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What's the best subwoofer design for classical organ?

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  • What's the best subwoofer design for classical organ?

    Over the age of electronic organs, I've seen bass cabinets of many types, including, but not limited to:

    Allen's big open-back plywood box with four 15" paper-cone woofers on an old TC-4

    Allen's 32B open-back cabinet with two 15" paper cone woofers, used in analog and early MOS organs

    Allen's HC-12 with a 15" foam-surround woofer in a sealed box about 18"x17"x33"

    Allen's HC-20, same as HC-12 but without any midrange or tweeter drivers, used in pairs or quads

    Allen's B-40 with a very sturdy 15" paper cone with textile accordion surround in a huge vented box

    Allen's B-20 with a 12" rubber-surround cone in a vented box the size of the HC units, used in pairs

    Allen's SR-1, a huge box with a single massive 15" driver and four passive radiators

    Allen's SR-5, box about the size of the HC models, a massive 15" driver and two passive radiators

    Rodgers P1 -- massive 30" EV woofer in a refrigerator-size sealed box

    Rodgers P2 -- pair of 15" paper cones in a small sealed chamber, speaking into a large folded horn

    Rodgers W2 -- a 15" paper cone and a 15" paper passive radiator in a sealed box, smaller than the above

    Rodgers P32 with two 15" foam-surround woofers in a very large vented box

    Rodgers P16 with two 12" foam-surround woofers in a somewhat smaller vented box

    Rodgers SW-x.x (7.5, 4.0, and other sizes), each with a single 15" foam or rubber surround woofer in a vented box

    Baldwin sealed box made of 1" thick particle board and holding a 12" foam surround woofer and a matching passive cone.

    Baldwin tall vertical "Q" cabinet with one 18" and one 15" woofer facing upward, and a vent at floor level.

    There are probably others from the best-known builders, but these are the ones I can recall right now. Some are open-back, some are sealed enclosures, some are vented, a few have passive radiators. I have heard good solid bass from several of them in top-notch installations, and I've heard many that fall short, especially in cases where the woofers are way undersized for a given church or auditorium. There seems to be no substitute for truly huge speakers in truly huge boxes.

    I might add that I've heard a few "custom" woofers that consisted of nothing more than a driver mounted on plywood with its back side facing into another room or into an attic, and some of these sounded amazingly good.

    My current set of Rodgers SW7.5 cabinets are probably pretty decent and not really undersized for the church, which only seats 150 or so max, but I'm not getting quite the bass that I want. I'm considering adding an active crossover and an additional two-channel amp for the bass channels, which ought to give more control over the bass and provide extra power to the subs.

    But I'm also considering starting over from scratch, looking out for one or more of the above, or perhaps building some custom subs. I've looked at some enormous 21" woofers at MCM Electronics, which can be bought for about $130 or so, which I might mount on baffles with their backs facing into some attic space or into a different part of the church, not connected to the sanctuary. But I've also thought of trying different woofers in the Rodgers boxes I have. The ones in there right now are rubber-surround, which replaced the original foam-surround woofers that had rotted out.

    Anybody want to offer opinions on these numerous subwoofers and how much truly profound bass one might get out of each one? And thoughts on the merits of sealed versus vented versus passive radiators? I'm looking for "palpable" room-shaking bass down to 16 Hz so I really feel the lowest notes of the 32' stop.
    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

  • #2
    John, I'm using Allen amps/speakers on the Moller/Artisan installed in my house. I have one Allen B-40 that does an excellent job producing room-shaking bass. When I sold Allen Organs, many of the installations included the B-20. The bass response is good, however my preference is the B-40 over the B-20. Later models I sold included the SR-1 & SR5 and they did an excellent job especially with the resultant 64' pedal rank. Allen


    • #3
      Thanks, Allen. I've generally been impressed with the stock Allen subs, especially the B40 and the SR series, and I've heard some powerful pedals from Rodgers subs as well, especially the ancient P1 and P2 and the P32 of the 1980's.

      My Allen MDS-45 doesn't have note by note leveling, of course, so I have no way of adjusting those last few notes at the bottom without affecting the entire stop. At least the 32' pedal bourdon is the only bass stop on its TG board, so I can tinker with the bass pot. I'm planning to spend a little time doing that this weekend.

      I've been searching for some definitive info on how to build a sub that is as flat in response as possible down to 16 Hz, and the info I find is conflicting. My gut feeling is that a very large sealed box with a pair of 15" foam-surround woofers might produce the flattest possible response curve, since any kind of vent is bound to have a resonant frequency of its own. Vents and passive radiators alike are supposed to increase output in the bass range, but I can't help thinking that output will be quite selective as to frequency.

