Midbass punch: spl, voice coil heating and Bl linearity - AVS Forum
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post #1 of 56 Old 03-09-2014, 12:45 PM - Thread Starter
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A bit ago, I was chatting with Matt and this topic was hit on a bit. It also seems to be an active topic in a couple other threads. I thought I'd bring about the question here and see if we can get an interesting discussion, and hopefully measurements on this topic.


The thought game is this: If you take the new Fusion-6, Tux-1099, and Sentinel and calibrate them all to 75db pink noise and EQ to a flat response, and then do an impulse response with each of these (100 Hz to 250 hz) at +20 db, how would they compare? By impulse, I mean something like gun fire or bass drum: loud, and quick in transient..the thump in your chest midbass. In theory, you may say that if they all have the exact same frequency response, and are all calibrated to play the same intensity, they should sound identical....but they won't.

In practice, how does Bl and thermal compression through VC heating come in to play? If you send a +20 db signal to each of those speakers, what do you actually get (this is where measurements, not theory come in to play. I don't have the means to do so, but one of you may). Vd is not the same for all the woofers, and the smaller ones need more travel, extending further down the Bl curve where efficiency drops. Likewise, thermal non-linearities in the coil will suppress excursion.

...how much midbass punch would each of these woofers lose to these effects? If you put in +20 db, does the sentinel produce +19 db, the tux-1099 produce +17 and the karma-6 produce +15? (I made those numbers up).


/discuss
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post #2 of 56 Old 03-09-2014, 01:18 PM - Thread Starter
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Here is some additional reading material

http://sound.westhost.com/articles/pwr-vs-eff.htm
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post #3 of 56 Old 03-09-2014, 01:19 PM
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I've never heard two speakers or amps that have ever sounded the same. But that could just be me (I've never subjected myself to a blind shootout).

That said, I wouldn't be able to tell you which field the wine was in made or the types of grapes used, but I could tell you the difference between wine and grape soda or cola. LOL biggrin.gif

I would expect the one with the highest combination of power handling, highest sensitivity and beefiest woofer config, to make the loudest bass and upper bass, beyond that, all else being equal, it shouldn't be "vastly" different. +-5db say.
(Assuming the crossover and box isn't doing something funky or special.)

My 2 cents.
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post #4 of 56 Old 03-09-2014, 01:26 PM - Thread Starter
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I think you completely missed the message :-D
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post #5 of 56 Old 03-09-2014, 01:42 PM
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Quote:
Originally Posted by Anthony_Gomez View Post

.how much midbass punch would each of these woofers loose to these effects?
Hard to say without data. Some manufacturers do put power compression charts on their data sheets, Beyma is one.

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post #6 of 56 Old 03-09-2014, 02:06 PM
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This is intereresting, will follow smile.gif
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post #7 of 56 Old 03-09-2014, 02:39 PM
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Sound on Sound did an article on just this quite a while ago, I will see if I can dig it up.

"You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes."
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post #8 of 56 Old 03-09-2014, 02:42 PM
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Here's the article entitled Monitors vs HiFi speakers.

http://www.soundonsound.com/sos/Jul02/articles/monitors2.asp
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post #9 of 56 Old 03-09-2014, 03:05 PM - Thread Starter
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Thanks. I'll give it a read. The link I posted earlier is a solid read and hope this is too smile.gif
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post #10 of 56 Old 03-09-2014, 03:18 PM
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Midbass punch/slam/kick.
There is a bit of magic to it I suppose.
From research I've done on the subject, you will get this tactile feel mostly between 50hz to 200hz. Though even tweeters can give a punchy sort of feel.
For a midbass driver, my research shows that you want a light cone. And a QTS below .50, QMS that is higher than not and a low FS.

