The purpose of this article is to provide advanced guidelines to ensure better results from an ART calibration.

ART - Expert mode

Reminder on how a Dirac ART calibration is composed:

1. Below 150Hz, Dirac-ART aims to correct the direct path of speakers and some of the room reflections with the help of other supporting speakers.

2. Above 150Hz, a “classic” Dirac-Live correction is applied to speakers.

Supports frequency range

An essential parameter to define is the capacity range for each speaker. First of all we will just define the lower frequency the speaker is able to reproduce and for subwoofers the lower and higher frequency in case it is lower than 150Hz.

Here is an example of what you should note in your system :

Table 1: Speaker Response Datasheet

Once we have extracted this information from each speaker's datasheet, we can define the support connection for each speaker.

Groups

Dirac Live gives the opportunity to set groups. In this case, our three subs have really different response ranges. Therefore it’s required to separate them into individual groups to properly set their support range frequencies. Globally, each different set of speakers should have its own dedicated group.

LFE management

The first rule we propose is to manage the LFE with precaution. LFE goes to a main SUB, and we can define support for this sub. The other subs are appropriate for doing this task. Your subs by themselves could be sufficient. If they are not able to reproduce some of the 20-150Hz we propose to add the front scene(L, C, R) to help in this task. You can also add the back/rear speakers if they are large enough to support the frequencies your subs are not comfortable with. Using only subs and if needed the front scene helps you to get a focused LFE with a right feeling of alignment. For sure in difficult rooms this may be not sufficient. Then we encourage you to experiment if adding other support may help you.

If you take our previous example, the three subs are not able to reproduce frequency above 120Hz. To ensure a good LFE reproduction, and give to ART more degree of liberty to correct LFE, we will add the L & R speaker as support. This leads to :

Table 2: Subwoofer Focused Response Datasheet

You may note that there is an overlapping frequency band between the L&R and SUB. In this example between 35 and 120, LR and SUBs are acting together. It is good to have an overlapping support range between speakers before relying on purely one group to become the only one to manage a frequency band. If in this case we define LR as 120-150 because we think that it’s only the frequencies we need, it will likely result in a bad optimization as ART will add a Low Pass and High Pass filter on the support filter, at 120 and 150 Hz respectively, constraining a lot the correction we need in the integration region. Be sure to give enough liberty to the ART optimizer’s parameters to ensure a good response.

Please also note that LR may not be sufficient to achieve a perfect result in your room between 120 and 150 Hz. In this case Ls&Rs could be considered to help as support. And so on with other speakers depending on the difficulty of the room.

Support range

The real first parameter to set is the support range. But in practice, first you will choose which groups will act as support for a group. The next phase will be to set the right supports range points. Each time you set a support for a speaker ensure to match it correctly to its support range using the speaker datasheet. The table we made earlier will help you make this task quick. Do not set a lower frequency range than the speaker is able to reproduce because this will lead to a very bad optimization from ART’s processing and could damage speakers. Be aware that the room gain isn’t the speaker response. Hence even if the measurements you’ve done define that your speaker is more capable than what’s published on it’s datasheet, do not set the frequency range lower or higher than the datasheet.

By default, there is no reason to not let a capable support speaker act as support until 150Hz. This is why we set “--” in Table-1. In the next chapter we define special cases where it can be tune but in the global situation let your speakers help on these frequencies.

Front scene

The front scene will need the subs to correct the lower frequencies. We encourage to use speakers in the main/ear level to help the front scene reproduce low frequencies as needed. Clearly, the front scene is the set of speakers that will benefit from being perfect as you will directly feel a new experience. If you have a large theater and there are not a lot of filters available, the front scene is the second priority after the LFE to be considered.

Because we encourage you to use the speakers at your ear level, here are some other consideration to be taken into account.

Directivity

We know that, for low frequencies, people are mostly not able to define the direction from where a signal arrives. This is true as long as your room has some reverberation, absorption, scattering and as long as you are far enough from your speaker. This means that if your head is close enough to a speaker, you will be able to define where this signal comes from. 80Hz from a speaker at only a few inches of a human head will be directive. Hence, you have two parameter to tune for close speakers used as support :

• Reduce the higher frequency support range. Less you choose, less it will be difficult for human physiology to determine the direction of arrival.

• Reduce the support level by increasing the value. The support level works in reverse as traditional understanding, think of it has the amount of magnitude the original speaker group needs supported. Therefore if you set it higher the level of support; if you set it lower, it will allow the support speaker to act at a higher level. This constraint on the level of the support filter leads to less or more energy in the support speaker. By reducing the level, you will reduce the perception of the direction of the signal’s arrival.

Coherence

We know that audio systems are normally symmetrical. This statement could lead you to define left support with less constraint than the right support for a left speaker. To do that you will need to separate your left and right speakers in individual groups and differently configure each support group regarding its position. To sum up this simply, speaker which are closer to each other, can help themselves with a higher level as this is coherent. But do not forget that speakers at the opposite side of the room of the speakers to be corrected have a really good position to manage reflections (in regards to phase).

Surround speakers

Every surround speaker must take the subs as support. This is a priority for low end response. Then you can add the ear level speakers as support because most of the time they are more capable than height or top speakers. Using the rules we defined earlier should provide a great response for each of these speakers. Height and Top speakers can use any of the available speakers. You can try to focus using the front scene to help front height and top, and surround to help middle and back height or top speakers.

Center Speaker

For some people, the center speaker is quite critical. If you have enough speakers, we encourage you to not use the center as support for any speakers and use only sub and the front scene as support for the center. This will help to not overload a center speaker which have most of the time a very important signal to reproduce for the immersion.

SPL

Because energy is spread between speakers on their support frequency band, you will technically save SPL. This is true if speakers used as support have a homogeneous response in the support range. Then by tuning the support level, you will be able to spread the energy between your supports and in doing so remove excess load from the speaker to be corrected (this is often critical for the LFE). However, most of the time this is not the case. Then the energy is spread through the speaker and its supports regarding their capacities in the room in term of magnitude and phase. This means that, if a speaker is this only one in the room to manage the frequency 53Hz for example, then all the energy regarding this frequency will be spread to this speaker. So you will, most of the time, end with an overall load that is split between your supports but with disparity. This will not ensure that your SPL is split between your subs for example. To overcome this issue if you need more power in your room, you can physically group some subs to be considered as one speaker in the ISP. Physically the power needed by each speaker will be divided by the number of speakers you group for a same SPL. The trade off you will face is the number of degrees of liberty in ART versus the maximum SPL you can manage with your speakers.