Room Calibration by Manny LaCarrubba
Larry Deniston | Published on 1/26/2024
On November 18, 2023 Manny LaCarrubba gave a presentation Audio System Calibration. The process of Audio System Calibration that Manny uses is Digital Signal Processing (DSP) to adjust the acoustics of the room in order fix acoustic room problems. According to Manny, a system is not done until it has been calibrated for the room in which it is playing.
Mr. LaCarrubba’s process is to utilize four calibrated microphones placed at the listening position in a diamond pattern (1 -2-1). White noise is then played through the system and DSP Equalization applied via a Speaker Management Processor as needed to achieve the Harman Curve (the in-room curve that presents different frequency ranges represented in a way that they are perceived equally and harmoniously by the listener.)
In order to demonstrate the benign nature of using DSP, Manny presented an A - B comparison of a piece of music signal that had gone through an A/D converter and then back through a D/A converter. This process went on for quite a bit, as our keen eared participants wanted determine whether or not they could the difference between the two signals played prior to processing. No one could pick out the processed vs the non-processed signal better than 50% of the time. The inability to consistently choose which signal is playing means that people were basically guessing and getting the answer right half the time, like flipping a coin.
Once there was at least some semblance of consensus that the conversion from analog to digital and back again did little, if not no, signal degradation, Manny then applied a bit of DSP to adjust the in-room frequency response. Prior to adjustment, Manny noted that the speaker set up and already done was quite good overall and that very little signal adjustment was necessary on his end. That being said, the first thing that was added was a bass boost in the right channel to account for the fact that there was a hallway behind the right speaker and that it wasn’t getting the wall reinforcement the left speaker was getting. Manny said that the room set up was really good when he started, and there was very little he needed to adjust. It should be noted that the overall improvements to sound quality were minimal and I’ve heard bigger improvements with swapping cables than through this process of adjusting things via DSP.
While there was some improvement in tonal balance and imaging at the intended sweet spot, this process also was very detrimental for those not sitting in the ideal sweet spot – like the wall at Fenway Park, it giveth and it taketh away. This would appear to mean that the DSP process is not well suited to listening sessions where multiple people are listening. Moreover, multiple people in the room would change room acoustic such that the DSP process would need to be done over when there are people in the room.
The software packages that Manny uses are Room Equalization Wizard (REW), Audio Highjack, and Ozone. The first of these software packages is a free package and can be downloaded here: REW Download In order to use this software, a calibrated microphone is necessary along with the calibration file. This software used with a calibrated microphone will present real world in room frequency response of a given system. Audio Hijack is a recording and editing software package that is very affordable at $64. The last software piece Manny uses is Ozone, which is a mastering software package, which is reasonable priced by audiophile standards at $249 (on up depending on Options. Through the use of these combined software packages, the user can not only adjust the in-room frequency response, but also add other effects, such as reverb or compression, which may be of use to the listener. For example, if someone has a hearing loss and needs to listen at a higher volume, using a compression would allow the listener to hear quiet parts of a music piece, but not push the overall volume past pain threshold or neighbor tolerance threshold.
All-in-all, Manny provided an interesting and educational presentation where the attendees were engaged and appreciative of the information conveyed.