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06-12-2006 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 1
Post ID: 2515
Reply to: 2515
Exceptional loudspeakers drivers

Audio people know that loudspeakers mostly define the quality of sound reproduction. Also, everyone knows that the capacity of the loudspeakers mostly determined by the capacity of the drivers that loudspeakers use. Regardless of the topologies, applications and many other things.... if you have "bad sounding” drivers then all your further efforts become irrelevant. I usually with laugh look at many audio people who seriously pontificate about the importance of the minute details of their amplification or front-end but who disregard the fact the they load their entire system to the loudspeakers that employ drivers made from gravestone marble.

In this thread I will slowly posting information about the drivers that from my point of view defend own class. They are so good that the entire system might virtually be centered to serve an interest of this specific exceptional driver. I will be talking only about the drivers that I personally know and personally heard (like anything else within my site). If you have your own experience with drivers that you find exceptional then feel free to share your views about the Hall of Fame of loudspeakers drivers.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-13-2006 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 2
Post ID: 2517
Reply to: 2515
Exceptional loudspeakers drivers: 18-inchers

Let start from the largest drivers and go down. There are larger then 18” drivers (23” and 30”) but looking at this magnet structures I do not find them serious. I addition to make the 23” cone stiff enough requires a lot of diaphragm’s mass or to use very “bad for sound” materials.

The 18” driver would certainly be a woofer. If 18” driver used above 60Hz then it is misused. To my knowledge there was only one exceptional 18” driver even made… or perhaps it was a small family of the drivers that pretty much derive from one father: the AuraSound 1808 driver.

Aura made their 1808 driver in 80s and most of the 90s and it was wonderful. It had huge high-temperature neodymium magnet, unique magnet geometry with underhung 4" edgewound aluminum voice coil.  It was the only 18-inchers underhand voice coil ever produced. The finny part that despite of the underhand configuration it had 98dB sensitivity with 2” total excursion – what a motor! The driver had paper cone, cloth suspension and had phenomenal articulation at lowest frequencies. The 1808 was suggested for 20 Hz - 200Hz but it did not sound good even at 80Hz. The Aura 1808 had free air resonance at 24Hz and required enormous sealed enclosure of 14-16 cu feet.  Wilson Audio used the Aura 1808 in their unfortunately-ported XS subwoofers and soaked from their relatively small enclosure an extra 19dB of port noise at 20Hz.

The mid of the 90s was great time for the “exceptional 18” driver”. If you do not like the large boxes of the Aura 1808 (that in reality had Fs from 24Hz to 28Hz) then you could get form North Creek Music their version of Aura 1808.  They call it Leviathan and it was a next step into the wonder of the Aura’s motor. George Short (the North Creek Music’s guy) took the Aura 1808 and changed the cone’s suspension, effectively dropping the free air resonance down to 11Hz-13Hz. Now it was possible to use this driver in 5-6 cub feet sealed enclosure and get out of it an amassing bass in context or relatively low size, Sure you would not use the 11Hz Leviathan with 500W amplifiers, as the crazy pro audio people would do at their stadiums, but who cares about the stadiums?

There was a lot of controversy how to drive the Aura 1808. People use a lot of power; many hundreds watts… I always thought was not necessary for home use. I use Lamm M1.1, 110W of class A, PP hybrid. However the best result I was getting out of Aura 1808 when I drove it, believe me or not, by the Lamm ML2, 18 watt SET.  I did not feel that it was enough power but when it was enough the bass was like nothing else. So, what would be the scenario for use of the exceptional Aura 1808/ Leviathan driver? Two appropriately large sealed enclosures, with added mass (use Leaded Soft Density Fibreboard) driven by some kind of SET around 833A tube, relatively light loaded. (Or perhaps I might be the New Zarathustra hybrid? Will see….).

Unfortunately in the end of the 90s the Aura become the AuraSound and the 1808 driver become the NRT18-8. The NRT18-8 uses the same basic motor with slightly less sensitively and slightly higher resonance.  However, nowdays the AuraSound saturated their paper cone with epoxy to accommodate the barbarian 1000W amplifiers of the DJ installations. Epoxy on a driver’s diaphragm means an instantaneous death for sound and the new NRT18-8 driver sounds with no tonal discrimination at lower octave: juts a high quality generic LF boom.  The NRT18-8 sounds like a Boolean: yes-bass vs. no-bass, It is good for the Patricia Barber’s double bass and the taste of an average hi-fi Moron™ but it is very bad for any more civilized reproduced sound.

