# Experts, midrange firing off glass, what to overcome?!?



## pionkej (Feb 29, 2008)

I searched under every possible combination of mid, midrange, glass, windshield, firing, reflecting, etc... What I came up with is that most people don't like it because it causes reflections and the glass kills certain frequencies.

What I did not find is how many people have actually tried this and what it takes to overcome (or if it can be overcome). If the mid is aimed straight at the glass, are you not hearing only reflections (and how is that bad)? What frequencies are affected by the glass (and can they be overcome with indpendent driver gain control and eq)? Also, if it is so bad, why do cars come from the factory with a mid in that location? I know they don't set up vehicles for audiophiles usually, but they also don't NEED to add a midrange in addition to a mid/tweet combo, so why do it?

I want to run a 3-way stage in my setup. It appears kick panels are going to be VERY difficult in my car because: I drive a 5-speed, the DS kick has a fuse box in the back, the PS has the ECU in the front footwell that wouldn't be accessable without removing the kick panel every time I need access to it. I can probably work around these things if I had to, but I also have the ability to put 4" mids in my dash at both corners with nearly equal PLD's. 

I know pods on the top of the doors, dash, or a-pillar are popular, but this car is a "fun car" for my wife and I to go on road trips in and to car shows with. I don't want it to sound great to me and bad to her, or average for both of us, and those locations totally screw up PLD's.

So, if it is possible to implement, what do I need to do or watch out for. If it is not possible to do, please let me know as well, so it can help future searchers and keep me from chopping holes in my dash.


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## ehkewley (Jul 19, 2008)

I would just try it first and see if you like it. I'm still a newb when it comes to audio affects of reflections and such, but in my last car (S40) I had 4" coaxials in the dash, and 6.5" woofers in the door. I very much liked this setup, and it didn't sound bad to me at all. I have since moved on to a newer vehicle, with 6.5" in the door, and tweets in the A pillar (stock). I think it sounds much less detailed than the glass reflected 4"


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## pionkej (Feb 29, 2008)

ehkewley said:


> I would just try it first and see if you like it. I'm still a newb when it comes to audio affects of reflections and such, but in my last car (S40) I had 4" coaxials in the dash, and 6.5" woofers in the door. I very much liked this setup, and it didn't sound bad to me at all. I have since moved on to a newer vehicle, with 6.5" in the door, and tweets in the A pillar (stock). I think it sounds much less detailed than the glass reflected 4"


I can't try it before without putting holes in my dash. I don't have any there from the factory, and the window is so tight steep I can't set them up there to test them out. I suppose I could move the about 5-6" back with a towell around them, but I am looking for some more detailed advice before tackling this.

Thanks for the input though.


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## ehkewley (Jul 19, 2008)

Whoops! Sorry, missed the last part of your post that stated you'd have to put holes in.


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## michaelsil1 (May 24, 2007)

Place them on the dash wrapped with a towel.


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## WLDock (Sep 27, 2005)

In general, this can work if it is just midrange freq. but treble creates a mess...don't aim tweets at the window. However, the main issues with mids are issue early reflections and the effect on the freq. response. Just takes more trial and error in terms of crossover, phase relation to the tweets and midbasses, and EQ...but doable.

However, with such nice and rare mids, I think you should try your best to get them on axis as well as out of the direct path of the sun if possible. I found that the mids sounded much better on axis vs. off. Also, the other issue i had about putting in the kicks is dust getting into the voice coil. 

Hard choices there as you have limited options. That is what I faced with those mids as well as the size...the 4" was just too large for my dash on axis....I think a 3" might work better for me.


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## [email protected] (Jun 12, 2008)

Mount them in the kicks and put some grill cloth over them


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## Foglght (Aug 2, 2007)

I run it firing at the windshield in a 3-way front stage. Sounds pretty good. Every once in a while, I'll just turn off the mids, and kick up the x-over to the mid-basses and it just doesn't sound as good, with imaging and with overall quality. 

YRMV

Someone told me that I needed to make sure that I take the largest wavelength and be assured that wavelength could produce 1 full wave before being reflected. Pretty easy to find the calculations for that. Not sure if that person was right, but I have a pretty decent stage. 

