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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #231
    Noob Truthunter's Avatar
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    Re: Ask an Acoustic Engineer (me)

    I've a question for you Justin,

    Parallel vs cascaded xover filters

    http://www.linkwitzlab.com/frontiers_5.htm#V

    I'm only aware of a couple of 12v market processors that can perform cascaded filters, and I suppose one could use APFs to accomplish something similar but I have doubts that it would actually make an audible difference in a vehicle.

    Can you share any thoughts on this?

  2. Back To Top    #232
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    I have spent a lot of time fiddling with the LX521 speakers that Linkwitz designed. I did not use the analog crossover board that he recommended. The analog board has many cascading filters with all-pass and a few others thrown in there that didn't really make sense at the time. I think they make a little more sense now.

    Instead, I have been using a dsp to do all of the crossover work for these 4-way towers and it's been working great.

    Your question makes me realize I'm not super familiar with the tradeoffs between parallel and cascaded filters like this since I'm more concerned with the acoustic response and less concerned with the filters themselves. I enjoy the approach of getting it to measure correctly at the microphone and using whatever filters I need instead of following a strict filter choice philosophy.

    I think I can see the point he was making: a closely spaced high-pass and low-pass filter on the same speaker can cause phase shift errors as the two filters overlap where they are not expected to. This seems to be more likely on a driver with a narrow electrical bandwidth such as a pure midbass driver that is doing 80hz-250hz like we do in cars.

    I wonder if I haven't found this problem because I'm used to using crossovers *and* parametric eq filters for every speaker and I don't try to separate them. I wouldn't see the effect to two crossovers that are too closely spaced because I'm already doing some kind of parametric eq work in that region anyways.

    I haven't been aware of this concept so I haven't paid attention to it. I will now though.
    Thank you for teaching us something new!
    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.

  3. Back To Top    #233

    Re: Ask an Acoustic Engineer (me)

    Little confused about phase adjustments past 360* vs. time alignment.

    I've heard phase described as a corkscrew, the implication there is when you roll phase past 360 degrees you are essentially making time adjustments and with that imagery it is quite intuitive that rolling phase would act like a micro adjustment of time alignment. But it seems that is not the case as is shown here: https://youtu.be/zFgftIW4ufk?t=207

    So rolling phase doesn't alter the timing of an impulse response but only alters how much the driver is displacing and in which direction it's moving? Rolling phase forward 185 degrees is the same as rolling phase backwards 175 degrees and rolling phase forward 185*+360* is the same a rolling phase backwards (175* + 360*)? If this is true the signal is simply being shifted X* based on your filters or other settings. If we consider phase plotted from -180 to 180 and we roll phase forward by 90* across the entire driver then at a point in the where the input signal is at 0* it would simply be 90*. And a place where it was previously 170* it would now be -100*.

    Am I doing this? Am I miles off?

  4. Back To Top    #234
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    That video is a head-scratcher, no doubt. I stared at it for a while too. I think you understand it right.

    If you have a phase shift, you may or may not have a time delay.
    If you have a time delay, then you must have a phase shift.

    I like the way Dan Worrall puts it in his video title:

    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.

  5. Back To Top    #235

    Re: Ask an Acoustic Engineer (me)

    Thanks that really clears it up for me. I struggled to define in time what 360* of phase was and how phase adjustments could be made without a defined range in the time domain and well, my calculus courses came flooding back.

    But when you release phase from the time domain you can suddenly just make a simple translation at any or all frequencies based on your filters. It's so simple I can't believe I struggled to see this.

  6. Back To Top    #236

    Re: Ask an Acoustic Engineer (me)

    Question for Jazzi. As an Engineer,are there any newer tech innovations that have caught your eye that you think may be game changing? More generally audio related but really anything is fine. Just curious

  7. Back To Top    #237
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Fun question!

    I enjoy seeing the advancements in materials used in speakers. The thin-ply carbon in TeXtreme is really impressive stuff. I've done some experiments and validated it when I was at Eminence and then my good friend Matt built it into the compression driver n314x. I left the company before the project was finished but I heard it has a really well-behaved sound like we were predicting during development. I see a couple other drivers on the market with this material and I'm excited to see something with performance similar to the "best" materials like beryllium but at a fraction of the cost.

    http://www.textreme.com/markets/audio-2/

    Click image for larger version. 