Four of the Dayton DA175 8" midranges per side are said to provide excellent midbass punch. Even though the parameters don't really match up with what I suggested above.
http://www.parts-express.com/dayton-audio-da175-8-7-aluminum-cone-woofer--295-335

edit: I think I missed the point of the thread also. Sorry. I'm too sick ATM to really pay attention to what I'm reading. smile.gif

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post #11 of 56 Old 03-09-2014, 04:30 PM
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Quote:
Originally Posted by michael hurd View Post

Here's the article entitled Monitors vs HiFi speakers.

http://www.soundonsound.com/sos/Jul02/articles/monitors2.asp

The problem is that they focus on the wrong parameters.
Thermal effects will affect macro-dynamics - louder passages will eventually sound less loud when the vc heats up.
Transients, which is what the physical impact is about, is not much affected by thermal properties because the effects have a relatively long time constant compared to the duration of the transient.

What is a very significant parameter is compression due to limited output capacity.
These bookshelf-speakers are really not even suited as satellite speakers if you want to play music at a realistic spl.
If you look at the pictures, you see a range of what is more or less the same - small speaker with small woofer.
Regardless of what is claimed these can never play loud with realistic impact.

I did some measurements when playing music at different levels, and this shows that transient peaks are often 30dB above measured rms level.
(Article with measurements and very nice graphs on my blog.)

That means you would need 110dB capacity to play 80dB.
Do you think a 8" woofer can do 110dB down to, say, 80Hz?
Not even close..

Some time ago, all studios had real speakers with 15" or bigger woofers, think JBL 4350 and alikes - speakers that has great output headroom, but there is more to it - they also had what can be called dynamics.
Then someone got the idea that you can use a small plastic box with tiny woofers instead, and now all studios have these bookshelves they call "near-field-monitor".

This is one of the reasons why todays music is totally devoid of real impact and slam - the microdynamics of the music - how loud a single transient is compared to the simultaneous rms level.
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post #12 of 56 Old 03-09-2014, 05:44 PM
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I'm going to try to keep up with the Smart Guys in this discussion, but with change of weather has brought me a massive head cold, and I'm finding it hard to think critically and deeply right now.

I think the topic is interesting, but flawed because of all the other variables, in particular electronics and the "listening modes" of most modern AVR's. Unless you simply compare a single speaker A vs a single speaker B with almost no electronics in between, I don't see how a reasonable conclusion can be reached.

In addition, what is being compared is charts and graphs against each other. Someone please correct me if I'm wrong, but no matter how the charts and graphs are made, there isn't a chart or graph which can give you SOUND QUALITY, ie, does a piano really sound like a piano when played through speaker X (X, the unknown).

To me, there are two basic types of speakers; those that sound good, and those that are accurate. They are not necessarily the same thing.

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice
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post #13 of 56 Old 03-09-2014, 05:54 PM
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Quote:
Originally Posted by Okv View Post

The problem is that they focus on the wrong parameters.
Thermal effects will affect macro-dynamics - louder passages will eventually sound less loud when the vc heats up.
Transients, which is what the physical impact is about, is not much affected by thermal properties because the effects have a relatively long time constant compared to the duration of the transient.

(respectful SNIP!)

This is one of the reasons why todays music is totally devoid of real impact and slam - the microdynamics of the music - how loud a single transient is compared to the simultaneous rms level.

I highlighted "todays music" because I think you are 100% right. Good music, to me, has dynamics in it. I'm not sure I hear any dynamics at all in music played on the radio (which I rarely listen to), and the little bit you do hear is heavily compressed. You almost always hear dynamics in symphonic music, some in jazz, but almost none in pop or rock music.

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice
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post #14 of 56 Old 03-09-2014, 06:03 PM - Thread Starter
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wvu80, while both those posts have interesting points, they fall well outside the scope of the OP smile.gif
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post #15 of 56 Old 03-09-2014, 06:06 PM
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Quote:
Originally Posted by wvu80 View Post

I highlighted "todays music" because I think you are 100% right. Good music, to me, has dynamics in it. I'm not sure I hear any dynamics at all in music played on the radio (which I rarely listen to), and the little bit you do hear is heavily compressed. You almost always hear dynamics in symphonic music, some in jazz, but almost none in pop or rock music.
What is "todays music"?

Is it pop rock? in which "loudness" seems to most important frown.gif

What about EDM? The most growing segment of music

Is it country? Which is basically 70s southern rock

Is it rap?

