Point of first reflection

August 29, 2021
 by Paul McGowan

In yesterday’s post, I wrote about acoustically treating the room. I had used a term unfamiliar to some.

The point of first reflection.

This is the point along the room’s sidewalls where sound from the loudspeaker first strikes and then bounces off back to the listener. When this happens we get a delayed reflection in addition to the direct sound reaching our ears. (The sound is delayed because it is taking a longer path than the direct route)

Here’s a drawing I scrounged off the internet.

By absorbing or diffusing that point of first reflection along the sidewall, you can dramatically improve the performance of your stereo system. If you refer to yesterday’s post, I had recommended placing a tall bookshelf on both sidewalls as an attractive and effective means of diffusing/absorbing that reflection.

Finding that point where sound first strikes is easy if you have the luxury of an assistant and a small mirror. Have your volunteer hold the mirror against their chest and place their back against the sidewall. As you sit in your listening position have them scootch along the wall until in the mirror you can see your speaker’s tweeter.

Bingo!

That’s where you place your bookshelf.

(These tricks and tips are all covered in my book, The Audiophile’s Guide)

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39 comments on “Point of first reflection”

  1. Reflect on this…

    Got $635K? Audio Porn perhaps? Then again, high-end audio is all about man’s best effort!

    https://www.stereophile.com/content/techdas-air-force-zero-turntable

    “Let’s just add it up: $450,000 for the base turntable. Add $50,000 for the tungsten top platter. Add $52,000 for the HRS stand, $14,250 for the Graham Elite arm, and an extra $9,000 for the titanium armwand. That comes to $575,250.

    Just to play records? Yes. Just to play records.”

    DS Audio Grand Master Optical Cartridge and Grand Master Equalizer + $60,000.

    https://www.theabsolutesound.com/articles/ds-audio-grand-master-cartridge-and-grand-master-equalizer

    1. Spending that kind of money on a vinyl record front end is in my opinion totally obscene. Perhaps if I was a kingpin in the porn industry I could throw that kind of money away which would be a lot less obscene. This may very well meet the definition of the law of diminishing returns in sound retrieval.

    2. Better reflect on this: why does the majority of audiophiles and recording engineers ignores the fact that the ideal stereo concept strictly requires that the signal captured by the left microphone of a pair of stereo mic should only reach the left ear and that of the right mic only the right ear avoiding inter-speaker crosstalk muddying the sound by unwanted comb filter effects??? And why not better starting with acoustic treatment of floor and ceiling? Absolutely mandatory for passing the LEDR(TM) test!!!

  2. Points (2 channels) of first reflection:
    I’m kinda stuck with full length (ceiling to floor) Venetian blinds on the L/H side (120cm/47″) from the tweeter, but on the R/H side the wall is (2.47m/97″) from the tweeter; about the same distance (2.6m/102″) as from the tweeter to my sweet-spot ear position…I can live with that, without noticeable delayed reflections.
    Btw, Paul you’re a great scrounger!

    Point of first destruction:
    I’m just hearing about hurricane ‘Ida’ (on our evening news) gonna hit Louisiana shortly…oh man!
    My thoughts, again, are with the folks down there.
    Can anyone tell me what happened with ‘Henri’ last week?
    It must’ve petered out because I didn’t hear about any destruction from anyone.

    1. Well fanboy, if your thoughts could possibly persuade the heavy rains nearing Louisiana to move northwest and make love to the Northern California wildfires there would be many folks who would consider you a demigod!

        1. The big late August news stories came early this year and they just keep coming (think princess diana and hurricane katrina). The Caldor fire is 10 miles away from Lake Tahoe and is knocking on their door. The skies are grey here this morning in the Bay Area though not nearly as bad as last year. They’re lighting backfires and throwing every resource the state and feds have to offer in an attempt to save this lovely resort community.

          I try not to worry too much about things in life that i have no control over particularly as it applies to mother nature, though remain in awe of what controls the grand order of the universe.

