Very large sized planar driver ( 180square feet) ...possible ?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I've posted this in the alternative forum, but i guess it will have more success of beeing answered here.

I have yet to come to some ideas about a driver with a radiating area that would cover a complete section of a wall .. ( searched quite a bit here, and on google )

my idea would be using subwoofer type motors,
to drive some carbon composite structure with laid on mylar or other diaphragm

would use the complete wall section in front of my room

application is of course, only for sub-frequencies
( 100hz less i guess )

wonder if it would be possible,
what kind of problems would it cause
rooms interaction ( no modes fron sides and top/bottom??? )

also if there are some mathematics that could be used to calculate the possiblities

so any links or ideas or comments
( maybe i am just plain stupid and this is an impossible driver ) are welcomed!!!

this came to me as i was trying to understand planar waves generation, and trying to grasp a design ..than thought about ESL diaphramgs ...

also would like to understand how waves coming out of a " moving wall" would be ??

thanks all
 
nah , i want it to move completly

probably would install anything from 8 to 16 motors,
spread evenly so they also hold up the wall and allow it to move all together ...

would require some type of sealed/suspension all around..probably bolted or glued to the walls

sice this would operate in IB setup
( garage room will be rear enclosure .. )

with CF using hollow tubes, i could make it seriously light weight since stretched mylar doesn't add much weight for a subwoofer ... i guess :p
 
would this make a completly planar wave ?
or would it buldge and mirror out of the side walls?

if pressure can't go anywhere , like in a horn or a tube,
does the wave stabilize or maintain it's pressure over all of the room distance? ( not perfectly i know ..but theoritically ? )

the effect i want to achieve for the sub frequency of my setup, is a serious planar wave bass from front to rear
where i would/could absorb most of it with some 1-3' thick absorber ...
 
I was just thinking that you wouldn't need to look at the surround so much if you were only "wobbling it" from the centre. And you wouldn't be putting so much strain on the motors in holding up your 'wall'.

If you've got that much space, have you thought of a seriously huge ribbon, etectrostat or other such planar driver - instead of a traditional motor?

I'd suggest that you should look up the way that line arrays generate waves in a room, as this will essentially be a room-width line array.
 
well i have still alot to learn about accoustics...
and i will devote more time to this this winter
( now very busy months )

i seriously want to have it all move forward and back,
since any other type of movements wouldn't help in producing a serious planar wave launch,
and thus would require room modal design and treatments for sub frequencies
( wich i am trying to avoid for now )

the assembly could also lay on some roller bearings or tracks...there is no mechanical limits to this type of driver
wich is basically quite simple

still don't have a clue onto how this driver would create the wave in front of it, and it it would do what i'd like it to do!
 
If you want to move the whole wall, it will need to be stiff or you will get 'cone' breakup distortion... To stiffen the wall will make it heavy, which will mean you will need large motors, and they will need to be very well secured to something heavy like a large lump of concrete... Sounds like something NASA would build, not for HIFI though...


Have you thought of heavily bracing and covering you whole wall in 18" drivers, that would have the effect you are looking for right?

As a rough calc, if you have 64 drivers, it will be up 27db compared to one, and if you pick a driver that can put out say peak 110db at low frequencies, you have 137db and that is before the room gain

DB

:)
 
there shall be not much room gain if i can accomplish some kind of planar waves ..

then, how can one calculate the breakup frequency of a driver ? i guess it is related to the diameter / size vs frequncy of operatino and its stiffness


then , my backup wall will be all concrete as my house construction is ICF ( all concrete forms from floor to flat roof ) so i will have no problem fixing the motors,
and i'd probably be able to take drastic ways to mount them ..i have all the rights to this section of the house!
( basement garage and service room are all mine!! )

64 drivers are a bit too much
my budget is high for this setup ..
but 64 anything at 100$
adds up quite fast ..

i have the CF ressource as we are R&D with carbon fiber right now ..so this is no cost for me

and i am pretty sure that with a mix of mylar and cf frame
i could get out with some very stiff and lightweight structure ... NASA ain't got nothin on me :p


the mechanical part of this don't scare me much,
the accoustical does ... i do not have a clue of the behavior this monster would create

keep in mind it would be used for <100hz only!
 
I think you should just try installing a whole bunch of IB subs into the wall.

Using an entire wall as a speaker diaphragm, while intriguing, is IMHO so experimental that the chances of success are remote.

A "wall" of IB subs will give you so much bass you'll feel like you're sitting inside a 32' organ pipe (with proper amplification, that is).
 
sdclc126 said:
I think you should just try installing a whole bunch of IB subs into the wall.