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post #16 of 56 Old 03-09-2014, 06:32 PM
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Anthony, are you thinking outdoors, or in a typical ht? If in a HT with reflections, mid bass performance is heavily influenced by the room, which means it'll be heavily influenced by the amount of eq required. For instance, if the smaller speaker only requires 1db boost at 150hz whereas the sentinel requires 20db (major exaggeration) then I'd put my money on the Fusion 6 actually.

Having said that, if we don't consider the room, then we should revise the scope to say the anechoic responses are eq'd the same. In that case, these are the subjective differences I would expect.

The smaller speaker's mid bass will sound more punchy, but have less impact. Yes, more punchy. This is cause the upper range will dominate, AND some harmonic distortion will contribute. HD is higher in frequency which have kind of a smack/punch sound.

The larger more capable woofers are going to sound more natural and easy going. Eq'd the same they may even sound a little unimpressive. The little woofer will have that "oh wow that's a lot of sound from such a tiny thing" kind of effect but the big woofer is going to be doing the job with ease meaning it'll sound clear and natural without strain.

Ok, so I don't actually have any personally done power compression measurements for any woofers handy, just dome tweeters. Based on that experience the HD does increase at the lower end of the drivers pass band, contributing to greater overall output. Yes, the tweeters I've measure out out MORE sound at high SPL in the lower ranges. This is why I said the small woofer will actually impress at first. The problem is, the added sound is all garbage and shouldn't be had.

I haven't personally done klippel measurements, but the ones I've seen have always showed a roll off of BL at the limits of excursion. So its safe to infer that the woofer would play the higher frequencies in accurately while excursion is at the limits while playing loud mid bass.

Finally. The bigger woofers have larger voice coils, therefore its safe to infer that they would keep their voice coil temperature more evenly regulated, thus more uniform mid bass output during long and loud listening sessions. Two woofers means two voice coils which is a significant advantage there.
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post #17 of 56 Old 03-09-2014, 06:59 PM
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Bose 901 series speakers. Filled with ten 4" full-range drivers.... gave some nice dynamics.
http://www.stereophile.com/standloudspeakers/425/

My next speaker build will be filled with several small midbass speakers rather than one large 12" or 15".

"The boom is dead, long live the bass"
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post #18 of 56 Old 03-09-2014, 07:34 PM
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I am sorry about the OT music-comment, I think my point also was lost somewhere because of that.

So, what can, and what can not cause differences in midbass punch, when looking at bass driver properties only.

Thermal issues are not significant because of the too long time constants involved.
The "punch" lasts only a few milliseconds, it takes in the order of seconds to heat or coll the voice coil.

Bl and excursion limits is what limits the output, for a given radiating cone area.
Longer excursion before Bl is lost equals more punch.
More cone area equals more punch.

To reproduce a transient signal there must be sufficient spl capacity to reproduce the full amplitude of the original signal.
If, say, 3db is lost, there is a loss of punch.
This is not something that one necessarily can hear as distortion, because it happens in a very short time interval.

The attached picture shows the waveform of music with a drum hit.
The upper graph is the original, directly from the source.
The lower graph is recorded at the listening position using a microphone.
The signals are clearly different, but in this case one can recognize the shape of the original drum hit in the recorded signal.
That is also how it sounds - or, rather, it doesn't sound, it just hits.
If the top of the impulse is cut off, there will be no impact but it will not necessarily sound bad or wrong.

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post #19 of 56 Old 03-09-2014, 08:19 PM
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Quote:
Originally Posted by Anthony_Gomez View Post

wvu80, while both those posts have interesting points, they fall well outside the scope of the OP smile.gif

I apologize, I was wondering if I had mis-understood what the OP was asking. I had been pondering the sound quality issues recently. I guess I just rolled my ideas into the closest thread. rolleyes.gif

Thank you for straightening me out. "He who corrects my mistake giveth me a gold coin." smile.gif

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice
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post #20 of 56 Old 03-09-2014, 08:35 PM
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Quote:
Originally Posted by Ivan Beaver View Post

What is "todays music"?

