speaker dispersion behind a grill - AVS Forum
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post #1 of 18 Old 05-28-2012, 11:56 PM - Thread Starter
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This is a car audio related problem, and yet I know from reading this particular forum that I might get a better answer here than on a car audio forum because it's about speaker theory. So bear with me, please

I have a 6.5" component speaker behind the factory grill in the bottom of a door panel. The original factory spacers were 1" off the door itself, but because it would not work, the installer used a 1/2" spacer. So now there is more of a cavity between the speaker and the door panel grill than there needs to be.

The tweeters in the component set (installed higher up the door) are overly bright even after attenuating them with the crossover. What I'm wondering is if a 1" spacer, which would bring the 6.5" driver closer to the grill by only .5 inches, would give the midrange a little more presence, thus slightly offsetting the brightness of the tweeters. And I wondered whether or not any additional undesirable (and audible) reflections are likely being introduced by having the speaker back further away from the grill.

I don't trust myself to change out the spacer, which is why I'm asking you guys before I pay an installer.

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post #2 of 18 Old 05-29-2012, 06:17 AM
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Quote:
Originally Posted by cel4145 View Post

This is a car audio related problem, and yet I know from reading this particular forum that I might get a better answer here than on a car audio forum because it's about speaker theory. So bear with me, please

I have a 6.5" component speaker behind the factory grill in the bottom of a door panel. The original factory spacers were 1" off the door itself, but because it would not work, the installer used a 1/2" spacer. So now there is more of a cavity between the speaker and the door panel grill than there needs to be.

The tweeters in the component set (installed higher up the door) are overly bright even after attenuating them with the crossover. What I'm wondering is if a 1" spacer, which would bring the 6.5" driver closer to the grill by only .5 inches, would give the midrange a little more presence, thus slightly offsetting the brightness of the tweeters. And I wondered whether or not any additional undesirable (and audible) reflections are likely being introduced by having the speaker back further away from the grill.

I don't trust myself to change out the spacer, which is why I'm asking you guys before I pay an installer.


The primary effect of the spacer is that it puts a ring around the driver's periphery. The technical effect of this ring is that it may reduce the dispersion of the driver at some frequencies, it might create diffraction that would actually increase its dispersion at other frequencies, and that it may cause a bump in response followed by a roll off at other frequencies yet.

The frequencies at which this ring has a significant effect is determined by the wavelength of the sound as compared to the height of the ring. For this ring to have negligible effects its height needs to be less than 1/10 the size of the speaker, which is clearly not the case when it is 1 1/2 inches high around a 6.5 inch driver. It is creating a cavity resonance which you may be hearing as excess brightness.
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post #3 of 18 Old 05-29-2012, 06:32 AM
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And that ring modification is not likely to make any difference in balancing the sound if the tweeter is bright. Most likely angling the tweeters so they are pointed somewhere toward the middle of windshield is the better solution. This is how I have my MB Quart tweeters mounted. If not, they would be terribly bright if pointed toward the listening position.

Just curious, what brand of speakers are they? and do you have a picture or drawing showing the whole mounting configuration?
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post #4 of 18 Old 05-29-2012, 09:06 AM
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Quote:
Originally Posted by MagicTK View Post

And that ring modification is not likely to make any difference in balancing the sound if the tweeter is bright.

Agreed. Taming the tweeter with a few power resistors would be more straightforward if that is the problem.
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post #5 of 18 Old 05-29-2012, 09:07 AM - Thread Starter
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Originally Posted by arnyk View Post

The primary effect of the spacer is that it puts a ring around the driver's periphery. The technical effect of this ring is that it may reduce the dispersion of the driver at some frequencies, it might create diffraction that would actually increase its dispersion at other frequencies, and that it may cause a bump in response followed by a roll off at other frequencies yet.

The frequencies at which this ring has a significant effect is determined by the wavelength of the sound as compared to the height of the ring. For this ring to have negligible effects its height needs to be less than 1/10 the size of the speaker, which is clearly not the case when it is 1 1/2 inches high around a 6.5 inch driver. It is creating a cavity resonance which you may be hearing as excess brightness.

Just to clarify, the ring is currently .5" in height around the 6.5" driver, and the idea would be to raise it to 1".

It seems less likely that the 6.5" driver is causing a cavity resonance since the doors have been well-deadened inside and out with 60 mil sound deadener, as well as a little bit of PS Ensolite closed cell foam behind the speaker to break up any sound wave reflections.

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Originally Posted by MagicTK View Post

And that ring modification is not likely to make any difference in balancing the sound if the tweeter is bright. Most likely angling the tweeters so they are pointed somewhere toward the middle of windshield is the better solution. This is how I have my MB Quart tweeters mounted. If not, they would be terribly bright if pointed toward the listening position.

Just curious, what brand of speakers are they? and do you have a picture or drawing showing the whole mounting configuration?

The speakers are Diamond Audio 663S components, and the tweeters have already been attenuated -2db using the built in jumper in the crossover. The car is a 2008 Honda Fit, and here is a picture of what the door panel looks like. The tweeters are mounted behind the factory tweeter location pointed directly in perpendicular to the door. Because of the size of the tweeter and that location, it's difficult to aim them anywhere else, and I don't want to install them elsewhere visibly in the car.

I think what I might end up doing is upgrading the head unit. Turns out that Pioneer has released the DEH-80PRS in 2012 that appears to be incorporating their MCAAC technology. It has L and R 16 band adjustable EQ with auto EQ and microphone for taking measurements at the listening position. Pretty cool that this technology is now making its way into car audio. Since I have a lower model Pioneer (which could be a little bit of the problem), this would be an SQ upgrade even without the auto EQ feature, and that auto EQ can probably tame the tweeter response much better than the five band EQ in my model.

