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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #371

    Re: Ask an Acoustic Engineer (me)

    Thank you for ur responses. It is very nice of you contributing so much for the community. I wish u luck on ur house plan, unfortunately i dont have any positions for sound engineer at the moment. Joking haha. Cheers.

  2. Back To Top    #372

    Re: Ask an Acoustic Engineer (me)

    Such an great explanation

  3. Back To Top    #373

    Re: Ask an Acoustic Engineer (me)

    I am also looking something related to this. Can you help me in configuration ?

  4. Back To Top    #374
    Noob Jdunk54nl's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by andrewgray View Post
    I am also looking something related to this. Can you help me in configuration ?
    can you be more specific?
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  5. Back To Top    #375

    Re: Ask an Acoustic Engineer (me)

    I've got a 2017 F350 SuperCrew. The door cards obstruct a little of the drivers in the front (6x9's) and rear (6.5's). A stealthy install is pretty important to me and I've been toying with the idea of a pair of midbass drivers and one midrange in the front doors. Say the midrange is unobstructed and plays 300-4,000Hz while the midbass is partially obstructed and plays 40-300Hz. This will likely be a subless install and I plan to build pods for the drivers.

    At these frequencies how much of the cone can be obstructed before the quality of the sound begins to degrade? Zero? 40%? 60%?

  6. Back To Top    #376
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by DirtyBumOAK510 View Post
    Thread revival!
    I just asked this one on Facebook and I got some answers but not necessarily the facts that I'm hoping Justin and others here can bring.

    So I have heard stuff like "You can't hear distortion in a subwoofer the same you can in a midbass", or that distortion in a subwoofer isn't a big concern due to how we hear those frequencies. I've also heard people say that low distortion subwoofers (such as XBL, Brahmas, C12XL, Ravens etc) suddenly make people get used to what a "low distortion" subwoofer sounds like.

    So how much distortion is audible below 100hz? between 100hz-1000hz? Tweeters?

    Part of where I was getting at is that a lot of amplifiers claim "less than 1% distortion", and we often shoot for .05 or less. With Dacs, these numbers can go into the .001 or lower. I've read on Audio Science Review many articles about the hard numbers of inaudibility for Crosstalk, THD, S/N etc. But how do these apply to subwoofers? Specifically for choosing an amp for a very "low distortion" subwoofer. I've also seen graphs from subwoofer makers that will show at what frequency their subwoofers get localized, which if I remember right was due to distortion where it suddenly becomes localized. So typically we have the rule of thumb that subwoofers become localized above 100hz. S/N ratio of 120db is completely inaudible unless you have "golden ears".

    Where's the data!? What's the number?! What can and can't we hear below 100hz (typical subwoofer duty)
    @DirtyBumOAK510

    Ive been stumped on this question this whole time and haven't found a good resource. Actually I haven't found any resource on this one. Might be a topic for study or a potential experiment to try and answer the question. I'm annoyed I couldn't find this one for ya!
    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)
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  7. Back To Top    #377
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Zoom_M5 View Post
    I've got a 2017 F350 SuperCrew. The door cards obstruct a little of the drivers in the front (6x9's) and rear (6.5's). A stealthy install is pretty important to me and I've been toying with the idea of a pair of midbass drivers and one midrange in the front doors. Say the midrange is unobstructed and plays 300-4,000Hz while the midbass is partially obstructed and plays 40-300Hz. This will likely be a subless install and I plan to build pods for the drivers.

    At these frequencies how much of the cone can be obstructed before the quality of the sound begins to degrade? Zero? 40%? 60%?
    Interesting question! I do not know the answer right away. It might be hard to offer a hard rule of thumb becasue a 50 percent blockage made from a very fine mesh screen will behave different from a 50 percent blockage where you just place a piece of wood in front of half the cone.

    You could learn a lot from some simple experiments. If you have something that can measure the resonant frequency of a speaker like a Dayton DATS or a 2 cha nel oscilloscope with an x-y mode or a variety of other tools... Try this:

    Put the speaker in the door with the grilles not installed so there is no airflow reduction. Measure resonant frequency, and ideally qts if you can. Then install the grilles and add all the airflow obstruction and measure resonant frequency and qts again.

    If the Fs and Qts do not change much, then the air restrictions might not be a big deal. If the Fs and Qts do change a lot, then you are observing the influence by witnessing the changing parameters. I imagine if you re-use the factory grilles in the car and keep the cone area similar then you should be okay. It sounds like you want to double the cone area by adding a second woofer in each door? You might have some airflow restriction, but if you do, you can mitigate (maybe?) by raising the high pass crossover frequency a little bit. Maybe from 80hz to 100hz, it might not take very much? I haven't tried this particular challenge yet so it's a bunch of guessing but I think you should be able to experiment a little and learn a lot real quick.

    In addition to any air flow restriction and sound quality change (if any) you might be adding extra stress into the grille itself by pushing and pulling more air through it than it was designed for. If that is the case, it's not a big deal, but you might want to reinforce the way the grille is mounted because you might be flexing it more violently than it was designed for, leading to extra rattles and fatigue that could, maybe, make it wear out faster or break apart in the future.
    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    #378

    Re: Ask an Acoustic Engineer (me)

    Fantastic guidance! While the cone area is similar with three smaller drivers, the Xmax and thus displacement is MUCH larger. I hadn't even thought of the stress on the grill.

  9. Back To Top    #379

    Re: Ask an Acoustic Engineer (me)

    What is the electrical/phase impact of using dissimilar electrical crossovers?

    In the past I've heard all of the following stated as fact:
    "The acoustic response is what matters. Choose the filter type/frequency that most closely approximates the target"
    "You can use dissimilar frequencies and slopes, but stick with the same filter type"
    "Use identical acoustic and electrical filter type, frequency, and slope, and fix the rest with EQ"

    They can't all be true.
    What does an acoustic engineer say?
    Thanks!
    Last edited by Uberverbosity; 01-16-2023 at 02:06 PM.

  10. Back To Top    #380
    Noob Jdunk54nl's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Uberverbosity View Post
    What is the electrical/phase impact of using dissimilar electrical crossovers?

    In the past I've heard all of the following stated as fact:
    "The acoustic response is what matters. Choose the filter type/frequency that most closely approximates the target"
    "You can use dissimilar frequencies and slopes, but stick with the same filter type"
    "Use identical acoustic and electrical filter type, frequency, and slope, and fix the rest with EQ"

    They can't all be true.
    What does an acoustic engineer say?
    Thanks!
    I am pretty sure I know Justin's answer here and it goes along the lines of the first thing you've heard stated as fact.

    "The acoustic response is what matters. Choose the filter type/frequency that most closely approximates the target"

    That philosophy is what he has built his rew tuning companion on.
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

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