Project – the Eikona 2 Djinn Open Baffle speaker

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The Open Baffle (or dipole) loudspeaker has a long history, with famous UK examples from Wharfedale and QUAD. At its most basic, an OB speaker consists of a drive unit on a flat board, the rear of the driver being open to the air. Whilst this may eliminate the colouration characteristic of some box enclosures, it has the disadvantage of introducing an acoustic short-circuit; sound from the front of the speaker saunters round to the back and happily cancels out all sound below a certain wavelength. The wider the board the speaker is mounted on, the lower in frequency the cancellation will take place.

In recent years, there has been a resurgence of interest in Open Baffles, particularly in the DIY community. At the end of 2016, one of our customers contacted us with details of his OB design, using the Jordan Eikona 2 and a Dayton Audio pro-audio 38 cm woofer.

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It is a distinctive design, featuring slot-loading for the woofer and an unusual edge-of-baffle position for the Eikona 2. At first sight, it looks as though the design cannot possibly work. But the designer has begun with specific aims and a carefully considered rationale to achieve them. The end result is both clever and genuinely interesting.

The Djinn OB Project is currently being documented on this DIY thread on Audiocircle.

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Firm Foundations – the Concrete Baffle

This is a contributed blog from Jonathan Espley of Matteis Loudspeakers. He has been a long-term user of Ted Jordan’s full-range drive units and is a passionate advocate of ultra-rigid, concrete baffles. These concrete baffles appear in his own range of loudspeakers but are also available to home constructors. Jonathan describes the background to their development.

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 Back in April 1982, Hi-Fi News & Record Review published an article, Tone Arms And The Twist. It suggested an alternative way of making a pickup arm. The idea was to use strategically-placed mass to provide stability for the cartridge at audio frequencies. In so doing, it removed the need for an ultra rigid arm and highly engineered bearings and virtually eliminated structural resonances. I rebuilt a Hadcock Unipivot arm to test the principle and it worked superbly well.

The loudspeaker drive unit and cabinet has a lot in common with the moving coil cartridge and pickup arm. The arm/cartridge converts mechanical energy into an electrical signal whereas the loudspeaker converts the electrical signal into a sound wave. In each case, the transducer should be held absolutely stable at audio frequencies.

High end pick-up arm manufacturers go to great lengths to engineer the arm to be as rigid as possible in order to extract maximum information from the record groove. Loudspeaker manufacturers design some superb drivers only to stick them in a highly resonant wooden box.

It’s not difficult to see where the main problem lies with conventional loudspeakers. The cone is driven in a backwards/forwards motion to generate the sound wave. This puts great pressure on the baffle to resonate in the opposite direction to the movement of the cone. Any movement due to flexure must be subtracted from the cones movement. Hence there is an inevitable loss of energy.

When it comes to side panels, they are solid in the front to back dimension and any resonance does not directly affect the motion of the cone and so has minimal effect compared to the baffle. I have built speakers with concrete sides and, believe me, it’s not worth the compromise as it’s very difficult to get an acceptable finish. 

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I started experimenting with a concrete mould for the front baffle then tried reinforcing it to obtain greater rigidity. To cut a long story short, I ended up with a mould (shown below) that has reinforcement right across the baffle. The concrete does not take the strain as it is not stable enough at 30mm thickness. Every improvement to the reinforcement brought an improvement to sound quality. The main difference is a sense of presence to music. Stereo image is more sharply defined, giving a much more realistic presentation of a musical performance.

There is still a small residual resonance as the pressure to drive the cone against atmospheric resistance is so great that the whole enclosure moves slightly. It helps if the enclosure is deep and narrow with the base as deep as possible, with spikes to pierce the carpet.

I have a new enclosure design formulated which I hope will overcome this problem. It has some novel features and will be the basis of a future blog.

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The Power of Radio 3

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Here at EJJ HQ, we’re big fans of Radio 3, the BBC’s classical music station. The station has an enviable reputation for quality broadcasting which goes back seven decades, with many notable innovations in both drama and music.

