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Thread: Active Loudspeakers - The what, where, why and how of your active loudspeaker project

  1. #31
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    In addition to my posts above on the audibility of noise from audio electronics I find it quite intuitive that two power amplifiers with different distortion profiles below -80 db can subjectively sound different.

    Given Robert’s observations on ambient room noise at -40 db how is it possible to determine the above? Major hifi brands trade on the fact their customers like the sound of their products. The distortion is not however at the ambient noise level of a room.

    As the great Nelson Pass says somethings cannot be explained by measurements alone.

    Edit attached is excerpts of an acoustic glass application guide.

    The guide does stage the db level in inside of the glass in not necessarily the noise level in the room and other sources of noise for example a ceiling or air conditioning might effect the noise level in the room. Board rooms, court rooms are generally quiet places but it’s the noise made by occupants that’s the issue.

    Having spent many hours in all sorts of secure environments l can state un categorically its the other people in a room that are the source of noise. I’m talking about quiet rooms, bank vaults. Air con rustles paper work. When people move their clothes they make a noise!

    This type of noise is distracting.

    When l have the time l do my critical listening late at night. It’s simply much quieter and that is when a systems noise floor really comes into play.
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  2. #32
    Administrator Robh3606's Avatar
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    "In addition to my posts above on the audibility of noise from audio electronics I find it quite intuitive that two power amplifiers with different distortion profiles below -80 db can subjectively sound different.

    Given Robert’s observations on ambient room noise at -40 db how is it possible to determine the above? Major hifi brands trade on the fact their customers like the sound of their products. The distortion is not however at the ambient noise level of a room."

    Hello Ian

    It's a safe assumption that everyone would agree a lower noise floor and lower distortion are not a bad thing and are desirable.

    I don't understand why you seem to lumping S/N and distortion together. I see it as two separate things.

    As an example lets say that the noise level in a room is 50 dB. You don't listen at 50db so lets say your average is 85 with a 30db dynamic range. So say 70-100dB and of course silence between tracks. It's possible that the room noise would be completely masked by the music playing.

    With distortion it increases with increasing SPL so at higher levels it may no longer be masked by the music. Kind of like HOM's in horns. As you say the higher order distortion elements are more audible. If you have not already check out the attached PDF. Masking can have a profound influence on the audible perception of distortion as well.

    Rob

    http://www.gedlee.com/Papers/THD_.pdf

    http://www.gedlee.com/Papers/The%20P...Distortion.pdf
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  3. #33
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    Hi Rob

    It’s an interesting discussion but l am not sure we are on quite the same page.

    I was referring the signal path. Not the inherent distortion of a loudspeaker system.

    What your saying is ambient noise in a room or the latent noise is around 40-50 db.

    My response to that is in several parts. What is the microphone- meter actually detecting?
    For examples is a subsonic rumble of a jet aircraft landing 10 km away or is it vibrations from an industrial zone or road noise. Was it someone finding a birthday card in the same room? Someone breathing? A refrigerator or something else.

    That in terms of a clear thinking argument- discussion first needs to determine factually the exact nature of any existing noise in the listening room.

    Are those numbers weighted and over what time interval ?? Is that noise always there throughout the entire day?. You haven’t drilled down into the detail to make it a valid statement.

    The principal premise of my discussion is on the relative residual noise in the entire signal path versus the actual signal level in the normal use of the above described system.

    My assessment included the manufacturers rated SNR which is published at the component(s) rated output. The JBL 5234A rated output is 6.2 volts and at the rated output is the ratio of noise to that signal. I then scientifically calculated the residual noise level and then normalised the SNR in actual use.

    “With line signal level of 0.211 volts the SNR of -90 will now be reduce by 29.36 to - -60.64 db.” The 0.211 signal level is the level going into the Crown power amplifier to produce 93 db at 2.5 to 3.00 metres. It’s amplified with a gain of 31.55 db.”

    “Typically amplifier gain for a domestic hifi amplifier used to power a full range passive loudspeaker is from 23 to 26db. Most domestic full range passive direct radiator systems have a sensitivity in the 86 to 90 db range at one metre with 1 watt.”

    “The JBL 4343 has a sensitivity of 93 db under the same conditions. Other JBL systems are in the range of 95 to 96 db. The penny starts to drop that the noise specifications quoted by some manufacturers bare scrutiny to ensure there is a noise margin that will not intrude on the dynamic range of the or introduce noise related impurities into the fidelity of the sound re production experience.”

