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In Reply to: RE: Dr.Bruce Edgar Plans posted by claudej1@aol.com on September 30, 2023 at 06:27:27
I've never seen any plans available for the Seismic Subwoofer, though something may come up following your post here. The original Speaker Builder magazine articles about the Show Horn and the Monolith Horn are still available on the Volvotreter website in the downloads section (see link here).
Paul
Follow Ups:
I respect Dr. Edgar. He was quite helpful to me personally, but If I were to decide to build more horn subwoofers I would prefer the designs of Bill Fitzmaurice over the Seismic Sub. The Seismic Sub is not without problems.
I dream of an America where a chicken can cross the road without having it's motives questioned.
Thanks for the response. I wasn't looking for opinions, just plans, or a simple yes or no about whether the plans were ever available. I own a Seismic, I was just hoping not to have to use a large bandsaw to see the guts of the the labyrinth. Besides, I have lots of other subs in the works, but to get twin of this one would have been nice. Instead, I'm working on a Servo Drive BT-7 conversion with twin 15's pumping bass with the equivalen Sd of a 21" driver. Basically 2 of the ones Bill F recommends, which are also approved by Tom Danley.I had 1 THT and Twin THTLP's on 2 occasions, before moving to smaller spaces mad them unsuitable. Things change a lot in 14 yeasr. Liked them all, but I sold them to people who could use them.
So now I will have a modified BT-7 in the rear for 2.2, and 3 tapped horns upstairs. Twin Danley TH-50's in front, coupling at 40 Hz.and the DTS-10 inspired Super Tapped Horn that gets down to almost 10 hz in the rear. Yes it scares strangers for sure in a Home Theater., But the full horns are strictly for music downstairs with the Time Aligned Titan II's.
Edits: 10/09/23
I think you might come close scaling Bruce's "Monolith" by 1.2 or so
Karlson Evangelist
and they are so sensitive that I find I am at either one or two steps above zero on the volume control of my RekHorn sub amp and would prefer 1 1/2 steps for most music.
Illusion that the bass is coming from the Edgar folded mid-bass horns is worth the price of admission as the subs blend in visually with the record racks along the walls and folks have no idea they are subs.
No 'boom' just bass extension down to 30-40 Hz or so, an octave or so below where the Edgar folded mid-bass bins will go.
Poorly integrated subs are worse than none at all in my view.
Bass wavelengths are very long-20Hz is 56+'-and so bass horns are going to be large.
Since I rebuilt my room for the Cogent arrays I did add some EQ to the woofers so I have a sold 20Hz now. It's wonderful.
I helped Bruce build many Seismics way-back-when. If someone has the external measurements I could reverse engineer the internals pretty easily.
eso
They were a carnival of American decay on parade, and they had no idea of the atrocity they had inflicted upon themselves." Henry Chinaski
Eso, be careful reverse-engineering Seismic sub - Bruce loved to cut corners to see just how far he can go. Ideally,
(i.e. without cutting corners) the 35Hz horn sub would require a horn length of about 10 feet. I have the numbers for the wave guide if you're interested.
EsoBruce supplied the external dimensions of the Seismic here some time ago (see link). When I helped move one back in the day, the top box section lifted off so we could move it, and the bottom folded horn section separately. That top box section held the JBL 2240 driver mounted to it's reactance annulling back chamber. Bruce used calculus to derive the volume of the back chamber, however there's the old pre-T.S. rule of thumb of: 45/V= the frequency where the box will resonate in Hz, and where V= the square root of the box volume. As Bruce had mentioned at one point (the Show Horn?) that he had to adjust the box volume a bit anyway, even with the calculus, then the old rule of thumb seemed close enough for those of us who are math averse. As a sub will be bandwidth limited at the top end, then Keele's formula for deriving the optimum horn throat size SR (for maximum efficiency) could be used: Sr=0.8Fs*Qes*Vas, where Sr is in sq. inches and Vas is in cu. ft. As I recall the horn throat began at the top of the lower box when the top section was off. It would be interesting how your memories of the Seismic match, if at all, with these numbers. The hard part of reverse engineering the Seismic would be the geometry of the various shelves on the interior of the bottom section which formed the folded horn. Back in the day when the plans for my Olson derived bass horns got lost at one point, I resorted to using an electronic stud finder and chalk to trace out the locations of the internal shelves which formed the folded horn, but luckily the plans were later found. Now if someone had a Seismic plus a stud finder and chalk.... Anyway, any ideas you have on the subject would be interesting. Your current rig is looking great! But of course this can result in jealous feelings in those of us with less attractive horn rigs with higher WAF Z.
Paul
PS the TS specs for the JBL 2241 are: Fs=35 Hz; Qes=0.43; Vas 11^3ft. So the volume of the horn throat for Keele's Sr would be 132.44 sq. in., or a square mouth of 11.50 square. Note edits here due to using wrong Vas in cu. meters initially.
Edits: 10/05/23 10/05/23 10/05/23 10/05/23
Those rear chamber calculations don't work, because they don't consider what's actually happening. The mass of the air in the horn and front chamber adds to the Mms of the driver, which pushes the driver plus horn system resonance down. When that resonance is below Fc sensitivity at and near Fc is reduced. There are two ways to address this. One is to start with a driver that has Fs considerably higher than Fc. The other is to make the rear chamber small enough to push the driver + horn resonance up to where it should be. It used to be a trial and error proposition, but using HornResp software that's no longer the case. The same applies to throat and mouth area and every other aspect of horn design.
