Hi, In the past months I felt that my system lacks something, then I realized that doesn't have the bass impact I wanted. I've looked around for a sub but the really good ones are quite pricey so since i love DIY projects, i've done some calculations to build a sub using a Dayton RSS390HF-4 and a Dayton SPA250DSP amp module. First of all, has anyone tried them, how they perform?
Math led me to a dual configuration: a bass reflex sub SBB4 aligned with Vb of 180 liters, Fb of 21Hz and F3 of 20.5Hz using a dual 75mm x 275mm reflex port (is this enough to prevent air blowing? Increasing diameter is not that easy because the length will increase too) which can be closed if necessary, leading to a sealed sub Bessel BL2 aligned with a Qtc of 0.577 and an F3 of 35Hz. Feel free to suggest something here, very happy to hear some comments, but this is not the point:
I'm actually using a power amplifier based on an Anaview class D module for the speakers, wired in XLR, the volume then must be regulated prior with the DAC. My question is: how can I use the full power (or at least, how can I be sure that the sub will not play lower than the speaker amp) if I send a volume regulated signal into it? Apparently, looking at the SPA250DSP manual, it can do a lot of things but the XLR outputs (those that go from the subwoofer to the speaker amplifier) cannot be lowered in volume.
Thanks!
Math led me to a dual configuration: a bass reflex sub SBB4 aligned with Vb of 180 liters, Fb of 21Hz and F3 of 20.5Hz using a dual 75mm x 275mm reflex port (is this enough to prevent air blowing? Increasing diameter is not that easy because the length will increase too) which can be closed if necessary, leading to a sealed sub Bessel BL2 aligned with a Qtc of 0.577 and an F3 of 35Hz. Feel free to suggest something here, very happy to hear some comments, but this is not the point:
I'm actually using a power amplifier based on an Anaview class D module for the speakers, wired in XLR, the volume then must be regulated prior with the DAC. My question is: how can I use the full power (or at least, how can I be sure that the sub will not play lower than the speaker amp) if I send a volume regulated signal into it? Apparently, looking at the SPA250DSP manual, it can do a lot of things but the XLR outputs (those that go from the subwoofer to the speaker amplifier) cannot be lowered in volume.
Thanks!
The Dayton RSSxxxHO series is great. I don't have experience with the RSSxxxHF series, though the differences appear to be that the HF series is designed for larger enclosures: lighter cone, weaker motor, more compliant suspension. This woofer could use a heavier amplifier than 250 W if you want to extract all of its output.
To check if the ports are sufficiently large, use this tool: Flare-it - Free Speaker Design Software
Building a large enclosure to obtain a certain Qtc isn't necessary if you have a DSP available. Just correct the response with the DSP and you end up with a system with the same transient response. The same applies for a vented box: it does not need to have a flat response. Feel free to tune as low as you want the subwoofer to go and make a box as small as you want. You 'pay' for these by sacrificing efficiency and possibly maximum output.
If the subwoofer plays at a lower level than the main speakers, just increase the gain in the subwoofer channel.
To check if the ports are sufficiently large, use this tool: Flare-it - Free Speaker Design Software
Building a large enclosure to obtain a certain Qtc isn't necessary if you have a DSP available. Just correct the response with the DSP and you end up with a system with the same transient response. The same applies for a vented box: it does not need to have a flat response. Feel free to tune as low as you want the subwoofer to go and make a box as small as you want. You 'pay' for these by sacrificing efficiency and possibly maximum output.
I'm not sure that I understand what you mean. You can control the volume before the signal is sent to the subwoofer. Then the outputs on the subwoofer will also be volume controlled. If you connect the (main) speaker amplifier to these outputs, the main speakers will also be volume controlled. The main speakers and subwoofer volume levels will track each other.
If the subwoofer plays at a lower level than the main speakers, just increase the gain in the subwoofer channel.
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thanks a lot for the answer! I've tried the software, it calculates the air velocity inside the port given a certain diameter, and it seems ok since using 75mm x2 return a maximum speed at 25Hz of 12.4m/s (chuffing is at 12m/s but i think it's acceptable). Shouldn't it depend also on listening volume and power? How can it estimates the air velocity without knowing the cone used?
My main concern was due to the fact that at the sub xlr input the volume is lower than the XLR standard (since it's regulated for the main speaker amp), then it's possible for the sub amp to output a lower power than the main amp even when set at 0dB.
Let's say you have two amps, we know that for the XLR standard, you have to provide 4V rms at the input of both in order to obtain the maximum rated power. If you provide for example only 1V rms, you can't reach the full power and it's possible that at 0dB on each amp, there's one of the two that has an higher output power.
However I later checked the datasheet of both amps, the dayton has a gain of 40.2dB (@100Hz, 1W output) and my main speaker amp has a gain of 27.5dB (@1kHz, 4 ohm load), so there's a good 13dB margin between the two, the dayton SHOULD still play louder.
Calculate the air velocity for a given port in WinISD at max power. Then enter these velocities in Flare It. 2x 75 mm seems to be too small for a 15" subwoofer.
great, thanks. I've found that dual 75mm should be okay for a max power of 80-90W, after this turbulence and compression can occur. The problem is that using a dual 100mm port it's not that practical because the length of the port should be 63cm, which is longer than the box itself (which is 60cm) and it's difficult to find such a long reflex.
the ports i'll use will have dual flares, these: Condotto Reflex per casse acustiche O 75mm, 04951, tithome
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