Sencheezy

Which way to aim a trunk mounted woofer box in a car has been quite a topic of speculation for years. Folks, through experimenting have found that oftentimes the woofer box sounds much better when aimed backwards, the explanations I hear for why this works are usually quite absurd. One absurd explanation is "the sound wave travels further when the box aims to the rear and by traveling further it sounds better. " Not true, sound actually looses volume as it travels, not becoming louder like his explanation seems to imply! Folks also say "the wave has more room to develop." Well I don't like this explanation either, sound can really reinforce itself amazingly well in a small enclosed space without the need for any wave developing space! And there used to be a story floating around called "bass trap" which inferred a magical property of some cars to eat up all the bass and not let it get to your ears. There still really exists, a problem of building a wonderful well thought out and superbly engineered woofer box which makes bass so perfect my eyes water, with only a few watts of input on my test bench, but then barely has any output when installed into the car, this has driven me nuts for years. Or, building a great box for 12's and installing it only to have less bass than the one I did the day before in a different car using only 8's. The big clue came when I noticed there was much more bass with the trunk open than with the trunk closed! How the hell can that happen??? Opening the trunk lets sound escape(!), letting sound go away cant possible be a good thing. Then why does opening the trunk make the bass inside the car much louder???? I dragged out the test equipment (audio Oscillators, RTAs, Pink noise generators, and built me a couple of test boxes to experiment with. After a few days of playing with all the fun toys I discovered the bass that goes away when opening the trunk was causing cancellation when kept in the car (trunk closed), and turning the box backward made less of a difference when opening the trunk, and moving the box all the way to the back of the trunk eliminated having an increase in SPL when opening the trunk totally. In summary I found: 1. box at front of trunk speakers aiming forward or up through the rear deck = poor in car bass response, much better with trunk open. 2. box at front of trunk speakers aiming backward = better in car bass response by far, slightly better with trunk open. 3. box at back of trunk with speakers aiming forward = better in car bass, no difference with trunk open. 4. box at back of trunk with speakers aiming backward = best in car bass response and gets less bass with trunk open. I used sine waves and mapped out the phase relationships between the incident (direct) sound wave entering the car and the reflected wave that hits the back of the trunk and reflects forward. Since the reflection is bounced into the listening area, you can treat them much the same as having two sources... I drew some pictures to illustrate what I found. In this picture, try to imagine the back of the trunk is the vertical black line at the left of the picture and the little square is the speaker box. This picture is an illustration of what happens when sound comes out of the right side (front side) of the little square speaker box. Sound actually goes forward into the car (incident wave (RED)) and also backwards to reflect off of the back of the trunk (reflected wave (YELLOW))... Both the incident wave and reflected wave get to the listener but they are way way out of phase causing mucho cancellation in the listening area. If you could open the trunk, the reflected wave would disappear and NOT reflect back into the car thus no cancellation... In this picture, the speaker box has been aimed at the trunk instead of in the car and it is plain to see the incident and reflected wave are not nearly so much out of phase as in picture 1! Resulting in much better bass! This picture it represents the speaker box being moved to the rear of the trunk with the speakers aiming forward. The waves are a little closer to being in phase with each other. (were gettin there!) Finally, in this picture we are aiming the rear mounted speaker box to the rear so the incident and reflected wave are very close to being in perfect phase, reinforcing each other quite well. These pictures are simulating a 60Hz bass note with the rear of the box mounted approximately 3 feet from the back of the trunk (reflector) ... Keep in mind we are only discussing the incident and rear reflected sound in an effort to try to simplify this, the reflecting sound waves in a car are much more complex than these drawings indicate but we must start simple before we work ourselves into the more complex, hopefully this will be a nice foundation for those of you who wish to study this phenomenon further. And for those that have the mindset that this can't be true because the interior of cars are small in relation to bass wavelengths, so what? The full wavelength does not have to completely develop to be OUT OF PHASE or IN PHASE with its own reflected sound. The pictures above are showing a 60Hz wavelength and the bounce distance to reflect back out of phase a complete 180 degrees is just over 4 ft. At higher frequencies the distance is less (120Hz is 2.3ft)

Yeah peavey. found on parts express

wow lmao, probably the worst thread / responses I've ever read on this forum. Heisenberg - You should probably stop responding OP - You should do a little bit more researching around here, and just in general. We are here to help you yes, to make informed decisions, but this can't be done if you think 12 + 12 = 24 when talking about sub woofers. What you are trying to compare is referred to as "sd". You want to compare the difference of the sd when comparing a 12 to a 15 etc. I would spend a month or two researching before making another purchase, of any kind. Bassink - Thank you for attempting to straighten this mess out. OP, to answer your question, in a basic response, I would chose the two 12" xcons vs the single 15 and tune it to 32hz with adequate port area. And pay someone to build the design.

http://lmgtfy.com/?q=groundpounder

I come up with 4.4 cubes net. I would do two dss ethos 12". Best option imo

Yeah, I like this one. Definitely has that "in your face" mentality I was describing previously.