I run the mids......from 250hz @ 12db - 5.5khz @24db


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## pionkej (Feb 29, 2008)

WLDock said:


> In general, this can work if it is just midrange freq. but treble creates a mess...don't aim tweets at the window. However, the main issues with mids are issue early reflections and the effect on the freq. response. Just takes more trial and error in terms of crossover, phase relation to the tweets and midbasses, and EQ...but doable.
> 
> However, with such nice and rare mids, I think you should try your best to get them on axis as well as out of the direct path of the sun if possible. I found that the mids sounded much better on axis vs. off. Also, the other issue i had about putting in the kicks is dust getting into the voice coil.
> 
> Hard choices there as you have limited options. That is what I faced with those mids as well as the size...the 4" was just too large for my dash on axis....I think a 3" might work better for me.


Yeah, I am trying everything I can to make them work. I really don't like the idea of firing up against the glass or kicks for those mids either. And who would want to hide THOSE mids with some grill cloth...they're beautiful.  The post from foglght gave me an idea though. 

I plan to have a phase switch box in my center console to help with tuning. They will have a 0/off/180 setting. I could mount the 720prs set with the the midbass in the door, the mids in pods at the top of the door by the sail panels on-axis, and tweets in the a-pillar. 

I can store up to 10 presets on my processor. So, I can run the 3-way front for whem I am in the car and tune for one seat. When we ride together, I can switch off the midrange (if it sounds bad), switch on my l-r rear fill, and tune for a two seat car. I will basically have two systems in the car then. One setting for one seat, and one setting for two seats! I already planned to have a setting for riding with windows up, windows down, and t-tops off, so why not pile more on? 

Also, for future searchers (if they decide to TRY and find an asnwer before posting the question), what are you calling treble requencies that would cause problems. Most midranges run anywhere from 200-6khz. I was planning on 400-4khz with my setup as a starting point. So are you talking about 1500, 4k, 8k, or you just really can't say as it depends on the setup? Again, I am just curious now, thinking that maybe you would have to cut your mid off short of it's high end potential....or maybe not.


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## benny z (Mar 17, 2008)

i would image that comb filtering would be a bigger issue than early reflections.


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## SSSnake (Mar 8, 2007)

It is and you can't fix it with EQ


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## TJ Mobile Audio (May 6, 2009)

I just finished an install that put 4x6" coaxials in the dash locations, and the SQ was acceptable. Just my $.02, it wasn't the best by any means, but I didn't notice any obvious holes in response. That was in a 1994 GMC Sierra.


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## SSSnake (Mar 8, 2007)

Issues are VERY dash geometry specific. Can it be done well, YES. Can there be LARGE problems, YES. As mentioned earlier wrap the driver in a towel and experiment.


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## lashlee (Aug 16, 2007)

I use dyn 3" domes firing straight up from the dash and have done it that way for about 3 years now. I've tweaked quite a bit, with a 701 and eventually made a simple dash pad to tone down some reflections. That is what seemed to help the most. I do prefer the height that I get but like you I had to cut and make some serious choices. To change anything that I have is a pain, I have to pull the dash which is a 4 hour process, at a quick pace!!! I'd say go for it if you've got the skills and processing.


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## SSSnake (Mar 8, 2007)

Processing won't fix a comb filter. It is a geometric issue... You must change the geometry or damp the reflections (in your case the dash pad).

BTW - the one third octave resolution of the 701 is not going to touch comb artifacts. In most cases, the 701 filters are MUCH too wide.


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## pionkej (Feb 29, 2008)

SSSnake said:


> Processing won't fix a comb filter. It is a geometric issue... You must change the geometry or damp the reflections (in your case the dash pad).
> 
> BTW - the one third octave resolution of the 701 is not going to touch comb artifacts. In most cases, the 701 filters are MUCH too wide.


Since I feel this is great for me, and others who want to learn as much as we can, do you mind shedding a bit more light on what comb filtering actually is?

Also, are you speaking of a dash pad light a regular dash mat? Since the driver is firing directly up into the glass, do you get a second reflection from the glass back to the dash, and is that the purpose of the dash mat?

Thanks, I just think this thread has the beginnings of some good information. Like I said, all I found searching before was: it works for me, it won't wont, it will mess up your FR, you will have phase issues. Pretty vague and I think we are finally getting somewhere.


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## vactor (Oct 27, 2005)

BeatsDownLow said:


> Mount them in the kicks and put some grill cloth over them


do this.


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## pionkej (Feb 29, 2008)

vactor said:


> do this.


