[ebag4]

Can a 8" and 12" driver be driven off a single servo amp?  Would this combination offer any improvement over 20-200Hz as compared to a pair of 12" servos or three 8"?  Just thinking out loud here.  I am not certain there would be a benefit over a pair of 12" because they are servos, but it occurred to me that the 8" might have an advantage over the 12" in the higher frequencies of that range.  What if I wanted the pair to play up to 250Hz?  I am sure the output would be reduced as compared to a pair of 12", but in my small room that would not be an issue.

Thanks,
Ed

[Danny Richie]

Can a 8" and 12" driver be driven off a single servo amp?  Would this combination offer any improvement over 20-200Hz as compared to a pair of 12" servos or three 8"?  Just thinking out loud here.  I am not certain there would be a benefit over a pair of 12" because they are servos, but it occurred to me that the 8" might have an advantage over the 12" in the higher frequencies of that range.  What if I wanted the pair to play up to 250Hz?  I am sure the output would be reduced as compared to a pair of 12", but in my small room that would not be an issue.

Thanks,
Ed

No, you can't drive the 8 and the 12 with the same amp.

And both the 8 and the 12 will easily play up into those ranges.

[ebag4]

Thanks Danny, that is what I figured but thought I would ask anyway.

Best,
Ed

[mlundy57]

No, you can't drive the 8 and the 12 with the same amp.

And both the 8 and the 12 will easily play up into those ranges.

So how do you choose which to go with? Would physical dimensions be the only difference in three 8's vs two 12's or are there other differences/considerations as well?

[Jonathon Janusz]

I remember reading, when this topic has come up in the past, that 3x8 has maybe a slight advantage at the very top of the frequency range due to the smaller moving mass on each driver, while 2x12 is at the advantage at the very bottom of the range; 3x8 is flat to 20hz rolling off quickly after that, 2x12 can play with real authority into the teens. 

3x12, for sake of completeness with what can be run on one single-channel amp, is for getting headroom and or getting the sensitivity closer to either highly efficient or (effectively more efficient) line arrays/planars that don't drop at the rate of a point-source. 

Having heard the LS-X, I would suggest that 6x8 or 6x12 on a dual-channel amp would be the real way to fly when configuring the biggest planars/electrostats and line arrays to get the wave launch to match across the entire frequency range.  In my humble opinion, this being significant not so much to get "more" out of the sub arrays, but to more directly compliment the effortless presentation of sound only these really physically large designs can do by virtue of their size.

Beyond this, I would suppose it becomes a matter of aesthetics among different designs (both the speakers themselves and the look as placed in the room), as well as getting as much awesome as you can for a particular front baffle width.  Case in point, the sealed version of the 8" drivers sold direct through Rythmik are the last puzzle piece which made the best-of-show new Salk Exotica 3 speakers possible.  Using the 12" drivers in that application would have been possible, sure, but the added complexity of the cabinet design would likely have both pushed the design into a completely different price point and made the final aesthetic something other than what - taken as the complete package that it is - really struck a home-run at the show with a lot of people. 

From an OEM perspective, the form factors the 8" drivers open the doors to, along with the really limited frequency range anything placed on top of them is asked to produce, I think is what makes the 8" drivers the best kept secret in audio that has yet to hit the mainstream.  The 12" drivers are awesome, but "big".  The 8" drivers mean designers can sneak up on monitor/lifestyle footprint designs at <$10K retail price points, reaching customers in these market segments with something "new" they may never have had the opportunity to have in their homes due to limitations of traditional driver/cabinet design compromises. 

[Hank]

...the really limited frequency range anything placed on top of them is asked to produce...

Jonathan:  I don't understand this - can you elaborate?

[Jonathon Janusz]

Hank, I tried to elaborate on the advantage as a tool in designing a full-range speaker in having these "subwoofers" capable of playing as high in the frequency range as they can - Danny routinely playing them up to 200Hz and measuring them comfortably up even higher.  This, in my mind, means that one has a lot of versatility in whatever goes on "top" of the servo drivers as a foundation for the speaker.  Whatever driver(s) are chosen for a design to play the midrange can potentially truly - and exclusively - play the midrange if so desired, or cross wherever one chooses further down the frequency range to fit the desired voicing or specific capabilities or limitations on a chosen midrange driver.

In the design of a speaker using these "sub" woofers, I think it is a real advantage that whatever midrange drivers are chosen don't necessarily have to make music all the way down to traditional 80Hz and below "subwoofer" territory, should it work out better if they did otherwise.  This both from the perspective of working more closely to the ideals of a particular driver's advantages as well as bringing drivers (or cabinet designs for that matter) to the table which otherwise may not be otherwise considered when creating a speaker design due to a more limited useable frequency range down low.

Only having to build a "top" of a speaker to work with the servos that has to play at its best down to 200Hz or so opens a lot of doors.

Hope that clarifies my thought.  Cheers!

[Hank]

It was your wording that was confusing, stating that what's on "top" of these would be a limited frequency range - mids and tweets cover a far wider range than the "subs".  I agree with your core message:  "...whatever midrange drivers are chosen don't necessarily have to make music all the way down to traditional 80Hz and below "subwoofer" territory..."