In the end, the Aura 1808 is the 18” treasury. In a proper sealed box it might give you an idea what theoretically possible to get out of the 18” driver. Find a good amplification for it, integrate it properly in your playback and forget about the lowest octave to the rest of your life. I doubt that more interesting 18” driver ever would be produced as there is no market demands for a good sounding 18-inchers… The Leviathan is no longer available, the beautiful Aura 1808 is replaced with Morons-accommodated NRT18-8, no one does 18” without those ports anymore… Cheating is good for high school exams but defiantly does not work for sound at lowest frequencies…

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-15-2006 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 3
Post ID: 2522
Reply to: 2515
Exceptional loudspeakers drivers: 15-inchers

The exceptional 15-inchers would be two fitted in two categories: the bass 15-inchers and wide-range 15-inchers. It is imposable to think about the exceptional and wide -range 15-inchers and do not mention the 1946 -1973 production of the Tannoy Dual Concentric drivers. The idea was wonderful, the implementation was very good and the drivers (Gold, Red, Silver) are incredibly interesting. The 15-inchers Tannoy Dual Concentric require custom very sensible enclosure (the default Tannoy enclosures were compromised) that required a lot to taste and understanding. However, if everything is made properly then the Tannoy Dual Concentric does incredibly well. Of course the contemporary production of the Tannoy Dual Concentric is garbage….


Tannoy Dual Concentric

There is one interesting contestant thought…. I have unconfirmed evidence that the infamous Harry Olson had his own 15-inchers Dual Concentric driver. I heard a speaker that reportedly was Olson’s speaker and it was very interesting, free from some problems I observed in the Tannoys. Unfortunately during that the only listening session the Olson’s speaker was in context of an installation where was very difficult to say anything more critical…

That lead us to another category: the bass 15-inchers. The bass 15-inchers are the mostly misused drivers. It is know that the lowest octaves (sub 40Hz) and upper bass (above 40Hz) must not be handled by the same driver. So, if the lowest octaves are the target then why to stay with 15”? The Exceptional 18-inchers would be the direction to go. For the mid bass – the primary duty of the 15-inchers there are: Vitavox AK-151, Vitavox K15/40 and Altec 515G. They all pretty much the same drivers with very slightly different come materials but they all sound very wonderful. Vitavoxes is more advanced tonally then 515G but it is not an issues. The biggest problem is that the 15-inchers mid bass driver practically always misused.  The AK-151 and 515G have free air resonance around 40Hz and they are perfect for a 50-60Hz horn (I mean  a property done horn only). In the 50-60Hz horns they do phenomenally and really define their class. However, the Morons™ are not satisfied with 50-60Hz horns and they do not complement the 50-60Hz horns with the desisted LF sections. Instead they try to push out of their 50-60Hz horns lowers frequencies and by doing this they screw up everything.


Altec 515B

They mostly do it by loading their horns with 15-inchers of lower resonant frequency. There are quite few of them available (even Altec did the 515B and E with Fs of ~25Hz) but as soon this type of the driver loading a 50-60Hz horn then the problems begin as if a horn cares the acoustic pressure lover then it horn rate then it severally compress the 1-3 octaves above the horn rate. As the result we have a family of wonderful paper suspended 15-inchers drivers, with great tone but completely usable: you can’t put them in horn and you can’t put then in a sealed box because they have no excursion. The only suitable mid-bass application for the 15-inchers with Fs of 25Hz that I see would be a large line array of 6-12 drivers per channels where the combined sensitivity would not alloy then to hit their max excursion. Still, it should be only for smaller rooms and good lack to fit in them a pair of enclosures with a dozen 15” drivers….


Vitavox AK line

In the end the 15-inchers is very strange animals. Even for midbass they decay too fast in HF in most of the cases. People use them to get more pressure for the larger rooms. It has usually it’s own set of problems that it very deferent subject…I think that 15-incher should die out at ~250Hz-300Hz where the “fundamentals channel” should take over”. Before the “fundamentals channel” kick in, if you select the “15-inchers solution” then you would hardly find anything more interesting then AK151….

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-16-2006 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 4
Post ID: 2528
Reply to: 2515
Exceptional loudspeakers drivers: 14-inchers

Oops, I almost forgot the size of 14”. This is kind of off the wall size but still there was two exceptional drivers in this size that I met.

The first is JBL 1400ND. The 1400ND was initially used in JBL K2 system. It had underhung voice coil, neodymium magnet and what is more important quite interesting sound. It was not particularly powerful driver but combined in array it was able to do very well in mid-size rooms. Nowadays the JBL 1400ND is long done and it replaced by 1500AL. I have no personal experience with 1500AL and do not know how good it does.

Another exceptional 14-inchers was Klangfilm KL-L405. It was far from prefect. It should be high-passed, it has low power handling, it had high resonant frequency for 14” and it had severs details deficiency. Actually it has no micro-details at all. However it has quite interesting macro tone that it in a way was exceptional. Properly used, in a correct horn and in relatively small room the KL-L405 was a very good solution for 70-500Hz.

I met once the filed-coil version of KL-L405. The electromagnetic version was very poor sounding and would not be suggested for any other reasons then just spread the electromagnetic paranoia and then sell it for some profit.