Thanks so much for the contribution!


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## benny z (Mar 17, 2008)

this is from a home theater posting, but touches on a lot of issues that are very applicable to car audio:

Horizontal Center Channel Speakers and Why They Should Be Avoided - Blu-ray Forum


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## pionkej (Feb 29, 2008)

benny z said:


> this is from a home theater posting, but touches on a lot of issues that are very applicable to car audio:
> 
> Horizontal Center Channel Speakers and Why They Should Be Avoided - Blu-ray Forum


That link shows a good example of what lobing and comb filtering is...thank you for that. 

What I am assuming, since no one has said it, is that since you are firing off the glass and the frequencies can then reflect right back off the dash, they will either be amplified by being in phase with each other or canceled by being 180 out of phase with each other. Is that correct? Would a dash mat not alleviate this problem? 

Most of the problems in the link posted are a result of drivers overlapping. I am guessing that the reflection could mimic what two drivers overlapping do to cause comb filtering.


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## benny z (Mar 17, 2008)

pionkej said:


> Most of the problems in the link posted are a result of drivers overlapping. I am guessing that the reflection could mimic what two drivers overlapping do to cause comb filtering.


now you're on to something...


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## SSSnake (Mar 8, 2007)

wiki on Comb_filters

As mentioned earlier, the reflections between dash and windshiled typically create a comb filter. A dash mat will help because it reduces (not eliminates) the reflection from the dash. However, the windshield is and always will be highly reflective. These reflections will create constructive and destructive interference that CANNOT be EQd out.

An additional note on dash pads... unless they are incredibly thick they do not effect midrange frequencies (read into some of the sound proofing threads)


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## TJ Mobile Audio (May 6, 2009)

pionkej said:


> What I am assuming, since no one has said it, is that since you are firing off the glass and the frequencies can then reflect right back off the dash, they will either be amplified by being in phase with each other or canceled by being 180 out of phase with each other. Is that correct?


Yes, and that also could explain why the GMC truck I did had respectable SQ with 4x6s in dash locations - the windshield is closer to vertical than it would be on a car, and the dash is mostly horizontal, so most of the sound only reflects off the windshield and not back down to the dash. It's a less acute angle than you'd have in a typical car.



pionkej said:


> Would a dash mat not alleviate this problem?


Probably not, though I haven't tried it. Most dash mats that I've seen claim to be acoustically transparent, so their sound absorbing qualities should be minimal. The very highest frequencies might be diffracted a tiny bit, but most of the mids (which you were primarily asking about) would remain untouched. Perhaps you could just remove the dashboard? Or cover it with 2" egg-crate acoustical foam? 



pionkej said:


> Most of the problems in the link posted are a result of drivers overlapping. I am guessing that the reflection could mimic what two drivers overlapping do to cause comb filtering.


Bingo!


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## mda185 (Dec 14, 2006)

Very interesting thread. Great question and lots of good info here. 

As SSSnake said, dash pad will not absorb reflections in the midrange. There is no hard data to say which frequencies are absorbed by dash pad, but an educated guess is that it is most effective from about 5 KHz on up.

There is a very good thread on this forum by BMWTurbo that describes what he has done in a BMW 7 Series that originally had dash mounted midranges firing into the windshield. Ultimately, he built pods that sit in the corners of his dash aimed at his listening position. This cuts down significantly on windshield reflections and his measured freq response plots look pretty good. His pod design is probably not what you will want in a car shared with your wife but that does not mean the concept is flawed. You may want to look into something that blends into the interior better if you have the fabrication skills or are willing to learn. Peerless makes a 2" full range driver currently on sale at Madisound that may be worth checking out if 3" driver is too big for your car. Either one will require a crossover to a sub or midbass.

FWIW, I am going through same issues with my two primary cars and I think I am going to make pods for 3" Fountek full range speakers for my 95 BMW 525 and 2001 Pathfinder. The off axis response of a 3" diameter driver starts to drop off above 5 KHz but this is perfect for cutting down on windshield reflections. It just means the driver has to be aimed at the listening position. The BMW has 2" mids from the factory that fire into the windshield. I thing they get around the worst of the comb filtering by rolling off the frequency response of the head unit well below 20 KHz. I don't think there is much response in the OEM system above 10 KHz.