      I think a 21" woofer in a wall between two rooms might do a good job as well, but that's a lot of money to invest for an experiment!
      *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!


      • #4
        I'm familiar with what you are experiencing. The bourdon 32 needs the bass cabinet. I sold a number of Allen Organs that had the bourdon 32, but the church didn't have the budget for the optional bass boost. Consequently, the bottom 12 notes performed poorly. Around the MDS-41S era, the bourdon 32 was replaced with a contra violone 32 and the bass response with the HC-15s was better. This is an excellent example of how important the role is for proper audio components. If you can find a used B-40, that may be the least expensive way to produce what you want.


        • #5

          You have already answered a number of questions I was going to pose to you. Since you want a rumble out of a 32' Bourdon, and you have your room and speaker, have to figure out what is not right.

          Well, start with the speaker. You mention you replaced the woofers with different ones with a different surround. Unless you are convinced that the speaker has pretty much identical response, you may very well have different results compared to the original design. That is one reason I prefer to re-foam as compared to replace woofers, as then at least I get the original design specifications working.

          Another issue, published specs. for woofers, and bass cabinets are generally untrue. Case in point. I just looked at the Rodgers published specs for the SW 6, which may be the replacement for the SW 7.5. Is said to have "twice the power handling" of the SW 7.5, and "even more low frequency capability" of the SW 7.5. Now the graph says that the speaker puts out 90 db @ 70 hz, 83 db @ 32 hz and 65 db @ 16hz, all 1 watt @ 1 metre. Published specs say the frequency response is 16 hz - 200 hz. Sensitivity is said to be 90 db. See the BS that is being advertised here. You can find the graphs on-line if you want to look at them.

          I personally don't really care for the 32' Bourdon on most installs, as they just don't do much. Contra Violone or Contra Bass tend to be better as they tend to add colour and weight much more effectively than a 32' Flute, and are also much easier on speakers. But if you want the shake the rafters sound, you will need to spend some decent dough just in amps and speakers. Another thing, on most electronic organs these days, it seems that the same driver that does the 32' stop, also does the 16' stops, the low end of the manual stops, etc. So, there will be the problem of phase sums and phase cancels that inevitably occur.

          The solution, that generally works, but is not cheap, are the powered cubes by companies such as Definitive Technology, or Earthquake. Basically, what they do is use say a 15" woofer in a roughly 19" cube, with 2 similar sized passives and drive it with a 1,500 watt amp. These amps are DSP controlled, and so boost frequency as it goes down. They will go all the way down to 16 hz and lower. The woofer itself is usually very heavy, with a cast frame, huge magnet. The Def. Tech Reference model weighs about 90 lbs. Yes they are heavy. Figure on paying around $2,000 - $2,500 for one.

          Going the traditional way, of big drivers in big sealed boxes will require some experimentation. Just remember that these extra low frequencies, you are dealing with extremes of what can be done. Typically tuned ported boxes have a hard time going down below about 22 hz.

          One other thing, it is important that the placement of the speaker itself is advantageous to getting maximum bass extension. Usually in a corner on the floor is best.

          Once we solve the bass angle of things, then we can deal with the high frequencies. Most electronic organ audio setups cannot do the higher than 12 khz frequencies right. But that is a subject for another day.



          • #6
            The woofer driver set into a wall which goes into another room is called an "infinite baffle". See the following discussion: As the man says, there is a lot to be said for an infinite baffle design.
            Bass reflex and ported cabinet are two other design philosophies. Lastly is acoustic suspension, where the box is sealed and damped with filler.
            There are a lot of discussions of these topics, along with calculators, and characterization of various drivers by their physical modeling numbers, which are only generally available on this or similar forums: Simulation software is available to those with windows computers and a technical bent.
            Have fun.
            city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112


            • #7
              CAVEAT: This is a very simplified discussion of the topics herein; for those of you who know loudspeaker design, recognize that it is only an approximation for people who aren't familiar with the details of speaker design.

              16 Hz is hard to achieve
              It is a VERY difficult task to get any woofer/subwoofer to provide smooth solid response down to around 16 Hz. Sealed boxes (unless they are as big as a refrigerator or larger) simply cannot do the job. Forget about open backed boxes, as well. The physics and math quickly show this.

              Three options really remain:

              1) Vented enclosures (and this includes those enclosures with passive radiators); the design of this is a little complicated, but it can be done, and excellent results are possible but very careful design and construction is needed. Design formulas are readily available.

