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Focal TBM beryllium help want a back chamber
Focal TBM beryllium help want a back chamber
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Old 15th September 2021, 09:05 AM   #11
GM is offline GM  United States
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You're welcome!

From down low to 'x' HF point defined by its VC diameter, all point source drivers are pistonic, so if both have 1" VCs, then both will be pistonic till ~ 13543/pi/1 = ~ 4311 Hz.

This is normally pretty obvious in the response plot as a notch, but is ~ centered in the ~ flat, drawn out 'm' shape in the response, so guessing the 'M' shaped dome is responsible, though judging by its off axis response, not much, if any, different than a dome except way up high where its shape is causing some severe eigenmodes across it [series of big peaks/dips], though with zero info on the Stevens I can't comment on it beyond it's probably a generic mobile audio design.
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Old 15th September 2021, 09:23 AM   #12
wesayso is online now wesayso  Netherlands
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Car audio, right? where are they placed and where are they aimed at?

Making a printed back chamber could give you some aiming opportunity.
I used Vifa ring radiators in my door cards, a tweeter not known for wide dispersion. So I made a small waveguide slightly aimed to match left and right off axis angles... smoothly shaped to limit diffraction.

Focal TBM beryllium help want a back chamber-xt25pod-jpg
Tweeter is XT25 SC90-04

I had it printed at Shapeways with SLS. Not cheap but better quality and more durable than with home filament printers.
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File Type: jpg XT25pod.jpg (180.4 KB, 35 views)
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Old 15th September 2021, 01:44 PM   #13
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by wesayso View Post
Car audio, right? where are they placed and where are they aimed at?

Making a printed back chamber could give you some aiming opportunity.
I used Vifa ring radiators in my door cards, a tweeter not known for wide dispersion. So I made a small waveguide slightly aimed to match left and right off axis angles... smoothly shaped to limit diffraction.


Tweeter is XT25 SC90-04

I had it printed at Shapeways with SLS. Not cheap but better quality and more durable than with home filament printers.
Aye thanks for the help.... yes I think this is what I want

I went to bed thinking what the others were saying.... woke up , and I was like ... the stevens tweeter has this little lip on it ..... I wonder if... then your post...

Of course thatís it.... yes. That lip is a tiny wave guide. The focal doesnít have that... I just need to make one.


So there pushed way far back into the dash board (yes a car!) and the focal is shooting HF into the glass...and I can hear it reflect and pull the image. Idk why I didnít think of that... (which another person gave me half the clues)


So... if this tweeter shape wonít let me put a 1Ē waveguide and the shape of the tweeter is not round but a bit oval.... so will I make a bigger flare or put it over the hole...


Could I just make a small ring out of acrylic and round all edges and place it around the dome....

That way I can keep the aesthetics. It only needs to narrow the top frequencies
And a back chamber should let it play lower without impedance problems in the crossover.....???

How will the waveguide change the impedance? Will eq fix any subsequent peaks ?
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Old 15th September 2021, 01:48 PM   #14
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by GM View Post
You're welcome!

From down low to 'x' HF point defined by its VC diameter, all point source drivers are pistonic, so if both have 1" VCs, then both will be pistonic till ~ 13543/pi/1 = ~ 4311 Hz.

This is normally pretty obvious in the response plot as a notch, but is ~ centered in the ~ flat, drawn out 'm' shape in the response, so guessing the 'M' shaped dome is responsible, though judging by its off axis response, not much, if any, different than a dome except way up high where its shape is causing some severe eigenmodes across it [series of big peaks/dips], though with zero info on the Stevens I can't comment on it beyond it's probably a generic mobile audio design.
The stevens is hardly generic lol

Itís made by Eric stevens , he designs speakers for a whole bunch of high end manufacturers. His horns are world famous for car audio and they are absolutely stellar drivers , I posted a link to the Facebook page that has specs. Just click read more to see specs
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Old 15th September 2021, 01:50 PM   #15
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by GM View Post
You're welcome!

From down low to 'x' HF point defined by its VC diameter, all point source drivers are pistonic, so if both have 1" VCs, then both will be pistonic till ~ 13543/pi/1 = ~ 4311 Hz.

This is normally pretty obvious in the response plot as a notch, but is ~ centered in the ~ flat, drawn out 'm' shape in the response, so guessing the 'M' shaped dome is responsible, though judging by its off axis response, not much, if any, different than a dome except way up high where its shape is causing some severe eigenmodes across it [series of big peaks/dips], though with zero info on the Stevens I can't comment on it beyond it's probably a generic mobile audio design.
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Originally Posted by 5th element View Post
The main thing that affects the focals dispersion is that it's a metal dome. Fabric domes breakup in the upper octave and this gives them better off axis response. I'm not entirely sure what to expect from the inverted dome of the focal though.