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## pionkej (Feb 29, 2008)

SSSnake said:


> wiki on Comb_filters
> 
> As mentioned earlier, the reflections between dash and windshiled typically create a comb filter. A dash mat will help because it reduces (not eliminates) the reflection from the dash. However, the windshield is and always will be highly reflective. These reflections will create constructive and destructive interference that CANNOT be EQd out.
> 
> An additional note on dash pads... unless they are incredibly thick they do not effect midrange frequencies (read into some of the sound proofing threads)


I appreciate the advice from everyone as I am trying very hard to continue learning. It is funny that many of my friends don't understand what a crossover is, other than the thing you connect your amp to that then goes to your two speakers.  So thanks for the help.

I have read up on TONS of sound proofing threads as well. I was under the assumption that the waves didn't need to be absorbed (which I know a dash pad wouldn't do at lower fequencies), but merely stop the reflections or at least disperse them so they were not reflecting directly back into the glass. I figured while it couldn't do the formed, it could accomplish the latter.

I suppose that even if it DID diffuse the frequencies, it wouldn't eliminate comb filtering, it would merely change the points where the constructive and desructive interfernce would occur compared to bouncing off the smooth OEM dash.

If the material had worked at simlpy diffusing, I would have planned to cover my dash with a dash pad or just apolster it in an ultrasuede material.


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## MarkZ (Dec 5, 2005)

Another approach to reducing the effect of comb filtering would be to somehow limit the dispersion of the driver. The simplest way of doing this would be to choose drivers with "poor" off-axis response, which generally means large radiating surfaces. You may want to consider, then, using a full-range driver for your top end. Maybe a 3" or larger -- perhaps something like that Fountek that everyone's raving about?

But then mounting location becomes crucial. And if you're dispersion-limited, you might want to aim for a one-seat approach.

Basically, do-able, but not impossible if you're willing to live with certain tradeoffs.


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## pionkej (Feb 29, 2008)

MarkZ said:


> Another approach to reducing the effect of comb filtering would be to somehow limit the dispersion of the driver. The simplest way of doing this would be to choose drivers with "poor" off-axis response, which generally means large radiating surfaces. You may want to consider, then, using a full-range driver for your top end. Maybe a 3" or larger -- perhaps something like that Fountek that everyone's raving about?
> 
> But then mounting location becomes crucial. And if you're dispersion-limited, you might want to aim for a one-seat approach.
> 
> Basically, do-able, but not impossible if you're willing to live with certain tradeoffs.


I see what you are saying, but if it limits me to a one-seat setup, I'm actually worse off than putting them on the tops of the doors by the sail panels on-axis. I would have to use t/a some there which may cause some phase issues, but I wouldn't have FR issues that can't be fixed with eq.

I was trying to find a good answer for two-seat that didn't involve putting them in the kicks.


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## TJ Mobile Audio (May 6, 2009)

SSSnake said:


> These reflections will create constructive and destructive interference that CANNOT be EQd out.


Could you clarify that a bit? It seems that at least the constructive interference could be corrected with a severe dip in the EQ curve. 

The destructive interference might be more difficult. It likewise could be overcome if your speakers can handle the increased power required for full response at that frequency, no? This is assuming of course that the interference is not _completely destructive_, in which case no amount of power could overcome the the dip, because an equally powerful destructive wave would be created by reflection. However, in most cases, the reflection is at least slightly less powerful, meaning you will still hear _something_ at the given frequency, just boost that "something" and you've fixed tonality. (By fixing tonality I mean you would have a flat response).

Perhaps in some cases the dips and spikes are too severe to EQ with a conventional EQ, is this what you mean? Because with enough EQ bands, enough power handling at the speakers, enough juice on hand, and an EQ with a large enough range, it seems like you could at least fix tonality. You would still have phase and vertical imaging issues, because some sounds would be coming from the windshield, some from the speaker, and some from the dash, each with a different path length to your ear.

Maybe I'm over-analyzing it and there is some fundamental reason an EQ can't fix the problem. Or I just misunderstood your statement. Any clarification would be useful for future reference, as I have rarely installed in dash locations and am still learning on this topic as well.



SSSnake said:


> An additional note on dash pads... unless they are incredibly thick they do not effect midrange frequencies (read into some of the sound proofing threads)


Ah, just as I suspected, this is perfectly in line with my comment about egg-crate foam.  I didn't see that before I posted, but it seems we're in agreement on that point.