    I then scientifically calculated the summed residual noise in all the other components to provide a complete picture of the system SNR. When you are bi amping these systems and can define the actual conditions in typical use those often impressive SNR numbers on a spec sheet go right out the window.

    But if you are using a full range passive loudspeaker as mentioned above with a rated sensitivity of 86 db @ 1 watt with a 50 watt Macintosh valve amplifier the immediately obvious difference is the dynamic range of the system with the 7 db less sensitive loudspeaker. The lower gain of the power amp with may only be 23 db. Looking at the comparative numbers there is a 15.55 db in the actual sensitivity of the full passive system taking into account the loudspeaker.

    Greg Timbers advises that a bi amp system adds 4-6 db of real gain to a system. I did not include that in my calculations because it’s a complex thing to explain.

    However adding that to the 15 db difference here and you have 21 db differential on the relative amplifier signal versus the noise. Put simply 21 db more input signal is required in the modest hifi system to produce the same sound level. The SNR is therefore improved by 21 db. Huh 🤔.

    In layman’s terms a 60 Db SNR is noisy and would not pass for high fidelity sound use.
    An 81 Db SNR would pass for a high fidelity system. SNR matters.

    On my comments of the audibility of the harmonic structure of distortion. This was bought up to highlight this event where withdistortion at -80 below the signal level people are able to identify differences on sound characteristics. This applies to Robs claim that most rooms have a noise level of 40 - 50 db. The point here is if a listener can determine a difference at -80 db below the 93 db listening level it means the 40-50 db of noise from what ever the source has little bearing on the listeners auditory abilities.

    The point l now get back to is the 40-50 db measurement of room noise relevant to the discussion. The astute person would ask can a typical person detect that measured noise in that room? It looks like a red herring I’m afraid to say without detailed qualification.

    As an aside most of us who are old enough to remember would recall the rumble noise testing in vinyl turntable reviews. A rumble figure of -60 was considered un satisfactory. Namely because you could hear it. It was obvious. My VPI turntable has a rumble measurement of -85 db. No l can’t hear it!

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  4. #34
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    Smile

    Following on from the debate on the audibility of residual noise from audio equipment and noise levels in a domestic dwelling l present the information below.

    This information should give some context to what sound levels are relevant in a domestic home.

    My take away is that 93 db spl from your sound system at 2.5-3.00 metres distance may exceed a comfortable level.

    70-75 db may in fact be more appropriate.

    In the context of my previous calculations with an spl of 73 db from the loudspeakers the residual noise will be - 39.63 db below that level. Not -60 db.

    The dynamic range of a vinyl LP will be limited to 40 db. That might seem like a lot. However the noise level will fall the audible range with your home based on the information below. The impact on CD play would be significantly more.


    The graphics above show the threshold of hearing is most sensitive in the 1-2 khertz region.

    https://en.m.wikipedia.org/wiki/Noise_weighting

    In tha above link more specific information is provided on noise measurement weighting standards.

  5. #35
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    https://www.brisbane.qld.gov.au/laws...and-complaints

    Guide to decibel levels
    Some noise regulations include a maximum loudness in decibels. Here are usual decibel levels for everyday situations:
    * quiet room in a house - 20 to 30 decibels
    * daytime in a quiet residential street - 35 to 45 decibels
    * large busy office - 50 to 60 decibels
    * lawn mower from 15 metres away - 70 decibels.

  6. #36
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    How many decibels is too loud in a house?

    Sounds at or below 70 dBA are generally considered safe. Any sound at or above 85 dBA is more likely to damage your hearing over time. Researchers have found that people who are exposed over long periods of time to noise levels at 85 dBA or higher are at a much greater risk for hearing loss.


    How loud is your home?

    Simply put, a noise becomes unpleasant when its level exceeds 75 decibels. The same noise becomes harmful to the ear at 85 decibels and above. Above 110 decibels, even limited exposure can lead to hearing loss.
But at home, the problem is rarely not to exceed these thresholds. Rather, it is to reduce the noise from appliances, ventilation, air conditioning, or the street. These sounds can degrade the quality of life and sleep of the occupants of a dwelling.

