Rodgers RW3 as Pedal Channel Subwoofer (modification)

[Eric Mack]

We've had a few discussions on how to modify the Rodgers RW3 Speaker to sound better, including removing the JBL-075 Tweeters (in progress) and even adding a midrange speaker in an enclosure. I've learned a lot already and I have expanded my journey of understanding different aspects of sound production.

Now, as I wait for parts to arrive for some of the projects you recommended (e.g. creating Walker T3 types speakers from my M6/M10's), I want to explore going lower.

I would like your advice on the suitability of modifying an RW3 speaker cabinet for use as a dedicated subwoofer for the pedal channel of my Rodgers 340 Theatre organ.

My thinking is that I could make the following two modifications:

1. Remove JBL Tweeter and crossover capacitor leaving only the single driver and passive radiator
2. Fill cabinet with fiber fill stuffing to lower resonance

I've already removed the internal amplifier from the cabinet and this modified RW3 will only be connected to the low frequency pedal channel, so I don't think it needs any additional circuitry. (?) It's a big cabinet so that ought to help, too, even without adding ports.

Why would I want to do this? Because I can? I'm using an old BSR subwoofer under the piano as my pedal channel as the P2 would not fit! I still have several RW3 speaker cabinets that came with the organ and my wife has already acquiesced to have in the living room. Also, this is a low budget hobby -- I do not even play yet -- so I'm learning how to make the most from what I have. It's been a delightful adventure and I'm learning a lot thanks to toodles, jbird604 and many other here.

Beyond the two modifications above, I can't think of much else I could reasonably do except, perhaps swap the passive radiator for a second driver or add ports.

What are your thoughts on this idea? Is it likely to work or be an improvement over my old BSR subwoofer? How would you change this approach to help me make the most of what I already have?

[toodles]

The usual Rodgers RW3 had a single JBL 15 inch woofer and a 15 inch passive radiator in addition to the bullet tweeter. Can you provide the part number on the woofer that is installed in your cabinet? The specs on that driver will tell a lot about what it can and cannot do.

[Eric Mack]

toodles, I was able to open and photograph the contents of the three RW3 cabinets that I have. Here's what's inside that I have to work with.

RW3-100 #1 (Originally with an S-100 Amp inside; I have since removed the amp )S/N: 72732 Location: by TV

This cabinet was given to me, separate from my Rodgers 340. It is the newest of the 3 cabinets.

Driver: JBL D140R, (Supposed to be a 15", could it be 14"?), 8 Ohm, S/N: 15880

Passive Radiator: JBL PR15R, 15", (all-paper 31044 cone/suspension)

Tweeter: JBL 075, 8 Ohms, S/N: 89008


The next two cabinets are older than the one above. They actually came with the Rodgers 340.

RW3 #2 (Actually an FW3, with a TA-50C Amp inside; I have since removed the amp) S/N: 61059 Location: By Piano

Driver: JBL D140R , (Supposed to be a 15", could it be 14"?), 8-16 Ohm, S/N: 10665

Passive Radiator: JBL PR15, 15"


RW3 #3 ((Actually an F3, with a TA-50C Amp inside; I have since removed the amp) S/N: 61058 Location: by Console

Driver: JBL D140R , (Supposed to be a 15", could it be 14"?), 8-16 Ohm, S/N: 11931

Passive Radiator: JBL PR15, (15") S/N: 1140 (or could be 11405?) (all-paper 31044 cone/suspension)

Tweeter: JBL 075, 16 Ohms, S/N: 45398

I hope that is helpful. In the next comment, I will post some web results I could find, in case they help.

[Eric Mack]

I tried to find some specs on my own. That was an adventure. From what I can find, here were the more credible sounding posts:

I found this post on-line -- no idea if trustworthy

JBL D140R Specs

Somewhere on line (don't remember where) I found these TS parameters for the JBL D140R 15" driver used in Rodgers organ tone cabinets. Can anyone confirm that they are correct?
VAS=10.5 ft^3
Qms=5.0
Qes=0.22
Fs=30 Hz

Also is there an easy way to determine the Fs of a passive radiator with just a signal generator and multimeter?
__________________
But I found on this thread a seemingly credible comment that the D140R was made custom for Rodgers (the R)

"But the real info: D140R seems very different from D140F in one respect (at least mine are). Fs on the two units here measures 21.6 and 22.5 Hz, respectively. Qts is .23 and .255 -- unchanged from D140F (but maybe would drop if the magnets were re-charged). So the "Rogers" version at least differs from the "Fender" version by having the 2216-style resonance."

