Read!!! My Thesis paper on everything sound

[PoorManQ45]

I posted this in the audio section, but there really isn't much activity there. I think this might actually get read if I put it here.

I am writing this for my own personaly use. I am posting it on here to help you guys/girls choose your audio equipment easily. Note, this is specifically about home stereos', but the principles are all the same.

Feel free to correct anything that you think/know is wrong. Please post a link with information contrasting what you think/know is incorrect.

This is the first chapter:

1

Speaker Enclosures

Speaker Enclosures Defined

One of the most common fallacies about the design and construction of a speaker enclosure is that the enclosure is some sort of musical instrument-that it should resonate or have tone. Various types of woods are thought to be more suitable because they are used in musical instruments; or various shapes are chosen because they are shaped like a timpani or a piano sounding board, etc.

The first clear distinction that must be made with regard to speaker enclosures, then, is that they are not musical instruments and that they do not generate musical tones. They are more accurately defined as precision reproducers of musical tones. This means that ideally they will add no tonal coloration of their own, but will remain passive, responsive only to the controlling input signal. The speaker and enclosure are as impersonal as a mirror. Any startling effects emanating from them must be only those produced by the original recording artist.

Two Factors To Consider

In order to construct a speaker enclosure, two factors must be considered in conjunction with each other: (1) the speaker or "driver" and (2) the baffle or "house" in which the driver is mounted. The approach can be from either of two directions: (1) the speaker chosen will determine the type of enclosure to be constructed, or (2) the choice of enclosure desired will dictate the speaker required.

Where decor, size, and limited available placements in a room are the ruling factor, good design consists of selecting the enclosure that best answers the problem at hand and of carefully matching optimum speaker to it.

If performance is the main objective, the speaker should be chosen first, and then an enclosure designed which will provide maximum utilization of the potentials inherent in the driver selected.

Today's designer is afforded a marvelous variety of acoustical devices from which to choose. Low-frequency speakers range from 8 inches to over 30 inches in diameter, with every degree of hard to soft suspension available in each size. The most commonly used sizes are 8 inches, 12 inches, and 15 inches. High-frequency drivers can be conic, ionic, and electrostatic or compression types.

Five basic Enclosure Types

A speaker by itself causes interference with its own output. This is primarily due to the fact that the surface which moves the air (called a diaphragm or cone) causes the air to move both in front and in back of it. These simultaneous impulses generated by the motion of the cone are, unfortunately, out-of-phase. This means that if they are allowed to meet, they will cancel each other. Therefore, if the front of the diaphragm/cone is not separated from the back of the diaphragm/cone, a large percentage of the energy fed into the speaker will be wasted in a fight between the air moved on either side of the diaphragm/cone surface.

There are five basic forms that this separation can take:

1.Finite Baffle - flat baffles, open-backed cabinets.2.Infinite Baffle - walls between rooms, large enclosures totally sealed.3.Bass Reflex - where the radiation from the rear of the cone is usefully added to the radiation off the front of the cone by means of phase inversion.4.Horn projectors.5.Combinations of any of the above.

Finite Baffle

Finite Baffles are most commonly encountered in furniture-type console radios and consist of a board about 2 feet square, with the speaker mounted in the center. This forces the back radiation from the diaphragm/cone to travel a longer path to reach the other side. The larger the board used, the lower the cutoff frequency (frequency at which cancellation starts to occur). The wavelength of the cutoff frequency can be calculated as follows:

W = V/Fwhere,

W = wavelength in feet, V = velocity of sound in air (about 1140 ft/sec), F = frequency of sound in Hertz (Hz).

It can be seen that to prevent cancellation of bass frequencies at 30 Hz, the board would have to be 38 feet square, or 19 feet each side of center.

Infinite Baffles

If the speaker were mounted on a board of infinite length and width, the back radiation would never meet the front radiation, and no cancellation could take place. Then the only determining factor would be the ability of the speaker to move enough air at very low frequencies to allow it to be audible.

An infinite baffle can be constructed by mounting a speaker in a wall so that the front of the diaphragm/cone is in an entirely different room. The area into which the back of the diaphragm/cone exhausts may be as small as 15 to 20 cubic feet if the surfaces are made non reflective to sound waves with fuzzy soft material such as glass wool, Kimsul, etc.

Closet doors, when the closet has a substantial amount of clothes hung in it, can be used as a mounting surface for an infinite baffle. When the door is closed and gasketed, it becomes an infinite baffle. Of course, service presents no problem because of the easy access.

A special technique used in many of today's smaller speaker systems compresses the infinite-baffle idea into a 2-cubic-foot box. In this case, the air that the back of the cone compresses, also serves as an additional spring in conjunction with the one mechanically designed into most speakers. The drawback to this method is very low efficiency as a result of having to substantially increase the cone's mass part of the design process.

