SynTripP: 2-way 2-part Virtual Single Point Source Horn

SynTripP© Syn·Trip·P (sĭn'trip-ē) n. The occasional tendency of two or more mental diseases to coalesce into one resembling or inducing the hallucinatory effect produced by taking a psychedelic compound.

The SynTripP© 2W2PVSPSH (2-Way 2-Part Virtual Single Point Source Horn) cabinet uses two B&C 10CL51 10" for low frequencies (LF) in an offset bandpass bass reflex arrangement with a Celestion CDX14-3050 three inch diaphragm 1.4" exit high frequency (HF) driver at the horn apex. The neodymium drivers and well braced 15/32" cabinet construction result in a very light and stiff (solid) enclosure, just under 34 pounds (15.5 kilos) for the 26.5" wide x 11.25" tall, 15" deep (67.3 x 6.075 x 38.1 centimeters) main cabinet which also incorporates an adjustable tilting stand mount adjustable over a 40 degree range.

The pyramid shaped second section of the horn is detachable, allowing the main cabinet to be much smaller and lighter than if it were included as part of the main enclosure. The secondary horn is 41" wide x 25.5" tall x 7.5" deep (104.1 x 64.8 x 19 centimeters), weighing about 5 pounds (2 kilos). The horns nest like Dixie cups, attached by a ratchet strap and bridle assembly to the main enclosure in about the time it takes to tie a pair of shoes. Dispersion is 86 degrees horizontal x 36 vertical, with pattern control down to 310 Hz (-6 dB 42.5 degrees off axis) horizontal and 460 Hz vertical.

Any person wishing to duplicate my Welter Systems designs for their own use is welcome to, any person or corporate entity that would like to produce them for sale please contact me to arrange a licensing deal to avoid violation of intellectual property rights as defined in section 27 of the Universal Declaration of Human Rights adopted as international law in 1976.

A pair of the main cabinets and secondary horns will easily fit in the back seat of most compact cars.
The cabinet can be used without the second section in venues where size is an issue, without the second horn section pattern control is lost below 430 Hz horizontal and 1100 Hz vertical.

The SynTripP© design started as some rough pencil sketches years ago, then more recently progressed with modeling in the free Hornresp simulation program. Another DIY forum member, "xrk971" also modeled an approximation of the design using Akabak. Simulations are quite helpful, but there were several design details that could only be determined by building, testing, and then rebuilding and retesting until the desired goals were achieved. One (of many) details specific to the offset bandpass bass reflex arrangement is how much effect the port size and location has on the HF response. Tests show that although the ports do affect HF response, the influence is rather minimal for the size ports ultimately chosen, while the benefits of having the LF and HF sharing the same horn make for remarkably good polar response. Each design iteration required extensive testing and crossover refinement, requiring drivers to be removed and reinstalled multiple times.

Sensitivity is defined as the sound pressure level (SPL) output at a voltage equivalent to one watt at one meter in a loudspeaker's nominal impedance rating, the SynTripP© is 4 ohms LF, 8 ohms HF. The sensitivity of 99 dB at 100 Hz (half space, 92 dB free space) is quite good for a cabinet of this small size, high SPL with "flea power" amplification is possible. Since sensitivity varies with proximity to boundaries (walls, floors, ceilings) and frequency, the raw response under varying measurement conditions and the equivalent SPL at "0 dB" is given below. The SynTripP© has an F3 of 82 Hz, so it typically would be used with one or more sub woofers, though in "step down" mode with one or more ports covered the response is adequate to reproduce instruments such as an upright bass at "live" sound levels.

No currently available commercially built cabinet incorporates all the features of the SynTripP©.

The SynTripP© design is rather challenging to build, and incorporates features that may be of little interest to those with only a casual interest in DIY, but achieves accurate reproduction of sound heard in very few designs, regardless of cost or size. Elimination of some of the features more specific for it's intended primary application, live sound reinforcement, would simplify construction significantly without compromising sound quality for typical home use.