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    Another material I hope becomes mass-produceable is carbon nano-tube technology but in the meantime a Canadian company is making graphene membranes which are also carbon-based. I bought into the kickstarter for the ORA headphones and I'm really impressed with them. It could be that I've never had a premium headphone before, but I'm really amazed how they sound. They are like nothing else I've ever heard.

    I'm also excited to see advancements in the digital signal processing realm. The first generation Apple and Google smart speakers solved a problem where the bass output of the speaker would change depending on where you placed it in a room. If you put it on a table in the middle of a room then the bass output would be less compared to if you put it in the corner of a room or up against a wall. These smart speakers had microphones that would detect it and adjust the bass output accordingly so it would always sound good no matter where you put it. They would also adjust how to distribute the higher frequency information to the array of tweeters too so when against a wall it would play a left and right channels to one side of the room and the other, or if in the middle of a room it would be more omnidirectional to fill the whole room and you'd never be on the "wrong" side of the speaker. I love this approach to make the technology "just work" so the consumer can put the speaker wherever the speaker fits into their lifestyle and it will adapt, but the neat trick was it adapted automatically and you didn't have to push a button to go into "corner mode" or "party mode" or whatever like some products have done before.

    Click image for larger version. 

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    Speaking of technology advancements, I'm also excited to see my friend Niick join JL Audio a while back. He has some wicked ideas and although I'm out of the loop on the cool stuff he's working on now because I'm at Rockford and we are competitors, I can't wait to see what he's been doing all this time. I'm sure something amazing is on the horizon and I'm looking forward to it. However, I'm doing my best to create amazing stuff at Rockford too so we might have a couple products that I'm excited about when they get released too : )

    The other thing that really sticks out to me was watching the Falcon Heavy test launch where Elon's Tesla Roadster was launched into space and the twin booster rockets landed side-by-freaking-side on the launch pad. I remember watching that in real time and I had goosebumps and was jumping up and down yelling at the screen. I guess that was my moon-landing moment where I got to see something magical happen for the first time.



    There is also Pozyx which created a local 3d positioning system that is accurrate to within 4 inches. This is kinda like GPS but it's local and uses radio waves and can work indoors or through walls. I find it neat because I've always wondered if you could attach location data to a microphone measurement, then what applications would that open up? If you could map the sound field inside a vehicle or inside a room, would that help you with positioning or aiming speakers or selecting and placing sound treatments?

    https://www.pozyx.io/

    I love technology so I could go all day with this so I'll finish with a neat little thing we can all afford. The Uni Kuru Toga is a mechanical pencil that automatically rotates the led as you write so you always have the sharp side facing the paper. I had one for a long time but lost it at the office and I just ordered another. The roulette version has a metal body that feels just right in the hand with the perfect weight and I freaking love it. And they are super affordable too. Best $10 I've ever spent on a pencil.

    https://www.jetpens.com/blog/kuru-to...e-guide/pt/706

    Click image for larger version. 

Name:	67503.jpg 
Views:	325 
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ID:	12934
    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    #238

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    Fun question!

    I enjoy seeing the advancements in materials used in speakers. The thin-ply carbon in TeXtreme is really impressive stuff. I've done some experiments and validated it when I was at Eminence and then my good friend Matt built it into the compression driver n314x. I left the company before the project was finished but I heard it has a really well-behaved sound like we were predicting during development. I see a couple other drivers on the market with this material and I'm excited to see something with performance similar to the "best" materials like beryllium but at a fraction of the cost.

    http://www.textreme.com/markets/audio-2/

    Click image for larger version. 

Name:	N314X_8--2.jpg 
Views:	227 
Size:	9.1 KB 
ID:	12932

    Another material I hope becomes mass-produceable is carbon nano-tube technology but in the meantime a Canadian company is making graphene membranes which are also carbon-based. I bought into the kickstarter for the ORA headphones and I'm really impressed with them. It could be that I've never had a premium headphone before, but I'm really amazed how they sound. They are like nothing else I've ever heard.