I know tim (14k) is really good at PS

Love this quote! And thank you for your response.

any update on that burp box of the driver you have on hand?

I say, make it something bold, and emasculate, create the image of performance and build quality. I like the darker colors, that goes along the image these woofer portray. That in your face, no holds bar performance. Something that represent nothing was left to chance. The image is everything, so it needs to represent so. I like the open-air font, I do, but I don't think of an 70 pound woofer when I see it either. So just try to find that balance, and I'm sure it will draw much interest.

I like it! But it definitely reminds me of chip foose font.

Hey Honda, it's interesting you bring up Tubes, I was doing a little bit research yesterday, (not to thread jack), so feel free to move. source http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/38784-given-cabin-gain-reality-do-we-need-low-fs-2.html Anyway, I think we now understand that damping factor, which is a quality associated with an amplifier, isn't an indicator of anything. I'm going to stop using that term now. The output impedance of the amplifier, if it's great enough, can have an effect on the sound of the system, and that amplifier quality is often called "outut regulation" and is included in the CEA 2006 standard. Here's how that works: As we know from yesterday, the amplifier's output impedance is in series with the speaker. By Kirschoff's laws, the voltage in a series circuit divides proportionate to the resistance. Let's say our amplifier has an output impedance of 1 ohm and we're using a 4 ohm speaker. If the amplifier makes 20 volts (100 watts at 4 ohms by P = E^2/R), then 1/5 of the voltage is dropped across the output impedance and 4/5 of the voltage is dropped across the speaker. 1/5 of the voltage is 4 and 4/5 of the voltage is 16. Now, we can figure out how much power is dissipated by the amplifier's output Z by 4^2/1. Which is 16 watts. 16^2/4 = 64. So, our amplifier that made 100 watts at 4 ohms makes 80 watts at 5 ohms and only 64 of those watts make it to the speaker. OK, an amp with an ouptut impedance of 1 ohm would make a better door stop than an amplifier, but it makes a good example and the math is easy. In that example, we used the nominal impedance of the speaker (as if it was a simple resistor). A speaker isn't a resistor, so if we wanted to figure out how the frequency response of the speaker would be affected by the output impedance we would use the measured impedance at a bunch of frequencies, do the math and plot the curve. Since the voltage from the amp divides proportionate to the series resistances, it's easy to see that the output impedance has a greater effect at frequencies where the speakaer's impedance is lowest and a smaller effect at frequencies where the speaker's impedance is greatest. If the amplifier's output impedance is really high, if you put a resistor in series with the speaker, or if you use 1000 feet of 30 gauge cable, resonance will be nearly unaffected, but the frequencies above that will be more affected. Lovers of Tube amplifiers claim that the 2nd order distortion makes them sound warmer, but I don't think that's what causes that effect. Our brains find very low levels of constant distortion objectionable--zero crossing distortion at 1% is nasty. Distortion on transient peaks has to be about 20% before we say it's as nasty as 1% constant distortion and it's nearly inaudible at 10%. If it was second order distortion that made tubes sound good, there would have to be whole lot of distortion. However, many old tube amps had VERY high output impedance. that output impedance attenuates the midrange and leaves the bass unaffected. If you're driving a full range home speaker, the midrange would be attenuated a little, but the bandwidth of the attenuation would be large--we can hear .5dB of attenuation if the bandwidth is more than an octave wide--but the bass would be unaffected. There's the "warmth" that tube lovers love. Passive crossovers don't screw things up, they're just tools that we use to modify the impedance of the loudspeaker at some frequencies to cause less power to be applied to the speaker at those frequencies. The simplest explanation of how they work is that they raise the impedance at frequencies we want to get rid of so the amplifier makes less power at those frequencies. A capacitor on a midrange or a tweeter raises the impedance at low frequencies so less power makes it to the speaker. There are many different ways to design passive networks, but two are prevalent. The cheesy way is to calculate the value of the components using the nominal impedance of the speaker (as if it was a resistor) and then apply the crossover to the speaker (like the way we use active crossovers). Passive crossovers depend on the load impedance to determine the frequency, Q and slope of the filter, and applying a filter designed to provide particular values to a resistive load won't have the same response when applied to a speaker with an impedance CURVE. People who design these kinds of crossovers often use a Zobel network to flatten the impedance that the crossover "sees", so the response applied to the speaker is what they originally designed. The other way to design the crossover (now made pretty easy since we can use computers to model the response) is to use the actual speaker's impedance as the terminal load in the calculations and to choose the component values according to the impedance curve of the speaker. that's the best and most economical way, but without modeling software, it's very difficult. To Scott's point, all passive components have their own DC resistance, which we often refer to as parasitic. That resistance only screws things up if we don't consider it in the design of the network. --- I was wondering what would your take be on this response, regarding the sound of Tube amplifiers?

awesome, looks like things are on track.

