The high-pass will definitely be needed - the QSC filters off somewhere ~10Hz, but it'll still be putting out a lot of power at 5Hz if you ask that of it.
You could just put an 18Hz high-pass filter on the input to the 3-way board. I see no reason that shouldn't work.
I'm sure you'll like the QSC amp, and FWIW you could build it into the subwoofer enclosure. It'd need a seperate compartment from the driver(s), and suitable ventilation**, but should be reasonably easy to do. The only downside would be the weight of the finished product. The amp ain't light, and neither are subwoofers. I suppose that one's up to you.
**it'd probably be easiest to leave the front uncovered, and put a hole at the back of similar size to the fan inlet. If you put the amp and driver(s?) on the front face, a bit of speaker cloth would cover everything nicely. I'd probably put the amp at the bottom of the enclosure for stability.
Chris
You could just put an 18Hz high-pass filter on the input to the 3-way board. I see no reason that shouldn't work.
I'm sure you'll like the QSC amp, and FWIW you could build it into the subwoofer enclosure. It'd need a seperate compartment from the driver(s), and suitable ventilation**, but should be reasonably easy to do. The only downside would be the weight of the finished product. The amp ain't light, and neither are subwoofers. I suppose that one's up to you.
**it'd probably be easiest to leave the front uncovered, and put a hole at the back of similar size to the fan inlet. If you put the amp and driver(s?) on the front face, a bit of speaker cloth would cover everything nicely. I'd probably put the amp at the bottom of the enclosure for stability.
Chris
When I was cleaning out the 850, I notice alot of variable dials inside, then I look at the spec and apparently there is already sub sonic filters (thats what its called, now I know)
"selectable 30Hz, 50Hz, out"
See specs on this page...
QSC Power Amplifiers - USA 850
The 850 manual says on page 3 under DC fault protection
"The USA Series limits the response below 20Hz to protect the amp"
See this thread also QSC USA 900 Amp Question...
Not keen on touching those variables but I suspect they are filters.
Not sure how I would measure either, maybe just into a 8ohm block and measure with computer...
Also, I've decided to go for a slightly more robust peerless woofer, 10 or 12 unsure, I need to see how much wood costs
. I have some lying around at my dads...
"selectable 30Hz, 50Hz, out"
See specs on this page...
QSC Power Amplifiers - USA 850
The 850 manual says on page 3 under DC fault protection
"The USA Series limits the response below 20Hz to protect the amp"
See this thread also QSC USA 900 Amp Question...
Not keen on touching those variables but I suspect they are filters.
Not sure how I would measure either, maybe just into a 8ohm block and measure with computer...
Also, I've decided to go for a slightly more robust peerless woofer, 10 or 12 unsure, I need to see how much wood costs
. I have some lying around at my dads...
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Do not touch those variable resistors.
Chances are they're for bias current. If it works, and there's no obvious distortion, there's no real need to touch them. You could maybe try to reduce the bias to get the amp to run slightly cooler, but the gain would be so minimal that I wouldn't bother: the engineers at QSC are, I suspect, much more experienced than either of us.
Dip switches? Are you sure?
I've had my QSC open (mostly out of curiosity), but didn't spot any. I'll go and have another look to confirm, but I suspect that website is inaccurate.
Edit - just opened mine up. No dip switches in here.
Chris
Chances are they're for bias current. If it works, and there's no obvious distortion, there's no real need to touch them. You could maybe try to reduce the bias to get the amp to run slightly cooler, but the gain would be so minimal that I wouldn't bother: the engineers at QSC are, I suspect, much more experienced than either of us.
Dip switches? Are you sure?
I've had my QSC open (mostly out of curiosity), but didn't spot any. I'll go and have another look to confirm, but I suspect that website is inaccurate.
Edit - just opened mine up. No dip switches in here.
Chris
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You would think a subsonic high pass filter would be easy to find online, where can I get one?