    I'm also excited to see advancements in the digital signal processing realm. The first generation Apple and Google smart speakers solved a problem where the bass output of the speaker would change depending on where you placed it in a room. If you put it on a table in the middle of a room then the bass output would be less compared to if you put it in the corner of a room or up against a wall. These smart speakers had microphones that would detect it and adjust the bass output accordingly so it would always sound good no matter where you put it. They would also adjust how to distribute the higher frequency information to the array of tweeters too so when against a wall it would play a left and right channels to one side of the room and the other, or if in the middle of a room it would be more omnidirectional to fill the whole room and you'd never be on the "wrong" side of the speaker. I love this approach to make the technology "just work" so the consumer can put the speaker wherever the speaker fits into their lifestyle and it will adapt, but the neat trick was it adapted automatically and you didn't have to push a button to go into "corner mode" or "party mode" or whatever like some products have done before.

    Click image for larger version. 

Name:	apple-homepagd-official.jpg 
Views:	245 
Size:	148.9 KB 
ID:	12933

    Speaking of technology advancements, I'm also excited to see my friend Niick join JL Audio a while back. He has some wicked ideas and although I'm out of the loop on the cool stuff he's working on now because I'm at Rockford and we are competitors, I can't wait to see what he's been doing all this time. I'm sure something amazing is on the horizon and I'm looking forward to it. However, I'm doing my best to create amazing stuff at Rockford too so we might have a couple products that I'm excited about when they get released too : )

    The other thing that really sticks out to me was watching the Falcon Heavy test launch where Elon's Tesla Roadster was launched into space and the twin booster rockets landed side-by-freaking-side on the launch pad. I remember watching that in real time and I had goosebumps and was jumping up and down yelling at the screen. I guess that was my moon-landing moment where I got to see something magical happen for the first time.



    There is also Pozyx which created a local 3d positioning system that is accurrate to within 4 inches. This is kinda like GPS but it's local and uses radio waves and can work indoors or through walls. I find it neat because I've always wondered if you could attach location data to a microphone measurement, then what applications would that open up? If you could map the sound field inside a vehicle or inside a room, would that help you with positioning or aiming speakers or selecting and placing sound treatments?

    https://www.pozyx.io/

    I love technology so I could go all day with this so I'll finish with a neat little thing we can all afford. The Uni Kuru Toga is a mechanical pencil that automatically rotates the led as you write so you always have the sharp side facing the paper. I had one for a long time but lost it at the office and I just ordered another. The roulette version has a metal body that feels just right in the hand with the perfect weight and I freaking love it. And they are super affordable too. Best $10 I've ever spent on a pencil.

    https://www.jetpens.com/blog/kuru-to...e-guide/pt/706

    Click image for larger version. 

Name:	67503.jpg 
Views:	325 
Size:	57.2 KB 
ID:	12934
    2 things:
    1) What are your thoughts on Aerogel sandwiched between some graphene/carbon nanotube as a speaker cone? Not headphones, something suitable for car audio.
    2) You like nice mechanical pencils, I suspect for drawing/sketching designs, try a stainless Parker Jotter pen with a Fisher Space Pen cartridge for your permanent writing.

  9. Back To Top    #239
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Northridge, CA
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    Join Date
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by ckirocz28 View Post
    2 things:
    1) What are your thoughts on Aerogel sandwiched between some graphene/carbon nanotube as a speaker cone? Not headphones, something suitable for car audio.
    2) You like nice mechanical pencils, I suspect for drawing/sketching designs, try a stainless Parker Jotter pen with a Fisher Space Pen cartridge for your permanent writing.
    1) Sounds cool. I thought Aerogel was more famous as a thermal insulator but it looks like there are many kinds. I wouldn't mind lining my entire house with the stuff to keep it cool in the summers over here in Phoenix!

    2) I'm on an ultra fine point kick right now so I'm trying a few 0.3mm and 0.4mm tips to see what happens. I'm also fussy and prefer dark green ink. The Pilot Precise V5 has been a go-to for a while but I'd like to try something different.

    Click image for larger version. 

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Views:	136 
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ID:	12936
    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.

  10. Back To Top    #240

    Re: Ask an Acoustic Engineer (me)

    Idk how pens are exactly for fine point but with my drawing micron pens. Anything smaller than about .5 is has a pretty fragile tip. If you put too much pressure down. You'll damage the tip and the ink wont flow right.

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