Is it pop rock? in which "loudness" seems to most important frown.gif

What about EDM? The most growing segment of music

Is it country? Which is basically 70s southern rock

Is it rap?

Hah! Thanks for me calling me on that, as you are right, of course. biggrin.gif Country music really is pretty good music, good vocals, good arrangements, I'm just not a big fan. Not a fan of EDM (I'm old enough to remember and have hated disco), no rap, no dub step, no grunge, no hip hop, and NO Justin Bieber!

Since I am old, I therefore define "modern music" as anything later than the 60-70's rock, not jazz and not classical. smile.gif
(there really is some good modern symphonic music, Bernstein, Copeland, John Williams, Zimmer, movie theme types of things)

Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice
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post #21 of 56 Old 03-10-2014, 12:59 AM
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I stumbled upon this link somewhere (not here, I think?):

http://dr.loudness-war.info/

It's a pretty cool database of the dynamic range of many(!) different pieces of music / albums smile.gif
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post #22 of 56 Old 03-10-2014, 05:21 AM
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Lots of good points and references here. Dynamic headroom requirements are often snubbed in most systems in favor of a smaller speaker size. There is no replacement for adequate displacement. 30dB transients require a system capable of not compressing with a power load 1000x that of RMS. This is not trivial. Most of the films with the highest dynamics out there have +30 to +33dB transient phenomena, with overall SPL peak demand of over 125dB for transients, and 114-118dB for longer duration sounds (125ms or longer), with a 7.1 configuration at reference level. No small feat.

JSS
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post #23 of 56 Old 03-10-2014, 05:53 AM
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Quote:
Originally Posted by Anthony_Gomez View Post

A bit ago, I was chatting with Matt and this topic was hit on a bit. It also seems to be an active topic in a couple other threads. I thought I'd bring about the question here and see if we can get an interesting discussion, and hopefully measurements on this topic.

Interesting idea. I'm not sure that measurements are as helpful here as controlled subjective preference tests. Something like what Tux described earlier: two speakers, different cone area and perhaps volume displacement*, equalized to the same anechoic response. Even better would be similar horizontal polars, though that's really hard to do for obvious reasons.

*Vd needn't be that different. Consider the case of twin Exodus/DIYSG Anarchies vs. a single larger pro audio driver with similar Vd, for instance.

I know of two tests that sort of address the issue. The first was Geddes' comparison of his Summa (15" woofer + 1" comp driver in OS waveguide with foam, at the time I think vented box) with the Gradient Revolution (7" custom Seas concentric in cardoid cabinet down supplemented by 12" woofers in open baffle), that failed show the superiority of the Summa to an extremely refined design with much lower output limits. Geddes says he would've organized the test differently, perhaps with different playback levels or musical selections. But still, it was done and the results were inconclusive.

The other is the well-known study by Dr. Olive's study of 40-odd different speakers of various sizes and prices, where smoothness and flatness of axial FR, smoothness of polars, and bass extension were shown sufficient to predict listener preference 86% of the time. That study is not quite on point, because neither cone area nor (except inferentially, through bass extension measurements at whatever SPL at which they tested) volume displacement were tested variables. It would be interesting if adding a variable to represent cone area to the (IIRC unpublished) model would change the results.

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post #24 of 56 Old 03-10-2014, 08:32 PM
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These will explain drivers with different diaphragm sizes:
https://community.klipsch.com/forums/storage/3/1095142/mod_dist1.pdf
https://community.klipsch.com/forums/storage/3/1095142/mod_dist2.pdf

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post #25 of 56 Old 03-10-2014, 08:35 PM
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Klippel has a bunch of measurements showing other excursion related nonlinear behavior.....I'd recommend just visiting the entire website.
http://www.klippel.de/know-how/literature/papers.html

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post #26 of 56 Old 03-10-2014, 08:37 PM
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A standard Klippel report will provide a ton of comparative insight into loudspeaker behavior.

