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Thiele small parameters for infinite baffle

The ability to choose the most appropriate loudspeaker for a particular enclosure is directly related to your understanding of the performance data that manufacturers provide with their products. Prior tothere were no easy or affordable methods accepted as standard in the industry for obtaining this data. The recognized methods were expensive and often unrealistic for the thousands of individuals needing loudspeaker performance information.

These papers were authored by A. Thiele and Richard H. 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. Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure.

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. 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. 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. This is the voice coil inductance measured in millihenries mH.

The industry standard is to measure inductance at 1, 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. 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. View these components like springs. Opposing forces from the mechanical and electrical suspensions act to absorb shock. As a general guideline, Qts of 0. Qts between 0.

thiele small parameters for infinite baffle

Qts of 0. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0. 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.Note - this driver has been discontinued and is no longer being produced.

There has been a lot of controversy in the past surrounding this driver. Some people claim it to be a Fostex FE made for Radio Shack, while others say that the drivers only share a few similarities. It is clearly not identical to a FE It appears that the cone material and frame are different but that the motor is the very similar. The FE is reported to have a touch less bass than thewhile the FE is more extended and better in the high end. Measurements have shown this to be true. The has a higer Q than the FE which results in more bass response, while frequency measurements show that the FE has a smoother and more extended response.

Regardless, the is a very well regarded driver that has been used in a wide variety of DIY speakers projects with a great deal of success. Unfortunately, the Radio Shack driver is no longer available new, but it can occasionally be found forsale on audio forums or eBay.

The pictures show two of the many boxes that the driver has been packaged in over the long period that the driver was produced. The measured frequency response of a driver is shown in the plot below. I don't know what version of driver these measurements were taken on.

The Single Driver Website indicates that the measurments were taken by Steve Sedmak at a distance of 1m, on an infinite baffle at 0, 15, 30, 45, and 60 degrees with no smoothing applied. The measurement system was CLIO. The first of the two parameters is an average of early drivers, while the second number is average of later drivers.

thiele small parameters for infinite baffle

It is unclear where these parameters originated from. Adding Ductseal the basket of the helps imrpove the sound. The picture above shows a stock driver and below is the driver after ductseal has been applied to the frame and between the magnet and the frame.

See the modifications and tweaks for the Fostex FEEn fullrange speaker driver for more examples. Last update 17 December Created 9 February It is a bit technical, and unavoidably requires some familiarity with electrical circuit theory.

The first section presents a derivation of the equivalent circuit of a speaker in sealed, and vented bass-reflexenclosures. Then the relationship between the equivalent circuit response and sound level is presented. The effect enclosure volume has on efficiencyfrequently misunderstood, is discussed. Then infinite baffle, acoustic suspension, and bass-reflex enclosure designs are compared.

Additional issues regarding bass-reflex designs are briefly reviewed. Sensitivity of results to misalignment is discussed, and finally the interaction between enclosures, crossovers, and cables is investigatedas well as the effect of the amplifier damping factor. The Thiele-Small approach is to first analyze the electro-mechanical behavior of a speaker voice coil, magnet, and cone, interacting with the cone suspension and the air in and outside the enclosure.

The resulting equation is mathematically identical to the equation describing a purely electrical "equivalent circuit" consisting solely of resistors, capacitors and inductors.

The sound produced by the loudspeaker can then be obtained via a relatively simple circuit analysis. The highly evolved theory of filter synthesis can be used to adjust circuit parameters to obtain a desired frequency response.

The parameters can then be translated back into physical quantities, such as enclosure size, to build the loudspeaker. This procedure provides a scientific framework veneer? A very useful result is that after the speaker has been assembled, the electrical impedance at the speaker terminals can be measured and compared to the theory. If it differs, the design can be tuned based on this measurement, which is both simple and accurate. The location and height of the impedance spike at resonance are sensitive to any errors in the design, as will be shown.

However, as noted below, for a bass-reflex design some shift in the location of the peaks can be caused by mutual coupling, rather than by a design error per se. This analysis is particularly valuable for designing bass-reflex enclosures where a ducted port also called a vent allows air inside the enclosure to radiate in conjunction with the speaker cone.

The driver parameters, which determine several of the equivalent circuit elements, are known as "Thiele parameters," and are fairly standardized; a table given here [ A method for measuring the parameters is given on the Subwoofer DIY page.

Thiele/Small Parameters for Newbies

The notation in this section generally follows Small's June paper he alters his notation between analyzing drivers, sealed enclosures, and vented enclosures, but all three situations are covered by the circuit derived here.

