Dolbytone's TuneThread - Experimentation Edition

There's not really a hard core tune thread that I can tell so I wanted to put down some things that might get you all thinking about what the hell is actually happening when you sit down to make tuning decisions. I'll be editing/updating this post as I do more tuning. Also, ignore the completely horrible acoustics in my truck, what a trainwreck. Keep in mind these grabs are from my truck with my speakers etc. and when I talk about delay numbers, what I've done here won't necessarily apply in your case.

First thing you want to understand is that whatever you can do mechanically to improve the stereo, you want to do because that means you have to apply less correction. The object really is to achieve an accurate sounding stereo with as little EQ as possible because every time you manipulate the signal, there is a consequence.

Imagine a string running between two poles and you pinch the middle and pull it down. The middle doesn't go by itself, you affect the string for some length on both sides as well. EQ works like this. When you raise or lower a frequency, you are also raising/lowering the frequencies that surround it with diminishing effect the further away from that frequency you go.



This is why a parametric EQ is preferrable over a graphic EQ where the Q (affected bandwidth) is adjustable and not constant, you have more control to minimize the damage to surrounding frequencies by narrowing the Q, or affect a wider range by widening it, enabling you to make a large adjustment with just one filter.

Here we have a measured response from a dome tweeter and you can see there are two lines showing the response of the speaker. One line is the on-axis response, directly in front of the speaker and including a certain number of degrees in all directions. Typically these responses will show changes in 30 degree intervals. So, more than 30 degrees out, you have a line showing you a different response. If you can aim that speaker to avoid making corrections due to the difference, you want to do all you can before busting out the microphone.



The OEM speaker in my truck that I replaced with a tweeter wasn't so much a tweeter, it was more like a 2.5" full range speaker. This means it was handling frequencies much lower than my current tweeter does (including all of the midrange), and the woofer in the lower part of the door was only filling in for much lower stuff.

So we put in these component systems and the setup is wildly different, where almost all of the spectrum is being handled by the woofer in the lower part of the door, and in my case, 3.2kHz and above are going to the tweeter. Almost all of the stereo's energy is now coming from a completely different place.

Well, the "tweeter" hole in our doors (and bracket) was designed for a different speaker, a speaker that would disperse much more evenly considering the frequencies it was reproducing because as you go lower on the spectrum, the greater the dispersion characteristics of the sound wave. Also, the OEM speaker was closer to the opening. Tweeters are much more directional, so it's important to try to do two things when you replace that speaker with a tweeter from your component system.

1. Try to get the tweeter as close to the hole as you can, so you aren't losing any dispersion inside the door.
2. Try to aim the tweeter at the listening position.

These two things will VASTLY improve the performance of your aftermarket tweeters when placed in the upper door panel position. Sail panel tweeters aren't so much of an issue, and with dash tweeters, everything is bouncing off the windshield so it's blending more before you hear it. So, in my case it made sense to put spacers on the factory mount so there's less of an angle for the sound to overcome. This also placed the tweeter closer to the door panel opening so less sound is getting trapped inside the door. You can accomplish this a different way, like a better custom speaker mounting adapter. I threw some washers in there because I had them, it was fast, and super easy.



Because frequencies have different dispersion rates, if you aren't doing this, you may hear your sound focus back and forth between the driver and passenger side because the driver side speaker is off-axis in relation to your ear but the passenger side is not, and as the prominent frequencies in your audio change, it will sound like it is steering back and forth across the cab instead of a nice even balance between the two. This is much less noticeable when you are not using time alignment. If you are using time alignment you're going to think damn, the guy that mixed this record was doing a lot of cool panning shit.

So here is a quick subwoofer time alignment example showing what happens when you have weird distances and how that affects the interplay between it, and the rest (primarily the front) of the speakers.

Linkweitz-Riley did a pretty good job of making their crossovers neutral (flat) across the crossover frequency. The problem is, we have speakers all over the place causing them to interact at the crossover point in strange ways. A small fraction of time can make a huge difference, seen in the example below.



This one shows the subwoofer with no delay, but before and after changing polarity 180 degrees. You can hear this under normal circumstances, this is just what it looks like on an RTA. One way or the other isn't the right way, it just depends on what's going on after you set levels and EQ, but you want to start with the settings that give you the flattest response before applying any equalization.