[tasar]

Hank, I tried to elaborate on the advantage as a tool in designing a full-range speaker in having these "subwoofers" capable of playing as high in the frequency range as they can - Danny routinely playing them up to 200Hz and measuring them comfortably up even higher.  This, in my mind, means that one has a lot of versatility in whatever goes on "top" of the servo drivers as a foundation for the speaker.  Whatever driver(s) are chosen for a design to play the midrange can potentially truly - and exclusively - play the midrange if so desired, or cross wherever one chooses further down the frequency range to fit the desired voicing or specific capabilities or limitations on a chosen midrange driver.

In the design of a speaker using these "sub" woofers, I think it is a real advantage that whatever midrange drivers are chosen don't necessarily have to make music all the way down to traditional 80Hz and below "subwoofer" territory, should it work out better if they did otherwise.  This both from the perspective of working more closely to the ideals of a particular driver's advantages as well as bringing drivers (or cabinet designs for that matter) to the table which otherwise may not be otherwise considered when creating a speaker design due to a more limited useable frequency range down low.

Only having to build a "top" of a speaker to work with the servos that has to play at its best down to 200Hz or so opens a lot of doors.

Hope that clarifies my thought.  Cheers!

Hi Ed, thanks for the thread and Jonathon for bringing things full circle. Danny and the likes of Gedlee's pursuits, make room for further consideration. Can the argument be made that full range design problems be mitigated both sonically and build/cost wise, by building separate dedicated servos and concentrating on T-M designs that excel ?

[Danny Richie]

The servo system does cover the 200Hz range and down in a way that no other option can. And with the flexibility of phase control, crossover control with slope variation, extension filters, shelving circuits, variable damping settings, rumble filter, and adjustable EQ systems all built into the amplifier it does allow easy matching to just about anything covering the 200Hz and up range. 

[Tyson]

With a 2 way speaker, I can see the need for a heavier mass driver with a large magnet and big rolled surround to get it to produce a decent amount of bass in a single box.  But a mid-woofer is a compromise in design to accomplish this.  Much better is a 3 way speaker with a mid driver that doesn't do bass at all, but only covers the midrange.  Lighter, stiffer, more efficient drivers simply give you better midrange clarity and detail. 

The tragedy of the high end is that most 3 was speakers don't do this - they simply add a bass diver to a standard 2 way and call it a day. Danny's designs tend to avoid this, at least as far as things like he Super V (and V2), and the Serenity Super 7 - all have dedicated midrange drivers that don't do much in the way of bass.  But they all have bass drivers that cover the full bass range and a mid driver that is really focused on the mids.  That is smart design.

[bdp24]

And for those who already have a 2-way speaker they like, adding a Servo sub or two is THE way to get a full-range system, rather than getting a 3-way that is not as good in the mid-to-high range AND not as good in the bass range. The old audiophile complaint about subs not blending with speakers has been made moot by the GR Research/Rythmik Servo Sub, IMO. What "full-range" speaker in the price range of a monitor speaker like one of Danny's (or, for those who want a fully built 2-way, the, for instance, KEF LS50) mated with a Servo woofer or two, has bass reproduced as well as the Servo sub? None.

[LFM]

What has to be done to the servo amp to play up to 250 hz? In the website pics, the crossover pic shows 125 hz as the upper limit.

[Danny Richie]

What has to be done to the servo amp to play up to 250 hz? In the website pics, the crossover pic shows 125 hz as the upper limit.

These are reference numbers on the amp that indicate electrical slope changes. It is not a reference to acoustic output. Remember a crossover point is where both drivers are 6db down in output.

[LFM]

Danny, I am still a little bit confused. Using the 24 db/ octave setting at 120 hz should really pull down the response at 250 more than 6 db. The 12db setting less so but still significant. The only way I can see to raise the outpu as the result t higher would be to apply boost at the 120 hz limit with the parametric eq. I don't think this is desirable as the result may really deviate from from flat response.

[Danny Richie]

Danny, I am still a little bit confused. Using the 24 db/ octave setting at 120 hz should really pull down the response at 250 more than 6 db. The 12db setting less so but still significant. The only way I can see to raise the outpu as the result t higher would be to apply boost at the 120 hz limit with the parametric eq. I don't think this is desirable as the result may really deviate from from flat response.

The 24db per octave options add another 12db per octave slope at 50Hz or 80Hz. So it is there for low crossover points.

The Super-V crosses in the 180Hz range. To get that the crossover setting needs to be set in the 80 to 90Hz range.

On the Super-7 that I designed for Serenity Acoustics the crossover point is in the 200Hz range and the setting on the amp is in the 90 to 100Hz region.

[rythmik]

Danny, I am still a little bit confused. Using the 24 db/ octave setting at 120 hz should really pull down the response at 250 more than 6 db. The 12db setting less so but still significant. The only way I can see to raise the outpu as the result t higher would be to apply boost at the 120 hz limit with the parametric eq. I don't think this is desirable as the result may really deviate from from flat response.

The amplifier is also used for a sealed version which has an upper limit of 120hz limit by servo operation. The OB physical design can extend a bit higher (Danny can answer that).  The actual LPF circuit itself has 200hz extension (12db/oct). That is also why Danny can use OB sub up to 200hz for super V. On the decal, the 80hz point is correct.  So for OB operation, the xover knob between 80hz and 120hz is actually 80hz to 200hz.

I know this can be a bit confusing. But it is a bit more difficult for us to have too many versions of same amp with one for each driver type.