Small's papers and Dickason's book skip the derivation of the equivalent circuit. You don't need this to build a loudspeaker, but I like to feel as though I understand what is going on physically, so I'm going to go through it in detail. Besides, I enjoy starting from bedrock physics. There are three basic equations:. The cone is assumed to be rigidly connected to the voice coil. All equations are in MKS units. The goal of the equivalent circuit analysis is to solve for the velocity of the cone, and velocity of the air in the vent.

The far-field sound pressure produced by a known velocity is then obtained from equation P6 in the physics section on piston radiation. This equation is an exact solution for a flat piston mounted in an infinite baffle, and is generally a good approximation for real speakers. The voice coil of a real driver is ring-shaped, and rests within a concentric magnet structure see illustration [8kb].

However the equations can be derived from a simplified rectangular structure shown here [3. The voice coil is represented by the yellow wire loop in the simplified figure. The driver permanent magnet produces a field B, shown in red, pointing in the positive y direction.

When the wire loop in the figure moves sinusoidally with a peak displacement x capplying Maxwell's equations Stratton's equation 1, page 2 shows that the motion induces a voltage across the loop terminals given by.Use this program to calculate Qts if you only have Qms and Qes. Data Input: Qms? Data Output: Qts:. Data Input: Speaker's Resonant Frequency fs? Hertz Qes? Port diameter for ported enclosures? Inches Vas? It includes topics from backing up computer files to small engine repair to 3D graphics software to basic information on diabetes.

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It also touches on field target competition. There are links to some of the better sites and forums as well as a collection of interactive demos. Basic Computer Operation :. This site helps anyone new to computers and anyone with a basic understanding of computers with a desire to learn more about the internal components of a computer.

If you have a computer that you'd like to upgrade but don't know where to start, this is a good site for you. Basic Go-Kart Mechanics :. This site is for those who want to begin racing karts but don't fully understand how the various parts work.

It's mostly interactive demos that show how the various parts of the kart work. Use F11 to go to full screen viewing if using Google Translate. I would strongly recommend reading it before you continue with this page. At resonance, the speaker's impedance increases dramatically. The speaker's impedance may go from 4 ohms to more than 20 ohms at resonance. The image below shows how a speaker's impedance changes across the audio spectrum.

You can see by the bar graph that the current flow through the voice coil is the least at resonance. The voltage applied to the speaker is constant for all frequencies.

Data Input:. Data Output:. Sealed Enclosure.Tags: small. Feb 28, 1. Nov 24, Pennsyltucky. When looking at a manufacturer's TS specs for a speaker does the Vd figure reflect the displacement in a vented cabinet or not? If it is for a vented cabinet is it for the low, mid or high volume vented cabinet size? Example: Speaker Vd is cc and recommended vented enclosure volume is 1. When is the speaker at cc? In an infinite baffle or at 1. Feb 28, 2. Feb 24, New Jersey.

Vd is the maximum displacement of the cone at tolerable THD, calculated as cone area Sd multiplied by linear excursion xmax. I'm not getting what you think it is, other than it isn't.

Kroagedhorse and DukeLeJeune like this. Feb 28, 3. Aug 6, SE England. I suspect the OP wishes to have the net volume of the speaker, in order to subtract it from the cabinet volume. Feb 28, 4. RColie and SactoBass like this. Feb 28, 5. Feb 28, 6. A cabinet manufacturer that says arbitrary numbers here when I put this cc Vd cc driver in my cabinet the total output is cc due to the cabinets design. In trying to compare it to another builders cabinet all I have is the manufacturers figure of cc so how do I figure the total Vd of a cc Vd speaker in a well-designed reflex cabinet.

It will be more than but how much more? Feb 28, 7. Feb 28, 8. My impression is that the person who is giving you this information is confused about what they are talking about. BadExampleDownunderwonderRick James and 1 other person like this. Feb 28, 9. Feb 28, DukeLeJeune likes this. Thanks everyone!

As usual these things are far more nuanced than a person with limited understanding and pre-conceived expectations is aware of! Old Garage-Bander and Passinwind like this. DrewinHouston likes this. Last edited: Feb 28, HolmeBass likes this.

No speaker thread is complete without a car analogy: Installing a better transmission won't increase the displacement of your engine.

Radio Shack 40-1197 (FE103) Speaker Driver

Mar 1, Most were specified in the early sixties and seventies by A. Thiele and R. Small, these two also published landmark papers on vented box ported low frequency systems in Thiele and later Small inboth papers were published in the JAES.

Leach and importantly Novak. So what does it all mean. I will not be going into great mathematical or mechanical detail here as this is aimed at the novice. The point at which all the moving parts of the driver sympathize or resonate. So a driver with an fs of 60 Hz will not produce 35 Hz very well.

