dave_Edwards

Three types of standing waves affect all previously manufactured loudspeaker enclosures. The first and most powerful is the axial standing wave---The axial wave involves only two enclosure walls that are parallel to one another. Next in order of strength is the tangential standing wave which involves four enclosure walls that are parallel to one another. This type of standing wave has only half the energy of an axial wave (3db down). The last and least powerful standing wave is the oblique which involves six enclosure walls and it has only one fourth the energy of the axial wave (6db down). A sound wave has a positive portion starting at 0 degrees to 180 degrees and a negative portion starting at 180 degrees. If the positive portion of the wave (i.e. compression) meets the negative portion (i.e. rarefaction), then the waves will combine and will be out of phase relative to each other. Likewise, if the positive portion of the waves meets another positive portion of the wave then the waves are in phase (i.e. the waves reinforce each other) the sound will be inordinately loud (i.e. the high pressure zone). Likewise, at locations in the enclosure where the sound waves are out of phase (one being negative and the other being positive) the sound waves cancel each other out and no sound will be heard (a low or no pressure zone). In any enclosure design standing waves produce a big problem but some simple ways of getting rid of them is to fiberglass the enclosed area of the enclosure on all walls--or to add wedge angles into the corners. Just remember standing waves are created when two waves moving in opposite directions interfere. When a reflected wave reinforces a reflection of the original waveform the sound waves reinforce themselves, increasing in altitude. hope this helps, Dave

Hello and feel free to ask me any questions you might have---I think i have a good reputation here