Speaker enclosures, in conformance with other facts of life, simply don't allow something for nothing.

Bass-Reflex Enclosures

Another approach is to add the radiation from the rear of the diaphragm/cone to the radiation from the front. This is done by using the volume of air in the enclosure which acts in conjunction with the mass of air entrapped in a tuned port hole to create an in-phase, additive relationship.

This combination of the rear radiation being added in phase to the radiation off the front of the cone results in almost twice the output for a given excursion of the cone than would be expected if the speaker were mounted in an infinite baffle.

These phase-inversion or bass-reflex enclosures offer greatly increased bass response with a minimum of structural and tuning work.

Horn Projectors

Bass response can be substantially increased if the front of the cone is coupled to a long, expanding horn. The old Edison phonographs had a diaphragm about the size of a dime. When the large "morning glory" horn was attached to the small diaphragm, each motion of the dime-sized surface was transformed from a "small-area" radiation into a "large-area" radiation. This means that horns act as acoustical transformers. Such transformers can take many shapes such as conical, hyperbolic, catenary, parabolic, and exponential.

In all types of horns, the effect is to present to the small diaphragm at the throat a very high but consistent acoustical impedance while transforming the high-pressure, low particle-velocity wave from the surface of the cone into a low-pressure, high particle-velocity wave with a low impedance, matching that of the air in the room as it reaches the mouth of the horn.

This consistent high impedance at the throat of the horn can be maintained as long as twice the square root of the mouth area times pi is greater than the wavelength required. If twice the square root of the mouth area times pi is less than the wavelength, then the horn does not properly "load" the diaphragm at the throat to the air impedance at the mouth. From this it can be determined that to have a usable low-frequency horn, large dimensions are required. For 30 Hz, a mouth area of 45 square feet would be needed. Nine times five feet is a large mouth in any room.

Folded corner horns can materially reduce the enclosure dimensions required to achieve such a large mouth area by folding the horn back and forth in its own path before using the corner of the room as the mouth of the horn.

For all these reasons, a horn-loaded speaker mechanism is very efficient; i.e., it will provide more acoustical watts output per electrical watts input.

Combinations

Combinations of these basic forms make up most of the commercial offering in the high-fidelity market today. Economy, decor, and associated equipment limit ideal theoretical considerations. The result is an engineered system whose compromises are not detectable under actual home listening conditions, even in direct comparison with so-called theoretical perfection. This is particularly true because no speaker system has yet achieved anything close to perfection, and while some come closer than others, it is still a question of how much distortion your personal ear enjoys or rejects the most. One person may be tone deaf but appreciate dynamic range. Another may be quite sensitive to pitch (which would require an expensive turntable) and yet completely ignore distortion, compression of dynamic range and regularity of frequency response.

Various popular combinations include:

1.Acoustical labyrinth Advantages: Increased bass loading over extended range. Disadvantages: Large size; out of phase at crossover.

2.Back-loaded horn: This is really a bass-reflex device in which a horn has been placed on the port. Advantages: Good, efficient bass response. Disadvantages: Rough response; phasing at crossover difficult.

3.Front horn-loading of woofer: bass-reflex loading of back of woofer, and straight axis horn for high frequencies. Advantages: Proper phasing can be achieved; high efficiency obtained; very smooth response; exceptional polar response. Disadvantages: Unless size is quite large, bass response falls off below 40 Hz; transient response slightly less than that of a horn woofer. These samples of commercially obtainable systems illustrate that almost any conceivable combination could be tried, and a quick look at the back issues of early High Fidelity magazine will show that indeed they have been.

Design Considerations

This chapter, then, has discussed the important design considerations that should be taken into account before one decides on which of the five enclosure types to plan around. These considerations are:

1.Decor and physical size2.Efficiency3.Smoothness of tonal response4.Range of tonal response5.Distortion in its many forms? A. Harmonic B. Intermodulation or Doppler C. Transient D. Phase6.Polar characteristics

Summary

décor and physical size will be determined by use. The owner of a small apaertment may desire to reproduce only string quartets (where the small infinite baffle with a "long throw" woofer is a good compromise); the owner of a 60-foot living room may wish the Boston Symphony present at a distance equal to first row center (where a large, straight, woofer horn carefully phased at the crossover to a multicellular or sectional horn would create a hard-to-disbelieve illusion). In other words, those who listen to small folk-singing groups, string quartets, modern jazz combos, etc., can accept a degree of power inefficiency in their speakers, whereas those who listen to pipe organs, symphony orchestras, massed choirs, etc., cannot.

No one accepts roughness of tonal response except as a compromise to expense; and in the systems described in this book, every effort is made to achieve the smoothest tonal response possible at any size, price, or performance level.

