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Audio Help

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jsampsell
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Audio Help

Post by jsampsell » Fri May 14, 2010 11:54 am

I didn't think this topic really fit into any of the car specific areas so I'm starting it here instead.

Recently I embarked upon a project to install sound deadener in my car. Well, that turned into an entire sound system overhaul as well. I've posted in the Interior section about the sound deadener install and the 8" subs I installed in the rear deck. Those posts go into detail about what the system is if you are interested. Here are the links for those posts:

Sound Deadener Install Pictures and Advice

8" Subs In Rear Deck

So now I'm in the process of tweaking the system to get the best sound out of it. And, although I know a lot about this stuff, I don't know everything, so I thought I'd post here and see if anyone may have some experience and advice about this.

I have a 5 channel amp running my four door speakers and then the sub channel. My questions really have to do with crossover points.

Let me ask the questions from a signal flow perspective relative to where the high pass filters (HPF) and low pass filters (LPF) are.

From the source, the HU, the signal for the front and rear channels can be run through an HPF at different frequency points OR it can be turned off allowing the signal to run straight through. Also at the HU, there is a setting to change the rear channel speaker type from full range to subwoofer. In addition, at the source, the subwoofer option has to be turned on to begin outputting the sub signal and the sub settings have a crossover that can not be turned off.

Then at the amp, for both front and rear, there is a crossover mode (LPF, Full Range, HPF) and a crossover frequency range adjustment. And for the sub there is just the crossover frequency adjustment.

I can understand why it would be nice to use the HPF of the HU since adjustments to it are much easier than stopping the car and popping the trunk to adjust the amp's HPF settings. BUT, if you set the HPF at the source, what do you do with the settings at the amp? You can't bypass them. So do you set them at the highest frequency point so that the range that is actually being allowed through the HPF of the HU is allowed to come through? I hope this makes sense. In a single HPF situation you would just adjust it for what you need but in the case where the signal can be modified from the source but it is forced through another filter at the amp before it gets to the speakers, how do you set the amp's HPF in order to let what you choosing to send from the HU actually get through to the speakers? In this case, since the HU HPF can be turned off, thus sending out a full signal to the amp, it would make more sense to use the amp's HPF since I can't turn it off if I wanted to.

The same thing applies to the sub channel. In this case, the source signal is sent through an LPF by default. So, if I set the HU LPF to send out at 80Hz, what do I set the amp's crossover point at?

Do you see my dilema? I'm not quite sure how to get the signal I want through both the HU filters and the amp's filters. The fact that you can turn off the HU's HPF is a way to eliminate the problem with the front and rear channels but since the LPF on the HU can't be turned off, what do I do?

Another way to put it: If the source signal is, let's use the frequency range that my door speakers are suppose to be able to handle, 53Hz to 22KHz and I want to send the entire signal to the amp where I can then set an HPF on the fronts crossed at 320Hz and the rears an LPF crossed at ~200Hz that would mean that the signal getting through to the front speakers would be anything above 320Hz and the rear speakers would get everything below 200Hz.

The sub channel is slightly different. I'm not exactly sure the frequency response is for my subs but let's use the frequency range that the amp's crossover adjustment allows which is 20Hz to 200Hz. If I understand this correctly, since the HU has to use an LPF on the source signal just to be able to send out only low frequencies over the sub channel so I understand why it can't be turned off. In essence, by turning the sub channel on you are actually turning the LPF on. If I set the HU LPF crossover point at it's highest which is 125Hz, that's going to send everything below 125Hz through to the amp. So if I can send the widest frequency range through to the amp's sub crossover and I want to limit what gets through to the speakers themselves, I would then use the amp's crossover at say 80Hz which would then only allow frequencies below 80Hz through to the speakers. Is that correct?

Yet another way of looking at this setup:

Frequency range from source signal: 20Hz to 22KHz

So, based on the above scenario, that means that the frequency range for each stage would be:

Front: 320Hz - 22KHz
Rear: 80Hz - 200Hz
Sub: 20Hz - 80Hz

Is this correct?

Anyhow, if you understand what I'm saying I sure would appreciate some enlightenment on this. I'm not quite a newbie but I'm not quite a pro either. Understanding how to install audio equipment is only half of the equation and I've got that down pretty well. It's just getting the final output to sound the best it can is where I'm trying to figure all this stuff out. It doesn't help that I'm a trained musician either. I'm a little more picky than others usually are.
Jeremy


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Re: Audio Help

Post by Meg's Dad » Fri May 14, 2010 6:05 pm

Thoughts from an amateur... :)

First of all, the signal comes from the head unit to the amp to the speaker, right? There is a separate wire for each of the 4 speakers and the sub. So, if the head unit is only allowing 80hz to the sub unit and it goes through the amp, then (depending on the order of the crossoover and if it is passive or active), then the slope of the frequency decrease will start at 80 and drop from there. So, the amount of frequency through the subwoofer circuit higher than 80 hz will be lower at the amp and then to the speaker.

