Rear Center Console

[blue missile]

I got the shop turned back around to wood working, so the rear console was first.
Because I have gone to alot of trouble to insulate the trunk from the passengers compartment, sticking any sort of speakers back there makes no sense. Come to think of it sticking speakers back there never made any sense to me if you had a back seat.
Also while I will have a very nice sound system, I will not be putting thousands of watts into this small space.
I have aquired 2-6"x9" triaxiels for the package tray, 2-4" Bi's to replace the 4"x10"in the dash, and 2 -4" Bi's for the door panels, Im not inclined to put speakers in the kicks.
All of those are fairly straight forward.
For the Sub-Woofer frequency range I will be running 1-6.5"MB-Quart. For you speaker guys it has an Fs=34Hz.
It only takes 150Watts RMS, and will out perform 3-12" 150Watt speakers.
One of the things I have been doing for the past 20 years is designing and building large front of house systems say for 250 people and up.
The secret to getting great sound, is efficiency.
There is a design called a folded horn that if built correctly will produce 5 times the SPL at 30% of the Wattage using a conventional box.
Now there are folded horns and there are folded horns, what makes one efficient is the lack of square corners and a proper horn flair for the frequencies desired. The ones I build are based on a design called "snails". A pair of subs for large venues takes 60 hours to produce.
The single cabinet I made for the car took 16 hours.
They are a real PITA to make which is why you cant go out and buy them.
Here are the pics, first is the pile of parts for the one box, next is the bottom, then the throat and duct assembly, then one side with the bottom & back attached showing the gussets for the corner pieces. the next three are views with the final side missing and then one of it in place.
I will paint it black, cover the exterior in carbon and put a padded arm rest in place in between the seats
Andrew

 

[rumblefish360]

Nice! A guy that understands sound and can work with wood. Sweet!
It's amazing what people will do with speakers and power amps with crap results.

 

[dustermaniac]

I applaud all your work and efforts and especially your innovation you are putting into the Missle! This car will be a one of one when you finish it up!!! Keep up the good work!!! _ Tom (maniac)

 

[mopardrt]

looking great as always cant wait to see this car done

 

[Tony Fields]

That looks like brain surgery to me :thumbup::thumbup:

 

[FISHBREATH]

Andrew, is there a calculation to be made regarding the distance between the speaker cone and the nearest solid surface? I am thinking of interference waves and pressure wave reflection back onto the cone. I do not know acoustics; just asking.

 

[blue missile]

In a 'loaded' system, the throat is physically as close as possible to the driver. That second 'ring' around the opening is for the flexible surround to operate within. The diameter of the opening is roughly the radius of the driver.
In the larger enclosures there is even something called a 'phase plug' which further restricts air movement and loads the driver even more. The depth of the acoustic passage is usally equal to the radius of the throat and flairs out in width first then in both directions. The design does not allow for reflected sound to get back to the driver. The ports cause the sound created by the rearward movement of the cone to have to travel twice the distance as the original sound and enter the horn behind the original sound further reinforcing it.
The reason you go to all the trouble of eliminating hard corners is to minimize the reflected sound within the 'air stream'
The other reason you create one large horn is to emphasize the low frequencies, the higher ones self cancel against the walls of the horn.
Does that help?
Andrew

 

[rumblefish360]

LOL, I think diagrams and arrows would be the way to go.
I needed them when I read my first basic sound book. It was a radio shack edition on who to build your own speakers. It covered the basics and a few math formulas to work out box & tube sizes. Told you what the numbers ment when you purchased speakers 1 by 1 for a custom system. Can't find that book now though.

 

[player1up]

I always look forward to seeing "what's next" for the Blue Missile! Andrew, I'd ask what you can do, but I'm guessing the "what you can't do" would be a much shorter list. :cheers:

 

[blue missile]

A quick update, no arrows and diagrams just data.
I put a driver in that a fellow FABO member got for me out of SA. While the enclosure worked as expected the driver did not. As it turns out what the Germans call a woofer doesn't make it so.
For you audio guys:
I re-crunched the numbers for the driver and while the Fs looked good @34Hz, the Vd did not.
I know for the rest of you VD is never a good thing:toothy10:
Vd in the audio world is the volume of air the driver moves per cycle.
So I ordered a driver with a Vd 4 times the original.
To help load the new driver I did install something called a phase plug. This restricts the flow by roughly 60%.
Pic attached.
Ill let you guys know how the new set up sounds when the driver arrives.
Andrew

 

[FISHBREATH]

Thanks for the info, Andrew. There is sure a lot to learn about acoustics.