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Teeny tiny PA 15" subwoofer
Teeny tiny PA 15" subwoofer
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Old 29th April 2015, 05:34 PM   #21
tb46 is offline tb46  United States
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Hi Chris,

After looking (quickly) at your PA thread: I know you want the subwoofer as small as possible, but would giving up a little low end, and increasing the size to Vnet=100L make sense if that would give you a TH? I'll attach a quick Hornresp simulation. Don't know when or if I'll have time to draw a fold for this soon, I have been thinking about something like a small THAM15 (THAM15 ~ Vnet=150L), or a symmetrical TH? The SPL chart is the TL v. the TH, both @ Xmax.

Regards,
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File Type: jpg TL_v_TH_SPL.jpg (30.1 KB, 501 views)
File Type: jpg TH_small_Input.jpg (37.5 KB, 489 views)
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File Type: txt TH_small.txt (979 Bytes, 11 views)
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Old 29th April 2015, 09:24 PM   #22
chris661 is offline chris661  United Kingdom
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Hmmmm...

I'm not sure, to be honest. I think I'd rather have the extension and use multiples to get SPL up - there's no way a 60Hz box could make it to 40Hz well.
A pair of the 40Hz TQWTs you've drawn up would match a single 60Hz box for output while staying in Xmax, but do the extra LF.

I suspect the problem here is that I've spent a lot of time working with a Nexo Alpha system that's installed in a fairly small nightclub. The double-18s are flat-to-40, and still do something useful in the 30s, and we have 3 per side, for about 500 people IIRC.
I'm trying to match that experience where the bass sweeps down and keeps going, with a couple of 15"s that have to fit in a small car. Compromises must be made somewhere, I just don't know where yet.

Chris
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Old 29th April 2015, 10:43 PM   #23
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by tb46 View Post
Hi Chris,

After looking (quickly) at your PA thread: I know you want the subwoofer as small as possible, but would giving up a little low end, and increasing the size to Vnet=100L make sense if that would give you a TH? I'll attach a quick Hornresp simulation. Don't know when or if I'll have time to draw a fold for this soon, I have been thinking about something like a small THAM15 (THAM15 ~ Vnet=150L), or a symmetrical TH? The SPL chart is the TL v. the TH, both @ Xmax.

Regards,
You're going to have a lot of chuckles trying to shoehorn a 15" driver into a 100L TH .

How about this - a 50 Hz single-expansion TH that fits into a 6.8 cu.ft. total box (smaller if you opt to use thinner ply in some sections). I took a guess at the driver's physical measurements.

It can't be made much smaller, because then the baffle panel won't be long enough to hold the driver....
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Old 29th April 2015, 11:39 PM   #24
tb46 is offline tb46  United States
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Hi guys,

I was just pondering. :-) You are probably both correct, the box would not go low enough, or be small enough.

Regards,
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Old 30th April 2015, 09:13 AM   #25
chris661 is offline chris661  United Kingdom
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I suspect Brian meant the 15" wouldn't fit into the TH nicely. He's probably right - I had a lot of headscratching when trying to get an isobaric pair into pretty much anything.

Still haven't decided if I want low or loud, but definitely small - my main mode of transport is a VW Polo with the back seats dropped.

I wonder if 4x tiny sealed boxes with the drivers facing inwards (magnet venting) would give me anything useful. Would certainly be tiny, but maximum SPL could be an issue at LF. Plenty >60Hz though:
4x 30L sealed boxes, 80v RMS each;
124dB @40Hz
130dB @60Hz
133dB @80Hz

113dB@20Hz, too.

It does nudge past Xmax slightly, but could almost be usable.

Some dynamic EQ could get the job done, giving lots of extension at low volume, and gradually cutting out the bottom end as SPL increases.

Chris
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Old 4th May 2015, 12:39 PM   #26
chris661 is offline chris661  United Kingdom
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Wonder if this is possible with some dynamic EQ settings on the DCX/DEQ.

Click the image to open in full size.

All 4 drivers, 35L sealed per driver, driving to ~14mm one-way travel. They go really non-linear around 20mm one-way, so nudging 28mm p/p sounds doable - that'd be the onset of clipping of the NU6000DSP, so these are absolute maximum SPLs in 2pi @1m.

Power:
Click the image to open in full size.

Excursion:
Click the image to open in full size.

Not sure on the highest frequency one, since the impedance peak is close to the peak in output, so voltage swing would limit before much current is drawn. I based the maximum power for that one on excursion, but it could be optimistic.

Anyway, I'm looking at around 117dB to ~26Hz, 125dB to 40Hz, or 130dB to 55Hz, from 140L of little boxes.

The "Really Quiet" one says to me I could probably use these for HT and get extension into the teens.


So, how would I go about getting the dynamic EQ to do this?
Or would it be better to just have a few different settings on the DCX?

Is 4x tiny sealed boxes even feasible? - it looks pretty good to me, particularly having a system that can be scaled very easily.
I know it doesn't get the most out of these drivers, but there's a lot more flexibility there compared to tuned systems, where the low cutoff is where the bass stops completely. Being able to use them for HT is a plus, too. Not sure how I'd mask the magnet vent noises, though. Hopefully the sound of things rattling will cover it.


