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Sundown Coaxial Observations


Rpg663

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I have a pair of Sundown's SA-6.5CX v2's in my 1997 Miata. The Sundowns wouldn't fit the door, so I cut the metal to fit them in there. The holes in the door panels are about 139mm and need to be about 150mm. Anyway, I put on some Fat Mat foam speaker baffles to seal the speakers from the inner door (gets wet in there when it rains).  After this on one side, I noticed that the speaker was moving less, vs the one on the other side without the baffle was moving a lot more.

 

Are these speakers not engineered to be in a baffle like this and benefit from the air acting as a cushion? I couldn't tell if it sounded better or worse either way. I might end up putting a hole in the back of the baffles so they can still breathe. Any input on the matter?

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I’m more of a regular on AVS forums, and I read through something that said if you’re dumping power into a speaker, you probably want it to be moving a fair bit to cool it better. I’m thinking this is correct, so I’m going to cut a hole in the back of the enclosure. I have a measurement mic setup so I might do near-field comparisonS and post here. Limited by the fact that I can’t move the Miata out of the garage (active aero and engine rebuild going on) hopefully that won’t affect the results too much. 

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So it sounds like the pods you put in are pretty air tight? If they are, I think you're not getting as much movement for the same reason big subs move different in sealed enclosures. There's more pull from the air inside the enclosure on the speaker than would normally be there. The air inside the enclosure is actually acting kind of like it's own shock absorber for the motor of the speaker, making it hardest for the cone to move out of control. On subwoofers, this isn't a bad thing. More cone control equals more low bass with less distortion. On midrange speakers, I'm not 100% sure, but I'm assuming it would be the same deal. 

Yes, the voice coil moving up and down does create the cooling for the coil. I'm not familiar with that particular speaker, but if it's not manufacturer in a way that allows air movement around the coil at rms type power without it having to use most of the suspension, I would think it could overheat. That's something you would have to ask someone familiar with that speaker or the manufacturer themselves. I've heard Sundown is pretty good with their customer service, it shouldn't be a problem asking them in order to be 100% sure

Hopes this helps a little

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My build log here. Check it out! 

 

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11 minutes ago, Dafaseles said:

I'm not familiar with that particular speaker, but if it's not manufacturer in a way that allows air movement around the coil at rms type power without it having to use most of the suspension, I would think it could overheat.

It does have a vented pole piece, but I truly think it's almost too bassy. Something sounds wrong, so I'm going to be measuring and publishing my findings. At the very least, the enclosure offers a good seal to the door.

 

 

15 minutes ago, Dafaseles said:

I've heard Sundown is pretty good with their customer service, it shouldn't be a problem asking them in order to be 100% sure

I have had this experience with them. I was hoping they'd chime in on here but I'm going to call now and keep everyone updated. My next post will probably be testing methodology.

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No one answered my call at Sundown so I sent an email through their form on their website. No big deal, I'm testing anyway really. The foam pods / baffles are $10, and what is audio if not constant testing.

 

So in nearfield measurement, the maximum frequency it can accurately measure depends upon the size of the cone. Since we're measuring a coaxial speaker with a tweeter and a midrange, I think the measurement will be interesting around these points. I'm using AudioJudgment.com's methodology for measuring. 

1. I first calculated where the the point of possible distortion of the test will be by finding the fmax of the speaker (I believe a measurement of where it starts beaming).

fmax = 10950 / cone diameter (cm)

fmax = 663.23 hZ (mid)                        fmax = 4311.02 hZ (tweeter)

 

2. There is no port currently so we don't need to scale the results to adjust for port size

 

3. Next up is baffle correction. Since the car door has so many holes in it, and it will have the door skin on top of it, I don't think that there will be a ton of advantage from this calculation. Beyond this, I'm not looking for measurements that are exact, I'm looking for differentials.

 

4. Next step is to open up my laptop and get my UMIK-1 right up next to the speaker as close as possible, and run sweeps, adjusting the volume as I go. My radio is set to a flat EQ with no bass boost or other modifiers.

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Answers, aho! The red line is without the foam baffle, the green line is with the foam baffle. The results are pretty telling, other than the dip at 751Hz which might be the max accurately measurable frequency for the cone size before things get weird (EDIT: or the crossover between woofer and tweeter, which for some reason Sundown decided not to publish). Additionally it's good to see the tweeter's region remains unsubstantially changed, meaning there's fairly good consistency between my measurements.

Starting from the bottom, it's obvious the Sundown component prefers no baffle under 148Hz, but benefits from it above with a +3dB bump from 148Hz to 434Hz. The doubling of loudness in the midbass region is definitely the reason I felt the baffle caused the Sundown to sound muddy and clunky. While the midbass would be welcome if it came with more lower bass, it sounds unrefined without it. The large drop off of bass can be attributed to the cone's movement being restricted as the air in the foam baffle acts as an acoustic spring, reducing compliance substantially and not allowing the suspension movement needed for bass in this implementation.

My next step is to bore a hole in the foam baffle and see if the added airflow can be tuned to produce a balance between midbass gains and a reduction in lower bass dropoff. Of course I won't be running the speakers below ~60Hz anyway, so that part can be ignored. Updates within the next day or two probably!

 

 

33234894_BaffleVsNoBaffleSundown6_5CX.thumb.jpg.18dad0aac183f0b10fefd3f4794be0b4.jpg

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