Like everyone, I’m continually redefining my understanding of audio, and the factors involved in our subjective experience as listeners. During recent experience in different rooms, playing with various speakers/subs in Axiom’s line and general audio research I’ve contemplated what factor effect our perception of “bass.” How come certain speakers or subs are more fun than others, but measure the same or have the same inroom spl? Why do some people think a subs orientation matters or doesnt? Or stereo subs are good or bad?

Recently, I’ve come to react to certain assertions made by reviewers and others when it comes to “acceptable” standards or metrics of audio performance. I think “Hmmmmm…. If that’s so then I must be wrong. Are my senses failing me? Why do I like this bad product.” Recent Audiosciencereview articles and recommendations have me scratching my head.

One vid which made me take pause was Andrew’s excellent vid on woofer size vs bass output. In general I like his content, and find his viewpoints reassuring as I continue to work with Axiom products. But this vid made me really sit and think about my experience vs his informative explanation.

Audio Myths Part 1:Woofers
https://youtu.be/dtz8Z0rpeio

So why is it that I prefer the presentation of an 8” woofer vs a 6.5” or 12” subwoofer vs a 10”. As he mentions, the Electro acoustic function of a loudspeaker system (box/driver/port etc) determine its output at various frequencies, but what makes sound “fun”? Why can I tune two subs to have the same in room output at a given frequency, but one sub “sounds” way better than the other. Way more fun. The answer is not related to sound level as we commonly talk about (dB or spl) but Sound Intensity.

Sound Intensity
https://en.wikipedia.org/wiki/Sound_intensity

Why does Mojo love his “discrete” mutichannel sub setup vs mono multisub setup? Sound Intensity.

How loud your system sounds to your ear relates to sound pressure. The warm rush or full body sensation that escapes most peoples recognition is related to sound intensity. They are related but not the same. Kind of like horsepower and torque. Sound intensity relates to energy over area and can be felt kinetically and measured as force.

So why isnt this measured or considered in more objective reviews? Why isnt sound intensity a metric considered in subjective reviews? Quite frankly its a complicated variable, and most readers or reviewers or home owners arent interested in what it requires. Big drivers.

So why arent manufacturers making speakers with big drivers and higher sound intensity capability? Well, up until recently, the notion of large drivers deploying uncontrolled bass into a room was cause for great concern…. Huge drivers make bad things happen in small rooms. Modes run wild etc. But recently more cardiod designs have become popular and can deliver high spl and intensity without as many negative room interactions as older big designs. The recent JBL 4367 review at erinsaudiocorner sure made me understand this relationship more. His interview with subjective loudspeaker expert Beth Mcmullin really drove the point home further.

Anyway, food for thought. Next time you see a measurement plot or distortion plot and think “Wow, gold star!” Is it really? Are you going to have more fun if you buy it than another “worse” measuring model? Tough one, but I wish manufacturers would start to share intensity figures as well as sensitivity. Certainly it should be measured in technical reviews!

Sound pressure level(SPL), sound power and sound intensity are analogous to temperature, heater power and heat flow for a heater:
- The temperature (deg C), which varies by location in the room, can be expressed by just a number (scalar) at that location. Just like SPL.
- the heater power (Watts), which doesn't depend on where the heater is placed, is also just a number. Just like sound power. When you put 500 electrical Watts into a sub, 5 Watts of sound power comes out and the 495 Watts make the sub get hot.
- the heat flows around the room so as it travels, it has a measurable power AND direction (vector). This heat's magnitude and direction can be measured as it flows over a specific area (Watts/square meter) just like sound intensity.

In pictures, sound power is a number AT the sub's driver. SPL is a scalar field represented by a number at each location in the room. Sound intensity is a vector field represented by a number AND direction at each location in the room.

I can tell you discrete, per-channel subs in my room sound and feel like multiple, large, channel-specific vectors.

My understanding is that with a bigger driver it's harder to minimize cone resonance in the frequencies your trying to produce. I.E. It's hard to come up with a material which is light, stiff enough to move a lot of air without resonating, and also have a large surface.

As far as the write-up on sound Intensity goes ...I only gave it a two minute glance ... since the particle velocity vector concept didn't jump out at me ... I'll have to look at it later.

My current thought is this has something to do with having two different drivers move a similar volume of air. A 12" cone will need to move less distance then a 8" one. How that relates to the equation presented needs a more awake brain then I have at the moment.

Good Analogy Mojo.

This was a eureka moment for me that brought the concepts of “loud” (spl) vs “slam” (sound intensity) together for me. I dont always want to crank my system to feel that nice sensation. I wanted to understand why some people report their subjective impression of tactile bass at low volumes.

If my understanding is correct, the larger the perpendicular radiating surface is to the vector angle, the greater the w/m2 possible for a given frequency. This is because the larger the cone area trends lower frequencies to a directional radiation pattern vs distance. -Like beaming tactile energy rather than emitting as a spherical pattern. This doesnt affect sound as spl as we hear it, just impression of tactile effects.

Very cool stuff!

I think audiophiles are drawn to the tactility of bass. Axiom had a video about the deaf guy who used a mylar balloon to listen to music. I know that I feel it in my chest and eyes if the volume is loud enough, and it's exciting the resonant frequency of my various body parts:

https://physics.stackexchange.com/q...esonant-frequency-if-so-how-strong-is-it

There is such a thing as too much though:

https://pubmed.ncbi.nlm.nih.gov/9306739/

Feels like deja vu.
I know this conversation came up many years ago though i don't recall if it visited the term "sound intensity". The info certainly helps to explain the concept though (good thought Trevor).

There are always several factors (aside from room) that determine how subs sound aside from solely driver size of course. There will always be 'industry standard' or 'scientifically standard' ways of measuring the metrics and less commonly known ways of measuring something related. Ultimately, when providing this to consumers, marketing has to balance too much info, too confusing, vs. what most average joes may know about or can comprehend more easily so i can see why you don't have these kinds of numbers reported (or maybe even measured) by speaker manufacturers, though the Audioscience site would certainly be one forum that would dig deep into the topic. From a sales point, asking about how loud a subwoofer gets is easier to understand with one number than two.

Ultimately, turning up any sub creates more 'slam', but if you want that hair to move on your legs when you hear no tone (the sub 20hz stuff), without cranking up a smaller sub, you need a bigger driver, bigger box. In the end, it is still all about moving air.
The EP350 and 500 share the same size of driver, but other things are significantly different. That being said, the EP500 has produced much more 'slam' in the same room. However, i have not verified if the EP500 SPL is producing that slam at the same or higher/lower SPL than the EP350 (sadly i no longer have the EP350 to test the idea).

So what else have i missed?