[Freo-1]

It's pretty obvious that getting good bass in general is not such an easy endeavor, and learned audiophiles across the spectrum cannot seem to agree on the preferred method to achieve. 
 
There is a host of approaches, from sealed box to open baffle, servo or non servo, transmission line loading (along the lines of a TBI Magellen), room equalization, and the list goes on and on. 
 
Is two subs better than one? (often, but not necessarily).   

It is little wonder that many audiophiles wind up with full range speakers, which in theory should make integrating bass easier (assuming some knowledge of placement).   For owners of monitors, planar, and ESL's, a sub (or subs) are necessary to get true full range sound.

I have learned the hard way that there is no one (across the board) right answer for a given system.  One has to gather as much information as possible, and then try different solutions until one finds one that works for them.

Planar/ESL speakers are especially challenging because the sub's output often sounds like it lagging in the time domain, and tends to be one dimensional (without clear definition). 
 

[mcgsxr]

I appreciate that the discourse has remained mostly friendly and level headed.

I hope we get back to the main question at hand, now that we have briefly sojourned into learning about some of the specifics of some of the implementations for bass on OB.

[Davey]

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 "stalk" (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.

Brian,

I wonder if you might elaborate on this a bit?  Are you saying your objective (with the servo control) is to lower Qts in an open-baffle configuration to something much lower than the "native" Qts of the driver?

Say I started with a driver that has Qts = 0.7.  Your objective would be reduce to reduce it 0.7/8 or 0.087?  Or your preference is to start with a driver that has much higher Qts and then reduce it to a more "nominal" value?

As an example, the GR SW-12-16FR driver is spec'd at Qts = 0.748.  Why would you want to reduce Qts on that driver by a factor of eight?

Maybe I'm not understanding your definition of Qts or "effective Qts?"

Cheers,

Dave.

[sfdoddsy]

This is the first I'm hearing of it. Who are his acolytes? Maybe his product is "hyped" because it is "the best"? Is that possible in your eyes? How are people including Danny supposed to respond when someone asks for a direct comparison?

On which forums is mention of his product banned?


Best regards,

Steve.

http://www.htguide.com/forum/showthread.php4?t=28354

[JohnR]

NEVER again will I go back to big box colored bass.

Yeah but Dave, this is the same false scent that others have been throwing out. You listen to a servo OB, then you say you won't go back to boxes. So what? What does that have to do with why servo is needed for a competent OB implementation? Apart from a condescending post by Brian referencing a 25-year old paper, there hasn't been a shred of technical data to support any of the claims being made.

[dBe]

Danny Stated - "Okay, Let me put it this way. I used a pair of SW-12-16FR servo controlled woofers in an open baffle speaker at RMAF as the lower drivers in a pair of speakers that I was demonstrating there. We measured them hitting 105db peaks in our listening room during the replay of a recording drum track. It was a high quality SPL meter that was sitting on my leg while I was seated in the listening area. They also played flat to 20Hz and were -3db down in the teens. And the stopping power and control of the servo system is quite evident even at lower volumes. Differences in resolution are not subtle regardless of volume."

**********************************************************************************************************************************************************************
Danny is being disingenuous here.

A decent dipole sub can easily hit 105db somewhere in the bass. At high enough frequencies they will output more than a monopole. Mine (2 x AE IB12s) will theoretically do 113 db at 71Hz and 104 at 50Hz. However they will only do around 80db at 20Hz.

So while his GR subs can probably hit 105db, and can also probably play flat to 20Hz, they can't do both at the same time.

In spite of this being pointed out numerous times, he persists in fudging in the manner above.

Frankly, his (and his acolytes) constant hyping of everything he makes and consequent slagging off of every other manufacturer is rather tiresome and why on some respected forums mention of his products is specifically (and uniquely) banned.

It makes many people dismiss all of his products as nothing but hot air.

I recommended his servo subs in the OP's other thread, but I did so grudgingly for the reasons above.

