Descent vs Descent i vs Depth i

[Dominick22]

I was undecided between the Descent and Depth as well-but after a few minutes of a-b comparison, it was clear that the Depth was just an attempt at making a cheaper Descent. I dont say this to be offensive, but I would go as far as saying that one Descent is unquestionable better than two depths.

Just my thoughts,
Dominick

 

[Caerus]

It is indeed. From a technical standpoint I think it's beautiful I think in general it's a great looking sub...I just can't stand the grill in the front.

If you ever meet my Depth i, I promise it will be "grill-less" just for you. :drool: Girl friend NOT though.

 

[IWalker]

Except the 8" cone doesn't need to cover twice the distance to produce the same frequency, and anyway, as I said, none of this has anything to do with cone motion and only with the ability of the transducer's diaphragm (whatever it's made of) to change direction and velocity instantly (or as close to instantly as possible.)

It has to cover twice the distance to produce the same output at the same frequency, ie, it has to move half the air twice as far. But the mass is unrelated to the rate of change of acceleration, as the mass is constant. The ability of the diaphram to change direction instantly has to do with Le, not mms, as described in the article I linked.

 

[IWalker]

If you ever meet my Depth i, I promise it will be "grill-less" just for you. :drool: Girl friend NOT though.

Haha, I think that's fair. Baby steps, right?

 

[nsgarch]

nevermind

It has to cover twice the distance to produce the same output at the same frequency, ie, it has to move half the air twice as far. But the mass is unrelated to the rate of change of acceleration, as the mass is constant. The ability of the diaphram to change direction instantly has to do with Le, not mms, as described in the article I linked.

you will understand in time , , , , , ,

 

[IWalker]

you will understand in time , , , , , ,

Probably not. I'm decidedly hard-headed! I'm very happy with my 12" sub as it stands, but will try to demo it against the Depth i when I get the chance...to see what I think the subjective differences are.

 

[akm3]

I could understand if a sub had 50% of the radiating area of a different sub that it would have to move twice as far to make the same sound, but we are comparing three 8" to three 10" right? That is no where near half the radiating area, right?

Is that what we need to understand in time?

-Allen

 

[IWalker]

I could understand if a sub had 50% of the radiating area of a different sub that it would have to move twice as far to make the same sound, but we are comparing three 8" to three 10" right? That is no where near half the radiating area, right?

Is that what we need to understand in time?

-Allen

Right, it's more like 64%. So it would have to move 1.5625 times as far to move the same amount of air.

Cone area is pi*r^2. 4^2 = 16, 5^2 is 25 15/25 = .64

Either way, it's linear. Doesn't matter if it's 1" or 50", the concept remains the same.

And I think it's me who's supposed to understand the error of my ways, in time.

 

[IWalker]

The part that has to do with mass/inertia, etc, has to do with acceleration, which has much more to do with the efficiency/sensitivity than the "speed." The force that is accelerating the cone in one direction is the same one that's accelerating it back in the other when the signal changes. F = m*a. In order to achieve the same ouput with a heavier cone, more force must be applied (ie, turning up the power). Thus, a heavier cone has impact on efficiency, as you'd expect...but not on the CHANGE in acceleration, which is completely unrelated to the mass of the driver.

 

[nsgarch]

Fast is "fast" regardless of the driver . . . . . . .

it has to do with the control an amplifier can impose over the driver's motion. If a driver is lightweight and presents no reactance back to the amp, it's much easier for the amp to make the driver accurately and precisely follow the signal. Because (most) SS amps have their output transistors coupled directly to the speaker, they can control heavier, reactance-prone drivers (like woofers and subs) much better than, for instance, tube amps which are coupled to the drivers through output transformers, which can exercise only limited control (damping) over difficult drivers (difficult = hard time exactly following the signal driving them due to their weight and electrical characteristics.)

To do this, an adequate amp (in power and damping capability) is esssential for high mass (heavy weight, small area) transducers (like woofers) but not so much for low mass (ie moderate weight but large area) transducers (like Martin Logan electrostatic panels.)

This is why I assert that although two ML Depths will put out about the same SPL (per watt output of each of their amps) as one ML Descent (per watt output of its more powerful amp) the TRANSIENT response of the two Depths playing (together) at a given volume will be more detailed than the single Descent playing at the same volume.

