Why 12" drivers can't be musical in the 40-80hz? (1 Viewer)

[Jack Gilvey]

Excellent observations,Tyson. This thread is not about nOrh,though, or their sub, It's about Jones' contention that 12" drivers can't go up to 80Hz in a linear fashion.
As far as ostensibly comparing two drivers, they must be in identical alignments, or in a system with the same Qtc, for the comparison to have any validity. If, as you say, the nOrh is designed to have a Q of .5, this implies a sealed design (I can't tell from the site). Comparing it to the vented SVS, which is probably an EBS tuned for max extension and SPL, is not comparing the drivers at all, much less presenting results which one can extrapolate to a whole size class of driver. As has been stated above, one need only hear a good 12" in a transient perfect (.5 Qtc) setup to know that @ 80Hz, it's not breaking a sweat. Only then is any comparison valid.
There are actually two phenomena being discussed here. One is the Q of the final system (Qtc, what some people call the "speed" of a woofer), and another concerns how high a driver can go, it's "breakup modes". The transient capability of a properly enclosed Shiva is beyond reproach, and it's breakup modes are high enough that a simple crossover, even one above the standard 80Hz, keeps them below audibility.
It's also common that a "sub" which rolls off first will be heard as "tighter".
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[Jones_Rush]

Jack,
You wrote:
"If, as you say, the nOrh is designed to have a Q of .5, this implies a sealed design".
The nOrh sub is a ported design. Actually nOrh say that a sealed design doeasn't have any advantages over a good ported design.
Jack, let's agree at least on one thing, you say:
"one need only hear a good 12" in a transient perfect
(.5 Qtc) setup to know that @ 80Hz, it's not breaking a sweat".
When you say a 12" with a Qtc of .5, you mean a relatively big enclosure. An ordinary small enclosure of 3 cu/ft will be too small for a 12" to sound at it's best. So maybe people who can't accumulate bigger than 3 cu/ft enclosures should use smaller cones than 12".

 

[TysonN]

Oh, absolutely, a sealed high Q 12 incher will probably have no problems at all with the 80hz crossover. Certainly you can have a woof that is nice & tight in that range, it just depends on the goal of the design & the tradeoffs you are willing to make. But, one thing that bothers me about a 12 incher like the shiva with a massive X-max vs an 8 incher with an xmax of only 4-6mm is IM distortion. If the big woofer is using a lot of excursion to produce very low, very loud bass, then the higher you cross it over, the more IM is going to be a problem, IMHO. But something like the shiva in a sealed box that starts rolling off, what? in the mid 30's without eq? I think you would be fine with that. Of course, with that design you are going to run in to the same problem that the 8 inch nOhr subs - lack of high output overall, and especially in the low regions. You could go with a 15 or 18 incher, but then you do start having problems in the 80-100hz crossover range
Also, the crossover you use will make a big difference in the performance of any driver at the edge of its operating range. A steep crossover like a 4th order will cut a driver off cleaner at the top end of its range than a 1st or 2nd order crossover (a lot of commercial subs have 2nd order crossovers, which IMHO, is obscene. Just use the 4th order crossover).
It is all a question of tradoffs of course - the 8 incher will play cleaner a lot higher than the 12 incher (generalizing here of course), but at 80 hz, I don't think either one will have any problem. Much higher than 100 hz & the 12 incher will probably run in to problems, but on the other hand, much below 30hz, the 8 incher is going to run in to problems. So, you make your choices & you swallow your poison (whichever that happens to be).

 

[Jack Gilvey]

Adding a subwoofer should not shake the walls. It should not vibrate your furniture. It should simply add depth and intensity to the music. When there are sections with deep bass, the bass should create shockwaves that you feel but don't hear. The sounds you hear of things rattling in your house is not from the bass. It is from the resonances (distortions) that cheap subwoofer amplifiers put out.

