[Davey]

"Adaptive Equalization" is just equalization plus feedback error correction.  One can certainly be implemented without the other.

You define a target response and then apply an equalization to achieve it.  Servo control just helps to make sure the actual cone movement follows the applied signal.  Two different things.

Nice (long winded) analogy, but this is not rocket science. 

Cheers,

Dave.

[rythmik]

Nice (long winded) analogy, but this is not rocket science. 

But scientific foundation for servo system is control theory.  Same is any close loop control system.  They all fall under the standard course in a 4 year university curriculum in electrical engineering called "control theory" . It is not rocket science, it is fundamental engineering.  You don't need to be rocket scientist to understand "control theory".  It only takes a semester to understand it.  But it may take far more than that of real world experience to master it.   Statement with tongue-in-the-cheek contributes nothing to the discussion. What purpose does it serve?

[sfdoddsy]

Davey, There was a question regarding their ability to play flat to 20Hz. Yes they do. My goodness.

The question wasn't their ability to play flat to 20hz. I have no doubt they do. Depending on the EQ I apply to mine, I can have them flat to 20hz, 15hz or DC if I wanted.

The question was whether they could play at 100db at 20hz from the listening position.

Your charts are meaningless because, as you say, you are measuring in the nearfield. And thus  before dipole cancellation has happened. So the driver can play at those levels when the mic is a few inches away. No-one doubts that. And we can see the boost that the servo system is giving to counteract the dipole roll-off.

That is as it should be. A 6db octave boost below F Equal.

What I'd like to see is the end result of that boost from the listening positioning.

[rythmik]

The question wasn't their ability to play flat to 20hz. I have no doubt they do. Depending on the EQ I apply to mine, I can have them flat to 20hz, 15hz or DC if I wanted.

The question was whether they could play at 100db at 20hz from the listening position.

Let me ask this question. Can a 12" sealed sub with 370WRMS amp in a 2cu ft box do 100db at 20hz?  OB does have dipole cancellation. But there are 4 drivers with literally more than 1-1/2" peak-to-peak excursion.  What peak-to-peak excursion can a sealed sub in 2 cu ft box give you?

.. [snip]. And we can see the boost that the servo system is giving to counteract the dipole roll-off.

Wrong statement. I don't want people mis-quote statements like this. The 6db/oct compensation is not from servo itself. It is from a 6db/oct shelving circuit implemented on OB version of servo amps.  One customer from this forum asked me as he cannot figure out how the same servo amp can work for both sealed version and OB version.  They are different.

[sfdoddsy]

Sorry about generalizing about the servo.

I also have four 12 inch drivers in my open baffle speakers. They have the same Sd as the GRs. They have the same Xmax. The Fs is slightly lower, but not so much it anyone would notice. Heck, they even have the same Qts.

My H-Frame baffle is about the same depth.

Like yourself, I apply a 6db octave shelving filter to counteract dipole roll-off.

So our speakers should have close to identical output capabilities. Lets forget bass quality for the moment.

And yet a 75db REW 15-200hz sweep has my woofers audibly and visibly flapping.

Danny is claiming you guys have managed to extract an extra 15db of output. Somehow.

Are you making the same claim?

If so, the proof is once again simple. Stick a mic at the listening position and play a 20hz tone, or even easier a slow 20-200 sweep at 100db.

In my opinion one of two things will happen. Your servo system will protect the drivers by reducing their output. This is one of the biggest advantages of a servo system. Or it won't and the drivers will hit their stops and possibly go kaput.

As for the sealed sub comparison, my ancient Velodyne HGS 15 stomps the combination of 4x 12 inch OB drivers. Which is why I cross to it below 40hz. I prefer the quality of OB bass above that, but I have learned to accept its limitations.

[rythmik]

Sorry about generalizing about the servo.
I also have four 12 inch drivers in my open baffle speakers. They have the same Sd as the GRs. They have the same Xmax. The Fs is slightly lower, but not so much it anyone would notice. Heck, they even have the same Qts.

Which 12" driver do you use? Standard Peerless drivers do not have same xmax has GR drivers.  GR SW12-16 driver has a driver coil of 52mm long. The sensing coil is even longer than driver coil and is easily linear up to 2" peak to peak excursion.  The mechanical max excursion is more than 2" peak to peak.  How about your driver parameters?  Without the information, all discussion can be off mark.  Let me know your parameters before I can make further comment.  How big is the amplifier that you use?  the output at 8ohms and 16ohms?

And yet a 75db REW 15-200hz sweep has my woofers audibly and visibly flapping.

