[stevenkelby]

Steven, I said why, right in the post that you quoted (although you left that part out). Did you read what I wrote?

Hi John,

Thanks and I did read it but I don't see how you reached the conclusion that "This thread has pretty much convinced me that servos for OB are basically a gimmick. "

Here is waht you posted:

Well... right. Box subs and OB subs sound different. I can see the reasons why a boxed sub would benefit from servo as there's nothing you can do in designing the driver to remove the compression of the air in the box. With a driver in free air, though, it's different... This thread has pretty much convinced me that servos for OB are basically a gimmick. (Not that I was about to buy any any time soon anyway, I have enough OB drivers to last me a while...)

What part where you referring to that I failed to quote? Is it

With a driver in free air, though, it's different...

? That doesn't explain much!

I thought maybe you read something in this thread (that I didn't) that might give you a reason to think servos in OB are a gimmick, without even hearing them, seeing measurements, reading a post by someone who has expereience enough to know more than you or I etc..

I didn't see the logic in your statement and didn't know what lead you to that conclusion, I still don't. It's cool though, sorry if I missed something.

Danny has suggested in the past that with his (Danny's GR) OB setup you get to have your cake and eat it too, but StigErik nailed that coffin shut in my book.

Again I can't see the link that would lead to that conclusion. How does StigErik's experience with many large non-servo OB subs "nail shut the coffin" on Danny's subs?

By having your cake and eating it too I presume you mean

it's just that his system is proof that with OB, low bass is effectively the impossible dream.

Surely Danny's servo subs either provide low bass with OB, or they don't. Either way I wouldn't answer that question based on the experience of someone else who is not using Danny's servo subs.

Danny has proovided measurements and graphs of his subs, they seem credible to me until someone posts measurements to the contrary, or until I measure mine for myself and see how low they go.

Sound quality is hard to measure and means different things to different people so subjectively, you're free to not like how they sound. As Early B says:

Some people are so accustomed to "boxy bass" that once they hear what "boxless bass" sounds like, they nonetheless prefer the boxy sound of a typical sub, and that's OK. Like any other speaker design, OB servo subs aren't for everyone. When I first heard the OB servo sub, I felt it wasn't producing sufficient bass, i.e., enough "punching power." Eventually, I realized that the bass I was hearing was very musical, and it transformed my point of view of what good bass is supposed to sound like. For example, the sound of a kick drum in a typical "woofer in a box" sounds like it came from a box, but when you hear a live kick drum, there's no extraneous bass reverberation, and there's no "room loading." Of course, I really didn't know what room loading sounded like until I heard an OB sub. Another major benefit -- in terms of getting great bass, the room plays a key role, but with an OB servo sub, the room is less of an issue. However, the OB servo sub takes a while to set up. There's a bunch of dials and switches on the amp, and you gotta find the right balance for your taste. A typical sub has a volume and phase switch, and you're done. 

Whether or not they provide low bass though (Rclark), is not something one can make an informed decision about based on anything in this thread, in my opinion.

Best regards,

Stephan.

[JohnR]

? That doesn't explain much!

With a driver in free air, there isn't any force pushing back against the driver like there is with a driver in a box.

[stevenkelby]

With a driver in free air, there isn't any force pushing back against the driver like there is with a driver in a box.

Thanks and I understand the cone has an easier time in OB, but that doesn't explain why "servos for OB are basically a gimmick."

Whether OB or boxed, the cone still has mass that should be better controlled by a servo system. Doesn't it?

Steve.

[JohnR]

Whether OB or boxed, the cone still has mass that should be better controlled by a servo system. Doesn't it?

Weee... ellll... you know, this is where the claims begin. Earlier in this thread there was the claim that lower moving mass was better. When it was shown that a different driver that is otherwise pretty much the same thing has almost half the moving mass, the claim was altered to the mass doesn't matter, what really counts is the whole system. The question about Le was avoided, twice, with the answer now being that none of the T/S parameters matter anyway.

I dunno man. As they say, YMMV...

[stevenkelby]

Weee... ellll... you know, this is where the claims begin. Earlier in this thread there was the claim that lower moving mass was better. When it was shown that a different driver that is otherwise pretty much the same thing has almost half the moving mass, the claim was altered to the mass doesn't matter, what really counts is the whole system. The question about Le was avoided, twice, with the answer now being that none of the T/S parameters matter anyway.

I dunno man. As they say, YMMV...

