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Coaxial frequency

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=42012
Printed Date: July 18, 2025 at 3:10 AM


Topic: Coaxial frequency

Posted By: Thuan
Subject: Coaxial frequency
Date Posted: October 31, 2004 at 10:19 PM

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.

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Thuan



Replies:

Posted By: kfr01
Date Posted: October 31, 2004 at 10:41 PM
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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Posted By: stevdart
Date Posted: November 01, 2004 at 7:36 AM
Use a test CD like this one.

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Posted By: Thuan
Date Posted: November 02, 2004 at 1:58 AM

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.



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Thuan




Posted By: stevdart
Date Posted: November 02, 2004 at 9:27 AM
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.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: DYohn
Date Posted: November 02, 2004 at 10:11 AM

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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Posted By: Thuan
Date Posted: November 02, 2004 at 1:05 PM

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.



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Thuan




Posted By: DYohn
Date Posted: November 02, 2004 at 1:58 PM

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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Posted By: stevdart
Date Posted: November 02, 2004 at 2:02 PM

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.



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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: stevdart
Date Posted: November 02, 2004 at 2:06 PM
Whoops, I said something that contradicted DYohn.  Good advice here is not to take anything I say over what DYohn said.....  ;)

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: DYohn
Date Posted: November 02, 2004 at 3:36 PM
:)  No we're not contradicting each other, I think we're talking apples and oranges.  You seem to be talking about loudness (db) and state you can tell the difference between 100db and 105db.  I'll agree with that statement.  I'm talking about sound spectrum and don't think the average person can tell the difference between 100Hz and 105Hz (althouigh a trained musician could.  They wound hear 100Hz as a slightly sharp G 2 octaves below middle C and 105Hz as approximately G sharp.)

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Posted By: stevdart
Date Posted: November 02, 2004 at 7:56 PM
DYohn is being polite.........truth is my brain got bamboozled.  Too many Hz's and db's!  What I meant to say is that you would hear the difference in decibels between the tone recorded at 100 Hz and the tone at 105 Hz......when the crossover is set properly at 100 Hz.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: Thuan
Date Posted: November 03, 2004 at 4:51 AM

Bear with my please.....I would hear the difference between those 2 frequencies through the coaxials right....but as for the sub I'm having crazy problems hearing any distortion. I'm going to run my speakers like you guys suggested at 250hz...so now when I make my test cd I want to listen for the difference between 250hz and 255hz...is it going to hurt my ears and should the HU volume be at it's max or just at a comfortable level?  My amp is a soundstream vga800.5. Thanks.



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Thuan




Posted By: stevdart
Date Posted: November 03, 2004 at 7:35 AM

Yes it will hurt, so don't do it, like DYohn said, without ear protection  Volume low....you are trying to pick a relative frequency so volume is not needed.  Crossover setting isn't something that has to be done the first day, doesn't have to be perfect, and can be tweaked from time to time.  In fact, I like to get the crossover setting with very faint volume, so that the frequencies fade out more noticeably at the cutoff point.



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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: Thuan
Date Posted: November 03, 2004 at 2:29 PM

My amp is rated at 50x4 and 400x1....I have a JL12w6v2 hooked up to the 400x1 channel...but it doesn't even seem like it's anywhere close to that...I can't even tell there's a subwoofer in my trunk while I'm driving. My gain is currently at about 60% of it's max....was I given the wrong amp ratings? You guys have been real helpful...Thanks!



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Thuan




Posted By: DYohn
Date Posted: November 03, 2004 at 2:55 PM
What's the amp?

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Posted By: Thuan
Date Posted: November 03, 2004 at 5:52 PM
Soundstream VGA800.5

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Thuan




Posted By: DYohn
Date Posted: November 03, 2004 at 6:28 PM
That's not a bad amp.  Rated at 50 Watts x 4 + 200 Watts x 1 into 4 ohms.  Assuming you have your 12W6 wired in parallel, it will place a 2-ohm load on the amp and draw up to 400 watts.  It should sound pretty good with 400 watts.  Make sure you do not have the voice coils in series though (if you like it loud.)  Series wiring will place an 8-ohm load on the amp, and although it will operate much cleaner and cooler with 8-ohms, it will produce only about 100 watts.  Your JL woofer likes more than 100 watts.  :)   OH, and make sure you don't have a HPF activated on you sub channel!

