[Tunz2]

Hello, I was wondering if anyone had tried to convert their spiral ribbon tweeters to the Aurum Cantus G series tweeters in an RM40? If so how difficult and mods needed to make this swap work. Pictures would be great.  I have older 40s with the higher Xover point.

[Brax]

I too have a set of 40s with the spirals that I plan to upgrade to the AC tweeters. I bought AC G3 tweeters for this upgrade..
 I talked to Brain and he did not want to guess at the crossover change requieted for this change. I planned to make a new faceplate for the tweeter to fill the space of the dual ribbon tweeters.

I have also seen the ribbons replaced with a single G2 ribbon tweeter and even saw a set with dual G2 ribbons.

[Stimpy]

There was a lot of talk, many years ago, concerning upgrading the RM-40 with a FST tweeter.  Brian even sold a 'Kit' for the upgrade.  Though, that didn't work out too well, as the Kit never included a new tweeter faceplate, as planned. 

Be that as it may, I was able to find a few threads that might help:

http://www.audiocircle.com/index.php?topic=678.0

http://www.audiocircle.com/index.php?topic=3170.0

http://www.audiocircle.com/index.php?topic=60430.0

Also, as noted, Brax has been at this a while.  So, the spiral tweeters must still be very good, and work as designed!   

Oh yea, it's also a shame that the RM-40 Series 2 never happened as planned.  I bet they would have been sweet!
Especially, since they would have used a side-mounted 12" passive radiator, in place of the bottom mounted 10"
passive.  Now, given the choice, and the skills, I'd try that even before upgrading the tweeter.  I guess I'm a bass-head
after all...!   

Good Luck!

[James Romeyn]

There was a lot of talk, many years ago, concerning upgrading the RM-40 with a FST tweeter.  Brian even sold a 'Kit' for the upgrade. 
Though, that didn't work out too well, as the Kit never included a new tweeter faceplate, as planned. 

Be that as it may, I was able to find a few threads that might help:

http://www.audiocircle.com/index.php?topic=678.0

http://www.audiocircle.com/index.php?topic=3170.0

http://www.audiocircle.com/index.php?topic=60430.0

Also, as noted, Brax has been at this a while.  So, the spiral tweeters must still be very good, and work as designed!   

Oh yea, it's also a shame that the RM-40 Series 2 never happened as planned.  I bet they would have been sweet!
Especially, since they would have used a side-mounted 12" passive radiator, in place of the bottom mounted 10"
passive.  Now, given the choice, and the skills, I'd try that even before upgrading the tweeter.  I guess I'm a bass-head
after all...!   

Good Luck!

Stimpy,
It's anti-intuitive, and looks less good, but there's one simple correct philosophy for locating PRs on stereo loudspeakers: PR location and firing direction must be as non-symmetrical as possible between L and R speakers.  For instance: On the L speaker locate PR on the R side panel (all views from the listening side), as close to the base as possible.  On the R speaker locate PR on the R panel as close to the ceiling as possible, or alternate for R speaker locate PR on the top panel firing up toward the ceiling.

The audibly worst performance philosophy is L/R mirror image for the PR on each speaker.  Search "Schroeder frequency" for better understanding why domestic rooms imprint completely different in the bass range vs. mid-treble, and the absolutely worst philosophy for ideal flat bass response and bass timing is mirror image L/R bass pair, which is pure fail from every possible viewpoint when the math is properly understood.   

I wish I could say why but I don't know: my experiments thoroughly convinced me that slot loading is the worst performing option, and Brian eventually changed this after I urged it for years, but not till his last product, the RM50.  Also, frankly, Brian's driver radiating ratios (PR vs. active driver) are generally lacking in PR area.  IMO approximately doubling PR radiating area in most cases is a very reasonable goal.  The worst case, which Brian eventually dropped at my urging too, was the original RM30 with active 10, which had way too small cabinet and woefully too little PR area (mine bottomed the PRs almost daily they were so badly over-driven....this model's Q was way too high from the too small enclosure).

       

[Tunz2]

Thanks for the info Brax and Stempy. Brax, will the G3's you have run off the spiral tweet leads? I understand the AC tweets have a transformer. Did I  read you had changed to the lambs wool behind the panels? Was this a worth while upgrade. Im sure this has been answered in the past. Is the opening left by the spirals deep enough to fit a G series tweeter?

