Check out the frequency response of the stock stereo. Measurements were taken from the speaker connections. I used 0db test tones and an oscilloscope with true RMS. Volume levels were set just below any signal clipping.

 

Thanks for objective data. Too often we rely on conjecture and opinion.

 

Wow, from those graphs it's clear that the low frequencies are cut from the rear speaker signal (hence why I don't understand that some people use this signal for their bass link or other sub).

I'm surprised to see low freqs on the front speaker signal however. If anything, I would have imagined the opposite.

 

Thanks for the graphs. This confirms my decision to replace my stock front speakers with a new 3.5 and 6.5" set. I'm going to just fade out the rears. Anyway, I usually do for my kid who sits in the back.

 

raz636, I'm confused now. In your other thread, you wrote:but the rear chart seems to show a high pass filter:

 

Good post, but for anyone watching the thread that's not familiar with response curves, keep in mind that what you're seeing here is the *input* to the speakers, not a response curve of their *output*. Changing speakers wouldn't significantly change these graphs.

What these graphs don't show is how the factory speakers respond to different input frequencies, or how the airspace inside the car amplifies or attenuates certain frequencies.

Raz - were you using white noise, pink noise, or a series of stepped tones to make these graphs?

 

Hmmm. A little knowledge is a bothersome thing and eventually fuels an obsession. I'm happy my front replacements will get low freq inputs since that is all I plan to do with my less than $200 stereo improvement budget. The stock "paper" speakers are sub-par.

 

True - any aftermarket speakers will likely be an improvement over the factory speakers. I just didn't want someone to look at the graphs in the first post and get the impression that they're going to get any significant response *out of* the front speakers at the 20-50hz range.

EDIT - Also, despite appearances, the frequency response from the head unit is actually very flat. The reason it looks like there are crazy peaks and valleys is that the horizontal scale (frequency) is logarithmic, while the vertical scale (voltage) is linear. This compresses the horizontal scale and blows the peaks/valleys out-of-proportion. Notice that the 0-10hz range at the left end of the graph takes up as much space as the 10,000-100,000hz range at the right end of the graph.

If you were to use logarithmic scales for both axes (which is the normal method of displaying a frequency response curve), or make both scales linear, the curve would appear much flatter. Looking at the graph for the front speakers, it tells me that the response from the head unit is within about 2dB of being "flat", all the way from 20hz to 20,000hz. That's typical for most amplifiers. I'm not sure exactly *what's* happening with the rear speakers, though. It looks as if the headunit has a high-pass filter on the rear outputs (which makes less sense then putting one on the front outputs).

 

You're right. It is filtered, not crossedover. I don't consider the rears to have a crossover because it is a single output single input setup. Crossovers are used to send different sets of frequencies to more than one device using a single output. Take a look at the pic in this post:
https://www.northamericanmotoring.co...73&postcount=4

I used 0db single frequency sine waves. I made a test CD and just sat through it an logged the results.

The speakers frequency response must be considered if you want to analyze the whole system. Since most will change their speakers, I didnt see the need to test the actual sound produced.

Here's the graphs again but with a log voltage scale. Things do look a little flatter.

 

The rear graph flattened out appropriately, but the front graph is still overly-compressed, because although you changed the vertical axis to a log scale, you're now starting off at 1V instead of the 0.1V that you used for the rear graph.

Just keep the range of the vertical axis at 0-10V like you originally had it, but change it from linear to log scale.

Nice work!

 

Fixed.

 

Some very useful information here. Now what can we conclude about strategies for upgrading the system?

The frequency response from the headunit is fairly flat, i.e. it was not equalized to compensate for stock speaker or in-cabin response. Thus will a product like Cleansweep yield relatively small benefit?

Inputs for a sub should be taken from the front channels, because the rears have high pass filters. It is bizarre that the rear channels have high pass filters, and they put the larger speakers back there. Why would they do that? Is it possible there was a manufacturing error? The rear channels are crippled for any nice speakers you might want to install there. Even with an external amp, you'd be stuck with the filter if you wanted to retain the headunit's fade control.

 

I would try to find out if the high-pass filter on the rear outputs is located in the head unit itself, or if it's somewhere in the wiring/connections. If it's in the head unit, I probably wouldn't use the rear outputs for anything when upgrading the stereo. I've never had much use for a fader in aftermarket installations anyway, since I just adjust the relative gains on the front/rear amp channels and leave them alone.

If the rear high-pass is part of the factory head unit, I don't know if the Cleansweep can correct for it - that would require a LOT of equalization boost in the sub-100hz range.

 

I was told that if you put two crossovers in sequence, the resultant crossover frequency will not be what the second one was designed for. So, best not to use a speaker crossover (one that came with the speaker) when there is already a crossover in the system.

Is it the same with a high pass filter? What happens when you add a speaker crossover after a high pass filter?

 

That is a common practice with add-on powered subwoofers in home audio systems. The subwoofer is given the full range signal, and it has a high pass output that is to be used for the main speakers. With low frequencies filtered out, the main speakers can play louder/cleaner than they could otherwise.