Rgs,
Romy the caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-16-2006 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 5
Post ID: 2529
Reply to: 2515
Exceptional loudspeakers drivers: 12-inchers
It always was mystery for me but there is no good 12” drivers outs there, at least that I know. There are many 12-inchers out there but all of them are not good.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-06-2006 Post does not mapped to Knowledge Tree
Knightcrawler
Posts 3
Joined on 07-07-2006

Post #: 6
Post ID: 2636
Reply to: 2517
Re: Exceptional loudspeakers drivers: 18-inchers
The Aura 1808 had free air resonance at 24Hz and required enormous sealed enclosure of 14-16 cu feet.  Wilson Audio used the Aura 1808 in their unfortunately-ported XS subwoofers and soaked from their relatively small enclosure an extra 19dB of port noise at 20Hz.

The 1808 was designed for a large vented enclosure. Just looking at the TS numbers would indicate a large vented box to be best. It also worked well in horn loaded designs as well.

PS: The wilson Audio XS was a great subwoofer just completely overpriced.
07-06-2006 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 7
Post ID: 2637
Reply to: 2636
I would disagree.

 Knightcrawler wrote:
The 1808 was designed for a large vented enclosure. Just looking at the TS numbers would indicate a large vented box to be best. It also worked well in horn loaded designs as well.
I did not says what it was designed for I said that “required enormous sealed enclosure”. I disagree with entire concept of recognition of T/S recognition in order the driver “to be best vented box”. How a driver could be at ”it’s best” if the ported enclosures do not produce acceptable sound? Also, Knightcrawler, the 18” throat with 2.5” max-to-max excursion? What link of horn you have in your mind? The only place where the 1808 was use were the shallow pro horns where the speakers “looked like horn” but essentially acted as direct radiators at lower frequency. Anyhow, I would personally never put the 1808 in a horn, regardless the side of the room (stadium).
 Knightcrawler wrote:
PS: The wilson Audio XS was a great subwoofer just completely overpriced.
 Hm, I have to disagree with everything? Right? It was not necessarily overprized. It cost $18.000. A pair of drivers is $2.000, a well made <30 x <30 x >80 enclosure is ~$3.000, making it $5.000 all together. 50-60% of the dealer mark up is 10.000 and $14.000 -$15.000 all together. Add here the marketing expenses, transpiration cost, replacement and warranty cervices and it would not look like a lot of money left. Of course it is expansive from a different perspective (a person need 2 subwoofers) but those type of objective must be expensive. My major beef with Audio XS that if person do go for this level of demands and pays such a huge amount of money for subwoofers, dedicated amplification and space on his/her room then the person deserve to have more interesting result then a ported enclosure of XS is cable to deliver. So, I would not call the EX overpriced but rather unreasonably designed.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-07-2006 Post does not mapped to Knowledge Tree
Knightcrawler
Posts 3
Joined on 07-07-2006

Post #: 8
Post ID: 2639
Reply to: 2637
Re: I would disagree.
 Romy the Cat wrote:

 Knightcrawler wrote:
The 1808 was designed for a large vented enclosure. Just looking at the TS numbers would indicate a large vented box to be best. It also worked well in horn loaded designs as well.
I did not says what it was designed for I said that “required enormous sealed enclosure”. I disagree with entire concept of recognition of T/S recognition in order the driver “to be best vented box”. How a driver could be at ”it’s best” if the ported enclosures do not produce acceptable sound? Also, Knightcrawler, the 18” throat with 2.5” max-to-max excursion? What link of horn you have in your mind? The only place where the 1808 was use were the shallow pro horns where the speakers “looked like horn” but essentially acted as direct radiators at lower frequency. Anyhow, I would personally never put the 1808 in a horn, regardless the side of the room (stadium).
 Knightcrawler wrote:
PS: The wilson Audio XS was a great subwoofer just completely overpriced.
 Hm, I have to disagree with everything? Right? It was not necessarily overprized. It cost $18.000. A pair of drivers is $2.000, a well made <30 x <30 x >80 enclosure is ~$3.000, making it $5.000 all together. 50-60% of the dealer mark up is 10.000 and $14.000 -$15.000 all together. Add here the marketing expenses, transpiration cost, replacement and warranty cervices and it would not look like a lot of money left. Of course it is expansive from a different perspective (a person need 2 subwoofers) but those type of objective must be expensive. My major beef with Audio XS that if person do go for this level of demands and pays such a huge amount of money for subwoofers, dedicated amplification and space on his/her room then the person deserve to have more interesting result then a ported enclosure of XS is cable to deliver. So, I would not call the EX overpriced but rather unreasonably designed.

Rgs,
Romy the Cat


The 1808 in a vented box produces some of the best bass I've ever heard. I know some have a beef with vented enclosures but when designed right the sound can be brilliant. I've heard plenty of sealed, vented, bandpass and horn loaded designs. The 1808 is pretty tremendous in a well design enclsure and a powerful amp.

