E30 Audio Overhaul - My Project Details

[rooster]

I don't know what's going on here but I like it.

im with danny... nice looking boxes

[reelop19]

As soon as you mentioned canoes I got a whole lot less interested:)

[5Toes]

Yeah because horn enclosures are natural amplifiers.

[Danny]

I don't know what's going on here but I like it.

[bmwman91]

^ I was like "Damn he's really into audio if he is designing cabinets like these!"

Haha but you just used some other plans. Damn 95db at 1 watt... that is super efficient

There are some MathCAD worksheets out there that people use to design stuff like this. It takes a lot of experience & intuition, as well as trial & error, to develop stuff like that. I am far from that level, but luckily some who are there are also willing to share for free.

And yes, the efficiency is nice. Horn-loaded enclosures can easily obtain 100dB+ from 1W, with other response trade-offs. The main trade-off is size & complexity though (these get worse by a factor of 10 once you marry from what I can tell lol).

[5Toes]

^ I was like "Damn he's really into audio if he is designing cabinets like these!"

Haha but you just used some other plans. Damn 95db at 1 watt... that is super efficient

[bmwman91]

Might as well post it up

Life is pretty busy right now so it will be a while before I can make detailed drawings of the 12 main parts & another few for the assembly. I'll try to get something up.

I have really been lagging on the car build too. I am in a competitive outrigger canoe club and we are in full race season, so 3-4 days of the week are spent practicing, and race weekends are basically useless for anything else. I really really want to get this done though. My next plan for some home speakers has been picked and I am excited.

(the one on the left...I discussed the modded ones to the right with the designer & they would either do nothing or screw up the response)


It'll use a Fostex 8" full-range driver and a Fostex tweeter crossed over with a capacitor at ~10kHz. This time around I am going to build my own amp. The sensitivity is ~95dB at 1W, so I really don't need too much power. Bass extension is flat to 50Hz or so. These bastards are 62.5" tall haha! The plans come from www.frugal-horn.com.

[reelop19]

Might as well post it up

[Schnitzer318is]

!

x2!

[StereoInstaller1]

it has 156L of actual internal volume (with bracing, the driver & the port accounted for) and the port is tuned to 18Hz.

!

[bmwman91]

Hey man I checked out the sub box you built...very nice. What do you do as a mechanical engineer? I finally decided to go back to college and finish up my degree in mechanical engineering. Have you posted up a design for your sub box yet?

Thanks. The build was a real adventure. It was tons of fun though. I haven't posted up any plans or anything. It was a custom design I came up with & never really made formal drawings or anything. The size, cost & weight of it sort of make it unlikely that anyone else will want to build it, except audio nuts who probably know enough to design their own. At 24"x24"x30", 130lbs and ~$500 in raw materials & a couple specialty tools, it's not going to be super popular lol. If you don't already have the $1500-3000 in basic woodworking tools it takes and a garage...you get the idea lol.

With that said, if there was moderate interest, I would publish detailed drawings. The basics are that it has 156L of actual internal volume (with bracing, the driver & the port accounted for) and the port is tuned to 18Hz. This thing will actually go plenty low without the port as well. I have played with plugging it.

I work as a hardware engineer in consumer electronics presently. I mainly deal with testing & instrumentation, and am slowly working on a masters in EE focusing on controls & mixed-signal systems.

[reelop19]

Hey man I checked out the sub box you built...very nice. What do you do as a mechanical engineer? I finally decided to go back to college and finish up my degree in mechanical engineering. Have you posted up a design for your sub box yet?

[bmwman91]

Alrighty, I got the opamps today. I will install them in the lab at work tomorrow at lunch lol.

I also returned that circle-cutter jig and bought a Router Buddy instead. It looks like it will be a very useful little tool!

Oh, and baltic birch plywood burns like a bitch when cutting with a router. Freaking annoying, I wrecked a bit a couple days ago. MDF was easier to work with than this stuff, which is sort of surprising.

[bmwman91]

Are you by chance interested in chopping out the entire crossover/gain control stage of my Harman Kardon CA260s?

Maybe. Can you take some pictures of the guts? It was a long, painstaking process involving a beeping multimeter (4 layer PCBs are a pain!).

I am certainly willing to give it a shot as long as you aren't in a giant hurry or anything. There will be some sort of "nominal" fee for this service ;).

[StereoInstaller1]

Time for an update:

I have spent a good few days reverse-engineering the amplifier's input stages. My main reason for this is bypassing the active filtering on channel 5 since the amp was designed without a bypass for it. CH5 uses a class-D power stage, and this one was only designed to do lower frequency stuff. Since I will be using a higher-order, nicer, external crossover before CH5, I feel that I can safely bypass it. The external cutoff frequency isn't too much higher than the limit on the amp's dial anyway.

I have succeeded in bypassing this and basically jumped the output of the gain-setting op-amp to the input of the final output buffer / RF filter. With 12V powering the amplifier, CH5 is close to clipping with the minimum gain setting and the expected maximum input level from the 6XS. I am going to change out one or two resistors to allow the gain to be adjusted lower than it otherwise would be in the input stage.

The other order of business will be to install some nicer op-amps. The unit currently uses some STMicro MC4558 units, which are OK for hobby type stuff, but are not really great for audio. Since the power stages probably aren't world-class or anything, I am not going to go dropping serious coin on ridiculous op-amps that headphone enthusiasts like, but I will put in ones with lower noise figures & such. I have ordered some OPA2134's to put in (same pin-outs). They are a good balance of performance and price. You also would not want to put in op-amps with >10MHz bandwidth because there is a lot of high-speed switching circuitry generating RF EMI in there, and you don't want that amplified.

What is the typical battery voltage in an E30 with a good battery when the car is not running? The power rails vary in voltage depending on the input (+/- 23V for Ch1-4 & +/- 41.4V for CH5 with 12V in, +/- 27.3V for Ch1-4 & +/- 48.4V for 14V input). As such, I want to set the gains to be just on the verge of clipping with the lowest reasonable battery voltage present in case I crank it up with the engine off. I am not after absolute maximum power or anything like that...just maximum power under worst-case conditions.

Oh yeah, and once I get the gains dialed in I am removing the potentiometers & putting in regular resistors in their place (of the right value). Cheap pots tend not to hold their setting, especially in an environment like a car, and more-so when mounted near a sub! That, and the dual-pots in there aren't very symmetric, so the gains between CH1/2 & CH3/4 differ a bit for a given position on the pot. Resistors will take care of that.

Are you by chance interested in chopping out the entire crossover/gain control stage of my Harman Kardon CA260s?