Using an entire wall as a speaker diaphragm, while intriguing, is IMHO so experimental that the chances of success are remote.

A "wall" of IB subs will give you so much bass you'll feel like you're sitting inside a 32' organ pipe (with proper amplification, that is).


That is what i would like to achieve, of course :)

There was a few threads already on my evergoing system design ..
the only part of the design that i need to completly figure out now is the bass, since it will need to be build within the house's walls ..

so .. it will be IB for sure and will use the garage as the back vent through a fairly large passage ( hidden passage :p )

So now i was up to restudying accoustics to try and grab the basics, so i can better understand the behavior of a multiple arrayed sub-bass system
wich i would like to design, so that it gives a pretty planar wave output

so then i thought about, why not use a big plane, isntead of some separated cone drivers if a planar wave is what i want ..

my goal is to use the HT room as a pipe through wich i will feed the sub bass waves from the front through the seating and be absorbed ( partly or almost totally if i can work it out ) at the end by some 1-3' thick absorber ...

so there came the idea of using a very light stretched diaphragm just like on an ELS
but using real sub driver motors to drive it through some
carbon fiber structure ( probably a mesh of tubes with only 1 prepeg layer for the outside )

wich would then move forward and back through the
regular "magnetic motors"


so the question now is not much if it is possible,
but if it is what i want/need
sure would be spectatular and very entertaining to design

so can anyone provide with the required math ?

can i use hornresp to modelize the required movement for DB ??

i wonder if a lot of mid driver with good motor structures but cheaper front end ( that i'd rip off neway ) would be better than a few sub bass motors ??
could be alot cheaper ( some good motor stuff for 4-6inchers can be found at 25-30$ each .. )
 
ahha ..just played quick with hornresp
model based on dayton IB sub 15"

with 90000cm2 of SD
1W 1mm xmax = 100db@10hz
120db~ from 20hz to 400hz

funny :)

wonder how it would sound at 3-400hz
there are probably other problems that would set in
because of the increased frequencies ..

but neway, this is for 100hz and lower!
 
First off it sounds like you are over stressing the importance of one woofer vs a couple smaller ones, at those low frequencies you wont need to worry about room modes. In addition large woofers (and arrays) should be used at lower frequencies only, the "100hz" is for undersized mids and satellite/sub systems. Also, it sounds like you are going for overkill bass, which is fine. However you don't need a "planar wave" to achieve this since the relative phase difference of low frequency drivers spaced reasonably close is negligible.
Now, if you just want a moving wall for fun, then this is my advice:

start with two layers of standard weave cf oriented at 45 degrees bond those to 6-8" of rigid foam (Insulation?) and then a duplicate layer of cf on the other side. This will make an ultralight and stiff panel, now you have to connect it to motors. I would recommend some load spreaders here, maybe some conical pieces made of plastic or cf and filled with expanding foam and bonded to the panel. For motors I would get some buyout woofers at $10-20 a piece and remove just the dust cap, this will leave the surround and the spider to help keep the vc centered, more on this later.
with the dust cap removed you can bond a tube to the inside of the vc and to the conical load spreaders.
This is unfortunately the easy part, now you have to hang the motors and the planar cone such that the cone can move in and out but not up and down (gravity!) and the motors can be supported but still move with the imperfectly supported cone. The spiders and surrounds that come with the woofers are designed to hold a couple of grams of weight, and will fail with the added mass. To hang the panel and center it I would use a trampoline type setup, a bunch of springs with enough preload to center the panel between floor and ceiling. The surround can just be flexible foam or rubber to seal the edges, a thick foam can increase damping to tune the q-factor, foam/fiberglass can also be bonded between the panel and the back wall for damping(highly experimental).

This is a broad overview of the project, it makes it sound easy. Approaching this project as an engineer, and I have thought about this before, I looked into the details a little bit and it sounds fun and all but it is not an appropriate project for acoustical purposes as it is more for exhibition, conversation and well, fun. You would be better off building an array of IB 15's or 18's maybe 4-8 of them, and believe me this would rock the hell out of any living room.

