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Old 1st January 2014, 12:44 AM   #11
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Quote:
Originally Posted by giro1991 View Post
What method would we say we preferred for music? Ported or Sealed?

Is that a seperate amp? googled QSC 1kW and it came back with 600 quid amp...?

Not keen on ported if low cut is required as my mains can only do -3 @ 50...

Thanks for the replies.
Low cut would be for the subwoofer. It cuts off frequencies below 15Hz, to stop the driver from even trying to produce those, because all it'll do below port tuning is produce distortion.

Both sealed and ported alignments will need some kind of signal processing. You'll have to implement a crossover (easy enough - its just a couple of op-amps), and then the sealed cabinet will need eq to get a flat frequency response (look up Linkwitz Transform), and the ported will need a steep low cut below port tuning.

Have you downloaded WinISD yet?

For amps, here's something that'll do:
Samson Servo 550 Audio Amplifier | eBay
More than I paid for my QSC, but those are very good amps. I thrashed mine and it just sat there and took it.

2nd hand PA amps are perfect here. The class AB ones have huge power supplies and plenty of heatsinking, and therefore weigh a tonne. PA users are in a hurry to get rid of them, as newer amps are much much lighter, so I tend to pick them up where I can.

My QSC is a USA 850, which is good for a little over a kilowatt when driving low impedance loads. They don't come up so often, but when one appeared in a 2nd hand shop, I knew I had to have it.

Choosing an alignment "for music" is very vague. What sort of music, how loud, what're the size constraints?

A sealed box like mine (~16" cube external) is pretty domestically acceptable. For those unused to subwoofers, its a bit large. It replaced a 15" 6th order bandpass PA subwoofer (the size of a medium fridge), so its considered small around here.
A ported box will provide much more output than a sealed cabinet (or, lower distortion for the same output), but is also much bigger.

HTH

Chris

edit - oh lookie here
edit2 - looks like the link's not working. Search QSC USA 850 on eBay

Last edited by chris661; 1st January 2014 at 12:48 AM.
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Old 1st January 2014, 03:29 AM   #12
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Quote:
Originally Posted by chris661 View Post
Have you downloaded WinISD yet?
Yes I did, I'm assessing the options, the diy approach, you suggest the QSC amp (though quite big) would require a box, driver and filter combo I understand.
If the cost/performance this way is better than say the BK XXLS400 then why not.
I know I'd need to implement a crossover for Mid-bass to Sub-bass either way. My father's familiar with this aspect so should be a doddle with his help.
Quote:
Originally Posted by chris661 View Post
What sort of music, how loud, what're the size constraints?
Space wise, I have a whole corner of the room... or I could have a sub under the 'coffee table' perhaps.
The room is 4x5m, if the system is level, I don't want 80dB or near deafening levels due to the nature of the space.
I know about that already by running my mids+highs without real bass, having a degenerative physco-acoustical effect on my hearing. Before I realised 'I need a subwoofer' I messed around and experienced some ear ringing.
So, optimum power for size of room.
IIRC a room acts as a secondary box so I'll use calibration after also, unless calibration software (REW+omni mic) by itself can do all the work in the first instance.
As for music...
50% is 'compressed' music whatever that is, typical CD material since 90s I guess all genres, but also older dynamic recordings.
I plan on getting LP deck in future also, I did consider digital crossover using PC but LP capability would be nice.

Excuse the depth here I'd like to get this right first time, I think it's great that such a place with expertise exists.

Sealed or ported whichever sounds more 'natural'? Thought I think this is probably just a figment of my imagination thus far as I have never compared either.
As another member said, as long as its accurate, thats what matters.

Last edited by giro1991; 1st January 2014 at 03:50 AM.
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Old 1st January 2014, 11:50 AM   #13
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The seperate amp will need to be hidden away somewhere, or you could build it into the subwoofer enclosure itself.

There's plenty of space inside the QSC amp, so I'd suggest tapping off the internal power supplies for the op-amps already there in order to implement your crossover. You can get PCBs on eBay that'll do the job nicely, or use stripboard to make your own. Either's fine.

