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Old 29th August 2008, 09:45 PM   #11
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Quote:
Originally posted by RobWells


Hi Patrick,

I've been doing a fair bit of measuring over the last couple months as I'm in the middle of installing my stereos in my commuter hatchback and my weekend suv. In both vehicles a sealed box does not measure like the car audio sites would have us believe.

Rob.
Andy Wehmeyer over at JBL posted some cabin gain measurements that his company did. Based on JBL's data, it looks like my numbers were off, but not by much. JBL shows about 15db extra output at 40hz, and 25db at 20hz. Here's the pic:

Click the image to open in full size.
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Old 29th August 2008, 09:45 PM   #12
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That doesn't mention my commuter car - here's a plot of the 'xt10' sub mentioned in that thread in this small hatchback.
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Old 29th August 2008, 09:47 PM   #13
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The Mini Cooper has 18DB of cabin gain at 50hz! Whoah.
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Old 29th August 2008, 09:48 PM   #14
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Quote:
Originally posted by RobWells
That doesn't mention my commuter car - here's a plot of the 'xt10' sub mentioned in that thread in this small hatchback.
That's pretty consistent with JBL's data. The notch in your car is at 60hz, instead of 70, and there's clearly tons of cabin gain kicking in at 50hz.
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Old 29th August 2008, 09:49 PM   #15
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Funnily enough my infinitys are part of jbl's parent company (Harman int) and their data sheet shows much the same plot as that you just posted. (as does the data sheet on my JBL gt4'S that are going in the hatchback)

I suggest you measure for yourself to get a 'real world' measurement as they just aren't so pretty.

Rob.
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Old 29th August 2008, 09:55 PM   #16
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Quote:
Originally posted by Patrick Bateman


That's pretty consistent with JBL's data. The notch in your car is at 60hz, instead of 70, and there's clearly tons of cabin gain kicking in at 50hz.
I'd say it isn't consistent at all with jbl's data - they show a general rise in spl below 50Hz, whereas my graph is dropping below 50Hz.

Rob.
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Old 29th August 2008, 10:01 PM   #17
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The only thing I can possibly think that explains the difference could be that both my vehicles are fairly old ('93 and '96) so probably not as 'gas tight' as the vehicles measured by JBL. Maybe if I spent a fortune on new door and boot (trunk) seals all round I'd get more boost in the lowest bass.

Rob.
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Old 30th August 2008, 11:22 AM   #18
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This thread makes the perfect place to ask about (tapped)horn loading and cabin gain. More specifically, I've seen the AutoTuba plots after googleing them, but they all seem to be taken *inside* the car and even there it still falls off at lower freq.

I've read somewhere that car horns go lower/louder with the doors open because there is less backpressure on the horn mouth. This concurrs with the lower cutoff point of my corner horn here at home when I open the large porch windows. (Could also be by reduced room nodes.)

Since a Tapped Horn is a lot less dependant on corner loading, I wonder if this windows-effect would also be for a TH in a car?

I'm just pondering about what to put in my trunck when I do an upgrade next spring.
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Old 30th August 2008, 05:47 PM   #19
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Quote:
Originally posted by Cordraconis
This thread makes the perfect place to ask about (tapped)horn loading and cabin gain. More specifically, I've seen the AutoTuba plots after googleing them, but they all seem to be taken *inside* the car and even there it still falls off at lower freq.

I've read somewhere that car horns go lower/louder with the doors open because there is less backpressure on the horn mouth. This concurrs with the lower cutoff point of my corner horn here at home when I open the large porch windows. (Could also be by reduced room nodes.)

Since a Tapped Horn is a lot less dependant on corner loading, I wonder if this windows-effect would also be for a TH in a car?

I'm just pondering about what to put in my trunck when I do an upgrade next spring.
I cloned an autotuba and had it in my car for a few months. It was a LOT of fun, possibly one of the funnest car audio projects I've ever done. After a while I got sick of it, because it didn't go deep enough. It has a ridiculous amount of 'slam' in the upper bass, around 80-100hz, but the low bass doesn't have the same impact you get from a pair of 12s. And this is no surprise, as far as I can see, it's basically an eight in a sealed box below the horn cutoff, which is quite high. I've got to hand it to Bill Fitzmaurice, his design raises the power handling of the driver in a huge way. I was feeding it something like 500 watts IIRC. I believe it's rated for 100 watts, and it's from MCM, so it's probably more like 50 watts IRL

As for corner loading a sub in a car, I really doubt it would make a worthwhile difference. I tried this myself with the autotuba clone I made, designing it so that mouth exited through the passthrough of the rear seats. The idea was that the rear deck would extend the mouth flare. When I measured it in car, my measurements didn't indicate that the rear deck was helping out the low end at all.

One thing that DID make a difference was opening up the rear seats - there's this myth that bass will magically travel through the rear seats, but this isn't true. Pushing the seats forward changed the frequency response quite dramatically (for the better.) Admittedly, most of the improvements were in the upper bass, so if your sub is only covering 20-60hz, don't bother.
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Old 30th August 2008, 07:59 PM   #20
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I tried half a dozen different designs using a Diyma12 yesterday, and kept running into issues. Basically I was just getting TOO MUCH low bass. Every design I tried wound up playing into the teens once you factored in cabin gain, and the box size was getting hella huge.

Danley made some comments on my other thread that made me think that I should try a woofer with a higher FS. So I've thrown together a couple of designs using an Audax HT240G0.

Here's a pic of the response in a single reflex bandpass tuned to 63HZ:

Click the image to open in full size.

It's being fed 1000 watts; with 25db of cabin gain at 20hz and 15db of cabin gain at 40hz, it will be basically flat to 20hz inside a car.

The problem is the excursion, shown here. I'm betting some tapped horn goodness could be used to improve the excursion, at the expense of a larger enclosure.

Click the image to open in full size.

Here are the parameters. I measured the woofer myself. It's an isobaric pair of Audax HT240G0 woofers in a single reflex bandpass. The rear chamber is 34.5L, the front is 18.7L. There are a pair of three inch vents, measuring 25.68cm in length. Two three inch vents are just a bit better than a single 4" vent; their big advantage is that the pipe modes are much higher in frequency.

Click the image to open in full size.

Of course I am a complete cheapskate - you can get this woofer for a whopping $28 at parts express.

http://www.partsexpress.com/pe/showd...number=296-138

I have something like eight of them in the garage, the build quality is really nice. I purchased them for a dipole project that I abandoned when I bought my Summas. Here's the specs, measured by yours truly. They're quite close to what Audax advertises.

* f(s)= 51.14 Hz
* R(e)= 2.84 Ohms
* Z(max)= 34.69 Ohms
* Q(ms)= 8.963
* Q(es)= 0.800
* Q(ts)= 0.735
* L(e)= 0.57 mH
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