One can go on comparing different diameter drivers' output ad nausium, but everything else being equal (driver Q, same throw:diameter ratio, efficiency, cone density) the smaller diameter unit will have better transient response.

 

[IWalker]

it has to do with the control an amplifier can impose over the driver's motion. If a driver is lightweight and presents no reactance back to the amp, it's much easier for the amp to make the driver accurately and precisely follow the signal. Because (most) SS amps have their output transistors coupled directly to the speaker, they can control heavier, reactance-prone drivers (like woofers and subs) much better than, for instance, tube amps which are coupled to the drivers through output transformers, which can exercise only limited control (damping) over difficult drivers (difficult = hard time exactly following the signal driving them due to their weight and electrical characteristics.)

To do this, an adequate amp (in power and damping capability) is esssential for high mass (heavy weight, small area) transducers (like woofers) but not so much for low mass (ie moderate weight but large area) transducers (like Martin Logan electrostatic panels.)

This is why I assert that although two ML Depths will put out about the same SPL (per watt output of each of their amps) as one ML Descent (per watt output of its more powerful amp) the TRANSIENT response of the two Depths playing (together) at a given volume will be more detailed than the single Descent playing at the same volume.

One can go on comparing different diameter drivers' output ad nausium, but everything else being equal (driver Q, same throw:diameter ratio, efficiency, cone density) the smaller diameter unit will have better transient response.

AH!!!! We've been talking about very different things then. My apologies. I don't dispute this point, as I indeed have no knowledge (secondhand or otherwise) on this subject...so can't agree or disagree. The tests shown in the adire article suggested that mass loading a cone caused a difference to efficiency, but none to the transient response (timing of the peaks was the same with or without mass loading) which would seem to dispute your point,...but I'm speculating wildly now so I'll stop.

 

[akm3]

But doesn't the fact that they are both servo controlled render the amplifier's capability to control movement somewhat moot? Since the servo does what the amp can't?

 

[nsgarch]

Good point, and . . . .

But doesn't the fact that they are both servo controlled render the amplifier's capability to control movement somewhat moot? Since the servo does what the amp can't?

I was wondering when someone would bring that up. You are sort of right here, in that if the woofer isn't precisely following the signal, or has inherent anomilies that are not part of the signal (like naturally occuring resonances) the woofer amp can be made to force the woofer to conform.

However, transient response means the response to short-lived phenomena , like the reversal of signal polarity. How well (quickly) a transducer responds to that (instantaneous) change in polarity by reversing its direction of travel (without lag or overshoot) determines how accurately it transduces (changes) the signal into air movement. So even though you can ask the amp to correct the motion of the woofer when it's moving, there is little you can do to make the amp better control the woofer when it's changing direction (i.e. not moving ) except use a more powerful amp.

BTW, this last part explains why folks think bigger amps produce "more" bass. I think they're really talking cleaner bass, not louder bass (of course cleaner can sound louder I suppose ) This explanation of transient response should also show why (lightweight) electrostatic membranes are perhaps the most accurate transducers: it's just sooo easy for even a tube amp to control their motion. Plus, all the frequencies (they're able to produce) are IN phase! So imaging is holographic, if the designer can just get the damn wave to spread out! And this should also tell you why matching cones to stats (transient response wise) is such a pain in the butt!

When I bought my pair of CLS's back in 1991, I must've auditioned half a dozen subs to match with them, and the ONLY woofers that did the job (i.e. had the same fast transient response as the CLS's) were a pair of Wilson Puppy 2's (and they aren't even technically subs!) Everything else available at that time sounded like muddy crap! Velodynes? Give me a break! Entecs would've been perfect except for one thing: they'd gone bankrupt! Do you have any idea what Wilson charged for Puppies in 1990 dollars? Think four Descents! Plus your own amp and x-ovr! Ah! what I did for the love of tunes :bowdown:

 

[IWalker]

Thanks for making this into such an interesting thread, nsgarch. (for me at least ) I'm always interested in learning more, or clarifying what I already think I know.

Doesn't transient response really only apply to higher frequencies?

