You know you should do this, do it

Discussion in 'Digital & Modeling Gear' started by Watt McCo, Dec 3, 2018.

  1. Lord N

    Lord N Member

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    There is no reason to think that i do that.
    I don't go to youtube for anything music related and argued against the importance YouTube 'celebrities' have on this forum quite often in the past.
     
  2. Elric

    Elric Supporting Member

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    Next you're probably going to tell us this is not how the high grade $200/hour studios do it. Insert eye roll.

    Can't I just get even more expensive monitors instead and call it a day? I want to improve my setup TGP-style.
     
  3. Watt McCo

    Watt McCo Supporting Member

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    Just a friendly reminder. We can all fall into a less-than-ideal setup for a few weeks/months for various reasons. Before we know it, our ears have adapted to it and we forget just how much better proper setup can sound. That's what happened to me.
     
  4. Guitardave

    Guitardave Supporting Member

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    It's all true.

    And always remember to change guitar strings. Over time tone, intonation and tuning all go to **** as strings wear out. It's a gradual thing...to me I've learned to recognize the signs...usually it's when my rig that's been sounding great all of a sudden needs a bunch of tweaking and it still doesn't sound quite right. Then I remember the strings are just old and dead. Change them out and the world is right again.

    Lots of little things add up...
     
  5. Elric

    Elric Supporting Member

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    You can change them?!? I thought they came with the guitar, no? WTF? This thread is turning my world upside down.
     
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  6. Guitardave

    Guitardave Supporting Member

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    LOL - yeah - it's the incredibly obvious thread.
     
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  7. yeky83

    yeky83 Member

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    FYI y'all, a couple/few feet from the wall is exactly where not to place speakers if you can.
    Here's a cheatsheet: https://www.fullcompass.com/common/...peakerBoundaryLocationMultichannelVersion.pdf

    A general rule of thumb I've come across is twice the port diameter away from the wall. As long as you do that, you should be fine, don't worry about the back port. Bloated bass effect happens with front ports too.

    I find this design to be idiotic... dunno what they were thinking.
    https://www.prosoundtraining.com/2013/01/25/tweeter-placement-two-way-loudspeakers/
     
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  8. Watt McCo

    Watt McCo Supporting Member

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    Where would you say this suggests placing them? Even if you've got front ported speakers, the baffle is going to be, after taking into account speaker depth and power/trs cables, etc., at least a foot out from the wall. The reality is that within confines of a typical domestic sized room, there's no winning spot.

    My experience is things are less congested and sound less boomy when moved about as far out from the rear wall as is pratical for the room, which has never been possible to be more than 3 feet in even the best room I've ever had access to.

    Re twice the port diameter this is what I've seen suggested toi, but it never made sense to me. If the idea is not make sure sufficient unrestricted air flow near the port to allow the "suspension volume of air" for lack of a better term to move in/out of the port, the diameter of the port is . . . Not a great guide. Who knows how long the port is? But yeah, it seems to be in the order of inches, in general - I base this on replacing a set of front ported speakers with a set of rear ported and as I was replacing them comparing where along the path towards the back wall the sound went from "changing in a similar fashion" to "changing in a very dissimilar fashion." Not the best data, but better than nothin' :)[/QUOTE]
     
  9. John Mark Painter

    John Mark Painter Silver Supporting Member

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    If you can afford to leave just enough space to walk behind your rig, that goes a long way.

    If you end up sitting too close to the middle of the room, that usually starts to get nasty
     
  10. yeky83

    yeky83 Member

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    There's no easy winning spot, but there's a clear range of bad spots as indicated by the chart in red, namely ~3 ft out. I'd say shoot for green or blue spots in the chart, no?

    Factor in room modes, and it gets a lot more confusing. But I just wanted to point out that in considering boundary interference, ~3 ft out is basically the worst spot :p
    Yeah, I think it's hard to get farther than 3 ft away from front wall in domestic rooms. I set mine up right up against the wall.

    Sounding less congested and boomy sounds like the effect described by the chart is working. Boundary interference is killing 90~140 Hz (3~2 ft from wall) with 1/2 wavelength cancellation, which is the boomy freq range.
    What I've read before (seems to make sense to me) is that too close to the wall and you effectively couple the wall to the port, elongating the port and lowering the port tuning (and I'm sure you also introduce some turbulence and whatnot). ~Twice the port diameter, you don't. I don't think the length of the port would factor in here...
     
    Last edited: Dec 5, 2018
  11. Watt McCo

    Watt McCo Supporting Member

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    The graph for close wall spacing is misleading, though. In that instance the first peak is not a sharp peak, but a pretty broad shelf.
     
  12. Watt McCo

    Watt McCo Supporting Member

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    Actually, I'm just not understanding the first peak at all. At those longest wavelengths isn't the reflection off the back wall always constructive, so it should plateau, and then only drop in relation to the drop off of the speakers output below it's cutoff?
     
  13. yeky83

    yeky83 Member

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    1/2 wavelength interference is destructive.

    So let's say 3 ft away from front wall. Sound wave travels to wall and back to speaker so it's actually 6 ft we have to consider (I forgot before in previous post's Hz calc, edited). 94 Hz has 1/2 wavelength of 6 ft (1125 ft/s / 12 ft = 93.75 Hz). So if you have a speaker 3 ft from the wall, the boundary interference causes a 1/2 wavelength cancellation at 94 Hz or thereabouts.
     
  14. Watt McCo

    Watt McCo Supporting Member

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    Yes, that's the 1st trough in the plot. My question is about that first peak at frequency lower than the first trough. It shouldn't be a peak. Once you're the distance from baffle to rear wall is well below the 1/2 wavelength, isn't the rear wall basically constructive at all frequencies? That's not what's shown in that graph.
     