This one is simple enough. "To 24dB/Oct or not to 24dB/Oct, that is the question." Really it just depends. Do you need a more subtle rolloff above the crossover point because you have tons of stuff stacking at 100Hz? If you're really flat to the crossover point there's no down side to making the crossover steeper.



This next screen is kind of what I really wanted to get into. I know everybody be like "Get a DSP or some HU that does Time Alignment" because everybody wants that focused sound stage aimed at their head. Yeah, I'm with you but I wanted to show you something else about time alignment. This is only something you can do with Bi-Amplification because only then do you have delay control over your woofer and tweeter separately. Essentially you are adjusting the phase relationship between the two because they are not in very close proximity to each other, and you want to correct that. This graphic is a single channel with woofer and tweeter, not all speakers playing sound.



For this reason, it's important to set all of your time alignments before applying any EQ. You don't want to spend an hour dialing in each speaker only to have the response completely change when you set your delays.

 

Awesome!!

 

I've had a chance to play around with a few things I think a lot of people wonder about, specifically Fast Rings and Baffles. This is a rabbit hole I went down trying to figure out the best way to resolve the huge amount of 100Hz - 315Hz I seem to have in my truck. At first I tried to EQ it down, and the results sounded squashed. I was pushing down the entire band 10-12dB just to see what the consequences would be. Bottom line is I didn't like it and started looking for other solutions.

First thing I did is swap out the speakers, so I went from Hertz HiEnergy HSK165 components to Audison Voce AV 6.5 and AV 1.1 components. Audison has a reputation for accuracy, so I needed to see if there was a difference between them and the speakers I've been listening to for 10 years. Turns out, no so much. I got the same response with both sets.

Next, I tried out Stinger Fast Rings.

https://www.crutchfield.com/S-6BEbyQMtC0P/p_541FAST6/Stinger-Roadkill-RKFR6-FAST-Rings.html

I installed them in all of the doors and I tried to convince myself they were helping but in the end it was a failed experiment, so I moved on to BoomMat baffles.

https://www.crutchfield.com/S-QdhubO8sfns/p_696B050330/Boom-Mat-6-1-2-Speaker-Baffles-Regular-3-depth.html

Below are the results, no EQ on all three experiments, no treatment, Fast Rings, baffles. Only left and right front channels are active, and the subwoofer is turned off as well.

This shows the difference between no treatment and Fast Rings installed. There is basically no difference that my RTA could see. There's basically no difference that my ears could hear either. Bottom line, I do not recommend FastRings. I think pushing the speaker out to as close to the door card's speaker opening is the best solution to preventing sound waves from getting trapped between the speaker and the opening.



This shows the difference between no treatment and BoomMat baffles installed. Here we see significant changes. Not only did it help out my problem area by a good 4dB, it also significantly limited the rolloff from the high pass crossover. After listening to this I like all of the low end response much more. The subwoofer handles everything that got limited by the baffles and the result is much cleaner.



My takeaway on all this is that using baffles is conditional. If you have a subwoofer they will probably help clean up your low end. If you aren't running very much power on your door speakers, or your low end is anemic, I'm not sure I recommend them.

In this case with my very specific problem they helped considerably. I still want to get the woofers at an angle but I'm having a time figuring out the clearance and I really need a band saw to make a custom speaker mounting plate.

 

What mic did you use? What RTA? Always interested in people’s setups

 

All these screens are from SMAART 8 using Rational Acoustics microphones.
https://www.rationalacoustics.com/smaart/smaart-v8/

I usually set up four microphones and either average a couple of them or EQ using the driver seat microphone. Last time I had one in the rear middle, one front middle and one each front seat.

Sometimes if I'm going to single mic, I'll use an Ivie IE-45 because SMAART entails a lot of setup.
https://www.ivie.com/index.php/ie-45-rta

 

Hi.

Question for ya. When using the baffles, did you leave the baffle completely intact? Or, did you open it up?

 

For the initial installation I left the baffles intact. After a while I decided it sounded too dampened and I cut them like you have in the picture. Probably unrelated but possibly not (ten years of hard driving), I discovered one speaker had a failing voice coil which would intermittently exhibit a scratching sound. If the baffle contributed, it would be my fault for running them hard sealed up like that, unable to dissipate the heat.

I had a set of replacements on order anyway because I wanted to get a pair of Mille PRO for the front, which are currently installed and actually sound quite nice.