Danny is claiming you guys have managed to extract an extra 15db of output. Somehow.

Are you making the same claim?

Do you know at what excursion of your OB driver when it makes this flapping noise?  Does it make 1-1/2" peak to peak excursion? Do you know if the flapping comes from amplifier clipping, or driver exceeding linear xmax?   You need to learn to tell the difference of the two becasue amplifier clipping also produces flapping noise.  It is easy to tell that. Put a white dot on your black cone to observe the excursion and put a scope on the amplifier  to observe if the amplifier clips already.  In addition, at 14hz (just  half octave below 20hz), the woofer needs 9db more excursion to make the same SPL as in 20hz (for OB sub, or sealed sub the figure is 6db).  That is 3x excursion. So if your system is somewhat flat down to 14hz, you will tax the driver way too much and you start the sweep at 15hz.  Do you hear the noise at exactly 20hz? Or you just hear noise during the sweep? If it is the latter, it can be very well the 15hz signal causing it. We have a flexible extension/damping setting simply because of this.   

[sfdoddsy]

I don't use the Peerless drivers. I have a pair of Acoustic Elegance IB12s a side.

Parameters are here:

http://www.aespeakers.com/phpbb2/viewtopic.php?f=3&t=1676&start=15

Whilst the GR may have an Xmech p to p of 2 inches, wouldn't your servo system pull that back a tad to avoid the inevitable distortion?

The 15hz thing was an example as it is the standard REW tone.

The cone indeed moves in and out to full excursion. so much so that I blew one a while back when I forgot to switch my prepro to small and it got the the full LFE signal of a not especially loud movie.

You can easily observe similar behaviour on tracks with really deep bass. Amongst other things I like  organ music, reggae and big orchestral music played loud so I have learned not to tempt fate.

[rythmik]

I don't use the Peerless drivers. I have a pair of Acoustic Elegance IB12s a side.

Parameters are here:

http://www.aespeakers.com/phpbb2/viewtopic.php?f=3&t=1676&start=15

Here is the parameters that I copied from John's web site.

Fs: 20.4hz
Qms: 5.9
Vas: 129L
Cms: .35mm/N
Mms: 174g
Xmax: 18mm
Sd: 509sqcm
Qes: .71
Re: 5.5ohm
Le: .3mH
Z: 8ohm
Bl: 13.1Tm
Qts: .64

You will be shocked to see SW12-16FR drivers T/S parameters:

Fs: 27hz
Qms: 2
Vas: 149L
Mms: 77g
Xmax: 20mm
Re: 13.46
Bl: 12.8Tm
Qts: .699

Notice the BL value is similar between both drivers but SW12-16FR is at 13.6DCR vs AE driver of 5.6DCR. You can lose up to 3db just becasue of that.  Now check out Mms. What on earth we need a Mms of 174g 12" driver?  It is even heavier than a driver designed for sealed sub. SW12-16FR has only half of Mms. AE's OB driver is a heavy voice coil driver and that can spell trouble (see comment below). On the other hand, the voice coil of SW12-16 is really feather weight.

Whilst the GR may have an Xmech p to p of 2 inches, wouldn't your servo system pull that back a tad to avoid the inevitable distortion?
The cone indeed moves in and out to full excursion. so much so that I blew one a while back when I forgot to switch my prepro to small and it got the the full LFE signal of a not especially loud movie.

This is another misconception about servo.  Servo does not have to pull back. As long as the amplifer does not overload into bottoming the driver out, it works just fine.   

Now there are a lot of reasons that a driver can make full excursion and then destroy itself.  One of them is the driver has a self DC characteristic that once they are push out of magnetic gap of the motor, the voice coil is push to one side of the magnetic gap and repeatedly making loud flapping noise and causing it to bottom out. Not only that, it also reduces the effective excursion.  Without looking at your case, it is difficult for me to conclude anything.  But that is certainly a way to destroy a driver.  SW12-16 does not have this problem that I know of.  I don't know of anyone that destroy a SW12-16 becasue of that. 

Another possibility is the voice coil rubbing because of heavy voice coil. If you put a driver like that at 45 degrees, you are asking yourself some big big trouble. Sagging at tail end just increases the possibility of premature rubbing.  For heavy weight voice coil driver, you either put it front firing or down-firing, but never odd angle mounting.  SW12-16's light weight Mms and voice coil does not have this type of problem.  Given all these analysis I can think of, why do you want to use AE IB drivers to start with?

[sfdoddsy]

The slight differences in parameters may, possibly, affect sound quality.

