# Tricks to getting 500hz response?



## BowDown (Sep 24, 2009)

Well I always attributed it to my crossover points, but 450-500hz always has a dip on my RTA. I have had 3 different midbass sets, and now instead of crossing over at 500hz @ 18db, I have a crossover point of 710hz @ 12db..

So I'm thinking it might be the car? 

Anyway, I can EQ it up.. but I was wondering if anyone has tricks to help without boosting the source signal? 

My midbasses are in the stock locations on the front doors. They aim slightly angled into the footwell towards the firewall center of the car. 


Not really looking for a magic wand here.. but just found it interesting there's a dip there with diff midbasses, amps, and crossover points.

Anyone else have similar issues?


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## minbari (Mar 3, 2011)

wavelength for 500hz is 2.25 ft. measure your car and see how far apart the speakers are.

if they are 3.37(1 1/2 wave)4.5,5.6(2 1/2 wave) or 6.75, then you may have hit some harmonic that is canceling 500hz.


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## BowDown (Sep 24, 2009)

I believe it's about 2.5ft from the speaker to the trim panel in the center (under dash) in footwell. I took the bike today, but can take measurements tomorrow.


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## minbari (Mar 3, 2011)

that would come out to about 450hz.


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## BowDown (Sep 24, 2009)

Wonder what would happen if I put some acoustic foam on that panel?


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## sqnut (Dec 24, 2009)

How big is the dip?


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## BowDown (Sep 24, 2009)

About 6db.


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## minbari (Mar 3, 2011)

if it is not teribly wide dip, could you eq it out? parametric set at 500hz with a Q of 2.


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## sqnut (Dec 24, 2009)

I'm leaning towards cars being an issue. Most cars I've tuned have had this, including mine. 

A peak is easy to manage, you cut the frequency and a bit around it maybe and you're set. The trick to curing a dip is slightly different. If you just boost 500 by 6db its going to mess up the balance with the rest of the sound, plus whatever's causing the cancellation is still there. 

But what if you let 500hz at flat and cut everything on both sides by 2-4 db? Of course while maintaining the overall balance. Now, how big is the dip? a 2-3db dip is easier to integrate. Adjust a bit for tonality. 

That's how I have it set. Try it see if it works for you.


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## ErinH (Feb 14, 2007)

does the problem occur from multiple locations or just one mic location?


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## sqnut (Dec 24, 2009)

I just assumed he was talking about ear level.


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## BowDown (Sep 24, 2009)

Just referring to ear level. I have only done 1 mic angle of ear level, looking forward. It has done it on an audiocontrol meter, my phone.. and I'll check with the trueRTA but I wouldn't be surprised there.


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## ErinH (Feb 14, 2007)

BowDown said:


> Just referring to ear level. I have only done 1 mic angle of ear level, looking forward. It has done it on an audiocontrol meter, my phone.. and I'll check with the trueRTA but I wouldn't be surprised there.


Use more than one location try a few in about 1sqft area and average them together. 

Also, cancellation occurs at odd orders of wavelength. Summation is even.


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## 24th-Alchemist (Jun 16, 2011)

Noob but I would nonetheless like to toss out a few thoughts for anyone to comment on.

First, assuming the 500 Hz dip is due to woofer cancellation, two ideas:
What about putting a 500 Hz dip in just one of the woofers? If they are cancelling one another, and a dip is introduced in just one, it won't be able to cancel the other as much. Perhaps a nice middle ground could be obtained through trial and error
What about introducing asymmetric phase between the two woofers just in the 500 Hz region,maybe with some sort of all-pass?

Second, are you certain the dip is due to cancellation? In my car I have run some chirps (frequency sweeps) with one and only one woofer active (all others muted). Nevertheless I hear what appear to be peaks and valleys. Furthermore the source of the sound seems to go back and forth between left and right as the chirp progresses. Such effects can't be due to one woofer cancelling another because only one is active. I've observed these phenomena with both tweets and midranges, and they're in different locations (sails and doors respectively).


