All sorts of barics

Isobaric speakers are a powered driver acoustically coupled to another powered driver. Usually a sealed enclosure with one speaker behind the other. Effectively doubling the driving force on the cone of the front speaker.

I have no clue what a hyperbaric speaker is. A sound system for divers returning from the deep? 

Prof Klyzlr is our resident audio expert. Perhaps he knows.

hyperbaric speaker

Never heard of it before but this is the best description I found.

http://www.drass.it/File/DC.ES.000%20Hyperbaric%20Entertainment%20System.pdf

You were closer than you think, Alan.

Some "sugar cube" speakers

Some "sugar cube" speakers come in isobaric and hyperbaric configuration on the sbs4dcc site and I wondered if anyone has used them.

Yves,

Ponoka, Alberta

Would your last name be Nemo?

A layout in a diving bell?

With this as motive power?

and this under the benchwork?

So, Alan, what is the difference between a blast and an explosion?

David Stewart

But,seriously...

It looks like this a bit of jargon coined by the folks at sbs4dcc to describe their face to face configuration of these speakers, thus:

Hyperbaric? Double the "pressure" in the speaker chamber?  

David Stewart

Iso and "hyper" baric speaker arrays

Dear Yves,

Thankyou for clarifying where you saw the term "Hyper baric".
Questions without context rarely generate useful or meaningful answers...

"Isobaric" is a known Audio term. It essentially refers to a form of speaker enclosure design where 2x (hopefully closely matched) speaker drivers are coupled together via a common sealed-chamber "block of air", and are electrically-driven "in phase". The result is that when one speaker driver "pushes in" to the sealed "Isobaric chamber", the speaker driver at the other end "pulls out". The block of air captured in between the drivers (in the sealed chamber) simply moves back-n-forth, like a piston in a cylinder bore between the drivers.

("Iso" = equal or standard, "baric" = pressure.
The implication is that the common block-of-air is being acted on equally from both sides by the paired speaker drivers, and thus the pressure is effectively zero or "equal").

In theory, when engineered and deployed correctly, the resulting Isobaric driver + enclosure "speaker" can reproduce lower frequencies at louder volumes than one of the same-sized speakers drivers on it's own. 

(or, stated alternatively, 2 smaller-speakers in "isobaric array" can "bark" just as low/loud as a single speaker/conventional-enclosure of twice the speaker size).

While in "pure maths" terms the Isobaric array should be able to "reach twice as low and twice as loud",
the actual practical benefits are usually only in the 150% range,
not a pure "200% doubling" in performance.
(Mathematical Theory meets,  Electrical, Mechanical resistance, and Acoustic Practice ).

"Isobaric" enclosures, at least properly engineered ones, are certainly capable of surprising performance which belies their relatively small cubic size. However, when the drivers in question are "sugarcubes", their square shape doesn't "nest together" (and therefore save cubic space) quite as well as a more-traditional "cone type" speaker drivers.

In practical "can I fit this in a loco?" terms, a close-coupled array of drivers is likely to be more-flexible,
and easier-to-fit in the typical loco-shell spaces.

An Isobaric may or may-not be able to out-perform a Close-coupled array in sheer "xxx Frequency @ +/- yyy dB-SPL" terms (I've yet to see a properly measured set of specs),

but if your ears say "that sounds good", and it fits in the loco, then by all means...

"Hyper-baric" appears to be a pseudo-jargonish term which has no direct connection to Pro Audio or Speaker design.
We know that "Hyper" implies "excessive", and as above, "baric" = "pressure".
Taken literally, this would seem to imply a situation where out-of-balance air pressure is (intentionally?) created, and fits with the idea of a divers "Hyperbaric chamber". (A _sealed_ pressure vessel designed to simulate excess-airpressure conditions at sealevel, useful for treating diving issues such as "the bends").

In audio terms, it would seem that we could create a "Hyperbaric chamber" using a "Isobaric enclosure",
and simply wire the speakers incorrectly/"out-of-phase".

If the speakers at either end of the isobaric chamber simultaneously "push in" or "pull out",
then the "block of air" in-between will be subjected to squeezing (added pressure)
or stretching (lowered pressure, or vaccuum),
which it will, as the laws of physics tell us, resist.

Problem, this resistance acts as a damping effect on the speaker driver "cones",
causing them to not move as far or as fast as they could
(or as far/fast as the electro-magnet being driven by the electrical amplifier signal wants to push/pull them!).

In speaker cone movement terms:
- Distance = amplitude ("audible volume" or "loudness" to normal humans)
- Speed = frequency ("pitch", "tone", or "musical note")

Thus a "damped" speaker will not be able to reproduce it's higher-frequency range as well,
or reproduce any frequency at it's maximum possible loudness/volume.
(This resistance-to-movement will also cause speaker-coil/electro-magnet heating,
and possible damage to the audio power amplifier attempting to drive the speaker...)

NB some damping in the operation of any electro-mechanical "flappy device" such as a speaker is desirable,
a speaker with _no_damping_ would likely rip the edge where the cone is anchored to anything solid, as it flaps around wildly. However, the aim is to _engineer_in_ the "ammount of damping", not have the speaker enclosure or other external force apply _unwanted_additional_ damping_ to the cumulative equation.

So, where does this leave the "Hyperbaric" enclosure listed on the SBS site? Well, firstly, according to the pics,
it does not have a _sealed_chamber_ between the 2 drivers, so the idea of a "solid fixed block of air moving backwards and forwards between paired speaker driver/cones" is not relevant.

