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21SW152-4 25Hz Ported measurements


lowerFE

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Am I reading this correctly? The 21SW152-4 in a 25Hz tuned ported cabinet is producing 18dB more output at 25Hz than the sealed cabinet equivalent? It has more 25Hz output than 31.5Hz and 40Hz. 

 

I've never seen measurements like this. Is this real? Most ported cabinets you've measured only provide ~10dB more output at the tuning frequency compared to its sealed cabinet equivalent. What's going on with this driver?

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Its about 17.4dB during Cea2010 burst testing but yes...That is correct. What is going on is nothing to do with the sealed cab and everything to do with the vented cab I designed and the driver. It is a big cab with a 25Hz tuning so it is right at that burst frequency which helps. Also port is a gigantic 10" round concrete form tube with a large flare on the inside and outside. Vents compress and detune once the air speeds get too high. This 10" vent will flow a huge mass of air compared to the little 3 and 4" vents on most subs or the skinny slot ports that are used. Even many multiples of those smaller vents overload far below the point that the 10" vent would. Lastly the driver has a huge 6" voice coil with loads of motor venting. It does not compress and heat up nearly as much as most other drivers. A vented cab has minimum cone movement at the tuning and maximum power delivered to the driver coil which = maximum thermal compression in the driver. Also the port is doing all of the work so it has to flow lots of air or it will compress and start to unload the driver.

 

To recap...We have a extremely high power driver. A gigantic high flow vent, and large cab for extra efficiency in the deep bass, tuning right at that frequency band and a ridiculous amount of power available from the amp.

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Thanks for the explanation!

 

Does that mean is it possible to achieve around the same 17dB gain at the tuning frequency on other high powered drivers like the Zv4 or LMS-R by putting it in a cab with a huge port with lots of amp power? How about in passive radiator designs?

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Possibly depending on how each driver deals with heating at port tune...look how big this cab is for a 25Hz time though. If you want tuning at 20Hz or below you are going to need a REALLY big cab or you will have to use a much smaller vent. That's partly why the small commercial subs don't have as much output around port tune. They are really undersized usually and so are the vents.

 

Passive radiators are more tricky. They have physical limitations. A 12" LMSR driver can overload a pair of 12" TC passives and with enough power can come close with a pair of the 15" passives. Drivers like the XXX and Zv4 are going to need at minimum 3 18" PR's and 4 would be better. That gets expensive and the box gets big quick. PR's are great but they will run out of stroke near tuning quicker than an equivalent port would overload completely. Still they allow tunings in box sizes that are impossible with ports. As usual tradeoffs.

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  • 3 weeks later...

around the tuning frequency, the driver excursion is very low, but power is very high.

 

so if the port is large enough and the driver and amp can manage the power, then very high gains are possible.

 

this can be hazardous to the driver's health though, as the combination of high current and minimal excursion place very high thermal stress on the coil. 

 

so while +18db may be possible for short bursts, for the same voltage, a large ported cab tends to run about +12db over sealed around the tuning frequency.

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