PATCHED Full Range Drivers For Open Baffle Design
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The Dipole15 woofers are designed specifically for open baffle/dipole use. The Dipole15 woofers were designed with a large underhung motor and Full Copper Faraday Sleeve covering the entire pole for incredibly low distortion and accurate reproduction.
The Dipole15 woofers are designed specifically for open baffle/dipole use. In open baffle applications, drivers are required to operate at much higher excursions than in typical boxed applications to compensate for the rolloff of the baffle. In applications where woofers are continually called upon to operate at higher excursions, Bl and Le linearity are extremely critical. To achieve this linearity, the Dipole15 woofers were designed with a large underhung motor and Full Copper Faraday Sleeve covering the entire pole. Full details on what makes this motor design different can be found here: The Lambda 001 Motor Design. This combination utilizing the Faraday ring and underhung motor provides the most possible linearity and low distortion during high excursion use. The high Q and low Fs allow the Dipole15 woofers to be very efficient at low frequencies and have very good low end extension. While EQ is typically needed to correct for the baffle rolloff itself, no additional EQ is required to flatten the response of the driver.
As with all of the TD drivers, the Dipole woofers have extremely low and linear inductance. The ideal Qts and soft suspension means the Dipole woofers are very efficient at low frequencies and can be pushed to high excursions with very little power required. The low power requirements and non-reactive load make the Dipole woofers an ideal match for use with tube amplifiers as well. In addition, they have some of the best midrange performance of any woofers Acoustic Elegance offers, extending up to 2KHz or higher. They are available in dual 8ohm and dual 16ohm options for a variety of wiring configurations.
Project Description:This project is called the Coley OB15 Open Baffle Speaker. It is a full range speaker with a manageable baffle size and integral electronic compensation for baffle losses. In addition, the impedance curve of the speaker presents itself as a light resistive load at high frequency, making it a good match for single-ended triode amplifiers with little or no negative feedback.
Design Goals:This project began as a desire to experience the transparency of an open baffle but with full range performance. Limited space meant limited baffle size so it was known from the beginning that compensation would be required. A theoretical efficiency loss of 10dB was deemed acceptable so long as the response was reasonably flat and extended to at least 50 Hertz. In addition, it was desirable to drive the open baffle with a single-ended triode (SET) amplifier. Since it is common for SET amplifiers to use little to no negative feedback, the open baffle impedance needed to remain at 8 ohms or greater at high frequency since amplifier impedance stabilization caused by negative feedback would not occur.
Enclosure Design:As an open baffle prototype, the enclosure consisted of nothing more than wooden panels for each speaker driver mounted to a desktop rack. An edge glued pine panel of 19x16x0.75 inch was used for the woofer and a cedar panel of 19×5.5×0.75 inch was used for the tweeter. Edges of the panels were finished with a router and round-over bit. The 0.75 inch thickness of both wooden panel types allowed easy mounting of components to both sides of the panel but does require countersinking of the rack mounting holes. Because solid wood is used, predrilling of holes is mandatory. MDF would be a better choice for most builders but was not a choice here due to people with formaldehyde sensitivities in my home. Two stains were tried for appearance, a simple light stain and a hand rubbed dark stain to produce a faux antique look. Once stained, inductors and resistors were screwed to the rear of the baffle panels and the large capacitor was soldered directly to the w oofer leads and cemented in place with silicone RTV. The binding posts for the cable were mounted on the lower left corner of woofer panel to be near the floor but any convenient location will work.
Enclosure Assembly:Assembly is quite easy for anyone with minor woodworking skills. Once the driver and crossover electronics are mounted to the wooden panels, they are then screwed to the Tripp-Lite 12U desktop rack with the tweeter panel mounted above the woofer as shown in the photos. The overall size of each open baffle speaker is 20x24x12 inches, the depth of 12 inches being the support feet of the rack.
Crossover Design:Since I personally like the sound and smooth transfer characteristics, an 1100 Hertz two-way shunt crossover was used. Crossovers of this type interact with the electrical characteristics of the speaker drivers so once these parameters are measured, the entire circuit can be modeled in SPICE to optimize the component values and performance. Multisim Touch, a National Instruments product, is available free for the iPad and was used for this purpose. In addition to the shunt crossover for the drivers, a series RL network was included to compensate the baffle losses that roll-off at 6dB per octave. The conjugate 6dB per octave reactance characteristics of the RL network will flatten the natural roll-off and thus flatten the frequency response of the entire system. When using RL networks of this type, some trial and error is unavoidable as is some loss in driver efficiency. A 10dB loss was deemed acceptable to have the necessary low frequency extension to make the Coley OB15 a full range speaker. Although the RL components are not available from Parts Express, they are easily available from sources like Mouser. The 50 ohm resistor used in the network is metal and highly recommended due to the higher heat dissipation capability.