I've never heard such bullsh**. If you play organ music, or certain soundtracks, at high (realistic/reference)levels, you'll hear all kinds of rattling and shaking. Saying it's from a cheap amp just to sell amps is nonsense. Whence the credibility?
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[Tyson Neidig]

Just wanted to make a quick clarification to my point about X-max and IM distortion - you are quite correct that the 12 incher will be moving a lot less to produce an 80hz tone than the 8 incher. But, throw in the probability that the 12 incher is quite possibly moving quite a bit to produce a high level 20 or 30 hz tone (say moving its full 1 inch peak to peak excursion for that 20 or 30hz tone) and at the same time as trying to produce the 80hz tone. That is where IM distortion would rear its ugly head. Conversely, the 8 incher is moving more to produce the 80hz tone (granted), but it simply cannot produce a 20hz tone, & thus does not move at all attempting to produce it (assuming a low pass filter). You don't have a woofer attempting to produce the 80hz tone at the same time that it is belting out massive excursion to try to get out a 20hz tone. Result is the 8 incher will have a lot less IM distortion than the 12 incher.
All of this assumes of course that you DO NOT have an 8 inch woofer with massive excursion that can be tuned to produce ultra low bass with that huge Xmax. In that case I think the 8 incher would be a WORSE choice with regard to IM distortion.
Of course, ideally I would simply build a 4 way fully active speaker (1 inch tweeter, 5 inch mid, 8 inch woofer and a seperate base module with a 15 inch high excursion woofer). I would build the tweeter, mid and woofer into a single "tower" and have the bass module seperate so I could put it in a corner. Active crossovers between all drivers & seperate amps for each driver too. But, that is just me. . . .

 

[Jack Gilvey]

Conversely, the 8 incher is moving more to produce the 80hz tone (granted), but it simply cannot produce a 20hz tone, & thus does not move at all attempting to produce it (assuming a low pass filter). You don't have a woofer attempting to produce the 80hz tone at the same time that it is belting out massive excursion to try to get out a 20hz tone. Result is the 8 incher will have a lot less IM distortion than the 12 incher.

That's what I thought you meant. I don't think this comparison is valid. This is what I meant when I said that lack of Xmax is not an advantage. All it means is that when an 8" driver is excursing near the bottom of its range, say 40Hz, its movements will also be massive at the same SPL. To compare one driver @ 20Hz and another at a different frequency seems invalid. You're saying that an 8" driver reproducing only an 80Hz tone is "better" than a 12" driver
reproducing a 20Hz and an 80Hz tone. I don't see the point. How about comparing both drivers reproducing only 80Hz tones? In your example, maybe a 6" or a 4" driver would make a great subwoofer. Or, we could EQ the 12" sub to roll-off deep bass at the same rate as the 8", then measure them both for distortion.
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[Tyson Neidig]

Hmm, I think I am probably just not able to write clearly enough to convey my point? I will give it one more try, but use examples that are very extreme to illustrate my point. Let us invent a mythical driver for the sake of illustration. Let us say that we have a 15inch woofer that is able to produce the entire sound spectrum of 20hz-20khz without cone breakup. On the other side we have your normal 1 inch dome tweeter that rolls off (or is crossed over) abruptly at 3khz, so it only reproduces from 3khz to 20khz. Between these 2 drivers, which will have greater IM distortion at, say, 10khz? Well, if the 15incher is producing high level 20hz tones (the bottom of its operating range) at the same time it is attempting to produce the 10khz frequency, then there will be a lot of IM distortion, where as the tweeter attempting to produce a 10khz tone at the same time as a 3khz tone (the bottom of its operating range), will have much less IM distortion.
Ahh, something just occured to me. Perhaps I am using the IM term incorrectly here - What I mean when I use it here is to refer to the doppler effect (ie, on a street, a siren sound from a firetruck sounds different as it approaches you than when it is moving away from you), so with a woofer producing a lower tone at the same time as a higher tone, the higher tone will sound a bit different if it is being produced while the woofer is moving forward or backward for the lower frequency production. Does that clear it up a bit? I apologize if I was using the IM term incorrectly here.

 

[RichardH]

Tyson,
So, what you're saying is something like this?...
There's a piece of music that has an extremely low/loud bass drum hit, let's say at 30Hz. On the exact same beat/measure, there's also a string bass being plucked, let's say at 70Hz.
So, the string bass will sound "better" on the 8" sub because the 8" sub can't even produce the 30Hz hit, so Doppler distortion doesn't enter into it. Correct?
On the 12" sub, since it *can* produce the 30Hz hit, the cone will be moving quite a bit as it then tries to play the 70Hz string bass pluck, hence there will be Doppler distortion.
While I see your point here, it's basically saying, upper bass is better when your system doesn't do lower bass.... We can extend that to an absurd level by saying that a speaker with only a tweeter will really excel at piccolo harmonics.....

