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Coaxial frequency


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Thuan 
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Posted: October 31, 2004 at 10:19 PM / IP Logged  
I have 4" MB Quart PKC110 coaxials....I'm running 50watts rms to each speaker. Should I set both subwoofer LPF and HPF for my coaxials at 100hz? I'm also having trouble finding out exactly where 100hz on my amp is.....the little knob for the frequency only shows 50hz(min) and 5khz(max). There's a total of 11 notches starting at 50hz and going all the way up to 5khz. ...how am I suppose to know where 100hz is? On top of all of this I can't hear the distortion from the sub when I turn up the gain...even all the way....maybe it's  just me but is there a distinct sound I should listen for? Thanks.
Thuan
kfr01 
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Posted: October 31, 2004 at 10:41 PM / IP Logged  
100hz is low for 4" drivers. But definitely put some sort of HPF on those babies or you'll bottom out like crazy. What is the slope like on your crossover, 12db?
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stevdart 
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Posted: November 01, 2004 at 7:36 AM / IP Logged  
Use a test CD like this one.
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Thuan 
Copper - Posts: 88
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Joined: May 20, 2004
Location: United States
Posted: November 02, 2004 at 1:58 AM / IP Logged  

How many hz should I have it set to? I haven't set up the slope for the crossover...I'm still reading through the instructions.  Is 12db a good setting? BTW, I'm using the crossover feature on my Alpine cda-7998.

I've already created a test CD with various tones....50,52,54,56,58,60 etc etc. I thought I was going to be able to turn the knobs over the frequencies I recorded and that once I past 100hz I wouldn't be able to hear anything but I was wrong...I still hear sounds past 100hz even though I only recorded tones up to 100hz.

Thuan
stevdart 
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Posted: November 02, 2004 at 9:27 AM / IP Logged  
You'll still  hear frequencies well past the cutoff.  If you look at a graph of a frequency response, you'll see that the cutoff freq of a crossover point is at -3 db.  You hear it but not quite at the same volume.  As the freqs go further along, they decrease (or increase, whatever the situation).  What you want to do is this - if you want 100 Hz as your crossover point, let's say in this case you want 100 Hz and below.......turn the crossover adjustment until your test tone of 100 Hz is just perceptably softer in volume than the 105 Hz tone.  As you play tones below 100 Hz, each one lower in Hz should be just noticeably softer than the last one.  It's called a crossover slope.
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: November 02, 2004 at 10:11 AM / IP Logged  

Yes, I definatly agree with the comment above that 100Hz is a bit low for a 4" speaker.  I'd suggest setting it up around 250Hz.  Also, those MBQ coaxials are rated at 30 watts RMS, so if you are bottoming them out it could be due to overpower.

Stevdart is correct concerning a crossover slope.  Crossovers are not like a cut-off switch.  If it is a 6db/octave crossover for example, that means the musical power will be reduced by 6db one octave (eight tones, or twice the frequency) above or below the crossover setting.  So if you have a HPF for your coaxials set at 100 Hz, you will still send 50Hz information to the speaker, only it will be attenuated by 6db.  Crossovers with steeper slopes (higher number of db/octave) will reduce the signal strength faster around the cross point.

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Thuan 
Copper - Posts: 88
Copper spacespace
Joined: May 20, 2004
Location: United States
Posted: November 02, 2004 at 1:05 PM / IP Logged  

Oh, I was under the impression that I wouldn't be able to hear anything once I past that frequency because it was going to cut off. My MB Quarts are actually RKC110's not PKC....the box said something like 80rms. When you guys are refering to the filters are you talking about the ones on my  HU or the ones on my amp...or both? So I'll definitely hear the difference between 105 and 100hz?

Howcome the knob on my amp goes all the way up to 5khz? Do some people actually have it go that high depending on the setup?

If my amp has a max rating of 800rms, when does it actually put out 800rms?

Stevdart, I've read some posts you responded to about setting gains and so forth and you recommended having the volume at 85% on the HU. Am I deaf because when setting mines I had it at 33 out of 35 and I didn't hear any distortion...so I just backed it back down to 26 just to play it safe.

Thuan
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: November 02, 2004 at 1:58 PM / IP Logged  

1.  Yes, "filter" usually refers to a crossover.  The one in your HU or your amp can be used, but I recomend you only use one and disable the other one.  The actual RMS rating fro those speakers should be listed in the owner's manual.

2.  I doubt very seriously you can hear the difference between 100Hz and 105Hz.  Like I said before, with a 4" speaker I would try 250Hz.

3.  Yes, an HPF up to 5KHz is very useful, especially if you are driving a set of tweeters.

4.  "Max" and "RMS" ratings are two different things.  Post your amplifier make and model and I will look it up.

5.  The recomendation that you use "85%" or any other setting to set input gain is simply a ballpark.  You may use any volume setting you choose as long as you stop before you drive the head unit into clipping and you never turn it up past that point.  As far as you not being able to hear distortion, if you are talking about hearing it in your subs that is not unusual.  Try using a tone (at, say, 80Hz) and (wear hearing protection!) try this:

Disconnect main speakers amp.  Set subwoofer amplifier gain to minimum. Turn up tone volume using the HU until you can hear the pitch seem to change.  This is the audible clipping point.  Back it off until it returns to normal and never operate above this volume level.  Increase the input gain on the sub amp slowly until you again hear the pitch change.  Back it off until it returns to normal.  This is your max gain setting for that head unit.

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stevdart 
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Posted: November 02, 2004 at 2:02 PM / IP Logged  

85% is not in my vocabulary, so maybe that was someone else.  I don't like to put a number on deck volume.  For instance, in my car I'm using the factory deck, and found that the max level that I felt it sounded good was just under 2/3.....about 60 to 65%.  So just use the volume level of the head unit that you think still sounds good without distortion.  You have to listen to it with the amp gain set all the way down.  Normally, 3/4 or 75% is the given default setting for maximum on the deck.

Back to question 1:  a decimal (db) is the unit of sound measurement that people can actually hear a difference in the sound level.  3 db is a noticeable difference in sound level.  So if the crossover is at 100, you will definitely be able to tell the difference between that and 105 db (if you're setting a mid/tweeter highpass).   Keep turning the setting until you hear the difference. 

There's no such thing as a max rating in RMS.  There's RMS, period.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
stevdart 
Platinum - Posts: 5,816
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Posted: November 02, 2004 at 2:06 PM / IP Logged  
Whoops, I said something that contradicted DYohn.  Good advice here is not to take anything I say over what DYohn said.....  ;)
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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