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Active Bass Trap using Computer Speakers

 

Gold Member
Username: Arande2

Rattle your ... Missouri

Post Number: 3089
Registered: Dec-06
Here's the deal. I've been focusing a lot on sound lately so my ears are attuned to things again, and I noticed as I was sitting here at my computer that the bass sounded "empty." My listening position is a null - I've known this for a long time, and I haven't done anything about it.

I had a hunch. The reason I've been getting back into sound lately is because I've been doing research to install a car audio system in my daily driver that I drive 7 hours a day. One of the things I noticed while I was testing was that if you fade the sound to any single speaker in the car there's almost no bass, but when you fade in a 2nd or all 4 speakers together, suddenly the bass pops into focus. With this in mind, I pulled out the old measurement software and ran a sweep from 40-700hz - BIG 13dB null in output from 70-140hz. Explains everything.

I know that people add multiple subwoofers to a system and add bass traps to smooth out nulls and peaks, but I didn't have any of those things. However, I did have a pair of old Bose computer speakers... Guess what I did? I hooked them to the subwoofer output of my receiver. I played a test tone at the null frequency and adjusted the volume until I didn't hear anything at all (it was weird hearing NOTHING because I knew a tone was playing). Then I flipped the phase and delay until the SPL meter read the highest.

Ran another sweep after that and guess what? The null went away and the overall response is smoother - it sounds much smoother and fuller now. They are actually running through an EQ so I may tweak that a little bit. Obviously a pair of 2" drivers is limited to low level listening but that's an easy fix - any time I turn it up just turn them off.

Moral of the story is that you can often fix problems with a little experimentation. In my car scenario the challenge is figuring out how to get the highs, mids, and lows to image together properly. Turns out it takes multiple drivers placed differently with separate EQ on each driver to hit the acoustics of the car properly at each frequency.

Any familiar stories out there?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18480
Registered: May-04
.

Hello, Andre, it's been a while.


One story is from the early '80's when I was selling high end audio. Car audio was getting yet another wind beneath its wings as a few high end manufacturers were venturing into the market of appealing to the high dollar automobile buyers looking for better than OEM systems.

I had sold car audio in other shops that were appealing to a more mid-fi to high end clientelle. We were discussing just how to put together the car display and talking to various manufacturer's reps about their products. At the time, "imaging" was an oft discussed value in a home system. So when one rep tried to sell us on the ability of his car system to "image" properly, we all looked at one another like we knew he'd been tipping a few back before he got to our shop.

"So you're telling us, you're driving down the road while you're listening for the imaging from your car system?"

"Sure, our stuff does it swell!"

None of us wanted to be on the road with another driver so intent on listening to their audio system.

A few people walked away at that point and I'm not sure the rep ever understood just how much credibility he had lost.


Sounds like you're having fun with comb filtering.


.
 

Gold Member
Username: Arande2

Rattle your ... Missouri

Post Number: 3090
Registered: Dec-06
Ha! Of all people who could have responded, it was you. That's crazy.

It's almost like you're trying to say something. If you're trying to say that I shouldn't be listening to imaging while I'm driving, I agree. I don't listen critically while I'm driving. But luckily, improving the imaging improves the emotional impact of the music and dramatically improves the quality of the ride because it creates a sort of acoustic environment that makes the car feel big and spacious. In fact, I'm interested not in just music but listening to atmospheric recordings and various soundtracks for that very reason.

Ha! There is ALWAYS comb filtering when you're in a room with a lot of reflections. That's something I'm super focused on right now - understanding how all the reflections affect things. I've been listening on headphones vs. speakers and trying to ascertain what is causing me to hear the sound the way I do and more importantly, why I have a certain emotional impact in one situation vs. another. Like the Bose - they improved the emotional impact because the bass regained a breathy palpable feel. I think it has something to do with fixing the phasey effects of the standing waves in the room because I can EQ the bass to low levels on headphones and it still has a "presence" to it.

Haven't figured it out yet...
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18481
Registered: May-04
.

You got the first post of 2018, Andre. Congrats!
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