The Two Channel Advice Thread

Discussion in 'Advice Threads' started by purr1n, Nov 10, 2016.

  1. Cspirou

    Cspirou They call me Sparky

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    Needs to be in the one-channel advice thread
     
  2. rlow

    rlow A happy woofer

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    Ok this wins Post of the Week. Hilarious because it’s true!!

    On a serious note, I agree with @monacelli recommendation to start off with - you want symmetry beside (and behind) the speakers and between them and you. What’s behind you doesn’t matter as much, and is probably better being asymmetrical to reduce room modes/reflections. Depending what’s on the walls, and assuming no treatments initially, you may need some toe-in to avoid too much reflections since the side wallls are fairly close to the speakers (assuming the speakers have a wide horizontal dispersion tweeter - if it’s horn loaded or has a waveguide, you could have less/none.)

    Aside from the symmetry issues, setting up along the long wall I don’t think would work as well. You or the speakers would be to close to the walls behind and you would sacrifice soundstage in this setup (not to mention get more reflections from behind, although you would reduce sidewall reflection) and you’d have to sit pretty close to them. Possibly too much bass as well if the speakers were too close to the wall, or you were.
     
    Last edited: Oct 7, 2020
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  3. Superexchanger

    Superexchanger Friend

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    Stereo wizards:

    I'm passively bi-amping my speakers at home with an AVR. It sounds a tiny bit cleaner to me, and it frees up the potential to slightly alter the balance of the speaker.

    Without going on a tangent, and after some serious pain-in-the-ass-and-back speaker placement experimenting, I'm extremely happy with the sound, but mostly when played somewhat louder than is comfortable for the rest of my family elsewhere in the house. I'd like to rebalance the speaker somewhat so that the mids/highs either project - or I perceive - a similar frequency balance relative to the woofer, when played at lower volume.

    I cannot independently set the levels on the biamping setup I have, so I wanted to ask about speaker-level attenuation. Does a product like an L-pad work for an application like this? Are there passive pre-amps that will attenuate a speaker-level signal? I'm really only looking for 3 dB insertion loss.

    The impedance curve of the speaker is well behaved above the mid/high crossover point at ~8 Ohm, and should be essentially resistive. Will a simple resistor matching circuit work here, or is there a more straightforward (by which I mean off-the-shelf) option?

    Thanks guys.
     
    Last edited: Oct 9, 2020
  4. Dr J

    Dr J Friend

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    I would also start with monacelli's layout. Maybe consider also the "listening position at 38% of the 12' room length" rule of thumb, either from the front or from the back wall. Usually recommendation is to put the listening position in the front half of the room, but in this size room may not be the feasible.

    I think speakers close to the 12.5 wall might work also if you can shelve down with EQ the bass gain from the wall reflection. But would probably need to treat the wall behind the listening position as it would be pretty close.

    Not sure how much you want to fine tune the acoustics and what is your aspiration level for the room with respect to acoustical treatments. Below some thoughts on those.

    Usually good to have some furniture to break the reflections and absorb the sound a bit. A couch or chair with thick pillows/stuffng, bookshelves with books, paintings, carpets or similar. Empty, flat walls and floor would probably not sound nice due to flutter(?) echoes.

    What kind of material are the walls? You may get quite a bumby bass-lower mid range response from the side wall reflections if they are stone, concrete, brick etc. hard/dense materials as the speakers would be pretty close to the walls. Unless you go for near-field type set-up with only ~3' between the speakers. (I might actually go for that, but I tend to prioritize the acoustics over general usability of the room.) I would personally consider robust (more than just an inch) absorbing panels at the side wall 1st reflection points to even the response a bit.

    Not sure how to deal with the window reflections, assuming the speakers are higher than the lowest part of the window glass pane... Thick curtain will help, but not sure how much. I have seen several layers of specific acoustic treatment types of curtains in some houses....

    Modeled quickly a rectangular room with similar dimensions and 7.5' height in REW for fun (attached). REW has a nice, simple but usable modeling tool for rooms acoustics below 200Hz (which is where most (but not all) of the challenges lie).

    Not sure how the diagonal wall will impact, probably beneficially, but there still might be room modes at 45Hz, 90Hz, 135Hz, ... and 64Hz, 128Hz, ... If you want to tame those, bass traps (absorbers) in the corners might do the trick. Or resonators. But modes below 100Hz would probably be pretty much untameable (well, you can EQ the peaks down, room mode dips (nulls) you cannot fix with EQ and maybe get a biggish resonator for those) as absorbing traps for those would pretty much fill the room :)

    The simulation is only a simulation and I set the surfaces to be very much reflective to show the possibly extreme case. Reality will be different esp. because of the diagonal wall. If you have furniture etc. in the room, it will probably be better.

    Edit: spelling....
     

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  5. fastfwd

    fastfwd Friend

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    If it's important to you for the attenuator to be built with fancy audiophile resistors -- or if you're the sort of person who already has appropriate resistors at hand -- then yes, just wire up a couple of L-pads.

