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Engineering LDLC

Limits of Distortion and Compression are centered on efficiency within the motor geometry.

LDLC provides firm set of manufacturing guidelines that are founded in physics and govern every Harbottle product . These guidelines are the commitment to our clients that make us dependable and reliable and serve to outline specific results and expectations in performance as well as quality control, so our clients know exactly what they can expect within set limits of system design and dependant on their person skill and ability in DIY.

LDLC stands for Low Distortion Low Compression and are limted to 70% BL (Xmax stroke) as minimum. To understand LDLC, we have to look back to the 1950's and the introduction of Hifi in the 1960's. After the world regained some steam from WW2, there was money to be made and the industrial revolution was starting to morph into the age of technology. Hifi was created in answer to the rise of entertainment and over time, the science of audio became better with fine tuning manufacturing processes.

Our ethos, Future Forward Audio, is the dedication to the advancement of audio reproduction as it pertains to the human experience, and LDLC is the method behind this mission statement.​ The term LDLC was created by The Harbottle Audio Company as the definition, standards, and method of communicating the engineering philosophy and manufacturing practice of Funk Audio. This acronym serves as the fundamental of our collective engineering and is the vehicle for Future Forward Audio.

LDLC is an engineering standard which consists of 5 fundamentals exercised ​within 4 principals of sound: distortion, compression, efficiency, and output. The defined minimum limits are at 70% BL, or more commonly noted as Xmax. It is important to know that we consider bandwidth an end use parameter and is not a characteristic of sound, because it can be manipulated in the crossover, whereas sound character is directly a result of driver function when all else is equal; source, interconnects, amplification, the room, and enclosure. This said, we use bandwidth to guide our design process to set system design goals. 

The following is the standard that we design to from the standpoint of the audio application that we solve for. From this standpoint we can see that Harbottle and Funk operate on a completely different level and design from a completely different position in relation to the rest of the audio industry.

Fundamental 1

F1 Threshold Curve: Distortion will only breach the threshold of audibility throughout the entirety of the design frequency response curve at as close to maximum output as possible. The audibility of many types of distortion change with frequency, this is what makes it a curve to determine at what point distortion becomes audible at each frequency.

This standard is based on extensive in-house testing that has resulted in the F1 Curve. This curve demands that the audio system, inclusive of the: driver, finished enclosure, and amplifier, will reach its maximum output right at the threshold of distortion audibility.​ The F1 Curve is based on ​all forms of distortion including but not limited to compression, and the harmonic distortion profile as they relate to the maximum output.

As a point of reference, most systems breach the threshold of audibility by as much as 10 dB or more far below their maximum output. In terms of output, the perception of what is being heard might still be “loud” however, the ratio of distortion to clean audio is drastically altered, resulting in inaccurate audio reproduction.

Fundamental 2

Distortion and compression profile has to fall within the parameters of the first fundamental based on intended use and bandwidth.

Different driver uses have different character. M1 are centered around studio listening; clean, uncolored, and at reference levels ​over a very wide bandwidth. The M2 drivers are centered around theater use, so they have lots in the low end and follow that idea of what cinema output should be, but with miles of room for dynamic content. This is our way of dealing with aspects of physics that limit driver design and allows for personal preference within microscopic degrees of change to suit the intended use. The M3 drivers are the ultimate expression of bass and displays no weakness when considering the intended use and bandwidth. The reason bandwidth is included is because our drivers have a habit of being able to run up the Fr curve with steadily decaying distortion. This means that our recommended crossover points are​ often far higher than what you would ​expect.

Fundamental 3

The compression character has to prove to be linear and predictable, it must be controlled and with no sudden and dramatic decompression or compression behavior.