Disingenuous?  Not at all.  I know because I was there.  SPL's in the 105-106dB range for the loudspeaker - NOT the sub by itself.  Powerful reproduction @ 18Hz as mentioned later on in this thread.  Tight, tuneful, power bass at ANY volume level.  Beyond that all of this is apples and oranges.

I really do wish that threads like these would not sink to the levels that some wish to drag them, especially by those that have no experience with the products that they deride.  This is really beneath the quality of the vast majority of the discussions here on AC.  Non-experiential discussion is called conjecture and should not be treated as gospel by anyone.

We also have a "dirty laundry" policy in effect that should preclude one from posting that X,Y or Z is the antichrist on another forum...  especially when other forums can have a definite agenda concerning some issues.

Just trying to "keep it real" here.

Dave

[Rclark]

I am also skeptical that servo's are needed for competent box-sub implementations either. For the guys that were curious, if you do your own forum searches elsewhere (or Amazon, etc, review sites), you will find plenty of people who have owned or heard Rythmik but felt that some other sub was just as good or better.

Here's a home theater focused comparison that compares 4 different subs in room, including a Rythmik and a HSU. The reviewers felt that out of the four, these two tied for sound quality and accuracy. I spoke to these guys at length later on and they both confirmed it. So it goes to show you that non-servo subs should also be auditioned and/or considered when shopping.

http://www.avsforum.com/t/1313176/shootout-epik-empire-vs-hsu-vtf-15h-vs-cht-cs18-1-vs-rythmik-fv15-vs-ed-a7s-450

"Then there's the HSU. It tied with the Rythmik in sound quality over the other subs, and again these two had their own distinct sound so you might prefer one over the other."

There is even video, sort of dramatically produced, and they show that the HSU starts and stops on a dime just as well without servo's

"(the HSU) Just always sounded clean, tight, no distortion or anything. Again, just look at the intro video, like the Rythmik you can tell this thing is as accurate as they come."

Again, that's just one example, but there's plenty of others like it. It wasn't a scientific AB test run by men in white coats, but it was real world, and unbiased. Anyway, Google is your friend.


Back to OB's.

[JohnR]

I really do wish that threads like these would not sink to the levels that some wish to drag them, especially by those that have no experience with the products that they deride.  This is really beneath the quality of the vast majority of the discussions here on AC.  Non-experiential discussion is called conjecture and should not be treated as gospel by anyone.

Why don't you lift the game then, Dave. Post some facts instead of conjecture and marketing BS.

[dBe]

Yeah but Dave, this is the same false scent that others have been throwing out. You listen to a servo OB, then you say you won't go back to boxes. So what? What does that have to do with why servo is needed for a competent OB implementation? Apart from a condescending post by Brian referencing a 25-year old paper, there hasn't been a shred of technical data to support any of the claims being made.

John, I take your point and fully understand your position.  I was there for a long time and just hated subs of any flavor.  My observation about "never going back" is simply a question of personal choice and the experience that almost 50 years being in the reproduction arts brings.  These years cover a lot of ground, but are primarily recording engineering, studio design and measurement work.  Doesn't make me an expert by any means.  It simply means that I hear the LF a lot better than the highs now and know what they are supposed to sound like.

I would not say that my predilections are a false scent... they are just mine.  A LOT of others with the same experiences as mine with the sensing coil servo control LF modules have the same opinions.  When it comes down to the final analysis the ear is the final arbiter in the appreciation of music.  The science is what it is having measured many systems and rooms over the years.  Physics don't change... just our understanding of them - at least on my part. 

I detest accelerometer based subs.  They never seem to get the LF right, sounding very mechanical in the low end.  They miss the microdynamics while getting the broad strokes right: hard to tell a P-bass from a Jazz.  The sensing coil is completely different in sound and feel. They get the "tuneful" portion of the lows correct.

As you said: YMMV.  I really hope you get to hear a good open baffle, servo (sensing coil) controlled LF module soon.  I think you will like it... a lot.   

Dave 

[JohnR]

it showed significant nonlinearity in speaker's suspension system and the box spring is 10 times more linear than that

Brian, I've seen a more recent analysis showing that the air is sufficiently non-linear to be significant. Shall I try and find a reference so you can give us your take on it?

