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DIY subwoofer - input problem

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#1
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!
 
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#2
I am neither knowledgeable in this nor have neither actual experience. I am just thinking out loud here ;)

I am guessing you'll need to calculate/estimate the sensitivity of your sub design, i.e. dB SPL per volt into the sub driver. Too bad the Dayton amp manual doesn't list its maximum gain, but we can make a guess as to what voltage input will give full output (or ask Dayton). Once we have these numbers we can calculate the overall sensitivity of the powered sub system (from line level input to dB SPL). Compare that to the value of the main speakers + amp. If the powered sub has higher sensitivity, you should be good to go. Otherwise, you'll need a passive pre-amp or some other means to attenuate the line level signal to the amp for the mains.
 
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#3
I am neither knowledgeable in this nor have neither actual experience. I am just thinking out loud here ;)

I am guessing you'll need to calculate/estimate the sensitivity of your sub design, i.e. dB SPL per volt into the sub driver. Too bad the Dayton amp manual doesn't list its maximum gain, but we can make a guess as to what voltage input will give full output (or ask Dayton). Once we have these numbers we can calculate the overall sensitivity of the powered sub system (from line level input to dB SPL). Compare that to the value of the main speakers + amp. If the powered sub has higher sensitivity, you should be good to go. Otherwise, you'll need a passive pre-amp or some other means to attenuate the line level signal to the amp for the mains.
thanks a lot for your answer, i was browsing the Dayton website and I found another possible solution, it's a "downgrade" to the SPA250 non-DSP version. The SPA250 has speaker level inputs that could possibly solve the problem, what do you think? Will the quality still be high enough?
https://www.audiophonics.fr/en/haut...-subwoofer-amplifier-module-250w-p-10294.html
or also the Monacor version which has a bit more power: https://www.audiophonics.fr/en/subw...tive-subwoofer-module-420w-4-ohms-p-7722.html
I've asked Dayton however if it's possible to reduce the gain at the XLR outputs via software, maybe they can consider it as a part of firmware update... It should be simple to add this function.
My fear is that the sub still hasn't enough power margin from the speaker amp since both speakers and sub have the same sensitivity rating of 91dB/V, plus bringing the sub amp close to 0dB could possibly add noise.
 

Juhazi

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#4
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https://www.parts-express.com/pedocs/manuals/300-8010-dayton-audio-spa250dsp-user-manual.pdf
Looks like a nice unit, and being able to set delay for main speakers is a valuable feature! If your room is not very large, you can also consider making the sub sealed, it's much smaller. Have you read this? https://www.audioholics.com/subwoofer-reviews/svs-sb16-ultra
Not being able to adjust volume of mains is not a problem, at least I haven't heard of such
Sadly it's a big room, it's an attic without walls with nearly 1000ft2 of surface, that's why i chose a 15" driver in a reflex configuration.
My main concern was not being able to reach full power since I use a lower voltage on the XLRs rather than standard fixed level.
 
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#6
https://www.parts-express.com/pedocs/manuals/300-8010-dayton-audio-spa250dsp-user-manual.pdf
Looks like a nice unit, and being able to set delay for main speakers is a valuable feature! If your room is not very large, you can also consider making the sub sealed, it's much smaller. Have you read this? https://www.audioholics.com/subwoofer-reviews/svs-sb16-ultra
Not being able to adjust volume of mains is not a problem, at least I haven't heard of such
@Juhazi When I looked for the Dayton plate amp manual, I obviously looked at the incorrect version (the non-DSP one). Thanks for the correct link.
Sadly it's a big room, it's an attic without walls with nearly 1000ft2 of surface, that's why i chose a 15" driver in a reflex configuration.
My main concern was not being able to reach full power since I use a lower voltage on the XLRs rather than standard fixed level.
@filo97s I apologize. Read the wrong manual :(. The SPA250DSP does offer a lot of beneficial features over its non-DSP sibling. Besides adjustable delays, you have full control of the high-pass filter for your mains. The non-DSP version only gives you a fixed 6 dB/octave 125 Hz HP filter for the high level output, and no filtering for the line level out. (It seems that the SAM-300D offers no HP filtering for both main outs.) I think you'll be better served by a steeper slope HP filter with a lower cutoff frequency (e.g. 80-100 Hz, depending on the size of your current mains).

My gut tells me the SPA250DSP is the better choice, and I agree with @Juhazi that lack of volume adjustment for the mains is unlikely a problem. With the DSP amp, while not ideal, you do have the option to boost sub output by playing with the PEQs :). And, if you so desire, you can also room EQ your sub (by manually adjusting the PEQs).
 
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#7
Good news, the gain for the SPA250DSP is 40.2dB @100Hz 1W output, the gain of the Anaview is 27.5dB @1kHz 4 ohm load. Then everything SHOULD be fine since there's a 13dB margin + another 15dB that derives from an "improper" use of the parametric EQ. Seems ok, isn't it?
 
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