My buddy just acquired a Porsche 356 Speedster kit car. He told me he wants to have a great sounding stereo that will be loud enough with the top down. He was looking in a Crutchfield catalog and was thinking of going the standard door mounted route but I stopped him and threw the catalog away. This car has a rather large and open firewall between the front trunk area and cockpit, its rear engine. The only thing on the firewall are the pedals and steering column on the drivers side, nothing on the passenger side.
I envisioned where feet will go and it seems like the most logical way to arrange the drivers is a vertical MTM on both left and right outside edge of the firewall, sorta near the kickpanel area, and a woofer just inside of it high enough off the floor that feet won't hit it and clear the pedals and steering column. Any necessary enclousure would be very easy as the trunk is on the other side.
Has anyone done an MTM arrangement in a vehicle either on the door or otherwise? Driver selection can some later if this doesn't have any inherent flaws I'm missing.
I envisioned where feet will go and it seems like the most logical way to arrange the drivers is a vertical MTM on both left and right outside edge of the firewall, sorta near the kickpanel area, and a woofer just inside of it high enough off the floor that feet won't hit it and clear the pedals and steering column. Any necessary enclousure would be very easy as the trunk is on the other side.
Has anyone done an MTM arrangement in a vehicle either on the door or otherwise? Driver selection can some later if this doesn't have any inherent flaws I'm missing.
Neat project.
I hope the car was properly equipped for fun. If not, it looks like you can help him out with that, too!
As far as I remember, MTM's gained momentum in the mid 80's in D'Appolito form. This used odd order crossovers and the MTM arrangement to control the polar response of the system.
In a car, the advantages of vertical symmetry are lost. However, there are no incompatibilities or reasons to stay away from an MTM if it fits well. MMT or TMM would be just as viable if the tweeter doesn't get cramped into a poor location.
I would suggest that if you're choosing between, say, a single 6" midrange and a pair of 4", that the 6" would be a better choice in terms of output to compete with wind and road noise. Simply put, larger will likely be better in this case.
Been a long time since I looked inside a 356. Is the firewall open to the trunk where the woofers will be located, so that they're using the trunk as an enclosure?
BTW, I almost did an MTM in the kick panels of my Alfa Spider many years ago. The front edge of the kick panel was wide enough for a 4", and there looked to be a half a cubic foot of enclosure space behind it. Perfect.
I didn't follow through because the engine already made beautiful driving music.
Maybe your friend just needs some good headers and a set of hot cams and big carbs?
I hope the car was properly equipped for fun. If not, it looks like you can help him out with that, too!
As far as I remember, MTM's gained momentum in the mid 80's in D'Appolito form. This used odd order crossovers and the MTM arrangement to control the polar response of the system.
In a car, the advantages of vertical symmetry are lost. However, there are no incompatibilities or reasons to stay away from an MTM if it fits well. MMT or TMM would be just as viable if the tweeter doesn't get cramped into a poor location.
I would suggest that if you're choosing between, say, a single 6" midrange and a pair of 4", that the 6" would be a better choice in terms of output to compete with wind and road noise. Simply put, larger will likely be better in this case.
Been a long time since I looked inside a 356. Is the firewall open to the trunk where the woofers will be located, so that they're using the trunk as an enclosure?
BTW, I almost did an MTM in the kick panels of my Alfa Spider many years ago. The front edge of the kick panel was wide enough for a 4", and there looked to be a half a cubic foot of enclosure space behind it. Perfect.
I didn't follow through because the engine already made beautiful driving music.
Maybe your friend just needs some good headers and a set of hot cams and big carbs?
The "firewall" is solid and maybe not technically the "firewall" as the engine is in the back. The fuel tank is in the trunk but I'm sure it can all be positioned to work.
I was just amazed at how much open space there was as the dash does not extend down very far like most cars. I sat in one of the temporary seats and put my feet where they would normally go which left alot of area, plenty of room for multiple drivers and large ones if necessary.
An MTM is not designed to work in this type of environment but it would fit perfectly so it came to mind. We have time to think about it as he has other assembly to accomplish. He is reluctant to cut holes in the door panels so he was happy to hear my idea.
He's gonna run a stock bug engine which is pretty mild and wimpy. I hope it has enough horsepower to turn the alternator and power an amp. Otherwise I'll suggest he get a battery powered boom box so as to not kill the engine.
I was just amazed at how much open space there was as the dash does not extend down very far like most cars. I sat in one of the temporary seats and put my feet where they would normally go which left alot of area, plenty of room for multiple drivers and large ones if necessary.
An MTM is not designed to work in this type of environment but it would fit perfectly so it came to mind. We have time to think about it as he has other assembly to accomplish. He is reluctant to cut holes in the door panels so he was happy to hear my idea.