With regard to suspension (and presumably motor) non-linearity, wouldn't the first step be to improve the suspension and motor? These things have happened in the last 25 years, haven't they - eg XBL2?

Finally, do you have measurements demonstrating some of the claims being about "stopping power" and the like?

Oh, one more question... are mms and Le significant parameters for a subwoofer driver?

[Early B.]

I am also skeptical that servo's are needed for competent box-sub implementations either. For the guys that were curious, if you do your own forum searches elsewhere (or Amazon, etc, review sites), you will find plenty of people who have owned or heard Rythmik but felt that some other sub was just as good or better.

Here's a home theater focused comparison that compares 4 different subs in room, including a Rythmik and a HSU. The reviewers felt that out of the four, these two tied for sound quality and accuracy. I spoke to these guys at length later on and they both confirmed it. So it goes to show you that non-servo subs should also be auditioned and/or considered when shopping.

http://www.avsforum.com/t/1313176/shootout-epik-empire-vs-hsu-vtf-15h-vs-cht-cs18-1-vs-rythmik-fv15-vs-ed-a7s-450

"Then there's the HSU. It tied with the Rythmik in sound quality over the other subs, and again these two had their own distinct sound so you might prefer one over the other."

There is even video, sort of dramatically produced, and they show that the HSU starts and stops on a dime just as well without servo's

"(the HSU) Just always sounded clean, tight, no distortion or anything. Again, just look at the intro video, like the Rythmik you can tell this thing is as accurate as they come."

Again, that's just one example, but there's plenty of others like it. It wasn't a scientific AB test run by men in white coats, but it was real world, and unbiased. Anyway, Google is your friend.


Back to OB's.

This shootout is useless for us. Those guys are home theater buffs. Two channel audiophiles are a different breed, and our desire for quality bass is quite different. I have two subs -- one for HT and one for audio, and they are very different for obvious reasons.
 

[JohnR]

I detest accelerometer based subs.

Are these OB or sealed?

[dBe]

Why don't you lift the game then, Dave. Post some facts instead of conjecture and marketing BS.

John, I'm not marketing anything.  Certainly Danny is a friend of mine and I am a customer of his.

I have years and years of measuring things.  I made a good portion of my living doing this for a long time.  My desire to measure things kicks in when they sound broken.  I have zero desire to measure things that sound right to me.  All I am saying here is that I like OB bass... never thought I would, but I'm a convert.

My other comments were made in an attempt to keep the discussion on track.  Nothing more, nothing less.  I just have a problem with personal attacks as you well know.  Ain't right.  I didn't mean to ruffle any feathers or step on toes.

Since I don't have measurements to contribute (I do not have a measurement facility with minimum dimensions of 2Fl = 125' - just to keep it linear without compression effects) and I seemed to have stepped into it, I'll bow out and let the chips fall, etc.

Dave

[dBe]

Are these OB or sealed?

Yes. Both.

Dave, out

[Rclark]

Like I said, it was just one example. And like I said, I did talk to them at length later and they did play music, etc. The subs were in the room and judged for their sound quality, as a seperate category, so it's relevent.

There are other examples out there, feel free to seek them out.

[JohnR]

Yes. Both.

Who makes an accelerometer-based OB servo sub?

[medium jim]

There is more than one type of subwoofer or bass that works peachy with Maggies...Dipole is one of them  

Jim

[dBe]

Who makes an accelerometer-based OB servo sub?

I did.  It sucked.  Used an old Velodyne driver/amp setup with additional bass boost.  Wouldn't play loud enough to continue on.

Dave, out... again

[JohnR]

I did.  It sucked.  Used an old Velodyne driver/amp setup with additional bass boost.  Wouldn't play loud enough to continue on.

 

Well, that's very adventurous of you, Dave, but I hardly think it qualifies as a data point.

[dBe]

Well, that's very adventurous of you, Dave, but I hardly think it qualifies as a data point.

True, but it told me enough to quit.  I'm old and slow you know.

Dave