Then I found a comment than mentions the D140 is similar to the K140, so I searched for K140 and found that JBL marketed it for Organ and Bass Guitar applications.

Another note I found mentioned that the JBL 2231H is sometimes used in RW3, but I do not have that model.

Nothing very conclusive here.

[Eric Mack]

And found this from an old usenet group - no way to know if factual. I 'm out of my league here.

In Reply to: JBL D140 specs posted by Mark McFarlane on November 27, 1999 at 00:46:08:

Fs 30
Pe 150W
Eff 3.5%
Qts .21
Qes .22
Qms 5
Vas 297.3,X-max 5.08
Re 5.5
Le 1.3

[toodles]

The D140R specifications don't seem to be readily available online from any published material. It may date from a time before JBL Pro provided such info.

Probably the best way to find the T/S specs is to test them. If you just want the resonant frequency, you need a signal generator to provide a sine wave output, a resistor about 1k Ohm, and a multimeter--or get the Parts Express woofer tester. Connect the output of the generator to the speaker through the resistor, and use the multimeter to measure the voltage across the woofer. Where the voltage peaks is the resonant frequency. Do this with the speaker outside the cabinet. Of course if you use the PE Speaker tester, you'll get more than just the resonant frequency.

Since the D series was a musical instrument speaker—read, “electric guitar”-- I would suspect the resonant frequency to be closer to 30 to 40 Hz rather than in the 20's. Qts in the range of 0.2 to 0.25 is quite believable. It is very unlikely that this woofer would do a respectable job on the 32 ft stop of the 340.

By the way, the RW3 is essentially a ported system—the passive radiator acts like a port.

[Eric Mack]

Thanks, good to know. I may pursue this, eventually buying the kit from Parts Express -- if only for the educational aspects of this endeavor. I appreciate you sharing and for the education along the way.

[Eric Mack]

I may re-read and think this through a few times. But one thing that should simplify this is the Rogers 340 that I have has only 16 foot stops

[toodles]

If your organ has only 16 ft stops, then the RW3 should work pretty well for one of the channels that has bass stops--the diapason or the tibia channel.

[Eric Mack]

If your organ has only 16 ft stops, then the RW3 should work pretty well for one of the channels that has bass stops--the diapason or the tibia channel.

Yes, toodles, that is correct. My Rodgers 340 has no 32 foot stops. While I have a dedicated channel for each, Diapason and Tibia, I also have a dedicated channel for what Rodgers calls the “Pedal” channel - which is where they route the 16' Diaphone and 16' Bourdon.

So, back to my original question of the RW3 (minus the 075 tweeter) and whether they would be suitable on the as a subwoofer for the pedal channel, it sounds like I should actually consider reassigning my 3 RW3 units for PEDAL, TIBIA, and MAIN #2 (Diapason), and then use the soon-to-be created Walker T3's for everything else, including my reverb channels. (See next comment below for attached PDF.)

[Eric Mack]

toodles, I have uploaded a spreadsheet (as a PDF) which shows my current channel assignments and speakers used, so you can see how your recommendation will fit with what I have. The only change is that I will soon have chopped up the M10/M13 to create the “Walker TP3” style cabinets, as you and jbird604 recommended in an earlier discussion thread.

See: 20190521 - Rodgers 340 Channel and Speakers after Jonas Redesign (NEW).pdf

I look forward to your comments on how I can best use the speakers that I have. This has been quite informative and I learn a lot each time I visit this forum. Thanks!

[toodles]

I don't see anything wrong with the channel assignments you are showing. It's probably about as good as you can get.