Where are the pics?

That looks awesome!

http://www.teamrocs.com/technical/ - great informative stuff

Understanding some Thiele and Small parameters: "Cms = The compliance of the suspension--how easily it's moved Vas = Cms expressed as a volume of air that has the same compliance These two are a measure of the suspension's restoring force--how much the suspension pushes back when the motor moves the cone. Q is a measure of the amount of overshoot allowed at resonance. High Q means that the speaker keeps moving after the signal goes away. Low Q means that the speaker stops moving more quickly when the signal goes away. Qms is the amount of overshoot that the suspension allows Qes is the amount that the motor allows Qts is the total and the formula for Qts is the product of Qms and Qes over the sum of Qms and Qes--like resistors in parallel. Now...if you look at the parameters for 99% of the speakers that are available you'll see that the Qms is always MUCH higher than the Qes. That means that the suspension allows MUCH more overshoot than the motor. Thinking a little further, you'll discover that what that really means is that the MOTOR controls the motion of the cone and the suspension contributes very little control. Both the motor and the suspension work to overcome the inertia of the moving MASS. The motor does a better job than the suspension. essentially, the suspension screws things up. The suspension is there mostly to keep the coil from leaving the gap and should be designed to apply very little force until that is about to happen. Resonance is the point where the motor and suspension make the hand-off. Above resonance, the motor provides nearly all the control and below resonance, the suspension does more work. Above resonance we say a speaker is mass controlled and below we say it's stiffness controlled. Above resonance the motor overcomes the inertia of the moving MASS and below resonance the motor overcomes the COMPLIANCE of the suspension. Here's an example: a super-ball is a high Q device and one of those squeezable things in the check out line of Bed Bath and Beyond is a low Q device. When you drop the super ball, it bounces back nearly to the same height as from where it was dropped. That squeezy thing falls with a thud and doesn't bounce at all. The super ball bounces back because the rubber has a VERY HIGH restoring force--very low compliance or very low VAS. The squeezy thing has a very high compliance--very high VAS. It ABSORBES the force of the impact. Now, back to the boxes. A woofer by itself with no box is controlled mostly by the motor but the restoring force of the suspension causes it to bounce around a bit at resonance after it should have come to a stop. When we put the woofer in a box, we ADD restoring force because the cone compresses (and rarefies) the air in the box when it moves, causing it to bounce around even more--it's a stiffer super ball. The Q is increased (and so is the frequency of resonance). If the box is bigger, there's less force applied to the cone when the air is compressed and more if the box is smaller. The box RAISES the Q. A small box raises the Q more than a large one. For a small sealed box, you need a woofer with a very low Q. A woofer with a higher Q will need a larger box. The box provides the additional overshoot necessary to achieve the desired Q. Here's how sealed box design works. The box raises the Qms of the speaker and we choose a box volume that raises it enough to produce the desired response. Qtc is a measure of how much overshoot the whole system of box and woofer allow at resonance. A Qtc of .707 provides the best combination of flat response and low frequency extension. However, there is some overshoot involved. A Qtc of .5 is critically damped or "transient perfect". There's less overshoot. Before you freak out and decide that you should always build a box with a Qtc of .5 for best accuracy, we have to think a little further: Choosing .7 is like saying, "well, I know it can't be flat, so I'll choose to make it as flat as possible to the lowest frequency possible and i'll deal with the group delay (inaccuracy) below the cutoff frequency." Choosing a lower Q is like saying, "Well, it can't be flat and I don't care about low frequency extension, so I'll minimize the SLOPE of the rolloff for less group delay. I'll make it more inaccurate at some frequencies and less inaccurate at the lowest frequencies." Why would we want overshoot? Because if the woofer contnues moving, it makes bass. We want the woofer to continue moving a little bit at resonance, to boost the bass at the bottom of the response for better low-frequency extension and flatter response. Choosing a lower Qtc is essentially managing the compromise a little differently. The reason we care more about flat response and low frequency extension more than minimizing overshoot is because flat frequency response from the system IS transient accuracy, by the Fourier Transform. Choosing a Qtc of .7 is like saying "I want perfection down to the lowest frequency possible". Choosing .5 is like saying, "I'd prefer to have the transient accuracy be less screwed up at the very lowest frequencies and in order to get that I'll let it be a little scewed over a wider range of frequencies" The easiest and best rule is to choose flat response and wide bandwidth if it's accuracy that you're after." - site http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/38784-given-cabin-gain-reality-do-we-need-low-fs.html