Got it, I think I understand now Calling them a gimmick seems like an ad hominem attack to me but no worries and thanks for the explanation

Best regards,

Steve.

[JohnR]

Calling them a gimmick seems like an ad hominem attack

You need to look up the definition of "ad hominem"...

[stevenkelby]

Sure thing, I'll send you some links tommorrow. I'm watching Walking Dead and about to pass out.

I missed this, thanks I'd love to see more info, always something to learn!

Steve.

[stevenkelby]

You need to look up the definition of "ad hominem"...

I think I understand the meaning. It seems a few people take issue with Danny's posts on the boards but that has no bearing on whether servo subs are a gimmick or whether they will play flat to 20Hz etc.

I would think that making statements about the product based solely on posts by the man qualifies as ad hominem but I may be wrong.

For example:

Earlier in this thread there was the claim that lower moving mass was better. When it was shown that a different driver that is otherwise pretty much the same thing has almost half the moving mass, the claim was altered to the mass doesn't matter, what really counts is the whole system. The question about Le was avoided, twice, with the answer now being that none of the T/S parameters matter anyway.

Now maybe Danny is right or wrong, maybe he's a genius or a fool, maybe he's a liar or a saint. He may be some where between those extremes, like the rest of us. None of that has any bearing on the question of his subs with respect to them being a gimmick or playing flat to 20Hz or anything else, does it?

There is no data or evidence in the post I quoted above, and no logical or empirical reason to call them a gimmick, just rhetoric and I am in no position to judge that.

Saying that, I have plenty of baseless opinions of my own!

Best regards,

Steve.

[JohnR]

Steven, I dunno what to say. I'm sure your subs are great. As far as I can tell, this thread is not about that.

[JohnR]

My idea is to couple those DAC's to a PC for The Monolith digital crossover.

Um. Well, getting back to this particular sidetrack, I'm not sure what "those DACs" are but I wish you well in coming up with a competing product.

[HAL]

With a driver in free air, there isn't any force pushing back against the driver like there is with a driver in a box.

With an open baffle servo woofer there is restoring force.  It is provided by the servo amp. 

The two 12" servo woofers in the Super-V's will go into the low 20's for frequency response.   I like pipe organs and they do very well for the low end. 

Have not tried the servo 8" yet, but that is happening soon.

[JohnR]

With an open baffle servo woofer there is restoring force.  It is provided by the servo amp. 

Sorry, but this is getting completely stupid. My comment was obviously made with respect to no servo in circuit.

[jtwrace]

You are looking for a new car with all out performance and handling. Your main options have been narrowed down to a Chevorlet Suburban, a Ford Expedition, or the Chevorlet ZR-1 Corvette.

Two have high moving mass that hinders acceleration and the high level of wind resistance due to the large surface area also really limits acceleration. The high moving mass also makes them difficult to stop especially at high speed. They are just not very agile vehicles. The third choice has less moving mass. So acceleration is great, and with less moving mass it makes it much easier to stop. More importantly though is that the huge carbon fiber brakes brings it to a stop much quicker than the others. It is really not a comparison really...

Ya think?      Not a very good one either.

[rythmik]

With a driver in free air, there isn't any force pushing back against the driver like there is with a driver in a box.

If you read the AES paper titled "Modelling of the Nonlinear Response of an Eletrodynamic Loudspeaker by a Volterra Series Expansion" by AJM Kaizer, J. of AES, vol. 35, No. 6, 1987 June pp 421-432, it showed significant nonlinearity in speaker's suspension system and the box spring is 10 times more linear than that. After one puts a driver in a sealed box,  the box spring acutally linearizes the suspension system (as opposed to say ported sub where the role of box spring is totally different).  If you, in addition, read papers by A.N. Thiele and R. H. Small AES papers on how to model the driver's parameters (nowadays becomes the standard T/S paramters), you will understand the box spring in sealed subs is "combined" with driver's suspection to become a new suspension with new compliance value and therefore the fp point and Qts value all change.  So from modelling point of view, box spring and driver's suspension are not separatable. My point is you  have relied on too much of your instinct.  But in reality is the question has been studied to death by researchers. If you know where to find the papers, it helps you to help us.  In short, the problem of driver's nonlinearity is same in OB as in sealed subs. The same technique can address both.  The goal of servo is to reduce the equivalent Qts value of the system by a factor of 3x for sealed and 8x for OB. Low Qts value has the same effect as high BL force factor value. The only way in real world we can implement something like that is with huge magnets. But then the effect of "stall" (an effect that back EMF is so large that it reduces the output of the driver) becomes significant.  So servo is really the best method to achieve excellent cone control (with low effective Qts) without suffering the stalk effect in the physical world.