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Posted By: Thuan
Date Posted: November 04, 2004 at 1:52 AM
I forgot how I had the VC for the sub hooked up...I think it was VC1+ to VC2+ and VC1- to VC2-...that's parallel right? I set my sub channel to LPF and for my coaxials HPF. If one of the VC jumpers came loose would I get this low power problem? Is it a good idea to solder the VC jumper wires?  

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Thuan




Posted By: DYohn
Date Posted: November 04, 2004 at 10:49 AM
+ to + and - to - is parallel.  Yes, if a jumper came off it will affect the power of the system (back to 4 ohms on only one voice coil.)  Yes, soldering is a good idea.  If you are not getting enough bass in your car with this setup, maybe you have the LPF set too low.  Try cranking it up to around 120Hz.  Also, how is the sub positioned in your car?  Have you tried moving it around/facing it towards the rear/changing the phase on the amp?  What kind of enclosure is it?

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Posted By: Thuan
Date Posted: November 04, 2004 at 12:39 PM
I have it in a sealed enclosure.....1.38cu ft with 1 pound of polyfil. I have the subwoofer facing the rear of the vehicle....it's in a lexus ls400. Changing the phase on the amp? On my HU there's 2 subwoofer options....subwoofer 0 degrees and reverse 180 degrees....what exactly does it do?

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Thuan




Posted By: DYohn
Date Posted: November 04, 2004 at 12:52 PM
Sounds like your enclosure is good.  Lexus cars can be a problem in that they are pretty well sound-proofed and designed so that noises from the trunk will not get into the passenger compartment..  You will get about a 3db or greater reduction in volume just from the design of the car and there's not much you can do about it. The phase on the HU will switch the electrical phase (+ and -) of the signal to the sub amp.  Try changing it and see if there is any improvement.  Use the position that sounds best (that's what it is for!)

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Posted By: Thuan
Date Posted: November 05, 2004 at 12:56 PM
Lexus' are real quiet but there is actually an 8" hole in the rear deck that is right above the JL sub I have in the trunk....this was were the stock subwoofer used to be located...I removed it. I pulled the JL out last night and soldered the VC's together just to make sure the connection was good....but I'm still getting no rumble. I tried switching the phase on the HU but it doesn't do anything for me. Since I lose about 3db...should I just turn up the bass boost on the amp +3db to make up the difference? How much bass should I expect to get/feel from my JL? I was expecting clean bass and enough bass where I would be able to feel the vibrations as I drive...am I expecting too much? I can't even feel anything unless I crank the volume up to max. This sucks.

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Thuan




Posted By: customsuburb
Date Posted: November 05, 2004 at 9:29 PM

Make sure everything is in phase (put your decks setting at 0 for phase and make sure all that the plus and minus going to the amp are on the plus and minus of the amp). Also try moving your sub around in your trunk and see if it sounds any different. Does it play well when you are just listening to it with the trunk open outside of your car? One last thing, dont use your bass boost!



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Posted By: Thuan
Date Posted: November 06, 2004 at 12:00 AM
It sounds okay when I have my trunk open but when I drive I don't really feel/hear much. +/ - for the RCA's? Does that matter because I switched the RCA's over and it sounds the same. Okay, I turned the boost off.

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Thuan




Posted By: DYohn
Date Posted: November 06, 2004 at 10:33 AM

Thuan] wrote:

I was expecting clean bass and enough bass where I would be able to feel the vibrations as I drive...am I expecting too much?

Could be.  If you really think something is wrong, I recomend going to a good car stereo shop and ask one of the pros to listen to your system.  They may offer to check the setup for you for a few bucks and it sounds like it might be worth it to you just so you can know for certain if it's just expectations not being met.



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Posted By: Thuan
Date Posted: November 06, 2004 at 4:17 PM
K., Thanks....I appreciate all the help I have recieved.

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Thuan





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