Understanding the limits of WinISD This is a short, simple tutorial on how to interpret the results of your typical subwoofer box modelling software such as Winisd. Here's our good old trusty Ascendant Audio Atlas 12" modelled up using the manufacturer supplied t/s parameters and Winisd. Notice the shape of the rolloff, and an F3 point of about 52hz. Not bad. Now take a look at the actual, measured frequency response (semi-anechoic) at 1 watt, 20 watts, and 75 watts of power. First off, you can see that while Winisd was fairly accurate, there was still some differences between the actual response and the calculated response. Note that the actual -3db point is around 56hz vs. predicted Winisd 52hz, and the actual -6db point is ~48hz vs. Winisd's prediction of 40hz. This is due to variance in t/s parameters between the actual sub, and the manufacturer's specifications. We can also see that the frequency response changes with different power outputs. At 400 watts of power I'm sure the response looks quite different, but unfortunately my amp would only do 75 watts before clipping Also, it's pretty evident that Winisd does not take into account the upper end response of the driver. Now let's look at the same sub in the trunk of a Honda Accord (Gold line). Now that looks nothing at all like what we modelled So you can see that the car's interior itself and placement has the greatest effect on the frequency response. So to sum up, what do box modelling programs like Winisd tell you? They can tell you: 1. The low end frequency response of the box+sub "ONLY", based on the manufacturer's supplied t/s parameters. The actual t/s parameters can vary by quite a bit, and will change the low end frequency response. For a ported enclosure, I wouldn't even think of using the manufacturer supplied t/s parameters, but rather I would measure the actual t/s specs myself. Reliable manufacturers are generally around 10-15% deviation from what I've noticed, while I've seen some t/s parameters that were off by at least 50%. 2. Frequency response changes with power output. The more linear your subwoofer's motor, the less shift you will see as power increases. 3. Frequency response changes DRAMATICALLY with the listening room/car, and placement. In conclusion, Winisd can be a powerful tool for comparing different driver's low end response in a variety of enclosures against each other, but the actual frequency response in-car is going to depend on quite a few more factors that Winisd(and similar programs) cannot account for. One last thing that I forgot to mention. If you subtract the in car response from the sub+box response, you can find the transfer function of your vehicle. Applying this transfer function to Winisd's calculated response can give you a much better estimate of how a sub wil sound in your car. -sited from http://www.diymobileaudio.com/forum/how-articles-provided-our-members/19-understanding-limits-winisd.html

Phase Plug "Phase plugs may be placed in front of woofer cones, especially in horn-loaded loudspeaker designs. In the same fashion as compression driver phase plugs, the intent is to minimize higher-frequency wave interference near the driver. In this case, "high frequency" is relative to the intended bandpass; for example, a 12-inch (300 mm) cone woofer might be expected to reproduce 550 Hz energy near the top of its intended range, however, the wavelength of 550 Hz is approximately twice the diameter of the woofer, so wave energy at that frequency traveling laterally from one side to the other will be out of phase and will cancel. With a phase plug in the center, such lateral wave energy bounces off of the obstruction and is reflected outward toward the listener. Phase plugs for woofer cones are typically solid plugs positioned over the woofer's central dust cap, or in the center of the woofer, replacing the dust cap." - Sited from The Cook Book

Transfer Function As the Polk/MOMO subwoofers are optimized for acoustic suspension enclosures, we suggest you use this type of design. The acoustic suspension cabinet is a sealed airtight box, and is the easiest box to build. It also is a very predictable enclosure with easily calculated parameters, and it has a smooth natural sound. Properly built acoustic suspension cabinets have a flat frequency response that begins rolling off at 12 dB per octave at the frequencies below its cabinet resonance. This works very well inside a car because of a natural phenomenon called "room gain" that gives you roughly a 12 dB per octave increase in bass frequencies. You can roughly calculate at what frequency this gain begins by using the equation F= 565/L, F is the frequency at which bass gain begins, and L is the longest dimension of your "room." If, for example, you measured the longest dimension of your car as 5.65 ft., the room gain begins at 565/5.65 or 100 Hz. If your goal was perfectly flat frequency response you would design your cabinet for this particular car to have a resonance frequency of 100 Hz. Since most people want more bass than a flat frequency response yields, tuning the cabinet at a lower frequency, say 50 Hz, would give you a gain of 12 dB per octave between 100 and 50 Hz and flat response from 50 Hz down. The larger the cabinet, the lower the resonant frequency, and the lower the efficiency. Two identical systems will sound very different in a Honda vs. a Cadillac. The bigger the car the lower the frequency at which room gain begins.

Since we are all very familiar with this phrase, I though that I, as well as anyone who is interested, to collectively share any real knowledge, related to car audio, into this thread. Preferably information that has been tested and proven and that has data to back it up. Such as formulas, graphs, and things of the like. If no URL is available, then go ahead and copy the material word for word, with the topic in bold letters before your response. I'm in hopes we could use this thread as one big knowledge base.

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