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Thread: Upfront bass illusion - Follow up

  1. #1
    Founding Member Subwoofery's Avatar
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    Upfront bass illusion - Follow up

    Hi guyz,
    I'm just doing a follow up on that thread: http://www.mobilesoundscience.com/f4...-illusion-417/

    I've noticed something a long time ago and I'm sure you guyz too but just wanted to know your point of view on the subject. Took me some time to post the thread but now it's ON!!!!!

    When playing a sweep (below 100Hz), there are only a few frequencies that excite panels. In my car, it's from 40Hz to 50Hz.
    In a DIYMA thread, I read the following and that was like magic: From Andy Wehmeyer: "be sure there's no huge peak at 45Hz and make sure the transition from 60Hz-160Hz is smooth. The response should be flat from 60Hz through the midrange." <-- to that I corrected my phase between my sub and midbass using T/A. I do have upfront bass now, lot's of it and that was mostly due to panel resonating - lowered 45Hz by 2dB on a wide Q with my PEQ.

    Now, 80% of people on DIYMA use a lowpass below 50Hz. I feel that they do this for 2 reasons mostly, they either:
    - don't have the ability to EQ the peak that makes their panel resonate or
    - because it works for others, why not do it :dw:
    ^ for me this is "wrong knowledge" and I don't think most know why they do it, just that it works.

    I have my lowpass set @ 63Hz 18dB/oct slope with my midbass picking up from 100Hz 12dB/oct slope. I never felt I needed a midbass with an FS of 40Hz or lower. I actually like my midbasses to be as efficient as possible from 80Hz on up.

    Please discuss :gr_grin:

    Kelvin

    PS: do you think I should post a thread on DIYMA too? Guess I should take down the bold statement before that :p

  2. #2
    Senior Member cvjoint's Avatar
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    Is this a well known fact that car panels resonate at 45hz? During my sweeps I generally get audible rattles for test samples under 25hz. The rattles themselves are upper midrange.

    Why would you EQ. out the frequency that "excites" your environment? I would think you want to dampen the corresponding panel instead.

    I now use 63hz 12db LP for the sub and 100hz 36db HP for the 7". I can get a smooth transition from 60-160hz and there is plenty output. In my last install I had 63hz 24db LP on the sub and 63hz 24db HP on the 10" midbass. Needless to say the previous setup with the larger woofers sounded much better on the midbass. I think most of it is because I would have 20hz-200hz boosted some 10db over the frequency response of the other speakers.

    I'm a big fan of the 63hz cross point, preferably 24db slope. I think it's a good compromise between soundstage and output. I was aiming for a 100hz cross point in this car since I have to use small 7" drivers up front but I dislike that setup. I'd rather underlap and raise the gain on the sub. I don't think it's resonance that prevents me from choosing a higher xover point. I have a large 36"x12" opening between me and the subs.

  3. #3
    Senior Member cvjoint's Avatar
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    I played a bunch of test tones to check this theory. I moved the subwoofer LP up to 160hz, turned off the midbass and played a sweep from 100hz to 20hz. There was a bit of resonance half way through the sweep. Starting at 100hz I could not localize the sound very well, it sounded like it was everywhere. Then it started getting pulled back. Towards the end it started sounding like it was everywhere again but for the lowest lows there seemed to be some mechanical noise of sort that makes it once again localizable.

    There is some truth that some frequencies resonate the panels more than others. To me it seems 40hz-80hz is the worst. I'm not sure what you can do about that however. If it was 80hz I can see how a steep 40hz xover would help but I played individual tones as low as 40hz and the buzz was starting to develop.

    I suppose some people build woofers in the dash but those are very anemic compared to what you can do in the trunk and they suffer even more from rattles. At the low levels of ouput of a dash mounted 10", 2 12"s in the trunk would be almost dead silent.

  4. #4
    Member Candisa's Avatar
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    Well, if the plan we have can work (see the thread: '5-ways in a car?'), a lot of issues that are typical for almost any car could be solved:
    - If the subwoofer(s) in the trunk are crossed too high, interior-panels in the rear can develop rattling issues that are hard to kill. Those rattles are not only annoying, they also pull the sound-stage to the rear.
    - If the midbasswoofers are crossed too low, the power handling drops really fast.
    - If you get midbasswoofers with very high linear excursion (1/2" rather than 1/4" one-way) to be able to get low with authority, you will have to compromise efficiency and probably some detail/attack too!
    - If the midbasswoofers are crossed too low, you might have to use quite some dampening material to get the doors rattle-free...

    So ideally, the subwoofer in the back has to be crossed low (<50Hz), but the midbasswoofers have to be crossed rather high (>70Hz), but you can't use shallow slopes to compensate, otherwise you get the same problems...

    An extra 'way' between the big, dedicated subwoofers in the back and the midbasswoofers in the door, mounted in a place that's not as likely to cause rattles as in door-panels, could be the solution for all these problems...

    Isabelle

  5. #5
    Tester Extraordinaire ErinH's Avatar
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    re: tuning the issue

    If it's an acoustical resonance, tuning it down can help but it will still be there in some tracks.

    acoustical is different than mechanical resonance.
    Your ears: The best tools you have... and they're free, too!