I'd head toward a sealed cabinet, for simplicity of construction. I tried a 75L ported box with one of my JBLs, and getting a big enough port in there was a nightmare - I used a 60mm by 200mm port, which had to be folded twice to fit in, and it still wasn't wide enough to avoid wind noises at higher levels.

With a sealed cabinet, there's no bottom limit to how low they can go. The maximum volume just gets more limited the lower you ask them to go. So, you could start by using a Linkwitz Transform to get to fc=20Hz, Qc=0.5, and see how that sounds. Not enough before you run out of headroom?
Go up to 25Hz, or get more cabinets.
The QSC amp is rated to power 4 JBLs (2 in parallel, per side), so you could do two small sealed subwoofers if that took your fancy.


FWIW, I checked out the BK subwoofer that you mentioned. The drivers in there each cost the same as 2 JBLs. Driver-for-driver, you'd get lower distortion from the Peerless XXLS driver they use. With 2 JBLs, you'd level up the playing field a bit. The JBLs would ultimately go louder, but the Peerless may still take the edge in lower distortion.
Either way, its 120 in drivers**. The amplifier can be almost anything, so long as it has plenty of grunt. The bit that matters at the electronics side is the processing.

** or you could build a couple of seperate 1x12" JBL subwoofers for a similar cost to a single Peerless. If you spread them around the room, you'll get a flatter frequency response as room modes are excited more evenly. One in the corner and one under the coffee table would likely give better performance than a 2x12" in the corner.

Even once narrowed down to sealed and 12", there's still lots of options available.

Chris
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Old 1st January 2014, 03:53 PM   #14
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Quote:
Originally Posted by chris661 View Post
There's plenty of space inside the QSC amp, so I'd suggest tapping off the internal power supplies for the op-amps already there in order to implement your crossover.
Ok, so this crossover you speak of is a Linkwitz–Riley HPF at 20hz, correct?

I'm not confusing this with the XO later on in the spectrum circa 100hz I'd need for connecting 'Bass' and Mids am I.
I was always confused about what to call this range and after hours of reading I concluded that the terms (Sub/Low/Mid and Bass/Mid) vary in systems depending on ones taste/expenditure.

Personally I like to think for avg. person like me;
Sub 0-100 (one for starters)
Mid 100-3500
High 3500-20000hz
is sufficient for entry level enjoyable sound.

For some a forth bi-amped 'range' exists, which is where I got confused.
I like to think regardless of this you can never have enough 'defined' parts of the sound spectrum.
Theoretically you could have a pair of speakers for every single hertz in the spectrum and a room with Forty-thousand speakers, Twenty thousand for each stereo channel, lol... But,
Looking at the logarithmic scale, I see three decades so I say a pair for each and be done with it.

I had 2.1 system which eventually broke but sounded phenomenal for 35, I think Logitech nailed it with the assignment of driver size relative to the spectrum, I think it was a 5inch sub and 2x2inch mids/highs. 'Balanced sound'.
But I then needed something with more bottom end and more robust obviously.

Quote:
Originally Posted by chris661 View Post
The QSC amp is rated to power 4 JBLs (2 in parallel, per side), so you could do two small sealed subwoofers if that took your fancy.
That QSC amp starting at 50 on ebay is tempting.

Quote:
Originally Posted by chris661 View Post
Even once narrowed down to sealed and 12", there's still lots of options available.
Probably will stick to sealed 12" as you say, for simplicity, however just one for starters and upgrade to two time permitting .

Stuck between suggested REF1260W and JBLGTO1214 Though?

and thanks again for your time and knowledge.

*Post edited by Moderator at Member's request
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Old 1st January 2014, 03:59 PM   #15
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Messing about with winISD now too, looks neat. Will read the manuals etc.
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Old 7th January 2014, 02:56 PM   #16
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Got the QSC USA 850 tank from ebay for 113 delivered

8 ohms, 255 watts (850 watts bridged)
4 ohms, 425 watts

Reading summary on Hoffman law on this thread and will take this into account when designing the box.