EDIT Found DIY KIT on ESP
EDIT Found DIY KIT on ESP
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Bridged to 8 ohm should be OK. If you look at car woofers, you can also find dual 4 ohm coils. That might be good, 1 coil per channel. Then later if you want you can add another of the same sub, rewiring each for 8 ohms.
I personally would not put the subsonic low cut filter on the sub. Every filter degrades transient response somewhat. The one time you need something like that is a ported box, if you are playing music with significant content below the port tuning frequency. That is pretty rare, assuming you tune down to 25 or 20 Hz. And, if you want to be playing 16 Hz organ pipes and crazy movie demos, then you really just should use a sealed box anyway. (Sorry, in this view I can't easily see what your final box idea was, if you said)
Sealed boxes almost always imply a Linkwitz Transform (or similar), which would, left unchecked, throw out a lot of power at very low frequencies. At the very least, a first-order filter ought to be added circa 15Hz, just to make sure movie effects don't send the coil smashing into the backplate. It only need happen once...
giro, one driver or two?
If you're set on the Peerless drivers, if might be worth going for 2x10" over 1x12": that'd give you a better range of form factors, slightly higher SPL (from increased cone area), at a similar price IIRC.
If they're 8ohm a piece, I'd consider either one per channel on the QSC, or paralleling the drivers and bridging. That's only if you need more power out of the amplifier: if the amp has no problems pushing the drivers to Xmax with one per channel, there's no need to eek out the extra power - the driver displacement is the limiting factor.
Chris
giro, one driver or two?
If you're set on the Peerless drivers, if might be worth going for 2x10" over 1x12": that'd give you a better range of form factors, slightly higher SPL (from increased cone area), at a similar price IIRC.
If they're 8ohm a piece, I'd consider either one per channel on the QSC, or paralleling the drivers and bridging. That's only if you need more power out of the amplifier: if the amp has no problems pushing the drivers to Xmax with one per channel, there's no need to eek out the extra power - the driver displacement is the limiting factor.
Chris
appreciate the help chaps
Probably will use Elliot Sound PCB 99
£15 delivered from oz for the PCB (not sure if its populated, probably not).
I will go for one woofer for now and perhaps get another If I feel I need more definition.
not sure if I need 12" though it would be nice to match the performance of the 400 from bk, which looks like a 12" paper cone.
Not sure what to make of tinnitus' suggestion?
I read that the lowest musical note is 27hz on grand piano so I think 25hz cutoff is what I need. Does Win ISD take into account the subsonic filter?
I found this on the peerless 830845 (paper). Does it matter that the response is not flat in this SPL graph? I'm assuming it can do flat to 25hz (but at lower level)
Not keen on that blue curve though I'm sure REW software could finalize this.
I was hoping to d this project over 2weeks but it seems it will probably take 2 a month or so depending on how fast things get shipped out.
Cheers
Probably will use Elliot Sound PCB 99
£15 delivered from oz for the PCB (not sure if its populated, probably not).
I will go for one woofer for now and perhaps get another If I feel I need more definition.
not sure if I need 12" though it would be nice to match the performance of the 400 from bk, which looks like a 12" paper cone.
Not sure what to make of tinnitus' suggestion?
I read that the lowest musical note is 27hz on grand piano so I think 25hz cutoff is what I need. Does Win ISD take into account the subsonic filter?
I found this on the peerless 830845 (paper). Does it matter that the response is not flat in this SPL graph? I'm assuming it can do flat to 25hz (but at lower level)
An externally hosted image should be here but it was not working when we last tested it.
Not keen on that blue curve though I'm sure REW software could finalize this.
I was hoping to d this project over 2weeks but it seems it will probably take 2 a month or so depending on how fast things get shipped out.
Cheers
You can make your own circuit boards using stripboard.
Here's some reading about sealed subwoofers:
ESP - The Linkwitz Transform Circuit
Here's some reading about sealed subwoofers:
ESP - The Linkwitz Transform Circuit
Strip board would be cheaper but its not much more expensive for P71 (Subwoofer Equaliser) I think
I understand most of that page until it goes into phase nearer the bottom, I notice 'Figure 4 - PCB Version, Complete Circuit' has two op-amps in the schematic, but the picture shows one?
