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Discussion Starter · #1 ·
A bit of a noob question here. This is my first experience with tuning and a DSP so I am going through a bit of a learning curve. I have started the process off by measuring individual drivers. I have 5.25" woofers mounted in the factory location, the lower door.

I measured the pair of these speakers individually and ended with the following frequency responses - I immediately assumed that these drivers were 180 out of phase but when I tried to swap either driver in the DSP software it didn't make a bit of difference? Should I physically try swapping polarity at the amp?

Should I measure in the passenger side and see if the problem persists?

Thank you in advance.
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Put them in standard polarity. Set time alignment. Measure them again with both playing, using the same volume, mic placement, etc. then overlay that graph with these two.
 

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You would only notice a phase issue if you took a measurement with both playing at the same time since phase is relative. Your measurements look pretty normal for 5" mids.

Keep measuring and learning from the changes you make in the dsp and best of luck on the tune!
 

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What are you seeing in those responses that makes you think they are out of phase? They look typical to me.
 

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Discussion Starter · #6 ·
I guess I was just surprised by how the frequency response of the left and right speakers were nearly mirror images, I.e. where one response peaks the other dips. I did not notice that with the tweeters or the midrange. I was trying to understand what could account for that.

As I said this was my first time tuning and gathering measurements so I was just hoping to find out if that was normal more than anything.

Thank you everyone for your responses. I will play the mids together and compare. I would hope that if there was a phase issue I would've heard by now as I thought the image was fairly centered after t/a and basic level correction between channels.
 

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I guess I was just surprised by how the frequency response of the left and right speakers were nearly mirror images, I.e. where one response peaks the other dips. I did not notice that with the tweeters or the midrange. I was trying to understand what could account for that.

As I said this was my first time tuning and gathering measurements so I was just hoping to find out if that was normal more than anything.

Thank you everyone for your responses. I will play the mids together and compare. I would hope that if there was a phase issue I would've heard by now as I thought the image was fairly centered after t/a and basic level correction between channels.
That’s not phase that is just how reflections effect the freq response, you’re sat asymmetrically to both drivers so the response will not be the same

there is no indication of phase in measuring a single driver unless you do it in a manner that gives phase/time domain related information

swapping polarity of one driver playing alone will not change anything about its resposne

playing together will show which parts are in phase (where they sum 4-6db) and out of phase (little or no summation)

here is a picture of the freq responses of two midbass that are nigh on perfectly in phase throughout the pass band except for at 100hz where there’s a reflection on the right driver

This is a very good midbass install in terms of phase response, the left and right sum by roughly 6db in 90% of the response, this means timing and phase are good (timing effects phase)

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the flip side is in an R35 I tuned recently

Summation is all over the place, timing was correct, but reflections played havoc with the response and summation… it gets 6db in places from one end of the pass band to the other but lots of places where it doesn't, this is typical of an average door mounted midbass, it’s a quirk of the location and it’s unfortunate that 99% of cars have drivers in this location in an area where phase plays a large part, it does get 6db summation in maybe 60% of its passband, that’s optimised as far as what it could have achieved and was at the end of the tuning process after eq was added

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The above skyline resposne also illustrates what I was saying about asymmetry and how the sides have very different responses at the listening position

there are the odd cars out there that have symmetric phase and amplitude response just because dimensions of the car are nigh on as good as can be, I measured a late shape bmw mini recently that was uncannily similar, but cars like that are few and far between
 

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Discussion Starter · #8 ·
That makes sense. I had read that the only way to get phase information was to use the sweep method with an Aux. Input on my head-unit. I guess reading something but then seeing measurements and applying that knowledge to actual results are different things for me.

Thank you for sharing pictures with explanations, that helps a lot not only to understand what I'm seeing now but give me a real-world example of what I can hope to achieve after eq'ing each side independently.
 

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That makes sense. I had read that the only way to get phase information was to use the sweep method with an Aux. Input on my head-unit. I guess reading something but then seeing measurements and applying that knowledge to actual results are different things for me.

Thank you for sharing pictures with explanations, that helps a lot not only to understand what I'm seeing now but give me a real-world example of what I can hope to achieve after eq'ing each side independently.
Yes you can use rew with sweeps as it has a set time so the pc can then compute what time between the reference and the frequencys measured and then see what time difference is and work out phase and timing from that, rew is very powerful in that sense

I use smaart which is a bit different and easier to use at a cost, but I can adjust phase and timing live as I’m tuning A dsp… it’s a grand roughly for a smaart two channel setup, so not cheap but worth it to me
 

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I've posted a bunch of articles on this, so check my post history. Here's the short version:

A car interior is about seven feet wide. 160Hz is seven feet long. What this means - is that when the sound from the RIGHT speaker arrives at the LEFT speaker they're out-of-phase at 80hz. This is because the cone of the LEFT speaker is 180 degrees out of phase, in the time that the sound from the RIGHT speaker takes to travel that distance.