A neighbor has two Wilson XS and loves them, they sound great for classical music and movies. The ports are to small for the design but the sound quality didn't seem to suffer from it.
07-07-2006 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 9
Post ID: 2640
Reply to: 2639
Re: Aura 1808 and Wilsons

 Knightcrawler wrote:

The 1808 in a vented box produces some of the best bass I've ever heard. I know some have a beef with vented enclosures but when designed right the sound can be brilliant. I've heard plenty of sealed, vented, bandpass and horn loaded designs. The 1808 is pretty tremendous in a well design enclsure and a powerful amp.

A neighbor has two Wilson XS and loves them, they sound great for classical music and movies. The ports are to small for the design but the sound quality didn't seem to suffer from it.

Knightcrawler, well we basically agree that the 1808 was a wonderful driver. Let keep our views about the cones and pros of the ported enclosure out of the thread. It was the “best bass you've ever heard” but you did not hear the 1808 identically well implemented in appropriate sealed enclosure, didn’t you? Also, I have to give to the Wilson XS some credit as the ported enclosure if you cross them very low (25Hz for instance) do not manifest many negative characteristic as there is not sound in there anymore but juts pressure. BTW, do you know that Wilson use the 1808 on few reiterations of their Whow subwoofer.  I believe they have 4 versions and one of them was made with 1808. Do I have to say that it sounded way more interesting then Whow usually did?

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-18-2006 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 10
Post ID: 2668
Reply to: 2515
Exceptional loudspeakers drivers: 10-inchers

We enter a complicated region as the lower driver we go the drivers could be used for different purposes and it is very hard to generalize. A 10-incher might be MF driver and LF driver. In my past I experimented with few MF 10-inchers, including some vintage field-coil 10-inchers, but I was not able to find any interesting driver. Giving this I have to note that in context of acoustic system that I was experimenting I had no proper application for 10-incher MF driver. Still, I did not see anyone ever has any reasonable use of the 10-inchers in MF. Sure there are wonderful older Tannoy dual-concentrics 10-incher but they are for different purposes. I’m sure that for correct application it would be possible to find/make a good MF (to be more precise: lover midrange – upper bass) driver.

What I did search and experimented were 10-inchers woofers. I very much like the Scan-Speak woofer made around their SD1 motors.  They use a very interestingly intentionally overhang constriction that has very soft sounding “enter into distortions”. The cones are very soft and the rubber suspension is very interesting for given resonance frequency. It has 20Hz of Fs but the suspension is not soft and uncontrolled like with most of the drivers. They are kind of stiff but flexible at the same time. What is the most beautiful in them that the “stiffness” of the suspension is very “smartly” relates to the firmness and mass of the cone. As the result, sonically the driver’s cone and the driver suspension act together as a semi-“varimotion transducer” when the stiffness of the cone is not identically access the cone but gently changes with radial proximity to the peripheral. Of course they are very much not varimotion but the special anti-resonance rubber that Scan Speak uses in their 25W/8565-00.

It is important to mention that there is a faulty notions the LF driver should act as a piston and the cone should not break. I do not feel this way and the best sounding “bandable” and breakable paper cone drivers are the direct evidence of it. Tone it is exactly what comes from the “band” of cone and it the cone is too stiff that you have the “jazzy upper pPPP’ass” bass…

For a first time I discover them when John Dunlavy introduce his Dunlavy SC-IVA model as a replacement of SC-IV. The SC-IV wee horrible speakers but had no bass at all, despite of their size. In the SC-IVA Dunlavy trashed the garbage drivers that he use and put the 25W/8565-00 in the game. The result was remarkable and the SC-IVA had much more interesting bass then SC-V and monstrous SC-VI. Of course Dunlavy normalized impedance of 25W/8565-00 and did some other thing that screw them up but still, even given all of this I feel that Dunlavy SC-IVA  (if they were properly used) had the best bass among all commercial speakers.

The only problem that I see in the 25W/8565-00 is to low sensitively. The key with them is to use more of them. Still, they do not handle a lot of power and should not care too much upper bass sound in them. I cross the arrays of 6X25W/8565-00 at 60Hz, first order and I do not feel that it is best configuration for them, since my line array is essentially a compromise between a line array and not existing midbass horn. I feel the best crossover point for 25W/8565 would be 40Hz and second order. It would be interesting to put them deep into low pass transition slope but with the restricted power handling it would be difficult to do.

So, if you find any other 10-incher with primary resonance of sub 20Hz and with “this tone” then let me know. Until then I would consider the SS 25W as an exceptional driver. Still if this drive would be 100dB sensitively then it would be ….more exceptional…

Rgs,
Romy the caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-06-2007 Post does not mapped to Knowledge Tree
NBC
California
Posts 22
Joined on 08-10-2006

Post #: 11
Post ID: 4162
Reply to: 2517
1808 Enclosure Details
Hi Romy,

1) What dimensions for 1808 baffle would you suggest?