And I think this incorporates a subsonic filter, so 2 in 1 with the P71
Will crack on with the spreadsheet for starters anyway...
like the idea of two 10s for stereo but not sure if difference would be worth noticing over one 12" so probably will stick to one for now.
EDIT: The wood my dad has is all chip board! will need to get MDF...
I understand most of that page until it goes into phase nearer the bottom, I notice 'Figure 4 - PCB Version, Complete Circuit' has two op-amps in the schematic, but the picture shows one?
And I think this incorporates a subsonic filter, so 2 in 1 with the P71
Will crack on with the spreadsheet for starters anyway...
like the idea of two 10s for stereo but not sure if difference would be worth noticing over one 12" so probably will stick to one for now.
EDIT: The wood my dad has is all chip board! will need to get MDF...
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With 2x10", you could still use one cabinet.
You'd get slightly more output due to larger cone area, and more flexibility when it comes to wiring the speakers to the amp.
You could also put the drivers in opposite sides of the cabinet, which minimises floor vibration as the drivers are always moving in opposite directions. This is what I did with my 2x12" cube sub. Works a treat, though the floor still bounces at 14Hz
On the other hand, the cabinet itself would probably be a little larger. Its all about tradeoffs.
You'd get slightly more output due to larger cone area, and more flexibility when it comes to wiring the speakers to the amp.
You could also put the drivers in opposite sides of the cabinet, which minimises floor vibration as the drivers are always moving in opposite directions. This is what I did with my 2x12" cube sub. Works a treat, though the floor still bounces at 14Hz
On the other hand, the cabinet itself would probably be a little larger. Its all about tradeoffs.
Could the single op amp on the board be a dual op amp?
IE.. 2 op amps in one package which just need 8 pins.
Dave
Thanks for pointing that out.
Am I right in thinking the HPF goes AFTER Linkwitz LF Extension EQ?
By Extension EQ I'm referring to the P71
An externally hosted image should be here but it was not working when we last tested it.
I did input 830845 (spec pdf) into WinISD. Not sure how to accommodate the filters into the simulation.
If I HPF at 25Hz, does that mean flat to 25hz? I think so as Linkwitz seem to sum the response flat judging by a quick google search
Minimizing filters is sensible but I do need them for LP functionality to prevent 'thuds' from damaging the sub, as chris said.
Cheers
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Also, I don't want mega loud, I do live in a residential area
Why not? what the hell! If you want to enjoy music before you go deaf, or worse before death. Go for the loudest...
never mind the neighbours
Why not? what the hell! If you want to enjoy music before you go deaf, or worse before death. Go for the loudest...
Believe me when I say that going as loud as possible is a bad move.
Definitions of loud may vary, but 200w/ch into 98dB@1w speakers 3m away is uncomfortably loud. It'll drive you out of the room without earplugs.
Giro, the level at 25Hz depends on your crossover alignment. Linkwitz-Riley crossover alignments have both the high-pass and low-pass in phase and at -6dB. This produces a flat frequency response through the crossover region.
Without the complementary low/high pass, the system will be 6dB down (ie, quarter-power) at that frequency.
Might be better to aim for 20Hz LR4 (Linkwitz-Riley, 4th order = 24dB/octave). That'd leave the 25Hz output more or less untouched. You can simulate in WinISD Pro to see what's happening.
Chris
Found the answer eventually, silly me.
Could not find a way to include EQ/filters in WinISD non-pro version, I think pro version has these functions, so I've downloaded the alpha and will try again.
- See input below, not sure about "PE". I used 175 for it.
SPL graph, no filters. 50Litre box 1w/1m (like the XXLS400). Does obviously need a boost around 25hz.
Chris you suggest I put HPF at ~20hz to get 25hz, seems logical, if doing it this way leaves enough power then why not.
Will input data again into pro version as I think I downloaded the basic 1st time.
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