Metal domes usually have phase shields in front of them, for protection and for improving their off axis response. The focal Be dome doesn't have this. You could try tilting the treble up to add some sparkle and see if that helps.
I want to narrow the dispersion. Above 5khz
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Old 15th September 2021, 09:16 PM   #16
GM is offline GM  United States
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Originally Posted by Oabeieo View Post
The stevens is hardly generic lol

Just click read more to see specs
OK, never heard of him, though lost interest in DIY mobile audio after DIYing a [4 chnl], somewhat Quadraphonic full-range system + [sub] woofer in my late wife's then brand new 'loaded' '70-1/2 split bumper Camaro SS.

It's performance was so far above what folks were doing at the time, especially after installing a Cadillac VHS tape system later on, that 'we' often paid more attention to the music than the driving to the point where all I was able to salvage was the tape deck and its super rare [I was told after ~giving it away] rear axle/disc brake system; so between our experience and the ongoing obnoxious 'boom-box' cars of today, two good reasons IMNSHO to severely govern the performance of such systems.

Regardless, without any useful info to answer your question [T/S specs, response plots with off axis measurements and/or polars], no way but to assume a generic ~1" mobile audio dome tweeter and now knowing its app/location, my 'knee - jerk' WG response was the most correct solution.
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Old 15th September 2021, 11:03 PM   #17
Oabeieo is offline Oabeieo  United States
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OK, never heard of him, though lost interest in DIY mobile audio after DIYing a [4 chnl], somewhat Quadraphonic full-range system + [sub] woofer in my late wife's then brand new 'loaded' '70-1/2 split bumper Camaro SS.

It's performance was so far above what folks were doing at the time, especially after installing a Cadillac VHS tape system later on, that 'we' often paid more attention to the music than the driving to the point where all I was able to salvage was the tape deck and its super rare [I was told after ~giving it away] rear axle/disc brake system; so between our experience and the ongoing obnoxious 'boom-box' cars of today, two good reasons IMNSHO to severely govern the performance of such systems.

Regardless, without any useful info to answer your question [T/S specs, response plots with off axis measurements and/or polars], no way but to assume a generic ~1" mobile audio dome tweeter and now knowing its app/location, my 'knee - jerk' WG response was the most correct solution.

I imagine you probably had some passive time alignment using hundreds of resistors amd caps and coils (lol) :-p kidding

That sounds like a fun car to do a system in , I would love to have one with under dash horns and some 8s in the kick panels !


Yeah so i put some foam on the glass right above the tweeter and itís a million times better ...

I think , Iíll actually just leave it now and do a custom mount that recess the entire tweeter into the dash , on axis , so itís 90deg plane is blocked from glass , I think then it will be just fine ,

I super appreciate everyoneís help and ideas!!!!

Itís sounding really good !!!
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Old 16th September 2021, 12:31 AM   #18
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No, 1st order two ways physically aligned 'close enough' using a Radio Shack horn + 5.25" 'full-range' driver and yes, the under dash horns were real crowd pleasers, both in its 'strangeness' and especially its 'life-like' presentation that drew them to it.

I would have used 8", but not enough space front or back to keep them close to the offset horns. Front-to-back 'balance' was a pair of 'high' power adjustable pots and the sub's XO was from a magazine [pg 56/62]: https://worldradiohistory.com/Archiv...cs-1970-06.pdf

I forget the rest of the components used, an 'all things electronics guru' friend that talked me into doing it found them at the local junkyard, mod/install them.

Cool! Yes, one can work wonders with damping, but assumed blocking the windshield/windows in any way wouldn't be legal.
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Last edited by GM; 16th September 2021 at 12:36 AM.
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Old 16th September 2021, 01:55 AM   #19
Oabeieo is offline Oabeieo  United States
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No, 1st order two ways physically aligned 'close enough' using a Radio Shack horn + 5.25" 'full-range' driver and yes, the under dash horns were real crowd pleasers, both in its 'strangeness' and especially its 'life-like' presentation that drew them to it.

I would have used 8", but not enough space front or back to keep them close to the offset horns. Front-to-back 'balance' was a pair of 'high' power adjustable pots and the sub's XO was from a magazine [pg 56/62]: https://worldradiohistory.com/Archiv...cs-1970-06.pdf

I forget the rest of the components used, an 'all things electronics guru' friend that talked me into doing it found them at the local junkyard, mod/install them.

Cool! Yes, one can work wonders with damping, but assumed blocking the windshield/windows in any way wouldn't be legal.

Iím a fan.... Iíve been in car audio since 1987 , Iíve seen some old installs that were completely unthinkable.... yours sounds like it was amazing for its time
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