Could there be an acoustic reason for thsi sort of frequency response graph? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 32 Old 01-17-2020, 09:48 AM - Thread Starter
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Could there be an acoustic reason for this sort of frequency response graph?

I bought this sub for my car. I didn't need much but it still wasn't sounding good so I took a REW measurement and saw a large suckout in my frequency response.

I measured with the mic right up on the sub with hatch open and then in the drivers seat to compare.

I've tried to ensure all filters are off on the source and amp.

Any ideas?
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post #2 of 32 Old 01-17-2020, 09:58 AM
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Quote:
Originally Posted by fabulousfrankie View Post
I bought this sub for my car. I didn't need much but it still wasn't sounding good so I took a REW measurement and saw a large suckout in my frequency response.

I measured with the mic right up on the sub with hatch open and then in the drivers seat to compare.

I've tried to ensure all filters are off on the source and amp.

Any ideas?
Its really difficult to interpret a frequency graph like that in car. There are so many things that affect the sound. Have you measured in the cabin where you sit? You were measuring with the trunk open right on top of the sub, that's a less than ideal way to measure as that is not the way it will be listened to. Are you noticing that it just doesn't sound very good in the cabin? Are you using a stock head unit, and what do you have the cross over set to on the sub?
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post #3 of 32 Old 01-17-2020, 09:58 AM
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I always thought that Corvettes suck, and now we know at which frequency.

Kidding aside, 1/2 the wavelength of 68 Hz is about 8.6 feet, which is probably near the length of your cabin.

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post #4 of 32 Old 01-17-2020, 10:20 AM
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Quote:
Originally Posted by Augerhandle View Post
I always thought that Corvettes suck, and now we know at which frequency.

Kidding aside, 1/2 the wavelength of 68 Hz is about 8.6 feet, which is probably near the length of your cabin.
I thought the close mic measurement would negate that, but would opening both front doors help with the effect? I'd expect you would see some type of change if the cabin is causing a cancellation. My clause: I'm not a measurement guru and less so in non HT settings.
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post #5 of 32 Old 01-17-2020, 10:25 AM
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You wouldn't see the dip with the same intensity in the close mic response if it was a reflection.

I'd pull the sub out and try and measure it using a different amplifier, or better yet hook a separate external amp (or old AVR) up to the sub with it in your car just to run another quick REW measurement. This will rule out either the amplifier in the corvette or the subwoofer as the source of the dip.
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post #6 of 32 Old 01-17-2020, 10:26 AM - Thread Starter
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Quote:
Originally Posted by liffie420 View Post
Its really difficult to interpret a frequency graph like that in car. There are so many things that affect the sound. Have you measured in the cabin where you sit? You were measuring with the trunk open right on top of the sub, that's a less than ideal way to measure as that is not the way it will be listened to. Are you noticing that it just doesn't sound very good in the cabin? Are you using a stock head unit, and what do you have the cross over set to on the sub?
Aftermarket head unit is the Pioneer AVH-W4400NEX.

The bass sounds anemic which in my view would correspond with the measurement. Crossover is set to 120hz currently.

I did the close mic measurement to negate the effect of the cabin (green line).

Then I did the drivers seating position to see the what I would normally hear (orange line).

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post #7 of 32 Old 01-17-2020, 12:36 PM - Thread Starter
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Quote:
Originally Posted by mtg90 View Post
You wouldn't see the dip with the same intensity in the close mic response if it was a reflection.

I'd pull the sub out and try and measure it using a different amplifier, or better yet hook a separate external amp (or old AVR) up to the sub with it in your car just to run another quick REW measurement. This will rule out either the amplifier in the corvette or the subwoofer as the source of the dip.
It's definitely the subwoofer. Thanks for the suggestion.

I did more measurements with a different amp in the car and with the sub on the floor of my garage. They measured almost identical, both with the suckout.

