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Hello,

I’m new to this site, so if this post should go in a different spot, please let me know. And sorry for the long post,..

I’m a novice. I know some basics of audio, but I don’t have RTA equipment or anything fancy, I just experiment a lot using an A/B speaker switch to try things out. The system I’ve built (and am continually trying to improve) is in my 1964 Riviera. Components are mid-grade: Pioneer 80PRS hu, Morel Virtus 5 ¼ components, Kenwood XR901-5 amp, JL shallow 10” sealed sub.

Over nearly 15 years I’ve done lots of noodling to try to get the system sounding decent. I started with fiberglass speaker pods mounted to the doors, tried speakers in the kick panels, stuffed things with polyfill and done things to stiffen and deaden resonance, tried different brands and prices of speakers, but no matter what I tried it always sounded weak or had a hollow, muddy droning through the mid-low frequencies. When I reluctantly cut holes in the doors and put the speakers in there, the improvement was shocking. It left me with the impression that even for smaller speakers, the enclosure is everything. Like, I knew it’s critical for subwoofers, but was surprised at how much difference the space behind the speaker could make for 5 ¼ or even 3” drivers.

But I also get the sense I’m missing something, some important key to making smaller speakers sound good without large volumes of air. My Orb Audio speakers at home have 3” drivers and sound very clean, but when I built a shallow box out of MDF to experiment with a center speaker in the dash (a 3.5” driver), the enclosure made it sound like a cheap boombox, no matter how much polyfill I stuffed in it. Simply having free air beneath it sounded drastically better, even if it meant backwaves were bouncing around and escaping everywhere.

Anyways, I recently found that my rear speakers were adding an annoying midrange ‘hollowness’. They’re mounted in the rear armrests, which have roughly ⅓ cubic foot of volume. That’s not much less than the box for my sub, so I thought there’s no way I would get annoying acoustic response. As another experiment, I put a 4” Morel hybrid driver in it, and then put the same driver in the door for comparison. Again, the door-mounted one is dramatically better. It’s not just the deeper low-frequency response, it’s that the armrest cavity creates a midrange peak that I can’t seem to EQ out without making the front sound bad.

I made this video to demonstrate the difference. Obviously it can't accurately represent the sound, but if you listen with headphones you should be able to get the general idea:

Other than the internal volume, both chambers are similar in that neither is perfectly sealed and the walls are sheet metal. The armrest has less depth, about 4” vs 8” for the door.
Any suggestions on how I can mellow out the peaky, resonant midrange in this armrest hole? Or general tips on making smaller enclosures sound more ‘balanced’?

thanks for reading this novel,
-Jeff
 

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A dense, solid mounting surface and deadening in the door does help. Typically the honky droning sound is because of peaky response in the midbass region. This can be compounded by loading and cabin gain as well as too small of an airspace (sometimes). Measuring your response from the drivers headrest area will tell you a lot, but you almost certainly need some well applied eq cuts to clean up peaky response.
 
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