Car build RS180-4 + MDM55 + DX19

[bmaupin]

I started this project last September and have been enjoying for a couple weeks now. This is in my '77 VW Bus.

After discovering that the doors are fully vented at the front by 6 1" x 2" oval holes and that on the freeway the plastic door panel cover/seal gets sucked out very tightly, I figured that I needed to isolate any drivers from the inner door air space and some sealed enclosures were in order. I first demo'd a few 7" drivers in a 5L enclosure and the RS180-4 won. I knew that the R180 would be best as a 3-way - so I needed a mid. I went with the Morel MDM55 for the mid because it's sealed and has a small faceplate and motor. The tweeter is the Vifa DX19. I'd go active, but a 55-amp alternator won't allow. I have an Alpine MRD-F752 Tripath to help with current draw.











I've never fiberglassed before. It isn't tough, but some experience certainly helps. Spray glue and fiberglass is a joke - a staple gun is best to secure the fabric, but the glue is handy to get it stretched in place. Using chopped mat strands mixed in with the resin is the best way to fill tight corners. I made my own strands by just cutting the chopped mat since I didn't need a ton. The Knytex mat is nice, but not necessary.

I figure that I ended up with about 10 liters of air space.

[bmaupin]

Re: Car build RS180-4 + MDM55 + DX19

I made covers to hide the fasteners around the woofer area. Pam works surprisingly well as a release agent for fiberglass.

[bmaupin]

Re: Car build RS180-4 + MDM55 + DX19

I took measurements inside the house and designed a crossover. Originally I took measurements with the mic position straight ahead and up at in-car ear level.



The design sounded fine inside, but after listening for the first time in-car I realized that the bass was much louder than the mid and treble - kinda what you see here:



From messing with the simple mid + treble eq on the head unit I figured I needed +4dB on the midrange and tweeter. I redid the crossover taking new measurements with the mic at the in-car location between driver and passenger heads and I am much happier with the sound. Very good overall balance and the left and right volume are just about the same. Drums are very punchy and on some songs maybe a little bit too much.

Borrowed a laptop from work and used Arta to take some in-car measurements. I am not real confident in the dB scale since I did not calibrate the mic w/ Arta. I also did not use my mic calibration file - my mic has a 3dB peak around 12kHz. You can see why drums are punchy - spike around 120Hz. Dips in the lower midrange evidently from environment. Response to 40Hz is surprisingly real, but cabin gain obviously at play - verified by adjusting low freq high pass from 30 to 50Hz.

Driver head:

Passenger head:

Between driver and passenger:

Near driver right shoulder (lower than ear level):

Seat pad height, between seats:

Nearfield:


Overall I think the process produced good results. I think that all cars are going to have cavity resonance issues that will be difficult to overcome. Not sure if a different woofer placement would fix all of what is happening between 300 and 800Hz - which fills in a bit better from the opposite channel.

[robert]

Re: Car build RS180-4 + MDM55 + DX19

Looks pretty fine - I am sure the MDM-55 works great in a car - well dispersed upper mids that often get lost with low-mounted 2 way systems and it is a super-fine driver.

The dips and peaks are just part of a car - before I had SE I used my semi-calibrated RS SPL meter and 1/3 octave warbles and it looked similar. Bet it's a ton better than anything stock.

Cheers / Robert

[ocdSCHACK]

Re: Car build RS180-4 + MDM55 + DX19

Man is that opening a can of worms...and you are going through this like it's nothing! I'm really impressed you'd take this on never using fiberglass! The pics are awesome, and I can't wait to the see the rest. Everything looks like it's being done the right way. Are you an auto body guy? I'd like to see how it looks in the car...are you already done?

[DjDisturbed]

Re: Car build RS180-4 + MDM55 + DX19

You need a good eq with alot of bands in a car if you want to tame your frequency response. And cabin gain is going to happen in any vehicle period.
Nice work on the door panels they look good.

[ecbmxer]

Re: Car build RS180-4 + MDM55 + DX19

Any thought of picking up a nice active crossover? There are tons out there that are stand alone (relative to your receiver) and could do 3way + sub. Check out some of the stuff from AudioControl (if you aren't already familiar).

[joeybutts]

Re: Car build RS180-4 + MDM55 + DX19

VERY very nicely done. Would love to see installed pics....

[bmaupin]

Re: Car build RS180-4 + MDM55 + DX19

Any thought of picking up a nice active crossover? There are tons out there that are stand alone (relative to your receiver) and could do 3way + sub. Check out some of the stuff from AudioControl (if you aren't already familiar).

I explained in the first post that a 55 amp alternator made 6 x 100W + 1 x 250W channels of amplification out of the question. I know that often people use 100W (woofer) + 50W (mid) + 25W (tweeter) because of varying sensitivities, but I picked an efficient woofer so that padding of the tweeter (0.5 ohm) and midrange (2 ohm) was a minimum. Besides standard crossover slopes do not provide necessary response shaping - something car audio does not understand. When you have the tools and know how, a passive crossover creates a system that takes a DCX2496 to surpass.

[bmaupin]

Re: Car build RS180-4 + MDM55 + DX19

Would love to see installed pics....

I am going to have custom doors panels made soon as I do not want to cut up the new ones I have that go with the complete new set I bought. I'll take some more pics if it is ever nice weather on a weekend again - PNW :(

[denton]

Re: Car build RS180-4 + MDM55 + DX19

I'll take some more pics if it is ever nice weather on a weekend again

I just noticed you are in Bremerton. I guess we'll plan on the next set of photos being shot in a garage. ;)

Nice work. I hope you get the sound quality you are looking for.