Reminds me of DLS amps

Alittle more in depth---and away we go! copied from the Basic Car audio web site and from FXN A power amplifier takes an input signal, usually a preamp level signal, which has both low current and low voltage characteristics, and produces an output which will have higher current and voltage levels. The power supply available to the audio output IC in a head unit is limited to the battery voltage of the vehicle. This means that the head unit can produce an audio signal with a limited (by the battery voltage) voltage swing, and therefore a limited power output to the speaker. Most amplifiers have a special circuit (switching power supply) to boost the available battery/charging system voltage to a higher voltage. The higher voltage developed in the amplifier's internal switching power supply will allow the audio output voltage swing to be greater. This allows the amplifier to produce more power into the speakers connected to the amplifier's output terminals. Most amplifiers will have some sort of level or "gain" control. This control is used to match the output of the head unit to an amplifier. The maximum audio output voltage from different head units will vary. If there were no gain controls, some head units would not be able to drive the amplifier to its maximum power level. Other head units may drive the amplifier to full power at a fraction of its volume control's range. Virtually all amplifiers have battery, ground and remote connections which must be connected for the amp to operate. The battery connection is the high current +B source that's connected to the battery via a properly fused wire. The size of the power wire is determined by the current the amplifier draws and the length of the wire (from the battery to the amplifier). The ground is another high current connection and is connected to the chassis (body/floor pan) of the vehicle. The ground wire is typically as large as the power wire. The remote connection is a low current control input that tells the power supply of the amplifier to power up. The remote input current for amplifiers varies with the amplifier and the model. Some draw minimal current. Others draw a little more. The upper limit of a properly functioning amplifier is approximately 50ma (0.05 amps). If you're using/controlling more than 2 amplifiers, it is (in my opinion) much better to use a relay to control the amplifiers. Actually I really prefer having a relay in the remote circuit (no matter how many amplifiers I'm using) because it protects the head unit's remote output circuit in case of a short circuit. The input circuit (sometimes called the 'front end') generally employs a noise cancelling circuit which compares the signal on the center conductor (the audio signal) to the signal on the RCA shield (which generally has little or no signal and is only used as a reference) and amplifies the difference between the two. The input impedance is the impedance (that the signal source 'sees') from the center conductor to the shield on an unbalanced input circuit. A typical input impedance would be ~10,000 ohms but some amplifiers may have an input impedance of more than 50,000. If the input circuit uses a mini DIN type connector, the input impedance could be measured from one signal terminal to the other or from the signal terminals to the shield ground. Ideally, the impedance should remain constant throughout the audio band. More than a few amplifiers employ some sort of high frequency noise filter which will cause the input impedance to fall slightly at the upper end of the audio spectrum. These filters are designed to reject high frequency noise from the amplifier's switching power supply. It should also remain constant regardless of the position of the gain control. Some amplifiers (especially budget amplifiers) will have varying input impedance when the position of the gain control is changed. Head units (or equalizers, crossovers...) with low output impedance will handle these variations better than standard head units. Generally, a head unit with high output impedance will have reduced high frequency response if the amplifier's input impedance isn't consistant across the audio spectrum. Unbalanced Input Circuit: This type of circuit has a shield ground that's not directly connected to the chassis ground but may have only a few hundred ohms of impedance from the shield to ground. This type of circuit would be designed to accept a single ended signal (signal only on the center conductor). Balanced Input Circuit: Some Amplifiers have balanced inputs. This means that both the center conductor and the shield (if they're using RCA type connectors) can accept an audio signal. If the amplifier uses RCA type connectors and has balanced inputs, it likely uses the chassis ground as a reference (which is a testimony to the noise rejection abilities of a balanced input circuit). If the amp uses a mini DIN or some sort of professional audio connector, the connector will have provisions for two audio signals per channel and a dedicated ground (reference) connection. Highly regulated amplifiers employ PWM switching power supplies. Unregulated amplifiers don't use Pulse Width Modulation to maintain a constant rail voltage. This does not necessarily make one design inherently better than the other. Both designs have their advantages and disadvantages. Capacitor: A capacitor is an electronic device which consists of two plates (electrically conductive material) separated by an insulator. The capacitor's value (its 'capacitance') is largely determined by the total surface area of the plates and the distance between the plates (determined by the insulator's thickness). A capacitor's value is commonly referred to in microfarads, one millionth of a farad. It is expressed in micro farads because the farad is such a large amount of capacitance that it would be impractical to use in most situations. Capacitor and DC voltage: When a DC voltage source is applied to a capacitor there is an initial surge of current, when the voltage across the terminals of the capacitor is equal to the applied voltage, the current flow stops. When the current stops flowing from the power supply to the capacitor, the capacitor is 'charged'. If the DC source is removed from the capacitor, the capacitor will retain a voltage across its terminals (it will remain charged). The capacitor can be discharged by touching the capacitor's external leads together. When using very large capacitors (1/2 farad or more) in your car, the capacitor partially discharges into the amplifier's power supply when the voltage from the alternator or battery starts to fall. Keep in mind that the discharge is only for a fraction of a second. The capacitor can not act like a battery. It only serves to fill in what would otherwise be very small dips in the supply voltage. Capacitors and AC voltage: Generally, if an AC voltage source is connected to a capacitor, the current will flow through the capacitor until the source is removed. There are exceptions to this situation and the A.C. current flow through any capacitor is dependent on the frequency of the applied A.C. signal and the value of the capacitor. TECH TIP: For a good ground: Get a 3/8 inch bolt, nut and lock washer, find a place on the body that can be accessed from the inside of the vehicle and out. You must be able to get to both sides so that you can hold the nut from turning when tightening it up. Drill a 3/8" hole for the bolt, making sure NOT to drill through any fuel lines, brake lines, the gas tank or anything else. Scrape the area under the bolt (inside the vehicle) to remove ALL paint and primer then bolt the ground wire's ring terminal down with the 3/8 inch bolt. As a side note: For grounding devices that draw only a few amps (like crossovers, head units and equalizers), you can use virtually any type of screw. Many people warn against using the black oxide coated screws but it won't make a big difference because the electrical connection is between the ring terminal and the metal surface that's been sanded clean and not through the screw. The screw simply holds the ring terminal to the metal. Amplifier mounting: DO NOT mount an amplifier on your subwoofer box. I know that there has been a great deal of discussion over mounting an amplifier to an enclosure and many people do it all of the time with no problems but those people probably build good enclosures from 3/4" (or thicker) MDF with extensive bracing. Most people (especially young impatient people) are too lazy to do that and build unbraced enclosures from 5/8 MDF. These enclosures will flex considerably more than a proper enclosure and will likely cause amplifier failure if the amp is mounted to the enclosure. REASON: When the woofer(s) moves in or out, the box flexes and therefore causes the sides of the box to vibrate. This vibration is transferred to the amplifier mounted to the box. All of the electrical components in the amplifier have mass. Inertia (an object in motion tends to stay in motion, an object at rest tends to stay at rest) tells them to stay at rest, the box vibration is trying to make them move. The energy from the box's vibration is transferred to the components through the electrical leads which are soldered into the circuit board. All of this will cause the components to break loose and therefore cause the amplifier to fail prematurely. Basically, the amplifier will commit suicide! I'm not telling you this because someone told me it was bad. I've been repairing amplifiers since ~1985. Virtually every amplifier that's come into my shop with parts rattling around inside them have been mounted on the speaker box. It causes the legs of the semiconductors to break (which causes amplifier failure). It causes the capacitors to break off of the board (which can cause catastrophic amplifier