Tips & Tricks:There is nothing special about using a rack for these speakers, construction could have just as easily been all wood which would allow omitting the rack. As long as the approximate width and height are maintained, the performance will be nearly identical. For those concerned about maintaining a constant load over frequency, a 12 ohm load across the speaker terminals can be added with little or no change in performance; simply size the resistor wattage according to expected power. Like any open baffle, it is best to place the speakers at least three feet from the wall for best results.
Conclusion:The performance of this speaker was beyond my initial expectations. For someone who is accustomed to the bass characteristics of a ported enclosure, the transparent and encompassing bass of an open baffle was a pleasant surprise. The sound from this open baffle speaker surrounds the listener and it is easy to imagine yourself in a smoky bar listening to a live jazz band.
Single driver loudspeakers havecaught my attention from time to time over the past decade, primarily at the Montreal show. Often they were small floorstanding models with relatively wide bafflesand shallow depth. The drivers were in the 3 to 6 inch range as best I canrecall and prices were very reasonable due to the single driver design whichrequires no crossovers. Sometimes they have been offered as kits, making themeven more affordable. The sound was usually well focused and smooth, but with adecided lack of mid and low bass. Interesting, but not interesting enough toreview.
All of this says the OB4.5 fairly begs for a subwoofer andthis fact has not escaped Eric Alexander who has developed a unique patentpending design that will hopefully be headed my way in the very near future.Likewise, at the upper extreme, Eric offers an exclusive 1-inch soft dome add-ontweeter ($50/pair) to fortify the upper treble for those with good hearing inthat range.
As all crossovers degrade time coherence, a top class fullrange system with one full range driver is a crucial reference for hearing. Inmany aspects the best of breed ones can not be equaled or eclipsed in theirhomogenous portrayal of music.
Be careful not to fall in love with the full-range idea for yourself. The best of them are so good that they may move upwards thetolerance threshold of future reviews of conventionalproducts...or even spoil it.
SpecificationsType: Full-range single-driver hybrid loudspeakerFrequency Response: 45 Hz to 20 kHzDrivers: Two 4.5-inch Fostex 127ETrue full-range-no crossoverSensitivity: 92dB/W/m Impedance: 4 OhmsWeight: 21 lbsDimensions: 22 x 13.25 x 12 (HxWxD in inches)Custom finishes availablePrice: $550, optional grills adds $45/pair Tweeter addition adds $50/pair
This is a tale of open baffles, vintage drivers, super-tweeters, and a fascination with simple enjoyment of recorded music. The "loudspeaker" is often the simplest component in a music reproduction chain, yet it can have a profound impact on musical enjoyment. Speaker drivers come ready-made, so what can be done with them, and what if this was as simple as possible? Over the past couple of years, I've been exploring in search of full-range and open baffle projects. Music is my daily pleasure and my quest for an engaging experience is always satisfying but never finished. As a member of the TNT-Audio team, I think an account of my experience traveling the road less travelled, far from the madding (some might say maddening) retail crowd in brandland might encourage and inspire DIY experimentation. By way of context for this story, a look at my introductory pieces for TNT-Audio (see here and here) will indicate my penchant for finding another way to pursue my hobby without succumbing to the siren call to be the "legal prey" of big-bucks brand-marketers. Why spend thousands on speakers? Could I side-step the large profit margins and excess of extravagance by turning to re-use? I don't believe that "new" is always better, and enjoy experimenting and DIY.Could frugality be an audiophile virtue - part of the quality syndrome? I'm a self-confessed frugal-audiophile muso experiencing music highs without the high-end prices. How so? This is the classic make or buy choice, but we are profoundly conditioned by seductive sales promotion to buy, and especially subject to snake oil promises. So, why buy retail when this means marketed product and inescapable hype? A quick glance at my Pinterest board "Loudspeakers that Inspire" shows two things: I like unusual speakers, and there is mega-variety in forms. A search of the Internet reveals an almost endless variety in speaker form - shape, materials, colour, size, degree of complexity, cost - I was inspired and started collecting interesting projects on my Pinterest board. In thinking "without a box", my criteria were: simple construction/easy home DIY, low cost / recycle, and a real enhancement to my listening experience. I previously used KEF iQ7s (cost in retail NZ$1,800 in 2007) with a recently new T&A Power Plant Balanced amplifer (which replaced a Cambridge Audio 840A that failed spectacularly). I was already using an REL Acoustics Quake Q200 powered sub-bass speaker (which operates down to 17Hz (-6dB)) in my music room which is 6.4 m x 3.9 m x 2.4 m, with three wooden doors, and glass doors on one side, and with a concrete floor covered with floating wood laminate. Cabling is hand-made bi-wire by Brendan of RuleConnect, Waimata (New Zealand). I wanted to reproduce recorded music with a big soundstage and musical realism to experience the excitement of the musical performance by hearing and feeling what the musician(s) expressed in the recording. But I had no intention of becoming a loudspeaker engineer.What level of music reproduction satisfaction could be acomplished with a DIY