I think you can have your cake and eat it too by getting large mains (with no larger than an 8" woof) and crossover at 60Hz or maybe even 40/50Hz, then let the 12" or even 15" sub do the work below.
This would seem to point to some of the Sony upper line models (as well as others) which allow flexible crossovers.
RichardH

 

[Poul Nielsen]

This may be nitpicking, but I will go back to the quote from nOrh about how a 8" compared to a 12" is like comparing a sports car to a dump truck. The quote started:
"The problem that a larger woofer has is that it has more mass and it also has more resistance as it pushes air..."
It just seems to me, that an 8" woofer will experience the same resistance as a 12" one, since it has to move the same amount of air to get the same SPL at any given frequency. It just has to move twice as far to do so. So using the analogy of the two vehicles, the sports car may accelerate faster, but it also has further to go, so in the end, they both reach their seperate finish lines at (about) the same time...?
My 0.02 $
Best regards,
Poul Nielsen

 

[Jack Gilvey]

Tyson, I believe you used the term correctly, and I understood your point, which I still don't consider valid, as I expressed. IM distortion and dopler effects are more of a concern for bass-midrange drivers, which are not only trying to reproduce some semblance of bass (say, 40Hz), but sometimes have to work all the way up to 3-4k or beyond, depending on crossover and slope. It's just not a concern with a good 12" and your typical 80Hz crossover, based on the experience of those using them, especially the IB installations, which show a good driver in the best light.
And what about THD? An 8" is going to have a lot more of that at a given SPL and frequency. (We'll pick 30Hz for the comparison, since this 8" doesn't seem capable of 20.)
Your comparison of the IM susceptibility of a 12" and an 8" remains invalid,I think, for the reasons expressed. A more valid comparison would be to compare the IM products of both drivers at Xmax. To say the the 8" is better because it simply leaves out frequencies is folly, I think.
(Tyson,just out of curiosity, what are the dimensions of the nOrh sub?)
Again, the actual evidence, stated by those who know a lot more than I do above, does not support these claims, nOrh's claims notwithstanding. It goes back to what I said before, that a speaker with less bass will sound "tighter" to many. This is what nOrh banks on. Actual deep bass has a certain "bloom" to it. A lot of folks probably think that thunder heard during a storm, or a passing train, sound too "boomy".

I think you can have your cake and eat it too by getting large mains (with no larger than an 8" woof) and crossover at 60Hz or maybe even 40/50Hz, then let the 12" or even 15" sub do the work below.

This is an excellent and popular option, but not because of a 12" sub's inability to work well up to 80Hz. Sometimes, subwoofer placement is difficult with an 80Hz crossover due to localization, phase, or room-mode issues. These would be an issue with an 8" "sub" as well.
Poul,
Yes, that dump truck analogy is flawed, and would only be valid if the motor stayed the same, while the cone got heavier. A proper motor can move a 12" cone just as well and a proper 8" motor can move an 8" cone. Again, that site is not geared toward the technically oriented DIY hobbyist.
This thread is starting to go in circles, with the evidence decidedly one-way.
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[Jack Gilvey]

When you say a 12" with a Qtc of .5, you mean a relatively big enclosure. An ordinary small enclosure of 3 cu/ft will be too small for a 12" to sound at it's best. So maybe people who can't accumulate bigger than 3 cu/ft enclosures should use smaller cones than 12".

There's an answer for that over on the
http://64.37.116.230/cgi-bin/config.pl?read=27401 ) has apparently already decided to use a 12" , and Paul expains that maybe 3 cu.ft. is even too large for the Shiva of the PE clone.
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[Patrick Sun]

A flat response to 20Hz with a sealed sub? *Chuckle*. The only way you'll get a flat response down to 20Hz is to EQ the hell out of the rest of the sub response to lower the SPL from 100Hz down to 25Hz so that it matches the response at 20Hz - a futile exercise IMHO.
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[Jack Gilvey]

Yep, unless you have testbook perfect room gain, which I can't even approach. Another possibilty, probably more common, is to boost the level around 20Hz, or that Linkwits-transform voodoo. Either way, you're running out of amp and excursion very quickly with a 12". Better have a Mass12, or a Tempest in a slightly larger box, like Terry's.
Even without going for "flat to 20Hz", a Shiva or PE in a 3 cu.ft box would be extremely tight and punchy, very nice for rock, and with very good power handling.
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[Mark Seaton]