failure). It causes solder joints to break on the semiconductors mounted to the heat sink. It causes transformer windings to grind into one another (which causes lots of smoke to pour out of your amplifier). People who repeatedly tell others to mount their amps on the speaker box because they've never had a problem remind me of people who drink and drive and say there's nothing wrong with it because they've never crashed their vehicle. Eventually, in both cases, problems will arise. AMPLIFIER INSTALLATION NOTES: When installing an amplifier: ----Disconnect the ground wire from the battery. It doesn't really matter which one is removed because removing either connection from the battery (positive or ground) will break the circuit but if you let the wrench touch to ground (any metal surface) when removing the positive wire, you may do significant damage or seriously injure yourself. If you let the wrench ground out when removing the ground wire, you won't have any problems (except maybe scratching the paint). ---- If you don't remove the wire from the battery, at the VERY least remove the fuse (or open the breaker) from the power wire which delivers power to the amplifiers. -----When making the power and ground connections on the amplifier, connect the ground wire first. I know it is tempting to connect the RCA cables first because it is instant gratification (having made a connection) but you may damage the head unit or the input section of the amplifier if the amplifier tries to ground through the RCA shield connection. -----If the amplifier has screw down terminal blocks which are designed to accept either bare wire or spade terminals, use the spade terminals. If you insert bare wire into the blocks, you may have a strand or two of wire touch to the neighboring terminal which is easily enough to convert the amplifier into a paperweight. -----Mount the amplifier down before moving the vehicle. If the amplifier falls or slides against anything, there is a chance that it will be damaged seriously enough to warrant a trip to a repair shop. I know how cool you are (because I know how cool I was at 15 or 16 years old) and nothing could possibly happen but... mount it down anyway. -----When making the ground connection for the amplifier, the floor pan of the vehicle is a better choice than some of the braces and other metal structures that you may want to use for ground. Braces and other such structures are sometimes connected to the vehicle's chassis (body) by a few spot welds which will provide a less than optimum ground return path. ------If the amplifier's ground is properly connected to the body of the vehicle, it will provide a better return path to the charging system's ground than will a ground wire run back to the battery. This is especially true if the ground strap from the engine block to the chassis is upgraded. Amplifier Classes: Most mobile amplifiers use complementary transistor pairs to drive the speakers. In this configuration there is a transistor (or group of transistors) which conducts current from the positive power supply voltage for the positive half of the audio waveform and a different transistor (or group of transistors) which conducts current from the negative power supply voltage for the negative half of the waveform. There are some amplifiers which use the same transistor(s) to drive both the positive and the negative halves of the waveform. NOTE:Amplifiers in classes A, B, and AB operate their output transistors in a 'linear' mode. Class 'D' amplifiers operate their outputs in 'switch' mode. Mode examples: Linear mode: Imagine that you are the amplifier's output device(s) and you must support a 10 pound iron weight (the speaker load). The most difficult method (linear mode) would be to hold the weight straight out in front of you. This would very roughly simulate the linear mode architecture. Your muscles would start to ache in a short amount of time. Think of this pain as the power dissipation in output transistors. Switch mode: In this example, you can support the weight in one of two positions. In the first position, you can hold the iron weight directly over your head with your elbows locked so that your're not really using very much effort to support the weight. In the second position, you would let the weight hang down by your side. This would also use very little effort from your muscles. If you held it directly over your head half of the time and by your side for the other half of the time, it's position would 'average' out to be the same as if you held it out straight in front of you like in the previous (linear mode) example. This would roughly simulate the switch mode which we will discuss later in this page. You can see that with this method (switch mode), there would also be little pain (power dissipation) involved in supporting the weight. CLASS 'A' Many class A amplifiers use the same transistor(s) for both halves of the audio waveform. In this configuration, the output transistor(s) always has current flowing through it, even if it has no audio signal (the output transistors never 'turn off'). The current flowing through it is D.C. A pure class 'A' amplifier is very inefficient and generally runs very hot even when there is no audio output. The current flowing through the output transistor(s) (with no audio signal) may be as much as the current which will be driven through the speaker load at FULL audio output power. Many people believe class 'A' amps to sound better than other configurations (and this may have been true at some point in time) but a well designed amplifier won't have any 'sound' and even the most critical 'ear' would be hard-pressed to tell one design from another. NOTE: Some class A amplifiers use complimentary (separate transistors for positive and negative halves of the waveform) transistors for their output stage. CLASS 'B' A class 'B' amplifier uses complimentary transistors for each half of the waveform. A true class 'B' amplifier is NOT generally used for audio. In a class 'B' amplifier, there is a small part of the waveform which will be distorted. In a pure class 'B' amplifier, the output transistors are not "biased" to an 'on' state of operation. This means that the the part of the waveform which falls within this .6 volt window will not be reproduced accurately. The output transistors for each half of the waveform (positive and negative) will each have a .6 volt area in which they will not be conducting. The distorted part of the waveform is called 'crossover' or 'notch' distortion. Remember that distortion is any unwanted variation in a signal (compared to the original signal). CLASS 'AB' As we said earlier, a class 'A' amplifier is very inefficient. This is not good for a car audio amplifier. We also said that a class 'B' amplifier will cause a signal to be distorted, which is not good in any audio amplifier. A class 'AB' amplifier is the best compromise. A class 'AB' amplifier is a class 'B' amplifier which has a small amount of "bias" current flowing through the output transistors at all times. This eliminates virtually all of the crossover distortion. The bias current is flowing because the output transistors are always conducting current (even without an audio signal). This differs from a pure class 'A' amplifier in the amount of current flow. A pure class 'A' amplifier has an enormous amount of current flowing through its output transistors with NO audio signal. A pure class 'B' amplifier has NO current flowing through its outputs with no input signal. A class 'AB' amplifier is much more efficient than the class 'A' but without the distortion of the class 'B'. MANY of the car audio amplifiers which claim to be a class 'A' amplifier are just a high bias class 'AB' design. These amplifiers are only class 'A' at very low power output levels. At higher power levels, one of the output transistors will switch off while the other output transistor is conducting. I don't want you to think that I am telling you that there are no class 'A' amplifiers. There are a few high quality mobile amplifiers which are a true class 'A' design. CLASS 'D' We said that class 'A' amplifiers were VERY inefficient. Class 'AB' amplifiers are also inefficient but are more more efficient than class 'A' amplifiers. Class 'AB' mobile amplifiers are generally 60% efficient when driving a 4 ohm load at maximum power (just before clipping). The reason that these amplifier configurations are inefficient is because there is a difference of potential (voltage) across the output transistors and current flowing through the output transistors. When you have voltage across the device and current flow through the device, there will be power dissipation in the form of heat. The power needed to produce this heat is wasted power. When there is (virtually) no voltage drop across a device (such as a large piece of wire or a transistor), there can be a significant amount of CURRENT flow through the device with (virtually) no power dissipation. This means that there is virtually no heat given off (highly efficient). The inverse is also true. If you have a significant amount of VOLTAGE across the device (transistor, wire...) but no current flow through the device, again, there will be no wasted power. OK, now to the point. A class 'D' amplifier, which may also be known as a switching amplifier or a digital amplifier, utilizes output transistors which are either completely turned on or completely turned off (they're operating in switch mode). This means that when the transistors are conducting (switched on) there is virtually no voltage across the transistor and when there is a significant voltage across the transistor (switched off), there is no current flowing through the transistor. This is very similar to the operation of a switching power supply which is very efficient. Dave Edwards