2) Is floor-firing vs. front-facing cone useful or preferred?


I believe you wrote LF channels should be placed in arc outside midbass channels.


3) Any *general tips* about placement of 1808 cone(s), in relation to midbass horn channel (e.g., time alignment) and room boundaries?


4) Your thoughts about digital equalization (DEQ2496) for <50Hz subwoofer channel ONLY? 

Regards,
Neil
04-06-2007 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 12
Post ID: 4166
Reply to: 4162
It is all depends…

 NBC wrote:
  1) What dimensions for 1808 baffle would you suggest?

It would be easy to circulate from the resonance frequency of the driver. The 1808 marked at 24Hz but in practice it could be anything from 23 to 29Hz. Since you will not despite a lot of power on the driver I would drop own resonance frequency as low as possible. The Northern Sound made it as low as 11Hz that should make the box much smaller. With default version go big, 14-15 cub feet will not hurt, larger is better but the exec number should be calculated, it very simple.

 NBC wrote:
  2) Is floor-firing vs. front-facing cone useful or preferred?

Depends of the frequency and the slope. If you make it to run only at the lowest octave then it would be no deference if were floor-firing or front-facing

 NBC wrote:
3) Any *general tips* about placement of 1808 cone(s), in relation to midbass horn channel (e.g., time alignment) and room boundaries?

Nope, there are never any “general tips”

 NBC wrote:
4) Your thoughts about digital equalization (DEQ2496) for <50Hz subwoofer channel ONLY?

It is all depends how good your LF amplifier and how evolved your reference points for bass reproduction.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-07-2007 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 13
Post ID: 4176
Reply to: 4166
Don't forget the wheels!
Hello NBC,

If you have the space, and the sense of humor, go with a large pair of SEALED enclosures.

If done right, it will change your life.

Regarding the Northcreek Audio version of the 1808 : According to some research I did a while ago, this driver has not been available for a long time.

Some say that Northcreek simply glued on a second cone, thereby adding mass, and bit of stiffness (depends how they glued the cone). I was also told that at one point they got the mass up by adding weight under the dust cap.

Adding mass will certainly lower the free-air resonance of a driver, but it is just that much more mass the motor will have to "articulate".... accelerate, stop, and re-accelerate in the opposite direction... in this case, anywhere from 15 to 60 times per second. Even with the neodymium-cocaine magnet, this is not easy... something like jumping rope immediately after gorging yourself on an XL pizza...

More moving mass for the same effective piston area has to result in soggier bass.

If you don't already have the drivers, you may want to consider a pair of 18" McCauley 6174s. This is a paper cone driver (at 222 grams the moving mass could be lighter ; the rear surface of the cone is coated). One or more of the same people who came up with the 1808 participated in the creation of this driver. The McCauley specs list Fs at 20Hz, but they have not updated this figure since changing to a different suspension material a long time ago.

These drivers are not perfect, but in a way, they are closer to the original 1808 (paper cone model) than the current Aurasound product. I would guess the McCauleys could be made even better if it did not have to take into account the demands of the "Pro Audio" world.

I use a pair of them in sealed enclosures (15 cubic ft each) made from concrete. In these boxes, with no EQ, they roll of at 40Hz. With some help (this is the only place I use EQ) from a Velodyne SMS-1, they can be EQed flat (or rising) down to 18Hz. This is because the drivers have a lot more excursion than is normally required for home use. They can handle, but DO NOT REQUIRE a lot of power (94dB/watt @ 1m)... A pair of Lamm M1.1s drives them very well (as a reference for power, this is more than enough to simulate Sunday mass in a cathedral... not that its your thing, but they will also effortlessly best even a good discotheque in both quality and quantifiable pressure).

In my opinion, the SMS-1 is almost mandatory... Not only does it allow you to completely control crossover frequencies EQ, phase, etc, but it also allows you to SEE a real time plot of the repeating swept tones it generates... you can see what is going on, and how it relates to the rest of your speakers. But it is not idiot proof... you can of course make a mess.

Last point : Before finishing the enclosures, I did a little testing with the lids off... The pressure from these drivers is out of proportion to what you might expect could come from a piece of paper... it was enough to lift and rattle two concrete slabs (2 X 36 lbs) I had placed over the top in a futile attempt to create a temporary seal.

Good luck,

(if you go with concrete, at a half a ton, you will want wheels in place of spikes)

jd*


How to short-circuit evolution: Enshrine mediocrity.
04-07-2007 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 14
Post ID: 4177
Reply to: 4176
What sets the Aura’s motors apart.