If the amp's cut off is higher than 80 hz, then the you will have a two tiered cutoff because the slope of the frequence decrease is not vertical (80 hz and whatever you set the sub amp at). Also, the output between those two frequencies will be diminished. I assume that if both the head unit and amp are the same, then the cutoff will be more steeply sloped downward as the cutoff at the amp will be decreasing an already decreasing frequency. Personally I think I'd prefer a higher cut off (say 125 or so) to the subs if they will properly replicate the frequencies without distortion.

Sorry to be so wordy.

If the sub cut off is 80hz, then frequencies higher than that will be sent to the other 4 speakers at full strength. So the frequency range will be 81hz (roughly) to 22hz or whatever the capabilities of the HU are. Of course, most radios only go to 14 khz anyway (I think). Since your amp has separate cutoffs for HPF's and LPF's for the front and rear separately (that must be a good amp), then you can tailor the sound fields as you mentioned. I do think that the HPF and LPF should be the same so that frequency "holes" between front and back don't appear.

For example, right above where you typed "Is this correct?", there is a frequency gap between 200 and 320 hz as the LPF will only allow frequencies below 200 hz to the rears and the HPF will only allow frequencies higher than 320 hz to the fronts. You will get some frequency bleed in that area because (as I mentioned above) the cut off is not vertical and some sound frequencies above 200 hz will make it past the LPF.


Frequencies that will be sent to the subwoofer:

3db

0db xxxxxxxxxxxxxxxxxxxxxxx
x
-3db x
x
x
x
x

10 hz 50 hz 80hz 100hz (etc)


So you see there will be some frequency bleed between the different circuits.

I really tried to shorten this reply but have failed miserably.

Good Luck
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Re: Audio Help

Post by Meg's Dad » Fri May 14, 2010 6:11 pm

The graph I paintakingly typed in didn't work as I intended. There is a better graph about halfway down the page at http://en.wikipedia.org/wiki/Low-pass_filter. The same information also applies (in reverse) for HPF's.
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Re: Audio Help

Post by jsampsell » Sun May 16, 2010 12:38 pm

Meg's Dad - Thanks for the reply. I'm a little on the wordy side myself when it comes to explaining things because "help" given when one doesn't know all the factors involved is really not "help". Sure, you could make certain assumptions about the situation but it may be so off from what is really going on that it can't be helpful. So, I actually really appreciate the wordy response.

What you wrote makes sense. I have played around with everything this morning and I think I have a combination that works well for me. I will write those settings down in order to come back to them if I really get everything messed up but I'll probably play around with it some more. Just to see what everything really does to the end result.

What I find challenging is how these settings end up affecting the equalization settings. I'm not sure if I need to start with a flat EQ while making these crossover settings and then EQ afterwards or not. I've kind of done a mixture. I understand why changing the crossover settings affects the EQ but I'm just not sure what my base should be. Or whether it matters. If both affect the final result then I have to start with one of them and factor in the other. It kind of makes sense to start with a flat EQ, adjust the crossover points and then EQ after that so I'll try that this afternoon and see if I get different results.

I checked out the wikipedia link you posted and am amazed at how much more to this stuff there really is. I had no idea. I am a musician and an electronics geek so I know what I want to hear from the overall mix and I've even mixed for live events before but I learned how to mix based on what knobs made the output what I thought it was supposed to sound like. After so long of playing with a mixing board you get used to what knobs make things sound the way you want them to. That was the limit of my knowledge about sound, though. I will definitely have to read up more on the subject. I find it facinating.

Thanks for your help!
Jeremy

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Re: Audio Help

Post by jsampsell » Sun May 16, 2010 3:50 pm

Well, I ditched the LPF on the rears option. Just didn't sound quite right to my ears. I did, however, use the HPF on the fronts crossed at ~250Hz and set the rears to Full Range crossed at ~80Hz. Then the subs at just under 80Hz at the amp and 80Hz at the HU. I'm very pleased with this setup. I think it's a keeper.
Jeremy

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Re: Audio Help

Post by Meg's Dad » Sun May 16, 2010 10:28 pm

Glad to help. I have tried to build some home speakers as a hobby. There is a lot more involved than just buying some raw drivers and slapping them in a box if you want good sound. I'm glad that you have found a set up that pleases you. That is the most important thing, after all.

