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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #341
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Nice!

    Also reminds me that the air in a port can stop oscillating much faster than a passive radiator can stop moving, because the air weighs almost nothing compared to how heavy a PR is.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  2. Back To Top    #342

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    Nice!

    Also reminds me that the air in a port can stop oscillating much faster than a passive radiator can stop moving, because the air weighs almost nothing compared to how heavy a PR is.
    And there's no suspension to oscillate! All that makes a vent more efficient and just arguably better. Plus, it's basically free.

    So why use a PR at all?

    Anyone who's had the bright idea to make a small box to keep their car practical, but tune low...
    ..."what do you mean my port needs to be 42 inches long and will add a cubic foot to my half cubic foot box?"


    Sent from my LM-G820 using Tapatalk

  3. Back To Top    #343
    Noob Cathul's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by geolemon View Post
    So why use a PR at all?

    Anyone who's had the bright idea to make a small box to keep their car practical, but tune low...
    ..."what do you mean my port needs to be 42 inches long and will add a cubic foot to my half cubic foot box?"
    Or you got a driver that requires you to build a small box with a port that is as big or bigger than the box itself, like the Dayton RSS265HO-4 driver f.e.
    SYNC3 headunit
    Mosconi Pico 8/10 DSP
    Mosconi D2 500.1
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    JL Audio 10w3v3 in custom enclosure (Blueprint by Mark @Caraudiofabrication)

  4. Back To Top    #344
    Noob TechUser's Avatar
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    Greg
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    Re: Ask an Acoustic Engineer (me)

    I know this is less technical in nature than the discussion on this thread, but I think some of you would have good input on it.

    I've just bypassed the OEM Sony amp on my 2014 F150, and have installed DSP/Amplifiers to handle discrete front L, R & Center speakers as well as a under seat sub-woofer. Another page on my F150 profile shows what I did specifically. I still have the OEM Sony speakers in my truck, but want to replace the front speakers with performance speakers for my front sound stage; front L(pair), R(pair) & Center.

    The below signals are being passed through a Helix DSP Mini (4X6):
    An Alpine PDX-F4 (100Wrms/Ch) drives the 4-channels for the front L (high & low) and R (high & low) doors.
    An Alpine MRV-300 (160Wrms/Ch) drives the front center channel.
    An Alpine PDX-M6 (600Wrms/Ch) drives two 12-Inch woofers (series connection) under rear seats.

    My goal is go purchase high quality speakers for the front sound stage that don't break my budget (sub $300 range) AND that sound great once they are time aligned. Yes, I want volume, but I really want crisp, clear and in-concert sound. As far as the center speaker goes, I would purchase it separately, depending on what I purchased for the fronts.
    I know I'm supposed to look for good sensitivity, impedance, and rms power that matches my amplifiers. I have some speakers in mind, but really want your opinion. What specifically should I look for in a good speaker? Build materials, plastic vs stamped metal frame, paper cone vs. plastic, etc?
    Last edited by TechUser; 10-20-2021 at 01:36 AM. Reason: adding link, clarifying questions.
    ~~~~~~~~~~~~~~~~~~~~~
    2014 Ford F150 SuperCrew Tremmor 5.0 with 8" Sync screen, w/ AmpPro, Alpine PDX-F4, PDX-M6, MRV-F300, Helix DSP Mini.
    "Gooooood quality music makes my soul smile."

  5. Back To Top    #345

    Re: Ask an Acoustic Engineer (me)

    I remember reading somewhere a while back about a "40/400" rule of thumb regarding vented subwoofer group delay, which goes roughly as follows: Multiply group delay (m/s) by frequency (Hz), and a sum of 400 or less at anything over 40 Hz is okay; and as group delay cannot be heard at or below 40 Hz, any sum at or below 40 Hz is okay. Does this make sense? Is there any truth in it?
    "That's all, folks!"

  6. Back To Top    #346
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by TechUser View Post
    Yes, I want volume, but I really want crisp, clear and in-concert sound. As far as the center speaker goes, I would purchase it separately, depending on what I purchased for the fronts.
    I know I'm supposed to look for good sensitivity, impedance, and rms power that matches my amplifiers. I have some speakers in mind, but really want your opinion. What specifically should I look for in a good speaker? Build materials, plastic vs stamped metal frame, paper cone vs. plastic, etc?
    This is a hard question to answer. I do not know what "crisp, clear in-concert sound" sounds like to you. Concert sound is generally loud as frick and makes generous use of horn-loaded midrange and treble so you could start with horns, maybe mounted under the dash. Or, you can look for pro-audio drivers which will have very high voltage sensitivity (dB/2.83v/1m) to get more sound out of a given amplifier. Try browsing at loudspeakerdatabase.com Also, concert sound has an absurd amount of amplifier power available so you might want to be bridging amplifier channels to get 200w/ch or more for the front speakers.

