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  • walkman
    replied
    I’m also in agreement that 1 or 2 watts is way to loud in many dwellings, with standard guitar speakers.

    The Yamaha THR5 I use for low volume practice is great for bedroom level playing but after a little playing there is still the feeling I need to turn it up a notch so that it feels loud in the room and give the right vibe.

    The speaker section has 2.5” or 3” speakers, that would not be super efficient and a ported cab.

    Has anyone experimented much with this size of speaker and cab?

    Leave a comment:


  • Gnobuddy
    replied
    Originally posted by bob p View Post
    bass players are actually pretty good about orienting their speakers vertically. the guys at talkbass are huge proponents of the vertical arrays.
    In my experience, generally speaking, bass players seem to be a lot more willing to abandon tradition when something new and improved comes along. Guitar players tend to cling to the past, whether or not it makes sense.

    Originally posted by bob p View Post
    i can't get over how funny a skinny vertical 4x12 stack looks with a wide head balancing on top of it.
    There's an easy fix for that, start making narrow heads!

    Originally posted by bob p View Post
    at least Leo was smart enough to place the 2x10 speakers at an angle in the early 50s V-front super.
    I'll bet he was simply trying to use as little wood as possible for the cabinet, and never had a clue about the acoustic aspects of the design. Leo never stopped thinking like an accountant!

    Originally posted by bob p View Post
    nobody's wife is going to want a vertical post speaker sticking out on top of the TV.
    No, but the solution is simple: raise the TV, install the vertical centre-channel soundbar underneath it.

    Even better, of course, is to toss the soundbar, and use a proper speaker speaker enclosure under the TV for the centre channel. You won't have to raise the TV as high, and you won't have to deal with the crappy sound quality that usually goes with a string of 2" drivers in a long pipe enclosure with poorly damped organ-pipe resonances.

    Me, I just use two-channel stereo sound, with one monitor (speaker) on each side of the TV. The centre channel often takes away too much of the stereo image for my tastes.

    -Gnobuddy

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  • bob p
    replied
    bass players are actually pretty good about orienting their speakers vertically. the guys at talkbass are huge proponents of the vertical arrays. as much as i agree with it, i can't get over how funny a skinny vertical 4x12 stack looks with a wide head balancing on top of it.


    at least Leo was smart enough to place the 2x10 speakers at an angle in the early 50s V-front super.

    Click image for larger version

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    as far as the soundbar speakers go, they're just an add on that fits underneath or on top of your TV. they do it that way for the acceptance factor. nobody's wife is going to want a vertical post speaker sticking out on top of the TV.

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  • Gnobuddy
    replied
    Originally posted by bob p View Post
    the principles you're describing are well known.
    Oh, I know. Just keeping it relatively simple and non-technical.

    There is a lot of physics from classical optics (diffraction and interference) that is quite directly relevant to speaker systems using multiple full-range drivers. And some odd gaps in our thinking about them when it comes to musical instruments, audio, and speakers.

    For instance, why does everyone seem to understand that "line array" speakers should stand upright, but continue to place two speakers horizontally, side-by-side, in 2x10 or 2x12 guitar amps ? That is a recipe for severe beaming in the horizontal plane, exactly where your audience is spread out!

    Same thing for those "sound bar" speakers that are supposed to go under your TV to provide the centre channel. That's a line array, placed horizontally, so it beams like a searchlight in the horizontal direction, and gives decent acoustic dispersion in the vertical direction. Exactly the opposite of what is actually desired! That sound-bar should be standing upright under your TV, not lying on its side.

    I have actually seen one bass guitar cab which placed its two speakers vertically, one above the other. It stood on its small end, tall and upright, like a vintage home Hi-Fi speaker. Whomever designed that speaker system got it right! (Unfortunately, I don't remember the brand.)

