Rant forthcoming – with dope research to back it up. We’ve seen many Cinema Sound members and non-members alike place their speakers in positions which are compromising to a mixer’s ability to hear what the speaker is really doing. We’ve seen everything from LCR speakers in a straight line, to off-axis positions to even ceiling mountings. One of the most difficult-to-overcome places to drop a speaker is against a wall – and a corner even compounds the problem. This article will show you why you should NEVER, EVER, EVER put your speakers in a corner and why your mixes (and maybe even you) will die if you do.
In a perfect world, the most optimum place for a speaker to live is suspended by acoustic coupling resistant non-rattling wire in mid-air pointed at the appropriate magic-triangle position to the listener positioned far away from any surface – including the floor. And while this is as impractical as it is flamboyant, why is this setup so good? Next to primary reflections (covered in the Cinema Sound education and in many articles here like this one), the acoustic coupling of a speaker next to a wall or a corner creates irreparable damage to the clean flat sound your speakers make. How does this happen? Sound travels through solids dozens of times faster than in air, and sound waves in solids happily coerce other solids connected to them to vibrate. If you have a speaker leaning up against a wall, the vibrations that the speaker cabinet makes will cause the wall to similarly (but not exactly) vibrate. This is the essence of acoustic coupling. The wall has now become a very large, very low fidelity speaker, and it sends its sound pressure waves in the direction it faces slightly delayed.
Because high frequencies have little power compared to low frequencies and because of their extreme directionality, low frequencies are the usual suspects which engage in acoustic coupling. As it happens, walls and other large frameworks also vibrate well with low frequencies as opposed to high frequencies. The result is a large 8′ wall being turned into a delayed subwoofer-amplifier of the sound coming through the speaker leaning against it. Now, at first glance this may seem like a great thing! All that low frequency – which may be missing from small diameter speakers anyway – boosted and made big! YES!
Not so fast.
Do we really want bass that is boosted from the speakers which we purchased to have a flat frequency response? Wouldn’t that just make our mixes too thin as we turned down bass frequencies to compensate? Moreover, wouldn’t the flubby and lethargic nature of the bass from the wall just turn everything into a mush anyway?
If so, wouldn’t putting a speaker on a corner make everything doubly worse?
Yes. Yes. Yes.
And while having speakers on a wall or in a corner can be fun for a party, it’s no way to mix. It’s why many speaker manufacturers have EQ settings built in to the speaker itself to try to compensate for the added bass frequencies of wall mounting – by attenuating bass frequencies in a draconian shelf. Generally, a flimsy way to solve a large problem.
But for those of you who don’t believe us, we’ve set up a test to prove our points using some of our favorite JBL speakers.
Why JBL speakers? Well, other than the fact that we’ve been telling all our independent creatives to purchase – at minimum – the JBL LSR 305 MKIs (now MKIIs) for over 5 years, and that the best speakers Mark has ever used to mix on were the now discontinued 6328Ps and their replacement the Series 7 708Ps – no reason. Well, to be fair, we happen to have quite a few JBL speakers on hand in various sizes and wattages, and so we figured it would be a good opportunity to see how each did.
We tested the sound of the speakers in a corner and in the middle (away from walls) of a living room which was completely untreated. The corner was comprised of a stone fireplace on one side and plaster wall (not dry wall) on the other. Speakers were placed on a padded chair 3 feet from the floor (carpeted) and faced directly at the testing microphone. The distance to the mic was 12 feet. For the middle-of-the-room position the speakers were placed in the middle of the room on the same chair at the same height and the mic was moved back to be at 12 feet again.
We tested the following speakers from JBL:
We also, just for laughs and giggles, flipped the position of the speaker and microphone in the corner so we could simulate what happened to the listening experience by being in the corner with the speaker in the middle of the room. For this we sent pink noise through the speakers generated from Adobe Audition – again at 80 dB. Fun right? Let’s see.
In this first example, you can see the LSR 305 MKI’s frequency response to the bass drum hit in both in-corner and mid-room performances. Green is mid-room and blue is corner. We break this down further below.
Here we can see several critical elements about having a speaker – any speaker – in the corner of a room. First, as compared to the mid-room example below, there’s a lot more bass frequencies. But not in the lowest frequencies…more in the upper double-digits…which really doesn’t help this snappy bass drum sound. You can see in the first few milliseconds that there’s plenty of high frequencies snapping in – thanks to the excellent tweeter pointed directly at the microphone, but the bass frequencies don’t appear in any kind of strong fashion for many milliseconds.
This flubby and late response is present in any speaker, but is exacerbated by the rear bass reflex port on the LSR 3 series speakers. This sends air – and no small amount of bass power – to the rear of the unit. Because of the corner positioned nature of the speaker, this sends this energy “backwards” into the corner – delayed – and is ultimately dispersed around the room via reflections. Normally, this rear-mounted reflex port has no bearing on the directionality of bass frequencies. Most well-made speakers are built around the bass reflex port and designed to throw bass frequencies forward. But because of the corner mounting, we experience this to no longer be the case.
Of course bass frequencies don’t like to be “reflected,” but our stone and plaster walls did a great job of disallowing penetration or absorption of bass frequencies Those frequencies were sent back into the room. This isn’t any kind of special room. Just a room you’d find in any-home-USA. Any time sound is reflected back toward the listener there is a high cost in delay, phase issues and comb filtering. It also happens over time. So as the direct signal quickly decays, the meat of the bass signal is still coming from reflections and experiences all manner of phase issues ms by ms.
