what the hell?????

[T3mpest 10+ year member]

I'm going to get flamed for this, but I have to say it because you're all wrong. It's called cabin gain. This is reduced by a smaller vehicle. It takes a long distance for a wave to develop at the frequencies we play. The shorter the wave the less it's developed and the quieter it is. Cabin gain is how well the waves are reflected to the listening area aka reducing cancellation. So in short, it's not the small amount of air to move. It's the reflective surface. The different degrees of angle on the hatches focus the waves in different ways. Some are more efficient than others.

Actually your incorrect. Cabin gain in reinforced when the wave cannot fully develop when the wavelength of the tone is longer than the car itself. This leads to the wave essentially backing up on itself and creating extra pressure. It doesn't cancel as the waves can't get out of phase since there is no space for them to develop that far most of the time. It's generally 12db/octave of gain once you get below the lowest frequency the length of your cabin can support. Just to prove you theory is wrong think about this. If cabin gain worked the other way subs would be loudest when put outside. After all in an open field we would no cancellation. Conversely your saying if I put you in a room with a 18 inch sub and the room was very tiny it wouldn't be very loud, after all, it would all cancel out... I hope you see the flaw in your logic...

If you want to argue go ahead but I can actually find alot of sources from both home and audio sections that will back me up as well as real life experience from anyone who has ever sat in a hatchback lol.

 

[Stalin-ohaulic]

Actually your incorrect. Cabin gain in reinforced when the wave cannot fully develop when the wavelength of the tone is shorter than the car itself. This leads to the wave essentially backing up on itself and creating extra pressure. It doesn't cancel as the waves can't get out of phase since there is no space for them to develop that far most of the time. It's generally 12db/octave of gain once you get below the lowest frequency the length of your cabin can support. Just to prove you theory is wrong think about this. If cabin gain worked the other way subs would be loudest when put outside. After all in an open field we would no cancellation. Conversely your saying if I put you in a room with a 18 inch sub and the room was very tiny it wouldn't be very loud, after all, it would all cancel out... I hope you see the flaw in your logic...
If you want to argue go ahead but I can actually find alot of sources from both home and audio sections that will back me up as well as real life experience from anyone who has ever sat in a hatchback lol.

Wow! Yes I do need sources for you to back yourself up. The inside vs outside argument does not hold water as I argued that the hatchback reflects waves and in an inefficient way becomes similar to a parabolic antenna. I'm certain you don't know what that is or what I/you are talking about.

Also, the acoustics of a "room" are almost always much better than a vehicle. Vehicles have horrible acoustics. This is why we use so much amplification and such high end speakers. If the wave doesn't matter, then why tune a box and why do vehicles have peak frequencies? Hopefully you see the flaw in your logic.

 

[T3mpest 10+ year member]

Wow! Yes I do need sources for you to back yourself up. The inside vs outside argument does not hold water as I argued that the hatchback reflects waves and in an inefficient way becomes similar to a parabolic antenna. I'm certain you don't know what that is or what I/you are talking about. Also, the acoustics of a "room" are almost always much better than a vehicle. Vehicles have horrible acoustics. This is why we use so much amplification and such high end speakers. If the wave doesn't matter, then why tune a box and why do vehicles have peak frequencies? Hopefully you see the flaw in your logic.

I was simply referring to a home needing more low end reinforment as they don't have a much gain from the enviroment, this is because a car much smaller than the average room. That's why small cars can get good bass with a single 12 sealed and yet almost all higher end setups use large subs tuned very low vs a car tuning, since room gain occurs much lower in frequency, the rooms are longer. Your correct in that the waves reflecting is what causes cabin gain but it's not cancellation it's almost always an increase. Tom covers it very well with a bathtub vs swimming pool analogy, the waves are simply too close together when you put a 45foot wave in a 10foot long car, it rarely creates nulls, it's just an increasing gain as you get lower and lower in frequency. Rooms are usually big enough to have a few nulls and have cabin gain kick in much lower since the rooms have a larger maximum dimension.

http://www.caraudiobook.com/car_audio_cabin_gain/car_audio_cabin_gain.htm

http://www.nousaine.com/pdfs/Free%20Bass.pdf

Note: cars are normally 10-15 feet long this corresponds to 112hz-70 as the starting figure for cabin gain using the formula linked. Most estimates are usually 12db/octave below 80hz for this exact reason. Shape of the car isn't nearly as relevant as the waves barely see the shape of the vehicle anyway. No matter which way you face a box in a big car your unlikely to get as much of a gain as you will by simply throwing it in a smaller car, a fact many on here can attest too.