approach using salvaged - perhaps vintage - full-range drivers and minimal woodworking skills? What is it achievable as a frugal audiophile? I sought appropriate technology for the purpose rather than what we are sold. I have oberved in my more than 40 years of music and hifi hobbying the law of diminishing return on investment in over-engineered products made for profit. Put another way, I wanted as simple as possible - no cabinets, no cross-overs, no tuning, suitable for my room setting, and no specialist equipment rnecessary - cutting holes for the drivers would be the hardest task, so a router was to be the most sophisticated tool needed.Recent experience in certain discussion forums reinforced my desire to escape brand, model number and price boasting. What could be achieved for my ideal price - as little as possible? I was told to leave one forum when I questioned the $10,000 to $250,000 price tags of the products everyone was advocating. I was aggressively told that I was not wanted in the group if I was going to be critical and suggest frugal alternatives. In another popular audio discussion forum, a member recently asked other members for opinions on performance and value-for-money of a loudspeaker brand and model - after he'd bought them for $43,000!! Is this staggering naivety or stealth boasting?So, here I'm telling my story of four projects in a 2-year journey of adventures in "no-brands/no fashion land" - largely inspired by my regular and avid reading of TNT-Audio reviews and other articles over several years. I began by asking why are loudspeakers usually boxes? Simplified, they are a baffle or mounting plate for the driver that controls the coupling of the driver to the air in the listening space. Keep looking long enough, and you can even find speakers without baffles!A combined airflow controlling, driver mounting, and aesthetically pleasing box is a complex design problem. Solutions to volume, shape, bracing for rigidity to deal with vibrations and resonances and other colourations, drivers mountings, and other design problems require a compromise of cost of materials and machining, assembly, size and weight, packaging and transportation, storage, presence in the domestic setting, etc. Some speakers seem to have been conceived in the region where advanced carpentry and engineering and sales glitz are more important than musicality.Project 1 - unknown drivers in simple transmission line cabinetsSimple transmission line projectIn starting this journey, two opportunities coincided that prompted action - Eric Cross at Vintage Audio World in Christchurch, New Zealand had a pair of 6.5" full-range drivers for sale for NZ$100. He had coated the diaphragms with Meranti Damar natural resin to enhance tone and they had an old Kauri wood puck glued to each magnet housing to "reduce resonances". I was intrigued. A local used audio trader had a pair of transmission line cabinets that were almost finished and a steal at NZ$25. They just needed drivers, internal wiring, and painting. I mounted the drivers on off-cut baffles that I attached to the cabinets, added CAT5 cable and banana sockets, and painted them. In use there was an immediate impression of more punch, yet delicacy and detail compared to the KEFs (which were relegated to the TV room). By now I had the experimenter's bug. If that was the excellent result of a cabinet mount, what might an open baffle sound like with bigger and better drivers?Project 2 - vintage full-range on an open bafflePlessey 8" full range driversI used new old stock Plessey 8" full-range drivers made in New Zealand in the 1970s (again from Vintage Audio World), and mounted them in waxed 900 mm x 450 mm x 35 mm Pine boards with the cable connectors soldered directly to the driver wiring tags. The baffles are held upright in position with hinged single leg props, so I can adjust their angle of recline. The sound is more open and detailed than the KEFs and punchier and more airy than the transmission lines. This project cost me NZ$200 total. Assembly of working speakers couldn't have been easier!After a few months of enjoying my music and further exploration of DIY speaker projects for my Pinterest board, I accepted that brand names and model numbers on drivers are important as indicators of quality of performance - and cost! (but for me not as a boasting badge). What could I accomplish with higher performance drivers?Project 3 - vintage 12" full-range mounted on a designed bafflePhilips in JE Labs bafflesA 12" diaphragm is about 2.25 times the surface area of an 8" driver and 3.4 times the area of a 6.5" driver, depending on the shape. Could I get greater musical realism from a bigger sound by moving more air?I got a pair of vintage 12" Philips AD 1256-M8 AlNiCo 8 ohm 30W dual cone full-range drivers in excellent condition (response range 45-16,000 Hz (98dB sensitivity) - some specs. show the upper limit as 17 KHz), made in Holland probably about 1969, for about NZ$400 from Eric Cross at Vintage Audio World. These drivers are quite rare nowadays and sought-after when in great condition. They are renowned performers, and have been described as "probably the best sounding full range driver ever". Eric promised me that they would sound great.I initially mounted them in a popular JE Labs design - with a 900 mm x 800 mm x 30 mm waxed Pine baffle. Materials cost $160 plus 15 hours preparation and assembly time.In situ these proved to be way too big for the room - and sounded rather dull and muffled and lacking clarity and openness. This was a big disappointment, especially after so much woodwork (relatively), and I removed the drivers for a further experiment. What if I again went as simple as possible - but more so?For the fourth DIY project you should wait for the second part of this article. 2b1af7f3a8