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Item: See below
Location: South Sydney 2226
Price: See below
Item Condition: New like
Reason for selling: Analogue dreams
Payment Method: Pickup - Cash, Paypal, COD Only
Gustard U12 USB / SPDIF XMOS convertor 32 bit 384k (New in opened box) $180 posted
Open DRC DA8 - DAC, room correction and 4 way electronic crossover and by Minidsp (New like, had a fiddle but has not been set up - with original box) $SOLD (will cost you $460 delivered from minidsp)
Photos from web: OpenDRC DA8
I'm considering plans for a new DIY project that's a variation on the portable boombox concept, hopefully with a more linear frequency response due to higher quality drivers and equalisation and (possibly) digital crossover using MiniDSP.
The other major difference would be that the system would be modular, i.e. each driver would be housed in its own box, as would the mimiDSP/battery/PS/amp, and all would slot and fix together making them usable as either a portable boombox, or, at home, a 3 component (2 x speakers + 1 x amp/crossover/psu) system.
It won't be dirt cheap, but I do want to keep costs down and try to achieve similar sound quality to a similarly priced consumer hifi system, so around 300-350€ (I'm in Germany these days, hence the Euro) or a bit more if I go for a more complex design.
Similar projects have been written up extensively online as 'DIY boomboxes', but the main differences I'm considering in my build are:
- the addition of a MiniDSP chip (or two) to improve the frequency response and (possibly) to replace the passive crossover with an active crossover
- the use of modular boxes, allowing the system to be utilised as separate components
I've chosen the PC165F because they are coaxial (making them easy to deal with) and relatively sensitive (91.9db @ 2.83V/1m), yet (according to Focal at least) have a reasonably linear frequency response and decent dispersion characteristics, as well as sufficient bass extension. On the other hand, I'm concerned about the high resonant frequency (70hz) and the high magnitude of the resonance peak (over 50 Ohm), especially given this will be powered off a cheap battery. So at this stage I'm also open to other driver suggestions.
Input will be stereo RCA (or 3.5mm jack) into MiniDSP.
From there, I am considering the following options:
(1) MiniDSP as EQ (only) / 12V lead acid battery
The MiniDSP would be used simply to create a high pass (maybe 40hz) filter, compensate for baffle step, and iron out frequency response problems in the mid and (particularly) high range.
I would house the coaxial drivers in well constructed 10-15 litre MDF boxes, and use either sealed boxes or more likely ported boxes, tuned (hopefully) to around 50hz. The MiniDSP would provide a quite steep high pass filter at 40hz-ish, and some EQ to compensate for baffle step and iron out irregularities in the response.
This is the concept in a microsoft paint drawing:
The basic equipment I have in mind for this is as follows:
1 x MiniDSP 2 x Focal PC165F 1 x Hifimediy T1-M TK2050 1 x 12V UPS lead acid battery 1 x switching PSU
With this configuration, I have these questions:
Is it a good idea to use a 12V UPS lead acid battery for something like this? The basic reason I have it in mind is that it's cheap (around 10-15€) and easily replaceable. Are there better ideas for the battery?
If I do use such a battery, how do I set up the system to: (1) run off the PSU when plugged in and switched on, (2) charge the battery when plugged in and switched off, and (3) run off the battery when unplugged?
I'm an electronics novice but a patient learner. Is this something I can realistically and safely achieve?
Is there a simpler way of doing this that I'm missing? For example, is there a ready-made battery/psu that I could choose that would recharge and provide power to the system at the same time, so that I don't need the PSU or any kind of switch?
The miniDSP also needs to draw a small amount of power from somewhere. Where would this come from and how would I make it work?
These drivers have slightly odd parameters as I mentioned before:
Will that very high magnitude resonance peak be a problem for a relatively low powered amp like the Hifimediy T1-M running off a 12V battery?
The amp is 57w into 4Ohm with a 24V DC supply, but where the resonance peak is it would be running off a 12V DC supply into probably at least 40 Ohm (I am assuming that the heavily damped ported box will move the resonance up a bit from 70hz and reduce its magnitude somewhat).
My understanding of how this amp works is that it might struggle to produce much power in this frequency region, is that right?
The driver parameters suggest a ported box will work better, and since these are going to be midwoofers, ports would make sense from the point of view of efficiency. Can anyone see a problem with using a 10-15L box with damping material, with a 5cm diameter port tuned to quite a bit below the Fs (hopefully 50hz), and a digital high pass filter just below the port tuning frequency?
(2) Extra amp and sub
This would involve adding an additional monoblock chip amp and a small high-efficiency sub, which would most likely be housed in the central unit with the battery and amps etc. This would change my power supply needs, but I'm not sure I understand how. Assuming I found an efficient D-class monoblack 50w or 100w change amp, how would I calculate my power requirements? Would there be any chance of sticking with the 12V lead acid battery or would I simply need to abandon this idea?
And does anyone have any suggestions for a decent, small (ideally 8 inch) and efficient subwoofer and amp for this arrangement?
(3) MiniDSP as crossover
This design idea would be very similar to (1), but in this case the miniDSP would split the input between the woofers and tweeters and replace the passive crossover in the driver unit. There would be an additional Hifimediy T1M amp giving a total of 4 channels.
My question here would again be about the battery and PSU. If I were now powering two Hifimediy T1-M's off one PSU or battery, how would that change my power requirements?
Would I need a more powerful battery? If so, how powerful would it need to be, and does anyone have any idea what I might use?
(4) Extra amp and sub / 2 x MiniDSP
This would be the most complex setup and would involve housing an additional sub in the central unit, adding a MiniDSP to create a 2.1-way crossover, and adding an additional sub amp.
My question about power supply / battery is similar to my question about the extra amp in design (2) and (3). How would I calculate my power requirements? Are there any suggestions for batteries / PSUs?
(5) 2 x sub / 2 x MiniDSP
This is basically like design (3), but there are 2 subs instead of one and an additional stereo amp (rather than a mono amp) to power them. The subs would either both sit in the central unit or would have their own boxes, ideally also not much bigger than 10-15L in size. I guess my questions about this design are basically the same as for design (3).
Many thanks in advance.
There are endless forums on miniDSP products and as such I'm hoping to save a few hours reading.
I am thinking about integrating my SVS SB13 Ultra into my 2 channel set up and if I do i was considering giving my amp and speakers an easier time by filtering lower frequencies.
All I want is to put a xover between my DAC and integrated (not interested in doing room correction with miniDSP. I am considering room correction with either acourate > HQplayer > microrendu/ SOtM) So either the 2x4 or 2x4HD is what I am looking at but open to other considerations being models or other brands/solutions. The sub has a lot of DSP processing too so I don't need miniDSP to handle any of that.
My question is.... is adding this going to be detrimental to sound quality by the introduction of noise or anything else audible that will outweigh the gains of the amp and speakers having an easier time?
Are there other solutions or crossover devices I could use instead of miniDSP? Maybe Behringer?
I know there is DEQX but it is a bit of overkill if I am happy with my pre, DAC and streaming.
Any help would be greatly appreciated