He's gonna run a stock bug engine which is pretty mild and wimpy. I hope it has enough horsepower to turn the alternator and power an amp. Otherwise I'll suggest he get a battery powered boom box so as to not kill the engine.
Open firewall? Need for lots of undistorted volume? This car sounds like it's begging for horns up front 
http://www.audiojunkies.com/blog/1072/image-dynamics-releases-new-horns-for-2008
Either ID or USD, Illusion Audio, or Veritas.
They'd need to be actively bi-amped with a fair amount of EQing, but they sound like they'd be perfect for that kind of install.
Rear engine would also lend itself well to a front-mounted IB sub
http://www.audiojunkies.com/blog/1072/image-dynamics-releases-new-horns-for-2008
Either ID or USD, Illusion Audio, or Veritas.
They'd need to be actively bi-amped with a fair amount of EQing, but they sound like they'd be perfect for that kind of install.
Rear engine would also lend itself well to a front-mounted IB sub
Well, with a beetle engine it'll still be true to 356 form and fun if he tosses it around! I hope it's a 1600...
I've never looked closely at a kit, does it use a stock VW pan?
I can only remember working on one 356, a very nice coupe, probably 20 years ago for an upholstery shop that specialized in European cars. There was no problem with tight working quarters.
Stay with a moderate power amp and there shouldn't be any alternator issues. There's really nothing else for it to power.
BTW... 901's? Aren't they a bit scarce?
I've never looked closely at a kit, does it use a stock VW pan?
I can only remember working on one 356, a very nice coupe, probably 20 years ago for an upholstery shop that specialized in European cars. There was no problem with tight working quarters.
Stay with a moderate power amp and there shouldn't be any alternator issues. There's really nothing else for it to power.
BTW... 901's? Aren't they a bit scarce?
IMO there is no need for double set of mids. Just get a great pair 6'' mids that can take 150W Rms each (look at Morel raw drivers) and build a sealed or aperiodic enclosures in kick panels. You can place 1'' dome tweeters in kick panels crossed at about 2 khz and another set of tweets in solar panels crossed at 3-5khz to draw the soundstage up. Use space in the the trunk to make sealed fiberglass enclosure for the sub facing the cabin through firewall. This should sound really good 
So is it better to have the drivers facing inwards or facing backwards towards the occupants? I realize kick panel mounting usually involves angling the drivers for proper imaging.
I'd like to use full range drivers and cross to a tweeter much higher out of the telephone band like say 8khz or so. The doubling up of a mid/fullranger will overcome inefficiency. A 6" is wider than what I had in mind but I'll take another look and see. A single centered sub is also a possibility as long as the main drivers can cross low enough.
Horns would fit too as they are nice and thin, I'll have to give that some thought as well. Surely its possible to build my own horns to fit if the orientation of the driver is not ideal on the premade items. I'd also prefer one that could cross to a woofer or subwoofer, good down to say 100hz.
The engine is a 1600 dual port and he may even go with a dual carb set-up! Woo Hoo, what is that now 70hp instead of 60hp? It should be able to power an amp no problem though and is so light it will still be plenty quick. This kit is on its own custom tube chassis, not a Beetle pan. Which 901's were you referring to as being a bit scarce?
I'd like to use full range drivers and cross to a tweeter much higher out of the telephone band like say 8khz or so. The doubling up of a mid/fullranger will overcome inefficiency. A 6" is wider than what I had in mind but I'll take another look and see. A single centered sub is also a possibility as long as the main drivers can cross low enough.
Horns would fit too as they are nice and thin, I'll have to give that some thought as well. Surely its possible to build my own horns to fit if the orientation of the driver is not ideal on the premade items. I'd also prefer one that could cross to a woofer or subwoofer, good down to say 100hz.
The engine is a 1600 dual port and he may even go with a dual carb set-up! Woo Hoo, what is that now 70hp instead of 60hp? It should be able to power an amp no problem though and is so light it will still be plenty quick. This kit is on its own custom tube chassis, not a Beetle pan. Which 901's were you referring to as being a bit scarce?
Personally, I'd prefer a mild inward cant to lessen off-axis issues.
The automotive horns have a lower limit in the 800Hz-2kHz range depending on the model and crossover slope used. You'd still need a mid. A 100Hz horn would likely be prohibitvely large for a car.
70HP? That would make it a Speedster! On a tube chassis at that, very cool.
I was referring to the first run of 901's that were actually labeled as 901, not 911. Ohhhh, silly me. All this Porsche talk has me confused... Bose, now I get it.