[Stimpy]

It's anti-intuitive, and looks less good, but there's one simple correct philosophy for locating PRs on stereo loudspeakers: PR location and firing direction must be as non-symmetrical as possible between L and R speakers.  For instance: On the L speaker locate PR on the R side panel (all views from the listening side), as close to the base as possible.  On the R speaker locate PR on the R panel as close to the ceiling as possible, or alternate for R speaker locate PR on the top panel firing up toward the ceiling. 

That makes sense.  Asymmetrical mounting of the passive radiators would help with the non-reinforcement of room bass nodes.  It would surely look 'different', but we're all after perfect sound, after all!   

Also, frankly, Brian's driver radiating ratios (PR vs. active driver) are generally lacking in PR area.  IMO approximately doubling PR radiating area in most cases is a very reasonable goal.  The worst case, which Brian eventually dropped at my urging too, was the original RM30 with active 10, which had way too small cabinet and woefully too little PR area (mine bottomed the PRs almost daily they were so badly over-driven....this model's Q was way too high from the too small enclosure).     

That's been my experience as well.  Roughly a 2 to 1 ratio.  One woofer, to 2 equal sized passive radiators.  Or at least similar to Brian's use of a 12" woofer with a 15" passive.  Something that I'd like to try myself one day.   

[James Romeyn]

I'm glad you "get" this.  As Duke LeJeune said when I mentioned non-symmetrical PR locations as ideal, he said it would be against marketing criteria as much as it helps performance.

Pierre Sprey of Mapleshade records/recording helped design control systems for the F16 and/or F18.  About 15-20 years ago my friend Mike Mindlin told me that Peirre told him that symmetrical woofer siting is always wrong, and that woofers should be as non-symmetrical L to R as possible.  I certainly had absolutely no idea what Pierre was up to at the time, but now have hands on experience confirming his philosophy.  I mixed together multiple bass source information of LeJeune, Tod Welti, and Earl Geddes with Bob Carver's siting instructions for a single sub, into very simple and efficient instructions for siting a distributed sub array for minimum bass mode effects.     

I presume a 15PR has about 50% more radiating surface area vs. a 10" active woofer. 

[/mp]

I presume a 15PR has about 50% more radiating surface area vs. a 10" active woofer.

2.25 times. In theory.
Area = Pi r^2.
5"^2 = 25. vs. 7.5"^2 = 56.25
56.25 / 25 = 2.25

Theory often fails to map 1:1 with reality.

[John Casler]

Thanks for the info Brax and Stempy. Brax, will the G3's you have run off the spiral tweet leads? I understand the AC tweets have a transformer. Did I  read you had changed to the lambs wool behind the panels? Was this a worth while upgrade. Im sure this has been answered in the past. Is the opening left by the spirals deep enough to fit a G series tweeter?

Hi Tunz2,

Don't want to discourage you from your project, but the move from the twin spirals to the G2 or G3 may not be an easy one, and involves the following considerations.

1) The actual physical sizes are different and may require significant wood working.

2) Depending on which one you use, its physical dimensions may also move it too close or too far away from the neopanels which can affect the wavelength interactions, which can cause comb-filtering/interaction issues.  Brian understood this well and knew precisely what distances each driver needed to be from the others.  As well he could adjust frequency ranges, slopes and phase coherence via the network.  The reason Brian selected the G3 for the couple Spiral Conversions he assisted with, is due to the "height" of the G3 not leaving too large a gap between drivers.

3) The specs of each of those drivers relative to sensitivity, and impedance would require a very specific cap value adjustment, for the XO to function properly.  As well the Spiral cap values are set at 5.9Khz (if I remember correctly) and the FST is at 6.9Khz, which is also set by the selection of the correct cap values.

If you, or your friends understand those needed changes and have the ability to make those adjustments, it should be a fun project, if not then it is probably better to let it be.  If your Spirals are not functioning well, we have a few NOS still available.

[Stimpy]

Pierre Sprey of Mapleshade records/recording helped design control systems for the F16 and/or F18.  About 15-20 years ago my friend Mike Mindlin told me that Peirre told him that symmetrical woofer siting is always wrong, and that woofers should be as non-symmetrical L to R as possible.  I certainly had absolutely no idea what Pierre was up to at the time, but now have hands on experience confirming his philosophy.  I mixed together multiple bass source information of LeJeune, Tod Welti, and Earl Geddes with Bob Carver's siting instructions for a single sub, into very simple and efficient instructions for siting a distributed sub array for minimum bass mode effects.     