              2) True infinite baffles, where the speaker is mounted in a hole in a wall or ceiling where the back is acoustically separated from the front. The hole must go all the way through to the open space behind the speaker. This approach is actually the easiest to provide excellent results, but means putting a hole in a wall or ceiling; by the way, the back side of the speaker produces just as much sound as the front, so don't plan on the back area being useful for things other than storage. There aren't really any design formulas--just choose the right speaker based on the Thiel Small specifications--a driver with low Fs (resonant frequency) which should be around 20 Hz or lower; and a Qts (total Q) of around 0.7 (maybe as low as 0.6) to 1.0 (perhaps as high as 1.1). It is possible to add mass to a speaker cone to reduce the resonant frequency (which also raises the Q). The Vas (equivalent air volume of the compliance of the driver) doesn't matter because you are not putting it in a box.

              Not many woofer match these requirements; Parts Express does offer a 15 inch Infinite Baffle subwoofer that comes close:; probably best used with additional cone mass to go as low as 16 Hz.

              3) Transmission Line speakers: these use an enclosure that is essentially a pipe of a tuned length to produce the desired frequency; dampening is added to absorb the back-wave above the tuned frequency. No solid design formuals are available, these are mostly experimental. The boxes become huge as you try to get down to 16 Hz, since the length is nominally 1/4 of the lowest wavelength; a 32' stop's base wavelength is 64 ft, so this enclosure needs 16 ft of length, though it can be folded (the same thing as mitering a pipe). The cabinet still becomes huge and heavy.

              Most of the successful organ subwoofers are of the vented (also called ported) design sometimes using passive radiators (also called drone cones) instead of ports. These give box sizes that are practical and affordable. Many also use equalization to make the response curve flatter than naturally occurs. This is at the cost of consuming higher amplifier power, but that can usually be provided.

              Some Important Woofer Topics

              a) common misconception about woofer/subwoofer driver size; the size of a woofer does NOT accurately indicate its low frequency performance; as an example, for a give vented enclosure size, you can generally find a smaller woofer that provides lower frequency response than a larger woofer provides.

              b) driver size does affect the ability to produce sound pressure levels; the actual specification that indicates this is Vd, or volume displacement. This is the surface area of the moving part of the cone (Sd) multiplied by the forward/backward movement of the cone (Xmax). So a smaller cone with a higher Xmax may displace more air volume than a larger diameter speaker with a smaller Xmax.

              c) it becomes harder to increase the Xmax of a driver above those commonly found in the best 10 and 12 inch woofers. The extra diameter in a 15 inch speaker allows greater off-axis movement of the cone as it moves in and out, which limits the amount of in/out excursion that can be allowed in order to avoid damage to the speaker in use. Thus, going to a larger cone for lower frequency response isn't always helpful. Larger cones can be very useful for high sound pressure levels at higher frequencies (I'm still talking about the bass range, like 50 to 200 Hz) in sound reinforcement and live music (not organ) applications.

              d) the sound pressure limits can be calculated based on the maximum acoustical pressure achievable (based on frequency, volume displacement, and efficiency) and also on the maximum electrical power usable; nearly all woofers and speakers provide the maximum thermal power limits rather than electrical power limits (to avoid distortion), but this can also be calculated; in the end, you need to know what acoustical sound pressure is needed, the acoustical power available from the speaker system at the maximum electrical power permitted, which must be below the thermal power limit (this is rarely a factor).

              Recognize that a church is a large acoustical space, and you'll likely need multiple units to achieve a high sound pressure level; every doubling of your systems adds 6 db; from 1 to 2 units, it's 6 dB; from 2 to 4 is an additional 6 dB, etc. This assumes they are not driven from the same amplifier.

              The most comprehensive design guide I know that covers almost all of it is the Loudspeaker Design Cookbook by Vance Dickason; available here: and elsewhere. This book is NOT for the mathematically timid, but all the formulas are there.

              You might also want to take a look at this chart from Parts Express: You can sort the chart by f3 (usually considered the cut-off frequency for a speaker system) by either vented or sealed design; you'll see that sealed designs will not get you where you want to be (the one with 3 Hz cutoff frequency is an error), and only a handful of vented systems are possible. FYI, I am pretty confident in the Dayton Audio speaker specifications, but am leery of some of the others.


              • #8
                You want a rotary woofer in an infinite baffle.

                This one has a frequency response of 1Hz(!) - 30Hz +/- 4dB has a Sensitivity 94dB 1 watt 1 meter @10Hz and a Maximum Acoustic Output: >115dB between 1 and 20Hz. Just add a 150 watt amplifier that is capable of putting out its rated power at 1 - 3Hz and a substantial wad of cash.

