Foam board speakers / exciters ???

[TubeHiFiNut]

Reminds me of the Bertagni speakers from the 70s.

 

Images borrowed from the Internet.

[hsosdrummer]

In the mid-2000s I worked at Sonance, writing their installation and user documentation. While I worked there they purchased all of the Bertagni patents and technology and even the services of Alex Bertagni for a few years.

 

This arrangement began a couple of years of R&D, the end result of which (and the ultimate expression of Alex Bertagni's original idea) was Sonance's Invisible Series of speakers, which are installed by cutting out a section of drywall, installing the speaker into the cavity and blending the speaker's flat front diaphragm with the drywall until it is undetectable. (Technically it's still visible.) This requires the services of experienced drywall and painting craftspeople, but when properly installed the speakers are indeed 100% completely undetectable. 

 

For anyone interested, here's a link to their latest incarnation: http://www.sonance.com/in-wall-in-ceiling/invisible-series/invisible-series

[karlson3]

and related were the Polyplanar speakers - I bought one as below in the late 1960's and loaded it into a bass reflex - the aluminum center cap was "tizzy" and motor strength - weak

 

[Emile]

15 hours ago, TubeHiFiNut said:

Reminds me of the Bertagni speakers from the 70s

Yes! Those speakers are often referenced by "better" designers  

[CECAA850]

16 hours ago, Emile said:

OK; ordered some exciters from PartsExpress and carbon fiber from another place ... picking up honeycomb panels from a local fiberglass shop   (Haha ... did not want to screw around with cheap styrofoam panels ... what's another couple of dollars for a hi-fi nut  ) Will post some results in the next couple of days.

Cheers, Emile

Looking forward to it.

[Emile]

13 hours ago, hsosdrummer said:

Sonance's Invisible Series of speakers, which are installed by cutting out a section of drywall, installing the speaker into the cavity and blending the speaker's flat front diaphragm with the drywall until it is undetectable.

Very interesting. Thanks  But ... not ready to break down walls  

[Emile]

11 hours ago, karlson3 said:

Polyplanar speakers - I bought one as below in the late 1960's

Awesome!  

[Emile]

Some technical info. NXT (New Transducers Ltd) was one of the pioneers in this field. Of particular interest is their 1995 US patent https://patents.google.com/patent/US6904154 which provides quidelines for panel size and exciter locations.  Recommended panel sizes are 1.134/1, 1.37/1 and 1.41/1. Exciter locations on 4/9th, 3/7th and 5/13th (x/y locations should not use the same node line for x,y). Preferred exciter mounting is on a fixed frame with the exciter then being glued to the panel.

 

Interesting because I've read hundreds of pages on various forms ... 99.9% of people just use scrap pieces of wood or foam and slap an exciter onto it ... guessing at sizes and locations   ... it is utterly amazing that they still seem to get decent results   

 

OK; waiting for my stuff to arrive  

[Dave1290]

23 minutes ago, Emile said:

OK; waiting for my stuff to arrive

Welcome back my friend!  Since your wife is now home I think you'd better cancel that order!   😂 😂 

[Emile]

12 minutes ago, Dave1290 said:

Since your wife is now home

Haha ... she left this morning to visit her mom for a week ... I can "play" now  

[Emile]

OK; got carbon fiber veneer panels (4 x 12*33 inches) and a 1/4" honeycomb panel. Cut one piece to 12x16.44 inches and glued it ... pain in the azz ... one pass through the carbon fiber and the utility blade is dull ... heavy duty glue does not spread ... will check it when it's dry tomorrow ... obviously not as easy as I thought  

 

Thought I had it all figured out ... use oversize carbon fiber and glue it to a frame ... then attach (glue) a (smaller) honeycomb panel to it and attach the exciters.  Nah  ... need a carbon fiber "sheet" (impregnated with resin) to attach to the panel   OK; we'll see what happens to my first test section  

 

Cheers, Emile

 

 

[Emile]

OK; no clue yet   Carbon fiber panels with honeycomb material are still in the press ... ok; between two pieces of wood with three clamps  So' measured my Cornwall's (yes; very bad placement; back wall speakers) vs exciters just sitting on top of small cardboard boxes   Cornwall's are "blue," exciters "brown." Obviously no "bass" from the exciters as expected, but reasonable (?) across mid-range. Any thoughts? 

