Setting the Stage for Battle!
Earlier this year Acoustic Frontiers had the opportunity to improve a two channel and home theater system in Tucson, Arizona. Our client owned a Polk / Onkyo system which incorporated the latest Audyssey XT32 ‘room correction’ algorithms. However he was unhappy with overall sound quality and wanted to know how it could be improved…
Enter Acoustic Frontiers. It started like most of our remote consulting engagements, with the client purchasing an XTZ Room Analyzer II Pro and our fixed price acoustic diagnosis package. This allowed him to easily take acoustic measurements and send them to us for analysis.
This particular room had many issues. The major one was very poor bass response with large peaks and dips and significant ringing at modal frequencies, a consequence of the brick walls in the room. This had led the client to Audyssey XT32, a well reviewed ‘room correction’ algorithm embedded in a few top of the range AV receivers and processors. Like many who use Audyssey, however, our client complained that despite the improvements XT32 made to the bass it also negatively affected the higher frequencies.
There are a few good and interesting case studies that came from this room. One we are going to share with you today is related to how Audyssey XT32 handled bass vs. hand dialed parametric EQ* in the subwoofer range. We’ll look at this from two perspective – frequency response and time decay.
* A type of equalizer that allows continuous control over three parameters: frequency, bandwidth, and amount of boost or cut. We used the miniDSP to implement the parametric EQ fllters for this client. The miniDSP processors are low cost and OK for use in a subwoofer chain, like in this instance. We do not recommend their use in the main speaker feeds. For this you need a higher quality unit such as a Xilica, as used by Procella and Legacy Audio or a DEQX.
Frequency response clearly looks like a wash doesn’t it! Audyssey is maybe a little flatter, but causes a suckout just above the sub range at 85Hz.
A spectrogram is a way of looking at how sound decays in the bass frequencies. It shows SPL over time at different frequencies. It is very easy to see the influence of room modes in these graphs by looking for extended ‘tails’ which stretch out in the time dimension. One has to try and not be misled by how differences in measurement levels can affect the charts – the scale is sized to fit the highest peak. If that peak is significantly higher than the average bass level then the room modes will stand alone, and be easy to spot. Such a graph can be seen in the ‘before’ example. In the after examples you can see that Audyssey does not do as good a job at reducing the long time decay of the modes around 20Hz and 43Hz as hand dialed parametric EQ. You can also see that in general the right hand side of the graph is significantly higher in level than for the hand dialed parametric EQ graph.
Clearly Audyssey XT32 does not deal with modal ringing as well as hand dialed parametric EQ from Acoustic Frontiers.
Please remember that we did all of this calibration work remotely, using our XTZ Room Analyzer II Pro. So, if you have a bass problem, and the room correction algorithms just ain’t cutting it, be sure to call the experts at Acoustic Frontiers!
A postscript message from Nyal Mellor, our founder…I am really looking forward to getting our demo room up and running so we can do more of these tests in a controlled environment! I’d personally like to look at Anthem’s ARC, do more investigation on Audyssey XT32 and also get to grips with Trinnov.