Compression Driver

What is a compression driver and comparison with dome Tweeter

A compression driver is a plane wave generator high volume capable, a regular tweeter is not, so the solution cannot be the same and the usage is not the same too.

We can constrain the radiation of a compression driver and choose a radiation angle, but with a regular tweeter it need phase plug or we will create some problems.

It’s why we talk about waveguide for tweeter and not horn, with a tweeter we just “guide” the tweeter.

But with the use of modern phase plug we can reach 100° without problems: see our tweeter waveguide

In more than the fact that the SPL is limited with tweeters, it’s why we dedicated tweeters for close distance or monitoring usage and compression driver for medium/long distance usages.

At mid-distance, so with a 90° coverage, horn with compression driver will be more adapted.

Throat Size

The throat size will in most cases dictate the top end control of the horn, so the constant directivity behavior of the horn. larger the throat size is, lower the top end control we will have, but there is some tricks, like on our bi-radial horn.

1" compression driver:

They are relatively cheap, they cannot go very down, the best of them have a limit of 950/1000hz (BMS and 18Sound), the throat is tiny so the radiation control is high in frequency.

2" compression driver:

It’s an historic size, the control in high frequency is limited, today we continue to see some of these throat size for very specific usage : Have a high SPL, low end device (for replace a tinier compression + medium couple) without taking account of top end control.

These needs find an use case Line Array, so for a very far distance, it’s typically the usage of the Celestion Axi2050, it’s have been create for this very specific purpose.

The usage of 2" is not recommended for our usage.

1.5" or 1.4" compression driver:

It’s an ideal, they goes down and the throat size is not too big. In fact some 2" inch driver are just 1.5" driver with build in adapter, like the JBL 2450 or TAD TD4002. For the perspective of the horn it’s way more efficient to use an 1.5" version of a driver rather than the 2".

1.4" drivers have a 3" diaphragm, so the break-up is upper. 1.5" drivers have a 4" so better max SPL capacities and lower THD at the bottom range.

On our 1.4/1.5 Bi-radial horn we use a smooth pinch for push the control like it’s an 1", this way we have all the advantages.

Exit Angle & Flare

A compression driver has a exit angle, sometime we talk about rapid flare vs slow flare it’s the exit angle of the device in degrees, we talk in semi-angle, for example an TD 4002/4003 have a semi-angle of 4/4.5°, so the “full” coverage is 8/9°.

More the flare is important more it’s difficult to smoothly bring the flare to reach the coverage angle of the horn, semi-angle 45° for example, so coverage 90°. Some compression drivers are designed with an important semi-angle, called rapid flare, that is not an advantage for our usage.

We prefer slow flare angle, aka an angle as close as possible to 0°, the JBL 2450SL is 0°, it’s a no-flare device, it’s why I advice it for 1.5" usage generally, it’s also find-able used at an acceptable price. The 1.4" 18Sound ND3 family or FaitalPRO HF1440/1460 are slow flare, it’s a good point for us also.

Note: about diaphragm materials, Truextends Be is embossed Be, not vaporized Be like TAD does (more expensive), so even if it’s Be it’s far that TAD does.

It’s hard to set precisely a new diaphragm in a compression driver, even if modern driver facilitated it. Diaphragm characteristic is taken into account in the full device, sometimes changing by another doesn’t bring a lot of improvement (and sometimes it’s worse), so be careful with this.