It's Carnival time and...

[Brian Steele]

...I'm going to be out taking pictures on Carnival Monday and Tuesday - not just of the revelers, but of the music trucks. I want to get involved in setting up one of those trucks next year (my brother manages a Carnival band, amongst other things) and I'm looking for ideas.

So... what would you put on the average flatbed truck to convert into a rolling music platform to provide sound at nightclub level to about 150 or so revelers in front of and behind the truck? .

To give you an idea of what I'm up against, the typical solution deployed on a music truck here is 15" and sometimes 18" "scoops" side by side at the back of the truck for for the bass matched with anything that can be scrounged up to handle the rest of the frequency range (usually bungie-corded on top of the scoops and at other locations around the truck). The result is midbass at chest-pounding levels, but almost nothing under 50 Hz or so, and the top is usually overdriven and, well, "sucky". Thing is, a lot of the "soca" music out these days is starting to include stuff below 50 Hz which these scoops can't produce all that well, and I'm tired of hearing distortion. I want to put together something that can reach at least 40 Hz if not lower, at the same levels those trucks are capable of - basically an earthquake on wheels . And of course I want the top to be clean as well.

Ideas?

[Music is life]

If what you mean is DIY, Bill has some nice DIY bass bins and tops.

The simplest possible DIY sub is this:
http://www.parts-express.com/pe/show...number=290-598

in a 5cu ft box. You would be below 45Hz and have a sensitivity of about 99db with a power handling of just over 400 watts.
IMO you do not need to go below 40Hz. I bet you those "scoops" are very weak even at 50Hz.

Others may have some other ideas.

[Brian Steele]

If what you mean is DIY, Bill has some nice DIY bass bins and tops.

The simplest possible DIY sub is this:
http://www.parts-express.com/pe/show...number=290-598

in a 5cu ft box. You would be below 45Hz and have a sensitivity of about 99db with a power handling of just over 400 watts.
IMO you do not need to go below 40Hz. I bet you those "scoops" are very weak even at 50Hz.

Others may have some other ideas.

Thanks for the feedback. That Eminence 15" looks like a great driver. For bass I definitely want to get to 40 Hz if possible, based on some of the samples of the music I've heard so far. Perhaps four of those 15" drivers in tapped horns might do the job...?

While my brother might be more "comfortable" with off the shelf stuff, economics will likely come into play here (shipping and duties can easily at 250% to the price).

[billfitzmaurice]

Ask on my Forum, http://billfitzmaurice.net/phpBB3/, one of our members does a float at Mardi Gras in New Orleans.

[dotzs]

That kind of bass can be done outside but more than 150 people will hear/feel it.Pulling permits will be the hard part along with generators and their placement and sound levels that seep thru open mics.

Scoops and horns were designed to not go down that low,they were made for the days when a few hundred watts of clean power was very expensive .
I would go with short throw speakers (lots of them for coverage where you want coverage ) then ad true sub woofers till you get what you need.you will spend many hours anchoring the gear even though the truck moves slowly ,wind is another quotient to deal with .

maybe a generator just for the subs will be wise ,most of your power consumption will be for the low frequencies .

[Brian Steele]

That kind of bass can be done outside but more than 150 people will hear/feel it.Pulling permits will be the hard part along with generators and their placement and sound levels that seep thru open mics.

Scoops and horns were designed to not go down that low,they were made for the days when a few hundred watts of clean power was very expensive .
I would go with short throw speakers (lots of them for coverage where you want coverage ) then ad true sub woofers till you get what you need.you will spend many hours anchoring the gear even though the truck moves slowly ,wind is another quotient to deal with .

maybe a generator just for the subs will be wise ,most of your power consumption will be for the low frequencies .

Thanks for the FB, Dotz.

The mechanics of strapping the speakers to the truck - I'm going to leave that to someone else to manage .

Instead of generators and pro-audio amps, I'm thinking class-T type autosound amps. I did notice last year that a few of the music trucks didn't seem to have any type of generator on them at all - they were obviously taking power from the truck itself, rather than a separate generator.

At the moment I'm leaning towards BFM OmniTops for the top end and tapped-horns for bass, using the same bass drivers if possible (to take advantage of bulk purchase discounts and make driver replacement a bit easier).

I have about 8 months to work with, and that's if my brother gives a thumbs-up on the project, so I've got a bit of time to change my mind .

[wg_ski]

Thanks for the FB, Dotz.

The mechanics of strapping the speakers to the truck - I'm going to leave that to someone else to manage .