That there are two speaker drivers pulling/pressing against the surrounding air means we need to consider:
- Phasing
(are the 2 speakers pushing in the same direction at the same time, or in opposing directions?)

- Interaction of the soundwaves from the two speaker drivers
(once the push/pull forces are applied to the surrounding air, can the pressure waves from one driver cancel/sum with the pressure wave from the other?)

- Is the distance the two speaker drivers are being held-apart by the "enclosure" critical?
(and if so, does it have particular operational characteristics at different frequencies?)

- What happens to any air "trapped" between the 2 drivers? 
(If the 2 speaker drivers "press in" towards the middle, does the block of air get squeezed,
and "squirt out" either side of the enclosure? The block of air is not sealed between the drivers, so applying pressure means it will try to go somewhere... and with the "under-pressure" central block of air trying to escape out from between the drivers, how does it them interact with the "front pressure wave"?)

- What happens to the "trapped/escaping air" and sound pressure waves,
as far as reacting to the enclosure mounting within the loco shell?

The answers to these and many other questions I have to say "I don't know".

However, Willy Occum was onto something,
(everything else being equal, the simplest solution is usually the best/most-appropriate one),

and as such, I'd be much more instinctively inclined to deploy a simpler close-coupled array of speakers,
(physical space within the loco shell permitting),
than an "exotic" Isobaric or "Hyper - baric" array,
as my "Go To First-Choice" approach...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS NB that in the SBS4DCC "Isobaric" array, the speakers are physically facing the same direction. This means that wiring them so they are _electrically_ "in-phase" means they will also be _mechanically_/_acoustically_ 'in-phase"

The "Hyper - baric" enclsoure in contrast has the speakers facing "back to back". Ergo, the drivers need to be wired _electrically_ "OUT-of-phase", so that they _mechanically_ move "IN-phase" with each other.
(IE so that the cones both move in the same direction when presented with a +ve-going signal).

Whether this is how the "Hyper - baric" design is _intended_ to be operated or not is unknown to me.

I appreciate the information,

I appreciate the information, Prof. It sounds (no pun intended) like a person would have to do a lot of experimenting to get the optimum spacing in the face to face or back to back configuration.

I just want to get a good sound out of a loco and sometimes we tend to outthink ourselves to come up with a good solution.

It might be simpler to just get two speakers and hook them up in series.

Thanks again,

Yves 

Ponoka, Alberta

Fascinating info

As always...

volume from small speakers

As the size (area) of a speaker becomes small compared with the wavelength of the frequencies being sent to the speaker by an amplifier, the volume produced depends more on the velocity of the speaker cone's excursions. The higher speed is needed to impart some "push" or "pull" to the air before the air can "slosh" out of the way. At low frequencies with small speakers, this results in extraordinarily large speaker cone excursions to produce a non-trivial volume level.

Unfortunately, for the tiny speakers we are able to fit in our locomotives, large speaker excursions are not reasonable. As an alternative doing a better job of coupling the speaker to the air you are trying to push around will help. Either make the speaker larger (speaker array?) or connect it to a properly designed horn with a sufficiently large mouth to improve efficiency when transmitting energy from a small speaker.

An example of a speaker that is well coupled to the air is the bass unit of  a Klipsch corner horn which can produce astonishing volume at low frequencies while minimizing cone excursion distance. But those are some BIG speakers (think of a horn attached to a 15" woofer!). They might be suitable for installation in a full size locomotive but not in a model.

Another problem with long cone excursion is Doppler distortion. You know the effect where as a moving object passes a stationary observer, the sound emitted by the object appears to drop. When a single speaker is used to produce a broad spectrum of frequencies the lower frequencies result in the sound source (cone) being carried closer and further from you resulting in Doppler distortion of the higher frequencies. In our model train sound systems ALL frequencies are generally produced by a single speaker maximizing the potential for this kind of distortion. As the volume (and speaker excursions) increase, so do the non-harmonically related extra frequencies producing a kind of acoustic mud. You reduce this distortion by increasing the speaker size, reducing the throw of the speaker cone, and reducing the frequency range handled by a single speaker. It's a much bigger problem when handling low frequencies.

You can miniaturize electronics. You can miniaturize speakers. You can't miniaturize audio wavelengths. Trying to reproduce audio frequencies with a 5' or wavelength (around 100 hz?) using a 1" speaker isn't going to work well.

FWIW

Charlie

Small speakers

Charlie your points are well stated. Mr. Pittney and Mr Boise might have some more to add but they aren't here. One example that I think illustrates your point very well is the quality of sound that comes from the Atlas Train Masters with their dual speaker set up. The volume can be turned up rather high as well. Sound quality is rather good as well, to my ears. I have also noted that sound from steam locomotives with large tenders and the inherent larger speakers that can be slipped in there sound good. I have heard some very small set ups with iPhone speakers that are very nice sounding via the computer as well.

I think it is quite impressive what can be accomplished in such a small size that was unheard of just a few years ago.

As to the smallest locos I have heard again via the web sound from items as small as a 44 tonner, but those sounded a bit on the poor side to me. I think that is more a limitation on what was available at the time in the way of speakers and the cramped space in the locomotive as well as the quality of the sound file. It just sounded a few octaves too high over all to my ears and that backs up your points as well.