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Old 24th August 2010, 09:55 PM   #1
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Smile Subwoofer phase problems?

Recently I designed and completed a rather simple ~3.2 ft3 sealed box with a Dayton 15" Quatro QT385-4. I have this connected to about ~150 watts or so in the trunk of my 2000 Chrysler Concorde.

My problem is this. With low frequencies of about 50 down, the sub is nice loud and smooth. Above that, nothing at all. It is on an active crossover of 85Hz. I know the crossover is not at fault because I previously used this setup with an 8" and it sounded just fine, 85hz down. I have experimented with changing the location of the subwoofer in the trunk.

Up in the front of the trunk, in the center is the worst. Again, low frequencies nice and loud, even vibrating the hell out of things If I wanted to, but nothing above say 60Hz audible from it in appreciable levels. I should note that, yes, the cone is moving at these frequencies, it is just not producing audible sound.

Towards the back of the trunk it is the best, but is not feasible unless I want to give up most of my trunk space, as the box is build as long and as tall as the trunk space, with the driver in the center. For some damn reason, I was not thinking of boundary loading when I cut the damn hole in the damned center of the baffle!

The thing that is odd is that below 50Hz or so, the low frequencies seem just as good with little to no difference perceived, but the upper bass frequency perception is increased the further back the driver is located.

I have the stock 6x9's in the car still, and they are really pieces of....

Do you think these could be canceling out the upper bass frequencies? The enclosure for these is the trunk itself, indicating the rear wave of sound travels into it. I suppose I should disconnect them and see if I detect an improvement, but they did not make the rear end of this car with audio modifications in mind. It is a tough job getting to those POS.

As a side note: I have experimentally reversed the polarity of the connections on the subwoofer driver, with still little or no audible difference perceived by me, either in the low Hz or high Hz.

Thanks again.
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Old 25th August 2010, 01:22 AM   #2
ppia600 is offline ppia600  United States
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3.2ft3 seems to be kind of large even for a 15, then again running 150watts rms might require that much. If you want higher frequencies you'll need to raise the crossoer frequency and/or lower box internal volume.

-high pass the 6x9's so the sub and those don't interfere with eachother
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Last edited by ppia600; 25th August 2010 at 01:25 AM.
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Old 25th August 2010, 02:39 AM   #3
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Quote:
Originally Posted by ppia600 View Post
3.2ft3 seems to be kind of large even for a 15, then again running 150watts rms might require that much. If you want higher frequencies you'll need to raise the crossoer frequency and/or lower box internal volume.

-high pass the 6x9's so the sub and those don't interfere with eachother
This sub was modeled using the T/S parameters as was my previous 8" sub, and used the same amp and lowpass settings. The 8" had a response up to 85Hz, but the 15" does not. The 15" does not require much power to put out an adequate level.

If a hump in higher frequency response, and a quicker low frequency rolloff is what I was after, I would have build a small box for it, but it is not, I was after a flatter response, taking the cabin gain into account. I also modeled the 8" the same way.

High passing the 6x9's is however a must in the future, but I am still using factory HU, and do not want to spend the money on a passive high pass xover, when I could use the money for a new HU, preferably one that will do this for me. Also, 85Hz is as high as a frequency I would want to send a subwoofer, afterall, that is what I am using it for, reproducing the frequencies that the rest of my speakers cannot.

Tomorrow hopefully I will get a chance to take the rear speakers out of circuit to see if the 60-85Hz response comes back. Unfortunately I cannot just use the fade to lower the level to my rears as the line out converter is connected through them.

I am mainly curious if anybody has run into this themselves. If you note my comment in the first post how I reversed the speaker connections, effectively changing the phase 180deg, you will see this did not change it much. I should think about getting an amp with a fully variable phase control. I'm not even sure car audio amplifiers exist with that feature as home subwoofer amplifiers do.

Thank you for your time, PPIA600.
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Old 25th August 2010, 02:44 AM   #4
ppia600 is offline ppia600  United States
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If you are using a factory deck and no high pass on the rears the bass will feed back through the deck speakers into your line out converter and then go into the amp that runs the subs. High pass them with some caps at least.
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Old 25th August 2010, 11:43 PM   #5
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Wow.

