Should you buy a subwoofer?

[BogdanH]

The question that many keyboard owners have: How much will I actually benefit if I buy a subwoofer?
And here I will try to help you, so you can find the answer by yourself.

The lowest tone that 61key keyboard can produce has frequency of ~33Hz -that's the most left key (C0) if we shift octave down (to the left). 76 and 88 key keyboards can go even a bit lower, but as you will see, that's not really important in this case.
For sake of simplicity, let's just say, that the lowest tone any real instrument (i.e. piano, bass guitar, etc.) can produce, is C0.

If we look at PSR keyboard specifications (which have speakers built in), the only info we can get is that speaker diameter is 5". The question is, what's the lowest frequency these speakers can reproduce? And so we compare these speakers with some other 5" loudspeakers, where we can read in specs that starting frequency is about 50Hz -this is far from truth, but let's pretend that we believe that. Anyway, having that info, we assume that speakers in our keyboard are able to play at least ~65Hz (which is tone C1).

Now comes the confusion... if our speakers are not able to play sounds below 65Hz, how come that we can still hear lowest octave (C0-C1) normally?
That is, we set volume to normal loudness, select piano sound, shift octave down and press most-left key (C0) -and we will definitely hear the sound. Well... that's not really the whole truth. Yes, we hear the sound, but not C0 sound... because 5" speaker simply can't play such low frequency. Ok, so what do we hear then?

Answer: what we hear are harmonic frequencies of C0. Harmonic frequencies are multiples of base frequency. For example, if base frequency is 33Hz, then harmonic frequencies are 66Hz, 132Hz, 264Hz, etc., but also frequencies in between, for example: 33+(33/2)=49.5Hz, 49.5x2=99Hz, etc. The loudness of each harmonic frequency that certain instrument produces, defines the timbre of the instrument. That way we can distinguish similar instruments (i.e. clarinet and sax). In short: in nature, every sound contains harmonics.
Back to "what do we hear then?"... I just explained that: we only hear harmonics above base frequency.

Now some will say "hey, but I can definitely tell that C0 sounds lower than C1. Yes, because C0 also contains harmonics between C0 and C1 and if we can hear only some of them, we will perceive sound as lower. We must keep in mind, that speaker doesn't start sounding abruptly at 65Hz -it can play lower frequencies than 65Hz, however not loud enough. The lower the frequency, the quieter speaker will sound and at 33Hz, it will be silent. Means, you can't hear actual C0 tone.

Next question that comes to mind is "specs say, that my 5" monitor speakers go down to 44Hz and so I can definitely hear C0". Let me just say that in this case incomplete specification is deceiving.
I have Yamaha YST-SW160 subwoofer which starts at 20Hz.. impressive huh? But there's also added "-10dB", which gives more complete data about it's capability.

And finally, here's how you can actually check how good your speakers are in bass range C0-C1? Btw. this frequency range is also called sub-bass range (hence sub-woofer).
I have mentioned, that in nature every sound contains harmonics. To make a test of what our speaker is capable of, we need a sound that doesn't contain harmonics. And that sound is sine (sinusoidal) sound. Sine sound only contains base frequency and nothing else. By having that sound, we only need to determine how loud we can hear it (if we can hear it at all).
In labs, loudness is measured at distance of 1m from sound source and at power of 1W. We don't have lab conditions, nor we have equipment needed for that and so we will rely on our hearing. In this case we can do that, because we compare relative differences in loudness (as we hear them).

Here's a link where you can download voice pack that I made: BH Sound test
It contains only two voices:
Bass sine C0-C1
Bass comp C0-C1

-Sine is what I just explained: pure (no harmonics) sound.
-Comp is the same sound, but it also contains harmonics up to 200Hz (so I call it composite).
In each voice separate samples are used for every white key C0-C1 (to avoid pitch shift distortion). Both voices have the same loudness and both voices occupy less than 3Mb.

1. Create install pack and load in keyboard
2. Select Sine voice for R1 and Comp voice for R2
3. Execute octave shift -1
4. Make sure volume isn't too high (volume knob up to max 12h position should be enough)

Now you can play with lower octave, while you only have R1 or R2 voice selected (not both) and compare the sound by listening from same distance (normally sitting behind keyboard). It's recommended that you disable touch sensitivity!
What you should pay attention on is, no matter what key you press, Sine and Comp should be about equally loud.

What you will observe is, for the same note, Comp appears to be a bit louder than Sine voice. That's because we can mostly hear harmonics in Comp voice -but Sine voice doesn't have them.
The second thing that you will observe is, even both voices (Sine and Comp) have same base frequency (tone), when you press C0 for Sine voice, there will be silence, but you will hear sound when you press C0 by using Comp voice.

Now you only need to find out at which Sine tone the loudness of the sound becomes comparable to the loudness of C1.
The result of your comparison might also depend on your hearing ability, but it will definitely tell you how much (if at all) you will benefit by buying subwoofer.
In ideal case, at the same loudness, all sine notes should sound equally loud -same is true for comp notes.
Yes, I can hear C0 sine sound on my subwoofer clearly, but is obviously a bit quieter than C1 sine sound. However, it's still loud enough so I can enjoy sub-bass octave.

Disclaimer: This is a subjective test, where result is only valid for your ears, depending on your speakers and your  room acoustic.

Wish you fun at experimenting.

Bogdan

[Lefty]

Hi Bogan,  I tested my SX900 with software/calibrated microphone designed for this purpose.  At 63hz my SX900 is at -3db.  It's -10db at 61hz, so the internal speakers fall off VERY rapidly below 63 hz.