 

[AlliumPorrum]

Maybe this information will answer that question better: http://www.rythmikaudio.com/smartQ.html

Thanks Danny, that solved a lot!

[AlliumPorrum]

... You can use something like a DEQX to EQ the lower end, but look at the expense of that. Plus it still isn't something that you want in the signal path to your main speakers.

For what I know, DEQX isn't adding anything to the signal path. Just the opposite; the main reason I'm interested on it, is the possibility to get rid off of one of the biggest problems in the signal path; crossover's analog components. During my 20 years of hifi hobby & DIY, I have noticed that the one place to get great improvements is tweaking the crossover with better quality components. Speakers even with 5k price tag seem to have a bottle neck in their XO's. Yes, amplifiers and DAC's do always add more or less coloration to the sound, but the coloration that crossover adds seems to be much bigger, and component changes can have a huge effect to the sound.

Of course, I don't have any own experiences on DEQX yet. But, during last 6 months I have read pretty much everything that there is written about the DEQX in the internet, and I haven't found a *one* article where DEQX would have not been better than original analog crossover. I found few articles where the result was not so great at first, but after more studying, it was found that it was not used correctly. It surely isn't simple "plug and play" solution, that's for sure.

And concerning the DAC's. First of all; Burr Browns on HDP-4 have been getting really good reviews everywhere. HDP-3 was way behind in this area, and older 2.6 seems to be total crap. Secondly; HDP-4 has digital outputs, so if really wanted, you can use any DACs you preferr.

[studiotech]

I don't always agree with Danny's replies or how he handles himself, BUT I've heard the OB servos on several occasions and whatever the reason, they have sounded really excellent each time.  I was very close to using them on my own project.  I just wanted a little more high SPL slam and choose the sealed Rythmik 15" to augment the 15" in the baffle below 50Hz.  Claims of flat to 20Hz followed by max spl numbers have to be taken with a grain of salt from Danny.  Max measured SPL is NOT for 20Hz.  At 20Hz, max SPL will be lower than say around 40-50Hz.

Greg

[dBe]

IIRC there are four columns, it's not really the same as a "room full of subs." But if you want high output into the teens, don't expect to get there with OB, everything is working against you. I found 30 to be pretty much the sweet spot... as they say, YMMV........

I've followed this thread with a combination of amusement and amazement and finally have to interject. 

If anyone is familiar with the old analog synth Roland 808 drop, the fundamental is 18Hz.  At RMAF we had people's pant legs flapping and glasses in the bathroom rattling around on the granite countertop.  The music piece in question is Pete Belasco's "DEEPER".  A low frequency tour de force.  Anyone that was there can attest to the feeling of air shuddering in the room at 18 hertz as well as the limit of audibility sound associated with it.

A high Qt, high excursion, properly implemented (NO accelerometers), servo controlled subwoofer is anything but a "gimmick".  It is an experience that is life changing.  At least it was for me.  NEVER again will I go back to big box colored bass.  This is the real deal

YMMV until you hear 'em.

Dave

 

[dBe]

I've followed this thread with a combination of amusement and amazement and finally have to interject. 

If anyone is familiar with the old analog synth Roland 808 drop, the fundamental is 18Hz.  At RMAF we had people's pant legs flapping and glasses in the bathroom rattling around on the granite countertop.  The music piece in question is Pete Belasco's "DEEPER".  A low frequency tour de force.  Anyone that was there can attest to the feeling of air shuddering in the room at 18 hertz as well as the limit of audibility sound associated with it.

A high Qt, high excursion, properly implemented (NO accelerometers), servo controlled subwoofer is anything but a "gimmick".  It is an experience that is life changing.  At least it was for me.  NEVER again will I go back to big box colored bass.  This is the real deal.

Another can-o-worms: dipoles in a room are not a zero sum game.  There is room loading and room gain.  It is at a tad less than 1/2 the gain of a monopole speaker due to the alternating pressurization effects and the null at the plane of the baffle.  At extreme low frequencies the room ends pressurize and depressurize with modes established within the room but not allowed to propagate end to end.  Ultimate room gain is determined by the side wall and floor to ceiling distances.

YMMV until you hear 'em.

Dave

[dBe]

Whoops, my bad. Premature fingerulation.................

Dave