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A few days back an audio guy from Mexico-city visited me from. We did listen some music, talk a bit about audio. As usually I interrogated him about the problem he hears in my sound. The people who were in my room know that I do it with absolutely anybody and I am very disappointed if my visitors not able to criticize what they hear. As I asked my guy about critiques of my playback sound he suggested that he feel that somewhere in midbass the sound become heavy and does not decay as fast as he would like it to be. I know that it is absolutely imposable in my playback and the proper balance of sound across the whole range is my very much signature source of pride. Regardless what kind music is being played, regardless of volume and anything else imaginable my playback maintain is very high integrity and to have those kindergarten mistakes with crossovers, decays, under or over performing specific segment of range is absolutely imposable in my installation. So, using my “authority” opinion (wink-wink) I begin to convince my guest that he is wrong and if he is hearing something is it is just result of his corrupted perception.

Last night I got home early and Amy was staying overnight in Portsmouth. I kind of semi-persuaded her to stay in New Hampshire as I would like to have some “audio quality” time on my own. Since we redid hardwood floors 3 month back in listening room I just reassembled the playback as it use to be but I never invested any time for critical listening. I played playback all time but I did not do that fine sonic equilibristic that I use to do in past. A few day back I was visited my local audio friend  and it gave me an inspiration to experiment with audio again:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=18791#18791

So, as Amy was out I decided to dedicate evening for fine moving of Macondo across the new floors, fine position it and perhaps to begin looking for the DPoLF.  I did move horn a bit and I was able to get much more interesting imaging with the new floors and with new areal rags. However, as I sat to listen in sweat spot and turned not my typical Bruckner-like music, life recording in large churches but rather well regulated and calibrated by my hearing reference trucks that I know for years I instantly felt that something was wrong. To my fear and shame I recognized that my Mexican visitor was absolutely spot on – it was some kind of strange fattiness in midbass region. I felt like an idiot, not because the playback has developed some kind of problem (it might always happen and particularly with the multiamping topology I use) but because my over-confidence made me completely discard those very lucid and very accurate comments of my visitor.

Anyhow, now is an interesting technical question: what happened? At this point I have no idea. I check the Macondo calibration in accordance with my “Macondo calibration check sheet”:

 http://www.GoodSoundClub.com/TreeItem.aspx?PostID=14994

Everything was perfect. Sonically it sounded as midbass horn are the problem but in my “Macondo calibration check sheet” I specified only way to drive the horns not the way to measure the horns output. So, I took a dBa muter and plunged it to the Milq’s bass channel output. The left channel has 7dB more output them right channel (!!!). Holly shit, how THAT might happens. Milq’s bass channel is DSET and there is absolutely no way SET suddenly will give over 2 times more gain.  Perhaps something freaky happen with the crossover for left midbass. The Midbass crossover in my estimation is impossible to go down. Take a look for this second order:

http://www.GoodSoundClub.com/TreeItem.aspx?PostID=14666

In addition I have one more order on speaker level – a huge toroidal air-core coil in series with the drivers – they also can’t go down. So, now I need to bring RTA back to the room and begin to sweep the midbass also with the rest of the system, find the problem and recalibrate the left midbass. I did measure the DCR of the driver’s voice coils and it looks that it was not the driver problems. I truly have no idea what it is and I hoped that I would not do it ever again in my listening room. Well, never say nether as they said and never to be too confident with multiamping…

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