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post #8 of 32 Old 01-17-2020, 01:16 PM - Thread Starter
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So I originally put 12oz of polyfill in this and took impedance sweeps with a Dayton DATS v2. The "suckout" seems to coincide with the impedance peak. I've never known a subwoofer drive to be defective in a way like this.
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post #9 of 32 Old 01-17-2020, 02:21 PM
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What is defective about it? Sounds like a typical car response. Did you try aiming it (left, right, front, rear), adjust the phase, adjust the crossover?

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post #10 of 32 Old 01-17-2020, 02:27 PM
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Quote:
Originally Posted by Fackamato View Post
What is defective about it? Sounds like a typical car response. Did you try aiming it (left, right, front, rear), adjust the phase, adjust the crossover?


If he’s had the sub out of the vehicle and powered by a different amplifier and it measured the same, I’d say its a subwoofer problem.

OP, what sub is it?

Chris
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post #11 of 32 Old 01-17-2020, 02:28 PM
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What happens when you run a sine wave sweep around that frequency? Or just use the generator in REW and scroll up and down around 50-80hz. Do you see a reduction in cone excursion centered on the dip in the response?
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post #12 of 32 Old 01-17-2020, 02:38 PM
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I missed the part where the response was the same when it was on a floor. Yeah, that doesn't look right.

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post #13 of 32 Old 01-17-2020, 02:55 PM
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Quote:
Originally Posted by fabulousfrankie View Post
It's definitely the subwoofer. Thanks for the suggestion.

I did more measurements with a different amp in the car and with the sub on the floor of my garage. They measured almost identical, both with the suckout.

There is still one common denominator in your testing, the Pioneer head unit. Possibly others if you're using any factory wiring, did you install new RCA directly from the head unit to the amp? Or are you using any other components in the signal chain?

I'd second MTG's suggestion of putting the sub on an entirely different system and see if you have the same response. Also his suggestion of using a mid-powered sine wave and see if you truly can't hear the sub at the deepest part of the suckout frequency (68hz) vs 75hz and 55hz.
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post #14 of 32 Old 01-17-2020, 03:41 PM - Thread Starter
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Originally Posted by a77cj7 View Post
If he’s had the sub out of the vehicle and powered by a different amplifier and it measured the same, I’d say its a subwoofer problem.

OP, what sub is it?

Chris
The sub is the at the link below. It's kind of like a cheaper version of the JL Audio Stealthbox subs.

https://www.sonicelectronix.com/item...-NSW104v2.html

This is the driver, it's nothing special. I tried to put a Dayton 10" Ref HF but due to the awkward shape there was not enough clearance for the magnet.

https://www.sonicelectronix.com/item...NSW104-v2.html

I measured the T/S parameters and besides FS being about 10Hz higher the rest of the T/S parameters weren't wildly off.
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post #15 of 32 Old 01-17-2020, 03:42 PM - Thread Starter
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Originally Posted by notfastenough View Post
There is still one common denominator in your testing, the Pioneer head unit. Possibly others if you're using any factory wiring, did you install new RCA directly from the head unit to the amp? Or are you using any other components in the signal chain?

I'd second MTG's suggestion of putting the sub on an entirely different system and see if you have the same response. Also his suggestion of using a mid-powered sine wave and see if you truly can't hear the sub at the deepest part of the suckout frequency (68hz) vs 75hz and 55hz.
I did eliminate the Pioneer head unit. I went from my laptop to a Dayton amp to the sub.
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post #16 of 32 Old 01-17-2020, 03:48 PM - Thread Starter
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Quote:
Originally Posted by mtg90 View Post
What happens when you run a sine wave sweep around that frequency? Or just use the generator in REW and scroll up and down around 50-80hz. Do you see a reduction in cone excursion centered on the dip in the response?
I'll try that with my laptop and Dayton amp later today. Two jerks I helped create came back from daycare and are stopping my progress.
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post #17 of 32 Old 01-17-2020, 03:51 PM
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Could there be an acoustic reason for thsi sort of frequency response graph?

Quote:
Originally Posted by fabulousfrankie View Post
The sub is the at the link below. It's kind of like a cheaper version of the JL Audio Stealthbox subs.



https://www.sonicelectronix.com/item...-NSW104v2.html



This is the driver, it's nothing special. I tried to put a Dayton 10" Ref HF but due to the awkward shape there was not enough clearance for the magnet.



https://www.sonicelectronix.com/item...NSW104-v2.html



I measured the T/S parameters and besides FS being about 10Hz higher the rest of the T/S parameters weren't wildly off.