A few points I would like to make. I do not know if the Northcreek dropped resonance by adding mass or by softening suspension. I hope they leave the cone along and softer the suspension of the driver instead off adding mass. Sure it would reduce power handling but acoustically suspended it would not be a problem for this driver. The 1808 was made to handle a huge amount of power in pro applications and a few dozen of watts on the driver in a small listening shoe-box room will not really stress the driver to its critical excursion. Also, some words about the McCauley 6174 and possible other contesters. There are good drivers out there and many companies (I do not mean the McCauley – I never had thier drivers) love to say about their drivers high excursion (with is not necessary is better BTW). However, what the companies always “forget” to mention is what percentage of their excursion is in the “underhanged” mode. The driver can run even across 4 inches but as soon the driver coil jumps out of the area of the linear magnetic lines of the perfectly saturated gap then any further excursion is good only for Rap music and for the taste of the Absolute Sound “writers”.  (in fact the moment when the coil switches from the underhang to over hang more is the worst) The whole beauty of the 1808 that it has a small “emerged” coil (it’s with high sensitively as the same time – big rarity!) and “complimentary” to the small coil it has a long “active” gap. This keeps the coil move in linear magnetic invariant over a very long excursion. If I am not mistaken then it is 1.5” in undaunted mode out of 2” of total excursion! I it the highest numbers among all know to me 18” drivers and this is what set the Aura motors apart… It is from one point of view a huge waste of magnet… but is it what it sounds so good.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-07-2007 Post does not mapped to Knowledge Tree
NBC
California
Posts 22
Joined on 08-10-2006

Post #: 15
Post ID: 4178
Reply to: 4166
Baffle Dimensions
Thanks Romy,

Yes, I received your advice in the past privately regarding proper size for 1808 enclosure, and I thank you for pointing me in right directions. Yes, sealed box is simple calculation using e.g., WinISD. I am experimenting with thick walled (5/16") 24" diameter Sonotube and fiberglass stuffing, yielding aproximately 14cft.

(Structural reinforcement could include placing a larger 30" cylinder around the 24" cylinder, and filling the gap with sand, which would allow me to break down, move or transport the sub if necessary.)

However, in the above post regarding "dimension of the baffle", I was referring to actual ***baffle*** dimensions, as opposed to cabinet volume. Although my cabinet would logically have a round baffle, it would be a simple matter to create a rectilinear one.

What baffle dimensions did you settle on?


Michael Green of Green Mountain Audio, for example, wrote the following about baffle geometry for low bass systems. (However, at the end of the article he states there is some (unknown to me) type of math involved in calculating proper baffle size, in relation to the room boundaries:
  

Considerations of shape

A cabinet face can be too large or too small. Too large, and it delays some of the energy in the low bass from reaching the wall behind the subwoofer as soon as possible. In the middle bass, it will also throw an 'acoustic shadow' onto that wall. Yet, this wall reflection is needed as soon as possible, because it will reinforce the low bass that is still being pushed out from the subwoofer driver. The result is less uniform bass in the room and a subwoofer that is more difficult to 'place.'


If the cabinet face is too small, the woofer cone's air pressure in the middle-bass range slips around that cabinet face before the cone can complete its pressure cycle. The result is an uneven tone balance and lack of impact in that middle-bass range.

The reason for this loss of energy is interesting, because it affects so much of what we hear: As a woofer cone begins to move, it initially pushes against the nearest air molecules. Those molecules say "Thank you!" and immediately speed away. As those molecules speed forward in all directions at a speed 10 times faster than a car on a highway, they collide with other air molecules. Through those collisions they transfer their momentum.

Thus, the energy of that cone's initial push continually slips away, which is called a 'loss of radiation resistance.' The lower down the scale towards the bass we go, the greater that loss -- because the cone is required to spend an even longer time pushing out and then 'pulling' back.

That longer time gives the air molecule collisions even more time to flow away from the cone. For a 30Hz, very low bass note, the first collisions have spread out to a radius of nearly 3 meters distant by the time the cone finishes its first outwards push. Those distant collisions are blissfully unaware that the woofer is still pushing forward. Behind those first collisions lies a trail of more collisions, extending all the way back to the cone's surface. Each is unaware that the woofer is still pushing, because the woofer is only moving forwards at 0.5 meter per second while those collisions take that push and distribute it at 340 meters per second.

Thus, the energy of the woofer's initial push and subsequent 'pushing' continually slips away, in all directions, and does so more and more as the scale is descended. Its radiation resistance is decreasing with decreasing frequency.

In this regard, however, the floor is our friend. It holds some of those collisions near the subwoofer's cone and helps increase the radiation resistance, particularly in the middle and lower bass. The wall behind the subwoofer and your ceiling also closely hold some of those collisions -- the ones from the lowest bass -- to increase the radiation resistance in that range.

The goal is to have a uniform radiation resistance. When the effects of the wall behind and the floor and ceiling are calculated, there is math which shows the size of the subwoofer's cabinet face that will smooth the transition between all those surfaces.


http://www.greenmountainaudio.com/Speakers/Hammer%20Brothers/DesignConcept2.htm

Regards,
Neil

PS: This may be getting off track from your original thread topic about the best drivers. Feel free to move and rename the thread to something like "Implementing sealed lower bass solutions" if you like.
04-07-2007 Post mapped to one branch of Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 16
Post ID: 4180
Reply to: 4178
A little excursion...
I completely agree that in a home setting, even if you love "Drum & Bass" and Hip-Hop, you will never ever use anywhere near 2" of cone excursion.

