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Thanks rob13572468, great info!

You appear to really know your stuff. So when are you making our subwoofer :D I have a feeling you could actually pull this off rather well. Perhaps even better then the local stereo shop.
 

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rob13572468 said:
All of the newer high power headunits incorporate switching power supplies that produce an internal "rail" voltage that drives the amplifier (the little 1"x 2" metal box attached to the main headunit by a cable) . this is because the laws of physics dictate that the greatest rms output power available is:

Pmaximum_rms = ( V / ( 2 x 2 ) )2 / R

which at 13.8 volts works out to be around 6 watts per channel (at 4 ohms). so a non switched mode unit can put out a total of 6 watts rms x 4 or 24 watts rms.
...
I agree with your analysis except for a couple of points.
1) You typed the Pmaximum_rms incorrectly. It should be
(V/2)^2/(2*R)
for a sine wave if you assume V is the total voltage range. For the example, this would be 0 to 13.8 Volts = 13.8. Hence, for 4 ohms, you get the roughly 6W maximum power per channel.

2) However, the slimely :mad: marketeers for the head unit manufacturers quote peak power when the amplifier is badly distorting. The limiting case is 100% clipping (still assuming AC coupled - no DC offset to the load), in which case the formula changes to
Pmaximum_rms = (V/2)^2/R
which yields a maximum of about 12 Watts per channel fully distorted, if you don't use a switching power supply to increase the DC power rails.

Of course, in addition to the fuse limiting the maximum amount of power that can be delivered, the DC power supply of the head unit can also limit it. I have seen home amplifiers where the analog amplifier peak power was not limited by distortion of the amplifier part, by rather by the electrical current capacity of the DC power supply. This can sometimes be helped by adding large output capacitors to the DC power supply for short bursts of power. I don't know if car audio head units suffer from this problem.
 

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ChrisH said:
Of course, in addition to the fuse limiting the maximum amount of power that can be delivered, the DC power supply of the head unit can also limit it. I have seen home amplifiers where the analog amplifier peak power was not limited by distortion of the amplifier part, by rather by the electrical current capacity of the DC power supply. This can sometimes be helped by adding large output capacitors to the DC power supply for short bursts of power. I don't know if car audio head units suffer from this problem.
yes, this happens quite a bit with both outboard car amplifiers as well as head units. in the case of the head unit, the typical power supply is a little box about the size of a large pack of chewing gum, naturally placed outboard so as to limit the noise it creates. since a head unit must typically fit the din standard, there is plenty of compromising being done. on the other hand, at least the better manufacturers are now using power supplies in their head units; there are still plenty that do not....
 

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1FASTMX5 said:
Thanks rob13572468, great info!

You appear to really know your stuff. So when are you making our subwoofer :D I have a feeling you could actually pull this off rather well. Perhaps even better then the local stereo shop.
i am actually an embedded electronics engineer by trade, but i did work for many years designing audio systems so luckily i can put my skills to use building cool things worthy of going in a lotus. i am particularly excited about the possibilities with interfacing to the vehicle network but i dont want to say too much just yet... more to come. :D




rob is hard at work learning the innermost secrets of the elise...
 

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rob13572468 said:
rob is hard at work learning the innermost secrets of the elise...
So, from that picture, it looks like Rob is the guy who will tell us what all the custom Lotus CAN bus codes are. Right Rob? :nanner: :bow: :shift:
 

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there is room behind the plastci back behind the seats, and the firewall... I've seen pics of amps installed back there. The elise is small; I don't see how you need rear fill speakers. so, why not use coax in the front, and use the space behind the panel/firewall, plus the stock rear speaker locations, to build a box or even a waveguide type of thing? I'm not technically proficient in this kind of thing, just asking.. I need some sound in my car!
 

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elise seeker said:
there is room behind the plastci back behind the seats, and the firewall... I've seen pics of amps installed back there. The elise is small; I don't see how you need rear fill speakers. so, why not use coax in the front, and use the space behind the panel/firewall, plus the stock rear speaker locations, to build a box or even a waveguide type of thing? I'm not technically proficient in this kind of thing, just asking.. I need some sound in my car!
I think this will work. Rear fill is pretty useless anyway. I will try to:

* fit the biggest coax speakers onto the dash. Another Elisetalker indicates that the MB Quart 5.25 coax will fit.
* remove the entire plastic speaker enclosure assembly behind the seats, and build a fiberglass box hosting two 8" subwoofers.
* fit a 4 channel amplifier in the rear boot
 

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I installed the Clarion SRV 303 sub-woofer under the dash above the passenger footwell. Originally I was going to install it on the plastic panel behind the seats similar to ScottyB but didn't like the idea of having to move the alarm microwave sensor. The sub fits perfectly under the dash.