  15. yeky83

    yeky83 Member

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    Ah! Gotcha. Well I'm guessing the x-axis goes down to 0, and since no speaker goes down to 0 Hz that's what the low end cutoff is showing which just happens to coincide with the 1/4 wavelength peak... You're right, I think it'd be a better illustration if it had a bit of a constructive shelf at the lowest end.
     
  16. warren3333

    warren3333 Gold Supporting Member

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    An interesting thread...

    Here’s my meandering thoughts :)

    I purchased some Genelec 8010s (the small uns) initially for use with my iMac. I had a break through moment when I coupled them with my Kemper... wow.

    I then purchased the bigger 8020s, and here’s my point, I then bought the proper Genelec stands after actually reading the instructions! Crazy I know, but once I had the correct placement, my whole set up came to life.

    Conversely, I had then placed the 8010s at floor level for those times when I sit and play. This 4 speaker set up works incredibly well with my Kemper...

    [​IMG]
     
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  17. Watt McCo

    Watt McCo Supporting Member

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    These graphs err by not including any adjustment for the natural roll-off of the speaker, but I find them more useful because that's their only inaccuracy, and they consider the impact of more than one boundary: http://techtalk.parts-express.com/forum/tech-talk-forum/56454-boundary-gain-room-gain-questions

    The Neuman plot you shared should give a 3db offset from speaker roll-off (assuming we're only considering a rear wall and the floor and walls are infinitely far away lolz) , but instead it starts dropping back off before the speaker has even hit its cut-off, and then tracks the speaker response...that's inaccurate and misleading.

    I guess theoretically if you go closer to the rear wall, shifting the ripple/comb filtering higher in frequency, then you could possibly minimize the ripple with some absorption treatment on the wall and eq to deal with the shelf-boost in the low end.

    But it seems to me that the minimal baffle spacing from the rear wall, in the real world, is a foot, factoring in speaker depth and required connectors on the rear. And now placing any absorption to deal with the reflection from behind the speaker is...problematic. So I can't minimize any of the constructive/destructive reflections. The comb filtering is higher in frequency where its going to be more noticeable, and I've done exactly what folks are trying to avoid by using small speakers -- made the stuff in the sub-150Hz range that much more difficult to manage.

    The red-area on that Neuman plot -- at least the shelf is low enough now to where its going to be mostly overlapping with speaker drop off. I've got enough room behind the speaker to place a pretty useful amount of absorption material to at least tame the ripple/comb filtering effect. There's going to be a big mess in the sub-150Hz region...but there's always going to be a big mess in that region in domestic sized rooms.

    We'll see I just cut a bunch of wood for more mineral-wool absorber panels (some are 6" thick, a few are 9" thick, and I'll have 15" triangles of mineral wool stuffed into both front corners for bass traps). Finishing the floor over Christmas. Will wait to attach any absorber panels in place until I've had time to experiment with moving both those and the speakers around a bit. Will be interesting to see where it all falls into place.
     
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  18. yeky83

    yeky83 Member

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    Yup again, you're right, the illustration is not totally accurate. I linked it as a cheat sheet, and I think it serves that purpose. Most people don't care to understand or calculate out the interference, and the table serves as a guideline while the graphs serve as illustrations contrasting interference effects on speaker vs speaker&sub.

    If you want actual real life measurements and whatnot, here's a good read: https://www.prosoundtraining.com/2011/08/29/how-boundaries-affect-loudspeakers/
    The boundary interference will start at a higher frequency, and though absorption behind the speaker is somewhat problematic, it's possible.
    I think it's far better than the alternative, but you should do whatever seems more appropriate to your application, with response measurements and all.
    I don't think it's made sub-150Hz range more difficult to manage...? It does the opposite, it gets rid of boundary interference issues in the sub-150Hz range.
    Depends on where your speaker drops off. If you're not playing anything under 150Hz, I think the 3ft boundary interference with a 94Hz center frequency notch would overlap. But I think most people want to play sounds under 150Hz.
    The absorption material isn't going to be very effective in the sub range, so I dunno how well you could tame the boundary interference of 3ft/94Hz.
    Agreed the sub-150Hz is likely going to be a mess in home studios. Measurements are helpful, and perhaps 3ft out matches with your ceiling and side wall interference. But a blanket statement like "3ft out from the wall" is a bad idea, it seems to me it'd usually be bad.
    Exciting! Just soffit mount those suckers! :p
     
    Last edited: Dec 6, 2018
  19. yeky83

    yeky83 Member

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  20. Watt McCo

    Watt McCo Supporting Member

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    Its made the sub-150 Hz range more difficult because of the massive boundary lift that happens below that last notch. I realize its not necessarily "adding more bass energy" to the room, but it definitely shows the rule-of-thumb "close to wall = boomy bass" is not misplaced.

    If you've got a front ported or non ported speaker, that's not very deep, use low-profile connectors, and can effectively surround the speaker with 4"+ of absorption material, I could see some potential benefit for trying to cram the thing as close to the wall as possible, assuming you've got a way to EQ out the overarching boundary lift. My speakers are rear ported so can't really do much experimenting with that mode of solving the issue.

    I played around a little earlier. Three arrangements: (1) as close to rear wall as possible given my speaker design, (2) two feet out from rear wall, (3) two feet out from rear wall with 6" of rock wool absorption behind the speakers. Not as much difference between #1 and #2 as I expected (though the room is still pretty under treated, so might be a bigger difference if so). Didn't notice the boominess of #1 so much as just an overall "smaller" sound for lack of a better description. But not a massive difference. BIG improvement for #3. Which is pretty basic stuff I guess...poorly treated room is a poorly treated room. This discussion did force me to think more about how to treat the wall behind the speaker, so its a winner. Thanks!
     

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