A driver with an fs of 32 Hz will produce 35 Hz, if the box is tuned low enough. These two examples relate to closed, ported and bandpass cabinets, horns are less affected by fs as they use the driver as a piston. Q is basically a describing word, it is used to describe a quality or characteristic about an electrical or mechanical part of the driver.

So Qts is the overall Q of the driver, both electrical and mechanical. Qts can be thought of as how strong the motor and magnet system are. A driver with a low Qts of around 0. This makes for a tight driver. A driver with a Qts of 0. So low values of Qts give a tight and punchy sound but with little weight or low bass and high Qts values give a slow and heavy sound that will give you lots of low frequency output.

Watch out for drivers with really high Qts values of 0. They are better of being used on the rear parcel shelf of your car, where they can enjoy a massive rear chamber. Qms is the mechanical Q of the speaker and only takes the speaker's mechanical properties into consideration. It is a measurement of the control coming from the speaker's mechanical suspension, which is made up of the surround and spider. Qms is calculated. Fs sqrt Rc. Drivers with a very high mechanical Q can sound more open, cleaner and have a better dynamic range.

DIY Audio & Video

This is because they have less loss. The surround is more flexible, the spider is better constructed, they have better air flow and usually have higher sensitivity. So a high mechanical Q is a very good indicator of energy storage behaviour. So Qts is just a product of Qms and Qes and an understanding of what they are is important when designing a loudspeaker system.

Qts, Vas and fs are all that is needed to determine the box size, but when you get to a very advanced stage of designing, its parameters like Qes and Qms which become the foundation of what you do. The higher the value the stronger the motor.

Given in tesla meters.These parameters are published in specification sheets by driver manufacturers so that designers have a guide in selecting off-the-shelf drivers for loudspeaker designs. Using these parameters, a loudspeaker designer may simulate the position, velocity and acceleration of the diaphragm, the input impedance and the sound output of a system comprising a loudspeaker and enclosure.

Many of the parameters are strictly defined only at the resonant frequency, but the approach is generally applicable in the frequency range where the diaphragm motion is largely pistonic, i. Rather than purchase off-the-shelf components, loudspeaker design engineers often define desired performance and work backwards to a set of parameters and manufacture a driver with said characteristics or order it from a driver manufacturer.

This process of generating parameters from a target response is known as synthesis. Small of the University of Sydneywho pioneered this line of analysis for loudspeakers.

The paper of Chester W. Rice and Edward W. Kelloggfueled by advances in radio and electronics, increased interest in direct radiator loudspeakers. InA. Progress on loudspeaker enclosure design and analysis using acoustic analogous circuits by academic acousticians like Harry F.

Olson continued until when Leo L. Beranek of the Massachusetts Institute of Technology published Acoustics[1] a book summarizing and extending the electroacoustics of the era. Novak used novel simplifying assumptions in an analysis in a paper which led to a practical solution for the response of a given loudspeaker in sealed and vented boxes, and also established their applicability by empirical measurement.

Inleaning heavily on Novak's work, A. Thiele described a series of sealed and vented box "alignments" i. It is important to note that Thiele's work neglected enclosure losses and, though the application of filter theory is still important, his alignment tables now have little real-world utility due to neglecting enclosure losses.

Many others continued to develop various aspects of loudspeaker enclosure design in the s and early s.

Infinite Baffle Subwoofers

From to J. Benson published three articles in an Australian journal that thoroughly analyzed sealedvented and passive radiator designs, all using the same basic model, which included the effects of enclosure, leakage and port losses. Beginning JuneRichard H.

thiele small parameters for infinite baffle

Small published a series of very influential articles in the Journal of the Audio Engineering Society restating and extending Thiele's work. These articles were also originally published in Australia, where he had attended graduate school, and where his thesis supervisor was J.

The work of Benson and Small overlapped considerably, but differed in that Benson did his work using computer programs and Small used analog simulators. Small also analyzed the systems including enclosure losses. These are the physical parameters of a loudspeaker driver, as measured at small signal levels, used in the equivalent electrical circuit models. Some of these values are neither easy nor convenient to measure in a finished loudspeaker driver, so when designing speakers using existing drive units which is almost always the casethe more easily measured parameters listed under Small Signal Parameters are more practical.

These values can be determined by measuring the input impedance of the driver, near the resonance frequency, at small input levels for which the mechanical behavior of the driver is effectively linear i. These values are more easily measured than the fundamental ones above. These parameters are useful for predicting the approximate output of a driver at high input levels, though they are harder, sometimes extremely hard or impossible, to accurately measure.


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