Digital EQ & XO to correct speakers & rooms (Off Topic)

by Rooze , Wisc USA, Sunday, January 13, 2008, 01:04 (5945 days ago) @ Bert

Very interesting comments in this thread on room correction and digital EQ.

I started the earlier thread (now closed) before the Holiday about using digital XO's with an Oris system, and it yielded many interesting comments, some of which I tried to implement with varying degrees of success.

I took some very useful information from the other posts, now I'd just like to give some feedback on my trials and tribulations with room correction and setting crossover points.

I realize people have very different approaches to achieving system bliss, and that this post won't be of interest to most people, but hopefully someone might glean some information and something worthwhile.

So, I'm using dual stacked Oris 150 with Fostex 208 Sigs and bass cabinets with 16" fostex drivers. Horns driven by Cary 2A3 mono's, with Sophia Electric 300b tubes, Audio Aero Capitole MKII CD player, and a Aesthetix Calypso preamp, just replaced with the focus of this post, a Lyngdorf TDAi 2200 - digital integrated amplifier with room correction.

Collecting data from around the web and from the designer of my speaker system, I was under the impression that optimum XO point for this system was around 150hz. This is how I've run the system for quite a while, using an integrated subwoofer amp and crossover from Gallo Acoustics - but I was never completely satisfied with results(poor bass quality and integration).
Though I've read various accounts of why a XO setting in the region 150hz should be optimal, I haven't fully understood the explanations so I've remained open-minded as to the best setting of the XO point, and decided to just trust my ears.

So the story starts around the holiday when I loaned a new piece of equipment (loaned to me by a local dealer in Port Washington WI) - the Lyngdorf TDAi 2200 - an impressive box with a very high quality digital amp, digital crossover and "room perfect", which is Lyngdorf's term for their room correction package. The unit is fully digital, so you can connect a transport and a pair of speakers and that's all you need, or you can control a more complex satellite speaker system using its various crossover functions, which is how I use it. In my configuration I use the internal digital amp to drive the bass modules, then use the line outs into my Cary 2A3 SET's. This is quite incredible, since I have the best of all worlds with SET amps driving my horns, a digital amp on the bass, and the whole system controlled by the room correction module.

My mission was to first set the best bass response I could, using the digital XO and also the delay function, which allows position of the bass modules against room boundaries.

Using a test CD and SPL meter, I measured output which was only 2db down at 90hz, without the bass towers active. I have the graphs, but this is really an overview so I won't get into too much detail.

Moving down in 5hz increments from 150hz, I now have the XO set in the Lyngdorf at 90hz on a eighth Linkwitz Riley. This has given me the best integrated bass that I've had from this system. I still plan to take the XO point even lower in small, measured increments. Note - Each time I adjust the XO point I first measure the output using test-tones and the SPL meter and record it, then attempt to confirm the measurements with extensive listening. That way I know I'm not painting myself into any corners. Of course, with the Lyngdorf I can manually set the gain of the horns, differently from the bass modules. So I can balance the bass of the system manually before introducing the room correction DSP. Getting the system to sound at its best without DSP, yielded the best results once DSP is activated.

So with the system manually balanced, the next step is to go through the room measurement procedure, which involves placing the supplied mic at the listening seat and measuring a series of test tones, then moving the mic randomly into other areas of the room, until the Lyngdorf has a good picture of your room acoustic, expressed back to the user as a percentage of knowledge gained.

The whole process of room measurements takes 20 minutes, at which point you can sit down and hit "play".

Room correction via the Lyngdorf is simply a revelation. The soundstage takes on a 3 dimensional shape that I've never been close to with a conventional system and many, many room treatment experiments. Layering, depth, width, space between instruments/performers, tonal balance, everything is so much more realistic.

So I'm close to reaching the goals that I set for my system a few years ago.
The tasks I have left are to complete the bass integration and arrive finally at the best XO settings, then the replace the Fostex T90 supertweeter with something that gives me more HF information and seamless integration (ideas welcomed).

So I understand people's skepticism about DSP, EQ and room correction, but if you can do it all without changing the tonality of your system and without essentially changing the character of your system, then it has to be a good thing?

Sorry for my lengthy ramble.

Rooze

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