    -Gnobuddy

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  • bob p
    replied
    the principles you're describing are well known. acoustic engineers refer to the phenomenon you're describing as "mutual coupling" between drivers. the math actually says that mutual coupling only occurs if the distance between the center of each adjacent driver is less than lambda/2 (one half wavelength).

    think about diffraction ... but occurring backwards.

    for mutual coupling to occur between 2 or more drivers they have to be reproducing the same signal, in phase, with a common axis of projection. the combined signal will propagate on-axis as if it were a single waveform with the multiple drivers behaving as if they were one driver with their composite surface area. the larger driver is more efficient in matching the impedance of free air at those frequencies.

    it's important to note that these coupling effects only occur on-axis, and for signals that are of adequate wavelength relative to the center-center distance of the drivers.

    the coupling effect is directional; the coupling occurs on-axis. the on-axis coupling actually occurs independent of the driver spacing, but frequency dependent combing will occur off-axis. as the wavelength of the signal increases relative to the distance between the drivers' acoustic centers, the off-axis angle at which mutual coupling continues to occur will increase.

    the effects are only practical at frequencies below ~ 500 Hz because of the physical size of the loudspeakers. if the speaker-speaker distance is > 1x lambda the gain in SPL will be +3dB. if the speaker-speaker distance is 1/2 lambda then mutual coupling occurs at that frequency and the gain in SPL is +6 dB.

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  • Gnobuddy
    replied
    The same Printer2 who is already featured in this thread for his 6AK6 amp, also had a thread in which he reported measurements using first one,and then two, identical speaker cabs; I think first one and then both speakers were wired to the same solid-state power amp, driven by a white noise signal. An SPL meter showed a 6 dB increase in loudness.

    The interesting part is that paralleling the two identical speakers draws double the power from the amp - but that only accounts for a +3 dB increase in loudness! The other 3 dB increase had to come from the increased speaker efficiency due to having twice the cone area as before.

    I think this sort of efficiency increase (from increasing cone area) only happens at frequencies low enough for the wavelength to be much bigger than the speaker diameter. For a 12" speaker with an effective 11" piston diameter, the sound wavelength equals the cone diameter at about 1200 Hz. Most of the fundamental frequencies in guitar music are under 664 Hz (12th fret on the high E string), so most of the sound energy is indeed at wavelengths much bigger than the speaker diameter.

    -Gnobuddy

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  • bob p
    replied
    Originally posted by Justin Thomas View Post
    They think the size of the speakers makes it more powerful or something.
    well, they do. it's about matching the speaker:air interface to the impedance of air.

    Leave a comment:


  • Justin Thomas
    replied
    Originally posted by Chuck H View Post
    I went to a gig (as an audience member) to see a guy that owns two of my amps as well as a little Mesa Subway Blues that I modified (his smallest amp). I asked the sound guy which amp he liked the best.?. He said "The little one".
    >:[
    Quoting from the guy in "Happy Gilmore":
    "JACKAAAAAAASSSSS!"

    On another note, it's hilarious when you show up with a "toaster" amp & plug it into a 2x15. They think the size of the speakers makes it more powerful or something.

    Justin

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  • bob p
    replied
    Originally posted by Chuck H View Post
    I went to a gig (as an audience member) to see a guy that owns two of my amps as well as a little Mesa Subway Blues that I modified (his smallest amp). I asked the sound guy which amp he liked the best.?. He said "The little one".
    Sound Guys -- It's like they're in a damned Union.

    Leave a comment:


  • Chuck H
    replied
    Originally posted by bob p View Post
    Attenuators are a necessary evil. If you piss off the sound guys with a 15 watter then you're really going to piss them off with a Plexi.
    I went to a gig (as an audience member) to see a guy that owns two of my amps as well as a little Mesa Subway Blues that I modified (his smallest amp). I asked the sound guy which amp he liked the best.?. He said "The little one".

    Leave a comment:


  • Gnobuddy
    replied
    Originally posted by Enzo View Post
    The sound may be coming out your stereo at a reasonable volume and sounding good, but that does not mean they were recorded that way.
    Sure thing. The musicians who made that music used the tools they had - and the big amps of the time only yielded those lovely distorted tones if you turned them up to ear-bleeding volume.

