Would love some help: DJ fold-back - trapezoidal, stereo, single cabinet.

[psin3t]

Hi all!

I am aware that this does not fit the ideal kind of high fidelity requirements of many, but as a 'Weddings.Parties, Anything' DJ and entertainment services guy, this is about finding the best workable solution to the given problem. That means cost, DIY, design, mobility and size, using currently owned drivers etc. Please join in and throw about your advice!

A pic of a home-made PA is attached, consisting of:
JBL 12" S3-1224 sealed sub.
Lanzar Evo294 Class AB amp plus 850W AC/DC powersupply.
2x Faital Pro 12FH520 12" mid-bass.
2x JBL Pro Selenium ST400 tweeters.
SYNQ DIGIT 2k2 amplifier.

It is a tiny portable system I built. Works amazing and measures amazing once setup for a space, and very sensitive. There is good feedback from average people - 'big' sound, 'detailed' and very happy. But bums wiggling is all that matters. I have been hobbling together foldback from old powerful book-shelf speakers, but they do not cut it if and when the punters want the FOH/sub louder for more raucous moments.

So - I have 2x 150mm 4 Ohm drivers to build into a cabinet. They are to provide the DJ/talent with the mid-melodic content from the front-of-house, that is muffled from the performers. Any good DJ/musician requires it during a paid performance. It is also so the DJ doesn't keep turning up the volume and ruining the FOH sound-stage. Essentially it is for one or two people back behind the FOH - on a desk, housed in a trapezoid-shaped cabinet, pointing from desk-to-ear, directly at the DJ/talent. Weight is less of a problem than size as a design requirement.

Here are the drivers I will need to use for the DJ fold-back (on hand):

http://prvaudio.com/wp-content/uploads/2015/04/PRV-Audio-6MR500-NDY-4-Datasheet.pdf

I will probably just power it with a Behringer A500 amp I have lying around that is in quite good condition. 230W 4 Ohm per channel. Combined, the SPL will blow-away my old fold-back. But how to design the cab?

I will open up the floor with a broad request of 'What would YOU do?' - given the above. Remember - you are the 'talent'/DJ, and you need it to help your performance shine. There are (loud) FOH and sub in front of you, pointing at the dance-floor/sound-stage. Those are full range and all sealed.

Thank you for your advice.

 

[xrk971]

I put the 5MR450NDY in a Nautaloss sealed spiral and it sounded great. No back chamber coloration. The 5MR can go to 15kHz and be full range. No tweeter needed. I have also put the 5MR450NDY into a tractrix horn. Now, that had to be the cleanest sounding 115dB/2.83V I ever heard. Zero distortion so you couldn’t tell it was loud. I came away with my ears ringing.

For your DH/talent monitor purposes I think the traxtrix would sound awesome for vocal clarity. Plus it is directional. It’s big though. Second choice is the sealed Nautaloss.

PRV 5MR450-NDY for FAST applications

Here is Nautaloss:

PRV 5MR450-NDY for FAST applications

 

[perceval]

If I get this right, fold back is a monitor.

Once I went with IEMs, I never went back to the traditional on stage monitor setup.
Each can get their own mix, no chance whatsoever at feedback, and it saves everybody's ear drums by playing a lot softer than a traditional monitor setup.

 

[psin3t]

I can agree, certainly for instrumental or vocal talent or multiples thereof. But my brain just temporarily broke trying to work out how to give DJ's in-ear monitors and a headphone/cue channel.......

 

[psin3t]

Here is Nautaloss:

PRV 5MR450-NDY for FAST applications

Hulllooooo....

Two of these as close to the DJ, and as close together as possible, powered by a Behringer A500 but with the PRV 6MR500-NDY-4, might be just what I want. Certainly powerful enough if needed....

The idea is to give the DJ a better sonic image of what the dance-floor is hearing, so they don't try to 'compensate' for their bad listening position, by fiddling with the FOH mix, turning it up and thereby making the dance-floor 'blaring' and 'tinny'.

I suspect it will rarely reach 25% output, except during witching-hour thump parties. But during these times, articulation of what the main-floor is hearing is crucial for the DJ to be properly in-the-mix, out the front.

 

[chris661]

Small ported box, tuned to 80Hz-ish (whatever works out roughly flat), on some short stands by the decks facing the DJ.

I'm amazed you're getting by with a single sealed 12" for bass. I used some good 15"s sealed for a while, and found them lacking in output. Going ported was a serious improvement.

Chris

 

[psin3t]

I have owned 18" ported subs many times - but moving them sucks.

Not all 12" drivers are made equal And 'bass' is rarely below 40hz. Sure, you might see it, but not really hear it. Shaking things isn't really music. The sub weighs 28kg as is (active).

