First, fix the rattles

I should have done this long ago.  The photo above was made after fixing the bookcase rattling by moving bookcases away from leaning on wall and removing junk on the left bookcase so it could be filled nicely with books and magazines, almost all the ones that were originally there.  (I never got around to photographing the bookcase before the change, it was almost unimaginably stuffed with random junk.)

The two big bookcases at the rear of the living room were rattling on deep bass tracks.  I'd noticed the rattling, and assumed it was coming from the walls.  But the walls usually were not doing the rattling, I discovered on Sunday.  It was the two big bookcases at the rear of the living room, or something on them.

I started clearing off some of the bricabrac at the top of the center bookcase, including my Fisher MPX-100 unit which I still haven't gotten around to testing.  Then I noticed a serious issue.  Both bookcases were actually leaning against the rear wall of the room.  That leaning meant that any wall vibration (and there is plenty of that) would shake the bookcase and all of its contents.  The bookcases are very heavy, but some of the nick nacks were light and flimsy, like a still-in-box Barbie Ferrari (I'm both a model car collector and a doll collector, and a red Ferrari is the iconic car of the iconic doll).  To mitigate bad karma, I also had a remote control Ford Focus on top of that.  BTW, I'm taking the Ferrari down for now, and it's been replaced by a removed-from-box remote control Tesla model car (barely visible on the top at the left edge of left bookcase in front of a white doll).

The corner bookcase would be very tough to clear out because it's jammed in partly behind my keyboard table.  But I managed to get it off the wall mainly by shifting the magazines in the bottom two rows toward the front.  That got it about 5mm away from the wall at the very tip.  Fortunately I think that's enough to handle even the worst vibrations of wall and bookcase.  Or at least it shouldn't happen often.

The left bookcase, which was not just packed but stuffed with books, VHS, cassettes, junk, magazines, etc., was unloaded down to the bottom two rows, then shifted out from the wall by an inch.  As I was doing this, I was rocking the bookcase and trying to determine where it would be absolutely free of rocking back to the wall.  I think now I moved the bookcase out too far, it is more than an inch out further out than the other bookcase.  In fairness, however, I would move the other bookcase out another half inch if I could, and the center bookcase needs to be almost this far out to make the electrical outlet near the floor accessible.  I don't plan to change it now, but I think I moved it out about 1/2 inch more than necessary.  I think when I added back all the books, and moved the magazines out to the edge, the bookcase leaned forward more than I was planning.

Keeping the bookcases from leaning against the back wall fixed the #1 rattle problem in the room.  Rattles take away greatly from the sense of dynamic range.  Of course when you fix one rattle, other softer rattles become apparent.  Another one that needs fixing is the door of the air handler for my HVAC system, which rattles on certain loud bass notes.

Now it has been written (by an acoustical treatment maker) that bookcases do not make for very good sound absorption or diffraction, which most rooms need a lot of. That may be true (and I'll think about it some more later) but when a bookcase has a rattle, it's like negative sound absorption.  Very negative to the listening experience.  Getting back to No Effect is a big step forward from that.

To be free of rattles, a bookcase should not be leaning on or touching anything but the floor.  Otherwise, when the surface it is touching moves because of acoustical vibration, and/or the bookcase itself moves because of acoustical vibration and it moves away from the surface, there may be moments where the pressure momentarily releases, and you get a rattle between the two.  Also, the surface may cause the bookcase to shake a bit, causing stuff, particularly the kind of flimsy stuff I used to have on top of my bookcase, rattle.

Now that neither bookcase is touching a wall, it is incredible how much the wall vibrates during deep modal bass notes, but the bookcase seems perfectly still.  The bookcase panels may themselves have some resonances, but they would be at higher frequencies that don't so much cause rattling, and the bookcase is made of particle board and heavy paper, which are very lossy and vibration damping materials.

If I have increased the sound level that would cause loud and annoying rattling by 10dB, it is much like (or perhaps even better than) increasing my system dynamic range by 10dB, or almost like reducing modal resonances by that much (which is very hard to do).

I discovered the need for this when testing 1 vs 2 plugged ports in my right subwoofer.  I decided NOT to bother with measurements, but to go ahead and make the change to 1 port because it is well known to be better (see earlier posts), but why not listen?  As I was listening to the 1-plugged-port case, which makes bass slightly louder down to about 15Hz, I noticed the back-of-room rattles.  I got the idea (though not confirmed) that I might be hearing worse rattling with 1-plugged-port than with 2-plugged-ports.  At the same time, I also thought I could hear the improved dynamic range of 1-plugged-port.  So I thought to myself, why not see if I can fix the rattle?