Deliberate limitation of tonal range, however, is often used and can provide many benefits. In a small speaker, extended low frequency response may be at the expense of excessive distortion, since the small woofer moves nonlinearly at the low frequencies. Much better sound can be achieved by limiting the speaker's low frequency response at the frequencies where distortion starts to increase too rapidly. This can often be achieved by inexpensive high-pass filters either in the amplifier or even in the crossover network.

If both low distortion and wide dynamic range are desired, "think big." If low distortion is desired and dynamic-range compression can be tolerated, then "think small." Cost and décor limitations usually result in a compromise between distortion, efficiency, and less control of irregularities. The better the balance, the better is the combination. Much latitude is offered to the designer in the choice of such balances.

Proper phasing of the low- and high-frequency units is a little-known art, and it will be discussed in detail in the chapter on infinite baffles and also in the chapter on crossover networks. Suffice it to say that without very correct phasing of high- and low-frequency drivers, transients will never be properly reproduced. Sound travels at about 1140 ft/sec, and the ear can detect as little as three milliseconds difference in short duration sounds (castanets for example). Since sound travels 1.14 feet per millisecond, sounds having less than a three-foot path difference can be heard.

While the variety of problems to consider and the infinite number of possible answers can at first seem confusing, approaching each basic design one at a time will allow today's knowledge of the art to fall into place naturally.

There are 7 more parts to come. 8 total. I will be posting them over the next few weeks. Then I will put them all together and present them to AZ and over mods to consider.


Modified by PoorManQ45 at 7:05 PM 10/11/2004

[Falkdesigns]

Holy crap!! That's a lot of work up there! Good stuff man.

[Q45tech]

"Sound travels at about 1140 ft/sec"? In Denver?http://www.tscm.com/mach-as.pdf

As you see the '"lapse rate'" is about 4 feet per 1,000 feet above sealevel correcting for temperature decline with altitude.

"the ear can detect as little as three milliseconds difference in short duration sounds (castanets for example). Since sound travels 1.14 feet per millisecond, sounds having less than a three-foot path difference can be heard" ?

Actually it is much worse than this as phase cancellation [1/2 wavelength] time distance varies with frequency.http://sound.westhost.com/pcmm.htm#2.0

[PalmerWMD]

I believe some members here owe PMQ a email of apology for their snide remarks.

Fred..

[elwesso]

If you are wondering where your posts are..... Please refer to this thread

http://www.nicoclub.com/zerothread?id=86411

Thank you

[AZhitman]

Mark my words - Next one lipping off gets the ban button. Permanently.

I am weary of this. Try me and see.

[PoorManQ45]

Thank you Fred, Wes, and Greg for cleaning up this thread.

I have completed the second chapter of my thesis paper. I don't know if I should post it considering the responses that I got from people.

Let me know if you guys want me to post it.

[AZhitman]

Go for it.

[elwesso]

Definitely... Ill see to it only good comments are posted, unless they are respectful corrections, because I assume thats what your after.....

[PoorManQ45]

There is a PDF file attached. It has all this information and a little bit more.

2

Drivers for Enclosures

Every enclosure alters in some way the performance of the driver placed in it. For best results it is therefore necessary to know the basic limitations of the driver.

Basic Information Table 2-1 illustrated some vital statistics that apply universally to cone-type woofer speakers. Rated cone diameter is the advertised size of the speaker. The three most common sizes are shown. While woofers as small as 3 inches and as large as 30 inches have been employed, good design criteria dictates one of the three sizes shown. If a woofer is smaller than 8 inches, it requires so many cones of that size to generate a usable acoustical power that phasing problems are encountered. This is due to their physical separation on the baffle board.

If the woofer is much larger than 15 inches, the mass of the moving parts becomes too great to retain effective control; and, therefore, poor transient response results.

Column B of Table 2-1 is actual cone diameter. This is the figure to be used in calculating the cone area of a standard size speaker:

A = (pi)D(D)/4 - 8

where,

A = actual cone area, pi = 3.1416, D = diameter of the circle.

Column C of Table 2-1 shows the effective piston areas. Column D shows the amount of peak-to-peak excursion (the distance from the farthest forward movement of the cone to its most rearward position) that would be demanded of any size of cone at 50 Hz if it were required to generate one acoustical watt. This figure has no fixed relation to electrical power required (which may from 2 watts to 500 watts) in order to drive the cone to such an excursion, but it is the acoustical power generated by the mechanical action of the piston moved that distance at that rate. It should be noted that 0.50 inch is the maximum excursion that can be considered without excessive loss of electrical-to-acoustical conversion efficiency. The final column in Table 2-1 shows how many cubic feet must be subtracted from the calculated interior volume of the enclosure due to the physical volume displaced by the driver itself.

Refer to PDF

Choosing The Number Of Drivers And Their Sizes

The following relations should be noted when one decides whether to use a larger or smaller driver versus a larger or smaller number of drivers:

A = cone area, E = cone excursion, F = lowest frequency desired, P = acoustical power desired.