I'm just glad to get back to work with Joe---He is a great man and very smart. Dave

Hi Joe, Long time no see---hopefully we can help and teach as much as humanly possable to these guys-----How is CIA doing? If you need anything Email me [email protected] Dave

hello Dave

It's deadened beyond belief. Picking new subs is a hard choice. I think running nothing but horns would work quite well for a while. - Steve 1 Brahma 15 + 3.0 cube tuned to about 25Hz = just a thought Dave

myself----If you didn't build it and don't know what you are doing leave it alone! but if you do know what you are doing----105 degree caps---TO3 output resistors----all that stuff really gets my blood going----to most people a good laid out board---not too much silicone----good weight is a good sign and try to stick to some type of name brand company-----do your homework---check on the amp before you buy---don't just buy it because every other guy has one. Dave

Well guys---I read alot of forums and it looks as though ALOT of people are misinformed about the "basics" of car audio----I need your help----tell me a topic in which we can all give our input and see if we can come to learn more-----I personally am sick of seeing these "which sub or which amp" topics----it is called "learn then deside for yourself". I will talk in depth about all of the topics you want but I need a start----you guys from FXN.net know me pretty well to know I can talk for days about car audio. for the guys that don't know me---- http://www.fordexplorer.net/viewforum.php?f=10 Alot of the stickys are mine. Read and enjoy. Live and LEARN, Dave