In that time, the station has also been at the forefront of audio developments. These include the introduction of stereo broadcasting in 1962, experimental quadraphonics in 1974, and more recently, binaural and 4-speaker surround sound from recent BBC Proms. In addition to broadcasting on FM and DAB, evening concerts are available in ‘HD’ quality via the Radio 3 website. This is a 320 kbps AAC stream that – in terms of audio quality – BBC recording engineers say matches the direct output from the concert hall mixing desk. If you follow the BBC Research Blog you’ll discover more interesting ideas under investigation, including object-based sound and surround sound with height (via Ambisonics).

This year, Radio 3 celebrates 70 years of broadcasting, from its beginnings on 29 September 1946 as The Third Programme. As part of the celebration, historian David Hendry gathered 70 memorable moments from the station’s archives and these have been spread across the schedule over the last four months.

Now you can now find these gems gathered together in one place on the BBC Radio 3 website. They’re well worth exploring – click here to view the selection.

 

Project – Aurora 400 2-way system

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One of the more unusual projects we’ve been involved with this year has been an two-way Aurora 400 system.

The initial enquiry came from a long-standing Jordan customer who was using one of Ted’s Linear Array designs. Each array consisted of four JXR6HD units crossed over to a JX150 Jordan bass system.

The electronic crossover was custom-designed by the customer and BBC engineer and is a first-order design, -3dB point at 275Hz. Our customer was intrigued by Ted’s claim that the Aurora reflector loudspeaker produces better stereo than the already superb imaging of the Linear Array.

As with all the Jordan Aurora designs, the cabinet was bespoke. Our customer chose contrasting veneers for the cabinet and reflector, an effect which is both striking and attractive.

The Aurora 400 takes the place of the Linear Array and is wall-mounted just above the bass enclosure. As sensitivity of the Auroras is lower than the array, gain adjustment of the crossover was needed to equalise the frequency response of the entire speaker system.

Our customer has connections to the audio industry and is a very critical listener so it was gratifying to receive his comments on the Aurora 400 system:

I’m impressed by the Aurora performance as bass reflex full-range speakers but as I don’t need the bass frequencies, I can put in much more stuffing than would work with a bass reflex design … “

“Impressions of the Aurora speakers is that they are better than the line array … the Auroras are quite special; very clean … they have better presence than the JXR6HD line array, so I’m impressed with the sound!”

For more details of the Jordan Auroras, see here.

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A New Jordan Eikona Loudspeaker

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We have just received exciting news from our American dealer, Ars Harmonia.

In addition to selling the Jordan Eikona full-range drive units, Ars Harmonia manufacture high-quality loudspeaker enclosures. They have had great success with the Jordan VTL and now they have launched their own, exclusive design, the Taliesin.

This loudspeaker follows a similar form-factor to Ted Jordan’s elegant VTL transmission line but is slightly larger at 99 cm tall, 34.5 cm wide and 15.24 cm deep.

The unique Taliesin enclosure was designed by Paul Kittinger using Martin J King ‘s famous MathCad loudspeaker  modelling software. The cabinets – one in solid cherry with bird’s eye maple and the other in walnut – were hand-built by Bruce Pea.

The first two pairs are already at dealers. Contact Bruce at Ars Harmonia for more details.

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Project – Classical Jordan DCR

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A very nice email arrived this week from one of our customers. He has just completed building the Jordan Eikona DCR loudspeaker design and is thrilled with the results:

“They sound fantastic. Very natural on the human voice (my wife is a classical singer, so listens to lots of song, opera, etc). They fit really well in the kitchen, either side of a chimney breast. Sound is seamless, much improved on the stack of 4x 50mm Jordan units & bass each side they replaced. Very much enjoyed making them, now enjoying listening to them and plan to make another pair…”

The DIY plan for the Jordan DCR enclosure is available on our website here

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Loudness Wars

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For over a decade, music producers have been fighting a loudness war.

Louder is more exciting and superficially appealing. This is important when you are competing for the attention of the music-buying public. It also helps overcome ambient noise if you are listening to music whilst in a vehicle.

Rather than just boost the ultimate sound pressure level of a piece of music, the trick employed is to bring the quiet parts up to match the louder sections. In this way, the overall dynamic range is reduced. The listener loses a dimension that is part of the complexity and richness of music.

