How to master the art and science of acoustics?

[altoncustomtech 773]

Brad and Sean, I imagine you guys will be the most help here but I'm looking for anyone's input with insight here.

I have noticed a bit of an acoustic phenomenon in both my vehicles that I'm sure exists in others but I'd love to figure out how to adapt or harness it to be put to real use. I'm also looking for the exact reason the acoustics work this way. In my Jimmy, for example, I have the doors deadened with CLD and CCF (MLV is in the works) and the Bravox components are mounted in good heavy MDF baffles. They sound great with good strong midbass and can even extend fairly low for their small size and low HU power. My only complaint is that they're a bit "forward" or "in your face" and there was a little beaming or resonance in the 2k-3k range which I was able to EQ out with the HU's EQ and it was only noticeable on certain music anyway. Otherwise they're some of the best components I've owned to date.

Now to the point of this post. If I sit in the back seat, or get in the back of the truck like I was the other day taking measurements for the complete redesign on the amp racks they sound COMPLETELY different. They're smoother, more subdued, less "forward" or "in your face" sounding and the midbass and bass are much more pronounced, fuller and warmer sounding. It was like listening to a really good set of house speakers. I started playing with different songs and some settings on the HU and simply couldn't believe the difference.

My questions are pretty basic unlike the answers. Why is there such a dramatic difference? What, if anything, can be done to achieve that same result while sitting in the front of the vehicle?

I know it takes some distance for the frequency waves for bass to fully develop and the seats are likely helping with the midrange and highs smoothing, so I'm sure that has some play in this. I also know that acoustics are just tricky, results are always going to be different when listener and speaker positions change, changes in the environment, placement of objects, and the materials of everything all play a role in the outcome. Vehicles only make all these acoustic effects harder to predict and work with, so I guess I'm just looking for a better understanding of WHY the dramatic difference exists. That will likely tell me if there is even a HOW to create the same effect/result from a front listening position.

[NDMstang65 403]

Transfer function..they are farther away from you.

Same reason why eldridge had speakers behind his headlights in the 4 runner

[ssh 924]

Another reason why adjusting the seat all the way back generally improves everything.

The noise in the 2k-3k range, was it heard from the mid drivers? If you sat on the opposite side and looked directly at the mid (on-axis) was the issue still there?

Edited May 3, 2012 by stefanhinote

[altoncustomtech 773]

Transfer function..they are farther away from you.

Same reason why eldridge had speakers behind his headlights in the 4 runner

Transfer function? Great. Makes sense, but i would figure there's not a way to utilize it on a scale of even moderately difficult in a vehicle.

[altoncustomtech 773]

Another reason why adjusting the seat all the way back generally improves everything.

The noise in the 2k-3k range, was it heard from the mid drivers? If you sat on the opposite side and looked directly at the mid (on-axis) was the issue still there?

Not a noise, simply harshness in the sound. Haven't tried moving to being on axis with the mids. It easily EQ'd out with a simple -1 at 2khz on the parametric EQ in the HU.

[///M5 2,833]

My questions are pretty basic unlike the answers. Why is there such a dramatic difference? What, if anything, can be done to achieve that same result while sitting in the front of the vehicle?

The difference was described above, but also shows you stand to gain potentially from some good tuning work. Hard to make up for pathlength, azmiuth, AND reflections but there are ways to address each.

I know it takes some distance for the frequency waves for bass to fully develop and the seats are likely helping with the midrange and highs smoothing, so I'm sure that has some play in this. I also know that acoustics are just tricky, results are always going to be different when listener and speaker positions change, changes in the environment, placement of objects, and the materials of everything all play a role in the outcome. Vehicles only make all these acoustic effects harder to predict and work with, so I guess I'm just looking for a better understanding of WHY the dramatic difference exists. That will likely tell me if there is even a HOW to create the same effect/result from a front listening position.

It does not take ANY distance for a wave to "develop". It is what it is a sound wave. If it needed to develop then you would be seeing phase and/or amplitude changes which aren't possible without something acting on the wave.

As for the how, you get to address each concern independently and sometimes at the compromise of disturbing another. Exactly why you never see me carte blanche recommend a speaker, mounting location, processing or any of the above. These are all trade-offs that you get to balance in your own ride.

[altoncustomtech 773]

My questions are pretty basic unlike the answers. Why is there such a dramatic difference? What, if anything, can be done to achieve that same result while sitting in the front of the vehicle?

The difference was described above, but also shows you stand to gain potentially from some good tuning work. Hard to make up for pathlength, azmiuth, AND reflections but there are ways to address each.

I know it takes some distance for the frequency waves for bass to fully develop and the seats are likely helping with the midrange and highs smoothing, so I'm sure that has some play in this. I also know that acoustics are just tricky, results are always going to be different when listener and speaker positions change, changes in the environment, placement of objects, and the materials of everything all play a role in the outcome. Vehicles only make all these acoustic effects harder to predict and work with, so I guess I'm just looking for a better understanding of WHY the dramatic difference exists. That will likely tell me if there is even a HOW to create the same effect/result from a front listening position.

It does not take ANY distance for a wave to "develop". It is what it is a sound wave. If it needed to develop then you would be seeing phase and/or amplitude changes which aren't possible without something acting on the wave.

As for the how, you get to address each concern independently and sometimes at the compromise of disturbing another. Exactly why you never see me carte blanche recommend a speaker, mounting location, processing or any of the above. These are all trade-offs that you get to balance in your own ride.

To the bold answers, when you refer to the tuning part, are you referring to tuning with a processor, physically or am I likely missing the real point? I would be more than willing to install and go through the trouble to tune to get the results I heard.

To the underlined answers, I've always understood why you don't just drop recommendations. Not saying I've always agreed with it, but I do understand it. I don't have any qualms about addressing the problems in my own rides, however I do lack the advanced experience and knowledge it takes to address them head on. Would you happen to have some resources (books, websites, etc) where a person could go and perhaps begin to gain an understanding on how to address the problems?

[///M5 2,833]

The books I could recommend wouldn't help you very quickly. I am a Physicist with a minor in Acoustics so needless to say they'd be college level text books that aren't applied directly to the subject at hand.

Tuning can be done either way. The net transfer function is the important thing to "tune". Obviously physical first to within your constraints and compromises and then electronically.

[j-roadtatts 1,129]

Sound waves can only travel through objects that are thinner than the waves lenght. So my guess is the higher frequencys are being absorbed by objects as they travel to you in the rear. Of course the lower frequencys can travel through a lot thicker object bc the waves are longer peak to peak.

I have the opposite problem. The closer I can get the drivers to my ears the better they sound.

[On3Hundr3dProof 19]

Would you happen to have some resources (books, websites, etc) where a person could go and perhaps begin to gain an understanding on how to address the problems?

http://www.amazon.co...g/dp/0859342018

http://www.parts-exp...tnumber=500-035

I've been reading these. An introduction to loudspeaker and enclosure design is alot easier to read and i definitely recommend reading it before the loudspeaker design cookbook.