    
As you may know, noise annoyance can lead to fatigue, irritation, and even depression, especially if the noise prevents good sleep.
    As long as the sound environment does not exceed 20 decibels, you are fine and sleep well, the noise is almost inaudible. Try not to exceed 40 decibels so that you do not hear any disturbing noise. Above 60 decibels, your quality of life and sleep decreases considerably and it is important to take action.
Hence the importance of choosing your equipment carefully: many air conditioners exceed a sound level of 40 decibels! So how can we measure this noise level and reduce it?

    Decibels is the measurement unit used for the intensity of sound. Humans can hear decibel levels starting from 0 dB and 120-140 dB is the sound threshold of pain.
    70 dB is in the middle of this decibel range. It is equivalent to the sound level of a regular washing machine. It is also equivalent to the noise level in an office environment or inside a car driving at 60 mph.

  7. #37
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    How Loud Is 70 Decibels?

    70 decibels is as loud as a washing machine or a dishwasher. It is a moderate noise level.

    70 dB noise is not considered harmful to human hearing. However, extended exposure to levels above 55-60 dB can be considered disturbing or become annoying.

    For public or general environments, the Environmental Protection Agency considers that exposure to 70 decibels over a period of 24 hours is a level that can prevent measurable hearing loss over a lifetime. Therefore, 70 dB is the maximum level of noise you should be exposed to during a normal day.

    This maximum level of 70 dB is considered for a 24-hour average. If you are exposed to levels above 70 dB you will need to balance out that exposure with a sufficient period of quiet to prevent hearing damage or hearing loss.
    For comparison, the generally accepted exposure to noise in work environments is limited to 85 dB over a period of 8 hours/day.

  8. #38
    Junior Member Galucha's Avatar
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    Quote Originally Posted by mattking52 View Post
    Ian,This could be a cool thread. I like and agree with your suggested approach of doing things in a very methodical, systematic way. Baseline measurements are super important.I think there are lots of us on the LH forums that have pursued a bi-amp setup with a two-output (high-pass and low-pass) external crossover, but probably fewer who have tried a full active tri-amp or quad-amp setup with the big JBL 3-way/4-way systems. This is something I've been wanting to try for a long time, and it might be fun to chronicle it here on the LH forums (if anyone is still around)!
    I've actually been running my 4343s quad-amped via DSP for the last few months. I'll see if I can write up a thread/guide on my approach to it over the weekend. Quite the learning curve, but very rewarding when you finally get everything in sync.I can attest to everything Ian is talking about. You have to be very methodical and take a step-by-step approach to implementing it.

  9. #39
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    I look forward to reading your write up.

  10. #40
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    Quote Originally Posted by Galucha View Post
    I've actually been running my 4343s quad-amped via DSP for the last few months. I'll see if I can write up a thread/guide on my approach to it over the weekend. Quite the learning curve, but very rewarding when you finally get everything in sync.I can attest to everything Ian is talking about. You have to be very methodical and take a step-by-step approach to implementing it.
    No doubt…

    Very much looking forward to this!
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  11. #41
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    Lightbulb

    The short how version of converting a passive system to an active system

    Rane active crossover references

    https://www.ranecommercial.com/legacy/note160.html

    https://www.ranecommercial.com/legacy/note135.html

    This assumes ideal loudspeakers with at least a one octave of flat response either side of the crossover point. A good starting point for an 80’s PA rid. Not help for an integrated multi way high quality play back system

    Tips - a diy active crossover

    This assumes:

    You are interested in an active loudspeaker and are prepared to put in the work.

    Key Success Factors.

    1. A void looking at other peoples measurements. These measurements are not necessarily helpful or applicable to your specific application.

    2. Do NOT attempt to simulate the active system crossover settings using 3rd party software. This will confuse you. Trust your ears.

    3. Lots of people go off on a tangent and attempt to re invent the wheel or make it better. Unless you are planning a 2- 10 year project time frame this approach should be avoided.

    4. As a rule the original design is sound and
    was obtained the considerable
    knowledge of the drivers, practical
    loudspeaker design and a huge technical
    resources.

    5. As a diy loudspeaker person it’s best to
    follow the path well followed.

    6. Assume nothing. Be curious and take a step by step methodical approach.

    7. Do not listen to the village idiot, smart ass or know it all with Masters EEl and talks to you like they they read it out of a text book. If you get lost it’s unlikely you will get found! Making or listening generalisations in the loudspeaker space will be your major undoing. Yes that sounds harsh. See item 8. If your planning on discussing your project do it with the same person consistently all the way through.