 

Whether it makes a difference depends on the relative frequencies of the filters. If you take a full-range signal, apply a 100hz high-pass filter to it, and then hook up some aftermarket speakers that come with a 2,500hz high-pass crossover for the tweeters, then everything will be fine - the final tweeter output going from full-range -> 100hz high-pass -> 2,500hz high-pass is identical to what you would get if you had just gone from full-range directly to the 2,500hz crossover. This is because 100hz is so far below the 2,500hz filter frequency that the effects of the 100hz filter are wiped out completely by the 2,500hz high-pass filter.

But, if you take a full-range signal, apply a 100hz high-pass filter, and then apply *another* 100hz high-pass filter, the overall filter frequency will still be 100hz, but the "slope" is going to be much steeper. The response below 100hz will drop off like a rock, because the frequencies below 100hz have been attenuated twice.

In general, you're okay applying filters to signals that have already been filtered, as long as the combination of filters makes sense. There's really no such thing as a "full-range" music signal anyway, since the signal has already been filtered during the recording process, the mastering process, and by dynamic compression. Many stereos also include a subsonic high-pass "rumble filter" at around 20hz.

So, filters will work as designed whether they're the only filter in the signal chain or not, but you do have to consider what passing through multiple filters will do to the overall response.

 

For a concrete example, how about the tweeter connection in the rear? I have Infinity Kappa 693.7i 6"x9" 3-way car speakers. They come with a separate crossover that splits the signal two ways. One goes to the 6x9 woofer and one goes two the mid tweeter and the high tweeter. I believe there is some sort of crossover inside the speaker that spits the signal between the mid and high.

The rear speaker location in the HIFI has a set of wires for the 6x9 and another for the tweeter.

If you connect the tweeter wires to the tweeter input of the Kappa 693.7i you have whatever filter the HIFI uses for its tweeter and whatever is internal to the speaker. I assumed this would have squirrely results and did not connect them. Instead, I used the separate tweeters that came with the Kappa 60.7cs speakers, and left the stock tweeters in the A column. Did I make the right choice? Am I wasting a perfectly good opportunity to use the tweeters built into the 693.7i?

 

Unfortunately, there's no good way to predict the results unless you know the factory crossover frequency and the low-to-mid crossover frequency for the Kappa.

If the MINI tweeter crossover frequency is close to the high-pass frequency of your Kappas, the mid/high speakers in the Kappa will receive the correct frequencies, but the slope of the filter will be steeper. This is actually a good thing, since most factory crossover and aftermarket speaker crossovers have a fairly shallow slope, for parts-cost reasons.

But, if the MINI tweeter frequency is significantly higher than the Kappa high-pass frequency, that means that the mid/high speakers in the Kappas won't be getting all of the frequencies they expect. In particular, the notes between the MINI crossover frequency and the Kappa crossover frequency will either be missing or greatly attenuated.

On the other hand, if the MINI crossover frequency is significantly *lower* than the Kappa frequency, all is well, because the frequencies cut off by the MINI filter would have been cut off by the Kappa filter anyway. (In other words, the output from a 5,000hz high-pass filter is essentially the same whether you feed it a full-range signal or a signal that's already been through a 1,000hz high-pass filter.)

 

I would guess that this would be the case. The MINI is set up for a tweeter. Here is a description of this connection on the Kappa:

"Emit Tweeter and MMD Dome Midrange: Each speaker has an Emit tweeter and an MMD (Metal Matrix Diaphragm) dome midrange. The benefit is increased power handling and reduced distortion at high output. This technology also allows for better integration with the woofer. The tweeter has an adjustable output level, +0 dB (flat) and +3 dB."

 

Well, I looked at the owner's manual for your speakers, and unfortunately, they don't list the crossover frequencies. But I suspect you're right, and the MINI crossover frequency is probably higher than the midbass/midrange crossover point on the 693's external crossover.

You could still connect the two MINI outputs to the two inputs on the 693 (discarding the Infinity external crossover entirely). You wouldn't end up with any missing frequencies, but it's likely that the midrange in the 693 would receive very little signal, and the midbass in the 693 would have to "pick up the slack" by playing the notes that the midrange would normally get if you were to use a single full-range input and the external Infinity crossover.

 

I guess I'm just as well off just hooking the 693.7i woofers to the MINI 6x9 wires and connecting external Kappa tweeters to the MINI tweeter wires, which is the way I have it now.

 

Yep - that way, you'll at least have all of the frequencies covered. The MINI crossover point may not be optimized for the Kappa tweeter, but it's probably not too far off.

 

If the MINI sent all frequencies to the 6x9s.
Unfortunately, not much bass goes there.

 

Oh, is that the case with the HIFI system too? I know the OP found that out with the stock system - I didn't know it was the same for the HIFI.

 

Yup. At first I thought it was my cabinet killing the bass. So, I attached an NHT 1.5 to it, and still no bass.