watt speaker will compress at the same level and the same goes for HE speakers. Again, the best dynamic speaker I have heard happens to be the highest in sensitivity. This is for the same reference level peaks. Of course I am just talking dynamics and nothing else. Coincidence? Maybe.
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post #375 of 824 Old 11-29-2012, 05:42 PM
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Quote:
Originally Posted by JerryLove View Post


How did almost the entirety of the audio world miss this; going so far as to move *away* from high sensitivities like horns? Revel, Focal, HK, McIntosh, B&W, Paradigm, Pioneer, Sony, Kenwood, Yamaha, Onkyo, Walsh, Kef, PSB, SVS, EMP, Emotiva, Lexicon, Mark Leavinson, Magipan, Martin Logan, ad nauseum?

WAF?
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post #376 of 824 Old 11-29-2012, 07:26 PM
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Originally Posted by zheka View Post

WAF?
Cheap watts, actually. Don Keele spelled it out 40 odd years ago when 200w SS amps started appearing on the scene. In a nutshell he said if you have more time than money build a horn, if you have more money than time buy a direct radiator and a big amp to power it with. But that was long before anyone dreamed of playing at reference, especially since the term had not yet been coined and subwoofers were yet to be invented, nor DVDs. Not even Betamax. mad.gif
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post #377 of 824 Old 11-29-2012, 07:58 PM
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Makes sense. smaller speakers are also easier to sell. There is no place for speakers with 12" woofer in a typical living room.
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post #378 of 824 Old 11-29-2012, 08:48 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Cheap watts, actually. Don Keele spelled it out 40 odd years ago when 200w SS amps started appearing on the scene. In a nutshell he said if you have more time than money build a horn, if you have more money than time buy a direct radiator and a big amp to power it with. But that was long before anyone dreamed of playing at reference, especially since the term had not yet been coined and subwoofers were yet to be invented, nor DVDs. Not even Betamax. mad.gif
That must be it.

When Abby Road studios decided to go mostly Bowers and Wilkins for all the new Rock they were producing; they must have lacked money and had no desire to play anything at elevated volume.

Heaven knows, as a child of the 80s, we never played anything loud during the punk era either. And low frequency? At the dawn of Rap and Club? Naw.

I think when Roger Russel starts discussing his entry into Loudspeaker design by mentioning "the Thirteenth AES Convention in October 1961 titled "Distortion Measurements of High Frequency Loudspeakers." ", That indicates that he too had no real interest in studying distortion, considering it irrelevant. In fact, "distortion" appears a mere 23 times on his 2-page description of the McIntosh loudspeaker division ("resonance" 3 times and "breakup" once)

" The first was a distortion versus power test at a frequency of 25.7Hz, A4 on the music scale. Power measurements were made up to 100 watts, or until the speaker distortion exceeded 30%. The second was a low frequency response curve of the woofer from 25Hz to 500Hz. The third was an impedance curve from 20Hz to 20kHz. When McIntosh speakers were tested, the required equalizer was used and response continued within 1 dB right down to 25Hz, the lower limit of the graph." - Roger Russell

100W sweep from 25Hz-500Hz. Don't know what he was using, but as this was 1972, most of the gear they put out was 89db efficient. (they were putting *4* 12-inch woofers in some of their cabinets.

Which reminds me suddenly of my favorite from the 1980s: Six servo-controlled woofers. You know I have it's little brother here at my house.

Thanks for clearing that up. It's why dead-heads have such good hearing. They didn't play loud; and by the time we started to we had forgotten what everyone knew.

Seriously though: I think this conversation is going nowhere and am moving on.
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post #379 of 824 Old 11-30-2012, 04:01 AM
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Send a message via Skype™ to popalock
Thanks all for weighing in.

This is the conclusion I have drawn:

With out amplification limitations, the same performance (output) can be achieved from similarly "capable" speakers regardless of sensitivity.

I guess that is what I'll take away from all of your input. Didn't mean to hi-jack or start a flame war. Great discussion though guys.

 

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post #380 of 824 Old 11-30-2012, 05:16 AM
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Because it's back to the OP, and because I'm hoping it will do more to *not* reignite the feud that ignite it:

Individual speakers are going to be individual. If you are concerned about distortion being an issue: find out of the speakers that interest you distort heavily at the volumes you intend to play them. No matter who is right on the general rule: having accurate data on the specific speakers you are looking at will not lead you astray.