    Otherwise, a search for "speaker level attenuator" will probably turn up something suitable. I found this adjustable thing that's rated for 100W and presents an 8 ohm impedance, but I'm sure there are many others: https://www.parts-express.com/parts...attenuator-100w-stereo-1-shaft-8-ohm--260-264
     
    Last edited: Oct 9, 2020
  6. Metamodern

    Metamodern Rando

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    This might be a dumb question but I am wondering if putting my floor standing speakers on a 2 inch thick wood or marble platform would affect the sound? The floor is carpeted, however I can certainly feel vibration in my feet 7ft away at the listening position.
     
  7. bixby

    bixby Friend

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    most likely
     
  8. Armaegis

    Armaegis Friend

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    Are they currently floating on the carpet or are there feet/spikes? As a general rule, you want them more stable. Putting a platform underneath sometimes makes them less stable. Just give it the ol' nudge test. Press it with your finger, can you feel it move or rock back & forth? Then put it on a piece of plywood or whatever and try to nudge again. The "better" option will be the one that moves less. The exception here would be if the sweet spot was too low and the platform brings it up to where you need it.
     
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  9. rtaylor76

    rtaylor76 Can't wipe his tag

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    So for a surround amp for my cinema JBL 8340A's, I have narrowed it down to two amps because they meet the budget:
    • Crest FA601 - 150W at 8 ohms.
    • Onkyo M-5000 - 105W at 8 ohms (not the M-5000R reference amp)
    Should I even be concerned with coming from an unbalanced source and the input impedance on the Crest is going to be 10K and sensitivity is at +4 (.775V)? I am mostly concerned with the Onkyo with such a low damping factor (40) and the fact I gotta run speaker cables through my attic for the rear surrounds.

    Which is the better choice here or the trade-offs?
     
  10. rtaylor76

    rtaylor76 Can't wipe his tag

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    Never mind.

    Went with the Crest FA601. Realized the Onkyo consumer amp was not real watts and more of a class H affair with a power pack even to reach the wattage it had, and no level control. The Crest also sets me up if I ever get a balanced surround receiver. I think the Crest is pure class A/B as well.
     
  11. nishan99

    nishan99 Almost "Made"

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    I asked this question on the 'All Purpose Advice Thread' but didn't had any luck. I think the question was not clear so I will try to ask it here a bit better.

    So I basically want to understand the current delivery of amplifiers.

    If for example we have amplifier A that has 40 amperes of maximum current and amplifier B which has just 20 amperes.

    Does the amplifier A deliver more current to speaker X that has a load of 4 ohms with a 4 volts signal compared to amplifier B powering the same speakers with the same signal?
    or is the amount of current delivery the same between the two amps and it only depends on the speakers and the input signal?

    That's of course assuming all other variables are the same for both amplifiers.
     
  12. rtaylor76

    rtaylor76 Can't wipe his tag

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    Given your example of 4V at 4ohms is only 4 watts. The current will be the same. Can only follow ohms law.

    Given that, at 4V at 4Ohm load, that equals 1amp with a power of 1 watt.

    Voltage (V) = Current (I) * Resistance (R)
    Power (P) = Voltage (V) * Current (I)

    Now some amps will have different input sensitivity ratings depending on the amount of gain and the power output of the amp. So you might have two 40W amps, but one has a higher sensitivity (meaning needing less V rms to reach rated power) will output more amps/power given the same source output. Does that make sense?
     
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  13. nishan99

    nishan99 Almost "Made"

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    It does. Thanks a lot!.

    I asked this question because I see some companies bragging about having ridiculous amount of amperage in their amps like say Hegel and Naim so I was thinking if it's doing something or just an overkill current reserve. It's seems the latter, headroom I guess : ).
     
  14. rtaylor76

    rtaylor76 Can't wipe his tag

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    Yes. Amps are rated at a certain power and distortion spec (THD). Higher wattage amps will have lower distortion at lower volume levels and higher headroom.
     
  15. Priidik

    Priidik Friend

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    Very high instant current delivery (tens of amps) often means just lots of psu capacitance, high psu rails, low impedance path (tons of paralleled output devices and good wiring layout) to a short. In an output shorted schenario, when the amp does not have a short detection or overload prevention, it will unload from the full reserves of the cap banks through rather low res path. Only limitation to the current would be the path impedance. This will be instataneous power surge, not continuous.

    No consumer amp can deliver 40A continuous to 8 ohms (12+ kW?).
    Not even to 4 ohms.
    Not even peak to said loads.
    This figure is for shorted scenario most likely.
    Shorted outputs, the loop impedance would be very low, thus even 100A+ would not be unreasonable to achieve momentarily from 40V rails.

    Marketing wank-talk.
     
  16. kee7a

    kee7a Rando

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    Hey, I'm playing around with the idea of building a new system (for movies and music) and wanted to see if anyone had any recommendations on speakers / general setup.

    I currently have LS50 Ws on my desk that I really enjoy. I may move the LS50s to the TV area, but am still looking at options and would need to get something new for the desk if I did move the current speakers. Also, I'm less familiar with speakers, but if it helps, I am a big fan of the focal utopia sound.

    I want to try using 2 aegirs if possible, but I'm concerned about the low wattage / synergy with some of the speakers I'm looking at. Currently I've been looking at the SVS ultra tower / bookshelf. If I cant use an aegir, I would probably get a vidar.

    Is it worth trying to use an aegir for the class Aish sound? Are there any other speakers that may work well with that amp? Am I missing something entirely here that I should look into? Thanks!
     

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