The Truth about 75Hz vs. 55Hz Guitar Speaker Cones

The Truth about 75Hz vs. 55Hz Guitar Speaker Cones

I’ll just bet that you have noticed that the WGS Reaper is available either with the (standard) 75Hz, or 55Hz cone.  Several other speaker manufacturers also offer this option.  But, what does it really mean in terms of tone?  Let’s talk about that.

First, we need to understand that the natural response of the raw cone is not the same as the final natural response of the completed speaker, which is expressed as the speaker’s Resonant Frequency (abbreviated Fs).  Here is the textbook description of a speaker’s Fs:

“Also called F₀, resonance frequency measured in hertz (Hz). The frequency at which the combination of the energy stored in the moving mass and suspension compliance is maximum, and results in maximum cone velocity. A more compliant suspension or a larger moving mass will cause a lower resonance frequency, and vice versa. Usually it is less efficient to produce output at frequencies below F_s, and input signals significantly below F_scan cause large excursions, mechanically endangering the driver. Woofers typically have an F_sin the range of 13–60 Hz. Midranges usually have an F_s in the range of 60–500 Hz and tweeters between 500 Hz and 4 kHz. A typical factory tolerance for F_s spec is ±15%.”

Here is a more abbreviated description:

“This is the free-air resonance of a speaker; it's the frequency that the speaker wants to vibrate at. This is a result of the weight of the moving parts (cone, etc) in balance with the stiffness of the speaker's suspension. At a speaker's Fs the speaker will over emphasize (make louder) that frequency and cause crossover points to change due to impedance variances. For accurate sound reproduction these frequency peaks must be controlled (kept flat).”

So, the final Fs of a speaker is: 1) the frequency at which it naturally wants to resonate, and 2) is a result of the balance (tuning) between the speaker’s moving parts and the suspension.  Think about those two points for a second.  Let’s make this comparison: take the A-string on your guitar; would you say that its Fs is 110Hz?  Well, yes and no.  When the guitar is TUNED to standard (A-440) then, yes, apx. 110Hz would be the frequency at which that string resonates.  However, the string can be tuned to resonate throughout quite a wide range.  Now, will a typical A-string (of around .036” diameter) be able to resonate at say, the low or high E pitches on your guitar?  No, its mass is to high to resonate at the pitch of the High E, and to low to resonate at the pitch of the low E string; that is, after all why all the strings on our guitars are not the same size.  The same basic principals apply to loudspeakers.

A raw speaker cone will have a frequency at which it naturally wants to resonate, based on the properties of the material it is made of and its dimensions.  Everything in life has an Fs!  Thump on a metal mic stand, it wants to resonate at a pitch of say 2000Hz, thump on your wall, probably resonates around 400-600Hz.  Everything in the Universe has a resonant frequency!  Okay, so, back to speakers.  The question I often hear is something like: “if the WGS Reaper 55 has a 55Hz cone, why is its Fs listed as 75Hz”. That’s easy!  The CONE may resonate at 55Hz all by its self, but the overall balance (tuning) of the speaker results in a Fs (for the completed speaker) of 75Hz.  There are other guitar speaker companies out there that simply list the Fs of a speaker with a 55Hz cone as being 55Hz, but that’s not accurate.  Oh, and then there is the fact that the Fs of a speaker lowers over time as the suspension loosens up.  The Reaper 55, with an out-of-the-box Fs of 75Hz will settle down to about 60-65Hz when fully broken in.

Okay, so now you know the truth, the whole truth, & nuttin but the truth.  Trying to get a speaker to produce frequencies much below it’s overall Fs doesn’t work very well.  So, what exactly does this equate to in guitar tone?  Well, I’m glad you asked.  A standard tuned 6-string guitar has a fundamental frequency range from about 90Hz (Low e-string, open) to 1,300Hz (high e-string, 24^th fret).  Upper harmonics extend to about 4000Hz (this varies greatly).  So, given this range, a speaker with a non broken-in Fs of around 80-100Hz works out quite well.  But what about drop-tunings and 7-string guitars that are all the rage in certain music forms?  Well, if the lowest note your guitar produces is a D, that’s about 75Hz, here is where a speaker with an Fs of 75Hz will really help you out.  A low C is about 65Hz, here is where you are in the range of drivers made for Bass guitar with an Fs of 65Hz or below!   A good guitar speaker, which needs to be nimble and articulate in order to sound pleasing, will not have an Fs that low.  Think about a hi-fi system; why do you have separate woofers and tweeters?  Because no one speaker can do a decent job of reproducing the entire sonic spectrum.  Take the 15” WGS Bass speaker, for instance, it has an insanely low 32Hz Fs … would it make a good guitar speaker?  Not if you want any sparkle and touch sensitivity.  But man can it move some serious air!

The point:  1) not all Fs specs are the same, 2) its a game of give-n-take. 

In my next blog I’ll do some video comparisons of the 75Hz and 55Hz Reapers.  Ya’all come back now!

email Vaughn     About Vaughn Skow

My outside blog recommendation this week is a serious breakdown of guitar tunings and relative pitches on Wiki!

http://en.wikipedia.org/wiki/Guitar_tunings#Standard_tuning