I used one of the brackets that come with the sub to mount the front of the sub on the underside of the dash with a couple of screws (had to drill 2 small holes). There is also a deep ledge approx 10" long on the right side of the passenger footwell (part of the aluminum tub) that I used to support one side of the sub. I had to make my own support bracket to do this but it was pretty straightforward. I used a door kick plate to fashion a template for the bracket. The kick plate is great for this since it is rigid but easy to bend and form by hand. Since you can't hold the sub in place and form the bracket at the same time it takes a bit of patience to get it right, but since the kick plate is so malleable it's pretty easy. Once I had the template made I did a temporary install to check everything was okay, and then made a heavier duty bracket out of a galvanized post tie, using the template as a guide. It took a couple of tries to get it right since the galvanized metal was not as easy to bend, but in the end it worked out perfectly. I used industrial velcro to secure the side bracket to the ledge. The other side of the sub fits snug against the "swiss cheese" part of the center console and I still have acesss to the sub controls if needed. All in all very secure.

My only concern with mounting the sub under the passenger dash is that it is now right below the heater/AC footwell vents. The air can still flow out of the vents unrestricted, and I doubt that the air will be hot enough anyway to mess up the sub. In addition I rarely have the heating on (So. Cal) and if I do it is usually out of the face level vents. Also, my size 10 feet are not hindered (i.e. do not hit) by the sub when sitting in the passenger seat.

The sub makes a huge difference, and although it's not window rattling bass it is certainly more than adequate for my taste.

I also ripped out the Blaupunkt HU and speakers and replaced them with an Alpine 9833 HU (on sale at Crutchfield) and 5.25" MB Quart Premium speakers in the front and back. Originally I bought 6.5" MB Quart for the rear but although the speakers themselves would fit, the oversize speaker grills (7+") would not due to the contours of the panel. Other 6.5" speakers would fit okay but I preferred the sound of the MB Quart Premium so I went with the 5.25". The fronts are mounted with the woofer & tweeter in co-axial configuration (crossovers behind the HU in the dash - very tight squeeze) and the rears as component (separate) with the crossovers in the foam behind the panel.

Overall the sound is like night and day compared to the Blaupunkt set up, and I'm very happy.
 

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Shot of the ledge (part of the aluminum tub) in the passenger footwell that I used with a home made bracket to secure one side of the sub. I also secured the front of the sub to the underside of the dash tray with a bracket supplied with the sub
 

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This is the side bracket template I made out of a door kick panel. Easy to bend and form but rigid enough to test the sub install. In fact I think the template may have been okay to use as a bracket since the sub actually wedges in place. The sub comes with screw holes and screws to attach the bracket to.
 

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I like that installation. I had actually been considering that myself, but I couldn't try it out because my Elise doesn't arrive for another 33 days. (Waiting Waiting Waiting).

I had also wondered just how much empty space is up inside the dash. I could imagine that if there is some space, then create a custom cabinet that would fit up inside the dash with some 6 inch subs pointing down towards the passenger's feet. I may be way-off base here, but, given I don't have a car yet, I can't test my theory.

Another way to get base that I expect I will do is mount 8 inch shallow mount woofers in place of the stock rear speakers. The will give mid-bass, and I will use 5.5 inch componennt speakers up front (no tweeters in the rear). That will mean widening the hole a bit, but, that is what a Dremel tool is good for. I am looking at the Directed Audio Studio S800 (also known as model 3084). They need less than 2 5/16 inches depth for front mounting and a 7 1/8 diameter hole. The depth doesn't seem to be a problem, but I have been able to look to see if the little bit of extra diameter is going to be a problem. If these 8 inch woofers work out as well as I hope, then I may not have need for a sub. Now that you have done the install of the rear speakers, could you comment on the feasibility of this 8" scheme?

I am still debating putting a Clarksynthesis Tactile Sound Transducer TST239 (ClarkSynthesis ) attached to the driver's seat. (Much better approach than the Aura bass shakers or the ButtKickers.) That way I can get good physical sound feelings and conductive hearing without having to crank up the audio bass.

I'm driving my wife nuts will all my little techno (and non-techno) projects. I keep getting "Why do you want to modify a perfectly good NEW car?". She just doesn't understand. And well, maybe neither do I, but I am driven to improve. :shift: Well, at least she puts up with me. I can be a bit of a rollercoaster ride in life (fun fun fun, if you don't fight it)
 

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elise seeker said:
what is better about the clarks? meant for mounting directly to the seat rather than chassis?
Frequency response, doesn't continue to ring like the others, and some other nice things. Clark's website has some good technical information on what to look for in a tactile transducer.
 
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