                But you want the best, right?


                Allen 965
                Zuma Group Midi Keyboard Encoder
                Zuma Group DM Midi Stop Controller
                Hauptwerk 4.2


                • #9
                  John, take a look at SVS products if you are not already familiar with them:


                  The PB13 goes down to 16 Hz with only 3 dB dropoff. SVS, unlike other sub manufacturers, dares to publish anechoic frequency response plots for their premium products. That practice tells me that they are making better products and describing them more honestly.

                  I own the ported-cylinder cousin to the PB13, but to be honest have only had it out of the box a few times to test it on pure-tone signals. Initial results have been impressive, and I await that magical time when I will have a chance to finish my audio installation and put it to work.

                  If you want to experiment with the PB13, there is one on eBay at the moment for $300, rather scratched up and possibly with an amp issue but with a good driver. It is located in St. Louis for local pickup.



                  • #10
                    I thought of the Thigpen woofer, too. (My Schober organ plays through old Fisher XP-18 speakers, which have an 18" woofer. It worked well for the the 16' pedal stops but I didn't have any 32' stops. I had an old vinyl test record that went down to 16Hz, though, and it was good there.)



                    • #11
                      There was also the Contra-Bass, which was a servo driven cone, for ultra low bass at high power--as I recall it was very expensive; but it really wasn't a speaker in the traditional sense.

                      To know if the SVS products would work for you, you'd have to know their efficiency at a given power level, and then see how much louder they can get as they go to maximum power. This is not shown on the specs I see on their website.

                      Daring to publish anechoic frequency response is only daring because most people don't understand them and assume the wrong thing from them. Real room response always increases bass response over anechoic, and this approach to measuring a woofer/subwoofer is a poor reflection of actual real room performance.

                      Still, SVS has been around for quite a while, and that's an indication that customers are happy with their products. I would definitely discuss your application with any commercial speaker manufacture you are considering--they do not design these subwoofers to sit on low C of a 32 ft stop for an extended time. They might not warranty the product for this application. SVS warranty looks good, but does not cover "abuse"--I'd make sure they do not consider musical instrument use a form of abuse.

                      I looked as SVS quite a while ago, and they had a cylindrical subwoofer that was supposed to go down to 16 Hz, and it was about $600 without an amplifier. Now they only sell units with amplifiers (which leads me to believe they achieve a lot of their lowest frequency extension via equalization--that's not bad, but it consumes amplifier power like crazy.

                      - - - Updated - - -

                      I found a site selling used Servodrive subwoofers at about $4600 US.


                      • #12
                        Best, I suppose, would be a front loaded horn slightly smaller than a Motel 6. ;) Seriously though a large horn would provide the lowest distortion, best extension (short of a rotory sub), and greatest SPL/watt of any solution I could think of but would only really be practical in a large installation because of the size requirements.

                        In smaller rooms (homes) true infinite baffles have been show to provide tremendous performance. These would be arrays of large high excursion woofers (15" and 18" seem to be the most common) driven by gobs of power with rear chambers (usually an adjoining room or the out of doors) with a volume well in excess of 10 times the Vas of all of the woofers combined. This works great in medium size rooms but the power requirements and number of drivers gets rather unreasonable for large churches or concert halls.

                        As I have investigated the options I have come to the conclusion (subject to experimentation) that an array af transmision lines or tapped line (tapped horns would also be a possibility but would require larger boxes and would have a narrower usable bandwidth) would be the best compromize for largish rooms.

                        In the end most any type can probably be made to work just fine if designed properly for the particular application.

                        If it is Caesar that you worship, then Caesar you shall serve.


                        • #13
                          Wow! Thanks for all the input. I've read every post and checked out the links in each one, so I'm learning a lot. No doubt the optimum solution would be both expensive and large, and I'm constrained in this project both by money and space. 16 Hz is indeed a very difficult goal to obtain. As Arie mentions, the Rodgers subs claim response down to 16 Hz, but the graphs on my SW7.5's tell a different story, with output at 16 Hz being about 12 dB lower than at 32 Hz. No wonder the bottom half octave of my contrebourdon is missing. I doubt that a different driver from my rubber-surrounds would make any difference.

                          No doubt rotary woofers would be the ultimate experience. I understand M&O has used these, and the theory behind them suggests that these things work more like real organ pipes than anything else we have, pumping air in and out of the room, moving more air than any simple cone could ever do. But they cost more than I paid for my last house.