I would really like to believe that people on both sides of this debate can agree with that.
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post #381 of 824 Old 11-30-2012, 06:47 AM
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Quote:
Originally Posted by popalock View Post

Thanks all for weighing in.
This is the conclusion I have drawn:
With out amplification limitations, the same performance (output) can be achieved from similarly "capable" speakers regardless of sensitivity.
I guess that is what I'll take away from all of your input. Didn't mean to hi-jack or start a flame war. Great discussion though guys.
it depends on assumptions behind the 'similarly "capable"' qualification. If sensitivity gap between the two speakers is the same across the full bandpass, then this maybe correct (leaving the distortion issue aside). But this of course is almost never the case.
As Bill has mentioned before, the sensitivity ratings are often misleading.
Quote:
"Between not accounting for thermal and mechanical power compression and driver excursion limits calculated maximum SPL figures can easily be overstated by 6dB or more, a lot more if the sensitivity quoted was measured at 1kHz or higher, rather than a much more honest 100Hz.".

This is also something Drew Eckhardt has posted a great deal about
e.g.
Quote:
Originally Posted by Drew Eckhardt View Post

For most practical purposes quoted low frequency extension is only a marketing number since it may not apply to the output levels you're interested in. A speaker that's "flat" to 40Hz may lack the displacement (product of driver size and how far they move in and out) to play comfortably down to 120Hz.
.....

Size is the nominal marketing size (cone speakers are usually sold according to their mounting flange dimensions, and manufacturers often embed this in the part number with the Seas W22EX001 being a 22cm driver), Sd effective radiating area of the cone, and xmax about how far it can move one way before the motor looses strength which makes distortion go up.

Size Driver Sd (cm^2) x xmax (mm) 120Hz 80Hz 40Hz 20Hz
4 1/2" Seas W12CY001 50 x 3 89dB 82dB 70dB 58dB
5 1/4" Peerless 830873 88 x 3.5 95dB 88dB 76dB 64dB
6 1/4" Seas L16RN-SL 104 x 6 101dB 94dB 82dB 70dB
7" Seas W18EX001 126 x 5 102dB 95dB 83dB 71dB
8.5" Seas W22EX001 220 x 5 106dB 99dB 87dB 75dB
10" Peerless 830452 352 x 12.5 118dB 111dB 99dB 87dB
12" Peerless 830500 483 x 12.5 121dB 114dB 102dB 90dB

Where a pleasant -10dB from Dolby reference level with dialog at 64dB SPL implies 91-95dB peaks at your listening position and perhaps 97-101dB at the speaker many consumer market 2-ways are likely to have problems with an 80 Hz cross-over.
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post #382 of 824 Old 11-30-2012, 07:08 AM
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Quote:
Originally Posted by popalock View Post

Thanks all for weighing in.
This is the conclusion I have drawn:
With out amplification limitations, the same performance (output) can be achieved from similarly "capable" speakers regardless of sensitivity.
Output, yes. Distortion, not necessarily. One of the flaws intrinsic to uber long stroke high power drivers is they will exhibit far higher distortion than either horn loaded drivers or a large grouping of drivers that can deliver the same total displacement while running with less excursion. Four drivers running with 5mm excursion will sound a lot cleaner than one of the same size running with 20mm excursion. And as a grouping of four drivers will have 12dB higher voltage sensitivity, or wired series/parallel 6dB higher power sensitivity, than a single driver with equivalent specs the four driver rig also has higher sensitivity, so the relationship between clean effortless output and sensitivity remains.
Another (I believe) unaddressed factor is the physical size of the speaker. By their nature high efficiency speakers, be they horns or grouped direct radiators, are big. That physical size alters their radiation patterns, and the result is that they sound, for lack of a better term, big.

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post #383 of 824 Old 11-30-2012, 07:22 AM
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I guess I lied on this one and am not yet staying away. Sorry.

So I have a speaker with no baffle at all (not sure that's possible at the highest frequencies; but we can look only below a certain hz if it makes everyone happy).
Now I shove that speaker in a wall and move from zero baffle to infinite baffle. The speaker just got 6db more sensitive. Does anyone here believe that distortion suddenly went down at the same power level?