Happy Listening.
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Re: Audio Help

Post by jsampsell » Wed May 19, 2010 4:52 pm

Meg's Dad - Here's something different.

I've installed 100 square feet of B-Quiet Extreme into the car (doors, roof, floor, rear deck and trunk). I've got everything installed and tuned perfectly. The problem is that when I make my tuning adjustments the car is either off or idling and when I go to work (an hour drive averaging around 55mph) the interior noise levels drown out the lower end of the frequency spectrum. In order to get it to sound the way I like it I have to pump the volume up to levels that I really don't care to listen at.

I know this is a Ford and not a Lexus or whatever other cars are known for how quiet they are from the factory but after putting the sound deadener in I kind of expected a little better results.

I started out by checking the sound levels in the car and have posted in the Interior section a request for others who may have tested theirs without the sound deadening but haven't received a reply yet. The more I think about it, though, the more I think that the sound level is only one part of the problem. The other part is the frequencies that the road noise generates. Seeing as how it seems to overpower the lower frequencies it would make sense that it is somewhere between 20Hz and 125Hz. It definitely affects the sub which is crossed at ~80Hz but it also affects some of the midbass frequencies as well so that's why I gave it that range.

Do you have any ideas about what I can do to at least minimize it if not do away with it altogether? I can't go out and get a different car, much less one that has very low interior noise from the factory, but I really would like to figure out something to help with this.

Your thoughts would be greatly appreciated.

Thanks!
Jeremy

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Re: Audio Help

Post by jsampsell » Wed May 19, 2010 5:00 pm

By the way, the tires are new with about 7,000 miles on them. They are Cooper CS4 Touring. Very nice tires.
Jeremy

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Re: Audio Help

Post by Meg's Dad » Thu May 20, 2010 7:41 am

I wish I could help more. Unfortunately, I think you may have maxed out your efforts unless you want to buy quieter tires... :cry: I think the main problem is the fundamental frequency of resonance of the car's structure. One of the reasons that a Mercedes is so much quieter than a domestic car is that the car resonates at a higher frequency than ours do.

It may be because of the extra strengthening of the body or whatever, but it is a real difference. I wish I could remember what article I was reading (years ago) that discussed the construction of the vehicles by make. The higher end cars were simply screwed together in such a way that they didn't vibrate as easily. The less flexible a car's body is, the higher the frequency at which it resonates (becomes mose active). I think this is why you get an increase in amplitude of the really low frequency sounds.

I am sure that I have butchered the explanation, so I hope that there is a sound engineer that reads this forum that can explain it better than I. Maybe a google search on car structure and resonance frequency will help.

Oh, I am sure that domestic cars have gotten better since that article was written.
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Re: Audio Help

Post by andysinnh » Thu May 20, 2010 11:26 am

I've noticed cars with modern suspensions are more apt to transfer road noise into the cabin than in the past. And it's not so much the sound deadening aspect as much as it is the transfer of the noise through the suspension to the body/frame of the car - so no matter how much Dynamat you put in - you'll get this noise transfer into the body, and thusly into the cabin. This is really noticible on things like Hondas and Toyotas that have lots of aluminum suspension components, but you can also notice it on our cars.

Case in point - the comparison of the family Freestyle to the family Montego. Identical setups (AWD, top trim line, similar stereo systems, etc). Both cars with the factory Pirelli P6's transferred tons of noise inside all the time, regardless of the road integrity. On the Freestyle, we replaced the Pirelli's with some Michelin Primacy MXV4's and, on a smooth road, it was amazing how much less noise got tranferred into the car. Very quiet tire. However, once the road got pitted or worn (like that travel-paths on highways) you could hear the noise transfer directly into the car thru the steering column and through the unibody panels. It's more of a "feeling" than a "sound" - but the impact is the same.

Anyway, even with mouse-quiet tires like the Primacy's, you can still get that noise transferred, and unless you want to start changing suspension bushings, etc, you'll never get rid of all of the noise...

andy
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Re: Audio Help

Post by ctrlraven » Fri May 21, 2010 1:31 pm

To my surprise my Hankook Optimo H727 tires are pretty quiet, they were surveyed at 8.5 out of 10 for Noise Comfort on www.tirerack.com
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Re: Audio Help

Post by jsampsell » Fri May 21, 2010 2:51 pm

I wouldn't have thought that there was that much structural difference between cars since there are DOT regulations on that in regards to safety. That said, I guess it really doesn't surprise me that DOT regulations would be as low as possible in order to make a decent balance between looking out for the safety of the people and looking out for the manufacturers who need to lower their production costs. In addition, it makes sense as well that a manufacturer that wants to put themselves in a higher priced market would use structural strengthening techniques to change the resonant frequencies as a way to quiet the interior. I just didn't think that would be a factor. Now I can see that.