 

[Rich]

So even though you can ask the amp to correct the motion of the woofer when it's moving, there is little you can do to make the amp better control the woofer when it's changing direction (i.e. not moving ) except use a more powerful amp.

This sounds good, but do you know for a fact that it is true? Do we really understand the advanced technology that ML uses in their servo controls? I'm not saying I do, but I am just curious as this seems to be a very generalized statement. By the way, you guys are making my head hurt with all this technical discussion.

 

[nsgarch]

About accelerometers:

This sounds good, but do you know for a fact that it is true? Do we really understand the advanced technology that ML uses in their servo controls? I'm not saying I do, but I am just curious as this seems to be a very generalized statement. By the way, you guys are making my head hurt with all this technical discussion.

Accelerometers (a tiny motion sensing device, like in your car alarm) are the heart of a servo-controlled woofer. Servo control was first commercially available (as far back as I can remember) on the original Infinity Servo-Statik 1 -- and has remained unchanged in it's basic design ever since -- comparing the output of the woofer cone's accelerometer with the signal, and then changing any parts that are "not signal" to negative feedback. This negative version of the "not signal" is added to the amp's output to cancel any "not signal" woofer motion. The difficulty in making this process work to improve transient response, is that the accelerometer can't sense the "quickness" with which the woofer changes direction until it already has, and then it's too late to tell the amp to put out! But an amp which can really pump out the big watts necessary to stop a heavy woofer cone and get it going back instantly in the opposite direction can really clean up the bass. Please note: an amp's max. power is called for not when the woofer is moving, but when it's changing direction. So you never hear that power as volume, but rather as better detail.

The ML subs (and the built-in powered bass sections of the Summit and Vantage) are excellent examples of bass with great transient response. They did it basically by not cheaping out (as opposed to inventing anything new )

1.) Providing amp(s) with truly enough power -- this is now possible (within the budget ) using a Class D amp which is only good for amplifying low(er) frequencies.

2.) Using a really long throw woofer (did everyone notice the "cone" is really only half cone and half surround! ) and by making the cone small, stiff, and lightweight aluminum, i.e., an easy cone to control, that doesn't have a lot of resonances and other nasties for the servo to fix in the first place.

3.) The "balanced force" woofer/cabinet layout. Personally, I think this is genius -- one of those things you look at and say, "Of course!" or, "Why didn't anyone think of that before?" Just for giggles, set a Depth or Descent on a thick bouncy carpet without any spikes, and a cup of water on top. Play loud. See any ripples in the water?
3a.) This is just my personal opinion, but the radiation pattern of the three-woofer layout really helps to better phase-match the sub to the dipole panels. I definitely do not think a Depth or Descent should be placed against a wall or in a corner -- that's my personal conclusion, not open to discussion :banghead:

There is a wonderful synergy between these three features, each one optimizing the other two.

 

[nsgarch]

In audio, "transient response" is usually . . . . . . .

Doesn't transient response really only apply to higher frequencies?

an attribute associated with drivers, (although it can be a characteristic of amplifiers as well.)

In the case of drivers though, transient response can apply to any kind of driver, regardless what part(s) of the audio frequency spectrum that driver is designed to reproduce.

 

[Caerus]

I definitely do not think a Depth or Descent should be placed against a wall or in a corner -- that's my personal conclusion, not open to discussion :banghead:

I am enjoying the discussion and concur with your statements, but why did ML state in the Depth i op manual to initially put the sub in the corner with the two grills about 2" from the corner walls? Here is an excerpt from the manual:

"Listening Position
Generally, subwoofers have the most output when placed
in the corner of a room. However, this can also exaggerate
the subwoofers output making blending difficult. We
recommend starting by placing the subwoofer in a corner.
It should be placed in such a way that there are 2 inches
between the grill and the wall. This will avoid blocking
the output of any woofers. If, after the full range of tuning
techniques have been employed, the subwoofer sounds
like it has too much upper bass energy try pulling it away
from the wall, toward the listening position. This will lessen
the reinforcement of these problematic frequencies
from the wall and likely smooth out the response. Repeat
the setup procedure with the woofer controls after you
move it (see figure 16)."

I think the fine tuning will end up being a way from the corner and in a position that probably suits your statement. Sorry I discussed it.