    8. Your success will come from determining some factual data from your own efforts


    The process.

    1. Take a full range measurement of the passive system you plan to bi amp. Preferably do this outside on a dry quiet day at a distance of 1 metre or 2 metres.

    2. This should be preceded by a basic understanding of how to make loudspeaker measurements and the various approaches.

    3. Down load REW. Learn how to use the free software and obtain a compatible microphone

    2. Take individual driver measurements of the passive system you plan to make active.

    3. It’s assumed you have obtained or have access to an adjustable active crossover.
    A Used Drive Rack, Mini Dsp crossover or
    the Dayton active crossover will get you
    started. An adjustable analogue active
    crossover like the Ashly, or a kit from
    Marchland or a kit available from
    Diyaudio.com shop for adventurous diy
    constructors.

    Don’t over invest in this piece of equipment think your are going to obtain perfection
    with it straight out of the box.

    4. Start a trial and error process to empirically come up with similar individual driver
    response measurements using your active crossover. Do l not expect to get
    measurements exactly the same as the passive system measurements.

    5. Conduct test and learn subjectively
    evaluations of the active versus passive
    system.

    7. Highly experienced loudspeaker design engineers advise very small differences less
    than one db in the driver response settings can make a profound difference to the
    subjective evaluations. Trust your ears. (See recent JBL engineer interview).

    This is a short edited guide.

    Edit
    Beyond this requires further insights that you start to obtain from the above exercise.

    Paul McGown founder of PS audio recently discussed on his YouTube channel an active version of one of PS loudspeakers for a recording studio. Paul discusses the pros and cons of both passive and active systems and the limitations he sees on active system in the hifi space until certain things come to pass. I completely agree with Paul. The industry is getting better through its learnings with active loudspeakers.

    The perfect active system is superior across a number of metrics to the equivalent passive system. Approaching the perfect active system is the challenge.

    Ian

    Edit

    To bring this post to life l have attached a couple of measurements.

    Please note. These attachments are for illustration purposes only as examples of a passive system / driver measurements. When you start adjusting your active crossover the goal is to try and obtain similar curves. However the active crossover signal is NOT this measurement. That’s really important. Of course some smart arse will use these files to flog an “equivalent ” world first active crossover on EBay.
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  12. #42
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    Exclamation

    What l have written above isn’t war and peace on the subject. It’s a guidance and advice to the diy audio enthusiast. A primer.

    It’s not a engineering specification on how to design an active loudspeaker system. Too many diy audio enthusiasts get swept up in the notion they can create their own end game loudspeaker before they even get started. They window shop for the best drivers, look in detail at concepts and off they go.

    The reality is those are just thoughts. Have you done this before? Do you have the time? Do you actually have the skills? Do you have the right tools? Do you have all the information?

  13. #43
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    For the most part organising any diy loudspeaker be it passive or active system is a journey and learning curve. With any luck it will give you a good result. There will be problems, mistakes and challenges. It’s much easier to follow or work with a known loudspeaker design when your walking into unfamiliar territory like active crossovers.

    A good loudspeaker system is far more than the sum of its parts. It’s about a journey of trial and error and discovery with listening and measurements. Often a good period of time will pass before setting on a final design.

    Most of what you hear is the sound of the actual drivers when they function and how they behave and work together on a known baffle with a known loudspeaker shape. Also how that loudspeaker as a system interacts in a particular room. This is in fact what goes into a reputable loudspeaker product. The drivers are the organs. The crossover network is the brain. The enclosure and the baffle are the skeleton and glue that holds it together.

  14. #44
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    An automated dsp process with a straight line response curve will not deliver you the ultimate loudspeaker system like a gene out of a bottle. Shock horror for the curve junkies idolising over that “curve “. There are numerous reasons on why that is the case. See the paragraph above.

  15. #45
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    Your loudspeaker is not the utopia of perfection. It’s about discovering as an individual we each like. What you like or dislike won’t necessarily be what someone else likes or dislikes.

    It’s a very personal thing.

    If you watch enough home recording studio YouTube clips it will become apparent that most of the emotion from a musical tune comes from the bass. The question is how well can or does a loudspeaker create those sounds? Does it sound real? Is it distorted? Compressed? Boomy? Tight or loose? You won’t know just looking at a response curve. Oh no! Then there’s all those other musical instruments, the human voice and all the harmonics the loudspeaker has to interpret and deliver.

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