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## TJ Mobile Audio (May 6, 2009)

pionkej said:


> I was trying to find a good answer for two-seat that didn't involve putting them in the kicks.


Mine's a pretty decent two-seat setup, but alas, I had to use the kick panels.


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## pionkej (Feb 29, 2008)

I am getting pictures of my possible locations. While doing so, I thought of another question. Everybody talks about minimizing PLD's, but what is a good distance to shoot for (I know as close as possible)? Basically, what have you guys settled on, and does it sound good for one-seat or two-seat? At what point do you actually notice delay differences? .2ms, .5ms, 1ms, 2ms.....

Thanks for any help, couldn't find anything after a quick search.


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## SSSnake (Mar 8, 2007)

you cannot EQ out the effects because when you put more power into the directly radiated sound at the null it also increases the level of the reflected sound. This typically makes things worse because of the phase anomolies that you introduce.

Again the way to fix it is geometrically. Either orient the driver/radiation pattern or the reflecting surfaces so that you minimize the effects. THis is NOT straightforward and is the primary reason car audio typically sounds much worse than home audio (too many reflective surfaces).

I am very interested in utilizing waveguides to control dispersion and decrease the negative effects of early reflections BUT the waveguides must be VERY large to control mid range dispersion.


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## Andy Jones (May 12, 2006)

All the theory is correct, but I've heard it done very successfully several times. I can think of a few cars that sound nice with midranges firing straight up. I know of at least one that has a tweeter firing straight up that sounds pretty good. 

In the perfect world you would angle the mid at the same angle as the windshield, but the perfect world rarely exist. Firing up can definitely work. At least in my opinion it can.


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## Andy Jones (May 12, 2006)

^my comments are one seat, not two seat.

I've never personally heard a dash mounted midrange system that sounded great from both seats. I've heard some that used some processing and had strong left, strong right and a strong center, but very little information in the middle of those positions. 

The reflection of the windshield is going to kill your PLD and the chance of you getting two seats is going to be VERY difficult.


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## SSSnake (Mar 8, 2007)

Andy,

I know that you have been in more cars than I have but I probably sat in some of the cars that you reference  and agree that they can sound very good. IMO geometry is the primary indicator as to whether or not it works well. Vehicles wo an acute angle between the dash and the widnshield (like trucks) should work better (I'm trying to remember how steep and deep the windshield is in the 300M).

I went down the path of a dash mounted mid on my Saturn and even with PLDs that were nearly the same as the kick locations, the freq anomolies ruined it for me. IMO it takes more work to get them to sound as good as a kickpanel mounted mid.


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## pionkej (Feb 29, 2008)

Well, here are the pictures, PLD's, and time differences in MS (I rounded to the nearest 1/4" since that is the accuracy my DSP is capable of with T/A):

Dash firing forward: DS=3'-1 3/4" PS=4'-0 1/4" Difference=10 1/2" MS=7.636










Kickpanel: DS=4'-3 3/4" PS=5'-0" Difference=9 1/4" MS=6.727










Sail panel/top of door location: DS=3'-4" PS=4'-3 3/4" Difference=11 3/4" MS=8.545










Dash location firing up (couldn't fit the driver for pictures): DS=4'-2 1/2" PS=4'-11 3/4" Difference=9 1/4" MS=6.727










Dog wondering WTF I was doing:










If you count for up firing reflections being bad, my options would be: 

Kicks-highest depth and shortest PLD's plus probable additional depth and shorter PLD's if mounted higher...but open to foot/dust damage and blocks fuse box on DS and ECU on PS

Dash-last in path length but second shortest PLD's which I believe would help a 2-seat car better with balance thought the stage won't be as deep...but not sure if I can get drivers that tight in the corner and may be up to 2" closer than measured

Sail-third in depth and last in in PLD's....but probably easiest to install and can get just as close to tweeter in a-pillar as dash location

Dash firing up-second in depth and tied for shortest PLD's...but has potential for all the problems mentioned above and can't know if I have problems until after I cut holes in my dash to mount!


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## SSSnake (Mar 8, 2007)

My thoughts (and they are worth what you paid for them  ):

The dash looks very good on the passengers side. The angle between the windshield looks to be around 90 degrees or more. The driver's side is not so good but still not terrible. I would think you would end up with more comb filter effects here but the shape is irregular and should mimimize them somewhat. 