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## subwoofery (Nov 9, 2008)

sqnut said:


> I'm leaning towards cars being an issue. Most cars I've tuned have had this, including mine.
> 
> A peak is easy to manage, you cut the frequency and a bit around it maybe and you're set. The trick to curing a dip is slightly different. If you just boost 500 by 6db its going to mess up the balance with the rest of the sound, plus whatever's causing the cancellation is still there.
> 
> ...


Just so you know, a dip that is due to a destructive phase cancellation is just that: a phase problem - meaning when you listen to 500Hz it will sound like the sound is drawn towards both speakers. 
Cutting everything on both sides to maintain a relatively smooth curve on the RTA will only make your system less loud. It doesn't change the fact that the dip will still be here. 
It'll look better on the RTA, that's all... 

IMO, not a very good thing to do. 

To answer the OP, using stock door locations will almost garantie a dip between 300Hz-600Hz due to either the floor or the center console (or even underdash)... Just leave it be or move your drivers from your door or aim your door speakers differently. 

Kelvin


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## sqnut (Dec 24, 2009)

subwoofery said:


> Just so you know, a dip that is due to a destructive phase cancellation is just that: a phase problem - meaning when you listen to 500Hz it will sound like the sound is drawn towards both speakers.


True.



subwoofery said:


> Cutting everything on both sides to maintain a relatively smooth curve on the RTA will only make your system less loud. It doesn't change the fact that the dip will still be here.
> It'll look better on the RTA, that's all...
> 
> IMO, not a very good thing to do.


Yes I will loose some db's overall. BUT the perception of the same dip is much less now, hence better integration. Lower decibels yes, but it WILL sound better. I have no clue how it would measure on the RTA, never used one. 

I would rather lose a few db's if it got me better balance. Everything in this hobby is a tradeoff .


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## subwoofery (Nov 9, 2008)

sqnut said:


> True.
> 
> 
> 
> ...


That's the thing... If the dip is due to cancellation, then it won't sound more balanced... It's just gonna sound like a phase problem @ that particular frequency - meaning you listen to a good song with male vocals... It's nice and centered on your dash... as soon as the song hits 500Hz, BAM it draws your attention to the sides. 

As said previously, it won't sound more balanced... You're just decreasing your system's maximum output... 

Kelvin


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## BowDown (Sep 24, 2009)

Here's my RTA plot. I did 3 readings... 1 straight forward at head location, 1 45deg left, 1 45deg right. Then I let trueRTA average the 3. This is the result.

Dips are at 160hz, 500hz, 810hz. First 2 are in the heart of the 53hz-710hz midbass, the 810hz is in the 710hz-4khz midrange in the A-Pillar.


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## Mic10is (Aug 20, 2007)

Im not sure why you are worried about it. Its normal. move on.
If its more for curiosity sake to to why its there, thats one thing--but donot boost it.


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## BowDown (Sep 24, 2009)

True. I tried to boost it for ****s and giggles and it actually went down lower.. :laugh: So I just reloaded the original preset (0db in those ranges) and forgot about it.


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## denetnz (Jul 31, 2009)

I don't know if this helps any, but I had a similar dip at 500Hz. Then I re-measured with me sitting in the car this time, and it wasn't nearly as bad. Actually, I was quite shocked how different the response was with me in the car - I'll always do it this way in future. Looks like I might have to get my wife to sit in the passenger seat with a book and a pair of earmuffs while I tune the car for two...


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## minbari (Mar 3, 2011)

BowDown said:


> True. I tried to boost it for ****s and giggles and it actually went down lower.. :laugh: So I just reloaded the original preset (0db in those ranges) and forgot about it.


that defintealy proves the cancelation theory if you add more 500hz and it canceled more.


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## BowDown (Sep 24, 2009)

minbari said:


> that defintealy proves the cancelation theory if you add more 500hz and it canceled more.


Tru Tru.

Makes me wonder if I should try cutting a couple db? Might try some acoustic foam treatments and re-measure just to see if it makes a difference. In the ends it's all about my ears anyway.. but has my curiosity.


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## Vital (Feb 23, 2010)

BowDown said:


> They aim slightly angled into the footwell towards the firewall center of the car.