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post #6 of 18 Old 05-29-2012, 09:10 AM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

Agreed. Taming the tweeter with a few power resistors would be more straightforward if that is the problem.

That's an idea. How do I learn how to do this?

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post #7 of 18 Old 05-29-2012, 03:51 PM
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Check the settings on your existing head unit. Maybe the treble is boosted? I'd use the tone controls in your existing head unit before spending any more money

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #8 of 18 Old 05-29-2012, 04:11 PM - Thread Starter
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Originally Posted by dknightd View Post

Check the settings on your existing head unit. Maybe the treble is boosted? I'd use the tone controls in your existing head unit before spending any more money

Nope. Been through all the settings.

And unfortunately, my home audio equipment has spoiled me. I want better SQ than just adjusting the tone control

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post #9 of 18 Old 05-29-2012, 04:18 PM - Thread Starter
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Looks like L-pad is the way to go for reducing tweeter output without affecting impedance. If I am reading this right, I should be able to use 2 ohm and 4.02 ohm resistors to reduce the tweeter by 6db, assuming the tweeter is 4 ohms.

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post #10 of 18 Old 05-29-2012, 08:18 PM
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It looks like you are reading it correctly. Just be sure you use appropriate sized resistors, by that I mean ones that are rated for higher power. Otherwise, you might let the smoke out of them at higher volume. The L-pad link http://www.bcae1.com/lpad.htm has a calculator at the bottom which might help you to determine what power of resistors to use in your case. So with 50watts of amplifier power, it looks like one resistor is just under 15watts and the other one is just above 10watts. If you have a higher power amp, you would need much higher power resistors. Of course, if the amplifier is powering the component set, then you have to figure out how much of that power is going to the woofer and how much is going to the tweeter.

Are your tweeters silk dome or aluminum? It looks like there was an option when you purchased them. The silk domes should have a pretty smooth response. In that case, your headunit upgrade should help. If they are aluminum, then the resistors and/or a headunit upgrade should work (or just the headunit change).

One other option is since the tweeters are behind the factory grill, you could try putting a piece of felt between the tweeter and the grill. This is similar to home speakers with their cloth speaker grills. You might need to experiment with different types of material, but it would also give you some attenuation without needing to add any resistors. I would try just taping some over the visible surface of your speaker grills then do some listening tests. If this worked for you, then you could remove the door panel and install the material as suggested.

Good luck.
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post #11 of 18 Old 05-30-2012, 09:32 AM - Thread Starter
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Thanks! That's a great idea about trying a piece of felt. It's such a simple solution if it works. Since I'm not very skilled with electronics (I had an analog circuitry course in the mid 1980s during college--LOL), I'm better off going that route first.

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post #12 of 18 Old 06-02-2012, 08:35 AM
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Quote:
Originally Posted by cel4145 View Post

Thanks! That's a great idea about trying a piece of felt. It's such a simple solution if it works. Since I'm not very skilled with electronics (I had an analog circuitry course in the mid 1980s during college--LOL), I'm better off going that route first.

Did you get a chance to try some felt? What do you think of the result?
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post #13 of 18 Old 06-02-2012, 09:19 AM
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Give it some time and the tweeter will smooth out. New tweeters are notoriously bright.

I have had the same experience with Blaupunkt silk tweeters as well as definitive Aluminium tweeters.
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post #14 of 18 Old 06-02-2012, 10:12 AM - Thread Starter
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Originally Posted by MagicTK View Post


Did you get a chance to try some felt? What do you think of the result?

The felt helped. Ended up ordering some 100 watt l-pads from PE, too.

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post #15 of 18 Old 06-02-2012, 10:15 AM - Thread Starter
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Originally Posted by chikoo View Post

Give it some time and the tweeter will smooth out. New tweeters are notoriously bright.

I have had the same experience with Blaupunkt silk tweeters as well as definitive Aluminium tweeters.

Not this much, even with the felt and the -2db attenuation on the crossover, I have the HU EQ set -6 db down and still not quite enough. Problem is part overly bright tweeter, part poor location.

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post #16 of 18 Old 06-02-2012, 10:56 AM
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Quote:
Originally Posted by cel4145 View Post


Not this much, even with the felt and the -2db attenuation on the crossover, I have the HU EQ set -6 db down and still not quite enough. Problem is part overly bright tweeter, part poor location.

My blaupunkt were the same. Initially i had to dial it down. But 6 months down the road and i had to bring them up.
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post #17 of 18 Old 06-02-2012, 03:21 PM
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I've had my MB Quart tweeters with titanium domes for almost 6 years, and they are still too bright, if I were to point them directly toward me. Certain speakers will never really smooth out. They are just inherently brighter. However, I have them pointed toward the middle of the windshield as I mentioned earlier and also have -3dB or so on the crossovers.

Glad to hear you had some luck with the felt. I am sure the L-pad will make a noticeable difference too.
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post #18 of 18 Old 06-03-2012, 07:41 PM - Thread Starter
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The L-Pad made a world of difference. From playing with the different adjustment, turns out the tweeters needed a lot of attenuation. I wonder if it's because they are convertible coaxial/component speakers, and the crossover was configured for the coaxial setup? Or because they are "convertible" speakers, maybe that means the tweeters are overly bright for listening to them with the top down on your convertible

Because the L-Pad did the job, I didn't end up adding the felt, too. But now I know that the felt would be a good option for someone wanting to tame tweeters a little.

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