The Speakers

Speaker Design

Speaker Design

Let’s start with some bad news: A flawed speaker in an acoustically difficult room won’t become a test winner with using and applying all these techniques.

The good news: As long as you have got a well-designed, good sounding speaker in a well thought through acoustical set-up, you will dramatically benefit from this concept.

The basic mechanical properties of you speaker are the effective limits of this approach. If for example your loudspeakers directivity plot looks like a Christmas tree this cannot be cured by the suggested approach. In most cases, you will have a well-designed speaker, in which the designer has optimized the transition frequencies radiation patterns to make them as smooth as possible.

A directivity plot of an already high-performance speaker

In addition, any membrane resonances, diffraction or other artefacts, mainly those originating from mechanical parameters or constraints, aren’t really correctable.

However, as said above, a well-designed loudspeaker will be able to be dramatically enhanced. The only thing you have to do is removing the internal crossover and route all chassis connections to the outside, so that you can directly connect them to the amplifiers.

Crossovers

Crossovers

Acourate offers a whole range of possible crossovers. One of the key properties is the possibility to use linear phase crossovers. Uli Brüggemann, author of the Acourate toolbox, is describing its advantages in a white paper. This cannot be achieved with conventional “classic” analogue crossover design, without major performance limits. 

The possibilites of generating a crossover in Acourate
A perfect linear phase crossover with UB filters

Experience and many listening tests have led to the preferred selection of the so called UB-class crossovers. Choosing a higher polynomial (such as pol-j11) to set behaviour in the transfer region is favourable. Any order higher than two may create adverse sonic effects.

Once selected, you get an almost perfect crossover. It is linear phase and the impulses add-up to a perfect Dirac pulse.

A perfect Dirac impulse of the perfect UB filters corssover

Driver Linearization

Driver Linearization

Each chassis can be measured individually. Please make sure, that when measuring your loudspeakers, that they stand free from any obstacles and that measurement distance is somewhere between 20 to 40 cm on axis. Feel free to also experiment with other set-ups, mostly generating a sonically different result.

If you also want to linearize the bass chassis you may either chose a ground plane measurement or a close-up measurement technique so that you do not accidentally measure the room instead of the chassis.

Important: Do not attempt to linearize any sort of dipole speaker. In case you use dipole speakers, it is much better to apply the Acourate overall room correction only.

Having a close look at the result or this one illustrates the potential for linearization, even for very high-performance chassis. 

A mid-range chassis frequency response
A tweeters' frequency response

Bear in mind, that while linearizing your individual chassis you also alter their way of reverberant sound pattern in your room.

Finally, the linearization is convoluted into the originally generated crossover and is replacing it.

Mid-range chasis and correction for linearization
The linearized crossover for all channels

The total outcome of this process will create a re-worked crossover.

Time Alignment

Time Alignment

With the loudspeakers’ chassis acoustical centres never being totally aligned your system does require time alignment. This is an easy task for a digital system, meanwhile in the analogue domain it is very complicated or even impossible.

To do so, one introduces an artificial delay. Knowing how Acourate works, the timing difference between the tweeter’s impulse response and the artificially delayed chassis can be identified. This is expressed as a delta in samples and compensated for. At 48 KHz one sample delay equals a physical distance of approximately 7 mm.

Bass pulse with artificial negative delay (@0.104)

Having now created a linearized, time aligned crossover, one can use the Acourate toolbox to optimize your loudspeakers in your room!