And they may, possibly, affect the the amount of EQ each driver needs to play flat to one's chosen frequency.

But they don't affect the overall output.

That is solely down to the combination of Xmax and SD.

Or do you disagree with this simple summary?

That's kind  of what my part in this fun debate is about. Do your servo OB woofers have more output at say 20hz than non-servo drivers with identical Sd and Xmax? Danny says yes! I say I can't understand how this can be possible.

As the for the high  MMS of the IB12, I believe that was to lower the Fs for IB use. The OB version has a lower MMS and higher Fs.

Same output.

[jtwrace]

Young man, I'd love to have you down here for a few days. You'd leave saying, man, those caps, wire, and connectors really make a difference.

When is the upgrade package (wire, caps & connectors) for the servo amps available?   

[rythmik]

The slight differences in parameters may, possibly, affect sound quality.

And they may, possibly, affect the the amount of EQ each driver needs to play flat to one's chosen frequency.

But they don't affect the overall output.

That is solely down to the combination of Xmax and SD.

Or do you disagree with this simple summary?

I agree. But you are stuck with a driver with high Qts. The sound characteristic of a Qts driver with twice Mms and heavy voice coil.  I assume you understand physics and you know when AE and SW12-16 both move at the same excursion at some frequency say 60hz, the kinetic energy of cone in AE driver is more than twice of SW12-16 (174/77). That is a disadvantage for AE as that kinetic energy will transmit to the frame and cause it to vibrate more. Once the energy is on the frame, you literally contaminate the sound.  You need to look at the big picture understand all the physics rules and their implication.

That's kind  of what my part in this fun debate is about. Do your servo OB woofers have more output at say 20hz than non-servo drivers with identical Sd and Xmax? Danny says yes! I say I can't understand how this can be possible.

I think the answer is from two parts. First, if you just compare the same driver with servo and nonservo, you know the sensing coil is longer and more linear than the driver coil, and the fact that in servo there is no catch in terms of excursion utilization, you do get incrementally higher output with servo. For instance in SW12-16, that is from 20mm to 25mm. Now if we compare the driver with same low Qts (say Q of 0.3) that implement with huge magnets and the one with servo (with physical Q value of 0.7 and effective Q value of 0.1), The improve is a factor of 0.7/0.3=2.33x.  Somehow I have heard too many comments that servo just does not have same output and that type of "stereotyping" is mainly from early day Velodyne implementation. Their servo subs  will be torn apart if the amplifiers get into clipping. So they put in a limiter severely limit their output potential. Our servo does not use limiter. The customers very often drive them into slight to moderate clipping without knowing it.  you  really need to try ours and compare to Velodyne's output, then you realize what you have been missing all along. Remember Velodyne even come up with a sub called 1812?  With that product, Velodyne is admitting their 18" driver does not move fast enough to keep up with other front speakers and they need a 12" driver as the bridging.   

Here is the plot demonstraton of how low Qts impact the excursion utilization (the excursion vs frequency when the amplifier power is same). First we show the case where fs=20, and Qts=0.7.



You can now understand the problem.  Let us say the max excursion of the driver is 12mm. You can never achieve 12mm excursion at 20hz.  If you do that, what would the excursion at 10hz be?  17mm!!! that is a sure way to bottom out a 12mm excursion limit driver.  So your idea of the SPL output is simply Sd times excursion is totally wrong..

Now check out the case when we change Qts to 0.5.



Now if we continue to reduce Qts, the 20hz excursion output continues to go down.

Now let us step back and see what the ideal case for us really is.  The Q value will be slightly higher than Q=0.7 which yields



Do you care to guess what Fs this plot is?  It is high at 40hz. It is like moving the first plot (fs =20hz Q=0.7) entirely to the right. So high fs is not a problem. It actually gives us better excursion utilization. By moving the fs higher, now we have another 3db higher output at 20hz (from 70% to 100%). Not bad. You just need to know how to address the downside of high fs.  The servo will correct the FR to lower extension. But the important lesson here is you can free yourself from the limitation of physical parameters and go direcctly after whatever works best for you.   
In short, how do we get higher fs? Because the Mms is lower.  Lower Mms also gives less vibration and everything converges to the same direction.  The only missing tool that others do not have is the servo to 1) improve the Qts value and make it sound clean and articulate, and 2) move the effective fs to a lower frequency so we have better extension. That is the big difference between servo and nonservo.

Now back to the Qts issue. We don't want Qts to go too high either as we need some room for parameter variability.  If we go too far by making Qts too high, it will become something like this:



If you consider all the stuffs I explained above, you know all these improvements add up to a larger number.  That is the second part of answer to your question.