Your sheet asks about the Orchestral Oboe as compared to the (English) Post Horn--the two are nothing alike except both are reeds. The post horn is a loud, brazen trumpet style reed, perhaps a little "honkier". It's never (except once in a blue moon) used with tremulant; it it's voiced on the milder side, trem might be OK. Use your ears to guide. The classical organ oboe is like a mild trumpet, but the orchestral oboe is brighter and more nasal. Reeds are classified as chorus reeds and color reeds (on the theatre organ); the chorus reeds are trumpet, brass trumpet, tuba, tuba horn, tuba mirabilis, and post horn. Color reeds are the clarinet, orchestral oboe, oboe horn (which is very similar to the classical organ oboe), kinura, krumet, and cor anglais. Note that on a Wurlitzer pipe organ, the English Post Horn is called English Horn. A true English Horn is the same as the Cor Anglais.

[Eric Mack]

toodles, you responded to a question that happened to be on my channel assignments by giving me valuable bonus information on the stops. Thank you!

However, I think you may overlooked the purpose for which I attached that file to this thread in the first place: I wanted to get your expert advice on where I could best use my 3 RW3's (with 075 tweeters removed) and the Walker TP3 Clones I am building -- at your recommendation, using parts from my M10/M13's.

I posted that file because you had commented that the RW3 might serve well on some of my channels and I wanted you to see what I currently had connected and where. I highlighted the speakers in yellow.

I'm eager to learn where to connect the speakers I have for best effect, and to know if you think they should be paired with other speakers -- or any other advice you care to share. (When I picked up my organ nothing was connected properly, so I have been learning what goes where and why.)


Please take another look at post #10, above. (Note: The lowest stop on my Rodgers 340 is 16'.)

(Note: The lowest stops on my Rodgers 340 are 16')

[Eric Mack]

toodles, if you have a few minutes whenever you login next, I would welcome any feedback on my comment above. Thanks.

[toodles]

It's hard to predict what would work best, as the tech manual I have for the 340 is very hard to read, so I'm not sure what's going on in the output preamp circuits, and, I don't know how your rebuilt cabinets sound.

The 340 is an unusual Rodgers instrument in that it is truly an all "unit" organ--most Rodgers organs are mostly unit stops, with the bass octaves are handled separately as well as a few straight voices. On the 340 there is no bass octave separation and there are no "straight" stops at all. Thus all the channels for the tibia, diapason, trumpet, post horn, and flute contain the lowest octaves. Other Rodgers organs confine these octaves to a "pedal" channel that is really a bass or subwoofer channel.

Probably it is most important to have your RW3's to be on the channels that have the tibia, flute, and diapason. Your rebuilt cabinets should be effective on the kinura, post horn, trumpet, and clariet, though perhaps the trumpet might like to be on an RW3 channel.

[Eric Mack]

Thank you, if there is a specific question or thing that you wanted to determine from the schematics, I may be able to get an answer from someone, but -- as I am still learning here -- I would need to know the exact wording of the question to ask.

[Eric Mack]

toodles, I'm happy to get an answer to your question if you can help me formulate it clearly so I can research it.

[Eric Mack]

toodles, I want to follow-up to your recommendations. This weekend, I removed the JBL 075 Tweeter from each of my RW3 cabinets. I removed the wires leading into the cabinet and sealed the entrance. (I had previously removed the amplifier, so the cabinet is empty except for the driver, the passive resonator and a tiny amount of batting stapled to the walls. In place of the tweeter, I installed a piece of 7 layer birch in which I mounted a binding post cup. These were caulked for a tight seal.


While I had the cabinet open, I also measured available space for possible future addition of a horn or 8" mid/full range driver in the future. There is room for a driver - with or without a box around it. (I think I remember you mentioned that idea in another thread.)

The three modified RW3's will be installed on my MAIN #1 (Flute, String, Etc.), MAIN #2 (Diapason, Celeste), and Tibia.

As you might expect, I have a few quick questions:

1. With this configuration do you recommend that I fill the cabinet with PolyFill? Would that do anything?

1. With the channel assignments noted above, should I add any speakers in parallel? (e.g. the TP3 clones) or should I want and see about possibly adding an 8" mid/full range driver in the future?

1. The panel that holds the driver and passive radiator screws in with 16 screws so it is very secure. There is no perfect seal. How critical is that to a box like this? Should I add weather-stripping before I screw it shut?

Anyway, I want to close the loop and thank you for your help by showing you that I followed your advice. Hopefully this will help/inspire others on this forum as you and others have inspired me.

I look forward to your comments on my questions.

Thanks again!