Romy wrote :
"...what the companies always “forget” to mention is what percentage of their excursion is in the “underhanged” mode..."

According to McCauley, the 6174 has a maximum total excursion figure of 50mm, but in their specs they give a "Max BL Excursion" figure (the linier part of the excursion) of 15.24mm, so this is one case where the manufacturer is quite honest.

According to Aurasound, the NRT 18-8 (what the 1808 has become!) has a similar max excursion, and remains liniar through 18mm of that distance, so it is theoretically a little (2.76mm) better. They both have similarly large and shallow voice coils (each having their own in-house terms to describe the winding). A more substantial difference is a result of the magnet materials ; Aura opting for neodymium, which results in a BL factor of 24.5 T/m, where the McCauley driver is at 15.3 T/m, and gets there using a pair of really big soft iron magnets. The weight of the magnets alone (26 lbs) is nearly as much as the weight of the completely assembled Aura driver.

The other notable difference I see is cone material. McCauley sticks with a natural fiber cone, while Aura uses composites.

Aurasound's spec sheet gives an Fs figure of 25Hz, so 20% higher than the McCauley driver.

To summarize : In the case of the Aura driver, you get the high-Tesla neodymium magnet, but with it you have to take higher Fs, and a cone that has been "reinforced with fiberglass and epoxy". This may appeal to some, but if you think of the cone in terms of resonance, instead of pumping air, you will start to see it differently.

If it matters, the cost of the drivers in the US is close enough in either case for it not to be a determining factor.

In my case, the final decision was tipped by availability, and by McCauleys French distributor, who is really very good (but does not sell directly to the public). The people associated with distribution of Aurasound products on the other hand were in general more difficult, and in all cases added a fat markup.

With regard to baffle size :
In my case (front-firing) : 2ft x 6ft
Driver sits one third of the way up from the floor.

The box is deeper than it is wide... I purposely stayed "small", reasoning that it would be a simple matter to extend the baffle surface (widening it with additional panels), and that it would not be so simple to make it narrower.

I do not detect the need to alter the baffle, so have not yet tried.

jd*


How to short-circuit evolution: Enshrine mediocrity.
04-07-2007 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 17
Post ID: 4181
Reply to: 4180
In the real world of the 18-inchers...

Hm, the 18mm out of 50mm in “fully in-gap mode” for Aura? It sounds too bad.  The last time I touched this subject it was 6 years ago and I remember I had better impression in term of the numbers.

I just looked at the Aura page:

http://www.aurasound.com/public/discontinued/images/spec/nrt1808_b.jpg

It has Xmax = 18mm(.71”) but, Jessie, you forget that Xmax is one-way excursion.

The next page sad:

http://www.aurasound.com/public/discontinued/images/spec/nrt1808_a.jpg

The Linear Excursion (pick-to-pick) 38mm (1.5”) out of 50mm (2”). That sounds more what the “consumer” numbers that I remember.

Also a few further comments. Aura is 5dB more sensitive then McCauley.  The other notable difference is the material of suspension. McCauley suspends fiber cone with rubber, while Aura uses fiber composites and suspends it with soaked fabrics. The epoxy reinforcement that you mention used only in Aura to glue the cloth to the driver. It  is not much epoxy but it is still not good – epoxy must not be use anywhere on the drivers (though we do not know how McCauley glue rubber to cone).  O do not know the neodymium vs. “soft iron magnets”. Generally higher BL factor considered better but it is not always the case. It should be heard in order to recognized how it warks all together.

It is possible that McCauley is fine 18-incher. The problem is that it is VERY difficult to sonically evaliate the sound of those drivers in the equal conditions. If one has in his possession for instance that McCauley 6174, the Aura 1808 and the Seismic 8196 then can you imagine a person to modify those huge boxed in order to make the operating conditions equal? So, I feel in the real workd a person makes a purely intellectual decision and then juts go with the selected driver, trying to get the best out of the given design/driver.

The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-07-2007 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 18
Post ID: 4183
Reply to: 4181
Corrections & thoughts on drivers perception
I was thinking about what I previously wrote while driving today... thinking about the way people "see" the function of a driver... and about resonant properties of various materials used for speaker cones... I think it is more interesting than comparing notes about the Aura and McCauley drivers.

Never the less, I will first respond to the subject at hand, putting these potentially more interesting thoughts at the end...

Regarding Xmax :
Oops, yes you are correct... double the Xmax figure for both drivers... The relative difference between the two remains the same (1.42" vs 1.2").

And a couple more corrections/explanations :

Sensitivity :
The difference in sensitivity (if we can believe the spec sheets in both cases) between the McCauley and Aurasound driver is not 5dB, but 2dB.

