Waveguides - are they effective in increasing sound levels?

[Bill poster]

I'm thinking a waveguide is like a small flare or shallow horn around the drive unit.
For example, if I were to put a shallow (1.5" deep x 2" wide rim) waveguide on a midrange driver of 4-5 inches, would it add a measurable increase in dB ( I am guessing above a frequency range associated with the size of flare)

[speaker dave]

Yes, they increase sound levels 2 ways. First they make the driver more directional, at least over some of the frequency range. This increases the on-axis pressure by the change in directivity index (d.i. in dB). This is an axial pressure increase, not a power (over all angles) increase.

Secondly, since the driver is radiating into a smaller solid angle the acoustic load goes up and efficiency improves somewhat. This is a radiated power increase.

David S.

[dirkwright]

It was explained to me that wave guides are mostly concerned with controlling directivity and horns are all about matching impedance. A wave guide may increase the efficiency of a particular driver, but not nearly as much as a horn does. A horn is an acoustical transformer, matching the acoustical impedance of the free air with that of the driver. A wave guide merely controls the radiating pattern of the driver and doesn't necessarily match impedances.

[vacuphile]

Beware that waveguides are effective in increasing sound level, but not equally at all frequencies. In other words, they change the FR of a driver.

[Bill poster]

Originally Posted by vacuphile

Beware that waveguides are effective in increasing sound level, but not equally at all frequencies. In other words, they change the FR of a driver.

yes I'm quite interested in this aspect ( I need to boost the upper midrange in a design I'm working on).

[speaker dave]

I've done a lot of directivity flares over the years (my Avatar shows one done at Snell). I tend to use the CD flare from JBL as a wall contour definition.

They must be done experimentally and they will effect the frequency response, but with care you can get a smooth response that works with a crossover and can even get better response than without, as the driver tends to see the cabinet edges less. I've had trouble with deeper (narrow angle) waveguides and totally circular waveguides degrading the frequency response.

As with a CD horn the inner dimension determines the upper frequency of pattern control and the outter dimension sets the lowest frequency of pattern control. Read Don Keele's early CD horn papers to understand that.

http://www.xlrtechs.com/dbkeele.com/...xp%20Horns.pdf

Finally, look at what Genelec has done in their studio monitors. I think they have achieved good results.

David S

[bear]

Geddes?

[Bill poster]

Originally Posted by speaker dave

I've done a lot of directivity flares over the years (my Avatar shows one done at Snell). I tend to use the CD flare from JBL as a wall contour definition.

They must be done experimentally and they will effect the frequency response, but with care you can get a smooth response that works with a crossover and can even get better response than without, as the driver tends to see the cabinet edges less. I've had trouble with deeper (narrow angle) waveguides and totally circular waveguides degrading the frequency response.

As with a CD horn the inner dimension determines the upper frequency of pattern control and the outter dimension sets the lowest frequency of pattern control. Read Don Keele's early CD horn papers to understand that.

http://www.xlrtechs.com/dbkeele.com/...xp%20Horns.pdf

Finally, look at what Genelec has done in their studio monitors. I think they have achieved good results.

David S

So using a flare with a full range driver wd in effect reduce output below a certain frequency (like a horn)

[gedlee]

Yes?

Its a complicated problem. For a wide waveguide the efficiency increase due to loading is minimal - it all comes from increased directivity. For an ideal waveguide the response from a constant acceleration source (i.e. a driven piston above resonance) the response along any axis will fall at 6 dB/oct, but the power response will fall at the same rate. The same piston without a waveguide would have a flat AXIAL response but the power response would fall.

In my waveguides the response at 10kHz is about the same as the response of the same sized unbaffled piston. This means that below 10kHz its response will rise as the frequency falls. So if EQ'd to flat, the displacement will fall below 10Khz at 20 dB/decade giving the waveguide loaded piston a 20 dB advantage in displacement for equal SPL over the unbaffled piston at 1 kHz.

[speaker dave]

Originally Posted by Bill poster

So using a flare with a full range driver wd in effect reduce output below a certain frequency (like a horn)

No, If the comparison is a driver without a flare on a baffle (cabinet) of a given size vs. driver and flare on the same baffle, then the version with the flare will be at least equal in strength at any frequency. i.e. you gain from having the flare.

The only exception would be cancelation notches from symmetry.

David S.