    As for a good speaker? Depends entirely on what you want to use it for. Plastic frames and plastic cones are excellent in harsh environments or marine because they do not rust or deteriorate like a metal frame or a paper could will. However, plastic cones can be heavier which works against the loudness that you seem to want. I think you would be happy with a pro-audio driver if that truly is your jam. Look for speakers with voltage sensitivity numbers in the mid/high 90's. These will likely be from brands that Parts-Express doesn't sell, for example. Check below for a few thousand ideas.

    http://www.loudspeakerdatabase.com/s...112.0/sort=spl
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  7. Back To Top    #347
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Grinder View Post
    I remember reading somewhere a while back about a "40/400" rule of thumb regarding vented subwoofer group delay, which goes roughly as follows: Multiply group delay (m/s) by frequency (Hz), and a sum of 400 or less at anything over 40 Hz is okay; and as group delay cannot be heard at or below 40 Hz, any sum at or below 40 Hz is okay. Does this make sense? Is there any truth in it?
    Sounds like a reasonable thing to try. I think it turns into an inequality like this:
    (delay in ms) * (frequency in Hz) < 400

    This does make sense because it assumes group delay in the lower frequencies is harder to notice, and there might be some truth to that. I have not found any good research on this topic in the low frequencies, or any listening/audibility studies on this subject. This might make a fun blind listening test sometime though.

    Sorry I can't be more helpful on this one. Seems like a reasonable rule of thumb where the trends seem right, but I don't know if 400 is the best number to compare against or if 350 would be better or 300 or ....
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  8. Back To Top    #348

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by TechUser View Post
    I know this is less technical in nature than the discussion on this thread, but I think some of you would have good input on it.

    I've just bypassed the OEM Sony amp on my 2014 F150, and have installed DSP/Amplifiers to handle discrete front L, R & Center speakers as well as a under seat sub-woofer. Another page on my F150 profile shows what I did specifically. I still have the OEM Sony speakers in my truck, but want to replace the front speakers with performance speakers for my front sound stage; front L(pair), R(pair) & Center.

    The below signals are being passed through a Helix DSP Mini (4X6):
    An Alpine PDX-F4 (100Wrms/Ch) drives the 4-channels for the front L (high & low) and R (high & low) doors.
    An Alpine MRV-300 (160Wrms/Ch) drives the front center channel.
    An Alpine PDX-M6 (600Wrms/Ch) drives two 12-Inch woofers (series connection) under rear seats.

    My goal is go purchase high quality speakers for the front sound stage that don't break my budget (sub $300 range) AND that sound great once they are time aligned. Yes, I want volume, but I really want crisp, clear and in-concert sound. As far as the center speaker goes, I would purchase it separately, depending on what I purchased for the fronts.
    I know I'm supposed to look for good sensitivity, impedance, and rms power that matches my amplifiers. I have some speakers in mind, but really want your opinion. What specifically should I look for in a good speaker? Build materials, plastic vs stamped metal frame, paper cone vs. plastic, etc?
    Quote Originally Posted by Justin Zazzi View Post
    This is a hard question to answer. I do not know what "crisp, clear in-concert sound" sounds like to you. Concert sound is generally loud as frick and makes generous use of horn-loaded midrange and treble so you could start with horns, maybe mounted under the dash. Or, you can look for pro-audio drivers which will have very high voltage sensitivity (dB/2.83v/1m) to get more sound out of a given amplifier. Try browsing at loudspeakerdatabase.com Also, concert sound has an absurd amount of amplifier power available so you might want to be bridging amplifier channels to get 200w/ch or more for the front speakers.

    As for a good speaker? Depends entirely on what you want to use it for. Plastic frames and plastic cones are excellent in harsh environments or marine because they do not rust or deteriorate like a metal frame or a paper could will. However, plastic cones can be heavier which works against the loudness that you seem to want. I think you would be happy with a pro-audio driver if that truly is your jam. Look for speakers with voltage sensitivity numbers in the mid/high 90's. These will likely be from brands that Parts-Express doesn't sell, for example. Check below for a few thousand ideas.

    http://www.loudspeakerdatabase.com/s...112.0/sort=spl
    Here is another place to look: https://usspeaker.com/homepage.htm
    "That's all, folks!"

  9. Back To Top    #349

    Re: Ask an Acoustic Engineer (me)

    Justin I know you've done the vehicle and sled audio so let me ask: What does your Target Curve look like on your bike? And have you thought of implementing that curve into your spreadsheet?

  10. Back To Top    #350
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    I just created a presentation on this for my office actually. The interesting thing is I only have one target curve. The trick is to realize as much of that target as I can, given the number and types of speakers I have available, the amplifier power available, and the kind of vehicle I have.

    With a sealed cabin and a pair of 12" woofers and a thousand watts of power, I can realize the whole target curve. But on something like a side-by-side vehicle or a motorcycle where I only have 6.5" speakers and an open cabin, I cannot reproduce all of the lower frequencies in my target curve so I get the most bass out of the system that I can... up to a point where I cannot any longer.

    I'm always aiming for the same thing, but I cannot always achieve the same target based on the practical limitations of what I have to work with.

    I do not think I can share the target curve I use at the office since Rockford has not shared it publicly, it is considered part of our secret sauce. There is a great thread on diyma titled something like Comparison of Target Curves and there is some really fascinating discussions in there.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

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