I won't bore you with extensive subjective flowery elaboration of the SynTripP's excellent sound characteristics, instead will provide actual measurements that substantiate it achieves the 10 design criteria listed below. After completing testing yesterday, listened to music at distances from about 6.5 feet (2 meters) up to 750 feet (229 meters) away, the cabinet elevated on a crank tower 4 meters high. Even at 750 feet the music could be heard clean and clear over the noise of Highway 14 traffic and a large backhoe digging in the Mineshaft Tavern's parking lot. The path of my bike ride while listening can be seen in the satellite photo below, the SynTripP© loudspeaker is near the telephone pole between the buildings in the lower center of the photo, the Mineshaft Tavern is the building in the upper right. The speaker was pointed approximately in the direction of the middle Highway 14 marker, it sounded great everywhere along 14 other than behind the large buildings to the East of the Tavern blocking the sound. Standing beneath the SynTripP©, discreet echoes from the various buildings could be heard, varying from about 600 ms to over a second in return time. To be able to hear those echoes when standing within two meters from the horn exit is a testament to the extraordinary directional control the SynTripP© exhibits.

Long and Boring History Time:
Just recently passed the anniversary marking 40 years of my adult life as a professional in the sound and lighting production industry, designing and building speaker systems, mixing audio for recording and in live settings for audiences ranging from 100 to over 100,000 people. During the course of my STS (Southern Thunder Sound) touring career I had the privilege of working with thousands of the best musical performers in the world, and directly learning from hundreds of the most experienced and knowledgeable sound (and lighting) engineers. As well as learning from the best, I find that mediocre and awful engineers and sound systems give important insight into the difference between the good, the bad, and the ugly ;^).

Managing the technical, logistical and personnel details for as many 800 shows a year, fulfilling technical contract riders up to 20 pages long eventually lost it's appeal. After selling STS in 1992 (finally) moved south to New Mexico, built a home recording studio, and have continued providing production on a smaller scale, continuing to build speakers for a wide variety of unique applications, each using design aspects culled from a large palette of sound concepts appropriate for the intended use.

Part of the joy of DIY is the feeling of accomplishment after completing a successful project. The warm feeling can continue long after the project is done. Now that the cost of commercially available loudspeakers of (almost) all types has dropped to the point where their retail cost is less than my cost just for the components needed to build them, I find little joy building something I could purchase for less money. Considering eating sawdust gets old quick, and the shop portion of a project usually turns out to be only a fraction of the time investment needed for design development, if a commercial product is "close enough", I'd prefer to buy it rather than build it, even if it costs considerably more.

Last winter decided to begin winding down from semi-large scale production to semi-retirement and sold my line array system originally built in the year 2000 (with a re-design in 2008). The line array system works great for it's main usage, outdoor events with audiences of up to around 5000 spaced as far as 400 feet away, yet was relatively small, light and could be effectively ground stacked, rather than flown.
I retained a smaller system suited for covering venues of around 1000 capacity. Although the conventional small format horn over woofer(s) speaker designs used in the (relatively) small system are fairly decent, they don't fully meet criteria that I have found crucially important for proper sound reproduction and playback. No speaker system currently commercially available meets all 10 criteria, so rather than wait for it to happen, decided to "DIY".

The SynTripP© design was developed to meet all these 10 criteria:

1) Flat and smooth frequency response to assure "what goes in is what comes out".
2) High output response to below 100 Hz so subwoofers do not need to be co-located with the main speakers, which are generally elevated. At frequencies below 100 Hz sound output (unless from a large array) is near omnidirectional, so the apparent sound image location does not wander between the sub(s) and main speaker location as it would with the higher acoustical crossover point a speaker with less low frequency output would require.
3) Smooth phase response, necessary for good transient response.
4) Wide dynamic range, the capability of reproducing levels equivalent to instruments such as brass and percussion which can peak in the 125-130 dB SPL (sound pressure level) range at one meter.
5) Low harmonic and amplitude modulation distortion at all SPL levels that will be reproduced. Quite a bit of even order HD can be tolerated, as musically it is simply doubling octaves, while odd order HD is much less tolerable, as it can change the composition, introducing notes not in the original. AM distortion, often (mistakenly) called "Doppler distortion" occurs when a driver's excursion exceeds the linear range of operation, which causes a change in level (amplitude) of the higher frequencies at the same rate (modulation) of lower frequencies. The effect is quite pronounced, making voices sound like they are gargling, and the onset is rather rapid after Xmax (the limit of linear excursion) is exceeded. Clean output at high SPL requires larger drivers with greater Xmax than would satisfy reproduction at less than "live" levels.
6) Low thermal compression during demanding musical passages. At high drive levels loudspeaker voice coils heat up, causing their impedance to rise. Amplifiers, being voltage sources, deliver less power at higher impedance, hence louder average signal results in less output than it would before the voice coil heated. As well as the thermal compression issues, large temperature rises result in a number of other driver parameter changes which can result in a drastically changed frequency response, especially when using passive crossovers.
7) Even SPL over a large coverage area. The low humidity here in the high desert causes high frequency air absorption losses (in addition to the usual 6 dB per doubling of distance loss) to be 10 dB or more worse than in humid environments. To make up for those losses requires as much as 10 times more HF power, making points 4, 5, & 6 more difficult to achieve.
8) Constant directivity (even polar response) with a well defined 90 x 40 degree coverage pattern over a wide frequency range, necessary for each listener to hear the same response. Well defined coverage "edges" are needed to keep reproduced sound out of unwanted areas to reduce reverberation and acoustical feedback caused when stage microphones "hear", and re-amplify the main speaker's output.
9) In addition to the above audio criteria, working in smaller venues (sometimes without additional set up help) and advancing arthritis in my left wrist (getting old sucks) require compact size and light weight, which made achieving the above criteria far more challenging.
10) Power is often limited in smaller venues, making high efficiency a necessity to achieve criteria 1-6, and energy efficiency is just plain good for the planet.

Criteria 1-6 are met by a number of commercially existing designs, though most of those choices conflict with 7-10.
#7 can be met using line arrays, but line arrays conflict with 8-10. Line arrays, having the "design feature" of a destructive near field interference pattern, dropping at 3 dB rather than 6 dB per doubling of distance, so can achieve a more even average SPL than a horn, but when elevated and angled down to the desired coverage area a large horn can actually achieve more uniform coverage. In either case, precise angle adjustment is required, hence the inclusion of the adjustable tilting stand mount in the SynTripP design.
Criteria #8 is the toughest to meet, as it requires a virtual single point source to achieve, and the waveguide must be large to provide defined coverage to a relatively low frequency. In theory, multiple horns can combine for seamless coverage, in practice, a single horn covering the desired pattern works better.

Co-axial speakers using a HF horn in the center of the woofer have been meeting most of the above criteria since the introduction of the Altec Lansing Duplex 601 in 1943. In the mid 1970s, Bill Putnam and Ed Long designed a crossover which time aligned an Altec 604, time aligned co-ax became the monitor of choice for many (if not most) large studio control rooms ever since.

A large studio control room is generally much smaller than a concert venue, to meet criteria 1-8 for large venues I developed the "Maltese" horn system in 1992, a pyramid shaped 3-way enclosure using a conical expansion HF horn centered in the mid horn centered in the LF horn. At 67.5" long with a 45x45" mouth, weighing around 350 pounds with a 13x13 degree HF dispersion pattern, around 18 Maltese horns would be required to provide the 90x40 coverage pattern of a single SynTripP©, which obviously would not fulfill #9. The nested horn concept has since been used by CSL, CV, EAW, JBL and probably many others, though none are as narrow dispersion as the Maltese.