The automotive horns have a lower limit in the 800Hz-2kHz range depending on the model and crossover slope used. You'd still need a mid. A 100Hz horn would likely be prohibitvely large for a car.
70HP? That would make it a Speedster! On a tube chassis at that, very cool.
I was referring to the first run of 901's that were actually labeled as 901, not 911. Ohhhh, silly me. All this Porsche talk has me confused... Bose, now I get it.
I found this site trying to figure out how to make a passive crossover for a pair of Bose901 I purchased rather cheaply, actually a trade for an irrigation pump. I'm now addicted to all of the info and builds the members here do and all of the other discussions that I only half way understand.
Yes, the 911 was originally supposed to be designated the 901 but Peugeot beat Porsche to it. Ironic that the 911 is still such a fantastic car where as Peugeot is unheard of except for Rally racing. Such is life.
This project is gonna be a bit slow going as he has 3 small kids, a wife and a job that get in the way so as long as I can keep him from buying any off the shelf crap and convince him to do it my way it will work out ok. I need to get a more accurate picture of what space he will have available once the pedals are in so I know what we are working with.
Yes, the 911 was originally supposed to be designated the 901 but Peugeot beat Porsche to it. Ironic that the 911 is still such a fantastic car where as Peugeot is unheard of except for Rally racing. Such is life.
This project is gonna be a bit slow going as he has 3 small kids, a wife and a job that get in the way so as long as I can keep him from buying any off the shelf crap and convince him to do it my way it will work out ok. I need to get a more accurate picture of what space he will have available once the pedals are in so I know what we are working with.
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Macrom SE-TV28 tweeters
Macrom 58.10 Midranges
Macrom 59.17 Woofers
(Morel made components)
That is simply beautiful, and there is still room for occupants. Do you run a subwoofer as well or are the two door woofers enough? What frequency do you cross the two woofers and the MTM unit over?
Nice work. I'm sure it sounds great!
So would the midrange be equivalent to the 4" Morel, or are they smaller?
Neat project, I'd be wanting to try an IB sub for sure. Anyway just thought I'd suggest some guys are talking about coax, but not auto made coax. They are running the ones from seas, hi-vi, and the like.
A BP box could work, but without large midrange/midbass they have such a narrow band.
You can run something like an icepower alpine pdx 4ch its all class d takes less power.
Otherwise my old rule is go larger drivers for more sound. When I was installing in boats (offshore vees) I'd always try for two pair of 6x9 to start with and 7x10 were better yet....could get away without subs with four of those. Open air sound is different than closed car, no doubt about it. (lot of them didn't want subs due to extra weight and lack of room.) It sounded a lot like a very good dj/sound system in a smaller bar.
A BP box could work, but without large midrange/midbass they have such a narrow band.
You can run something like an icepower alpine pdx 4ch its all class d takes less power.
Otherwise my old rule is go larger drivers for more sound. When I was installing in boats (offshore vees) I'd always try for two pair of 6x9 to start with and 7x10 were better yet....could get away without subs with four of those. Open air sound is different than closed car, no doubt about it. (lot of them didn't want subs due to extra weight and lack of room.) It sounded a lot like a very good dj/sound system in a smaller bar.
Currently i dont run a sub, but i plan too look into it as soon as some substensial work to the car itself are finished (suspension and brake repairs)
The problem with this car (85 929 (Cosmo) Coupe are that the gas tank steals as much luggage space in the trunk as a large sub box would do, so a quarter panel installation migth be a solution.
X over betwin tweets and mids are 3200hz/18db oct and betwin mids and woofers are 200hz/18db oct
I use a Alpine CVA-1000 with a PRA-H400, so i have on screen adjustment for x over frequenzies and time correction
The speakers are powered with a RF 400x4 wich feeds the tweets 50Wrms each
and the mids 50Wrms each (100W a pair due too 2ohm load)
The woofers are powered with a RF 200x2 @ 100Wrms each (200Wrms a pair due too 2 ohm load)
They are identical too Morel car 4"`s (i belive their outside dia are 102mm) but have a sligthly smaller flange than Morel home versions
An externally hosted image should be here but it was not working when we last tested it.
Inner baffle with cutout for mids
An externally hosted image should be here but it was not working when we last tested it.
Mids are sandwiched betwin inner and outer baffle (grills are sligthly smaller than the mids themselves)
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You have some pretty serious money tied up in those kick panels!
4" midrange with 2" voice coils? I assume they easily deal with 50W each.
901Fixer:
With 6" Morel woofers, you could bypass the mids and use a stout tweeter that can reach 2kHz or so. Those woofers are good down to about 50Hz and handle (also require) hefty amounts of power.
Or the 4" Morels in MTM with a larger woofer or two would be reasonable.
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