Comments on: The Tandem subwoofer https://johnr.hifizine.com/2013/08/the-tandem-subwoofer/ Technologicality, at work and play Mon, 02 Mar 2020 23:33:22 +0000 hourly 1 https://wordpress.org/?v=4.9.26 By: John Reekie https://johnr.hifizine.com/2013/08/the-tandem-subwoofer/#comment-5236 Sat, 28 Dec 2013 02:50:58 +0000 http://johnr.hifizine.com/?p=640#comment-5236 Hi Andrew, just to be clear I reference two different drivers above. In the BTL mode with a single driver it’s an 8 ohm 12″ driver. In “tandem” mode with two drivers it’s a pair of 4 ohm 10″ drivers. The reason I suggested using an 8 ohm driver in the BTL configuration is because of the continuous power rating of the amp module in that configuration – this information is in the ASX2 datasheet and also in the PWR_ICE125 amp user manual. In BTL mode, each channel is effectively seeing half the load impedance, so if using a 4 ohm driver each channel is effectively driving into 2 ohms. Under these conditions the continuous power rating is substantially less than the short term power output. It seems to be fairly common these days to have a continuous power rating less than the short term rating, as it allows for less heatsinking, even with Class D….

So, the conservative choice (for someone like me who started building kit amps when we used to calculate the heatsinks’ thermal resistance for continuous full power output…) would be an 8 ohm driver. However, does it really matter? I don’t know. It just depends on how you use it. Also bear in mind that the difference between 250 and 450 W is less than 3 dB in output. And the final data point, with 250W the RSS315HFA-8 in 3 cuft reaches Xmax about 27 Hz, and at 38 Hz with 450W. So below those frequencies you are excursion limited not power limited. Somewhat paradoxically, I suppose I might use the 4 ohm driver for music applications and the 8 ohm driver for HT applications (and look to add a second unit when funds allowed). But that’s simply a personal choice.

I’ve started building some subs and do have some 4 ohm 12″ drivers that are a bit similar to the RSS315HF, so perhaps I’ll make one with a slot for the amp and try it.

]]> By: Andrew Nelson https://johnr.hifizine.com/2013/08/the-tandem-subwoofer/#comment-5211 Tue, 17 Dec 2013 22:49:13 +0000 http://johnr.hifizine.com/?p=640#comment-5211 Anything good. 🙂 I was going to initially use that same driver except in a 4 ohm load in a home theater setup. But then your choice of 8 ohm confused me. Would the 8 ohm speaker with this amp be enough for a 19x19x8 room? I know you can never have enough but I’m just looking for a well balanced setup with some “presence”. Thanks for asking!

]]> By: John Reekie https://johnr.hifizine.com/2013/08/the-tandem-subwoofer/#comment-5210 Tue, 17 Dec 2013 15:46:20 +0000 http://johnr.hifizine.com/?p=640#comment-5210 Hi Andrew, what driver are you thinking of using?

]]> By: Andrew Nelson https://johnr.hifizine.com/2013/08/the-tandem-subwoofer/#comment-5203 Fri, 13 Dec 2013 21:48:34 +0000 http://johnr.hifizine.com/?p=640#comment-5203 Forgive my lack of audio knowledge, but could you explain in more detail why the 8 ohm speaker choice was better for this amp than the 4 ohm load its rated for? Is it something to do with the RMS of the amp? I’m on the fence about using this amp for a future diy sub build.

Thanks.

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