During that '92/93 time period the introduction of Christian Heil's L-Acoustics V-DOSC line array using multiple entry HF and offset mid drivers sharing the same horn began to dominate the live sound market. It's fast set up time using less labor and slim form factor allowed more latitude in the placement of the increasingly popular (and progressively larger) video screens, ever more important in selling tickets, as (most) people go to "see" shows. Soon after, most every major speaker company developed their own versions of line arrays, each with enough minor variations of the V-DOSC theme to avoid patent disputes. Decades later, line arrays have "trickled down" and are becoming popular for home use, offering the same low visual impact that has made "column" speakers popular decades before they were commonly referred to as "line arrays".

Already familiar with Tom Danley's Servodrive sub woofers, on a trip to (or from) Florida sometime in that time period I stopped by the Intersonics lab in Illinois for a quick tour of the facilities, getting a chance to actually see his fascinating acoustic levitation device. Before this meeting, I had only seen a patent drawing of the levitator Tom had FAXed me after graciously answering some acoustical questions raised during the development of the Maltese system. I demonstrated to him the directivity, efficiency and "natural" sound of the Maltese HF horn with the tried and true method we old "hornys" still employ, speaking directly through the horn. After a quick description of the Maltese project, I was back on my way.

Sometime later, Tom developed his first line of single point source horns, the Unity (while at Intersonics/Sound Physics Labs) and then the DSL (Danley Sound Labs) Synergy, sharing the classic rectangular two part conical horn form developed by "Don" Keele in the mid 1970s (also used in the Maltese), but without the diffraction throat (and problems associated with it) that Don generally used in his designs as he went from company to company back then. Although the Synergy line has not gathered much traction in the large scale portable live sound sector, and with billions of dollars worth of line arrays deployed, won't for the foreseeable future, Tom's large Biblically named versions are doing well in both sales and performance, and are actually replacing line arrays in fixed installations in many sports stadiums.

Though the SynTripP© shares design features with some of DSL's and other loudspeaker manufacturer's offerings, nothing currently available specifically meets the unique requirements the SynTripP© fulfills. Even though at the rate I'm presently doing production it may take years before the use time will catch up to the design/build time, the achievement of the 10 goals made development of the SynTripP© worth it.

Post #9 lists the tests undertaken between 10/14/14 and 11/5/14, and DSP settings used with the horn extender. Post # 25 has a more detailed horizontal dispersion chart. Post #41 contains plans and a preliminary parts lists, Post #61 has the completed parts lists and assembly instructions, Post #100 has photos of the bass reflex port details, Post #115 has the throat port detail. Posts #128,138, & 568 have injection port and cone filler details. Posts around #729 have alternate HF driver options. Posts 897, 898, & 914 go into details of the throat adapter plate and attachment.



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Very rewarding project Art! Always look forward to your posts. Even liked the history :)

How does the Celestion hold up to the EV's you were using?

I have been using EV DH1AMT drivers since 1992, they hold up great, and nothing i have tested or listened to has been any better for the parameters I find important.

The Celestion CDX14-3050 has less sensitivity than the DH1AMT due to the plastic surround, but may have a bit less distortion in the SynTripP HF pass band.

A friend gave me the CDX14-3050 16 ohm production sample (unavailable in less than an order of 96 drivers) which resulted in the unfortunate problem that getting a matched pair of the standard 8 ohm CDX14-3050 required me to purchase an extra 8 ohm diaphragm to replace the 16 ohm production sample.

My usual diaphragm replacement protocol starts with a thorough cleaning of the magnetic gap, but the CDX14-3050 gap has Ferro-Fluid (a ferrous metal impregnated oil that wicks heat from the coil to the magnet structure) in it.
The replacement diaphragm was not accompanied with any replacement Ferro-Fluid, removal of the 16 ohm diaphragm reduced the FF level (some came out on the voice coil), and to maintain the reduced FF level little cleaning could be done. Disgusting, like changing a car's motor oil and leaving in the old dirty oil filter.