If you want your SX-600/700/900 to reproduce fundamental frequencies below 60hz, you must have a subwoofer, or external mains.  A grand piano will produce fundamental frequencies as low as 27hz, so if you want to reproduce these you need a subwoofer that is flat down to 27hz +-3db.

Disclaimer:  Your keyboard will still sound good without a subwoofer.  It will just sound more like a real piano/bass/etc with those fundamentals being reproduced.

I'm using a Kali Audio WS-6.2 Dual 6-Inch Powered Studio Subwoofer on my keyboards, along with the 6.5" Kali studio monitors.  It specs out within +- 3db at 31hz, so is close enough for me.

Should you buy a subwoofer?  I don't know....   I already had the Kali's in my studio, so I just added them to my keyboards outputs.  Sounds great!

Best Regards,
   Craig

[BogdanH]

hi Craig,
-thank you for responding.
63Hz -3dB is an important info! -it seems that your measuring confirms my guessing  .

I know that few instruments can go below 33Hz (C0), but I just thought that that's less important for my article -in sense, that we can feel lucky if we manage to reach C0 properly 

Greetings,
Bogdan

[Lefty]

I know that few instruments can go below 33Hz (C0), but I just thought that that's less important for my article -in sense, that we can feel lucky if we manage to reach C0 properly 

Some other instruments do get down where the internal speakers don't reproduce the sound accurately.  With accompaniment on, the bass and kicks are down there, and the kicks especially need a lot of headroom to sound good, as there are large transients.  Pianos certainly have fundamentals below the threshhold of reproduction on the internal speakers.

Improving on the sound quality is pretty easy, but it is expensive if you are exclusively using it for your keyboard.  My Kali sub is about $500 US, and the mains are about $400/pair. As an alternative to a subwoofer, a decent pair of studio headphones sound great, are easier to implement, and are a LOT cheaper. (If you are playing for yourself at home.)

Another alternative is the $200 Yamaha sub that's built for the keyboards.  When I looked in the manuals to see how to set it up, it appeared that the main volume control on the keyboard would not change the volume of the attached sub.  Could someone who has one of those subs comment on how the volume control actually works? I'm sure I must have misunderstood what I was reading.

Best Regards,
   Craig

[Simone1972]

hi Craig,
-thank you for responding.
63Hz -3dB is an important info! -it seems that your measuring confirms my guessing  .

I know that few instruments can go below 33Hz (C0), but I just thought that that's less important for my article -in sense, that we can feel lucky if we manage to reach C0 properly 

Greetings,
Bogdan

Interesting topic Bogdan.
Looking at the Yamaha KS-SW100 specs, the frequency range covers from 28 to 200 Hz....

This seems the perfect addition to the PSR-SXxx speakers and should answer the question of this thread....

Regards

[BogdanH]

Lowest drum frequency starts at about 40Hz, which is in sub range, but not really that low. Lowest bass guitar frequency is 31Hz, which is only one semitone lower than C0. And so grand piano is one of the rare exceptions by going even a bit lower. But then, who would seriously play piano on arranger keyboard? -ok, Korg Pa5X 88-key owners are excluded 
What I'm saying is, if we can cover range from C0 onward, then we can feel happy 

The idea of my article is not about when and how useful subwoofer is. It's more about helping others to find out by themself, if they will benefit having it (that's why I provided those two voices). Exaggerated example: if someone is not able to hear frequencies below 48Hz (say, because his hearing is damaged), then it makes no sense to buy a subwoofer.

@Simone
As I keep repeating, the problem nowadays is incomplete specifications. For Yamaha KS-SW100 it's said frequency range is 28Hz-200Hz. Now I need to know how loud the speaker will be at 28Hz. But that info is not given and so knowing it starts at 28Hz is not really useful information -it's only a rough guidance. Which means it can happen, that another subwoofer that starts at 34Hz, can have much better sub-bass reproduction.

I personally wouldn't buy KS-SW100. Not because I would thing it's not good (we don't know that actually), but because it has very poor connectivity and practically no settings are possible:


-actually I have no idea how to properly connect it on my SX700 directly, or how to use it with external monitor speakers and finally, how to control the sound.

A future proof and versatile subwoofer should have control panel like this:


-because we might change keyboard in future, but subwoofer will stay.

Bogdan

[KurtAgain]

Another alternative is the $200 Yamaha sub that's built for the keyboards.  When I looked in the manuals to see how to set it up, it appeared that the main volume control on the keyboard would not change the volume of the attached sub. Could someone who has one of those subs comment on how the volume control actually works? I'm sure I must have misunderstood what I was reading.

PSR: A subwoofer should be connected to the jacks labeled OUTPUT or MAIN OUTPUT. The MASTER VOLUME control also adjust the volume of the sound output at these jacks.

PSR-SX900: The output level from the SUB (AUX) OUTPUT jacks is fixed and cannot be controlled with the MASTER VOLUME control.

Kurt

[Graham UK]

(if someone is not able to hear frequencies below 48Hz (say, because his hearing is damaged), then it makes no sense to buy a subwoofer).

Not stickly true because dependant on the Sub Bass Unit a very good quality sub-bass system produces more of a low frequency FEEL...I have had the experience.

Many so called Sub-Bass units are just BOOM boxes and can't produce true low frequencies.

[BogdanH]

Graham, you're absolutely right. When we say that we hear sub-bass frequencies, it's actually a combination of hear & feel.

Bogdan