Should I go 4 or 8ohm chris? I think as suggested automotive woofer would allow more headroom as they are 4ohm.

Thanks
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Last edited by giro1991; 7th January 2014 at 03:10 PM.
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Old 7th January 2014, 04:59 PM   #17
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A few things:

1) You are making an electronic crossover, right? Passive sub crossovers cannot work due to the impedance peaks of the sub and satellites. Unless you make passive filters at the inputs of the amplifiers, which could be easier than messing about with opamps.

2) 850W bridge for 113! Nice! That seems like a REALLY low price, especially delivered.

3) Do not believe that lower impedance is always better or will give more headroom.
In fact, it draws more current out of the amp, therefore generating more waste heat inside the amp. And therefore likelier to clip the amp or run out of the safe operating area of the transistors. My experience from many years in car audio was that amps rated to run at 2 ohms *might* on a good day with a tail wind deliver 1 dB more peak power, at the price of a lot more heat and a lot more current out of the battery. This was even so of amps which "doubled their power" from 4 ohms to 2, because when you actually measured such amps what you found was the 4 ohm spec was underrated in order to make it appear the power was doubling. Plain-technology amps like the 850 won't be any different just because they are running from 120V instead of 12V (maybe somewhat less heat in the power supply section).
Having said all that, 4 and 8 ohm woofers of the "same" model always have different specs. If the Thiele-Smalls are somehow the same, it means likely the excursion (voice coil overhang) or some other factor is different. So pick the woofer(s) that will work for you and don't worry about which impedance is "better"-the amp is beefy enough to run either impedance.
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Old 7th January 2014, 11:16 PM   #18
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head_unit,
The QSC amp will (just about) drive 2ohm, but will only give ~550w/ch. It'll bridge into 4ohm, 1100w, but will get very hot doing it: the manufacturer recommends extensive testing under these conditions before being put into permanent use, as there's a fair chance it'll go into thermal protect (ie, it'll shut down) operated like this.

giro, that rather depends on how many drivers you'll eventually have, but I'd go for 4ohm. You're never going to overload that QSC, so you'd be safe enough running it into a 2ohm load if you end up with a pair of drivers in parallel per side.
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Old 9th January 2014, 04:09 PM   #19
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Please excuse if this a double post.
----

Quote:
Originally Posted by head_unit View Post
A few things:

1) You are making an electronic crossover, right?
Ye, though I definitely prefer active crossover at line-level over a passive crossover for simplicity.
Quote:
Originally Posted by head_unit View Post
2) 850W bridge for 113! Nice! That seems like a REALLY low price, especially delivered.
Thank Chris for suggesting,
Quote:
Originally Posted by head_unit View Post
3)So pick the woofer(s) that will work for you and don't worry about which impedance is "better"-the amp is beefy enough to run either impedance.
I understand. For time-being I would like to stick to just one woofer.
Because QSC is bridgeable at 8ohm would it not be a good to use all the power available, as opposed to making one channel redundant?
I wont be driving the system to beyond 90dB (or 80dB considering how small the room is).

I'm unsure on final Low Cut frequency because I live in an
end terraced (✓) bungalow (✓) but multiple neighbors quite close.
I don't not know what 25hz sounds like never mind 20hz.
I know for a fact that these levels will be obvious through concrete, but how much I'm not sure .

Also, however acheived it'll involve line level active xo/filtering as suggested. See below for my idea regarding a 4way, which I think would be a much simpler approach considering they can be customer-defined on ebay for good price.

Click the image to open in full size.
Sorry if it appears as if I'm asking alot but I'd like to get this right, and the way I see it anyone else reading is also enlightened with (y)our help.
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Last edited by giro1991; 9th January 2014 at 04:27 PM.
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Old 9th January 2014, 04:18 PM   #20
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*there was* a 4way PCB but it's proving un-re-findable...
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