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Old 11th February 2004, 12:20 PM   #1
sma is offline sma  Indonesia
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Default Speaker Response Problem

Hi,

I make passive crossover on focal utopia driver in car.cutting frequency at 3500 hz between woofer and tweeter.cutting frequency is fine and already flat between woofer and tweeter.but i see on RTA the response is peak at 1Khz and 1.25 Khz +6db!!,this is woofer frequency range.i don't know why this driver can peak,maybe this is about acoustic problem and phase problem since the speaker is location at car door factory location .off axis and face to face between left and right speaker.

Anyone know passive crossover schematic for reduce this peak?
i don't want to use active equalizer since that will add noise.

now i use 6 db with zobel for woofer and 12 db for tweeter.

please advice and any suggest for this.

I already replace the woofer with other brand like vifa M18WN,Eton but the peak is at the same location 1kHZ and 1.25 KHz,....the midrange voice very attack to my ear because this peak...please advice.
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Old 11th February 2004, 08:37 PM   #2
Bose(o) is offline Bose(o)  Canada
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This is very possible.

You may use what is called as a parallel notch filter. Now, I'm not exactly sure on its effects with phase and such, though I know that generally this can be applied to circuits for on-axis response. Here is a link to a calculator. Notch Calc .

Phase aside, the peak may be caused by early reflections as the woofer is in a car, car's are known for early reflections which usually allow people to bump the xo point between tweeter and crossover an extra 500Hz. or so. I don't like to do this personally, as breakup modes are breakup modes so, crossing over at a low point is good. Hope this helps. BTW, is it a problem with your SPL meter? Just for gazing purposes, can you post a picture of your response?
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Old 11th February 2004, 09:01 PM   #3
sreten is offline sreten  United Kingdom
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A parralel notch filter is straightforward but you will need
the Zobel network on the driver for the filter to work well.

In reality your very lucky if thats your only problem.

With a friends in car set up the main problem was a 12dB
dip in the same range, chucking boost at a big dip doesn't
work remotely as well as cutting back peaks.

sreten.
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Old 12th February 2004, 02:19 AM   #4
Bose(o) is offline Bose(o)  Canada
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So, that would be a parallel notch filter in addition with a zobel?

The zobel would be used to flatten the impedance increase as frequency increases, correct? A zobel calculator can be found here .

Anyway, I'm curious to find the position of the microphone (SPL meter) relative to the transducer being measured. Sreten, where was the mic located? How far? (as best as you can measure).
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Old 12th February 2004, 02:44 AM   #5
sma is offline sma  Indonesia
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Thank you bose,my rta is audiocontrol,i think no problem with the microphone since that already calibrate at audiocontrol 1 month ago.and the peak 6db at 1.25Khz can hear by ears too.

i use the calculator for notch filter and found very big value for inductor.

I don't have digital camera so i can't post the response picture.

the response from 20 up to 900hz is normal just +/- 3 db and will up at 6 db from 1-1.25khz,than down again at 2.5khz and flat up to 16khz.so the problem only in 1-1.25kHz.

how about use the parametric equalizer??
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Old 13th February 2004, 12:56 AM   #6
Bose(o) is offline Bose(o)  Canada
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Sma,

I guess that rules out any measurement equipment. Don't sneer at me for asking this though, as many people OFTEN forget about the calibration of their devices.

Parametric Equalizer? That'd work too! And, it would be smaller and a lot easier to test with as well. You may be already thinking about this, but boosting the response above and below your bump may not be the way to go as it would do gross things to power requirements and excursion. Detracting from however, is easier...Hope you figure out your bump problem.
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Old 16th July 2004, 01:45 PM   #7
jomor is offline jomor  Greece
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Hi everybody. I have the same problem!!!!!

I just bought a set of Utopia 165W for my car. I noticed by hearing and measuring them, both at home and in car, that they have a smooth yet large spl bump around the 1Khz. And its not just something shown in measurements, its audible too.

Its definetly a speaker problem since i dont get the same bump with other speakers i used, neither in the car on at home.

I made a notch filter ( parallel RLC 10, 0.8m, 32F) in series with the signal, and the bump disappeared, giving me a very flat response. But the IMPEDANCE AND PHASE curves got like a heartbeat diagram, so i removed the notch for the obvious reasons.

WTF?? So expensive and well reputated speakers, are they supposed to be like this?? Anybody has experience on this?

Thanks for any reply.
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Old 16th July 2004, 02:04 PM   #8
tiroth is offline tiroth  United States
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Couldn't it simply be the tweeter's resonance? Fs is supposed to be 1379Hz.
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Old 16th July 2004, 02:53 PM   #9
jomor is offline jomor  Greece
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Nope, I measure the midbass alone, with and without the crossover, and i get the same bump.

Besides the high pass filter is 24db/oct at 3Khz.
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Old 16th July 2004, 03:02 PM   #10
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I have a good friend that owns a car stereo shop and I know from him the utopia mids, especially the 6.5's, have some peaky response. It is inherrent in the design, focal's crossovers compensate for the artifacts but they are fairly difficult to tame diy. The old Xpert series did not have this problem.

My advice is to contact Focal directly. Any time I have talked to anyone there they have been very nice, never patronizing. For instance I had a set of TN-51 tweeters and I lost the flush mount cups while moving. i called them up and told them exactly what happened and they overnighted a full mounting set to me with flush mount, angle mount, and new grills. Great service.
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