  6. #6
    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by cvjoint View Post
    Is this a well known fact that car panels resonate at 45hz? During my sweeps I generally get audible rattles for test samples under 25hz. The rattles themselves are upper midrange.

    Why would you EQ. out the frequency that "excites" your environment? I would think you want to dampen the corresponding panel instead.

    I now use 63hz 12db LP for the sub and 100hz 36db HP for the 7". I can get a smooth transition from 60-160hz and there is plenty output. In my last install I had 63hz 24db LP on the sub and 63hz 24db HP on the 10" midbass. Needless to say the previous setup with the larger woofers sounded much better on the midbass. I think most of it is because I would have 20hz-200hz boosted some 10db over the frequency response of the other speakers.

    I'm a big fan of the 63hz cross point, preferably 24db slope. I think it's a good compromise between soundstage and output. I was aiming for a 100hz cross point in this car since I have to use small 7" drivers up front but I dislike that setup. I'd rather underlap and raise the gain on the sub. I don't think it's resonance that prevents me from choosing a higher xover point. I have a large 36"x12" opening between me and the subs.
    Dropping 45Hz with a shallow slope actually kills 2 birds with 1 stone...
    I'm lowering most of the freqs that made my panel resonate and
    I'm lowering my peak in the sub range... My car peaks @ 43Hz.

    One more example... I've read many times that crossing the subwoofer higher (+63Hz) makes the sound muddy. I won't say it's a wrong statement coz I'm not that knowledgeable...
    However, I've found that if the phase between the midbass and the subwoofer is not correct (or at least close enough), the subwoofer will sound like it's lagging. I usually listen to a fast techno song and listen for the sub integration and use the delay (T/A) until I either don't hear the transition or don't really hear the rattle.
    I never felt my substage was muddy even with a LP @ 100Hz 12dB/oct slope - using a low distorsion sub might help though ;) (XBL^2).

    Kelvin

    PS: my car is a hatchback and the trunk is 70% deadenen. Don't want to spend more coz my car is not that powerful :p

  7. #7
    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by cvjoint View Post
    I played a bunch of test tones to check this theory. I moved the subwoofer LP up to 160hz, turned off the midbass and played a sweep from 100hz to 20hz. There was a bit of resonance half way through the sweep. Starting at 100hz I could not localize the sound very well, it sounded like it was everywhere. Then it started getting pulled back. Towards the end it started sounding like it was everywhere again but for the lowest lows there seemed to be some mechanical noise of sort that makes it once again localizable.

    There is some truth that some frequencies resonate the panels more than others. To me it seems 40hz-80hz is the worst. I'm not sure what you can do about that however. If it was 80hz I can see how a steep 40hz xover would help but I played individual tones as low as 40hz and the buzz was starting to develop.

    I suppose some people build woofers in the dash but those are very anemic compared to what you can do in the trunk and they suffer even more from rattles. At the low levels of ouput of a dash mounted 10", 2 12"s in the trunk would be almost dead silent.
    Pretty much my point for this thread...

    Kelvin

  8. #8
    Founding Member Subwoofery's Avatar
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    Quote Originally Posted by Candisa View Post
    Well, if the plan we have can work (see the thread: '5-ways in a car?'), a lot of issues that are typical for almost any car could be solved:
    - If the subwoofer(s) in the trunk are crossed too high, interior-panels in the rear can develop rattling issues that are hard to kill. Those rattles are not only annoying, they also pull the sound-stage to the rear.
    - If the midbasswoofers are crossed too low, the power handling drops really fast.
    - If you get midbasswoofers with very high linear excursion (1/2" rather than 1/4" one-way) to be able to get low with authority, you will have to compromise efficiency and probably some detail/attack too!
    - If the midbasswoofers are crossed too low, you might have to use quite some dampening material to get the doors rattle-free...

    So ideally, the subwoofer in the back has to be crossed low (<50Hz), but the midbasswoofers have to be crossed rather high (>70Hz), but you can't use shallow slopes to compensate, otherwise you get the same problems...

    An extra 'way' between the big, dedicated subwoofers in the back and the midbasswoofers in the door, mounted in a place that's not as likely to cause rattles as in door-panels, could be the solution for all these problems...

    Isabelle
    I have the same philosophy... Agreed on pretty much every points

    Kelvin

  9. #9
    Tester Extraordinaire ErinH's Avatar
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    IMO, sub integration typically is as simple as proper level matching (via gain and/or crossover) and that's about it. Phase correction certainly helps bit by and lage, most systems that I listen to have the sub jacked up and expect their little midbasses to keep up. Truthfully, a nice system doesn't need much low end at all... Just enough to fill in where the mid bass cannot.
    Your ears: The best tools you have... and they're free, too!

  10. #10
    Senior Member cvjoint's Avatar
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    Candisa/Subwoofery theory is legit, at least the part that outlined the difficulties and drawbacks of rear mounted bass drivers. However I'm not sold on the solutions. To some extent this is like having your cake and eating it too. For a given SPL, the front of the car will rattle more than the rear. Either the doors or the dash have far more moving parts and sources of rattles than the rear deck. By shifting output to the front all you do is move the rattles up front and imo exacerbate their output. The vast majority of setups that move subwoofer duty upfront trade off output for front rattles. I've done both methods so far and I'm a big fan of taking subs up to 63hz. I spend time taming the car rattles instead.

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