This whole nonsense with IM distortion is getting out of hand. We are not talking about any voo-doo phenomenoms. First, we need some definitions. I believe what Tyson is thinking of is more so Doppler distortion rather than I.M. Long ago Paul Klipsch apparently proved the audibility of Doppler distortion, yet I hesitate to really consider it a real issue in and of itself. The problem is that until someone can produce a truely linear driver, it's nearly impossible to separate Doppler distortion from I.M. distortion. Reduce one, and by definition you should be reducing the other.
So here is the difference between the two:
Doppler distortion is the resulting shift in actual frequency of the reproduced signal which is only dependent on the vector velocity (direction matters) of the cone producing the signal. No other issues are included.
Intermodulation Distortion is a distortion resulting from TWO OR MORE signals passing through some non-linearity. The resulting distortion is in the form of a sum and difference of the two signals. SO, you can't compare IM distortion unless you are maintaining the signal level and frequency in both tests. Furthermore, I.M. distortion has no relation to cone diameter, but is instead entirely dependent on motor design and suspension linearity.
Back to work...
Mark Seaton

 

[Tyson Neidig]

yes, like I said before, I don't think the nOhrs should really even be called subwoofers. They appear to be a woofer box designed to basically turn their bookshelf sized speakers in to full range towers. For that function, they work quite well. But if we are talking about what a subwoofer is designed to do (loud, clean, linear bottom 2 octave extension) then you are much better off with a bigger driver and a bigger (probably vented) box, like my SVS 20-39. Put an active crossover between a good 15 inch woofer/box and the 8 inch woofers at 80hz, use a 200hz active crossover between the 8 inch woofer & the 5 inch midrange unit, and an active crossover between the mid and tweeer at 2-3khz & you have pretty much my ideal speaker system. My point on this is that I do not really see the 15 or 12 inch "subwoofer" in competition with the 8 inch "woofer". I actually see them in more of a complimentary role with each other.

 

[Jack Gilvey]

oops.

 

[Jack Gilvey]

SO, you can't compare IM distortion unless you are maintaining the signal level and frequency in both tests.

Thanks, that's why I questioned the validity of the comparison.
Tyson...what are the dimensions of that nOrh sub, if you don't mind...
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[Tyson Neidig]

Dimensions in inches are 24h, 13w, 15d.

 

[Jones_Rush]

Jack,
You wrote:
"Yep, unless you have testbook perfect room gain, which I can't even approach. Another possibilty, probably more common, is to boost the level around 20Hz, or that Linkwits-transform voodoo."
Jones (from PE) wrote that he have a small room (funny, so do I), I don't know how small his room is, but if the lowest room mode in his room is in the 40-50hz region (typical for small rooms), then he will get room gain of 12db per octave below this room mode frequency. 12db per octave can only happen in theory, but 4-6db per octave can happen in real life. I don't know what is the Titanic 1200 F8 at 20hz, but If I'm not mistaken, the Shiva in a sealed 88 liter enclosure is rated at 20hz to be -8db unechoic, now let's add the 4-6db gain he'll probably get, and unless he is sitting at the center of a null, he'll get ~ -2/3db at 20hz. not flat, but pretty close. On the other hand, what exactly happen at 20hz for music ? I don't even have 1 cd with a lower than 28hz signal. I guess you have to like organ music to need such extension.
References: http://www.linkwitzlab.com/rooms.htm :
"At frequencies below the lowest room resonance the sound pressure will increase at a rate of 12 dB/oct for a closed box speaker that is flat under anechoic conditions, assuming that the room is completely closed and its surfaces are rigid."

 

[Jack Gilvey]

Thanks for the dimensions,Tyson, I just want to play with the specs of that Vifa driver and see how nOrh aligns it.

12db per octave can only happen in theory, but 4-6db per octave can happen in real life.

Jones, I can't seem to rely on even that, although I'd love it.

My room is small, only 12x13, but it's got big, old windows, and two doors, all of which conspire to make it the anithesis of the ideal room as described by Linkwitz in your quote. In fact, my Hsu 1220HO in this room measured about the same as when tested anechoically by Audio, with maybe a slight boost as it approached 20Hz. Still going strong @ 12Hz, though, so gain did seem to kick in very low.
I find I've got to shoot for flat anechoic, and any boost around 20Hz is gravy.
If you,however, can truly rely on your room gain to be that much, I'd certainly give the Shiva or PE driver a shot in 3cu.ft.
The Linkwits transform is beginning to look very attractive to me, allowing one to maintain low Q and group delay while lowering the f3 appreciably. Need lots of amp,though.
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