It also makes sense that suspension would transfer noise into the car since that's really what connects the car to the wheel and tires. I figured that there would be at least a little of the noise coming from the tires but they are still very new and don't have feathering and they are much quieter than the Pirelli's that came on the car from the factory. The smoothness of the road definitely comes into play in this kind of noise, too, I realize.

I guess what I'm saying is that I know there are certain things that are just going to be inherent in regards to interior noise level but I was wondering if there was anything additional that could be done to help it out any more than I've already done. Based on all of this feedback, I'm beginning to agree that I may have exhausted all of my options and will just have to deal with it. It's not like it's a work truck or anything. It's still MUCH quieter than my wife's Explorer so I'm not complaining. Just looking for possibilities if there were any to be had.

Thanks guys!
Jeremy

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Re: Audio Help

Post by PMCErnie » Sat May 22, 2010 12:50 pm

I have a cheap and simple solution. I turn up the volume.
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Re: Audio Help

Post by Meg's Dad » Sat May 22, 2010 3:10 pm

Yes, and 20 years you'll be saying "What did you say, I can't hear you."

Hearing loss is cumulative and permanent. Because it happens so slowly, you don't realize that you lost it until time for your hearing aids.
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Re: Audio Help

Post by PMCErnie » Sun May 23, 2010 6:20 pm

Meg's Dad wrote:Yes, and 20 years you'll be saying "What did you say, I can't hear you."

Hearing loss is cumulative and permanent. Because it happens so slowly, you don't realize that you lost it until time for your hearing aids.
What, I can't hear you?
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Re: Audio Help

Post by Meg's Dad » Mon May 24, 2010 9:36 am

:lol:
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Re: Audio Help

Post by jsampsell » Mon May 24, 2010 10:16 am

PMCErnie wrote:I have a cheap and simple solution. I turn up the volume.
After many years of playing trumpet for jazz, orchestral and general band gigs, I've already noticed that my hearing is not what it used to be. And, as a musician, the one thing that would absolutely drive me to insanity would be never being able to hear music ever again. So, yes, I realize I could turn up the volume but I don't really want to unless I have to. That's why I seem like I'm being a little too picky about this. I don't really want to spend more money making my Ford as quiet as a Mercedes but since I'm stuck with it for awhile I'd like to at least explore my options. And, based on the discussion I've had with Meg's Dad and others on other forums, it sounds like all I can do is either turn up the volume or throw more money at it. Looks like I'll have to deal with it for now. I'll save up and try adding some actual sound deadener product instead of the vibration reducing product that I've already added.
Jeremy

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Re: Audio Help

Post by jsampsell » Tue May 25, 2010 7:53 pm

Well guys, I found a reasonable solution and thought I'd share. It was actually two-fold. It started when I got the missing remote level control module for my amp in the mail today. As soon as I opened it the thought popped into my head that I could just turn up the lower volumes to compensate. Then I realized that the remote level control didn't really deal with raising and lowering the sub channel volume but the bass boost factor. Well, on that train of thought, it occurred to me that I really needed a way to turn up the sub channel volume without affecting the front and rear channel volume to really compensate correctly. So I figured with the new remote level control giving control over how much bass gets to the subs, I could either turn up the gain on the sub channel and turn down the bass boost or turn the gain on the front and rear channels down which accomplishes the same thing as turning up the sub channel gain but for me it just took out that very last bit of high pitched sound from the gain being up just too high. So, now with this setup I have control over every genre of music I listen to and the levels at highway speed and at idle are no more than they need to be for my liking. Problem solved. I can't believe I didn't think about it this way before. Oh well. At least I did. Thanks again for all the help!

Jeremy
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Re: Audio Help

Post by RStabb » Wed May 26, 2010 9:00 am

What? I can't hear you... :P

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Re: Audio Help

Post by jsampsell » Wed May 26, 2010 9:09 am

I'll take responsibility for that. I thought I was writing loud enough for everyone to hear. I'll adjust the gain on my browser here so that it shouldn't be a probably going forward. :lol:
Jeremy

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