FF affects damping and Fs (resonant frequency), I need to inquire the manufacturer as to how critical the FF volume is to the CDX14-3050 frequency response, and what removing the FF may do to frequency response and power handling. Power handling is not my primary concern, as HF drivers generally distort so badly at a fraction of their rated power that I won't use them near that level.

"Classic" HF drivers do not use FF, if operated in clean air (no floating ferrous metal particulate) they will last almost forever. FF, like any oil, will be contaminated by airborne debris and eventually "go bad".

The 8 ohm replacement diaphragm does seem to be a bit smoother than the 16, but either it is reversed polarity from the 16, or (more likely) I installed it backwards.

After completion of the second SynTripP I'll find out which is the case.
Tests, tests, tests...

10-10 let's do it again, & again :)

WoW, that's a LOT of thought/time/energy etc etc you've put into this, which has obviously paid off. So you should be rightly proud of what you've achieved. It's a shame we can't hear them ! I liked the history too ;)

I know what you mean about riders. A lot of people who should know better, just take the urine on purpose, just because they can :( I've heard about some really crazy ones over the years. If more venues had told them to eff off years ago, it wouldn't be as stupid as it's got !
Founder of XSA-Labs
Joined 2012
Paid Member
Nice work Art - that is one flat freq response curve. Do you have a plot that shows both woofer and tweeter on same plot to see the XO behavior? Is the XO pure DSP bi amp or have you managed to make a passive XO? I like how the extension turned out - almost looks like a fiberglass molding.

Btw, you might want to add a link to the development thread.
Nice work Art - that is one flat freq response curve. Do you have a plot that shows both woofer and tweeter on same plot to see the XO behavior? Is the XO pure DSP bi amp or have you managed to make a passive XO?
I will be developing a simple passive crossover, but have not yet. Other than the plot in the OP that shows the combined response with no processing, all the crossovers have been DSP. Of interest, the crossover EQ settings created for the tests at two meters high were quite different than the 4 meter high settings below, they were correcting for ground bounce.

After completion of the second cabinet, I'll conduct new polar tests at 4 meters high.

The build came in at 59 hours, I expect finishing the second cabinet will come in at a fraction of that time. The real time "black hole" is all the testing and review/write up process, 155 hours. Between design and build, that's an average of 5.8 hours per day for the last 37 days.

The lists of the tests is quite extensive, the files total 18.1 mega bites.



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"Classic" HF drivers do not use FF, if operated in clean air (no floating ferrous metal particulate) they will last almost forever. FF, like any oil, will be contaminated by airborne debris and eventually "go bad".

My replacement apt-80 diaphram job must be filthy lol. It was my first project which was mainly used in a shop setting. Will take a look at it sometime.
XO and filter data studied

.....Is that 800Hz -24dB/oct?.....
By curiosity i studied picture two post 9 allow me from that study to post this:

LF section
HP 75Hz BW24dB gain 0dB / LP 950Hz LR24dB gain -3dB
PEQ 132Hz Q2,63 +7dB
PEQ 560Hz Q2,03 -7,5dB

HF section
HP 800Hz BW24dB gain 0dB
PEQ 1180Hz Q1,22 -2dB
PEQ 4250Hz Q2,03 -4,5dB
PEQ 12500Hz Q3,41 +4dB

More unshure parameters:
A parameter says 250Hz gain -1,5dB, guess could be a high shelfe in LF section.
A parameter says delay 0,4mS the other 0,0mS, quick guess LF delayed 0,4mS because of physical placement but don't known if the acoustic bandpass for LF section would take time and demand the HF section to wait fire and the delay placed here.
Thanks for posting the XO plot - looks beautiful. Is that 800Hz -24dB/oct?
The 10" "mid" is using a 800 Hz BW (Butterworth- sharper cutoff at the crossover frequency) and the 1.4" exit "high" is using a 950 Hz LR (Linkwitz-Rieley, softer cutoff at the crossover frequency), the high output is delayed by .4 ms. The 10"s have more clean output potential at 800 Hz than the HF driver, raising the HF crossover point to 950 Hz reduces HF THD (total harmonic distortion) by quite a bit at high drive levels, the electrical "underlap" (gap between mid and HF crossover points) results in a smooth acoustic frequency and phase response in the crossover region.

