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Here's a theoretical question that hopefully someone will be able to shed some light on. Apologies if this is the wrong forum, I figured the electrical engineering community would be more into loudspeakers but they probably don't understand acoustic resonance as well as the physics community.

I want to design an unconventional loudspeaker that can provide extremely high SPL in a small size low-voltage battery powered application.

Rough specs:

  • Available gain from amplifier: about 7 Vrms
  • Desired power level: around 40W continuous
  • Desired SPL: around 105dB @ 1metre (table saw, sporting event)
  • Max diameter of loudspeaker: about 4cm. Depth unlimited.

Given the voltage and power requirements, Ohm's law dictates a very low speaker impedance of around 1.2 Ohms.

There are amplifier IC's that can provide enough current for such a low impedance at this power level. That part of the problem is solved. The remaining problem is to build a speaker that presents such a low impedance while maintaining (roughly) full-range output in a small size.

Flat frequency response is not a concern. I don't mind if the speaker has a bumpy frequency profile. But it should have somewhat usable low frequencies.

I understand that such speakers aren't really available off the shelf (correct me if wrong), so I'm thinking about unconventional designs. A couple of approaches that I think might work are making use of horns and acoustic resonance.

Would a tiny speaker attached to a long hollow horn-like structure, that flares at the end and contains chambers for acoustic resonance along it's length, be able to achieve these specs? (Horn length is not a constraint)

What are the relevant equations for relating the acoustic properties of a loudspeaker to the electrical impedance presented by the loudspeaker's transducer?

How can I most efficiently convert electrical power flowing through a tiny transducer into acoustical energy, using unconventional means without caring about a flat frequency response?

Any ideas or suggestions towards solving this problem would be greatly appreciated :)

Any solution that addresses the key main points of 1. very high SPL 2. small cross sectional area and 3. low voltage/impedance will be considered the correct answer.

Thanks!

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closed as off-topic by David Z Feb 9 at 7:15

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What you will need is a device called a horn driver. These are used in very high-power stadium and theater sound systems and are connected to large, flared acoustic horns for efficient radiation of midrange frequencies (800Hz to 4000Hz) at power levels of 100 watts RMS or more. JBL's professional sound division was the main manufacturer of these and you can still find them on the market.

They are typically equipped with voice coils that are wound for 4 ohms to 16 ohms, depending on the application and the type of crossover used to separate out the midrange. You can then use a high-powered audio matching transformer to match a JBL horn driver to a 1.2 ohm power source.

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