The McCauley 6174 is quoted at 94dB/watt @ 1m
The Aura NRT18-8 is quoted at 96dB/watt @ 1m

Aurasound is presumably getting an additional 2dB sensitivity via their super-magnet (?).

Cone material :
The new version of the Aura driver (see material link below) uses fiberglass, where the version you are referring to may not. The older version may be closer to what you originally identified as an exceptional 18" driver. I was replying in the context of NBC's questions, who, if he wants an Aurasound driver, is presumably going to have to buy the evolved version (as first and second generations of this driver are impossible to find on the used market). The details of the currently available version, the NRT18-8, state that the cone material includes fiberglass, most likely on the back side of the cone. Fiberglass must be laminated with some sort of resin, presumably epoxy or polyester.

See the evolved version and some details of the materials here :
http://www.madisound.com/cgi-bin/index.cgi?cart_id=3766372.28865&pid=2076

The McCauley driver is not better in this regard; they start off with a nice pressed paper cone, and then unfortunately dope one side.

Suspension :
The Aura NRT18-8 uses a polyester suspension (polyester fabric) which is also likely impregnated with resin (probably epoxy) so that it will hold its form.

Though epoxy damps resonance somewhat, it is not as bad as rubber. This is one area where the Aura driver is more to my liking, as McCauley use resonance-killing rubber, but then they do have lower Fs, and this is probably why.

In the end, I would agree that either of these drivers would be a good choice... As far as I know, they are alone in their class. The Aura driver seems to take a more high-tech approach, and in some cases has more impressive numbers (BL factor for example), while McCauley tends to be more "old-school". As mentioned, my choice was based as much on availability as projected preference.

On a more interesting note...

I was thinking about it while stuck in traffic getting supplies for the horns... I am convinced that the key to tone lies in the resonant properties of the material(s) from which it is made, and of course its architecture... Ok, what I just wrote might seem obvious, but people tend to see the cone as piston in an air pump. I feel strongly that this is incorrect. Just as when you strike a tuning fork to set up a secondary resonance, I don't believe the sound of a driver is a direct result of the first action; i.e. the cone being projected outward or sucked back... Instead, I think the sound is gnerated by the resonance this action initiates. Different materials will sustain the resonance differently, or absorb it... The magnetic force of the motor can initiate resonance, or cancel a sustained resonance. Again, maybe it is obvious, but I feel this is a more correct vision of what is really going on, and goes a long way to explaining the tone of a driver.

Getting back to the above discussion; rubber suspension, speaker dope, and epoxy/polyester resin, go against tone, as they all kill resonance to varying degrees.

But it is not so simple... Obviously a metal diaphragm will resonate nicely, but in a way that is probably not good for bass... The character of the resonance should match the application... Metal has a more MId-Range resonance.

I have to think more about this, but not in this thread.

jd*


How to short-circuit evolution: Enshrine mediocrity.
04-07-2007 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 19
Post ID: 4184
Reply to: 4183
Correctection
jd wrote :
"... I am convinced that the key to tone lies in the resonant properties of the material(s) from which it is made, and of course its architecture..."

jd meant :
... I am convinced that the key to tone lies in the resonant properties of the material(s) from which THE DIAPHRAGM OR CONE is made, and of course its architecture...


How to short-circuit evolution: Enshrine mediocrity.
04-08-2007 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,534
Joined on 05-28-2004

Post #: 20
Post ID: 4186
Reply to: 4183
A good driver is a fragile driver…
Jessie, I do not know why I stuck with the Aura NRT18-8. The Aura NRT18-8 and Aura 1808 are very deferens drivers and I do not think I even mentioned the NRT18-8 as something that worth attention, and particularly in the “Exceptional Drivers” thread. The 1808 was papers driver. I do not know what grade of cellulose they use but it was as “paper” as it could be when you touch it. The cone was stiff, light and beautiful… however Aura had a low of problem with it. The Aura users were pro folks why ran Aura 1808 with 1000W Clowns and Crests at open air installations. Do not forget that Aura 1808 was 98dB sensitive driver and it had tremendous motor force. So, with those monster amps the motor obliterated the driver, yanking the coil of if cone of breaking the out suspension apart. In response Aura made the NRT18-8 where they socked the cone with epoxy, making it stronger. I never heard the NRT18-8. I generally hate any epoxy on cones and consider that it was very bad for sound. I have touched the NRT18-8 driver though with my hands and remember that it had completely different feel then Aura 1808 it felt more “plasticy” then paper. I did not research what else was done different in NRT18-8 as at the time when Aura begun to make their NRT series motors (NRT comes from the Neo-Radial Technology) they were already different company with very different objectives. Anyhow, it do not overload the Aura 1808 with powers (that never happens in listening rooms) then it fragility was not a big deal. In fact the more fragile driver is the better it is for sound…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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