1. If the cone area is doubled, the cone excursion is halved:

2A = E/2

2. If the cone area is halved, the cone excursion is doubled:

A/2 = 2E

3. If the frequency is halved, the cone excursion is increased by a factor of four:

F/2 - 4E

4. If the frequency is doubled, the cone excursion is reduced by a factor of four:

2F = E/4

5. If the cone excursion is halved, the acoustical power is halved:

E/2 = P/2

6. Conversely, if the excursion is doubled, the acoustical power is doubled:

2E = 2P

7. If the cone area is doubled and the cone excursion remains the same, the acoustical power increases by a factor of four:

AE = P 2AE = 4P

8. By the same token, if the cone area is halved and the cone excursion remains the same, the acoustical power is decreased by a factor of four:

(A/2)E = P/4

Using these parameters one can determine the number of drivers desired to ensure achievement of at least one acoustical watt at 50 Hz with low distortion and peak-to-peak cone excursion less than 0.50 inch: Refer to PDF

The maximum acoustical power each size can produce at 50 Hz without exceeding 0.50 inch peak-to-peak cone excursion is as follows:

Refer to PDF file

To mount multiple drivers as woofers, care should be taken to ensure that they are close together. They should operate as nearly as possible as a single diaphragm. The high-frequency drivers should also be mounted close to the low-frequency woofers to minimize phase differences that can occur at the listener's ear if the angle between high frequencies and low frequencies becomes too large.

Efficiency Of The Driver

Changes in cone mass affect efficiency above the point of cone resonance. Tripling the cone mass reduces the acoustical power output by one-half. Conversely, reducing the cone mass by one third would increase the acoustical power output by a factor of two to one, or 3 db.

While reduction of cone mass increases efficiency it also increases distortion. Cone mass is therefore chosen as a compromise between efficiency and distortion requirements. Magnet weight, or magnet mass, changes the efficiency of the driver. Magnet flux is directly proportional to magnet weight and/or volume. The efficiency of a speaker is directly proportional to the flux up to a limit of around 20,000 gausses where saturation of the magnetic circuit occurs. This means, if all other factors remained constant, that doubling the magnet size would approximately double the efficiency of the driver.

It is very possible in actually comparing different drivers to find, for example, that Speaker A has a magnet twice the size of Speaker B, and yet Speaker A has an efficiency one-half that of Speaker B. This could be because Speaker A may have a much greater cone mass, its voice-coil gap may be much larger, its voice-coil resistance may be higher, or it may have a mechanical suspension that is stiffer and more difficult to overcome.

All parameters of the driver-cone area, cone excursion, weight of moving system, magnet size, voice-coil material, size and gap, and the form of mechanical suspension employed-are interwoven with the enclosure design to obtain a speaker system.

Matching Driver And Enclosure

The designer of a successful speaker enclosure cannot change the characteristics of the driver chosen (unless he is also a speaker manufacturer), but must rely on the action of the driver in the enclosure to adjust those parameters needing change.

In using the information gathered here to select a suitable woofer-driver for an enclosure, the following material must be calculated or obtained from the manufacturer:

1.How great an excursion of the cone, for the size driver being contemplated, would be required at the lowest frequency and highest sound pressure level (spl) desired?

2.At the lowest frequency and highest spl desired, is the electro-acoustical efficiency of the driver high enough to allow?A. A commercially available amplifier to be used?B. The required sound pressure to be reached without exceeding the power capabilities of the speaker?

3.If a smaller diameter driver is chosen, does the number of drivers required for sufficient bass response lead to detrimental phase relations as the frequency is increased?

4.Does the driver chosen retain linear response, low distortion, and acceptable polar characteristics at least to the nominal crossover frequency?

In considering all these factors, realize that no single unit can possess all the qualities required. Engineering design consists of Balancing the choices available to achieve the greatest harmony between conflicting requirements.

A Low-Cost Example

An excellent example of a low-cost, small-size, wide-range 8-inch would have these features: a large magnet to help raise efficiency, a large cone excursion to allow useful amounts of air to be moved at low frequencies, a subdivided cone to allow minimum variations in amplitude response as frequency is increased, and a flat cone in order to avoid a restriction in the angle of coverage at high frequencies.

Importance Of Balances

An important factor to consider in speakers is balance. Regardless of whether or not the full range or less than the full range is to be reproduced, the multiplication of the highest frequency by the lowest frequency to be reproduced should equal a figure close to 500,000. For example, a really full-range unit operating from 25 to 20,000 Hz equals 500,000. A system that operates from 35 to 15,000 Hz equals 525,000. If the highest frequency to be reproduced were chosen as 10,000 Hz, then 50 Hz would be preferred as the lowest frequency, and 60 Hz the highest compromise at the low-frequency end of the system's response.