1) Can you describe how you have the sub amp connected to the factory head unit?

2) Your subs are pressurizing the trunk, therefore pressurizing the 6x9 cones. I'd be curious what happens if the 6x9s were disconnected and the + and - terminals shorted (greatly increasing the resistance of the cone to moving). But seems like this would be hard? Maybe at those frequencies there is a kind of resonance or feedback set up between the 15s and 6x9s, that the 8s just didn't excite.

3) What happens if you connect a Discman or iPod to the input of the sub amp, and play a sweep tone with the rest of the system off? Same problem?

4) I wonder if you have partial cancellation i.e. like 90 out of phase. Then if you flip the subs 180 you'd still be 90 out of phase. The phase response of your 8s and 15s are probably quite different, regardless of what any simple box simulation program says.

5) Some amps do have "phase control" but usually it's really polarity: 0/180. A rare few have allpass phase shift circuits. But really, if you had adjustable highpass and fiddled with the lowpass you should be able to get the same effect.

6) Various aftermarket head units from Alpine at least have built-in crossovers, which can even cross over the built-in head unit amp.

7) Passive crossovers at bass frequencies don't work. Let me repeat (having even designed such a product which sold OK), they DON'T WORK. So forget that nonsense. Well, OK, at very low frequencies the cone may move somewhat less. But at resonance the caps will do nothing. And the phase will now vary more, not helping anything.

8) Possibly, your 15s just roll off really low, especially if they have a huge heavy coil and heavy cone. Most box simulators besides LEAP can't show you that, but it is a real effect caused by mass and by eddies in the magnetic circuit.
8b) Outside the car play a sweep-how do they sound?
8c) What happens in another trunk location? Are the 15s at EXACTLY the same spot as the 15s?
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Old 26th August 2010, 01:15 AM   #6
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Quote:
Originally Posted by head_unit View Post
Wow.

1) Can you describe how you have the sub amp connected to the factory head unit?

2) Your subs are pressurizing the trunk, therefore pressurizing the 6x9 cones. I'd be curious what happens if the 6x9s were disconnected and the + and - terminals shorted (greatly increasing the resistance of the cone to moving). But seems like this would be hard? Maybe at those frequencies there is a kind of resonance or feedback set up between the 15s and 6x9s, that the 8s just didn't excite.

3) What happens if you connect a Discman or iPod to the input of the sub amp, and play a sweep tone with the rest of the system off? Same problem?

4) I wonder if you have partial cancellation i.e. like 90 out of phase. Then if you flip the subs 180 you'd still be 90 out of phase. The phase response of your 8s and 15s are probably quite different, regardless of what any simple box simulation program says.

5) Some amps do have "phase control" but usually it's really polarity: 0/180. A rare few have allpass phase shift circuits. But really, if you had adjustable highpass and fiddled with the lowpass you should be able to get the same effect.

6) Various aftermarket head units from Alpine at least have built-in crossovers, which can even cross over the built-in head unit amp.

7) Passive crossovers at bass frequencies don't work. Let me repeat (having even designed such a product which sold OK), they DON'T WORK. So forget that nonsense. Well, OK, at very low frequencies the cone may move somewhat less. But at resonance the caps will do nothing. And the phase will now vary more, not helping anything.

8) Possibly, your 15s just roll off really low, especially if they have a huge heavy coil and heavy cone. Most box simulators besides LEAP can't show you that, but it is a real effect caused by mass and by eddies in the magnetic circuit.
8b) Outside the car play a sweep-how do they sound?
8c) What happens in another trunk location? Are the 15s at EXACTLY the same spot as the 15s?
...wow?

1) As I have said, I am using a line out converter between the rear channels of the factory head unit and the subwoofer amplifier. All of the connections are correct. And it would be with wires..

I know my way around wires, in fact I repair televisions for a living. I am just getting into DIY loudspeakers.

2)Yes, you are correct, they do create pressure, and this is why I simply asked if anybody has experienced this, if it is common. I stated I do plan on disconnecting the 6x9's to see if I perceive an alteration, which I am betting I will.

3) No, Not the same problem, all frequencies are beautiful.

4) This is my guess, phase is off. You are correct, the phase response of the 15 and 8 are different. Not my much.

