Loudspeaker Installation in RC Models

Loudspeaker Installation in RC Models

We cannot make specific recommendations for loudspeaker enclosures as they are so dependent on the individual model. Here's a few tips on building loudspeaker enclosures for model planes. Much of this also applies to model boats and tanks.

• The whole point of putting a speaker in a box is to stop the sound pressure wave coming from the rear of the speaker cone from reflecting off nearby surfaces and destructively interfering with the wanted forward sound pressure wave. The rear sound wave is in anti-phase to the forward one, so if it mixes with the forward one, it will tend to destroy it and also mess up the frequency response as the reflection is frequency dependent.
  
  
• The sealed box tries to emulate an “infinite baffle”, which is the ideal situation. If you can get some acoustic wool (insulation), put some in the box but do not stuff it too full. Failing that, use ordinary pink fibreglass insulation.
  
  
• Based on that requirement, a speaker box should be as large as possible and it's walls should be as dense and as rigid as possible, given space and weight limitations. If they are flimsy and not rigid then they will vibrate and act as sound radiators themselves, thus reducing the effectiveness of the enclosure.
  
  
• If the box is small. i.e. just large enough to fit the speaker in, it should be "ported" at the back or side to relieve "back pressure" which occurs when the speaker cone is pushing air backwards. If you leave a small say 1.5" - 2" diameter hole at the back, the whole wing or fuselage can then act as the speaker box which will improve efficiency and low frequency response.
  
  
• So, based on the above, use aircraft grade plywood, not balsa, and make it as thick as you can tolerate, given the space and payload capacity of your plane.
  
  
• You want to hear the speakers when the plane is in flight, so they should always face downwards or sideways. Placing one in each wing is a good plan, again given space and weight limitations.
  
  
• Cover the speaker hole opening with a coarse open weave fabric, aluminium window screen mesh or other aluminium grill and paint it to match the wing.
  
  
• Keep the speakers near the plane’s C of G to avoid upsetting the balance of the model.