Multiple Arrays

In order to produce the same acoustical power at 50 Hz, a 15-inch speaker will have to move only about one-half the distance that a 12-inch cone has to move. Two 12-inch cones mounted closely together can produce the same acoustical power with one-half the cone excursion for each unit.

When speakers are used in multiples for the same frequency range, danger of phasing problems arise. Phase should not be confused with polarity. It is a simple matter to ensure that four 12-inch speakers on a panel have the same polarity (that they all move forward at the same time and all move backward at the same time), but the phase difference of the radiation from the far left cone on the panel compared to the radiation from the far right cone on the panel can be substantial at certain frequencies and at certain listening positions in the room. To minimize these phasing problems, multiple-cone arrays can be arranged in a few ways.

If two speakers are separated by an excessive distance, phase cancellation will take place when the listener is positioned at unequal distances from the two speakers (angular displacement). This phase cancellation will occur at those frequencies where the difference in distance from one speaker to the listener is one-half wavelength of the distance from the listener to the second speaker.

It is this problem that rules out the use of many small but inexpensive speakers to obtain a high-performance speaker.

Phasing Woofer And Tweeter

Still another aspect of phase relations has to be considered-time delays between drivers operating at the same frequency in the crossover region. Sound travels at approximately 1140 feet per second. This means about 1.14 feet per millisecond-a foot every 1/1000 of a second. It has been demonstrated that the ear can detect differences as short as three milliseconds on sounds such as castanets. This was strikingly illustrated when, in 1935, the movie sound track of the tap dancing of Eleanor Powell reproduced the taps with an added echo on the two0way speaker systems then in use. It was soon discovered that the low-frequency driver and the high-frequency driver used for there recordings were some eight feet apart due to the difference in the length of the horns employed.

When the high-frequency unit was moved back to the point where both drivers were in the same vertical plane, the echo disappeared. Subsequent study of the problem proved that a delay of less than three milliseconds was not detectable in systems using crossovers in the region of 350 to 800 Hz.

Efficiency

Just what is meant by efficiency In the final analysis it means the usable loudness in the listening space. A full symphony orchestra can reach an spl (sound pressure level) of 120 db at the listener's ear. If one wished to reproduce the original dynamic range of an orchestra, this is the level one would need to reach in the listening room.

The power required to produce this level in a concert hall of 600,000 cubic feet (such as Symphony Hall in Boston, Mass.) and the power required to reproduce a similar level in a living room 30 ft x 20 ft x 8 ft, or 4800 cubic feet, is quite different even though the spl is the same.

Assuming that one is willing to sit as close as eight feet from the speaker system, then the goal would be 120-db spl peak intensity at eight feet from the system as a maximum acoustical power output. At eight feet, 0.4 acoustical watt would be approximately 100 db; 120 db would be 40 acoustical watts.

The large, built-in system described in Chapter 3, on infinite baffles, has a measured peak efficiency, in the 50- to 400-Hz range, of 40 percent (plane-wave tube measurements). This means that an amplifier peak output of 100 electrical watts would give an acoustical peak output of 40 watts from the speaker. It should be noted that most of the sheer power present in a musical passage that would reach 120-db spl would be concentrated well below 100 Hz, and as the ear does not hear sounds in the bass regions as efficiently as it does in the midrange, the loudness of these sounds is more ?felt? than heard; but the power required is high. Yet there are on the market today, speaker systems with efficiencies as low as 0.1 percent. This means that for the same loudness at any given frequency, the less efficient system would require 400 times more power than the 40-percent efficient system.

In order to achieve 120-db spl at eight feet, with a speaker of 0.1-percent efficiency, the peak electrical input power would have to be 40,000 watts; if the speaker were 1-percent efficient, then 4000 watts would suffice; and if 10-percent efficient, 400 watts would do the job.

One also has to bear in mind that even if amplifiers were free, and one had 40,000 watts available, the speaker that would require such an input never is capable of handling such power. It usually is rated at a maximum of 250 watts before burnout. If enough units are put together to withstand power-handling problems, then the same type speaker no longer exists, but instead, a new multiple-driver type comes into being with all its attendant phase problems.

Efficiency And Equalization

One of the major disadvantages of the low efficiency that often is not readily detected by the novice is the limitation it places on any chance to use a bass-boost control on the amplifier (often desirable because of a poor listening room and/or recording).

Consider a system that is 1-percent efficient. To produce 100-db spl at eight feet would require forty electrical watts from the amplifier (100-db spl at eight feet requires 0.4 acoustical watt from the speaker). Suppose still further that a 60-watt amplifier is being used-real continuous watts, not music power, peak, or other short-term values. In quality amplifiers, a 12-db bass-boost capability is usually considered conservative. A mere 6-db boost in bass response requires 160 electrical watts (40 watts times four), 100 watts more than the 60-watt amplifier can provide; 12-db boost would require 640 electrical watts. This means that the bass-boost controls are not really usable with the speaker selected.