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post #27 of 56 Old 03-10-2014, 08:40 PM - Thread Starter
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Thanks. Thats a ton of reading for me to do while I'm supposed to be doing work :-D
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post #28 of 56 Old 03-10-2014, 11:26 PM
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as far as i understand it, okv hits on the major points.

to understand the issue, an understanding of how drivers work will help and an understanding of the spectral content and dynamic range of the material is also required.

first, the driver.

here is a picture of a speaker.



the voice coil sits in between the top plate and the pole piece (which runs down the center of the speaker and connects to the back plate).

as the field is energized the cone begins to move.

as the voice coil moves away from its center position, the "BL field" changes. B for magnetic field, L for length of wire in the coil.

to move a lot of air, either the speaker must move a lot back and forth AND/OR the speaker must have a large cone to move a lot of air even with a small amount of linear travel.

so there are two ways to do it, either a small cone that moves back and forth a great deal or a large cone that moves back and forth a little.

an 8" driver has to move about 10.0 mm in order to produce 106db @1m@60hz.

a 15" driver has to move about 2.4 mm in order to produce the same 106db @1m@60hz.

xmax is typically specified as the point where the bl field has dropped to 70% of the value with the driver sitting at rest at position 0.

if both of these drivers have an xmax of 8mm, the 8" will be way out past its xmax and its force will be dropping off, while the 15" will be well within its xmax and its force will remain strong.

...

now the second topic is dynamic range of music. the loudest part of the "kicks & crescendos" vs. the average level of the content. for well recorded music, that difference can be 20db or more. so now if you are listening to music at a very loud average SPL, say 90-100db, the peaks in the music could be 110-120db or more.

obviously, if you are listening to loud, well recorded, music with 120db peaks, the 8" driver simply can't do it. as we already saw, it is running out of gas even before reaching 106db, so 120db is completely out of the question.

...

the third topic is spectral content of music. because the ways our ears/brains work, we are much more sensitive to sounds in the 300-2000hz region than we are too the 50-150hz region where the kick drums/synths/bass guitars et al have fundamentals. see "equal loudness curves" for more on the topic. suffice to say that most music has 10db or so of eq built in to the low end to account for this. if it didn't drums would sound weak and music would lack power. you don't have to do anything with your tone controls, it is already baked in during recording/mastering. what this means though is that for an average level of "loudness", we need an additional 10db of spl just for mid-bass. so now instead of 120db, we are looking at systems capable of 130db. if that sounds like a lot, it is. rock concert level tends to be up in the 120's depending how close you are to the speakers.

...

therefore if you want truly uncompressed, full-level, loud, music try to get a system that is capable of 120-130db with drivers moving about 1/2 their xmax or so. that will allow for full force all the way up to the volume required for the "kicks and crescendos".

how many speakers is required to do this? a pair of really good pro-audio 15" drivers might have xmax ratings around 8mm. at about 5.5 mm of travel, a PAIR of 15's will hit 120db @60hz. the single poor little 8" driver would have to move almost 48 mm to produce the same amount of sound...and of course, that would be the end of that driver!

it is about that simple. almost all of the confusion surrounding this topic comes from manufacturers who try to convince you that a single waf-friendly 8" driver is all you will ever never need and/or is "more than sufficient" when in fact the truth is...it ain't even close.**

power compression, distortion, inductance, phase, air-coupling, air-velocity...there is more to the story, but it is mostly just hitting the target spl in the linear range of the bl field in the driver. get that and your most of the way there...





** now I'm not saying that everybody needs full rock concert spl. that is a personal choice. the point is simply what is required to get there for those who want it.
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post #29 of 56 Old 03-11-2014, 04:42 AM
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as far as i understand it, okv hits on the major points.

to understand the issue, an understanding of how drivers work will help and an understanding of the spectral content and dynamic range of the material is also required.

first, the driver.

here is a picture of a speaker.



the voice coil sits in between the top plate and the pole piece (which runs down the center of the speaker and connects to the back plate).

as the field is energized the cone begins to move.

as the voice coil moves away from its center position, the "BL field" changes. B for magnetic field, L for length of wire in the coil.