Previous tests had used a production sample of the CDX14-3050 HF driver with a 16 ohm diaphragm, for best phase alignment the output polarity had to be reversed when wired with the positive (+) signal to the right hand side red terminal.

The 16 ohm version of the CDX14-3050 is only available to OEM (original equipment manufacturers) in orders of 96 units or more, so to get a matched pair required purchase of a standard CDX14-3050 (8 ohm) and an additional 8 ohm replacement diaphragm.
If anyone is looking for a spare 16 ohm CDX14-3050 let me know!

After replacing the old 16 ohm diaphragm with a new 8 ohm diaphragm, the polarity now had to be "normal" with the positive wire to the right terminal. This particular diaphragm is self aligning, the terminals go through holes in the compression chamber back cover, the back holes align the diaphragm so the flexible lead in flat wires are properly placed in two "divots" in the magnetic gap.

There are three possible reasons for the change in polarity:
1) I accidentally installed the diaphragm upside down, then plugged the spade connector to the right terminal, which had become the negative terminal.
2) The 16 ohm production sample I received is wired opposite polarity to the current 8 ohm version.
3) One of the two diaphragms was labeled incorrectly at the factory.

#1 is the most likely, I'll find out when I finish cabinet #2 and check it's HF polarity, and will probably have to open up the box for the fifth time to flip the diaphragm.



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Hi Art;
Nice result!

I'm intrigued by the fact that your measurements showing response with 1,2,3,4 mid vents plugged showed the response changing at both the low and high ends. The change of box tuning is of course expected. Why does the response change up near crossover? Is that simply evidence that the holes are too large too hide in the corners, so to speak? (assuming that is where they are, they aren't visible in the photos)

Hi Art;
Nice result!

I'm intrigued by the fact that your measurements showing response with 1,2,3,4 mid vents plugged showed the response changing at both the low and high ends. The change of box tuning is of course expected. Why does the response change up near crossover? Is that simply evidence that the holes are too large too hide in the corners, so to speak? (assuming that is where they are, they aren't visible in the photos)

The upper 10" response changes because the BR (bass reflex) port has a pipe resonance peak that is out of phase with the woofer's offset horn output, causing differing null depth depending on the amount of ports used.

The 10" offset port holes also affect the HF (high frequency) response slightly, they don't completely "hide in the corners", but that is a different issue than the BR (bass reflex, AKA phase inversion) port response pipe resonance, a "feature" any BR design shares to a lesser or greater degree dependent on the length of the BR port.

As mentioned in the OP, the slight HF response changes the 10" offset port holes cause in the SynTripP are more than offset by the smooth vertical polar response that can't be achieved with LF and HF drivers located with a vertical separation distance near the wavelength at the crossover frequency.



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How is it possible to mount diaphragm upside down? Isn't concave?

I wonder if Art meant that it was rotated 180 degrees, so the 'top' of the diaphragm was on the bottom, and the terminals were reversed...?

I may have a PA application for these at some random point, but that would involve that particular band buying the drivers ;)

Are the SynTripP speakers completely unnecessary for home use? :D
I wonder if Art meant that it was rotated 180 degrees, so the 'top' of the diaphragm was on the bottom, and the terminals were reversed...?

Are the SynTripP speakers completely unnecessary for home use? :D
Correct, diaphragm reversal left and right, "upside down" in reference to the driver's orientation in the cabinet.

Have not listened to the SynTripP indoors yet, after the second is complete will compare them with my home stereo speakers, and report if they then become a necessity ;).