As the for the high  MMS of the IB12, I believe that was to lower the Fs for IB use. The OB version has a lower MMS and higher Fs.

Same output.

You have simplified the world. In addition to SPL output, what else matters to you?  Most of us are really not that simple-minded. On on hand, you are really after output, you should have gone with horn front speakers instead of Maggie.  If you really like the light membrant of Maggie, you should have gone with OB driver with lower Mms.  I truly don't understand your logic. 

[JohnR]

You have simplify the world. In addition to SPL output, what else matters to you?  Most of us are really not that simple-minded. If you are really after output, you should go with horn front speakers instead of Maggie.  I truly don't understand your logic.

He was just pointing out why that particular driver has a higher Mms. For a driver with low Mms, look at the AE Dipole12, which has half the Mms of the SW-12-16FR (55g vs 105g).

[rythmik]

He was just pointing out why that particular driver has a higher Mms. For a driver with low Mms, look at the AE Dipole12, which has half the Mms of the SW-12-16FR (55g vs 105g).

SW12-16FR has only 77g. We sent the driver to Klippel test and the report is 77g Mms and 71g Mmd.  If Danny has listed 105g as Mms, then that is a typo. If AE has Dipole12, then he should sell his IB12 drivers and use Dipole12.  Now that is another myth. Why the manufacture will come up with two different drivers, one for IB and another for OB?  Both are based on the same principle except the latter needs a 6db/oct shelving EQ. 

BTW, Dipole12 has Xmax listed as 12mm. That has way less excursion than SW12-16. 

[JohnR]

SW12-16FR has only 77g. We send the driver to Klippel test and the report is 77g Mms and 71g Mmd.  If Danny has listed 105g as Mms, then that is a typo.

It seems like more than a simple typo on Danny's part, as putting the specs published on your website into Unibox comes up with an Mms of 102g. Looks like you guys need to check your numbers again.

Now that is another myth. Why the manufacture will come up with two different drivers, one for IB and another for OB?  Both are based on the same principle except the latter needs a 6db/oct shelving EQ.

They're different motors.

[Danny Richie]

SW12-16FR has only 77g. We sent the driver to Klippel test and the report is 77g Mms and 71g Mmd.  If Danny has listed 105g as Mms, then that is a typo. If AE has Dipole12, then he should sell his IB12 drivers and use Dipole12.  Now that is another myth. Why the manufacture will come up with two different drivers, one for IB and another for OB?  Both are based on the same principle except the latter needs a 6db/oct shelving EQ. 

BTW, Dipole12 has Xmax listed as 12mm. That has way less excursion than SW12-16.

Brian, I think that 105 grams was manufacturers specs from the first run. I will pull some of the newer ones and burn them in a little and test the T/S on them then report back.

[rythmik]

Danny,

Here is the parameters I had from Klipple test:

[rythmik]

They're different motors.

you are stating the obvious. My question is how OB and IB operations are different that requires two motors with such a different set of  parameters (in particular Mms).  Or was it a trial and error process and see which one sticks. If you have been burnt by John (when he was still with Stryke Audio), you should have learnt a lesson about what heavy voice coil can lead to.  At least I do.

[JohnR]

you are stating the obvious. My question is how OB and IB operations are different that requires two motors with such a different set of  parameters (in particular Mms).

I don't really see what the problem is. Your own website has two different 4 ohm 12" drivers with different parameters.

But as far as the motors on the AE drivers go, my understanding is that the IB drivers are much cheaper to make. I could only guess that since IB people are buying them in fours and eights and more, there was demand for a lower cost driver with higher excursion than the underhung dipole motors. Although, let me revise that: a demand for a cheaper overhung motor with IB-like parameters than the Lambda-designed TD motor.

[rythmik]

I don't really see what the problem is. Your own website has two different 4 ohm 12" drivers with different parameters.

But they are for sealed subs. They are not for IB/OB.  We have different drivers optimized for a particular application. SW12-4 is for compact enclosure. DS1200 is for slightly larger sealed enclosure. SW12-16FR is for OB/IB. But if you check their Mms, they are among the lowest in each of their respective class and that is our goal. 

[Danny Richie]

And John,

I am going to get you the Le figure that you asked me for when I measure them next. As of right now I do not have that figure to give you or I would have given it to you.

And! You guys are still bench racing the numbers of the drivers only. Once the servo system is applied the total system parameters are going to change a lot. I am sure that Brian can explain this better than I can.