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Discussion Starter #1
While taking some measurements earlier today i noticed that my subwoofer response falls off a cliff at 55Hz, talking a 10dB drop...



The picture above is no EQ applied. I checked settings on the amplifier and DSP, then took a 2nd measurement with the mic in front of the sub, no EQ and crossovers off.



In front of the sub, the response looks pretty good. At this point I tried various locations in the trunk:

Right side, against back seat, firing towards trunk (usual position)
Right side, against seat back, facing forward
Right side, facing both back and forward against tailgate
Right side, facing sideways
Left side, same as above on positions.

With all of the different positions I tried that drop was still present. Do I just live with it? Any suggestions? I only have 6.5" midbass, so covering it sub them is unlikely.
 

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I have a null at about the same freq in my car. Only thing that alleviated it somewhat was removing the rear deck speakers. Moving the sub around the trunk didn't help much. I think it had to do more with the vertical position of the sub with respect to the floor and roof than the horizontal position. Cancellation in a car is just something you have to live with, some cars are much worse than others.

my planned solution to further reduce my 60hz null is to tuck a ported 7' or 8" raw driver in a little ported enclosure in the middle of the rear seat/floor. Some might upgrade their rear deck speakers to fill the null. I think having rear deck speakers interact with the same airspace as the sub just seems like a bad idea, unless you can make an enclosure for them you are prob better off just removing them.
 

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Discussion Starter #3
I'm not sure what I'll do with mine, I have a wagon, so there's no deck speakers (or deck) just a roll up cover.... which I half wondered, yet have not tested, if that has anything to do with it. I typically keep it unrolled to prevent people seeing what's in the trunk. No idea if it has an effect, it's a plastic sort of fabric, but maybe worth a test.
 

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What kind of midbass can you use?
Maybe this is one of the kind situations where you should cross the midbass lower than usual to make the sub and midbass blend and larger midbass drivers can help with that (i.e. 8 inch or 6x9 midbass drivers). Did you try down- or side firing the sub?
 

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Agree with dumdum... maybe pull down the spike at 40Hz down around 5-7db and remeasure.
If the sublevel is too low you can gain up the subchannel a bit and remeasure again.
Lots of things you could try.
 

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Discussion Starter #7
What kind of midbass can you use?
Maybe this is one of the kind situations where you should cross the midbass lower than usual to make the sub and midbass blend and larger midbass drivers can help with that (i.e. 8 inch or 6x9 midbass drivers). Did you try down- or side firing the sub?
I can only fit 6.5" midbass, at least without doing some pretty major fabriction. Side firing made no difference, although that was firing sideways across the trunk, not sideways into the side of the trunk. I have not tried down facing, I'd need to get some blocks to raise the sub up first. May be worth a try.

You are assuming it’s just a big null, it’s very likely you have the typical giant boost at 40-50 and a giant complimentary dip at double that at 80-100hz which makes it look far worse
Good point, certainly worth a try of lowering the spike manually and then seeing how things stand.
 

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What sub is this? What type of enclosure? The frequency is falling off the cliff more from 40hz down...

I would worry more about that... a sub is supposed to play sub frequencies that graph is telling me you have a big midbass driver rather than a sub...

A good sub plots upwards towards 20hz not downwards from 40hz - I would say your sub bass is sounding anemic...

Your box is either way to small or you have some sort of subsonic filter at 40hz...


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Dumdum beat me to it. The curve looks pretty good, it doesn't look like it's falling on it's face, it just looks like you have a huge boost in the 40-50hz range, close to where a lot of bass boost features sit. Do you have boost turned on at the head unit, or amp?
 

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Discussion Starter #10
What sub is this? What type of enclosure? The frequency is falling off the cliff more from 40hz down...

I would worry more about that... a sub is supposed to play sub frequencies that graph is telling me you have a big midbass driver rather than a sub...

A good sub plots upwards towards 20hz not downwards from 40hz - I would say your sub bass is sounding anemic...