And vice versa.

So if you've ever noticed that you have 6.5" woofers at home and they can play down to 40Hz, but the 6.5" midbasses in your car can barely do 90Hz, that's why.

DSP time delay can't easily fix this because we use DSP to adjust the center image NOT fix the midbass suckout.

For instance, if the pathlength of your left speaker is six feet long, and the pathlength for your right speaker is nine feet long, you might use DSP to equalize those pathlengths. That will "center" your image but it does not address the issue at 80Hz. Because the issue at 80Hz is due to a pathlength difference of SEVEN feet not THREE feet. (Seven feet is the width of the car, three feet is the pathlength difference between the left speaker and the right speaker.)

Most car audio folks just "brute force" it and use midbasses that are really big / powerful

Andy W suggests overlapping the subs and the midbasses, that's a good solution

I like using multiple midbasses, to mix up the pathlength differences between left and right

If you're brave you could probably fix it using FIR filters, but I haven't messed around with them, I've only used IIR filters

 
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I've posted a bunch of articles on this, so check my post history. Here's the short version:

A car interior is about seven feet wide. 160Hz is seven feet long. What this means - is that when the sound from the RIGHT speaker arrives at the LEFT speaker they're out-of-phase at 80hz. This is because the cone of the LEFT speaker is 180 degrees out of phase, in the time that the sound from the RIGHT speaker takes to travel that distance.

And vice versa.

So if you've ever noticed that you have 6.5" woofers at home and they can play down to 40Hz, but the 6.5" midbasses in your car can barely do 90Hz, that's why.

DSP time delay can't easily fix this because we use DSP to adjust the center image NOT fix the midbass suckout.

For instance, if the pathlength of your left speaker is six feet long, and the pathlength for your right speaker is nine feet long, you might use DSP to equalize those pathlengths. That will "center" your image but it does not address the issue at 80Hz. Because the issue at 80Hz is due to a pathlength difference of SEVEN feet not THREE feet. (Seven feet is the width of the car, three feet is the pathlength difference between the left speaker and the right speaker.)

Most car audio folks just "brute force" it and use midbasses that are really big / powerful

Andy W suggests overlapping the subs and the midbasses, that's a good solution

I like using multiple midbasses, to mix up the pathlength differences between left and right

If you're brave you could probably fix it using FIR filters, but I haven't messed around with them, I've only used IIR filters
Sorry but no, that’s not why you get a suck out at 80hz

It’s normally due to the length/height/width of the car, the wave from the driver leaves omni directionally, then it travels to the listening position and also to the boundary’s of the car and bounces back, as it gets back to the listening position it then has changed phase due to the distance it’s travelled and the phase is now likely 180 degrees out to the direct sound, that in itself is why you get a dip at 80hz or whatever freq coincides with the difference between the direct sound pathlength and the reflected sound pathlength, if one minus the other equals 7 feet then the dip in the drivers midbass will be approximately 80hz (half wavelength is 7ft) he isn’t playing drivers together to make the above graphs so I’m not sure why pathlengths between left and right have anything to do with this particular post?

this is why moving drivers to kicks often lowers the dip, gets a bit more reinforcement and can help phase at the crossover, it lengthens the direct pathlength but also raises the reflection pathlength by a chunk more so it makes the half wave difference longer and therefore lower

mathematically there will be a place to put midbass which has the best effect on the dip by making the length height and width of the car space out the modal dips and to a degree neutralise the dips with complimentary peaks also, kicks very often make the maths better I think

fir won’t help as it will effect both direct and reflected equally and both will have the exact same phase relationship at the listening position

6.5” woofers at home play down to lower freq because we use a port to extend there useable freq response
 

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Sorry but no, that’s not why you get a suck out at 80hz

It’s normally due to the length/height/width of the car,
Yes, you get a suck out at 80Hz in a car due to the length / height / width of the car.

160Hz is seven feet long

The width of a car is seven feet long

When the sound radiated from the RIGHT speaker radiates, it meets up with the LEFT speaker after a delay of seven feet.

160Hz is seven feet long

This creates a null at 80Hz (nulls occur when the sound of two sources is 180 degrees out of phase.)

Reflections off of the floor and the ceiling ALSO cause cancellations, but the frequencies are comprable because the ceiling of the vehicle acts as a reflector.

IE - the main issue is that you're sitting much closer to the left speaker than the right speaker.

Andy from Audiofrog has posted a solution to this issue that uses all pass filters, it's worth doing a search.

I like using arrays to solve it.

 
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Discussion Starter · #14 · (Edited)
Wow, I just want to say that this forum is amazing. Quality content like this is why I ended up joining and posting this question. It's awesome to get these in-depth technical explanations from people that are much smarter than me.

