Delta Dual 21″ Passive PA Speaker 18MM Marine Birch Plywood 3000W RMS For Touring


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£799Incl. VAT Our Price
£1,299Incl. VAT Typically This represents the average price across other brands that offer the same level of functionality and features as this product

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This is my 21-inch Dual Subwoofer made with 18mm Birch Plywood. This passive neodymium subwoofer delivers 3000w RMS and over 139 dB SPL. Each driver in the box is 1500w RMS and 4-ohm impedance.

Use these to deliver the Sub Bass frequencies that an 18" cannot deliver. Use these at low volume under the 18" subwoofer to truly experience low frequencies.

Key Features:

  • 18mm, 13-ply birch marine plywood wooden enclosure
  • Countersunk Extra Tick "ding proof" grille to prevent grill damage when on tour
  • Acoustic foam behind the grille to prevent moisture and dust ingression
  • Point Source
  • Frequency Range = 29~1000Hz
  • Impedance = 4 ohms per driver
  • Power = 3000w RMS - Program 6000w - Peak 12,000w
  • Max SPL (dB) - 139
  • Cross Over (Hz) - 150
  • Connection - 2 x Speakon in/out on each driver

To get even lower sub low bass plug the ports and seal the cabinet.

The Twin 21" is housed in a sturdy cabinet and finished in a durable hard-wearing protective waterproof coating. The coating has a primary use for automotive linings, industrial and military coating markets due to the superior finish and the very high abrasion resistance. This box is perfect for touring or fixed installations.plywood ported box for sub-bass very little comes near for sound quality and power.

This is a superb subwoofer and very little comes near for sound quality and power.

Many believe a 21" driver is only good for near field applications. Our Bishopsound 21" delivers far more.

We are happy for you to test our 21" subwoofer at any weekday by appointment please email for more information.

You can learn more about Bishopsound by watching my videos on my Youtube channel I am adding more Video every month. Simply go to Youtube and type BishopSound.

Important information about subwoofers

Subwoofers are designed to reproduce low bass audio signals between 30Hz and 150Hz. Driving them with full frequencies will cause permanent damage, so they should only be operated with a passive low-pass filter, a crossover network, or an active electronic crossover or speaker management system.

  • Frequency Range = 29~1000Hz
  • Impedance (OHM) = 4 ohms per driver
  • Power = 3000w RMS - Program 6000w - Peak 12,000w
  • Max SPL (dB) - 139
  • Cross Over (Hz) - 150
  • Connection - 2 x Speakon in/out on each driver
  • Weight = 78kg
  • Dimensions = 70cm x 122cm x 65cm



  • Overall diameter 548 mm
  • Net weight 12 kg
  • Shipping weight 14 kg
  • Shipping box 590x590x300 mm
  • Magnet NEO
  • Flux Density 1.1 T


  • Nominal Impedance 4 Ω
  • Musical Power 3000 W
  • RMS Rated Power 1500 W
  • Sensitivity@1W/1m 96 dB


  • Voice Coil DC Resistance Re 3.6 Ω
  • Resonance Frequency Fs 35.0 Hz
  • Voice Coil 125mm
  • Mechanical Q Factor Qms 10.5
  • Electrical Q Factor Qes 0.45
  • Total Q Factor Qts 0.43
  • Mechanical Moving Mass Mms 335 g
  • Mechanical Compliance Cms 252 um/N
  • Force Factor BL 24.3 Wb/m
  • Equivalent Acoustic Volume Vas 260.0 It.
  • Maximum Linear Displacement Xmax ±14 mm
  • Reference Efficiency ηo 2.250 %
  • Diaphragm Area Sd 1680 Cm2
  • Losses Electrical Resistance Res Ω
  • Voice Coil Inductance@ 1K Hz LE m H


  • Magnet NEO
  • Voice Coil Winding Copper
  • Voice Coil Former Glass Fibre
  • Cone British Paper
  • Surround Treated Cloth
  • Dust Cap Paper
  • Basket Aluminium
  • Depth 252 mm
  • Bolt circle diameter 525 mm
  • Baffle cut out diameter 505 mm
  • Flange and gasket thickness 15 mm

Your Guarantee is for 12 months and starts from delivery date but please read on. The warranty is recorded with the BishopSound Order number which begins with a B. Please download and keep a copy of your invoice and keep it safe.

We know problems can occur from time to time so even after 1 year I am here to help. We carry parts and we treat everyone as we expect to be treated ourselves so we will work hard to get a win win.

We still help people who bought from us at Carlsbro 30 years ago with parts (if they are available) repairs and solutions. BishopSound prides itself on treating every customer as a family friend.

In short if the problem was caused by me its up to me to fix it. If you had an accident then I will try my hardest to fix it at little or no cost to you. This guarantee is in addition to, and does not affect your statutory rights or the other right of consumer purchases.

For more information, please see our Terms & Conditions

    Get in touch with BishopSound today for professional and friendly advice. Alternatively, you can call us on 01765 698 233 or 07973 223949. If you want to send a direct email please use or

    If you have a question use this form or Live Chat and if you're interested in becoming an official distributor of BishopSound products, please get in touch below.