That's somewhat 'odd'.  The first job that I had after graduating, was at a aerospace avionics company.  I worked on angle-of-attack systems, for both the F-16 and the F-18.  It was a Teledyne company, and as such, I got to purchase my Acoustic Research AR-90's, at an in-house discount price.  That started this sickness!!!

My next job, was at a CD/DVD replication plant.  I worked in the Premastering & Audio Mastering department.  Working there, I actually met Pierre Sprey.  He came down to visit our plant, and to conduct listening tests, as we were about to start CD pressing for Pierre's Mapleshade catalog.  A 'unique' man, to say the least!

[John Casler]

The employment of randomly or irregularly placed multiple subs is certainly a reasonable and effective way to ameliorate room interactions of fewer bass radiation positions as perceived at a specific listening position.

The reason is ultimately quite simple.  Each sub interacts with the specific room boundaries based on its SPECIFIC room position.  This interaction is perceived at any specific listening position complete with all those interactions.

Adding additional subs, creates a "multiple different" interaction patterns and a summed perception at the listening position, and begins a "smoothing" of the specific interaction of a single or fewer subs.  This also explains why irregular placement of even stereo subs will often offer advantages.  However, if a room is irregularly shaped and each of a stereo pair "sees" a different set of room boundaries from their specific position (that is you are not in a perfectly rectangular or square room) then that balanced positioning can be quite effective.

I really don't see any value in irregularly spaced drivers in a single sub, as they ALL sum to radiate the bass frequencies of that single sub into a hemispherical radiation into the room.  The exception to this might be a dipolar example where the radiation pattern can affect the overall directivity in a small way.

Brian also often suggested a multiple sub placement where the front sub(s) were in phase, and employing rear sub(s) out of phase in a push-pull scenario.  This too can be quite effective in some applications if care is employed in its implementation.  I should mention that the rear sub(s) can also be placed immediately behind the listening position (mid-room) "in-phase" and firing AWAY from the listener to further change the room boundary effect, and add POWER to the bass via the close proximity to the listening position.

I actually employ "all of these" in my system to a very nice result.

[Housteau]

Adding additional subs, creates a "multiple different" interaction patterns and a summed perception at the listening position, and begins a "smoothing" of the specific interaction of a single or fewer subs.  This also explains why irregular placement of even stereo subs will often offer advantages.  However, if a room is irregularly shaped and each of a stereo pair "sees" a different set of room boundaries from their specific position (that is you are not in a perfectly rectangular or square room) then that balanced positioning can be quite effective.

I have run into this over the years.  I believe that there can be better potential and possibly be easier to achieve good quality smooth bass in non-rectangular more open spaces, rather than in smaller rectangular isolated dedicated rooms.  Even larger dedicated rooms will have those issues to deal with often requiring extensive bass treatments to achieve what an open floor plan listening space has the natural potential to provide.  What the dedicated space can excel at is basically everything else we value, plus it does allow the full implementation of whatever room treatments are needed.

My newly remodeled room has worked out really well.  I do have the VLA bass towers in a symmetrical setup though.  What I believe helps this to work is what John mentions above.  My new room extension is slightly offset to the one side by 4 ft.  So, the VLA on that side sees a length dimension of mostly 15 ft. while the VLA on the right sees it as 25 ft.  The differences in measured response can be seen on the graph when measuring just one side at a time.  The vertical array of woofers creates multiple sources in the vertical dimension against all boundaries and a sloped ceiling.  I believe this helps that part of the symmetry. 

However, the width presented a pure symmetry with no offsets, at least originally.  To help counter that I did what would normally be considered another no-no.  I placed each column so that the woofers were equal distant from both the side wall and the one behind them.  This created another boundary mode issue that I was able to use to counter the symmetrical width problem.  You see, one created a peak and the other a dip close in frequency, so they must have helped to balanced each other out.  To be honest I really do not know exactly how this worked, but it did.  Sometimes you just accept the gift and don't ask too many questions . 

My listening seat is also equal distant from the side walls, another no-no.  This places the listener right at either peaks, or nulls depending on the frequency fundamentals of that dimension.  I am assuming that these location created issues add in with the speaker placement ones to create the response my room treatments then had to deal with and tame down.   Then, of course comes the parametric EQ notching power of the DCX to help with the remaining humps.  To say that I am pleased with everything would be a huge understatement.