Your box is either way to small or you have some sort of subsonic filter at 40hz...
It's an SI SQL-12, sealed enclosure, 1cf. Per the spec the enclosure should be fine, also checked the subsonic filter yesterday and it was off (well, as off as it can be with a PDX V-9)

Dumdum beat me to it. The curve looks pretty good, it doesn't look like it's falling on it's face, it just looks like you have a huge boost in the 40-50hz range, close to where a lot of bass boost features sit. Do you have boost turned on at the head unit, or amp?
It's a factory head unit, no bass boost turned on, using a Helix SDMI25 to grab the audio signal and feed the DSP. I'm going to triple check the subsonic filter, then add some EQ to pull down the spike and see where that puts things.
 

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It's an SI SQL-12, sealed enclosure, 1cf. Per the spec the enclosure should be fine, also checked the subsonic filter yesterday and it was off (well, as off as it can be with a PDX V-9)



It's a factory head unit, no bass boost turned on, using a Helix SDMI25 to grab the audio signal and feed the DSP. I'm going to triple check the subsonic filter, then add some EQ to pull down the spike and see where that puts things.
Just EQ 40-60hz to bring them inline - you could have some cabin gain or something like that - I know In my X3 I have a bump in the 40hz region which I need all of my EQ to get it more or less ok...

Did you model the sub? Or just use the manuals recommendations? I find the manual is the minimum spec not the optimal spec.

1CF sounds a bit small for a 12” usually 45lts is a minimum for a 12” unless it has a very low QTS - what’s the QTS of the sub?


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Discussion Starter #12
QTS is 0.53, 99% sure I remember modelling it and unless I did something wrong with WinISD it coming out as a Qtc of not far off from 0.707.

I went out to EQ it just now, but my car battery is low. Ordered a new one yesterday, that should have been ready yesterday (in 30 minutes per the order) get to the store only to have them tell me they don't have that battery in stock. So, can't do much without a new battery.
 

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QTS is 0.53, 99% sure I remember modelling it and unless I did something wrong with WinISD it coming out as a Qtc of not far off from 0.707.

I went out to EQ it just now, but my car battery is low. Ordered a new one yesterday, that should have been ready yesterday (in 30 minutes per the order) get to the store only to have them tell me they don't have that battery in stock. So, can't do much without a new battery.
That’s a similar QTS to the JBLW12GTI that sub needs 55lts for 0.7QTS - I know they different subs - 1cf for 0.53QTS sounds on the minimum side to me - I could be wrong.


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Discussion Starter #14
OK, just went to double check, the enclosure is actually a hair over 1.2cf and not 1.0cf. The sub itself was designed to work in smaller enclosures, it sounds good, gets plenty loud and low. But, obviously from looking at the measured response could be better.
 

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What sub is this? What type of enclosure? The frequency is falling off the cliff more from 40hz down...

I would worry more about that... a sub is supposed to play sub frequencies that graph is telling me you have a big midbass driver rather than a sub...

A good sub plots upwards towards 20hz not downwards from 40hz - I would say your sub bass is sounding anemic...

Your box is either way to small or you have some sort of subsonic filter at 40hz...


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Most sealed subs look like his nearfield measurement, the car then adds to the bottom end and boosts it, however in my old van I had the exact same as this, I had massive spikes at 40-45hz and massive dips at 80-100, I also had zero low end, it was down to the length and width of the van being multiples of each other, so I had constructive reinforcement at 40-45, and a dip at double it also, but the massive peak at 40-45 where most cars would get 5-8db and the van had 12-14db... and any small dips were made a lot, lot worse, and the big dip at 80-100 was approx 20db off of the peak of the response

I tried all sorts to boost the low end... but the more energy I put into the low end the more it cancelled - think of a phase dip in midbass that doesn’t respond to eq... there is more energy in the nearfield where you boost, but at the listening position you don’t get anymore boost as the reflection is boosted also and that cancels the direct peak energy also, I was able to sort of get around it, basically two subs at different locations in the van was able to fill the voids with careful eq. But it still didn’t sound natural... I had more phase issues and reflections at other frequencys so I bought a different car to compete with 🤷🏽‍♂️
 

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Most sealed subs look like his nearfield measurement, the car then adds to the bottom end and boosts it, however in my old van I had the exact same as this, I had massive spikes at 40-45hz and massive dips at 80-100, I also had zero low end, it was down to the length and width of the van being multiples of each other, so I had constructive reinforcement at 40-45, and a dip at double it also, but the massive peak at 40-45 where most cars would get 5-8db and the van had 12-14db... and any small dips were made a lot, lot worse, and the big dip at 80-100 was approx 20db off of the peak of the response