This may be one reason why some enthusiasts prefer original vinyl releases to CD or streaming counterparts; it’s nothing to do with the carrier format, it’s how the music has been mastered. It’s certainly true that in some recordings we’ve explored, the remastered, more modern release can lack the dynamic range of the earlier – to the extent that we default to the earlier version wherever possible.

Here is an excellent primer on the loudness wars, viewed from the production perspective and published in industry magazine Sound-on-Sound:

http://www.soundonsound.com/sound-advice/dynamic-range-loudness-war

Audio Building Blocks 4

 

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One of Ted Jordan’s most popular systems was the Linear Array. This vertical arrangement of four Jordan 50mm units gave many of the benefits of a taller, floor-to-ceiling line source but at much lower cost.

The 50mm Module Array required an additional bass system but a Jordan Eikona Array is a stand-alone system. Four Eikonas are equivalent to a single 250mm bass unit in terms of cone area but have lower mass, faster transient response and greater sensitivity. This makes an Eikona Array a compelling alternative to the industry standard of speakers with passive crossovers and large, heavy bass units.

The design can be realised in a number of different ways. One of the simplest and most elegant is a reflex enclosure. By adjusting the height of the Array for seated listening, we arrive at a floor-standing loudspeaker which is 1200mm high, 340mm wide and 125mm deep. The cabinet can be constructed from 18mm MDF or Baltic birch ply. In general we prefer ply as it is more pleasant to work with, weighs less and is more robust. We recommend fitting a low-profile grille as it protects the drive units from dust and inquisitive fingers. Arguably it also has a psychological benefit as it’s easier to concentrate on the music when you aren’t distracted by moving cones.

In use, the speakers should be turned-in 60 degrees so that the listening axes cross in front of the listener. This gives the most stable stereo imaging, with a wide listening angle; central images remain central as you move left or right. The system sound integrates at distances above three metres so these are not near-field loudspeakers but work very well in larger rooms. The increased sensitivity over a single Eikona system makes the Array a good match for high quality, lower-powered tube amplifiers.

A full plan is available here.

Eikona Linear Array specification:
Size (external) – 1180mm (h) x 340mm (w) x 125mm (d) excl. base
Impedance – 6 ohms
Sensitivity – 92 dB/watt
Peak power handling – 400 watts
Minimum amplifier – 4 watts

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A triangular, sealed-loading version of the Linear Array is featured here.

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Last time we looked at a line array speaker system using 16 Jordan Eikonas per enclosure. Whilst capable of terrific performance, a 2.5m high loudspeaker may be more than many people (and rooms) require.

One of the requirements when assembling a loudspeaker array is to ensure that the total impedance of the drive units does not fall below that of a single unit. The next stage down from 16 units is – somewhat counter-intuitively – nine. Using the Eikonas in this way provides a system with 95 dB/watt sensitivity and 121 dB peak SPL and the opportunity to dispense with the cabinet altogether.

Mounting the array on a flat panel gives us a classic open baffle speaker with the benefit of no internal standing waves, fewer panel resonances and a cleaner sound. It also introduces a major drawback; an acoustic short circuit.

Below a certain frequency – approximately 500Hz for a 30cm wide panel – sound from the front of the speaker will leak round to the back, be out of phase and start to cancel out. This cancellation results in a 6dB per octave, which is considerably less than the 24dB/octave of a reflex enclosure. The array’s increased sensitivity and power handling means we can use equalisation to extend the bass below 500Hz. How low depends on the maximum loudness we’re trying to achieve. Nine Eikonas have the same cone area as a single, 30cm cone but for high SPL or large spaces, it might be prudent to add a pair of dedicated bass units.

The CAD drawings show a customer design for just such a system for installation in a church. The wall-mounted panels are manufactured from Perspex with the wiring loom bonded onto the surface. The panels fold away when not in use and the whole effect is extraordinarily elegant. It could easily be adapted to a home environment.

Next time we’ll conclude this short series with an enclosure project for a four Eikona array.

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CAD drawings © David Smith, Fathomtree Ltd

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