Every Speaker Needs 'Its Own' Enclosure Design and Every Discreet Linear Amplifier (except chip amp) needs Bias Current Setting

Ravindra Desai

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Hello all,

While DIY audio is a section where people are free to experiment to achieve their needs, there are certain guidelines which, if followed, saves you a lot of time, effort and money. These guidelines are based on laws of physics and math associated circuit design and holds true for every type of design be it tubes, discreet semiconductor etc.

One such area which has very strict guidelines is loudspeaker enclosure design.
The truth is that every unique speaker will need its own enclosure designed based on its electrical and mechanical parameters popularly called Thiele Small Parameters or simply T-S Parameters.
While it is completely possible that you may 'land up' with an enclosure design that brings up the best out of your speaker without any math, it will mean relying too much on luck or trial and error methods.
Copying enclosures designs made by 'big brands' has been the trend in PA systems. Little does one know that copying mechanical enclosure dimensions and putting a different driver, even if it is from the same company often leads to disastrous results and can even pre-maturely destroy the speaker.

Another area that needs a mention is amplifier design.
There are a lot of reference designs shared by expert designers. However, if its a linear amplifier (class A or class AB) based on discrete components, then it is important to note, understand and follow the procedure, to set the bias current, associated with each and every design. Unfortunately bias current setting is a manual process and needs to done separately for each and every channel.
By not doing so will result in either class B operation (which results in poor distorted quality), or you may end up creating an expensive cigarette lighter.
Again, it is possible that you may 'land up' in class AB or class A region, but then again, you are chancing your luck.

Power any loudspeaker with any amplifier and you will get sound.
But good sound does not just happen. Laws of physics and math cannot be ignored.

I hope that you will find this topic helpful.
Do let me know if there is anything that needs clarification and I will do my best.

Regards,

Ravindra.
 
@ Ravindra. Thanks for the writeup. Btw, how warm/ hot does this amplifier design goes?
 
Hello all,

While DIY audio is a section where people are free to experiment to achieve their needs, there are certain guidelines which, if followed, saves you a lot of time, effort and money. These guidelines are based on laws of physics and math associated circuit design and holds true for every type of design be it tubes, discreet semiconductor etc.

One such area which has very strict guidelines is loudspeaker enclosure design.
The truth is that every unique speaker will need its own enclosure designed based on its electrical and mechanical parameters popularly called Thiele Small Parameters or simply T-S Parameters.
While it is completely possible that you may 'land up' with an enclosure design that brings up the best out of your speaker without any math, it will mean relying too much on luck or trial and error methods.
Copying enclosures designs made by 'big brands' has been the trend in PA systems. Little does one know that copying mechanical enclosure dimensions and putting a different driver, even if it is from the same company often leads to disastrous results and can even pre-maturely destroy the speaker.

Another area that needs a mention is amplifier design.
There are a lot of reference designs shared by expert designers. However, if its a linear amplifier (class A or class AB) based on discrete components, then it is important to note, understand and follow the procedure, to set the bias current, associated with each and every design. Unfortunately bias current setting is a manual process and needs to done separately for each and every channel.
By not doing so will result in either class B operation (which results in poor distorted quality), or you may end up creating an expensive cigarette lighter.
Again, it is possible that you may 'land up' in class AB or class A region, but then again, you are chancing your luck.

Power any loudspeaker with any amplifier and you will get sound.
But good sound does not just happen. Laws of physics and math cannot be ignored.

I hope that you will find this topic helpful.
Do let me know if there is anything that needs clarification and I will do my best.

Regards,

Ravindra.
Well written Ravindra,A more detailed and practical DIY help could help enthusiasts greatly,starting from elemental knowledge to profound.A separate thread could be made by you and joined with other helpful experts.
-Regards,
Rupy
 
good write up. will add more to this.

every speaker system, be it sealed, ported, t-line, 2way, 3way , 4way, active, passive or anything needs to be tuned after all the drivers and crossovers are put in the enclosure. while most people seldom rely on the ts parameters and response graphs given by the manufacturer, which i reckon may vary with the actual product. so to build a properly tuned and calibrated speaker system any audio enthusiast should have some audio measurement tool to fine tune the simulated design. speaking of passive crossovers, an ideal crossover should have inductors the size of a large transformer, to keep the dcr very low, almost all the inductors available in the market have dcr > 0.5ohm, would be even higher for 1mH and above, which makes the damping factor of the amplifier useless. so, there is this trade off to bear.

Active systems are the most accurate and most efficient. where the speaker is directly connected to the amplifier output, it is here, the damping factor of the amp comes in to play as the amplifier can damp odd harmonics and resonances. Also, as very good dsps are available now at decent prices, a really good system can be realized, while carefully setting the crossover and equalization parameters of the system, to achieve a near flat response across the audio band.

Speaking of linear amplifiers, Class A, AB, G etc, its about the whole design and circuit topology of the amp which gives it its character. every stage in the amplifier design has to be carefully biased and loaded. while most commonly used domestic amplifiers are class AB, they have their own sweet spot of the quiescent current setting, which may alter the tonality of the amp completely even being in class AB region itself.

TBH, this is just my opinion based on my experience, and most importantly, every person perceives differently, while one system may sound perfect to one person and rubbish to other. that's purely subjective. So, i rely more on my unbiased tools rather than ears.

Regards,
Aniket
 
@ Ravindra. Thanks for the writeup. Btw, how warm/ hot does this amplifier design goes?

This is not about any specific amplifier design. It is a general statement about all class A/AB designs.
As bias current increases, you go from class B towards class AB. When bias current increases to the level of load current (power spec of the amplifier), you are in pure class A. So no signal (idle) current is nothing but heat or lost power.

Well written Ravindra,A more detailed and practical DIY help could help enthusiasts greatly,starting from elemental knowledge to profound.A separate thread could be made by you and joined with other helpful experts.
-Regards,
Rupy

I would love to take a live session to discuss about amplifier design. However posts on the forum on a general topic would be difficult.
For anything specific, I do jump in as needed/ possible.

Regards,

Ravindra.
 
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