Tweeter Waveguide, Acoustic Directivity Adapted to Psychoacoustic Tweeter Waveguide

ReShape ©, our Phase Plug technology

Phase Plug

We have developed a proprietary Phase Plug technology in FEA, ReShape©.

It allows any tweeter to be really constant in terms of directivity in a regular OS horn or an X-shape.

This phase plug is more efficient than a simple phase shield, it allow the tweeter to be a plane wave radiation device and allows to use a tweeter bellow his natural radiation (~120°).

He don’t use difraction as do Phase Shield by create standing wave and difraction to create a directivity, the Phase plug act as as compression driver phase plug, without creating any accident. It’s why the tweeter inside theses horn have the same polar as a 1" compression driver.

Having a tweeter with a radiation bellow 110/120°, his natural radiation, is usually not possible, it’s require advanced FEA phase plug mecanisms.

This phase plug is recalculated by tweeter and familly horn, for now available for the SB26ADC but can be available for other bigger tweeters like the Bliesma T34B, not the A version because the dome shape is not suitable for WG with phase plug.

OS for Tweeter with phase plug

Here we use a 1" OS 90x60° (it can be 120*80 or whatever we whant), polar map of the 14cm one in a regular box, the polar respect psyckoacoustic recommendation of Dr Floyd Tooles, directivity should increase slowly from some point in HF.

The 15 and 17cm with full return side by side : Somasonus
attach system : Somasonus polar

It use an ogive and a special form bellow it, not visible on the picture, the load is specificelly “sent” where it’s needed due to FEA calculations and the add of the phase plug don’t add any accidents.

The SPL curve show a very smooth response without accidents and easy to filter (for a horn/Waveguide), as the waveguide have a constant directivity behavior it cannot be straight on axis, energy is not “create from nothing”, we distribute it and not waste it in a way.

   
Somasonus polar raw    

   
90*60 waveguide : Somasonus polar raw    
   
100*70 waveguide : Somasonus polar raw    

Here is the polar and the DI (in red) with the SB26ADC :

For demonstrate importance of full return we just use an improved version of the 6 and 6.5" Somasonus :

The improved continious curve free air version : Somasonus
Polar map of our optimized version : Somasonus polar
Polar map of the original in a regular box: Somasonus polar raw

We can see the improvement.

The use of a 1" tweeter is for "low" SPL.

Below 90dB SPL continuous, so when measured at 1m, with some peak at 95dB SPL, it's fine but if we want more the compression driver will take a serious advantage : In distortion and power compression.

First there is the harmonic distortion of the SB26-ADC at 95 dB SPL after been EQ flat, he is well helped by the huge load given by the horn in the low end :

   
        X-Shape Horn 25    

Still very good for a 1" tweeter, one of the best.

But there is a more important things than the distortion here, every device that produce sound, so tweeter also, have power compression :

Past a certain level of power, loud, sending for example 5dB more will not give 5dB more at the speaker output, but 1 or 2 dB, and the louder we go, the worse the compression will become.

On the other hand a woofer that is bigger than a tweeter will continue to produce theses 5dB more when the teeter become to produce less, in every speaker this behavior exist when we push the power level bottom too far.

Obviously after a while we burn the voice coil and the tweeter will be destroyed in our example.

This moment happens very quickly on a tweeter, much less on a compression where it will take tens of dB more before you notice or measure it.

        X-Shape Horn 25  

What we see here is that after 100 dB SPL (so at 1m only) the power compression happens if we look the red curve, but instead of being on all bandwidth it happens gradually only from 7kHz so after the sensitive area of the ear. The Horn trick the power compression bellow 7kHz by givving "free" Db more.

The point to use a waveguide with a tweeter is the price, the capacity to be cut passively due to smooth response and not too deep horn, so it works in a X-shape but the dedicated 1" OS is more advised.

Of course the bigger the tweeeter the later we will have power compression but it will reach the price of a regular compression driver, it's a matter of choice.

As we know, on every horn the return is very important, as we see in the Somasonus experience upper.

A waveguide can be used for time allignement beetween tweeter and mid-wooferor mid but even a 120° waveguide at the same width of the woofer is too deep comparing to the woofer, there is somes solutions to this :

  1. On front solution: do a square boxe, mount the woofer by the front as usual and glue the horn at the top of the cabinet, in this case the return is “on” the front cabinet and a 4 sides return is needed, of course the width of the cabinet is the same as the complet horn.

  2. On top solution: put it on the top of the cabinet in another box/in a specific design like high end B&W, we provide this kind on design on demand, like elliptical free air OS for tweeter, as we do for the Somasonus but in the reverse way, Somasonus is not too deep but too short for time allignement.

  3. Integrate to the front panel: take the version where the bottom of the waveguide is removed, the width of the horn must be the same as the cabinet, continue the return round over on the cabinet, mostly for design puprose.
    As the tweeter will not be time alligned this way: correct the delay in DSP if active filtering is used. In passive filtering do asymetrical slope crossover by adding 1 order more to the woofer.

  4. Integrate to the front panel, mecanically time alligned: do as point 2 but add a mecanical time alligned system : by mounting the mid-woofer by the rear, on the rear of the front baffle. You will need to acces the speaker by internal.

In each case the tweeter is mount by passing it by the woofer hole, it have been designed to be easily mounted this way.

Features

   

Price and size:

Every price is with Phase plug, in two part, default coverage is 90*60, that is make the more sens for a tweeter in a saloon even at short listening distance.

The horn is provided with full return on 4 side or on 3 side for baffle integration, see the point upper for more details.

5" waveguide (15cm) :

  • Width: 15cm
  • Height: 10cm
  • recommended crossover : 1800hz/2000hz
  • Price: 55€/U

6.5"/7" waveguide (17cm) :

  • Width: 17cm
  • Height: 12.5cm
  • recommended crossover : 1500hz/1600hz
  • Price: 65€/U

Recommended Woofer :

7.5" waveguide (19cm) :

  • Width: 19cm
  • Height: 15cm
  • recommended crossover : 1100hz/1300hz with 33mm tweeter like the Bliesma T34B (A version is not suitable for WG with phase plug due to dome shape)
  • Price: 85€/U

Recommended Woofer :

  • SB acoustics MW19TX

For bigger sizes X-Shape and Compression Drivers are advised.