I have an old subwoofer whit a blown out 10 inch speaker - enclosure is ported. I will put in a DD210 S4 speaker because I have an 300 Watts RMS amp for 4 Ohms. I designed a box with same volume and same port size just because I want to know how it will perform: https://speakerboxlite.com/project-info/3c8c0f4abbc4477ba13f60e37590c82827d9349703de084355d0627336c312f8 . There is a sealed box for comparison what will sound quieter but way deeper. If my knowledge is right, in car the ported box will sound better because of cabin gain, in room is almost no cabin gain - the sealed will sound better (outside there is no cabin gain - sealed will be better).
So I have 2 questions: 1.: My knowledge is right - cabin gain effect? 2.: If the answer is no for my first question, which box how will perform in what enviroment?
If the sealed will be better, then I hide the port and that is all...
Vpeti, those are some great questions. The problem with answering them is some of it is a matter of personal opinion and what goal you are trying to achieve. It’s hard to say which is ‘better’. Help me understand what you mean by ‘quieter but deeper’ and I think we can figure it out together. I don’t want to make assumptions so help me help you. I look forward to your response.
Hi. Thanks for you answer. In the simulaton the 2 boxes are the same: they have the same Vb: red - sealed - if I hide the port, green - ported - if I unhide the port. The ported box have a peak around 77 Hz - it seems to be it is "louder" because of that peak. The sealed box controls better the bass at lower frequencies than 48 Hz - it is "deeper", but if I watch the SPL graph, there is 100 db @ 35 Hz on ported - in my opinion it is enough. So, in your opinion which is better for general music listening? - because it seems to be it will be better when I hide the port on my box, and if I unhide the port, it will be better for that one 70 Hz-ish note. And I just do not understand how exatly works the cabin gain. So, maybe first I will try out to hide / unhide the port... Btw, I have an answer from DD on this, that in their opinion the ported is acceptable for a car...
Vpeti, thanks for clarifying your question. I hear you saying you prefer a flat response. You are correct that where you see peaks, you will have more audible output. It is worth noting that humans do not perceive sound level increases/decreases in a linear fashion. Without getting too in depth, it is due to the amount of energy and the size of sound waves and their respective abilities to move air which then moves the parts of our ear drums (or windows and trunks lol). With cabin gain you get an effective standing wave and corresponding addition of volume especially when the frequency is matched to the vehicle size. So to simplify that even further, we notice more output at lower frequencies when the enclosure moves from free/infinite space (out in the open) to half space (in this case, a vehicle). Similar to when a speaker moves from open air (infinite space) to an infinite baffle (half space or the like). Think of half space as the point where air/sound divides when moving from an affine space to a 3d space with hyperplanes. There is a +6db increase. At 1/4 space (dissect half space with another plane) there is +12db gain. At 1/8 space (or pi/2 steradians) there is an +18db gain. Imagine 3 infinitely large perpendicular planes. A horn would take your speaker even lower than 1/8 space. But you get the idea, hopefully. Baffle step is also part of the equation but becomes more pronounced at certain audio bandwidths.
Without getting too too crazy in explanations, you were more specifically looking to know how spatial loading affects your enclosure within the realm of a listening environment (car). Two helpful measurement units are radians (circles) and steradian (spheres). Sound radiates like a sphere (steradian) until it meets an obstruction. These obstructions (windows, people, doors, seats) can absorb or can reflect the sounds. That is what more people are referencing when they talk about cabin gain, or extra gain in the lower output of the sub box in a car.
Ported enclosures are a 2nd order bandpass. They have a steeper roll off at frequencies below the tuning. That’s roughly 12dB per octave or 40dB per decade. This brings a slight bump in Q which gives us about a +3dB increase around and for a small group of frequencies immediately above the tuning frequency. Cabin gain can be beneficial when taken into consideration and applied appropriately because it can help offset that rolloff and the gain can still be had from the ported enclosure increase of Q.
ported enclosures can be tuned to be very flat in their frequency output at various frequencies. It is an acceptable and widely used enclosure for the reasons stated above. For ultimate simplicity, stick with your acoustic suspension (aka closed/sealed box) and enjoy your flat response if designed correctly.
I know I rambled on but I hope you understand where I was going with some of the explanations. Please ask if you have any questions and don’t hesitate to put up your final design for some helpful critique from others here as well.
A long time ago someone hit me with the explanation that car audio is basically all bandpass enclosures. His reasoning was that cabin gain was basically the product of locating your newly designed and constructed enclosure inside of an already existing speaker enclosure ( cabin of the vehicle) which most times has another existing enclosure inside of it ( your trunk) so basically the speaker is operating as though it is in an 8th order enclosure??? I'm not as good with the labels as others so maybe someone will help me out here lol. I don't know if I completely agree with the logic but I definitely understand the reasoning behind this.
I can follow that logic except I would add the caveat of whether the windows or doors were open. Essentially a sealed enclosure in a car with windows down has become a fourth order bandpass due to a sealed chamber firing into a vented enclosure (the car). A bass reflex (ported enclosure) when placed in a car windows down is now a series tuned 6th order because you have a vented firing into a vented enclosure. The tricky part is then whether or not the windows down adds or detracts from the tuning in respect to the listening position. It has been observed that some woofers come to a violent end when the doors are opened in a high powered 4th order (bandpass) enclosure (most attributable to unloading of the woofers). I think we all have listened to various systems in vehicles that sounded better with the windows up or vice versa.
Browse this paper below if you have time. I’m trying to find the other links I had but I have misplaced the files on my desktop cpu. Here:
C. P. and R. E. Boner, “The Gain of a Sound System,” Journal Audio Engineering Society, volume 17, number 2 (1969)