          1. True.
            I just gave someone else that same piece of advice a couple of days ago.

            19-15 months ago, here on the East coast of Australia, we had the biggest ‘n baddest wildfires ever in our recorded history.
            Last summer we had a reprieve because of the La Nina weather event here (rain, rain, rain) however I suspect that this summer, in a couple of months, we will be burning just like CA again.
            Best to you dr. g

    2. Bill Graham Presents the all time 70s hoe down? How’d they persuade all those hotties to congregate in the first ten rows?

      https://www.youtube.com/watch?v=QxIWDmmqZzY

      PS -> I read the online BBC everyday and see that England produced a perfect game in third Test victory over India. I’ve read a few overviews as to how the game of Cricket flows and frankly it remains a fucking mystery to my humble inexperience of the game.

      1. I was 17yo, by that date stamp.
        All “those hotties” are in their early 60’s now.

        I’m the same with Gridiron (American Football)…it’s got me f#@ked.
        Much like Baseball, the team in the field tries to get all of the batters out & then they change over & after each team has been in the field (fielding) & batting twice, the one with the most ‘runs’ (home runs) wins the match…e-e-easy 🙂

    3. Hurricane Henri took its worst toll in Tennessee which was a disaster of flooding and then headed up to the Tri State Area, Massachusetts, Cape Cod, and Rhode Island. It was a low level hurricane but still did plenty of damage. Maybe Tony Plachy can give you an update about what happened in his area which is about an hour north of New York City. Hurricane Ida Is just at the Louisiana coast at 150 mph and may go higher. No one knows if the levees will hold and this could be a total catastrophe especially with the rate of Covid in Louisiana unbelievably high

  3. For a moment I considered to place an order for this exquisite piece of engineering with a “trouble-free, non fiddly performance” (that’s what I like most about this TT), and then, of course, the full-blown version as described by dr.goodears (575,250).
    But it’s the weight that puts me off.
    I don’t like the idea that everytime I want to move the TT (try out best position) I have to invite at least 6 strong neighbors to help me and then run the risk they would like to play some of their cheap and dusty records on my TT. That’s not going to happen !
    Another small problem is the fact that the bank won’t lend me the modest amount of money I needed (574,250) for this purchase.
    I guess they don’t like audiophiles.
    On topic: first point of reflection on my right wall is a window…so placing some bookhelves there would turn my room in some kind of a dark room (darkroom).
    Maybe I just toe-in my right speaker a bit (more).
    OR…I could ask my girlfriend whether she likes the idea of having a darkroom in da house… 🙂

    1. You gotta love those highly passionate driven folks who invest their minds, time, energy and resources to push the envelope in terms of what is humanly possible engineering high-performance high-end audio solutions not unlike Arnie Nudell back in 1968 (SS-1) and 1988 (IRS V).

      If you read Michael’s review you would note that Hideaki Nishikawa and TechDAS is at least halfway through a 40-unit run of these half-million-dollar, 725.5lb objects of audio art. High-end audio is all about man’s best effort. Having owned a Goldmund turntable and three Linn LP-12s over the years, one can only imagine the rock solid music performance of this beast.

      Personally, i would never consider spending – from $205,600 for an Aston Martin DB-11. That said, i totally dig the design, engineering, technology and production that created this fine piece of automotive art. I can only imagine what it must feel like to sit behind the wheel for a drive.

      1. I read the whole interview. And I love this TechDAS TT.
        And I can tell you that my most exciting audio moment ever was in the year 1982, when I first saw the most beautiful (IMO) piece of audio equipment ever created, the Goldmund Reference TT. A piece of art.
        And now, almost 40 years later, still my favorite of all time.
        Number 2 on my list: the Goldmund Eidos Reference cd/dvd player.
        Goldmund, my favorite audio brand, including the speakers. The epitome of what is possible.
        And no, I cannot afford it, but that’s okay.

    1. Many of you may have heard of the window overlooking Harvard square that has gold lettering “Dewey Cheetam & Howe” Attorneys at law for everyone to laugh at. I still don’t know if it’s a joke or not but it’s been there forever and a day.That’s how I feel about this set up. When you read the list of the richest people in the world, it doesn’t give you many names of people that are not required to show their worth as they are private individuals and not public corporations. I can’t begin to tell you how many of these type of people I have run across in South Florida because of my best friend who is ultra wealthy and ‘birds of a feather flock together’. Most of them have no interest in High End audio at least the people that I’ve run across. The message I get from the drgoodears post is that this type of equipment sends to me is an indicator of the unbelievable number of the ultra wealthy that we have no idea about in this country and world.