Super cheap driver, any warranty?

If not, pick up another to see if thats the issue?

Or drop in something much higher quality, say an alpine T10. I ran a pair of T12’s in my dakota, super impressive for shallow subs.

Chris
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post #18 of 32 Old 01-17-2020, 03:54 PM - Thread Starter
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It's still under warranty. The enclosure itself cost as much as the enclosure and sub so I thought I'd try it since the Dayton 10" I bought had too large of a magnet structure.
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post #19 of 32 Old 01-17-2020, 04:19 PM
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Could there be an acoustic reason for thsi sort of frequency response graph?

Quote:
Originally Posted by fabulousfrankie View Post
It's still under warranty. The enclosure itself cost as much as the enclosure and sub so I thought I'd try it since the Dayton 10" I bought had too large of a magnet structure.


Ahh yes, no reason not to get the loaded enclosure to try out.
Might be worth it to warranty it to see if thats just a bad driver.

I haven’t really looked since 2015, but the alpine T10 and T12 were the best shallow drivers available.

Chris

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post #20 of 32 Old 01-17-2020, 04:59 PM - Thread Starter
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I tried to look at the excursion with sine waves but there's a protective grill and it's too hard to tell. The dip is clearly audible though. I'll have to pull it out of the enclosure tomorrow.

Thanks for the tip on the Alpine...I have an 8" type R sitting around that I may put in the garage.
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post #21 of 32 Old 01-17-2020, 05:13 PM
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You could try swapping polarity on one of the voice coils and see if it helps. Maybe test each VC separately one at a time.
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post #22 of 32 Old 01-17-2020, 05:47 PM - Thread Starter
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Originally Posted by BlueGhost View Post
You could try swapping polarity on one of the voice coils and see if it helps. Maybe test each VC separately one at a time.
The version that came in the enclosure only had a single set of binding posts.

I've never thought of what would happen if sub coils were wired out of phase. If this was internally wired out of phase, would this be the result?

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post #23 of 32 Old 01-17-2020, 08:03 PM
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Quote:
Originally Posted by fabulousfrankie View Post
The version that came in the enclosure only had a single set of binding posts.



I've never thought of what would happen if sub coils were wired out of phase. If this was internally wired out of phase, would this be the result?


Very little sound at all, the two coils canceling each other out.

Chris
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post #24 of 32 Old 01-18-2020, 12:01 PM
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If you haven’t already, rule out the measurement mic / soundcard etc by taking sweeps of something else (to see if it’s showing weird dip on unrelated equipment)
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post #25 of 32 Old 01-18-2020, 07:01 PM - Thread Starter
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Unfortunately it’s not the measurement system. I measured other speakers and it comes out normal, plus it’s clearly audible from the sub with sine waves.

I measured 6x9s in the doors and it doesn’t have the same dip in frequency. I never got a chance to pull out the driver. I’ll do that and play sine waves free air to see what happens.
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post #26 of 32 Old 01-19-2020, 11:40 AM
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Try the Dayton magnet side out?
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post #27 of 32 Old 01-19-2020, 12:30 PM
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Magnet out is a good idea. More box for the driver and better cooling.
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post #28 of 32 Old 01-19-2020, 01:22 PM - Thread Starter
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The reason I bought this enclosure was so it could hide away in the corner and my targa tip could still store in the back. The inverted driver mounting would interfere with storing the top.
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post #29 of 32 Old 01-19-2020, 01:48 PM
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I really only suggested it as a troubleshooting idea. Temporary style just to find the root of the problem.
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post #30 of 32 Old 01-19-2020, 01:57 PM
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ask the people who designed the box...or use winisd or online software and see what the measurements tell ya. i experimented alot back in the day with car subs and for a car design like the corvette having sub shoot up of window was best. for trunk...shooting of tailgate. you want the wavelength to be long as possible.

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