So I build a speaker with a FR 50hz-20khz @96db efficient.
I realize that I am -9db @35hz, so I use the crossover (active or passive) to introduce -6db above 50Hz.
Now my speaker is 90db efficient but "flat" from 35Hz-20khz.

Does anyone believe that my crossover taking away efficiency has made the drivers distort more?
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post #384 of 824 Old 11-30-2012, 07:51 AM
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WE are talking increased THD when driven too hard. If you run any speaker within its power band it will be fine. It is harder to overdrive a HE speaker because the levels become insanely loud but still clean. I love those B&W 802D's and they would be awesome in my living room, in my theater they won't play loud enough without compression.
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post #385 of 824 Old 11-30-2012, 08:07 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Output, yes. Distortion, not necessarily. One of the flaws intrinsic to uber long stroke high power drivers is they will exhibit far higher distortion than either horn loaded drivers or a large grouping of drivers that can deliver the same total displacement while running with less excursion. Four drivers running with 5mm excursion will sound a lot cleaner than one of the same size running with 20mm excursion. And as a grouping of four drivers will have 12dB higher voltage sensitivity, or wired series/parallel 6dB higher power sensitivity, than a single driver with equivalent specs the four driver rig also has higher sensitivity, so the relationship between clean effortless output and sensitivity remains.
Another (I believe) unaddressed factor is the physical size of the speaker. By their nature high efficiency speakers, be they horns or grouped direct radiators, are big. That physical size alters their radiation patterns, and the result is that they sound, for lack of a better term, big.

Ok, so let's narrow this down further.

- 1 Driver vs 1 Driver
- 8" Radiator
- Same general design used for the same general purpose
- Different sensitivity ratings
- Same (or very similar) THD measurement for each speaker
- Both playing 500Hz producing 122db of output.

Would that be enough to narrow it down to "amplification needed" to power each speaker to reach that output level?

Thanks guys, I'm soaking all of this up the best I can! Not my intent to derail the thread.

 

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post #386 of 824 Old 11-30-2012, 08:53 AM
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Originally Posted by zheka View Post

Makes sense. smaller speakers are also easier to sell. There is no place for speakers with 12" woofer in a typical living room.

NONSENSE!!! biggrin.gif
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post #387 of 824 Old 11-30-2012, 09:30 AM
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Quote:
Originally Posted by MKtheater View Post

WE are talking increased THD when driven too hard. If you run any speaker within its power band it will be fine. It is harder to overdrive a HE speaker because the levels become insanely loud but still clean. I love those B&W 802D's and they would be awesome in my living room, in my theater they won't play loud enough without compression.

Can you help me reconcile your above 'fine within its power band' statement with your below comment?

Quote:
Originally Posted by MKtheater 

In reality there is [a difference between a hypothetical 90db efficient 100w speaker and a hypothetical 80db efficient 1000w speaker], it has to do with how each speaker stays linear, no compression, etc... near it's limits.

I didn't state power driven, but the inference from the question I answered should have been "both driven at the same N% of max"
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post #388 of 824 Old 11-30-2012, 09:33 AM
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Quote:
Originally Posted by popalock View Post

Ok, so let's narrow this down further.
- 1 Driver vs 1 Driver
- 8" Radiator
- Same general design used for the same general purpose
- Different sensitivity ratings
- Same (or very similar) THD measurement for each speaker
- Both playing 500Hz producing 122db of output.
Would that be enough to narrow it down to "amplification needed" to power each speaker to reach that output level?
Thanks guys, I'm soaking all of this up the best I can! Not my intent to derail the thread.
If they have differing sensitivity then the driver with lower sensitivity will have to be driven to a longer excursion for the same dB level, and therefore will have higher THD.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
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post #389 of 824 Old 11-30-2012, 10:00 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

If they have differing sensitivity then the driver with lower sensitivity will have to be driven to a longer excursion for the same dB level, and therefore will have higher THD.

I'm pretty sure that SPL is a direct function of surface, excursion, and frequency and that sensitivity has nothing to do with it.

A driver of A surface area moving B distance at C frequency will put out D SPL (yes, there can be issues of cone breakup or such, but that's not efficiency either).