That will be the bulk of the liability. You'll need some of that industrial strength webbing they tie down pallets or cars with. A stack of speakers won't go anywhere at highway speed properly tied down.

Instead of generators and pro-audio amps, I'm thinking class-T type autosound amps. I did notice last year that a few of the music trucks didn't seem to have any type of generator on them at all - they were obviously taking power from the truck itself, rather than a separate generator.

That's probably why the systems were so distorted - underpowered. You need a BIIIIG class D (T) car sub amp - most competition amps don't put out much into 8 ohms even bridged - they typically run into sub-2 ohms to get the kW output levels. And horn loading just tends to raise the impedance.

At the moment I'm leaning towards BFM OmniTops for the top end and tapped-horns for bass, using the same bass drivers if possible (to take advantage of bulk purchase discounts and make driver replacement a bit easier).

Good plan overall - but I doubt you should use the same sub driver as mids unless you seriously compromise both. The subs either need a 15 or long-throw 12's or 10's. Neither option is best for the tops.

I have about 8 months to work with, and that's if my brother gives a thumbs-up on the project, so I've got a bit of time to change my mind .

8 months goes by in the blink of an eye - don't underestimate how much time it will take to complete such a project.

[billfitzmaurice]

At the moment I'm leaning towards BFM OmniTops for the top end and tapped-horns for bass,using the same bass drivers if possible

Drivers well suited for tops are not well suited for subs, and vis-versa.

[dotzs]

The only luck I've had with a car amp is my pricey one hooked to 12 inch 2 ways and I don't push any bass to speak of because its just people speaking.

The generators provide real power and when the gear isn't being used in the truck you have a land P/A -sound proofing the generator can get their volume down to a low roar but car amps are grungy unless you buy very good ones and go with the extra batteries the auto sound gang go with.

The power ratings of auto amps is a total stretch also and P/A gear wants real and clean power with some dampening factor ......Let me know when you fire up the system -I wanna hear it in L.A.

[wg_ski]

The power ratings of auto amps is a total stretch also and P/A gear wants real and clean power with some dampening factor ......

True. A suitable car amplifier would claim fifteen or twenty thousand watts (into 1.3 ohms or something), be about 3 or 4 feet long (fills the entire trunk), have 2/0 gage power hookups and a 300A fuse, and cost about $4,000. About the same real power as an EP2500 (or a CA-9). A little "1000 watt" car amp is 100 into PA cab impedances, if that.

The Honda generators run pretty quiet - especially when lightly loaded. Which is when the music is quieter. Cranked, it should drown out the generator. Resist the temptation to cover them with something because you do NOT want carbon monoxide build-up. They're designed to be run open-air. When people improperly use them in RV and marine apps without the proper filtration, people die. The same thing could happen here.

[Brian Steele]

Drivers well suited for tops are not well suited for subs, and vis-versa.

I've come up with a TH for the 12" Deltalite driver recommended for the OmniTop 12 that can theoretically do 120dB from 30 Hz to 100 Hz without exceeding Xmax according to HornResp. Efficiency is predicted to be just above 106db/1W/1M. I'm trying to see if I can push the cutoff point a bit higher (40 Hz) to improve peak output in the passband without introducing too much ripple. Your site doesn't provide a peak undistorted SPL figure for the Omni12 or a diagram displacement graph for 1W input, so I'm not sure how good a match this might be for it. However, perhaps a short 40Hz TH with two Deltalite 12" drivers might do a better job of keeping up.

[Brian Steele]

The only luck I've had with a car amp is my pricey one hooked to 12 inch 2 ways and I don't push any bass to speak of because its just people speaking.

The CEA-2006-rated car amps will provide their rated power, and sometimes more, into their rated loads.

My intent is to be able to use these speakers for a land P/A as well though .

[billfitzmaurice]

I've come up with a TH for the 12" Deltalite driver recommended for the OmniTop 12 that can theoretically do 120dB from 30 Hz to 100 Hz without exceeding Xmax according to HornResp. Efficiency is predicted to be just above 106db/1W/1M. I'm trying to see if I can push the cutoff point a bit higher (40 Hz) to improve peak output in the passband without introducing too much ripple. Your site doesn't provide a peak undistorted SPL figure for the Omni12 or a diagram displacement graph for 1W input, so I'm not sure how good a match this might be for it. However, perhaps a short 40Hz TH with two Deltalite 12" drivers might do a better job of keeping up.

