The Stereo Subs Project

[chessman]

After endless research, hand wringing and procrastination I finally set my Fathom F113's up as "stereo" for two channel music. It was a big jump for me. The Sophia 2's already went down to 30H, the system already sounded darn good, and the expense for a mere 10H of added range was not easily judged as a good idea.

First decision: "Direct second interconnect" from my preamp to my subs (loss of integration control, still taxes the amp, much cheaper) or "active crossover" (much more control, easier on the amp, more money). I chose the active crossover and began a search for a Bryston 10B-SUB.

Second decision: what cables? I would need interconnects from the preamp to the Bryston 10B-Sub, could reuse the IC's from there to the amp, but would need two new subwoofer cables. The choice of WireWorld Silver Eclipse 6 for the short interconnects was easy (matching the others). The sub cables were very hard to decide - 20 feet long and how many? I finally dug deep in the Fathom F113 user manual and discovered I needed only one XLR ended cable per sub for a stereo sub setup. No way I was going big on this length, plus I doubted I needed silver clad for low end frequencies. I consulted with Masterlu and went with the blue colored WireWorld Oasis cables.

Third decision: how am I going to integrate all this? I decided to use the Velodyne SMS-1 that I already owned as a diagnostic tool. This is NOT being used for EQ or signal manipulation in any way. It is not even hooked up after I finished.

What follows is a (warning!) lengthy description of how I did it (with pics ). They are also in my album with some additional notes. You have to read the gallery in reverse order because they loaded backwards and would not let me adjust them. http://www.audioaficionado.org/membe...s-project.html

[chessman]

The first pic is the before image. The second one shows what are being added to the system. The third one shows the cabling. The point is that a full signal is being sent by the preamp and then being split between the blue cables going to the subs and the silver cables going to the amp and ultimately the mains.

Before setting anything else, I set each Fathom to "master" and ran the ARO on each one individually. I realized that the room would hear them cumulatively, but I wanted to avoid as much electronic EQ as possible. I had previously gotten a table top flat frequency response response using the SMS-1 as an EQ device and it sounded like crap. ARO only knocks down the biggest hump and sounded much more natural. (Sidebar: the real issue in my room was excessive decay time of certain notes, which cannot be fixed with EQ anyway and which I tamed with bass traps).

I assumed the Sophia 2's were more agile than the F113's, so I decided to cross them low. However, I mistrusted the F3 point claimed by Wilson (30H), if only to the extent that it would be asking a lot of the amp (although it is a mighty beast and never showed an ounce of strain). However going too high would be wasting the high fidelity capability of the Sophias. I tried both 40H and 50H and preferred 40H.

[chessman]

The first pic shows the Velodyne SMS-1 connected to my preamp as a source. It is not connected in any way to the signal path from preamp to Bryston 10B-SUB to subs/amp. It has a built in frequency seep tone that will repeat as long as you want an will cover 0H to 200H in about 30 seconds. It also has a microphone input for a calibrated microphone that will measure that test tone and a video output that will display the frequency sweep on a television screen.

The second pic is the tv I used as a monitor. The third pic is the welcome screen when the SMS-1 is powered up. It is very important to reset to the default settings before beginning to ensure that there is no EQ still being used.

[chessman]

The first pic is a calibrated mike that connects to the SMS-1 to measure the frequency sweep. Note the magic green cloth that works its way into all my new installations.

The second pic is the sweep with the subs disabled by using the mute on the Bryston low pass filter. At this point the subs have had the ir own built in ARO systems used, polarity was checked and left at "0," and relative phase was at "0." I extensively experimented with relative phase after this shot, but never found a better setting than zero. That was not a huge surprise since each sub is right next to each main.

The third pic is the final frequency sweep with subs on and integrated. Again, I want to emphasize that there is no EQ going on except the ARO on the Fathoms. I ended up with low pass filter at 40H and the high pass filter on 40H for each of the left and right channels. I set the slope on the low pass filter at -18dB and the slope on the high pass filter at -12dB. Since slope will have an effect on relative phase I tried them all and watched the effect on the frequency sweep at 40H.

I spent a lot of time trying to level match the subs with the mains. Obviously there are three volume controls at play: preamp and each individual sub. I kept turning down the sub volume on the master gain control on the Fathoms (set to variable), but when the graph looked great it did not sound great. I bumped it up until it sounded like I liked and declared victory. So long as you cannot localize the subs while playing it is a matter of taste. You cannot tell mine are playing unless you touch them.

[chessman]

The obligatory "after" pic.

So how does it sound? I will give a fuller report when the cables have burned in, but initially I would say it sounds great.

Remember I was looking for one octave at the bottom, cleaner mid-range, a little more ease at the top end, and a wider sound stage. I definitely have some of that already, but I do not want to declare victory until I am sure it is not mere wishful thinking. So far, Kind of Blue, The Girl in the Other Room, Winelight, and John Barleycorn Must Die all show distinct improvement.

[Wasatch]

Sorry, as far as I'm concerned. No subs in 2 channel reproduction of music.

[Masterlu]

Originally Posted by Wasatch

Sorry, as far as I'm concerned. No subs in 2 channel reproduction of music.

Sorry, your loss.

[bradleyc]

Originally Posted by chessman

First decision: "Direct second interconnect" from my preamp to my subs (loss of integration control, taxes the amp, much cheaper) or "active crossover" (much more control, easier on the amp, more money). I chose the active crossover and began a search for a Bryston 10B-SUB.

Randy......interesting thread, please forgive me for asking but why would a direct 2nd interconnect from pre-amp to subs tax your amp? Aren't the amps in the F-113 subs doing all the work, and the pre-amp would just be passing a low-level signal to the subs?


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[chessman]

Originally Posted by bradleyc

Randy......interesting thread, please forgive me for asking but why would a direct 2nd interconnect from pre-amp to subs tax your amp? Aren't the amps in the F-113 subs doing all the work, and the pre-amp would just be passing a low-level signal to the subs?


Sent from my iPhone using A.Aficionado

I was already "taxing" the amp by sending a full range signal to speakers that are not truly full range, but I addressed that by buying a beast of an amp (600 watts into 4 ohms). That would still be going on with a second set of cables going to the subs with an active crossover in the path. The active crossover lets you send only what the high filter lets through to the amp, i.e. what the speakers can handle, with the result of less strain on the amp.

You are right on the second cable to the subs - the subs' amps would be doing all the work on the sub cables. The effect of the other cables (direct to amp) is what I was talking about.

[Wasatch]

Originally Posted by Masterlu

Sorry, your loss.

No problem, I can live without.