    But a 2W amp doesn't need to be turned up quite that loud to get a similar level of distortion - all else being the same, 20 dB less SPL than a 200W amp, yes?

    Originally posted by Enzo View Post
    I can listen to old Jimi Hendrix records at polite levels and I can guarantee you won't get the sound by playing at that level.
    Not with the equipment Jimi used, certainly. But that doesn't mean it's impossible - in fact we know that it *is* possible, since it comes out of your stereo. So the remaining big question is, what does it take to make an amp that sounds like, say, Eric Johnson playing on your stereo - but at volume levels like your stereo, and not 120 dB?

    Originally posted by Enzo View Post
    Just one example of many is the sustain you get from auditory driving of the guitar strings. Happens at stage volume but not at dentist office volumes.
    Conventionally, yes.

    But you're an electronics tech of vast experience. Tell me, what is the mathematical condition for an amp to oscillate? You have to have positive feedback, and the loop gain has to be unity, (slightly greater to start oscillating) right?

    Notice that the oscillation condition says nothing at all about the amplitude of the output - only about the total gain in the loop.

    The other thing we know about oscillations induced by having loop gain greater than unity is that the amplitude of the oscillation grows exponentially with time, until something happens to lower the loop gain to exactly unity, at which point the oscillation stabilizes. In a Wien bridge oscillator, we might deliberately use a thermistor, or LDR, or JFET to lower the gain to unity when the right amplitude is reached, to maintain stable oscillations.

    Now, if you take a 100W Marshall, turn it up, and then move your Les Paul close to your 4x12 stacks, you can get the loop gain - including the acoustic transfer of vibrations from speaker to air to guitar strings - up above unity, and acoustic feedback starts. It very quickly gets louder and louder (exponential growth) until the amp begins to overdrive, meaning gain is lowered on signal peaks. The average gain falls, and eventually the oscillation stabilizes. Since the amp had to be pushed all the way to full output to begin to overdrive, you now have ear-bleeding SPL along with your acoustic feedback.

    But this is not the only way to create acoustic feedback. Remember, we need only two ingredients: enough electronic gain to make the total loop gain greater than unity so that oscillation starts, and then some mechanism to to start to lower the gain as the amplitude grows, until average loop gain drops to exactly unity, and oscillation stabilizes.

    Several years ago, I reasoned that I could use a compressor element that lowered the gain to unity once oscillations had started to build, and any kind of gain pedal to to get the loop gain high enough to start acoustic feedback. It turns out that this works quite well. Turn up the gain enough to get acoustic feedback oscillations from speaker to guitar to start; turn down the compressor threshold so that the gain drops to unity and maintains oscillations at an SPL that isn't ear-damaging. It helps to be using a fairly low-wattage amp, so that you don't blow your ears out before you get all the knobs set where you want them.

    Compressor doesn't have enough gain? Then you have to add some more. A clean-boost pedal, or an overdrive pedal, will usually do the trick. The compressor will still do the job of stabilizing the acoustic feedback level once oscillation starts.

    Will I sound exactly like Jimi with a compressor and a low powered amp? Surely not, there are other psychoacoustic and psychological factors at work, that give loud sounds an impact that quiet sounds never have. But then again, I wouldn't sound like Jimi if you gave me all the exact equipment he used, either. And I would be deaf in short order (Jimi would have gone deaf if he'd lived longer than he did.)

    In the end, it comes down to something very simple. I love music, and therefore it makes no sense at all for me to do things that I know will cause me to lose my hearing; that's would be like a dancer who deliberately chooses to chop off a toe every time she performs, no?

    So I have exactly the opposite philosophy from Chuck and Jason. If I have to lose some "tone" to keep my hearing, so be it. I'd rather have my hearing, and be able to still enjoy music, and the voices of the people I love.

    But that viewpoint leaves open a window of opportunity: to hunt for ways to get great electric guitar tone without the deafening SPL levels.

