Anyone measure in car?

[michael hurd]

Hello, this is a first post on measurement on this board, I measured 1m GP of my AV-12X as well as in-car at head level front seat. The enclosure was 1.3 cu ft net sealed, low Qtc~ .578 cold. The car is a 1989 Honda Accord, my daily beater.

There was a bit of wind outside, but no other noises, miles from everything. ( I live in the sticks literally... ) I was on a blacktop 2 lane road, with very little traffic, maybe a car every half hour if that.

This is the graph, I adjusted it to the limits you prefer for scale. Red is in-car and blue is the 1m GP trace.

I used a 120v inverter for the power for the mixer... and the laptop was on battery.

[michael hurd]

I forgot to mention that the ECM-8000 was at head level clamped in the headrest, and all windows were up and doors sealed. Laptop was outside the car on the roof, and RCA cables ran into the trunk to the sub amp. Rear seat was in the upright position as usual.

[brucek]

Red is in-car and blue is the 1m GP trace.

Is that all cabin gain, or is there some EQ involved?

brucek

[michael hurd]

Bruce, that's with no eq whatsoever, just gain from the interior. Looks like about 30 db gain at 20hz.

[Mike P.]

Josh posted a graph of measured cabin gain a while back, hopefully he'll chime in here.

[HDtiger.N.O.]

I have been thinking about running the REW software in my car, since I listen more on the road than in my HT. Given the impact of a single 10" JL sub with a Class-D Alpine 300w amp, I can believe your graph is accurate in terms of "room" gain. I drive a Ford Expedition, so the interior is much like a small rectangular room. Dramatic changes result from the laying down different seats, etc., so I would have to run it many times, but the gain is incredible - and highly frustrating as integration with the mid/high is tough to balance. I'm curious of the impact of road noise as well.

[Ricci]

Here you go Mike...
I slapped a sealed sub in my Jeep and compared it to the outdoor 2m response in this thread. looks about like yours. MASSIVE gain down low.


http://www.hometheatershack.com/foru...room-gain.html

[michael hurd]

Wild, that's a pretty flat response down there, I guess it helps when you don't have to filter through the rear deck and seats.

[atledreier]

I measured my cheap tube sub in my car, and was AMAZED how flat it was, and the amount of gain. I'm at work now, but I think I have the files on my laptop at home. I had to add a little gain at 80Hz (lopassed at 110) but other than that it was what I'd characterize as ruler flat, especially coming from HT and nodes galore. The problem with cars is comb filtering, assymetric listening position and small cabin problems like that. I run an DCX2496 to manage my 3 way system right now, and it's great. It's not a great system, but a good amp and good DSP. The rest will come some other time.

[Ricci]

michael hurd wrote:

Wild, that's a pretty flat response down there, I guess it helps when you don't have to filter through the rear deck and seats.

Yep. Look at the level I used though. That was with the amp a click below clipping. I also found out at the GTG that my CM140 that I calibrate my ECM8000's to needs calibrated itself. It measures about 4db too low compared to the other CM140 and professional test rig that were there. I'm not sure whether your bit of weirdness there at the bottom is due to the trunk and deck or just the level. From what I've seen you get more accuracy below 20hz with more volume to overcome mic insensitivities and background hash. If you ever do it again use a level that the the sub will easily handle but that's also pushing it pretty good and use the longest sweep time too.

[michael hurd]

I have a cheap Radio shack analog meter, and it's way wayyy out to lunch now, I am not sure if it got messed up from high SPL or what, I am thinking from what I have measured in the past it's probably 10db low.