Maximizing the sound output

Hi, diyAudio members,
I'm maybe a newbie in sound handling, but currently have an challenging task to produce max amount of dB utilizing as low power, as reasonable possible. In certain frequency range of course (about 1500Hz).
There are no requirement about fidelity, so this task laying a little bit aside from this forum general theme.
Generally, two different approaches was tested. Conventional loudspeaker-based one and piezoelectric disc benders.
So, what interesting details was noticed.
1. Usage a horn in combination with a straight hyperbolic horn and correct volume of throat chamber gives an excellent results, +11.5dB SPL in comparison to the same driver as direct radiator.
Next stage was folding a horn in order tore obtain a usable dimensions. Folded horn required +40% of electrical power to obtain the same SPL as straight. In dB expression it means, that folding attenuates about 1.5dB. And it's relatively good.
2. Piezo discs with Helmholtz chamber shows also enough good results, especially taking into account extremely low power consumption in comparison to loudspeaker system.
Another experiment was combining piezo disc sounder with hyperbolic horn. Throat camera was adjustable, so optimal volume obtained easy in practical way.
But I was surprised, that SPL output of horn in combination with piezo was just a little more (+1.5...2dB) than that in case of pure Helmholtz chamber.
So what I want to ask, is it should be that horn acoustic is not effective in combination with piezo benders as driver, or may be something was done wrong?
 
I believe you would have to use an active crossover with fast limiting if you elect to use piezoelectric tweeters. A quote from Paul Klipsch:

We used to sell a bank of five piezo tweeters. The piezo tweeter is a good tweeter as long as you keep the power level within its capacity. The minute you
overload it, the response narrows and the power handling capability decreases.

The limiters found in virtually any DSP crossover are fast enough to limit voltage over-excursions, in my experience, but you must set them up correctly.

As far as other designs considerations for maximum SPL output, I think you're looking at horn loading. Are there any requirements for polar coverage of the loudspeakers , especially at higher frequencies?

You can look at the older Klipsch cinema designs (MCM, etc.) or Danley Sound Lab designs (Synergy Horn or Jericho series) for ideas. Note that the Danley designs are mostly still patented (if that means anything to you). The Danley designs will be the smallest physically, and produce outrageous amounts of SPL for their size (Jericho series, etc.), but will also be quite dense (heavy) if that means anything to you.

Chris
 

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Piezo is not very efficient at 1500HZ. They start to get into their element around 3000HZ upwards.
And sound awful!
Looks like it.
Although 105dB (@1m) was obtained from piezo disc 50mm dia with Helmholtz chamber. Power consumption of piezo was around 50mW at the same time.
Dark side of piezo's with resonance chamber is bad repeatability, so you should intentionally operate a little bit aside of resonance point in order to achieve repeatable results, paying the efficiency.
But you are right, piezos sounds enough cheapy, like Chinese toys.

@Cask05 , thanks for your considerations, but I do not need broad spectrum response, but only high efficiency in narrow window from 1400 up to 1600 Hz.
Danley's designs looks like hi-end acoustic for large areas, my task pretty more simpler. Sure I wouldn't like to violate intellectual property rights.
 
@phase_accurate
Quaqrter wave was not considered, but why not to try.
How do you think, if build some variation of resonant chamber (Helmholtz), but instead emitting hole use lambda/4 pipe. And make this pipe curved for space saving reason. Sure, chamber should be adjustable for catching the best output point.
Is it looks trustworthy?