'Mobile', one man, no roadies, not even a trolley. Home made. Would anyone check out the driver list and calculate the SPL for me? It has been years since I did that now.

That JBL sub would be the best I have heard. I also own a heap of Richard Allen gear and all kinds of stuff. I have a very special collectors 12" driver from the early 80's supposed to be a 'best ever' from the UK....

I use Yamaha NS-7171's and Sansui B-2101 in top condition (thank you Clarke Audio) to compare anything.

I went for that sub because all competeing 'hifi' OR 'pa' speakers were not ACTUALLY subwoofers. 'Car audio' JBL sells ACTUAL subwoofer drivers (as in they cannot reproduce over 200hz due to the cone design).

I fail to see why 'pro' gear does not use them, except to keep cost down and reuse the 'sub's in two-way systems.

 

[psin3t]

I do know one reason not to use that driver (for a sub) - getting the tech specs online first, is hell - but they are in the box.

They are very good and I can scan and upload them if anyone needs. Unbelievable that you can't find them - maybe they are new?

(JBL 12" S3-1224). The forward excursion makes me..........aroused? Same deal when a punter sees them moving.

 

[chris661]

I have owned 18" ported subs many times - but moving them sucks.<snip>

With 15mm Xmax (educated guess), you can get 110dB at 40Hz. Piston Excursion calculator

I was getting similar numbers from a single 15" in a sealed box (Beyma 15P1200Nd), and found four of them was the minimum required to get a good amount of output.
That said, I was applying a Linkwitz Transform (low-frequency boost to flatten the response), so there was a lot of power going in at the bottom end. If you haven't EQ'd your 12", I expect it'll go quite loud in the 70Hz-upwards range, but the 40Hz notes will be quite a lot quieter.

Pro gear doesn't use car subs because they're often exceptionally inefficient, but good at going fairly low in a small box. In PA, we can use bigger boxes and get efficiency in the 40Hz-and-up range.

Playing around with something like WinISD will tell you a lot.

Chris

 

[psin3t]

Hey great reply. A lot to think about. I wonder how hard or worthwhile it is to go about porting the current design. I have a 100mm port lying around and 100mm pvc.

I do like being able to unpack and pack up in 30 mins alone. What are the basic requirements, considering the cab volume is set?

 

[chris661]

My advice would be that if you're happy with it, leave it be. Going ported is a bit of work, especially for long-throw drivers where you often find you need a lot of port area to keep air speeds sensible. You'd also need a highpass filter to protect the driver from over-excursion below the port tuning.
To give you an idea, for the 15"s I mentioned earlier, the port is 400mm x 125mm area, and around 700mm long (folded). It forms a good chunk of the cabinet's internal volume.

Have a play with WinISD and see what you think. I'd estimate that the cabinet you've got would be too small to do a good ported box, so if you wanted to keep a cabinet that size, I'd keep it sealed.
Try seeing what pro drivers do differently, too.

Chris

 

[psin3t]

One realistic option I have is to build a 2nd identical one, since the amp is designed to run in 2x2 Ohm at 800W RMS per channel. It might mean upgrading the power supply, but I am not sure. BTW, the specs claim that driver is 92db sens (2.83V @ 1m), with a frequency response of 25Hz-175Hz.

If they are even close to correct, is that not astonishingly efficient for the frequencies in question?

 

[psin3t]

Maybe Google can crawl this thread and help others, maybe some diyAudio'ers would like to use or just peruse:

JBL S3-1224 Specifications

Comments/thoughts on the driver data there, anybody?

Curious about peoples opinions. I will post these over on subs forum.

Yep - pretty sure you have convinced me to build the second sealed sub, and hook it up in a 2x2 Ohm config. The Seasonic PRIME 1300 W GOLD power supply provides 108 Amps at +/- 0.5% load regulation, at less than +/- 10mV ripple. That is insane and should run the amp and both drivers fairly easy.

OR - should I build a whole new PORTED cab, with the 2x 12" drivers?

 

[chris661]

One realistic option I have is to build a 2nd identical one, since the amp is designed to run in 2x2 Ohm at 800W RMS per channel. It might mean upgrading the power supply, but I am not sure. BTW, the specs claim that driver is 92db sens (2.83V @ 1m), with a frequency response of 25Hz-175Hz.

If they are even close to correct, is that not astonishingly efficient for the frequencies in question?

At 2.83v input (4w into the 2ohm load) into the 21L suggested cabinet, with Lossy Le enabled in Hornresp, I get these numbers:

94dB at 66Hz,
77dB at 25Hz.