Now actually it seems to me that a bookcase can have some desireable bass trapping qualities (if not as good as engineered bass trap).  To get this, you first need to abolish rattles, because if it rattles it is worse than useless acoustically.  Then, the books, should be pulled out to the edge, to get them as far away from the wall as possible.  Heavy books or magazines should also fill as much of the frontal area as possible.  Behind the books, there will be trapped air, and behind that, my bookcases feature a lossy paper back, which serves a bit like a panel or membrane resonator.  The trapped air behind the books is squeezed in and out by vibrations of the panel, and the released energy is lost moving the books and bookcase panels.  This does in fact operate like a bass trap.  An engineered bass trap would likely use fiberglass in front instead of books to do the lossy absorbing, but would otherwise be similar.

Actually, the bottom two shelves of my bookcases are filled with very heavy paper Stereophile and The Absolute Sound magazines...probably better than books for a bookcase acoustical damper.

Accurate Stereo

In this great post, Sigfried Linkwitz describes accurate stereo reproduction.

With the listener in the "sweet spot" a virtual sound scene should open up in front of him.

Linkwitz details 3 cases, the traditional equilateral triangle with speakers and listening position, a wider listening angle of 90 degrees given by making the distance to speakers 0.7 times the width (W) between the speakers, and a long distance 2W which loses imaging detail but can be pleasant and is less sensitive to sitting off axis.

This is where I've been this year.  I started at my old 2W position, moved in for something close to 0.7W, and now am pretty close to 1W (though I suspect it's about 0.85W).  I've observed the same things he describes.

Online Jazz

A friend suggests I listen to smalls jazz club.

Discussion of Bag End E-Trap

Here's an interesting discussion of the Bag End E-Trap (which I'm thinking about getting) that wanders seriously off topic to address questions about sabins, etc., that I had been unable to answer earlier this year.

Asymmetric Port Tuning

At the very close new sweet spot (VCNSS) listening position, the image is very transparent and 3D, and the bass seems about right on Bass E (see earlier post about this recording).  Elsewhere in room, the bass is very boomy.  I thinking of getting an active bass trap for that.  I now think Living Room sounds better than Bedroom on Bass E.

Right now I have one subwoofer tuned with 1 port plug (15Hz) and the other tuned with 2 port plugs (10Hz).  I'm thinking of changing 10Hz to 15Hz, because that is the tuning most recommended by Ilkka from his distortion tests, and even SVS themselves no longer recommends the 10Hz tuning on the newest edition.

Adding these plugs has seriously improved my bass in Living Room.

But now I'm also wondering if there isn't an advantage of having the Subwoofers tuned differently.  One problem with stereo subs is that most bass material is actually mono, and therefore if played back through two speakers there can be comb filtering.  If the subs are tuned differently, there is a small amount of random phase between the two subs which could suppress the comb filtering effects.

So when I remove the second plug from the right sub, I should test not only that sub, but the whole system, looking particularly for evidence of comb filtering effects.

I've ordered a tiny amount of Auralex open cell foam.  Just to get started.  I was going to get a pair of Auralex 12" cubes, which are in an inexpensive $80 two cube kit, but decided to get 4" cornerfill (4x4x24) instead.  It seems like nobody actually stocks the cubes, they're drop shipped often with no explanation of what shipping will cost, but Sweetwater had the 4"cornerfill, which I'll call sticks, at a nice discount price with free shipping.

The sticks can be placed in the corner behind the left subwoofer.  The bass in that corner is so intense the wall and windows rattle,  and it would be great if that could be ameliorated somewhat.   I'll arrange the 4" sticks similar to a triangular LENRD in the corner.  A real LENRD would probably be slightly too large, and LENRD's are not available except in $300 sets of 8.

Auralex foam is auralex foam.  There is nothing special about the shaping on the surface of a LENRD, a flat surface would work just as well (or better) for bass.  What really counts is the total volume and where you can squeeze it into your room layout, and the more the better, stuffing all corners would be nice.

To Do List

Usually when I make a To Do List, it winds up that everything listed gets bypassed for the next thing that actually gets done.  But years later, many of the things got done anyway.  I don't take these things very seriously, they're just ideas.

1) Subwoofer tuning: though some more measurements might be nice, I've pretty much decided now that one port plug tuning (15Hz) is the best for the PB-13 Ultra's in my living room.  So I can just change to this and be done with it.

2) Deep bass tuning...short of full on room correction, which I have mixed feelings about, continuing to check out the bass in various ways and doing tuning with parametric EQ's, crossover adjustment, etc., can be helpful to the deep bass (below 80Hz).