to move a lot of air, either the speaker must move a lot back and forth AND/OR the speaker must have a large cone to move a lot of air even with a small amount of linear travel.

so there are two ways to do it, either a small cone that moves back and forth a great deal or a large cone that moves back and forth a little.

an 8" driver has to move about 10.0 mm in order to produce 106db @1m@60hz.

a 15" driver has to move about 2.4 mm in order to produce the same 106db @1m@60hz.

xmax is typically specified as the point where the bl field has dropped to 70% of the value with the driver sitting at rest at position 0.

if both of these drivers have an xmax of 8mm, the 8" will be way out past its xmax and its force will be dropping off, while the 15" will be well within its xmax and its force will remain strong.

...

now the second topic is dynamic range of music. the loudest part of the "kicks & crescendos" vs. the average level of the content. for well recorded music, that difference can be 20db or more. so now if you are listening to music at a very loud average SPL, say 90-100db, the peaks in the music could be 110-120db or more.

obviously, if you are listening to loud, well recorded, music with 120db peaks, the 8" driver simply can't do it. as we already saw, it is running out of gas even before reaching 106db, so 120db is completely out of the question.

...

the third topic is spectral content of music. because the ways our ears/brains work, we are much more sensitive to sounds in the 300-2000hz region than we are too the 50-150hz region where the kick drums/synths/bass guitars et al have fundamentals. see "equal loudness curves" for more on the topic. suffice to say that most music has 10db or so of eq built in to the low end to account for this. if it didn't drums would sound weak and music would lack power. you don't have to do anything with your tone controls, it is already baked in during recording/mastering. what this means though is that for an average level of "loudness", we need an additional 10db of spl just for mid-bass. so now instead of 120db, we are looking at systems capable of 130db. if that sounds like a lot, it is. rock concert level tends to be up in the 120's depending how close you are to the speakers.

...

therefore if you want truly uncompressed, full-level, loud, music try to get a system that is capable of 120-130db with drivers moving about 1/2 their xmax or so. that will allow for full force all the way up to the volume required for the "kicks and crescendos".

how many speakers is required to do this? a pair of really good pro-audio 15" drivers might have xmax ratings around 8mm. at about 5.5 mm of travel, a PAIR of 15's will hit 120db @60hz. the single poor little 8" driver would have to move almost 48 mm to produce the same amount of sound...and of course, that would be the end of that driver!

it is about that simple. almost all of the confusion surrounding this topic comes from manufacturers who try to convince you that a single waf-friendly 8" driver is all you will ever never need and/or is "more than sufficient" when in fact the truth is...it ain't even close.**

power compression, distortion, inductance, phase, air-coupling, air-velocity...there is more to the story, but it is mostly just hitting the target spl in the linear range of the bl field in the driver. get that and your most of the way there...





** now I'm not saying that everybody needs full rock concert spl. that is a personal choice. the point is simply what is required to get there for those who want it.

Nice post! I am curious though, with regards to your statements about using an 8" mid-bass driver covering the frequency up to 2000hz in this critical range, versus a 15" mid-bass driver in the same frequency region, you state that the 8" driver simply is not capable of the large dynamic range and overall accurate SPL levels compared to the 15" driver. What I am curious about is how this same 15" driver would sound in the higher mid-range frequencies, such as 1,500hz and above, compared to the smaller 8" mid-bass driver? Would the 8" driver not have as much breakup and beaming at the higher frequencies?

I have always had the impression that the larger, (ie 15"), drivers have a harder time on the upper end of the mid frequencies compared to a similar 8" or 10" driver. Correct me if I am wrong, though.
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post #30 of 56 Old 03-11-2014, 06:07 AM
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What I am curious about is how this same 15" driver would sound in the higher mid-range frequencies, such as 1,500hz and above, compared to the smaller 8" mid-bass driver?
.
Not very good, because it will start beaming around 1.2kHz. Better designs seldom run a fifteen higher than 800Hz. PA cabs routinely run fifteens to 2kHz., but they tend to be used at listening distances where wide dispersion is far less of a concern than high output.
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