With the 2241 in a maximally flat maximum sensitivity horn the throat area would be 42 sq in, the rear chamber 1.5 cu ft. But both of those figures are dependent on the dimensions of the horn and front chamber. If you change those you change everything. That's where trial and error is problematic, but software modeling makes it easy.
Bill
HornResp is a wonder of the ages, and us audiophiles of the future here can look back at how those in the past struggled. The box volume resonance rule of thumb ignores anything about the driver, or any resonances caused by the geometry of the box, or what frequency the resonance would need to be in order to counteract the effect of the mass of air in the horn to choke off the bass near the lower end of where the horn should be expected to go. Keele's optimum horn mouth math/Sr was criticized on this forum by Tom Danley for typically resulting in a horn which failed to reach a usable high frequency response (which could be a plus in a subwoofer), so he preferred Leach's more complicated math which stressed bandwidth over efficiency. Some time ago on this forum there was speculation on which of these two approaches were used in HornResp, and then it was revealed that HornResp existed in some form before the Keele and Leach AES papers and was derived from Olson's Dynamical Analogies. Back at the '03 Midwest Audio Fest at one of Bruce Edgar's presentations, I asked him what he thought of HornResp. He answered that he had designed a bass horn at one point which had a resonance in the response which he tuned out by just proping the horn up a bit off the floor. He asked David McBean if this could be accounted for in the HornResp program, but he answered that it could not in a one dimensional program like HornResp. Bruce then said that he still uses a calculator to design horns, so from this I have to assume that the Seismic was designed that way. It would be interesting compare details of the Seismic design to another bottom firing subwoofer horn for the JBL 2241 (with similar dimensions to the Seismic), but designed with todays HornResp, which itself has evolved quite a bit during the last 20 years.
Paul
Had often wondered over the past years what evolution that room had experienced.
Couldn't believe you ripped out previous built in room horn subs to make even newer ones.
Conicals now I see. And as always the quality design details that look exceptional and functional.
What amps and pre are you running now?
I retired 6 years ago so I don't visit the South Bay often.
Extremely glad to see your post and your evolved room. The previous was spectacular too!
How are you ED? I only demoed the mouths of the horns to reconfigure so I could push the conical midbass back further. The backchambers, throats and first part of the flares are the same.The rear wall is all diffuser now and are the little shelves for the CDs I rarely use.
Pre and Amps are all the same: C-J Premier 17 (now with teflon cap upgrade), Laurel 300B amps With WE tubes and Cy Brenneman fixed bias mods, and the VTL MB-125 of the bass horns.
But with the added room treatments and Cogent mains it is a hole new level from what it was before. The windows are insulated low-E glass and operable now.
All that new millwork was material left over from a custom place I build above Malibu. It's a south American hardwood called Garapa.
eso
They were a carnival of American decay on parade, and they had no idea of the atrocity they had inflicted upon themselves." Henry Chinaski
Edits: 10/04/23
Always a pleasure to see your refined touch on your creations.
I thought you had some Cy creations at one point but possibly bad memory. His stuff was dead quite even on 100 db plus setups.
Are you using the field coils? What power supplies? Always a big point for Mr Schell and Mr Drysdale
Yes, I have both the DS 1448 midbass drivers and the original DS 1428 midrange drivers. Still using my old Fostex T-925a tweeters.
Since I'm still raising a family I couldn't justify spending on a Tungar power supply for the field coils. So I was using a couple of the pretty good old Radio Shack DC supplies for a while.
And then Pavel-whom you may have met over at Bruce's why back when-designed these tiny little cards that are a current source. I've got modular 20V supplies that can each driver two of the current source cards to maintain a constant 12V to the field coils regardless of what is happening in the VC gap. They are very nearly the quality of a Tungar.
It makes no sense that a field supply would make a big difference but everyone I know that has compared them agrees.
And simple 1st order network with 10Ga inductors and I charge coupled the Soviet PIO caps...
eso
They were a carnival of American decay on parade, and they had no idea of the atrocity they had inflicted upon themselves." Henry Chinaski
Was initially puzzled by each having two sets of connector posts but of course two coils per side.
I think the T92A fits in very nicely as few conventional HF drivers can hit that 100+ db mark, but they sure can.
Glad to know a survivor set of Cogents are in a "every day type guys" hands and not reserved for billionaires jewelry.
Te main problem with the Seismic sub is it's size and weight (see link). I was part of the Chicago Horn Club crew that did the move in/and out back in the oughties when Bruce demo'd the Titan rig at a Chicago Audio Society meet here. It was like moving a large refrigerator. Also to be considered for subwoofer duty are the Danley Labhorn and Taped horn which perform very well and are referenced on the volvotreter link. I have'nt heard any of Bill Fitzmaurice's subwoofers yet but they certainly look like good candidates for DIY subs. However I live in a 130 year old wood house, and I gave up on the idea of making a horn loaded subwoofer after hearing some of the Danley designs actually shaking the old houses they were demo'd in. Forget about harmonic distortion in the playback equipment, with horn subs in old houses you run into exciting harmonic resonances in the house itself!
Paul
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