                          From what I've read above and in the links, there seems to be a lot of support for the "infinite baffle" idea, and something approaching that is actually a possibility for my church. I have two chambers, one at each side of the chancel, and each one measures about 8' deep, 16' wide, and 12' high inside. Each has an opening out into the chancel, about 3' x 7' with grille cloth, plenty of room to mount a baffle for some large woofers. These chambers have concrete floors and heavy wooden walls and ceiling, so they shouldn't rattle and ought to contain the bass quite well. Each chamber has a door for access, but the doors are in the baptistry area and can be weather-stripped and closed tightly if necessary to optimize the bass results.

                          I'm thinking my best approach would be to cover the chamber opening with a big slab of thick plywood with cutouts for four 15" speakers, wired in series/parallel. I would need to get an active crossover and direct the lows into their own amp to drive these speakers.

                          Arie, I know what you mean about the out-phasing and such. The old Galanti had the pedals mixed to mono and there were obvious cancellations and beats between the two 16' stops. Fortunately, our Allen MDS-45 has the pedal stops split between the two great/pedal channels, with the 32' contrebourdon and the 16' principal in one channel and the 16' bourdon, leiblich gedeckt, and posaune in the other. Normally, Allen would put a subwoofer only on the 32' channel, but I'd put subs on both these channels so the 16' bourdon can be a really massive stop in its own right, though obviously the 32' will require far more power.

                          Anyway, I'm enjoying the comments. As with my plans to put that Allen into the church (which didn't happen for about 10 months after I began dreaming about it here on the forum), it may be a while before I get around to trying this out. I'll be sure to let you all know how it works out.

                          Bass extension in church organs is one of the hardest parts of doing an extraordinary installation, but I believe it is worth the effort. To me, one of the things most often missing from an otherwise good digital is authentic deep bass. As we've been discussing in another thread (on preludes/postludes) the ultra-low infrasonic frequencies that good organs generate may have effects upon the listeners that we don't yet understand. Personally, I think infrasonics may be one of the keys to exciting traditional worship, one which is rarely understood and used to best advantage.
                          Last edited by jbird604; 01-17-2014, 07:11 PM. Reason: sp
                          *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!



                          • #14
                            Toodles write up post 7 is the best I have ever seen.
                            The problem with horns that some persue with great passion, is time alignment of the lower frequencies to the rest of the music. Horns are slower. Probably why I wasn't impressed by the super expensive Klipshorns I heard in a store in a special Klipshorn room in 1971.
                            The infinite baffle with a fan looks easy to do electronicly. A dc high speed fan motor, modulating the voltage to the fan with an AC source, making negative peak voltages zero fan voltage and positive voltages full fan speed. I would use a 8" fan motor packaged in a duct like in a large electronics rack. Trouble is the motor response speed is non-linear, you would have to fool with an op amp curve device to linearize the fan speed curve. Then there are the bandpass filters to make this thing work only 16 to 40 hz or something. Infinite baffle is usually quite doable in churches, if there is not a baptismal robing room, there is usually an airconditioning equipment room somewhere attached to the auditorium that can act as the speaker cabinet. The problem is damping out the AC motor noises while letting the bass through.
                            I grew up low class Baptist, I view 16-25 hz as noise, personally. but have fun, your congregation likes you, so they have selected themselves for this sort of worship. One of my peak audio experiences was hearing an 800 hp geophysical truck pump the ground sweeping from 0.5 to 25 hz as they tested out the hydraulics, but I wouln't have called that "music".
                            city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112


                            • #15
                              I-Joe, as I understand the rotary woofer, the fan blades themselves are controlled by a voice coil as the motor speed remains constant. The trailing edges of the blades are "bent" back and forth just like the cone of a woofer so that they go oscillate between blowing and sucking air at the frequency of the input signal. This physical bending of the blades is only possibly up to a maximum of about 40 Hz, so conventional woofers must be used above that frequency. Of course conventional woofers will have no problem handing the bass once you get above 40 Hz.

                              Because the fan blades are turning at high speed and can move quite a bit of air, a small flexing of the blade produces a very large change in the air being blown into or pulled out of the room, thus creating ultra-low sound waves far more powerful than any cone could possibly do. It is indeed the missing link in organ sound creation, but as along as they remain at those high prices they are not going to be available to most of us!

                              I know that a lot of people consider the frequencies below 32 Hz to be junk or out-of-band noise, but I just can't get over the feeling I've had a few times when hearing some enormous 32' pipes playing in a vast cathedral. There is nothing else like it, and I WANT that in my own church!
                              *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!