I tried all sorts to boost the low end... but the more energy I put into the low end the more it cancelled - think of a phase dip in midbass that doesn’t respond to eq... there is more energy in the nearfield where you boost, but at the listening position you don’t get anymore boost as the reflection is boosted also and that cancels the direct peak energy also, I was able to sort of get around it, basically two subs at different locations in the van was able to fill the voids with careful eq. But it still didn’t sound natural... I had more phase issues and reflections at other frequencys so I bought a different car to compete with
Yeah I noticed in the BMW I got massive rise in the 40-50hz like 12dbs + the bass was actually distorting if you put too much power in it - I had to drop 40hz and 50hz and 30hz by nearly 14dbs to get a reasonable curve - car actually sounded decent.

Now that was with the Esotar and Focal 10WM subs - I now have the JBLW15GTI and I have a bit of a weird response - there seems to be a 5db jump from each frequency except 20-30hz is actually flat but 5-8dbs louder than 40hz and the same to 50hz - not sure if I should do anything as the bass is actually pretty good - not sure what the db steps between frequencies should be...

The JBL is an absolute animal if you power it properly - I am actually using the same amp that I used for the 10WM except the JBL is running 4ohms and the 10WM was running 2ohms - so the amp was actually running more power to the 10WM - yet the JBL just blasts the 10WM out the water in terms of sheer output and low end extension - it’s currently in a 2.1cf sealed box - so I am going to build a 3.1cf sealed box to see how the JBL responds - but just by going from 1.5 to 2.1 CF the 20-30hz range jumped by almost 3dbs so I wonder what an extra 1cf would result in...

From what I have experimented in the 10WM wants a massive box - it may even be a IB candidate - if measuring of winisd has any believable plotting capabilities - the 10WM actually looks better than the JBLW15GTI - but that’s with a huge box of like 3+ cubes...

I really don’t think the 10WM should go anywhere near the printed enclosure sizes...


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While taking some measurements earlier today i noticed that my subwoofer response falls off a cliff at 55Hz, talking a 10dB drop...



The picture above is no EQ applied. I checked settings on the amplifier and DSP, then took a 2nd measurement with the mic in front of the sub, no EQ and crossovers off.



In front of the sub, the response looks pretty good. At this point I tried various locations in the trunk:

Right side, against back seat, firing towards trunk (usual position)
Right side, against seat back, facing forward
Right side, facing both back and forward against tailgate
Right side, facing sideways
Left side, same as above on positions.

With all of the different positions I tried that drop was still present. Do I just live with it? Any suggestions? I only have 6.5" midbass, so covering it sub them is unlikely.
Sounds like a car issue. My subs start dropping like crazy above 60 hz when measured at my head, they don't have that drop if I measure in the kickpanel area. What I hear agrees with the kickpanel measurement.
 

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I'm not sure what I'll do with mine, I have a wagon, so there's no deck speakers (or deck) just a roll up cover.... which I half wondered, yet have not tested, if that has anything to do with it. I typically keep it unrolled to prevent people seeing what's in the trunk. No idea if it has an effect, it's a plastic sort of fabric, but maybe worth a test.
Ah, a hatchback-like car, that problem seems common among hatchbacks. Don't worry about the fabric, if it's not acoustically transparent enough it'll just move with the bass, it's likely light enough that it won't affect the sound, unless it slaps against something.
 

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Discussion Starter #19
Ah, a hatchback-like car, that problem seems common among hatchbacks. Don't worry about the fabric, if it's not acoustically transparent enough it'll just move with the bass, it's likely light enough that it won't affect the sound, unless it slaps against something.
Great, that confirmed what I was thinking that it unlikely to have any real effect.


So, I added some EQ to the sub with a pretty narrow Q, but then when running Dirac it was showing up as just as bad as before. Changed the Q to (IIRC) 1.5 and ran again, the subwoofer response looks a lot smoother in Dirac with that. So, re-ran the set of 9 sweeps, loaded a target curve and at least to me, it's sounding pretty great, plenty of low end, just need to get Volvo to hurry up and carry out the recall on my car so I can put some treatment on the doors.
 
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