I would not use a 2512 in a sub, and 120dB is about 6dB shy of pro-sound requirements.

[Brian Steele]

I would not use a 2512 in a sub, and 120dB is about 6dB shy of pro-sound requirements.

That's why I was considering two in a 40 Hz TH rather than 1 in a 30 Hz horn TH. Should easily exceed 126dB with ~ 100W.

Or I can shift to something based on the Deltalite 15 instead, the driver you use in the OmniTop 15.

[Brian Steele]

BTW, one of the music trucks can be seen at the video embedded in this page: http://spiceislandertalkshop.com/tal...es/651046.html. Looks like 4 18" scoops below and some tops of Selenium design above. The distortion in the sound is actually caused by the camera's input being exceeded by the SPL level from the truck.

Rain affected the turnout quite a bit, so they've rescheduled the pageant part of this year's Carnival to Saturday. Quite unprecedented.

[DJ Big Ronn]

Brian, I have a lot of expierience with floats and flat bed trucks. I normally DJ 4- Mardi gras floats a season as well as Christmas. I wouldn't use car amps, because they will tax the alternator that is powering them severly. Use prosound amps and a generator. I run 4- DR 250's and two T-48's V-plated. I would use four subs, but I am very limited for space. On most of the floats, I have to stand the subs upright and put the tops on them and it still rocks. If you can fit four, then do it ! If you have questions, fire away.

[Brian Steele]

Brian, I have a lot of expierience with floats and flat bed trucks. I normally DJ 4- Mardi gras floats a season as well as Christmas. I wouldn't use car amps, because they will tax the alternator that is powering them severly. Use prosound amps and a generator. I run 4- DR 250's and two T-48's V-plated. I would use four subs, but I am very limited for space. On most of the floats, I have to stand the subs upright and put the tops on them and it still rocks. If you can fit four, then do it ! If you have questions, fire away.

Hi Ronn:

Thanks for the feedback. Yes, the effect of the current draw on the truck's alternator is a concern. Still, that doesn't seem to have stopped some of the chaps here. Some of the others have gone in the other direction - I saw a truck with one of those 11kW diesel standbies strapped on to its tray once for power - it took up almost 1/3 the space, LOL.

Do you have any experience with tapped horns? I notice that the T48 is about 97dB/1W/1M around 40 Hz. While fiddling around with some TH alignments, I came up with one that theoretically does just under 110dB/1W/1M at the same frequency, using a Deltalite 2515, and reaches 126dB (50W input) across its passband before Xmax starts to be exceeded. Response above 100 Hz goes to crap though . I don't know what size it will be though - the TH is 276 cm long with an Sd that varies from 747 to 1542 cm^2. I'm still fiddling with the parameters to see if I can get a better 40 Hz horn with the same driver.

[wg_ski]

T48 will do a whole lot better than 97dB/W at 40Hz in groups. You just need to get enough mouth together to support the frequency. Single-driver TH won't do much better all by its lonesome on a flatbed. If you're running Hornresp and using 0.5 Pi radiation, that's corner loaded or group-of-four on the ground. Put in 4 Pi, and that low end droops (and excusrsion goes through the roof).

[Brian Steele]

T48 will do a whole lot better than 97dB/W at 40Hz in groups. You just need to get enough mouth together to support the frequency.

Agreed. I was comparing apples to apples - one T48 against my theoretical TH

Single-driver TH won't do much better all by its lonesome on a flatbed.

My plan is to use at least four.

If you're running Hornresp and using 0.5 Pi radiation, that's corner loaded or group-of-four on the ground. Put in 4 Pi, and that low end droops (and excusrsion goes through the roof).

Good call on HornResp - I was using 0.5 Pi radiation. 2 Pi would actually be better for modelling purposes, come to think of it. I switched to 2 Pi and the low end response actually flattened out a bit, but peak linear output dropped to just above 115dB. Of course, if I use four of them...

[billfitzmaurice]

Good call on HornResp - I was using 0.5 Pi radiation. 2 Pi would actually be better for modelling purposes,.

Good luck finding a corner with 28 foot walls to either side on a flatbed.
2 pi is the only way to model. Always figure on worst case, never best case, unless you know you'll be indoors with a corner available.
BTW, there's nothing magical about a tapped horn. What they achieve in response they give away with excursion. A tapped horn has maximum excursion at Fc, a sealed chamber horn has minimum excursion at Fc. That's why, with the exception of the Table Tuba, I don't use them.