For the record, the original hypothesis that started in the ULF thread 3 or 4 years ago was:
- Ported produced more TR than sealed around port tune.
Within the ULF Thread, Vibsensor, this thread and really the Subwoofer/DIY forums, there have many accounts both anecdotally ("I switched to ported, and it just feels more visceral" or "my couch didn't shake this much when I had sealed") and quantitatively (via the Vibration Meter, Vibsensor, and DIY accelerometers) that demonstrate that ported is more tactile.
In my mind, I consider that to be truth. Whether folks choose to buy into this or not is certainly up to them...
Originally Posted by ViciousDelicious
I think most people here aren't "resisting" this new approach but are just trying to understand the physics. I personally want to understand it to see how it can be applied to a sealed sub.
Currently it looks like the reasoning goes like this (correct me if I'm wrong):
A sealed and a ported sub with allegedly similar perfomrance parameters are measured given similar calibrated SPL and vibration is registered.
Due to the SPL assumed being constant (all things equal) and the ported sub generated more vibration it is assumed that therefore the ported sub generates more particle velocity.
Yes, increased PVL and resulting increased Sound Intensity was the second hypothesis as to WHY ported produced more TR. Up until this year, we really didn't have any theoretical or measured data to support this...until
made the discovery in the simulator; hornresp. As described in the first post in this thread, hornresp mathematically calculates the particle velocity for a given design.
As a result, 3 created multiple models in hornresp to try and determine the different levels of particle velocity for different types of subs (sealed, ported, horn, bandpass, etc.).
Summarizing of his findings:
- Ported produced ~10X the amout of particle velocity near tune compared to sealed
- Different driver sizes for sealed designs did not increase PVL. IOW, for sealed subs regardless of driver size, SPL at x level would always produce PVL at y level linearly
- There are ways with vented designs that you can optimize PVL
So while particle velocity has never been measured directly, mathematical simulations show that there is in fact increased particle velocity around tune for ported designs.
Assuming hornresp is calculating particle velocity correctly (3ll3d00d validated this with the author of hornresp), then given the equation:
SIL = SPL * PVL
Mathematically, there would be increased SIL around tune for ported subs.
Certainly, to validate the math we would need a tool to measure these, but in my mind validation would just be to measure the mathematical precision of the SIL and PVL compared to the SIM, not so much as to prove if the levels are increased or not.
The issue I have with this is that the actual particle velocity was not measured separately to answer this question with absolute certainty.
The logical reasoning above makes a generally very difficult to verify assumption that "everything else is being equal" and if that is not the case the logical conclusion of higher PV might be flawed.
Here are specific points that in my opinion would need to be proven absoutely equal between the ported vs sealed sub to verify this assumtion:
[*]Spectral composition of the measured signal
Both compared subs would need to generate absolutely the same output signal in each frequency during measurment. It's not enough to just measure the overall SPL which would be some acoustical average. For instance if the ported sub outputs 5db more at 30hz during the test then it would therefore generate more measured vibration ,even if it would output 10db less across 60-80 range, which would result in equal average SPL but not equal spectral composition, thereofre not the same physical energy measured.
In the single sine wave tests as described in the first post, would these not be identical?
[*]Dynamics and headroom
Both subs would need to have the same or close to the same absolute impulse response with the tested signal.
A sealed sub would need a much stronger amplifier or motor design to count the athmospheric pressure with greater xmax to reach the same dynamic range compared to the ported sub. Therefore even if the averaged SPL levels are the same the ported sub might produce a lot stronger "dynamic kick" and in the shape of the resulting air pressure (generated sound wave) might be less smeared over time due to less driver damping therefore potentially more generated vibration at the listening position.
A good test here would be to measure a ported sub against an amazingly powerful sealed sub with great dynamics (like JL Fathom 113v2 or Funk Audio) to rule out this variable.
In the single sine wave tests where SPL levels were played well within the frequency and output ranges of each sub, how does this come into play?
[*]Time Domain Response of the sub
Similar to the previous one it's important to test things like overhang around the port tune. It's widely accepted that sealed subs would have "tigher" base around that area with less energy generated over time becuase it would more closely follow the actual output signal.
So if a ported sub would have more overang, it would produce more base energy over time for the same signal which would translate into more measured vibration.
Is this relevant for a single sine wave test?
Another very interesting thing to look into is the base response of the room. For instance a room that exhibits a lot of ringing in lower frequencies compared to a room that doesn't. Lots of poeple report that installing proper base traps (carbon membraine ones) makes the base much tighter and more tactile.
So it could be that this is why there's need to install near field subwoofers, because by installing those nearfield you're potentially reducing the effect of room reflection becuase the faster produced wave from a ported sub reaches the listener before the "smeared" reflected waves do.
So a theory to test here would be whether or not room ringing would "smear" the base response and therefore make it feel less sharp, ie, less tactile.
In the single sine wave tests, the "base response of the room" would react with the sub identically.
I personally am really interested in tactile effect, for me this is one of the more exciting aspects of a good system so I'm very interested in knowing how to achieve that with the sealed subs.
Your 2 or 3 points above are definitely things you can look for to optimize TR in your room, whether that be for sealed, ported, horn, etc. However, you won't be able to produce the same PVL and resulting SIL levels from a sealed sub relative to ported.
Make no mistake, ported isn't necessary to get great TR. Many have done so...but for those that want absolute optimal TR, then I'd say ported is the right path to go down.