Brad

 

[IWalker]

Accelerometers (a tiny motion sensing device, like in your car alarm) are the heart of a servo-controlled woofer. Servo control was first commercially available (as far back as I can remember) on the original Infinity Servo-Statik 1 -- and has remained unchanged in it's basic design ever since -- comparing the output of the woofer cone's accelerometer with the signal, and then changing any parts that are "not signal" to negative feedback. This negative version of the "not signal" is added to the amp's output to cancel any "not signal" woofer motion. The difficulty in making this process work to improve transient response, is that the accelerometer can't sense the "quickness" with which the woofer changes direction until it already has, and then it's too late to tell the amp to put out! But an amp which can really pump out the big watts necessary to stop a heavy woofer cone and get it going back instantly in the opposite direction can really clean up the bass. Please note: an amp's max. power is called for not when the woofer is moving, but when it's changing direction. So you never hear that power as volume, but rather as better detail.

The ML subs (and the built-in powered bass sections of the Summit and Vantage) are excellent examples of bass with great transient response. They did it basically by not cheaping out (as opposed to inventing anything new )

1.) Providing amp(s) with truly enough power -- this is now possible (within the budget ) using a Class D amp which is only good for amplifying low(er) frequencies.

2.) Using a really long throw woofer (did everyone notice the "cone" is really only half cone and half surround! ) and by making the cone small, stiff, and lightweight aluminum, i.e., an easy cone to control, that doesn't have a lot of resonances and other nasties for the servo to fix in the first place.

3.) The "balanced force" woofer/cabinet layout. Personally, I think this is genius -- one of those things you look at and say, "Of course!" or, "Why didn't anyone think of that before?" Just for giggles, set a Depth or Descent on a thick bouncy carpet without any spikes, and a cup of water on top. Play loud. See any ripples in the water?
3a.) This is just my personal opinion, but the radiation pattern of the three-woofer layout really helps to better phase-match the sub to the dipole panels. I definitely do not think a Depth or Descent should be placed against a wall or in a corner -- that's my personal conclusion, not open to discussion :banghead:

There is a wonderful synergy between these three features, each one optimizing the other two.

Not all servo subs are accelerometer based.
http://rythmikaudio.com/servosurvey.html

Transient response is shown in the graph in the adire audio showing the signal peaks...which show the mass loading having no effect on said transient response. As you mentioned, it is related to damping...both in the sub box, and amplifier.

http://www.answers.com/topic/transient-response

The balancedforce design is certainly a nice one...both with reduced cabinent movement (though this is a complete nonissue with any sort of heavy box...it definitely makes it more commercially friendly) and also helps cancel out mechanical distortion, which is a good thing.

The cone is half surround and half cone because it's a small cone and it needs a lot of excursion to be able to play that low. Dropping 1 octave requires doubling of excursion. It looks less ridiculous when that kind of surround (or even bigger) is on a 12" cone.

Phase matching the dipoles? dipoles will often have a lot of comb filtering, because the front and back are playing out of phase, and reflections from the back wall then overlap the front wave, some in and some out of phase. Having the 3 woofers, phase adjusted, at the frequencies it plays, (where the wavelength is such that the waves are essentially omni-directional) shouldn't sound any differnt than a single front firing cone, except for the mechanical distortion reduction. A good sub should be playing in phase (or if playing in the reverse direction 180 degrees out of phase) through it's entire range....though some subs cross 0 degrees within their operating range. I don't think there's a phase advantage to the balanced force design. But I've been wrong plenty of times before (so could very well be wrong on any or all of this! )

 

[babydoc]

I know the Descent i is better then the Depth i, but is the Descent NOT-i better then the Depth i?

Where does the abyss fit in to all this?

I got Vistas on the way. Which sub should I be trying to pickup? I want hometheater kick you in the gut bass, but tight and musical =D

I can't afford Descent i so it is between a descent, perhaps a depth i, and maybe 2x abyss.

Any idea of their relative merits?

You might consider a "4-sub" approach using either depths or descents depending on the size of your room and your budget. I have two Descent i's and two Descents in my system placed out of each room corner. The sound fill in the system is just amazing with this set up. My primary speakers are Summits.