    As an aside, I started tinkering with solid-state electronics when I was quite young, around eight years old. By the time I was in my twenties, I had seen and learned and built enough stuff that the challenge had gone. Not to mention, the solid-state Hi-Fi audio chain had essentially reached perfection; now even cheap chip amps had so little distortion that the remaining imperfections were undetectable by ear. The only remaining progress to be had was in lowering cost, size, and weight, and those things didn't interest me much. So I pretty much stopped building my own electronics. I also started playing guitar at around the same time, more or less coincidentally.

    Guitar faded out of my life when college, marriage, a mortgage, and my first real job all took over my life. But eventually, guitar clawed its way back into my consciousness; and this time, I discovered what I had not understood before, that it was imperfect amps that made electric guitars sound good. And that made electronics interesting again, because I didn't know how to make deliberately imperfect amps that sounded good when you put a guitar through them.

    And now there is an additional challenge: making deliberately imperfect amps that sound good when you put a guitar through them - and do it at SPL levels that don't destroy human hearing!

    Can it be done? What will it take? Tune in to the next thrilling installment to find out!

    -Gnobuddy

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  • bob p
    replied
    Originally posted by Gnobuddy View Post
    Ever wonder why virtually every recording you ever hear has compression on it?
    Probably because vinyl and radio transmission have such limited dynamic range. Those were the main ways of selling recorded music in the Dark Ages. Could you imagine driving in an old noisy car and trying to listen to a radio broadcast that had wide dynamic range? You wouldn't hear the quiet passages over the road noise without turning the radio up so loud it would be deafening. Compressed dynamic range not only helps the signal fit onto a vinyl groove, it makes it possible to broadcast it and to listen to a broadcast in a noisy environment.

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  • bob p
    replied
    Originally posted by Justin Thomas View Post
    Well, it was a joke, after all... But I can honestly say I've never used an attenuator or compressor.
    Then you are missing out!

    Compressors are very popular with country music pickers and acoustic guitarists, not so much with rockers who are only interested in compression at high gain. But they can do great things for you if you know how to use them. They're particularly helpful with effects like octave doublers and dividers, which rely on a reliable consistent signal for proper tracking. These kinds of pedals won't handle a sustaining note well because they lose tracking, and the effect ends up bouncing around inconsistently and ends up sounding like crap. I think the main reason these effects aren't very popular is because not that many people know how to use them. They get a new breath of life if you use them with a compressor and provide a constant signal to their input so they can track reliably. I prefer my Foxx Tone Machine, my Octavia and my Blue Box used in combination with a compressor. I've even re-housed two circuits into one box so that they'll always be together. I wouldn't play Fool in the Rain without one.

    Attenuators are a necessary evil. If you piss off the sound guys with a 15 watter then you're really going to piss them off with a Plexi.
    Last edited by bob p; 10-09-2017, 07:16 PM.

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  • Enzo
    replied
    The sound may be coming out your stereo at a reasonable volume and sounding good, but that does not mean they were recorded that way. I can listen to old Jimi Hendrix records at polite levels and I can guarantee you won't get the sound by playing at that level.

    Just one example of many is the sustain you get from auditory driving of the guitar strings. Happens at stage volume but not at dentist office volumes.

    Leave a comment:


  • Leo_Gnardo
    replied
    Originally posted by Gnobuddy View Post
    And here's the "different strokes for different folks" thing popping up again!

    My favourite guitar tones have all come off a recording (not live), played at comfortable listening levels in my living room. So I know it's perfectly possible to get great guitar tones without huge SPL - there they are, coming out of my speakers! For me, beyond a certain loudness, there is increasing physical discomfort - my ears hurt, my head hurts, my ability to discern fine details in the music decreases. It's not an enjoyable experience, but the reverse.
    An additional advantage, you can use small, lightweight speakers. There's a special attractive quality to being able to use small cones that have little momentum for recordings. Indeed I've done some in the mid 1980's using cheap mini stereo speakers, only 4 inch diameter. With Neumann U87 mics - the mics were bigger than the speakers. Huge sound! "What kinda stacks were you using for that???" was often asked. Mouse size stacks, heh heh heh....

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