(skipping)

7) This statement is not applicable. I am not using any passive crossovers, and do not plan to.

8) This is the driver: Dayton QT385-4 15" Quatro Subwoofer 4 Ohm | Parts-Express.com

I tested and broke the subwoofer in at the house before loading into trunk. Smooth response. Used plate amplifier, even played lots of music and movies. Played sweeps. No issues. Even tested the unit at 125Hz down. Still smooth.

This is not a bad driver, in fact it is quite nice.

As I have said, If I place the box closest towards the very back of the trunk the upper frequencies are more audible. When I say upper I am speaking of ~65-85 cycles. At all locations the lower frequencies are still beautiful with little to no deviation at all, and smooth.

I used WinISD Pro for modeling. Also BassBox 6 for printing the final design and simulating the cabin gain.

Simply, Just was a post out of curiousity to see if this was common, and what have people done to solve it. Thanks.

Last edited by odysseybmx414; 26th August 2010 at 01:18 AM.
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Old 28th August 2010, 05:00 PM   #7
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[QUOTE=odysseybmx414;2283877]

1) As I have said, I am using a line out converter between the rear channels of the factory head unit and the subwoofer amplifier. All of the connections are correct. And it would be with wires..
@ I must have missed that part
@ This sounds dumb, but I wonder what happens if you connect to the front channels instead. I know, shouldn't matter, but...

I know my way around wires, in fact I repair televisions for a living. I am just getting into DIY loudspeakers.
@ Wow, out of the frying pan and into the fire!


2)Yes, you are correct, they do create pressure, and this is why I simply asked if anybody has experienced this, if it is common. I stated I do plan on disconnecting the 6x9's to see if I perceive an alteration, which I am betting I will.
@ Do short the terminals, it will help

7) This statement is not applicable. I am not using any passive crossovers, and do not plan to.
@ Good! I wasn't rarfing at you, just at anyone else even thinking about doing that...

8) This is not a bad driver, in fact it is quite nice.
@ Looks like a good driver, but not the kind that would roll off super low by itself, so I don't think that's the problem.
@ Maybe there is JUST enough phase difference from 8 to 15 to push a bit of cancellation into a lot of cancellation?


@ By the way, in your situation (depending if my front speakers were decent) I'd probably tear out the 6x9s so the sub could vent better. I don't believe in rear speakers at all, they are just a historical accident and don't really belong there any more except to cover up how crappy the factory front speakers are.
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Old 28th August 2010, 09:58 PM   #8
ppia600 is offline ppia600  United States
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1-:lol: at you two back and forth
2-the sub/box isn't going to perform the same in your vehicle as in the home environment so you'll have to model your setup around the car or vice versa. You're basically creating a higher order bandpass by putting it in the trunk and magical things will happen.
3-the concorde is going to accentuate the low frequencies naturally and attenuate the highs due to trunk volume, vehicle shape and insulation
4-there will always be percieved phase problems in the frequency area that crosses over from sub to you mids because of placement, you can change that some by mounting your subs in the kicks or something outrageous or cross your mids and the subs lower so the directional (higher range) will never be produced by the sub. Unless you like the soundstage to move back and forth between your trunk and front doors.
5-and yes, some car amps have variable phase control

I sold and installed car audio and video professionally for eight years and while I'm no Richard Clark or David Navone people will tell you this comes second nature to me.
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Last edited by ppia600; 28th August 2010 at 10:05 PM.
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Old 29th August 2010, 01:50 AM   #9
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What sort of frequency response did the speaker and enclosure have in your home?

If it was nearly flat down to 20Hz, the cabin gain at low frequencies will make the in-car response very heavy on the low end. Have you tried removing the lowest frequencies with equalization?
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Old 30th August 2010, 03:13 AM   #10
ppia600 is offline ppia600  United States
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Also, depending on the system your concorde came with the rears could only be getting a low passed signal. Are they beefy 2ohm 6x9's or normal full range models? Some of the chryslers had the infinity systems with a decent amp that ran dedicated high and low pass outputs to the speakers. I had to rewire tons of those vehicles and also explain to customers why they couldn't just pop in a cheap set of full range speakers, lol.
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