I have read Andy's tuning guide, but I thought that overlapping the electrical crossover points was just to try and achieve a matching acoustical slope due to the target curve having the 10dB increase at the low end.

I am unsatisfied with the results of the 5.25" woofers in the door, and was planning in the future to add additional mid-bass drivers under the seats, preliminarily I thought it would be a fun idea to try and build an under seat enclosure with the Dayton Low Profile 6.5" Woofer. However, now that you've mentioned these issues I will have do dig further into your post history to understand your comment about using arrays.

I don't think that my DSP, the Dayton, has the ability to do all-pass filters. I'm still kicking myself for not getting a Helix with more bands, higher voltage output, and the ability to view transfer functions - but I didn't know what I would be missing until I got deeper into the project.
 

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Wow, I just want to say that this forum is amazing. Quality content like this is why I ended up joining and posting this question. It's awesome to get these in-depth technical explanations from people that are much smarter than me.

I have read Andy's tuning guide, but I thought that overlapping the electrical crossover points was just to try and achieve a matching acoustical slope due to the target curve having the 10dB increase at the low end.

I am unsatisfied with the results of the 5.25" woofers in the door, and was planning in the future to add additional mid-bass drivers under the seats, preliminarily I thought it would be a fun idea to try and build an under seat enclosure with the Dayton Low Profile 6.5" Woofer. However, now that you've mentioned these issues I will have do dig further into your post history to understand your comment about using arrays.

I don't think that my DSP, the Dayton, has the ability to do all-pass filters. I'm still kicking myself for not getting a Helix with more bands, higher voltage output, and the ability to view transfer functions - but I didn't know what I would be missing until I got deeper into the project.
Don't get too lost in the math, basically the idea is that your left and your right speaker are out of phase at about 70Hz, depending on the geometry of your vehicle.

Adding a second set can break up the symmetry.

When I had multiple midbasses per side, I had one under the dash, one on the edge of the floor, and one under the seat.

If you really wanted to make it perfect you'd use DSP delay so that all the drivers arrived at the same time.

Note that you don't want to run these midbasses very high in frequency. This thing I describe isn't really practical if you're running a two way front stage. 1000Hz is 13.5" long, so if you try to run the midbasses up to 1500Hz or even 750hz it won't work. I used multiple midbasses for about 2.5 octaves, from 80hz to 480Hz.

480Hz is twenty eight inches long, so as long as the midbasses are within about nine inches of each other you'll be fine. If they're further than that you can shade one of them.

(In case anyone's curious, "shading" is the process of reducing the output of some drivers in an array so they interfere with each other less. For instance, if you have two drivers in an array and you reduce the power to one of them by 50%, your maximum output will fall by about 2dB but they'll interfere with each other much less. And 2dB is basically inaudible.)

 
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Yes, you get a suck out at 80Hz in a car due to the length / height / width of the car.

160Hz is seven feet long

The width of a car is seven feet long

When the sound radiated from the RIGHT speaker radiates, it meets up with the LEFT speaker after a delay of seven feet.

160Hz is seven feet long

This creates a null at 80Hz (nulls occur when the sound of two sources is 180 degrees out of phase.)

Reflections off of the floor and the ceiling ALSO cause cancellations, but the frequencies are comprable because the ceiling of the vehicle acts as a reflector.

IE - the main issue is that you're sitting much closer to the left speaker than the right speaker.

Andy from Audiofrog has posted a solution to this issue that uses all pass filters, it's worth doing a search.

I like using arrays to solve it.
except you still get an 80hz null with one driver playing, so it is mostly down to the dimensions of the car…

driver vs driver isn’t an issue as although the width works out right you seem to be skipping is delays that are applied to one side that means the null won’t be at 80hz even if the width mathematically works out as 7ft, and the energy will likely get cancelled as it goes across the car and not at the listening position assuming a mono 80hz note as it will be in phase at the listening position from the two direct sources, however the out of phase 80hz from down the car that creates the null in one driver also messes up the phase for the sim of the left and right at the listening position also

All pass won’t solve it as will still end up with lots of different sources and phase angles at the listening position from direct and reflected sound, and for me an array is only an option when you cant put the midbass in a better location, and even then I wouldn’t pick an array as again more lots of phase angles do not generally add up to make good phase regardless of what an rta says
 

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I wouldn’t pick an array as again more lots of phase angles do not generally add up to make good phase regardless of what an rta says
RTAs are 1980s technology

Nobody should be using an RTA in 2022
 

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RTAs are 1980s technology

Nobody should be using an RTA in 2022
Good job I’m not just using an rta then, that’s why I know midbass arrays are not the best solution if you can move midbass

ps room eq wizard is what most refer to as an rta these days among some of its features, that’s very useful!

I use a bit more advanced software in smaart 👍🏼
 

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Gated measurements are far superior.
 
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