If to drivers are otherwise identical (8" direct-radiating CMMD cones, for example), their excursion at a specific spl+frequency combination is a fixed number without regard for their overall efficiency. (for example: if I lower my efficiency by making my cone physically heavier; I still have the same extension for the same SPL)

To be specific:
SPL = 112 + 10 * log(4 * pi^3 * Ro / c * (num * Vd)^2 * f^4)
Vd = (.83 * diam)^2 * pi / 4 * Xmax

There are things that would change that math, which might also change sensitivity at the same time (baffle or waveguide, ported enclosures, TLs, etc); but they would change equally regardless of the sensitivity.
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post #390 of 824 Old 11-30-2012, 10:34 AM - Thread Starter
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Quote:
Originally Posted by popalock View Post

Quick question for you guys.
I don't know the exact definition if "dynamic capabiliy," ...

Dynamic Capability would be:

  • Whether the speaker can provide the "dynamics" of the program. This is the changes in volume in music or a soundtrack.
  • Analogous to the video world, where if you have a lowest light level of some "blackish," how many times brighter can the display get? 100? 500? 5000?
  • And even given that ratio, are we happy if it doesn't get "bright" (loud) enough for the application? Film might be 12-16 foot-lamberts. But other applications like sports might require more.
  • Similarly, while we could technically say that any weak speaker that can provide the 20dB swings from average to peak levels has that 20dB "dynamic capability" (contrast level), I think it's understood that it's meant "has dynamic capability that's more difficult to obtain: at higher absolute output levels in SPL." So, while any speaker can provide 20dB swings at some volume level, only some speakers can do so where the average level is 80dB and the peaks are at 100dB at the listening position.
  • This should include the "quality" of the dynamics: does the distortion rise to noticeable/objectionable levels on those content peaks?
  • This can be achieved by either higher efficiency or higher power handling.

 

It's like subwoofers

Probably more intuitive than video is subwoofers. We can argue all day about which sub was more musical and had those owner/marketing/home_theater_mag attributes of "pounding," "dynamic," "palpable," "room-filling," "thunderous," etc. But those are all subjective, relative terms; they have their place, but they convey limited meaning to me.

 

The sub that a reviewer loved in her room might only achieve 105dB max at 12 foot distance. If she's listening at -10dBFS to film soundtracks, that peak output might be enough, as long as:

  • distortion didn't rise to objectionable levels
  • all the desired frequencies are at that level of 105dB (recognizing that LF is exponentially difficult to attain as you go down, so there has to be a user goal of 10Hz, 20Hz, 30Hz, etc.)

If the above aren't met, I'd suggest that sub was not dynamically-capable enough for her application.

 

Someone else might need to listen at -20dBFS and can get by with less sub. Someone else will want -0dBFS or even +5dBFS, and thus they need 115dB or 120dB at their seats.

The latter require a more dynamically capable sub(s).

 

Can a small-diameter driver provide the required bass? Maybe, but there are tradeoffs in output, extension, box size, distortion, amp requirement, etc.

Can a low-efficency driver provide the required bass? Maybe, but there are tradeoffs.

 

Speakers

As Bill explained, if the speaker has been pushed at a high average level and then is asked to provide a big peak, it'll have more trouble than if the driver was cooler. A hot voice coil has a different resistance than a cold one.

 

Just like everything else: engines, people, trampolines: speakers perform better when not operating at their absolute limits.I can lift some maximum weight only a few times before I'm spent. If you need a hundred heavy rocks to be moved by hand, you'd better choose a guy who can lift much heavier rocks easily. Don't choose me, who can barely move one of those rocks once.

 

Thermal Compression - average levels

While a speaker manufacturer may claim that the model can handle 100w RMS, there is in fact distortion at some fraction of that number. 10w may yield .5dB compression/distortion. 50w may yield 2dB compression/distortion on your average levels if there's a long passage of demanding music, for instance. You have to decide if that's acceptable, or would you rather the speaker were loafing because it can handle 300w RMS, so the application workload requires a smaller percentage effort. Or find a higher efficency speaker.

 

Magnetic / Physical Compression - peak levels

And then, regardless of what the continuous average levels are doing to the speaker, you have peak limits in even best case scenarios of cold voice coils. The magnetic field will behave differently depending on the excursion. There are magnetic flux eddy currents. The speaker's max power handling may be "don't feed more than X watts in a .5 second peak or else ABC type distortion will rise beyond what we deem an acceptable 10%," but more likely it's "don't feed more than X watts in some peak or else the speakerer will break." I believe the experts say that some fraction of X peak watts will still yield objectionable distortion.

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