QTS=in simple terms---is it goning to be boomy or smooth sounding Vas=air displacement of the subwoofer Fs=free air resonace BL=flatter the better SPL=how much power is really needed to get them loud xmax=linear movement of the cone RMS=Rarely Means chit---RMS from the manufactor is measured so many ways now a days it doesn't really mean anything. If I have the same sub----one 1.0 cub and one 10.0 cubes-----which box can take more wattage?Right the 1.0 cube-----it is always back to simple physics---smaller air chamber----less air to "pressurize" hope this helps alittle Dave

Prior to 1970, there were no easy or affordable methods accepted as standard in the industry for obtaining comparative data about loudspeaker performance. Recognized laboratory tests were expensive and unrealistic for the thousands of individuals needing performance information. Standard measurement criteria were required to enable manufacturers to publish consistent data for customers to make comparisons between various loudspeakers. Thiele-Small Parameters In the early seventies, several technical papers were presented to the AES (Audio Engineering Society) that resulted in the development of what we know today as 'Thiele-Small Parameters'. These papers were authored by A.N.Thiele and Richard H. Small. Thiele was the senior engineer of design and development for the Australian Broadcasting Commission and was responsible at the time for the Federal Engineering Laboratory, as well as for analyzing the design of equipment and systems for sound and vision broadcasting. Small was, at the time, a Commonwealth Post-graduate Research Student in the School of Electrical Engineering at the University of Sydney. Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure. However, they can be invaluable in making choices because they tell you far more about the transducer's real performance than the basic benchmarks of size, maximum power rating or average sensitivity. Fs------This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well. Re--------This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load. Le--------This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs. Q Parameters---------Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same. As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance Vas/Cms--------Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature

<----I, myself am not a RF fan but I hope they prove me wrong with the new line they are putting out. Dave

sorry---I was gonna say either Brahma 12 or XXX 12 Either one in a 1.5 cube tuned to about 30hz with that power would make about anyone happy. Dave

well the 1501 can be modded for daily drive @1 ohm----a few resistors and a new set of caps----the 81000d is also a good choice for mods---the only thing is that the heatsink wasn't really made for the higher temps it produces when driven hard daily @ that low of a resistance rating. need any more ideas--email me Dave

Very good young grasshopper-- 90Hz out of the box----it comes with moddable chips---well they will be when I get done with them Dave

Finally I am getting a Crossover for my system---$150 for a AudioControl 3XS---not bad. just thought I would share

Well----I will give my 2cents here if I may----30, you seem cool and all---i personally think your enclosure is cool---but looks kinda rushed---but guess what------that is my opinion----if you like it and it sounds good---cool----as for all the other guys bashing and all----quit---grow up---give the man 15 minutes in the light and let him show you what he did---you know you would be proud of what you built----am I right?----and 30----you are welcome here-----try to add to this forum as much as you did to the others. Thank you, Dave

Well---I got an EQX instead-----sorry----lol Dave

Well----it is easier to just find out for yourself---- http://www.the12volt.com/caraudio/boxcalcs.asp there ya go--- Dave

Thank you all---I sat back on that night and had a Jack and Coke while watching WWE----the wife was out of town---so it wasn't that bad---I got a EQX also Dave

My brother lost the fight of his life on March 11th at 10:45pm---He had been fighting Leukima for 9 years now---it was in remission last week---he went to get a check up and he had a seziure and they admitted him---his temp was 103 that day---the next day they found a ceribral staff infection on the base of his spine----he was on life support for 3 days and he had a living will so @ 7:00 the family had to do the hardest thing in our lives----we had to say good bye to a great and funny man that loved music and his family with all his heart.I never got to hear him say good bye but I know he heard me---I talked with him for at least an hour----he died in Baptist Hopt. in Winston Salem NC--about 2 hours from my house---he loved playing the drums--so---I like to think he is playing in Heavens band. He was only 51 years old, father of one 14 year old son, and 3 year husband to his 2nd wife. Buck Jr.---I love you and I will miss you---- I just thought I would share with you guys..............

2.25-2.5 cubes tuned to about 30Hz for LOUD SOUND QUALITY applacations---32-34Hz for more of a street vehicle. Hope this helps,

go with the recommended size and tune to a few Hz above the Fs of the sub. That is the way I would do it.

well--I tested a set a few months for Dan Wiggins---the install was the hardest part---they are deep about 3inches or so----they have good weight to them---and I hooked up a Phoenix Gold M100 to them(125 to each speaker)---great off axis responce--and a ton of midbass---for the price you can't get a better sounding set of comps----as for the comparision to the others---yes they "look better" but I will tell you I have Alpine SPX 177a's and I wish I would have bought the Kodas. Dave