Chris
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Old 4th May 2015, 02:12 PM   #27
tb46 is offline tb46  United States
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Hi chris,

It should be easy to set up an experiment for your sealed x4 idea. Don't quite like the idea of no driver protection, when you add driver protection you might just as well turn the dirvers w/ magnet facing inwards? How about 2 each way, and a way to plug them together similar to djk's PPSL? Either way you'd be giving up a lot of SPL v. a vented box. I happen to prefer the sound of a sealed box, but for PA?

Regards,
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Old 4th May 2015, 03:58 PM   #28
chris661 is offline chris661  United Kingdom
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I'd be giving up a lot of SPL at LF, for sure. But I have the cone area and power available to make up for some of that.
4x sealed would do roughly the same as 1x tuned cabinet of the same cutoff. However, with the sealed design I can choose a higher cutoff and go louder than a box tuned lower.
Alternatively, I could push an awful lot lower.

I'd probably sink the baffle into the box by the depth of the driver, so the magnet is near the grille. That adds ~180mm to a box that's only 230mm deep. Not great, though there might be a better way of doing it. I don't want to be dissipating 1kW into a small sealed chamber, though - that's just abusive.

2x sealed in a dual-opposed configuration is of interest to me - the moving mass isn't small, and even my 40Hz OD-QWT attempt can jump around a hard floor.

Having reviewed Art's thread on inverting drivers, I think I'd like to keep the odd-order harmonics. Lower distortion is nice, but I'd prioritise a smooth distortion profile first. Could be an interesting experiment though.


To give an idea of the SPLs I run at so far, I'm hitting around 122dB @1m peaks out of my midbass drivers, one per side, sim'd in a 4pi space. In reality, they're often near walls/ceiling, so actual SPL may be higher. NB - I'm running them 100Hz-1kHz.
Fane International Ltd Loud Speakers

So, I'd like something that'll do 122dB peaks per side, in 2pi. 2x 15" sealed will do that with a -3dB of 41Hz. Though that'd be 2x15" a side - non-trivial to transport.
I was hoping I could get away with 1x15" a side for smaller gigs, which would be a pair of cute little cubes with not-inconsiderable LF heft.

I have some scrap 1x15" cabinets here, so I might do some experimenting. If a pair of sealed cabs can keep up with my 1x15" QWT thing, I'll probably go ahead with 4x sealed boxes. A pair of those 1x15" QWT cabs would cope with pretty much any gig I've had so far, including small outdoor festivals. Used it upstairs in a pub last night with a bridged PV2600 for 1800w and things were rattling.

Chris
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Old 28th May 2015, 06:30 PM   #29
chris661 is offline chris661  United Kingdom
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Okay, so I'm still mulling this over, and starting to get pretty silly.

I took a right-angled isosceles triangle, 300mm on each short side, gives me a 450cm^2 area. Put two of those big-face to big-face, and you've got a square box section with a 45 degree board down the middle. Starting to look like a TH. Stick an expansion on the end to get exit velocity down, and you're all set.

One of these with a ~2m path length looked rather promising for a single driver - it'd be a box 35cm x 35cm x ~1.2m, ~95dB@2.83v, and flat to 40Hz. At 61v, it runs out of Xmax, doing 122dB.

Then I remembered you can put 2x isobaric pairs into the same cabinet as one driver. That doubles my available air displacement, giving me 128dB at 61v per driver, at Xmax. Of course, I'm using 4x the power here. Still easily done with an NU6000, though - put a pair of drivers on each channel. Some heavy-duty 4-core would be in order.

If I push past Xmax, this is a 120L box that will pass 130dB down to 40Hz (15mm peak travel gives 132dB in passband), and, with neodymium drivers, shouldn't weigh the Earth (though I'd guess around 40kg, which isn't light when it comes to stairs).


Now, since I'd be dissipating around 1kW per driver, I was thinking of cutting through the cabinet wall and getting the magnets to vent externally, perhaps with a grille over them. Of course, I'd seal the venting channel from the cabinet.


Crazy enough to work, or just plain crazy?

Chris

Edit - Hornresp inputs...
TH1;
S1,2,3,4=450
S5=900
L12=40
L23=160 (to be played with)
L34=40
L45=20 (haven't chosen a way to flare it yet, so this is TBC.

Last edited by chris661; 28th May 2015 at 06:44 PM.
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Old 28th May 2015, 09:07 PM   #30
BP1Fanatic is offline BP1Fanatic  United States
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Try

S1=206.45, S2=309.68, L12=20.32
S3=722.58, L23=203.20
S4=825.80, L34=20.32
Eg=69.28

16" x 2" throat to 16" x 8" mouth for 8 feet, F3=40hz, 127.5L, 25.5" H x 17.5" W x 23.75" D.

Last edited by BP1Fanatic; 28th May 2015 at 09:15 PM.
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