Using a system that is 40-percent efficient would require one electrical watt for 100-db spl at eight feet; 6-db of bass boost would require four electrical watts; and if all 12-db bass boost available were used, the amplifier would be called on to produce 16 electrical watts. In this case the choice of speaker would allow full use of the capabilities of the amplifier chosen to power it.

If one either sits closer that eight feet (at four feet a 6-db increase occurs) or accept some compression of dynamic range, efficiency becomes an allowable parameter to compromise. For example, the listener who enjoys folk music and small jazz combos finds that such groups seldom, if ever, exceed 100-db spl. Let's imagine that this same listener lives in a quiet apartment. The ambient noise in the listener's apartment is about 45-db spl total reading. This means that with a top level of 100-db spl there is 55 db of dynamic range available. To achieve this degree of dynamic range, the 1.0-percent efficient speaker needs a 40-watt amplifier; the 10-percent efficient speaker needs four watts; and the 40-percent efficient speaker will need only a 1-watt amplifier.

The choice of a maximum level of 100-db spl permits the listener to consider a speaker with efficiency as low as 1 percent.

Unfortunately, little information is available on speaker efficiency. That which is available specifies one-watt electrical input to produce x number of db spl at a given distance. For example, a speaker with an efficiency specification of 95.5-db spl, at a distance of four feet, from one watt of electrical input. At 15 watts, the speaker can be expected to produce 107.2 db at four feet. If the speaker has an efficiency of 103 db from one watt at four feet, 35 watts would produce 118.5 db at four feet, 70 watts of power would yield 121.5-db spl at four feet.

In short, be sure to give consideration to the anticipated power requirements of the system at equalized settings as well as at ?flat? settings on the tone controls.

At this point still another factor enters the picture. It is a simple matter to get even a three-inch speaker to move back and forth within it's limits at 30 Hz, but the amount of air which it moves remains totally inaudible. A sound that is judged to be a given loudness and measures 60-db spl at 1000 Hz, a 30-Hz tone would have to be 90-db spl to be judged equally loud. At minimum audible frequencies (the quietest tones the ear can detect at a particular frequency) the softest tone the ear hears at 1000 Hz is about 5-db spl. However, a tone that is just audible at 30 Hz must be at least 60-db spl.

High-Frequency Drivers

High-frequency drivers do not normally require special housings; however, there are a few factors that relate to matching a suitable high-frequency unit to the woofer-enclosure combination chosen are:

1.The efficiency of the high-frequency unit should be close to that of the low-frequency unit so that the final exact match at crossover can be accomplished with a minimum or even a lack of attenuators.

2. The two units should be mounted so as to minimize differences in phase (distance form woofer diaphragm to the ear as compared to distance from high-frequency diaphragm to the ear).

3. The quality of tonal response, the polar pattern, and the impedance should harmonize with the low-frequency driver.

Coaxial and triaxial speakers solve all these problems inasmuch as they are mechanically, electrically, and acoustically integrated systems adjusted by the manufacturer.

If one is building his first enclosure, it is possible to greatly minimize the potential problems by choosing a coaxial or triaxial driver unit. For those who are ready to attempt simple measurements and are willing to do some experimenting on their own, the separate driver units offer a much wider latitude of performance.

Refer to the PDF file for charts and tables


Modified by PoorManQ45 at 7:05 PM 10/15/2004

[AZhitman]

OK, smart guy, time to make yourself truly useful.

Wanna help me with some ohm issues?

I have a good 4-ch amp, a big-arse capacitor, a cheap bridgeable amp, a set of good components (2 @ 6.5" and 2 @ 4"), a passive EQ and a bass tube. All hardware must remain constant, as it was... hold your breath.... wait for it.... CHEAP.

I wanna hear about running the speakers (Infinity Reference and MB Quart) at 2 ohms - pros / cons and how-to.

Also, any other suggestions to get the most bang for my (already spent) buck.

Hahaha, look who's asking questions NOW!

[pito11213]

Nice stuff you got there Hitman. What is the wattage of the amp? How many watts do the components speakers handle at RMS? On the bass tube does it have an internal amp like a bazooka? Are you going to keep the Bose HU? Infinitis are some top of the line speakers. Having the capacitor may not be necessary depending on how much power you have coming out of that amp. But every little bit helps.

Come on PMQ show your stuff.