3) Supertweeters.  Currently offline.  Put back online in far HF augmentation mode.  Adjust by ear and measurement.  Decide again if they are actually beneficial.  This year I have been adjusting HF balance by changing Acoustat angle...this is very effective, might have eliminated need for supertweeters (though I doubt it).

4) Bass traps.  Start experimenting with bass traps, possibly including active bass traps (e.g. Bag End).

5) FM Notch Blend Filter.  This has been stalled because I lost the drilled panel I created a few months ago.  Meanwhile, KPAC is now doing station upgrades, which may obviate the need, or require something different.  Last I checked, KPAC was operating at a fraction of normal power, and either stereo or mono sounded horrible.

6) Kenwood KT-6040: fix time constant to US standard.  When KPAC is fixed, I need to change put Pioneer F-26 back online as main tuner, and then use 6040 as whole-house tuner through Sonos.

7) Oppo vs Denon: do comparisons of Denon 5900 and Oppo BDP-95 playing various kinds of high resolution audio discs.  Simple start would be comparison of mechanical noise on DVD-Audio discs.

8) Move Oppo (or Denon) to back of room to lessen impact of mechanical noise from chassis drive and fan.  Use remote extender to enable nice control, and have some sort of connection to TV (hdmi?).

9) HDMI link: currently one OWLink transmitter seems to have died, but it might actually be a power supply problem.  This is not an audio problem, but I do need to fix some sort of HDMI link from kitchen to living room to watch video sources from kitchen including Cable.  Another test of the OWLink might help, or buying new kind of CAT-5 based balun.

10) Set up HCA-1500A amp in bedroom, along with PS Audio Power Plant Premier regenerator.

11) Make CD copies of a set of cassettes I have (using Nak and Masterlink).

12) Set up turntable in bedroom (using Linn, Panasonic, Behringer).

13) Krell: re-test, take apart, photograph, reassemble, send in for repair.

14) Koss phones: make adapter cable for Stax amp, photograph amp, get optimal cables for phones and install with Stax plug; disassemble and photograph second E90 unit, measure E90 bias in operation.

15) Get PSX800 turntable repaired, install new Dynavector 17D3 cartridge.

16) Replace old cap on left Acoustat with Solen (already done on right).

17) Send in Ivie IE30 for repair.

Bass even better up closer

For my monthly party last Sunday I moved listening chair from center of living room.  On Tuesday I moved it back, but positioned to the tape markings I made about a month ago, and NOT to the most recent super-forward listening position.

When I moved up again to that position on Wednesday, the imaging on the Bass E album was fantastic.

Now I've marked all the new positions (chair and speakers) with masking tape.  Other speaker and chair positions are still marked as well.


My ear now lines up with front edge of sidewall bookcase.  The slightly back position puts it in line with the second book.  Anywhere in between those positions is fine, though with the forward position I can lie back and still have great image, and I think the slightly wider speaker angle is better.  There is a slight tendency to miniaturize the image, I imagine a large 5 foot thick fishtank at the front of the room that the musicians are playing in.  But not so bad, actually, and the coherency is wonderful and brings the kind of 3d transparency that headphones can have.

While the bass does sound a bit boomy on this recording around the room, particularly at the Kitchen doorway, in the listening position(s) it settles down very nicely, rounded but not boomy.  Still, the need for acoustic or other bass treatments is still obvious.

At the listening position, living room system bass now sounds very similar to bedroom system bass, which has long been a reference after it was carefully tuned by manually set parametric filters.  I listened to Bass E on bedroom for awhile.  It is quite amazing what the comparatively compact SVS 1646 subwoofer can do.  That unit has always amazed me, I had never been so amazed by my pair of SVS PB13 Ultra's, until recently discovering the benefits of plugging at least one port.

A recent review of the newest PB13 Ultra shows that SVS no longer recommends plugging two ports with the 10Hz cutoff, and no longer provide the 10Hz cutoff.  They recommend all ports open, one port plugged, or all 3 ports plugged.

Here are some measurements of the PB13 with two ports plugged (10Hz tuning) at Home Theater Shack.  While the flatness of response is superb, the distortion gets very high at 110dB.  Ilkka doesn't recommend the 10Hz tuning except for music listening at low to medium levels.  He feels the added extension is barely noticeable but the added distortion (if you are playing loudly) is very noticeable.  Here are the measurements of the PB13 with 15 Hz (one port plugged) tuning.  OK, comparing the two, it's indeed easy to see the lower distortion at levels above 100dB.  Ilkka feels the added extension in the 15Hz mode is worth it compared to 20Hz mode (no ports plugged) and causes only a tiny loss in clean output above 20Hz.