 

 

PS, very interesting, but certainly not hi-fi (sofar)  

[Emile]

OK; tried my 12x16.44 inch carbon fiber panel with a single exciter ... actually pretty impressed  

Here is a frequency plot ... "red" my Cornwall's for comparison ... "blue" one exciter on carbon fiber plate ... "green" two exciters without a panel.  Really no clue if it means anything, but sound is pretty amazing (actually sounds "clean") with just one exciter on the carbon fiber panel. OK; making a second panel (pain in the azz ... takes 2 days  )

Cheers, Emile

 

[Emile]

Still experimenting ...  

 

[Emile]

Yeah ... stereo  Have some crazy ideas on how to fit this onto a frame ... getting supplies tomorrow ... stay tuned  

 

[garyrc]

IMO, your CORNWALL should look better.  Results vary with graphs, but there is no way the response should be down by 12 to 15 dB (compared to 1K) above about 8K, unless the mic was way off axis, or you are measuring from inside a pillow.

 

[Emile]

11 minutes ago, garyrc said:

Results vary with graphs, but there is no way the response should be down by 12 to 15 dB

Thanks garyrc  Still "new" to measuring   Have not found a good way to set (relative) measurements between speakers equal.   OK; trying again (tomorrow)   

 

PS ... love the pic  

[Emile]

@garyrc ran a frequency test on my Cornwall's again ... now it looks a lot worse   Mic place equidistant from speakers ... any advise? 

Many, many thanks, Emile  

 

add-on ... my CW's are not in a "great" location. Back wall; partially blocked by furniture  

[Emile]

Oops ... had my Carbon Fiber test speakers on   Cornwall's below ... still no clue  

 

[garyrc]

43 minutes ago, Emile said:

Oops ... had my Carbon Fiber test speakers on   Cornwall's below ... still no clue  

 

 

• Put microphone where the center of your head would be (the Main Listening Position, MLP), and point it at ONE Cornwall; test them one at a time -- turn the other one OFF, somehow.  To avoid blowing up your speakers, be sure all of your amplifiers are OFF before unplugging an RCA plug or an interconnect, if that is the only way you can turn off one speaker.  Don't plug one in with an amplifier on, either!  So, with just one Cornwall on, aim the mic right at the speaker with no furniture or anything else in the way, and no reflective coffee table to bounce some stray treble into the mic.   Most people would say that you should be able to look down the throat of the tweeter from the MLP, at least that's what Klipsch used to say. 
• REW has the following important adjustments: 1) a way to enter your microphone calibration into REW, so it knows what it's dealing with.  2) A way to set REW up so it is correct for a mic aimed right at the speaker (the method outlined above) OR a mic aimed straight up at the ceiling -- usable with an omnidirectional mic only).  Although many people prefer the mic-aimed-at-the-ceiling method, with REW set that way, I don't.  a) You don't listen that way, b) If your ceiling is weird, how do you factor that in? c) If you have a shiny backed recliner (e.g. leather) you will pick up all the reflections from that, which, during actual listening your ear structure will partly block.  Either way should get you results that are approx. comparable to the others on the forum (which are still in your future😁).
• In any case the mic should be ON AXIS, IMO.
• If your Cornwalls are anything like the older Cornwalls I'm familiar with, you should get about +/- 5dB or 6dB or 7 dB above Schroeder (in my room, 144 Hz); below that, everything goes to Hell in a Handbasket in most rooms, unless one uses room treatment, &/or bass traps &/or electronic room/speaker correction.  Your curves are in said handbasket all the way to the top, with variation in the neighborhood of +/- 12 dB -- or more -- above your probable Schroeder (a guess).  With the room corrections mentioned, you should get +/- 2.5 dB or so above Schroeder, and maybe +/- 3 full range, if you are very lucky.  IMO, your tweeter's plot should cross the 0 line for the final time about 12K, 13K, ... 15K, and be no farther than 5 dB down somewhere between 15K and 20 K.  Another guess.
• Adjust your left hand dB scaling (on the ordinate) to 5 dB increments.  You have 20 dB increments now.  I don't know what smoothing you're using, but people often use 1/6th octave.  If that is too depressing use 1/3 smoothing.