radarcontact

So,
I'm not new to car stereo installs, etc. - I'm 54 years old and I've done many, many, many of them over the years, both for myself and others.

That said...

I am putting a custom subwoofer in my trunk. I am concerned (a little, anyway) that the pressure from the sub will cause issues/distortion/coloring of the tiny 4" rear deck speakers since they share the same space. I picture them acting as little tiny passive radiators! lol

(in all my years of owning and customizing cars, I've never had a trunk sub in a car with rear deck speakers -- usually they were in the rear doors or other place besides the deck. Or I didn't use a trunk sub)

I thought about removing them but I like the rear fill effect.

Anyway...

For those that "know", please offer your opinion. Others... well, please don’t.

Thanks.

// Radar //

FormerE30Owner

I expect Audiophool to chime in, but I wouldn't worry too much about the woofer interacting with the 4" speakers. At any rate, you won't hear any difference. Since you are willing to remove the 4" speakers, try your the set-up with them and see (hear). If you are really concerned after the trial, try building a box around the rear of the 4" speakers.

radarcontact

Box option not practical. Thought about venting to the cabin via a rear deck cutout and grill, but I really would rather not. That’s a bit drastic.
However, I plan to run some test tones, say 30hz, and see if there’s significant movement in the midranges’ cones.

FormerE30Owner

30Hz is below the resonance of the 4" spk and will not affect them. Also, you will not see a 30Hz movement. Try "feeling" the 4" spks. I would put a 120 Hz tone which has a much better chance of stimulating the 4" speaker. Again, try to feel the speakers. If you vent the sub, you will be changing its resonance point and its performance. At the levels that you think that the sub will interact with the 4" spks, you will never hear the difference anyway. But, I suspect you want to be thorough.

radarcontact

I think maybe I’m not explaining my concern right.

The trunk is sealed.
There are mid ranges in the rear deck that have the rear of their baskets exposed to the trunk. I.e., they are also sealed to the trunk space.
When I put a 12” sub throwing 1”-1.5” xmax there is going to be pressure generated inside that sealed space.
That pressure will surely push on the mid-ranges because they are the path of least resistance to the cabin. I.e., before it flexes my trunk sheetmetal, it will push on those cones. If those cones are trying to reproduce a 250hz signal, little fast movements, the cone will be fighting against that big steady bass pressure to do so.
A 30hz signal is a huge wavelength and will be the most pressure I can generate. *20hz is longer=stronger but 20hz is probably not achievable with this single 12” at the same dB levels.

Picture a big speaker cabinet with a single 6” speaker. Now imagine there’s a 10” speaker that is sealed INSIDE that speaker box that’s playing different music than the 6”. That 6” is GOING to be affected by what that 10” is doing.

Hopefully that makes sense.

FormerE30Owner

No need to explain. I am an audiophile for the past 50 yrs and have dealt with speaker design and acoustics for almost as long, albeit home systems. With respect, your knowledge of speaker resonance and interactions is limited, at best. It is not the wavelength of a signal that determines its pressure, but the amplitude. As for interaction among speakers, the relative resonance of speakers determines how each is affected by the other. If your subwoofer is producing notes of 250 hz, then possibly it could affect the mid-range. A 30 hz note might cause a doppler effect on the midrange, but that would be much less heard than the harmonic distortion already present at those sound levels.

Since it is even more impossible to reproduce accurate sound in an automobile due to its small and noisy environment, than in a home, I don't pay much attention to the sound systems in automobiles.

Final word - Try your proposed installation with the sub and listen - if you think that you hear some distortion due to the doppler effect, than try something else.

I have a feeling that you want to do more than simply install the sub and are looking for some reason to do so.

Good luck,

radarcontact

Unfortunate you are wrong about every aspect of what you wrote. Um... “with respect”.

You aren’t going to get pressure from a 15khz signal but you will get pressure from a30hz signal. Amplitude doesn’t matter, and the Doppler effect has NOTHING to do with it.

And god help me if my subwoofer is set up to play at 250hz. [facepalm]

Referring back to the OP, “For those that "know", please offer your opinion. Others... well, please don’t. ”

I don’t think we need to continue this, so thanks for taking the time. Have a nice day.

// Radar //

FormerE30Owner

You are welcome. I suggest that you consult another forum where they do know something about the Doppler effect,resonance etc., for information about how to set up a loud distorting automobile noise system. You are correct, enough said. Good day.

audiophool

All I'll say is the trunk is not sealed. It has a 'port' in the form of air valve/vents to the outside that are used for the car's flow-through ventilation. Unless you account for this and other paths back to the interior, your model is incomplete. If you did seal the trunk (ventilation would be poor when you're driving as the HVAC would pressurize the cabin rather than flow through) and kept the small deck speakers open to the trunk, their cones would split as they'd be the path of least resistance for the pressure from the sub.

I gave up worrying about acheiving any kind of fidelity in a car - there isn't enough volume of air in the cabin. Sure, you can make it LOUD, but for my money, (and my 55yo ears with tinnitus) the L7 system is just fine, especially with talk radio. Radio1 baby!