  4. I haven’t conducted the mirror experiment but from a quick visual it’s likely my first point of reflection on the left hand wall is a door. A connecting one between lounge and dining room so bookshelves there could limit unwanted interruptions when having a serious listening session.

    I’ve just watched the video link that Nephilim 81 sent yesterday, great link, very interesting. What struck me and made me smile was that the emphasis was very much on offices and commercial spaces. Home theatre got a mention but not 2 channel or the audiophile aspect so it would seem they don’t think it’s a market worth considering or perhaps a reflection (pun intended) on a perceived dwindling audiophile base. I think they underestimate the determination and obsessive nature of a committed audiophile 😉

  5. Guys, I need to ask a non-audio question. For the past two days I have not gotten my Paul’s Posts email. I re-registered yesterday, but still no email today. Is anyone else having this problem?

    1. Tony, email me directly with the email address you’ve registered under in our email sending program. I looked using the Gmail email address you have registered on PS Audio’s site and there’s no record of you.

      I assume you must have been receiving Paul’s Post with a different email address?

    2. I had the same issue in the past. Paul’s Posts just stopped to an email address I have had for 20 years. It showed under my profile but nothing would appear. Didn’t go to junk or spam.

      I had to register a totally different address, a Gmail account I use periodically, and all started to come through again.

      For a short period of time I seem to recall that Paul’s Post notices would come to the Gmail address and replies to posts would go to the old email address. It all comes to the Gmail one now. Scott’s pitches and update emails still come to both.

  6. The room is the speaker too so why not take the same scientific care we take in the setting up a new cartridge or cables or anything else. Why leave it to chance? Yes bookshelves, rugs, etc all do something but not necessarily the correct thing. Acoustic treatment in the type and amount is critical for good sound. I would rather hear mid-fi set up correctly in a good room than expensive hi-fi speakers in a bad room. Take the time to listen and measure.

  7. Just borrow your significant other’s full length mirror, lean it against the wall, and adjust it’s position along the wall until you see the tweeter.

  8. Paul, it might have helped understanding if you had included a not too technical explanation.

    Studies by Bell Labs determined that a 10 ms delay between direct and reflected sounds is necessary for best clarity/resolution. Fortunately sound travels at about 1 ft/ms. So a greater distance of 10′ minimum is needed for reflected sounds. When that cannot be done by placement (a long wall behind the speakers), which is true for many of us, then some means of dispersion (scatteration) or absorption (reduction) can improve clarity by further separating reflected sounds from direct sources. Furnishings like bookcases can be effective for this.

    1. This is really a key factor, m3. I’m fortunate to have walls 12′ to the left and 18′ to the right of my respective speakers. It also yields incredibly wide soundstage, regardless of the speaker I’ve used.
      Glad you brought this up about the 10 ms delay.

  9. This obsessively creating the “perfect acoustics” in a listening room is a typical “audiophile” thing.
    Ever heard live concerts (inside or outside, amplified or unamplified) in an acoustically perfect room ?
    I certainly not and I think most people not.
    All I did at home was get rid of the coffee table in between and in front of the speakers and lay a carpet on the floor (obviously) in front of the speakers.
    Works very well, good enough for me. After all my living room is no studio and i like to keep it that way.
    YMMV.

    1. jb4, That is exactly what I did for acoustic treatment in my listening room. The wall of shelves with my LP’s came later when my wife retried and she could not stand looking at my haj paj of record storage.

  10. All this good talk, but are there major differences between a dipole line array set up versus a more traditional speaker?

    In my experience the answer is maybe?
    I did all the mirror and first reflection tricks described. Then on a whim I removed what I had done on the side walls. Now on certain recordings the sound stage almost seems to ‘hug me’ from the sides. The width and depth aren’t much changed. The detail and imaging aren’t changed.

    It’s been 4 years so far adding, removing, and playing with various forms of treatments and bass traps. Each time the room takes on a new personality.

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