This form of distortion is more difficult to understand. Compression is one main factor that makes a subwoofer "difficult to blend" with main speakers, even at low volume levels. The effects of compression can: exaggerate the levels of other forms of distortion, cause localization problems especially when a driver suddenly decompresses, make the drivers usefulness seriously debatable, and thus adding to the notion that the only way to benefit from a subwoofer is to have multiple subwoofers. By controlling the compression character within the design, we are inherently controlling the compression behavior of the driver's harmonic distortion profile. This fundamental now exercises control and direction over the first. This means that the decaying harmonic distortion combined with controlled compression results in predictable behavior to the maximum system output while: reducing localization issues, increasing ease of blending with an existing system.


Fundamental 4

All fundamentals must combine to create greater efficiency over the intended bandwidth.

Efficiency cannot be given a value because each intended use will determine the character of efficiency of the driver. We specify that the fundamentals must combine to create greater efficiency than what is normally designed for that size of driver in reality – real world measured results. What do we mean by efficiency?  Efficiency looses are generally first seen in compression. So when the driver compresses more than the audible limit or erratically , then they must be inefficienct and are not combining to create greater efficiency over the inteded bandwidth. Our drivers love voltage, they make better use of each watt when you give them the voltage they love. This means that we can guarantee the result for the client, we can state that the result of a measure like CEA will represent the worst case senario, and in content playback our systems generally over perform by a large margin. When run simulations using our drivers, we can determine the efficiency of the driver in the system to a scary level of accuracy, and this is where we can accurately determine that our drivers will hit intense levels of bass while retaining the 1st, 2nd, and 3rd fundamentals.

Within these fundamentals you will see a relationship, a recipe, and efficiency is a key ingredient that makes our products able to perform far beyond their simulated limits. These fundamentals have varying degrees of influence and can be altered to suit the end result. This is why we offer customized drivers that take one of our designs and bias maximum efficiency, minimal distortion, minimal compression, or capitalize on all of these aspects to their full potential.

Fundamental 5

The materials used for the driver must prove to be of a specific grade and quality and tested and verified for use for every driver and subwoofer built. This is to ensure that each driver or complete bass system will conform to LDLC standards. This is our QC standard that makes our low variation targets possible and as a result each driver is inspected over 100 times and each bass system is inspected over 500 times. So if you order 4 finished subwoofers from us, you will be the recipient of 2000 quality control check points.

Each part and materials are tested and verified for use before manufacturing begins.

Each part is inspected during manufacturing.

Each part is inspected during assembly.

Each part is verified for use during assembly.

Each assembled driver is tested, measured, and approved for use by Nathan Funk.

The relationship between performance variance and low distortion low compression character is that one cannot exist without the other. Taking these steps in quality control is actually necessary to ensure that each and every driver will work to the LDLC standard.


From the LDLC standard we are able tune a driver design to bias one of the 4 principals of sound while maintaining the 5 fundamentals. This means that our clients can experience linear performance regardless of application at a wide variety of manufacturing levels; one off custom to full frame order production, and all without having to buy a design or be subject to expensive prototyping. This saves tens of thousands of dollars or more. Again, this isn't a guessing game. We can predict changes in performance to within +/- 5% of TS parameters.

How can we just say that we don't use small parameters and then refer to them? Because we don't design to them, we will refer to them after the design work is complete, and use them as  a reference point that is twice as accurate at the design stage than the industry standard is at the manufacturing stage.

The industry has no set standard that includes as many forms of distortion as they relate to various frequencies and the audibility of them, and barely touches efficiency. We had to set our own standards for each aspect and we treat all of them as equals in balancing the equation of driver design and extending into system design. Considering audio as a sum of all parts is what sets us apart. When the argument is made that we over engineer our product, the reality is that this statement couldn't be farther from the truth. The end result only appears like the driver is over engineered when it is stacked up against speaker drivers that are designed to small signal parameters. The result is a perfectly balanced speaker according to 4 principals of sound. The application of this standard is not easily integrated into standardized production methods as it directly affects all processes of design, development, and manufacturing.

We are innovators as designers, engineers, and manufacturers. The mark of innovation is the ability to see the depth of a problem and resolve it by embracing change and new thoughts of what is actually possible when applying the full spectrum of science to audio in order to create a whole new level of audio science.

by Cody Hiebert and Nathan Funk




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