Ribbon tweeters

March 30, 2021
 by Paul McGowan

5 comments on “Ribbon tweeters”

  1. Hi Paul,

    Jargon will get you every time! Ribbons are not planar-magnetic drivers.

    Being an old school DIYer I built a pair of 6′ (182cm) “True Ribbon (current sheet)” tweeters back in 2000 (having started the project in 1987). In 1997 I bought a pair of the B-G RD75 “Planar-Magnetic” nominal full-range drivers. I understand you have RD-75s in your home theater setup? My first planar-magnetic tweeters were in the Infinity “Infinitesimals” – which are the same as the IRS 5 tweeters I think (they looked the same).

    Hence I feel justified in being a nomenclature snob. A true ‘current sheet ribbon’ is a different beast all together than a planar-magnetic. A true ribbon is rather a delicate beast which has the following general characteristics:

    1. The ribbon itself is completely conductive over its entire surface (the current sheet) – it is not bonded to a plastic substrate. Meaning that only the mass of the conductive sheet is driven (i.e. extremely low mass, no plastic membrane).

    2. This means that the true ribbon is extremely low impedance – which means there is often a problem driving them with ‘normal amps.’

    3. The ribbon is affixed at the top and bottom, with its sides being unattached. A planar-magnetic driver’s membrane is usually clamped on all sides. When a planar-magnetic driver has unclamped sides it is often labeled a “quasi-ribbon”.

    4. The ribbon is classically un-tensioned, i.e. limp in the magnetic gap. Also the ribbon is usually corrugated to mitigate resonances in the ribbon during motion.

    5. Finally, and I’ve never seen this in print from any ‘expert’ – the True Ribbon is a gravity sensitive device in that it being ‘limp’ in the magnetic gap it will sag if not oriented parallel to the pull of gravity (I mean straight up-and-down).

    And you really don’t want any sagging ribbons do you?

    I was so pleased that Chris remembered me from the ‘good old days’ of the flame wars at the old Bass List. I did a lot of measurement work on the RD-75s in the “RD-75 Dipole Baffle Study” (sadly no more on-line at the defunct “DIY Speakers” website).

    And when you break at 6.5′ long true ribbon you cry – a lot. Hand cutting 1cm wide Reynold’s Wrap ribbons is not for the faint of heart.

    John – Acoustic Line Source Research

    1. Thank you. I agree 100%. I can’t count how many times I’ve tried to explain the difference between planar magnetic and ribbon tweeters. You’ve done a good job. The IRS has no ribbon drivers. Both the mid ranges and tweeters on the IRS are planar magnetic drivers.

    2. Finally someone with some real knowledge has set the record strait. I am a 74 old audiophile with electrostats and Sequerra ribbons who remembers the terminology before it got bastərdīzd.

    3. Hi John,

      I definitely remember you and your RD75 baffle study from the DIY basslist site and the tons of great info. Funny thing about the RD-75 is that RD stands for “ribbon dipole”. Yes, it’s a planar but most manufacturers don’t strictly adhere to the nomenclature that you mention. Planars have been called magnetostatic, isodynamic, planar magnet, planar ribbon, quasi ribbon, ribbons (or pro ribbons by Alcons Audio), PMD (planar magnetic devices) and others.

      When I was at BG, they explained called them planar ribbons because they wanted to distinguish them from the wide bass panels of something like a magnepan.

  2. I can’t say I’ve ever had a “bad” tweeter…from the Peerless domes that Polk used to use to the Ceramic coated in Monitor Audio. But by far the most glorious was the true ribbon in the Maggie 3 series. Current speakers are Maggies with the quasi ribbon and GoldenEar Tritons with their folded ribbon. All good. I guess it’s all in the implementation.

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