[AZhitman]

Got the following:

Kenwood head unit (no clue, came with the car)Clarion 6-disc changer (came with the car)Sony 12-band passive EQ with sub outs (used to have a Yamaha EQ and I LOVED it)Lightning Audio S4.600 (you'll hafta look it up)Majestik 180x2 (cheap amp)Infinity 6.5" Kappa componentsMB Quart 4" 2-ways8" passive Bazooka (might swap it out for a Basslink, put the Zook in the Pathy)5 Monster RCA cables (3 @ 12' and 2 @ 1') and 50' of 16 ga wiring

Total spent? $228 including shipping.

p.s. This isn't for the Q, it's going in my 'vert.

[PoorManQ45]

I wanna hear about running the speakers (Infinity Reference and MB Quart) at 2 ohms - pros / cons and how-to.

I don't know about your specific speakers, but I can give you some general information.

Though your question seems complicated, the answers are very simplistic.

Pros: You get more power than if you were to run the same amplifier at a higher Ohm load.

Cons: Your amplifier will generate more heat than if you were to run it at a higher Ohm load.

These are the only to PROVEN pros/cons of running an amplifier at 2 Ohms.

Now, this is all assuming that your amplifier is designed to handle a 2 Ohm load. If it is designed to handle a 2 Ohm load, there should be no problem with reliability.

Now, if your amplifier is not designed to handle a 2 Ohm or lower load, you might have a problem.

As Ohms Law states: As resistance(Ohms) drops, the current must increase.

If your amplilier is not designed to handle a 2 Ohm or lower load, and you run it at 2 Ohms or lower, it will will cause the amplifier to generate a massive amount of heat. This increased heat usually causes the amplifier to fail prematurely.

So, basically, if your amplifier is designed to handle a 2 Ohm load there should be no major problem with running it at 2 Ohms.

Now, notice that I didn't say anything about your speakers being able to run at 2 Ohms. This is because the speakers that you use will only affect the amplifier in one way: A higher Ohm load will cause the amplifier to run cooler than if it were run at a lower Ohm load.

Contrary to popular belief, the Ohm load that is placed on an amplifier should have no effect on the power output of the amplifier. When a manufacturer states that their amplifier puts out 500w RMS @ 2 Ohm and 250w RMS @ 4 Ohm they are not measuring the output of the amplifier at the higher Ohm load. They are measuring the amount of power that a 4 Ohm speaker will draw. A 2 Ohm speaker will "draw" more current than a 4 Ohm speaker will. This simply means that the 2 Ohm speaker will use more of the available power.

^^^ So, I guess you could use this as an advantage of running a 2 Ohm load rather than a 4 Ohm load.

I have a good 4-ch amp, a big-arse capacitor, a cheap bridgeable amp, a set of good components (2 @ 6.5" and 2 @ 4"), a passive EQ and a bass tube. All hardware must remain constant, as it was... hold your breath.... wait for it.... CHEAP.

See now, isn't the grass greener on my side of the fence . Your statement there basically proves what I have been saying all along. You don't have to spend alot of money to get good stuff. Thats why somebody invented EBAY

Also, any other suggestions to get the most bang for my (already spent) buck.

Do you mind spending a little bit more money? If not, I would suggest using a sound deadning material in the doors, under the carpet, and in the trunk. Now, you have a few choices for sound deadning material. You can go will the popular choice and use DynaMat or something similar. Or, you can do it my way (read: cheap)

For the doors, I would suggest going to a Home Improvement store of your choice and buying some fiberglass insulation. I would suggest between R-12~ R-19. Now, this stuff have a cardboard paper backing. You want to seperate the fiberglass from the paper. This is easily done with a T-square. Now, you cut the fiberglass into 6~12 in sq pieces. You take these pieces and shove them in to the doors. When you have the doors sufficiently "stuffed", you should "roll" down your windows to make sure that they operate properly. If they don't go all the way down, remove some of the insulation.

Now, the floor is a little bit trickier. I don't think you'd want standard fiberglass insulation exposed on the floor . Again, you have to options. You can either use Dynamat or go to the hardware store and buy compressed insulation tape. The insulation tape is basically dynamat, but alot cheaper. Take up all the carpet and start sticking this stuff to the bare metal. Try to not leave in of the metal exposed.

Oops, I just read that you are putting this stuff in your convertable. I don't think you can really do much about outside noise in a 'vert

[AZhitman]

OK, the effect on the amp I understand. And it CAN be run at 2 ohm.

So what's the benefit? More power to each speaker?

I'll be using some Dynamat for the doors and rear panel, the floor ahs already been completely covered.

[PoorManQ45]

Sony 12-band passive EQ with sub outs (used to have a Yamaha EQ and I LOVED it)

I love EQs.

5 Monster RCA cables (3 @ 12' and 2 @ 1') and 50' of 16 ga wiring

You might have an issue with the 16 ga wire. I would suggest getting some 12 or 14 ga wire. Now, it doesn't have to be anything fanci, ie. Monster Cable. Any wire will do as long as it can handle more current than it is required to transfer.