This is why we see an even stronger bass spike after the attack of the sound. Again, this happens with any speaker, but it’s exacerbated by rear port bass reflex ports. Also, we see in corner positions the bass frequencies “rattle around in the room” up to 50 ms after the initial attack. If there were a series of fast hits or even an explosion event, the low frequencies from every transient would continue to color the listening experience long after the speaker had moved on to another sound. You can see this in the ongoing low frequency “rolling” long after the directing signal and high frequencies had ended.
Contrast that with this mid-room image where we see an expected diminishing curve of bass amplitude. Naturally, not anywhere near the kind of reduction over time that would be present in a finely tuned room, but it’s far better than the corner mounted version before. The bass reflex spike is still there, because even in the middle of a room, low frequencies/energy sent to the rear will still find its way to the listener later. You’ll also notice a bit of a low frequency shelving directly after that spike which indicates low frequencies sent around the room arrive slightly delayed in sequence. If the room were larger, this “secondary impact” would happen later. Notice how little rumbling of the bass frequencies there is now that the speaker position has removed the corner bass amplification and delay. Although this isn’t the most optimal frequency plot, it’s far better than having the speaker in the corner. Were this in a tuned room, this plot would be quite short and demonstrate an accurate plot of the original waveform. This is a plot from a 5″ speaker and cabinet, and we’ll see different responses from the larger products.
Here we look at the 305 MKII mid and corner frequency plot. Notice a far more accurate attack from this update to the MKI in both cases.
Like it’s older brother, the rear reflex port causes an undue spike in bass frequencies and the expected secondary reverb sustain. However, notice how much more bass response there is, and notice how quickly the bass response occurs. Although this is still far too much bass amplification, there is no “flubby” or late response as experience by the MKI.
Here with the mid-room plot of the MKII, we can see a more appropriate bass frequency response. Still suffering from a ringy room and the reflex port issue, the bass is siphoned off quickly into far less reflection than it’s corner performance. It should be noted again: the bass reflex position is not the main reason for the sustained or wonky bass response. The nature of the room and the corner are causing that via reflection, standing waves and reverb. As we’ll see with the 708s, a forward reflex port helps, but doesn’t solve these issues.
The 8″ variety of the LSR series appears as a definite contrast to its 5″ brethren which can be easily seen from this dual plot.
Here we see an attack nearly devoid of bass and a powerfully delayed response. Room reflections and a rear bass reflex port has the usual amplified bass frequencies. However, with the 308, those frequencies are much lower in Hz as can be seen by the space between the line plots and the power of their spikes. This denotes the frequencies being amplified are in the 70 Hz and below zones. This is due to the larger woofer size. Also notice the quick dispersal of low frequencies after the delayed response – in contrast to the 5″ performances. And although there are ongoing low frequency reflections, they are much reduced over their smaller brothers. Still, this corner presentation brings unwanted low frequencies which would otherwise be fit for a rave – not a mix.
The LSR 308 MKI does an excellent job mid-room of a sharp attack of bass frequencies as we’ve come to know, a quick decay and little post-attack reflection. In addition, one of the tell-tale differences in sound between the 305 and 308 MKIs is the 2kHz-3kHz bump in frequency response. This can be seen in the smaller wave decay.
The $1,999/speaker JBL 708P is the clear winner in this mash-up of things-not-to-do. And even in this somewhat cluttered view, the deep bass frequencies that are amplified from this corner position of the 708p can be seen.
No matter what the cost and value of a speaker, nothing can compensate for a corner or wall position. Even here, high frequencies are snappy and sharp, but low frequencies take many ms to arrive. When the do arrive however they’re like a freight train. Contrast the space between waves of this plot vs. the priors and you’ll see amplification of lows in the 50 and lower Hz. Also, the 708p is the only speaker in this test which has a front mounted bass reflex port. As a result, notice the lack of a distinguished spike or secondary sustain of anything but the lowest frequencies. Also notice the ongoing bass reflections’ lack of amplitude in contrast to the other speakers. This is because the frequencies being reflected, on the whole, are so low that they strongly resist being reflected and instead are absorbed into the walls instead of thrown back into the room.
In the mid-room presentation, the 708p reigns supreme with a near accurate response to the snappy bass drum signal. Transient bass, the expected decay – given a ringy room and near inaudible post-reflection are its hallmarks. It is interesting to note the low frequency spike present here. We figure its appearance is due to the front mounted bass reflex port being far enough away from the rear wall to allow high two-digit low frequencies to jump back/go around the room and coalesce a few ms later.
One More Insult
For those of you still not convinced, we also placed these speakers in the middle of the room and placed the microphone in the corner to see what listening too close to a wall or corner revealed. We used pink noise as mentioned before. Here are our not-really-very-surprising results. Note that the red line is the frequency response of the microphone. The closer to the red line, the closer to perfectly flat.
Naturally, the 708p scored highest considering it’s known slight high frequency drop. But no matter what speaker, no matter how good, if your speaker or your head is anywhere near a corner or wall, your bass frequencies will not be true. In fact, you should consider them “false.” We haven’t even started on the upper mid-range phase issues or the high frequency comb filtering that goes on with such a listening environment. We can’t make a louder or more pronounced case for having your speakers as isolated from structures as possible (including the stand they’re on).
The Wagging Finger
Hopefully this shows you reason why you must NEVER, EVER, EVER put speakers on a wall or in a corner. That is, if you expect to create mixes which translate. If not, take these plots as excellent examples of what to do with speakers in order to get that “Beatz headphones sound.”
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