As far as on axis or firing into the windshield, for me it would depend on the upper xover freq and the size of the mid. If the mid is still omnidirectional at the xover freq, I would fire them at the windshield. If not, fire them more on axis (how much depends on the dispersion pattern).

Finally, like I have said repeatedly... wrap the mids in towels, hook them up, move them around and listen. Theory should only be used as a general guideline. There are way too many varibles to speak in absolutes.

OK one last comment, I would try those mids further under the dash as well. Again depending on the xover freq you might be able to squeeze out a little lower PLD.


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## pionkej (Feb 29, 2008)

SSSnake said:


> My thoughts (and they are worth what you paid for them  ):
> 
> The dash looks very good on the passengers side. The angle between the windshield looks to be around 90 degrees or more. The driver's side is not so good but still not terrible. I would think you would end up with more comb filter effects here but the shape is irregular and should mimimize them somewhat. *Is this referencing the dash firing forward setting? If so, are you saying I would encounter comb filtering on the driver side dash firing forward because of the gauge cluster and steering wheel? *
> 
> ...


See comments above. ^


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## pionkej (Feb 29, 2008)

^^ Also, this was just a quick setup to get approximate locations, so if you are referencing anything to what axis they are on, that can change. I just put them in there where they wouldn't fall while I made my measurements and took pictures.


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## SSSnake (Mar 8, 2007)

The dash looks very good on the passengers side. The angle between the windshield looks to be around 90 degrees or more. The driver's side is not so good but still not terrible. I would think you would end up with more comb filter effects here but the shape is irregular and should mimimize them somewhat. Is this referencing the dash firing forward setting? If so, are you saying I would encounter comb filtering on the driver side dash firing forward because of the gauge cluster and steering wheel? Actually I would expect some comb filtering with either facing forward or facing up (at least through most of the passband). Remeber the driver is going to be largely omnidirectional up until (not sure if those are 6.5s or 5s) around 2khz. But yes the culprit is the dash cluster (steering wheel, not so much).

As far as on axis or firing into the windshield, for me it would depend on the upper xover freq and the size of the mid. If the mid is still omnidirectional at the xover freq, I would fire them at the windshield. If not, fire them more on axis (how much depends on the dispersion pattern). I was planning to start with 500hz/4khz @ 72db, but have no idea what the final points would be. If you go that high you will likely want them more on axis rather than firing at the widnshield (this really depends on the driver - those mids could have a rise in the freq response to compensate for off axis mounting - just not familiar with the pioneers)

Finally, like I have said repeatedly... wrap the mids in towels, hook them up, move them around and listen. Theory should only be used as a general guideline. There are way too many varibles to speak in absolutes. Don't disagree here, but the thread started by asking about firing up into the windshield, and I can't try that out without cutting the dash first, I just showed the other options now for an idea of what else I could do and some input there as well. I understand the dilemma but the difference between dash mounted on axis and firing into the windshield should be minimal. It will likely show up around 2Khz and above. The biggest difference should be between kick and dash mounting. My suggestion is place them in the kicks, listen, and make notes. Move them to the dash, listen, and make notes. Repeat kick and dash locations and then decide. If you settle on dash then you will just need to be careful on the mid to tweet xover setting.

OK one last comment, I would try those mids further under the dash as well. Again depending on the xover freq you might be able to squeeze out a little lower PLD. I mentioned that at the bottom (sometimes it is easier to just look at the pictures and respond) But I figure if I go higher, I can get another 2" or so of length and move PLD's closer to 6" or so.


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## pionkej (Feb 29, 2008)

SSSnake said:


> Actually I would expect some comb filtering with either facing forward or facing up (at least through most of the passband). Remeber the driver is going to be largely omnidirectional up until (not sure if those are 6.5s or 5s) around 2khz. But yes the culprit is the dash cluster (steering wheel, not so much).*The speakers are 4" midranges. That just shows how tight the dash to window line is since they are wedged in there. I am not sure why I would suffer badly from comb filtering in that location if firing forward. I could see a BIT I suppose on reflections from the dash cluster, but I just figure that no reflections would form a true cancellation. Maybe I am wrong here, and a bit more education would be helpful*
> 
> If you go that high you will likely want them more on axis rather than firing at the widnshield (this really depends on the driver - those mids could have a rise in the freq response to compensate for off axis mounting - just not familiar with the pioneers)*I was actually planning to follow the suggestions of Rick from RAAMaudio as a starting point. Measuring my ear location on the glass, going XX" forward and XX" down, and aiming the drivers there. I was planning for that either mounted in the kicks or the dash.*
> 
> I understand the dilemma but the difference between dash mounted on axis and firing into the windshield should be minimal. *Not sure I understand this at all. If it is minimal, why do people who have dash mounted setups go for on-axis all the time and I can only find one or two examples of non-OEM setups firing into the glass? Not saying it isn't so, just asking here.* It will likely show up around 2Khz and above. The biggest difference should be between kick and dash mounting. My suggestion is place them in the kicks, listen, and make notes. Move them to the dash, listen, and make notes. Repeat kick and dash locations and then decide. If you settle on dash then you will just need to be careful on the mid to tweet xover setting.*What do I need to watch for here? If they are mounted on the dash, they will be around 2" away from the tweets on the a-pillar. Wouldn't crossover point not matter since both would benefit/suffer from whatever you speak of?*


*Thanks for all the help so far. To everyone. This has really benefitted my further understand of all things audio!*


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## Patrick Bateman (Sep 11, 2006)

pionkej said:


> I searched under every possible combination of mid, midrange, glass, windshield, firing, reflecting, etc... What I came up with is that most people don't like it because it causes reflections and the glass kills certain frequencies.


You can predict what frequency is going to be a problem. Here's how you do it.

#1 - figure out where the mid will fit
#2 - measure the distance to the windshield
#3 - pop it into this equation : (13500 / distance / 4)

So if you can get it with three inches of the windshield, you'll have a notch at 1125hz.

IMHO, the dash is the best place in the whole car to put speakers. You just have to work with it's shortcomings. It's superior to the kick panels IMHO.

The best way to get a speaker to sound good on the dash is to get it as close as humanly possible to the glass. That drives the frequency up very high.

For instance, the stock speakers in a Honda Accord have a tweeter that's right at the apex of the windshield and the dash. Because the distance is about half an inch, it creates a notch at 6750hz. At that frequency, it's not as audible as it would be in the midrange.


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## Patrick Bateman (Sep 11, 2006)

SSSnake said:


> you cannot EQ out the effects because when you put more power into the directly radiated sound at the null it also increases the level of the reflected sound. This typically makes things worse because of the phase anomolies that you introduce.
> 
> Again the way to fix it is geometrically. Either orient the driver/radiation pattern or the reflecting surfaces so that you minimize the effects. THis is NOT straightforward and is the primary reason car audio typically sounds much worse than home audio (too many reflective surfaces).
> 
> I am very interested in utilizing waveguides to control dispersion and decrease the negative effects of early reflections BUT the waveguides must be VERY large to control mid range dispersion.


SSSnake, I'm building some new waveguides, you might be interested in this:

diyAudio Forums - Creating a Soundstage with Waveguides and Psychoacoustics - Page 1

I suffered through an afternoon of measuring in 105 degree temperatures yesterday, the results are VERY good. I'm surprised how well they are working.

I came up with a "trick" over the weekend, which is to squash the vertical coverage dramatically, to a point that it goes omnidirectional over the entire passband. Wasn't sure if that was going to work, but the results are very promising.

The trick is that there's a dip in the frequency response when the directivity collapses because the waveguide is too small, but squashing it like crazy pushes the dip above the passband.


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## pionkej (Feb 29, 2008)

Patrick Bateman said:


> You can predict what frequency is going to be a problem. Here's how you do it.
> 
> #1 - figure out where the mid will fit
> #2 - measure the distance to the windshield
> ...


This is great info for me and for future searchers to know! I am curious, as to where you take the measurement from though? Are we talking the center of the speaker, closest side, furthest side? Do you take into account the entire range? 

My speaker based on eyeballing would be withing 1/8" of the glass at the tight end, but it will be whatever distance the 4" width plus the slope of the windshield is at the other end. Say, 3" MAX without measuring.

Also, a point was brought up in an earlier post. Do I have anything to worry about with the mids facing directly into the sun? The car is garaged when not driven, and I plan to get a reflective blocker for the front windshield. But when I am driving, direct sunlight hitting it.

Thanks again!


