BillFitzmaurice.info

I've decided that my first build will be a T24. I've read through the plans a couple times which made me start thinking about driver selection and how to power em.

Quick background. The T24 (hopefully plural) will complement a pair of JBL Eon 515xt's that we have on a rental rig. We find the built in mixers and look to be attractive to the rental world. The JBL's by design have no low end, they roll off around 100 Hz. Our mentality in regards to rental is that it has to be simple. We are trying to keep a rack full of equipment from intimidating anyone or scaring them off. It would be our desire to rent out the T24's. I certainly understand that placement is more important with horn loaded subs, but really feel like some sub is going to be better than no sub if a renter would setup it up in a non ideal fashion.

I'd like to build with the BP102 driver for starters. Primarily for initial (or replacement) cost. I plan on building 2 single driver cabs for starters. I currently have no amplifier or processing equipment for these subs. I've been considering getting a lower power, 2 channel amp and running each driver on it's own channel. Something like the Crown XLS1000. My thought process was to use the on-board crossover to low pass the signal at 100 Hz and utilize the amplifier max output to limit the power to the speakers. I believe that whether I choose a 4 or 8 ohm driver would factor into this equation. My goal would be to prevent overpowering the drivers and prevent the need for additional processing. It looks like if I chose the 4 ohm driver and the 350w @ 8 ohm XLS1000 my max voltage would be 37V (or do I need to figure this at 6 ohms?). If I chose the 8 ohm driver at 215w I would expect 42 volts. If that is an appropriate way to evaluate that, I'd choose the 8 ohm driver. What other factors do I need to consider and what amp do you think I should choose?

I'm certainly new to this world and looking to learn. My goals for this initial project are to compliment a small DJ setup for weddings, parties of up to 300 people. I'd like to avoid additional processing for complication and cost reasons. (I also want to know if that is a big mistake)

T24 will probably not keep up with the JBL in output, especially when placed improprely.

A reccomendation:

Since this is for the rental rig, and placement isn't going to be ideal, use Simplexx 15 or 18 and stick Bash 500 plate amps in them. You'll need to add transformer isolated XLR jacks to the plate amps (not a big deal really) or supply a cabling solution to do that, but they have a sufficient crossover built in and you won't have to worry about setup for the client, or blown drivers (use sturdy drivers in the Simplexx cabs).

The result will be more like what the client is expecting, you still get the savings of DIY, and you won't have as many blown drivers to deal with (you can safely assume that stupid renters will destroy T24s, even with precautions taken).

kpeyton wrote:The T24 (hopefully plural) will complement a pair of JBL Eon 515xt's

'Hopefully plural' should read 'absolutely plural'. The power and size demands on a speaker double with each one octave lowering of frequency. One ten inch loaded T24 is not going to keep up with a pair of 15 inch loaded mains.

I would not rent Tubas or Titans. They do not distort when pushed too hard, they just die without warning. That's not an issue with skilled operators using limiting per the plans. But when dealing with renters you must assume that they are terminally stupid and that they don't give a crap if they destroy your speakers. At least with direct radiating subs they will hear them distort well below where they'll blow. They'll probably ignore it, but they won't be able to say that they couldn't hear the magic smoke coming. I agree that Simplexx would be better. To keep up with a pair of 15 loaded mains you will need a pair of S18s.

My thought process was to use the on-board crossover to low pass the signal at 100 Hz and utilize the amplifier max output to limit the power to the speakers.

Think again. Amps are power rated at very low THD. They can put out far more than their rated power when pushed into clipping, and with rentals they will be.

I also read your intro thread.

The JBL's by design have no low end, they roll off around 100 Hz

This isn't strictly true if JBL's own specs can be considered to be correct.
According to:
http://www.jblpro.com/ProductAttachment ... 11.web.pdf

the 515XT's response at +3dB is 42Hz to 18K
and the SPL chart on the same page shows response at 80Hz to be 100dB and 95dB at 60Hz.
While that is falling off, response isn't dropping like a brick.

I certainly understand that placement is more important with horn loaded subs

No, placement is important with all subs. You can get more output for free with direct radiator subs as well, using the sub sticky rules:
http://billfitzmaurice.info/forum/viewt ... f=10&t=398

You can utilize the sticky in your rational.
For example, if you plan to have a pole on sub situation for the Jaybees, then, if you only put in one tophat, provide one pole, and add a stand for the other Jaybee, and tell renters that the subs should be together because it will sound better and louder, well, you see where I'm going.

I also agree on some simplexx subs.

But just to fill you in a bit more on why, lets look at what you proposed intially:
The BP102 driver;
The 8 ohm version is displacement limited in Bill's designs to 35V (at a specific High Pass frequency, depending on the amount of cabs) and IIRC, the 4 ohm version is limited to 27V.
You can't just look at amp output alone because of this, as per your own calculations, even the XLS 1000 is capable of putting out more than the above voltages. Without limiting, that = blown drivers.

Maximum excursion in Hz in a sub doesn't occur at it's upper end of operation, but it's lower end.
That's where a brick wall limiter is required to protect your investment in drivers and build time.

Since you don't want an overly complicated rental system, or a large rack of gear, that means you don't want to include the required limiter.
So I would stay away from any cab that requires limiting.
One could argue that all subs should be limited!

Cost saving is a relative thing.
Repairing (if that's even possible) or replacing blown drivers on a constant basis comes out of your own pocket (while you argue with the renter over who blew them and why), so you can keep the rig running for the next hire. However, if you protect your rental system with a processor in a rack that you blank off so no one can alter settings, it may cost you more initially, but be cheaper in the long run...

For rentals, I'd use an amp like the Peavey IPR 1600 DSP. It can be set up and the settings locked so that it can't be tampered with.

The amp won't put out much over 50 volts even on a good day, and won't clip, which works just fine for a pair of bp102's in series or maybe a 3012LF or something.

From the IPR user manual:

"The IPR™ DSP allows the user to safely lock the settings of the
amplifier (Fig. 27). This feature can be extremely useful when using the
IPR DSP in an installation environment, preventing unwanted persons
from changing the settings and potentially damaging the speakers. The
user can choose to disable the security lock, lock ALL DSP settings, or
lock ALL of the settings EXCEPT the volume controls (input attenuators).
If the security lock is engaged, users will be prompted to enter the
security code before being able to edit any of the DSP settings. The
control screen will automatically relock when the user returns to
the main menu. Please contact Customer Service if the lock code is
forgotten or misplaced. "

Maybe the XLS1000 has a similar feature not sure.

Even so I'd STILL hesitate to rent out any pro system without my being there....