 

[Stalin-ohaulic]

I was simply referring to a home needing more low end reinforment as they don't have a much gain from the enviroment, this is because a car much smaller than the average room. That's why small cars can get good bass with a single 12 sealed and yet almost all higher end setups use large subs tuned very low vs a car tuning, since room gain occurs much lower in frequency, the rooms are longer. Your correct in that the waves reflecting is what causes cabin gain but it's not cancellation it's almost always an increase. Tom covers it very well with a bathtub vs swimming pool analogy, the waves are simply too close together when you put a 45foot wave in a 10foot long car, it rarely creates nulls, it's just an increasing gain as you get lower and lower in frequency. Rooms are usually big enough to have a few nulls and have cabin gain kick in much lower since the rooms have a larger maximum dimension.
http://www.caraudiobook.com/car_audio_cabin_gain/car_audio_cabin_gain.htm

http://www.nousaine.com/pdfs/Free%20Bass.pdf

Note: cars are normally 10-15 feet long this corresponds to 112hz-70 as the starting figure for cabin gain using the formula linked. Most estimates are usually 12db/octave below 80hz for this exact reason. Shape of the car isn't nearly as relevant as the waves barely see the shape of the vehicle anyway. No matter which way you face a box in a big car your unlikely to get as much of a gain as you will by simply throwing it in a smaller car, a fact many on here can attest too.

I can take the subs out of my blazer and stick them in a tiny trunk car and they will certainly get quieter. Also, to back me up, when you roll your windows up, you are letting the "pressure" escape and now have infinite space instead of just a tiny car. The bass still comes. This is because the hatch is acting as a parabolic antenna. I can use logic all day long to disprove you.

 

[T3mpest 10+ year member]

I can take the subs out of my blazer and stick them in a tiny trunk car and they will certainly get quieter. Also, to back me up, when you roll your windows up, you are letting the "pressure" escape and now have infinite space instead of just a tiny car. The bass still comes. This is because the hatch is acting as a parabolic antenna. I can use logic all day long to disprove you.

That's not really logic. Trunk cars are hard to get loud because the trunk physically holds the sound in the trunk keeping it away from the cabin. This has an even bigger effect than cabin gain. However an open small vehicle aka a hatchback is usually louder than an open large vehicle, aka an suv, try holding variables somewhat constant if you using logic. Heck cavaliers are usually known as one of the louder trunk cars, they also dont' have a great seal between the cabin and the trunk and are relatively tiny for trunk cars......

When windows go down your effectively creating a ported box inside the car. The windows act as a helmholtz resonator and amplify more audible frequencies. If you actually look at overall energy though, you do lose by opening a door or window. It's all 20hz and down though. John Janowitz from AE speakers did measurements on several cars and found this to be the case every time. If you want more proof look at the extreme cars like alan dante. They are super tiny on the inside and completely sealed. They take advantage of the cars resonance frequencies and then seal up and pressurize a very tiny area to hit silly high numbers, often with very little cone area (world record right now is 2 18's for **** sake)

The part your wrong about is the wave development. A soundwave doesn't have to fully develop within a space in order to be loud. If it did no car would have good SPL levels at 20hz, after all a 20hz wave is over 50 feet long. Yet every car has extreme cabin gain near 20hz, usually upwards of 30 decibels or more. It's because the wave cannot develop in inside the car without reflecting back onto itself multiple times, increasing it's overall pressure. Again the basic formula is (speed of sound)/(frequency) = wavelength. Given most vehicles are 10-15 feet long that means a wave would fold back on itself 4-5 times give or take a bit. Each doubling on itself is 6 decibels of output. 6x5=30, which again looks pretty close to basic theory estimates. Now if the wave has to fully develop then cabin gain should be crap at 20hz and we should be using super small sealed boxes in the home in large rooms as according to you, they would be able to support a 55ft wave, meaning it would be louder and big boxes tuned low wouldnt' be needed.

Anyway I've shown you links explained the mechanism and even showed that the well known formula used in both home and car audio holds constant with the real world. If you would like to believe pressurizing a small area is harder than a bigger one, go ahead....

Lastly any sort of parabolic antannae doesn't apply here. The relatively short wavelength of electromagnetic radiation at these frequencies allows reflectors to have a highly directional response for both receiving and transmitting. A soundwave in the subbass frequency can't be aimed like that, not without a VERY big opening. Go look at a true subbass horn, the horn mouth is massive even to get directional response down to 40hz. Again a soundwave that long doesn't really see the enclosure it is in, the waves are too long. It's simply pressurizing a room smaller than inself folding back on itself at it goes, increasing the pressure. Not to say you can't add SPL by aiming a sub in a vehicle but no matter which way you aim a sub in a hatchback the cabin gain will be better than in a much larger open spaced vehicle.