Would changing an angle your midbass are at help your midbass responce?
Say aim speakers up and somewhat to the center of the cabin, not towards the firewall as you have them now.


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## BowDown (Sep 24, 2009)

Vital said:


> Would changing an angle your midbass are at help your midbass responce?
> Say aim speakers up and somewhat to the center of the cabin, not towards the firewall as you have them now.


Only way to change the angle is to recreate the stock baffle build-out. I just made cutting board adapters to go from 5x7 to 6.5". The stock build-outs are a complex piece. Check my build log for pics. Not saying I can't do it.. but at this point the system sounds great, not sure i want to risk other cancellations by changing the angle.

Some experimenting with acoustic foam and such is about as far as I want to go.


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## minbari (Mar 3, 2011)

not to mention, that chances are it wont do much. the wavelength at 500hz is too long for it to be effected by speaker aim.


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## BowDown (Sep 24, 2009)

How thick of open cell foam would be needed to dampen 500hz?


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## minbari (Mar 3, 2011)

honestly, I dont think you will be able to absorb it, but try some of the egg-crate or "W" shaped foam. this will redirect and break up those standing waves.


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## BowDown (Sep 24, 2009)

I believe I have some 1.5" egg crate foam laying around. I'll give it a shot one of these lunch hours.


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## ErinH (Feb 14, 2007)

minbari said:


> honestly, I dont think you will be able to absorb it, but try some of the egg-crate or "W" shaped foam. this will redirect and break up those standing waves.


At that wavelength, it's going to require something real thick. About 4.7" thick.

Here's a link to my speaker measurement calcs. I made this back when I was prepping the test room for driver measurements. It has some of this info.
https://docs.google.com/spreadsheet...NnTTFkOUdFZVE&authkey=CITsrqkB&hl=en_US#gid=0


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## minbari (Mar 3, 2011)

^^^ yup, I dont think it will work very well, but worth a try


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## BowDown (Sep 24, 2009)

Tru Tru. Wont cost me anything to give it a shot.


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## michaelsil1 (May 24, 2007)

Before I got a decent processor I was experimenting with different material behind the drivers. It had a dramatic effect with the frequency response.


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## ErinH (Feb 14, 2007)

BowDown said:


> Tru Tru. Wont cost me anything to give it a shot.


Don't forget to try varying density materials.


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## BowDown (Sep 24, 2009)

michaelsil1 said:


> Before I got a decent processor I was experimenting with different material behind the drivers. It had a dramatic effect with the frequency response.


Maybe I should try to reinstall my speaker tweakers... Last go around they didn't stick to the foil backing of the spl tiles.


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## 24th-Alchemist (Jun 16, 2011)

> I tried to boost it for ****s and giggles and it actually went down lower.


I have observed the same effect in my car.



> that defintealy proves the cancelation theory if you add more 500hz and it canceled more


How?

It's not clear to me how the observed effect proves it's cancellation between the two speakers -- especially since I've observed similar effects with just one speaker running.

It appears as though it's some sort of destructive interference, but I don't see how it's certain it's one driver cancelling the other and not anything else (e.g. destructive reflections).

Can anyone explain?


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## minbari (Mar 3, 2011)

24th-Alchemist said:


> How?
> 
> It's not clear to me how the observed effect proves it's cancellation between the two speakers -- especially since I've observed similar effects with just one speaker running.
> 
> ...


no, its not one canceling out the other. he is getting some kind of cancelation against his center console or the firewall. I dont think it is being caused by the other speaker.


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## 24th-Alchemist (Jun 16, 2011)

OK thanks.


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## subwoofery (Nov 9, 2008)

bikinpunk said:


> At that wavelength, it's going to require something real thick. About 4.7" thick.
> 
> Here's a link to my speaker measurement calcs. I made this back when I was prepping the test room for driver measurements. It has some of this info.
> https://docs.google.com/spreadsheet...NnTTFkOUdFZVE&authkey=CITsrqkB&hl=en_US#gid=0


Sweeeet... Been looking for 1 of those for a long time. Thanks Erin. 

Kelvin


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