If you look at Ron's short statement you'll notice it is quite fundamental, what is your goal and how can you achieve it, along with what assumptions you are making as to what requirements need to be met.
BTW Ron E. you sound like an engineer, are you?
 
nunayafb:

thanks for the good ideas....
a compelte CF pannel will have to much weight,
this is the reason why i tought about a CF frame
with stretched mylar sticked to it
and a complete CF frame would cost too much neway,
as i only use prepeg ( wet layup wouldn't give good results in consistency of weight i believe )

this is an idea that i wanted to discuss about,
as my decision is still set on using 16 18" in IB to achieve some kind of good front wall coverage
but if this idea turns out possible to achieve, i'll be seriously thinking about using it as it sounds crazy and fun to try !!

then about engineering ....
( personal opinion here ... )engineers don't often invent or innovate as far as i know, so i tend to try and not think engineer ways or don't rely on engineers to tell me
what we should try as more often you guys are too sticked to reality and fundamentals to be able to see further ( i have engineer employes )
to be able to create something, a team is required
wich is a 2 part..one engineer and one creator/dreamer

Magnetar:
i have already seen this video,
but thanks for reminding me!
it is an impressive setup
but is it innovative? ...
some rich kiddo could've tried that and end up with close results to this engineered semi-trailer :p
 
JinMTVT said:
nunayafb:


Magnetar:
i have already seen this video,
but thanks for reminding me!
it is an impressive setup
but is it innovative? ...
some rich kiddo could've tried that and end up with close results to this engineered semi-trailer :p

Very innovative, He obtained the results no one else could.

I doubt that some kid could come close to these results. It is an engineered tapped horn, not a bunch of woofers mounted on a wall
 
"cf panel is too much weight...."
a panel this large needs to be stiff or what is the point, mylar cannot be stretched tight enough to be of any use as a cone unless the driving force is spread evenly across the surface ie ribbons and planar transducers. Mylar driven by motors will have so many flexure modes that it will produce more distortion than music, and in fact will end up being grossly inferior to separate woofers since those will operate as almost perfect pistons at low frequencies, instead of a "loose" diaphragm panel.

"as for engineers..."
Not creative, have you ever met an engineer? Invention and innovation are all we do, my love for creation and invention are what drove me to engineering school.
And I think you missed my point about the importance of the engineering process, what I was trying to convey to you was that if you approach a job as an engineer you can minimize the number of "wrong turns" you make along the way by focusing on the most important aspects and less on the less important aspects.

If someone hired me to produce bass in their theater/stadium I would not start by inventing a moving wall speaker or anything else, I would start with the equations of acoustics which will enable me to predict the Sd needed to achieve the required SPL at the required distance factoring in room losses and see if existing and purchasable technology will do the job. Now if I was hired to, or desired to learn the effect of really large panel speakers vs line arrays for example then I would design a panel speaker. But the first step in designing a panel speaker is understanding the forces involved and what parameters are needed to achieve the end goal, so instead of saying "I want to use mylar", I would start with what I mention earlier(based on knowledge of stiffness/mass) and analyze it's stiffness and resonant modes using an FEA package. Engineers are not "stuck in reality" we try to do whatever it takes to achieve the end goal, most companies want it to be cheap, which is usually what destroys quality and invention/innovation, not the engineers.

FYI, I plan on building some subs like this one day so dont think Im trying to rain on your parade because I think this would be a fun and challenging project that if done correctly will yield amazing results despite cost and complexity.
 
nunayafb: ok ...again stand corrected!
( but that is all i deserve neway .. i am not very wise...
yet ( hopefully ) )


then let's work together on that!!!

i guess that first step would be to determine if there is any point at all in working on this design of a moving wall ..

the SD is interesting, and if it can be made stiff enough,
it would achieve high spl with minimum movement of the motors wich could equal to better performance
( distortion and efficiency ?? )

my personal goal here is to built the ultimate
( my ultimate ) HT for my new house

after analyzing most possible sub-bass systems,
i stopped on arrayed subs in IB setup
because it seems to give the best performance on all
the different aspects of accoustics

then i read on the double bass array configuration,
cancelling out the front-rear room modes
using a delayed rear mirrored wave ,
since the front was made to approximate a planar wave, that would reduce or remove axial room modes

i do not want to use a delayed rear reversed wave as this would be very expensive with the kind of "big setup" i am after ( budget would suffer in other areas then ... ) but i am/was atracted by the disaperance of perpendicular room modes taken care of by the use of some mirrored front array shelling out a planar wave approximation

this then led me to the idea of using a "plane" at front instead of conical drivers to generate a better planar wave ... having the idea of an electrostat in mind with its "weightless" diaphramg , wich is more or less important here since we are talking about sub bass only design

so is this continuity valid ?
cause if it is not, it will not serve any purpose to go on with that design

i will need to study fluid mechanics and accoustics abit more before i can start to understand how waves propagate from the drivers, and how we could make a planar wave from conical arrayed piston drivers


my guts also tells me ( often correct ) that having a front planar wave pass through the listening spot, clean and loud, can be something desired for HT sub-bass reproduction!!!
it may not have anything more than a regular bass setup, but i do have a feeling of something better...
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.