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## mb2452 (Nov 7, 2009)

Patrick Bateman said:


> You can predict what frequency is going to be a problem. Here's how you do it.
> 
> #1 - figure out where the mid will fit
> #2 - measure the distance to the windshield
> ...


So the notch effect geometry dependent? For example, if the speaker in the dash is near the edge of the dash and the windshield is sharply angled so the rectltions don't appear to be directed onto the dash then will there still be a notch in the frequency response?


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## Patrick Bateman (Sep 11, 2006)

mb2452 said:


> So the notch effect geometry dependent? For example, if the speaker in the dash is near the edge of the dash and the windshield is sharply angled so the rectltions don't appear to be directed onto the dash then will there still be a notch in the frequency response?


Yeah, you can calculate where the peak and the dip will be located. It's not "perfect", but it gets you in the ballpark.

If you look at stock locations, you'll notice that they push the speakers right into the apex of the windshield. For instance, in an Accord the stock full range is about 1.5" from the apex.

By pushing it into the apex you push the peak and the dip higher in frequency, where it's less audible.

It's kind of counter intuitive, because you would think that things would get worse the CLOSER you get to the windshield.

Here's a mathematical example:

Let's say you have a three inch full range, and it's located four inches from a reflective surface. You're going to get a dip at 844 hz and a peak at 1688hz. (see formula above.) _That's right in the range where our hearing is most sensitive - those peaks and dips will be very VERY audible._

OTOH, if you can jam that full range right into the corner, so that the reflector is just 1.5" away, the dip moves up to 2250hz and the peak moves up to 4500hz.

As you can imagine, a peak at 1688hz is a lot nastier sounding than a dip at 2250hz; in fact some people intentionally put a dip at 2khz using EQ.

Does that make sense?


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## I800C0LLECT (Jan 26, 2009)

Oh wow....Good Reading guys. I had a theoretical idea of jamming a mid-range and tweeter into the corners of the glass.

This works out wonderfully. So basically, the goal is to mash each speaker as close as possible to the windshield/dash apex. However, when using a tweeter should you place it on the same plain as the mid-range?

Because if you're trying to mount them next to each other, rule of thumb, you'd be pulling the tweeter away from the apex. But maybe jamming into the corners/A pillar where the dash meets at say a 15 or 20 degree angle for both will give you the benefit of imaging too?


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## Patrick Bateman (Sep 11, 2006)

I800C0LLECT said:


> Oh wow....Good Reading guys. I had a theoretical idea of jamming a mid-range and tweeter into the corners of the glass.
> 
> This works out wonderfully. So basically, the goal is to mash each speaker as close as possible to the windshield/dash apex. However, when using a tweeter should you place it on the same plain as the mid-range?
> 
> Because if you're trying to mount them next to each other, rule of thumb, you'd be pulling the tweeter away from the apex. But maybe jamming into the corners/A pillar where the dash meets at say a 15 or 20 degree angle for both will give you the benefit of imaging too?


At high frequencies we're very sensitive to frequency, and less so at low frequencies. (At low frequencies path lengths become important.)

So if I were going to put a mid *and* a tweeter up on the dash, I'd push the mid as far back as I possibly could.

That helps generate a deep and wide soundstage. There's going to be reflections, but remember, it's less important in a mid than in a tweeter.

Then I'd throw the tweeter in a location where reflections could be minimized. For instance, in a sphere that's away from the glass, flush mounted on a flat surface and cross fired, or best of all, in a waveguide.

This is another one of those counter-intuitive things - you'd think that you'd want to get the *tweeter* back further, not the midrange. But pathlengths are more important at low frequencies, and since you have to compromise one or the other, I'd bring the tweeter forward, not the mid.


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## I800C0LLECT (Jan 26, 2009)

It seems, at that point you'd want to minimize the distance between the two and place them on-axis. I definitely understand the point being made. Apparently a full range speaker might be the best alternative depending on the nature of the environment.


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## mb2452 (Nov 7, 2009)

Patrick,

Thanks!

As an example, my old Mercedes has the dash speakers almost at the dashboard edge nearest to the driver and passenger next to each A pillar. Since primary reflections appear to miss the the dash, do you agree that I shouldn't have a notch in the frequency response from dashboard reflections?

(btw, the distance from the center of my dash speaker cone to the windshield is approx 3.5" for a frequency of 1164 Hz)


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