Take 6dB off for 1w numbers.

With 35v input, you'll exceed Xmax around 55Hz, and will be doing 110dB at 40Hz. 116dB at 60Hz. That's around 600w input.

A quick comparison to the Tiny15" sub:
2.83v input (1w) gives around 95dB @1w (93dB at 40Hz, 97dB at 100Hz), and if you hit it with a kilowatt, you'll get around 125dB across the band. 40Hz (tuning frequency) is 123dB in the simulations, and there's 2dB of port compression, for a total of 121dB at 40Hz. Vent airspeed exceeds 20m/s at those power levels.

If the 12" you've been running has been more than enough for what you're doing so far, keep it! It's great that you've found something that you're happy with. If you find you're constantly needing more bass, another 12" might (might) be the way to do it.

I had a quick play around with some simulations and found these drivers quite difficult to work with for PA use. You want a tuning somewhere around 40Hz, but taking them that high means a very peaky response. It's easy to get these drivers in a big box and tune them low, but trying to run them higher up is much more difficult - it's not really what they're designed to do.

The easiest thing to try would be to add another of those 12"s in a sealed box. That'd give you 6dB more output with the least amount of fuss.

Chris

 

[conanski]

Hulllooooo....

Two of these as close to the DJ, and as close together as possible, powered by a Behringer A500 but with the PRV 6MR500-NDY-4, might be just what I want. Certainly powerful enough if needed....

The idea is to give the DJ a better sonic image of what the dance-floor is hearing,

But that isn't what a real DJ uses a monitor for, they use it sync the upcoming track to the current track so there is no need for stereo, they just need a single monitor on the opposite side from whatever ear they prefer to use with headphones.

 

[conanski]

With 35v input, you'll exceed Xmax around 55Hz, and will be doing 110dB at 40Hz. 116dB at 60Hz. That's around 600w input.

Which is a total waste of 600w IMO, any pro sound sub in a ported box will produce 10-20dB more output with the same power.

psin2t.. if you do add another sub just get a proper pro amp to drive it, simplify things.

 

[nigelwright7557]

I DJ'ed for many years and got away with a 225WRMS amplifier and four Fane 12-50WRMS speakers. Very loud and sounded good. Good enough for small to medium sized gigs.
The main thing with disco speakers is being able to move them. I started off with a 12 by 4 cabinet but it was huge and far too heavy. I split the box down into two cabinets with two Fanes in each and that was more manageable.

I never used monitors. I could hear OK what was going on.

 

[psin3t]

So many great responses. I am going to spend some time digesting it all and return.

 

[psin3t]

But that isn't what a real DJ uses a monitor for, they use it sync the upcoming track to the current track so there is no need for stereo, they just need a single monitor on the opposite side from whatever ear they prefer to use with headphones.

I guess I fail to see how any artist or, to quote - 'real DJ' - is supposed to interact with sound without a proper image of it. When I DJ I use the headphones to cue the next track. I think you will find most DJ's do this and simply alter how much of the FOH/main is in that headphone mix. Myself and many others have found that they prefer a straight cue mix of the next track in the headphones, with the 'atmospheric' audio being a decent reproduction of what the 'audience' is hearing. That makes your headphone mix the source of your next 'secret' beat-mix. It is also the essence and source of 'proper' DJing.

And since I am the main DJ on the rig, it follows.

 

[chris661]

I DJ'ed for many years and got away with a 225WRMS amplifier and four Fane 12-50WRMS speakers. Very loud and sounded good. Good enough for small to medium sized gigs.
The main thing with disco speakers is being able to move them. I started off with a 12 by 4 cabinet but it was huge and far too heavy. I split the box down into two cabinets with two Fanes in each and that was more manageable.

I never used monitors. I could hear OK what was going on.

Nigel,

While I appreciate you must really like your Fane 12" full-range units, they're not really bass drivers.

This neat little calculator - Piston Excursion calculator - tells you how much SPL a given amount of cone area and linear excursion will achieve in the bass. Being fairly generous and saying 3mm of one-way travel for the old Fanes, four of them in sealed boxes will do 108dB at 40Hz, or 120dB at 80Hz.
A modern 15" in a fairly small ported box (440x440x600mm) will do 121dB at 40Hz (after port compression), and 125dB at 80Hz.

I recently used two of those cabinets for a small gig - room was around 60'x50' in a community centre. Doors were rattling when the bass dropped, which was great because it's exactly what the organisers wanted.

Again, I get that you like your Fane full-range speakers, but I strongly suspect they'll come up short in both quality and output compared to a decent modern PA system. If you're ever passing by Sheffield, I'd be more than happy to give you a demo of such.

Chris