[Build] Rockford Fosgate P115S4


I wanted to share my most recent build. Subwoofer is RF P115S4 and enclosure - 4th order Bandpass: V1 = 50 l; V2 = 50 l; Port = 260 cm^2 x 40 cm.

Did some test runs with a "Stereo Power Amplifier Koda KD-261 (110 wRms @ 8 ohm)" and "T.Racks 4x4 Mini DSP". It's my first time using DSP so I run into some problems. During the listening "Gain" indicator at most times was at -5 dB. High pass LK -24 @ 25 Hz and low pass LK -24 @ 120 Hz. All the PEQ parameters was off and I didn't add any additional "Gain" when listening. Just a pure power from the amplifier. PC volume was at 80 %. On the amplifier "Bass knob" was left at default position and the volume knob on the amplifier was at around 70-80 %.

I don't have hardware and software to measure response, but songs that has a lot of extended bass like hip-hop, house, etc. felt pretty good. There was a lot of pressure in the room and the punch was soft and clean. However with some songs I had a weird interaction. During those songs for some reason DSP showed that output reaches +5 to +12 dB for a split of a second and I could hear a lot of distortion and clipping. During distortion/clipping I didn't add any more volume. Actually I tested and it didn't matter how much volume on the PC or amplifier. I could hear them at any volume. It felt like some kind of resonance from the enclosure. Any ideas what could that be?


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Subwoofer T/S parameters taken from data sheet (attachment). Amplifier doesn't support 4 ohm load, however it was just for a test run and I will not use it to power that subwoofer. I wanted to buy T.Amp E-800 to drive subwoofers at home, however someone said it lacks bass coloring so I hesitated and didn't order it together with my DSP.


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Test only or not, 'sounds' like an amp problem, though read that this basic model has some issues with its preamp: DSE A2760 wattage? - General Hi-Fi Discussion - StereoNET

Anyway, not much into the tech side of electronics other than having experienced what hooking up amp sucking 4 ohm woofer drivers to cheap 8 ohm only amps can do, so will leave that to others.

I'll have a look-see with the sub design later. Did find a revised set of specs dated 10/04 with a generally weaker motor, so will try both: https://www.rockfordfosgate.com/rftech/library/2004/5_subwoofers/1230_50197b_rf_p1p2svc-man.pdf

I mean it makes sense if that is an amplifier issue. I will update a post after testing it with a proper amplifier that is certified at 4 ohm. Before this enclosure I had another one with V1=37 l, V2 = 37 l, Port = 300 cm^2 x 30cm and I didn't had any issues while listening in the car with Ground Zero GZTA 2155x amplifier. So it's safe to assume this is because of amplifier. I have tested DSP with the same amplifier but with Visaton BG20 8 ohm speakers and didn't had this issue.