BTW, for connections, it is BEST to use either Copper or Silver. If you don't believe me, go read a high end audio magizine or book once. Audiophiles always use Copper and/or silver connections.

I read somewhere that it will sound better if you use silver connections for the high frequencies and Copper connections for the low frequencies

[PoorManQ45]

So what's the benefit? More power to each speaker?

Basically, yes. The speakers will draw more of the available power than higher Ohm speakers.

[PoorManQ45]

I'm wondering, where are you going to be mounting your amps. Most people mount them in the trunk, but this is not a real good idea if you run a "high power" system. The problem is, there is no air circulation in the trunk. This causes the operating temperature of the amplifier to continuously rise. This could lead to a premature failure, also.

Does your 'vert have a back seat? I have no clue what car you have.

[pito11213]

If cooling is a problem you could mount fans on the amp itself, that run when the amps are on. That EQ is a beautiful addition to any system. For the Q I would want to keep my current HU but instead of having the storage tray underneath I would get a digital EQ. They just sound good and look cool with all the jumping lights.

[PoorManQ45]

If cooling is a problem you could mount fans on the amp itself, that run when the amps are on.

The problem is, there is nowhere for the air to go. It is stagnent. Meaning there is no new air coming in or going out. So, all you would be doing is blowing around hot air.

It's kind of like a convection oven. It has a fan it it. Does the fan help cool the oven? No, it just moves the hot air around

[pito11213]

How about mounting the amp so that it is ported through the back seat. Hitman do you have flip down seats in the back or how about an armrest in the middle. If so you could work it so that when you fold the armrest down the amp would be exposed and the fan would draw in fresh air.

[PoorManQ45]

Ok pito, I can see where we got off the topic.

The problem I stated about excess heat build-up shouldn't happen that quickly in an average system. Which I think that is what Greg's system would be classified as. The excess heat build-up mainly occurs in very high power systems. With 3~4 amps or more. But, it is always better to keep your amp as cool as possible. But, I don't think you should really worry too much about heat build-up. If it's too complicated to try to cool the amps, I would suggest just leaving them alone. They should be fine.

[AZhitman]

A-HA!!!!

Gotcha both!

Neither of you looked at my amp - it has 2 MONSTER fans mounted on it.

Also, the trunk of a 240 is plenty ventilated for amps. The air inside the trunk isn't gonna reach 140-160 degrees, more like 90-110 max in the summer, so it'll accept a lot of heat off the amps.

[PoorManQ45]

A-HA!!!!

Gotcha both!

Neither of you looked at my amp - it has 2 MONSTER fans mounted on it.

Also, the trunk of a 240 is plenty ventilated for amps. The air inside the trunk isn't gonna reach 140-160 degrees, more like 90-110 max in the summer, so it'll accept a lot of heat off the amps.

You were just waiting for a reason to say that, weren't you.

Are you satisfied with the answers that I gave you?

Do you have anymore questions?

Does anybody else have any questions?

[AZhitman]

Wanna diagram a 2-ohm setup for me?

[PoorManQ45]

I don't really know what your speakers Ohm rating is.

Could you please tell me. Then I'll show my good Paint skills.

It seems that noone else is reading this thread . Does anybody else have any questions, or things they'd like to correct or say?

[Jesda]

No. But Pioneer is one heck of a bang for the buck for speakers.

[squeefoo]

It seems that noone else is reading this thread . Does anybody else have any questions, or things they'd like to correct or say?

It appears that my original assessment of your knowledge was incorrect.For that, and my unkind remarks... I'm Sorry.

If you stop being goofy, you could be the go-to guy for stereo questions!Now I'm not as afraid of those 16 Ohm speakers I have.

[PoorManQ45]

^^^ I completely agree with that. For some reason, peolple have gotten the notion that pioneer is a lower quality brand. Just because they're cheaper than most brands, that doesn't mean that they're of a cheaper quality. That's like saying since a 92 Q45 costs $4.5k and 92 MB cost $8k, the Q45 is of a cheaper quality. Totally untrue.

Another under rated brand you should look at is Cerwin Vega. They make some amazing stuff. Very high sensitivity, good frequency response, good cone material, and most importantly, they sound great.

[PoorManQ45]

It appears that my original assessment of your knowledge was incorrect.For that, and my unkind remarks... I'm Sorry.

Appology accepted. I have often been told that I initially come across as a complete dumba**. But, once people start to talk to me, they usually change there opinion of me.

If you stop being goofy, you could be the go-to guy for stereo questions!

I like that Idea. I'll try to stop being goofy. But some things that appear to goofy, are actually good ways of doing things. Example: Using home insulation in a car for sound absorbtion. This is a cheap alternative to dynamat.

Now I'm not as afraid of those 16 Ohm speakers I have.

May I inquire as to what those speakers may be?