BillFitzmaurice.info

Hey guys,

I have a friend who wants me to help him build a T24. We're gonna load it with a single 3010LF. Just looking at the cheapest options for him to be set up well, I found a cheap 2nd hand DCX and also a cheap 2nd hand Crown XLS 402. He already has an amp for his stereo tops (home use).

The 402 only puts out 300W per channel at 8 ohms, which is not quite enough to bring the 3010LF to full noise. Is it ok to bridge this amp (8 ohm bridged mono = 900W / 85V) to get the driver to full noise? Obviously this is now way too much power for the driver, so the next question is, does the DCX have enough limiting capacity to bring the limit down to 55V?

Thanks in advance.

Dan,
There's a few things to consider going this way, ie bridging.

1. Don't bridge wherever possible, unless it's the only way to get the required voltage swing.
At least one of the main reasons for that line of thinking is that, if an amp non bridged is capable of transients 10 times the RMS output value, then the same amp is also capable of 10 times the output value when bridged!

2. Limiting bridged output. IIRC the DCX can limit by up to 24dB. That should allow the 30V reduction in output you require when bridged, BUT, you don't want to end up with a situation where, because of a large amount of limiting required to reduce voltage adequately, the system ends up hitting the limiter constantly (vs not just occasionally). You can have to much amp!
Hitting the limiter constantly sounds terrible.

3. In the plans it states that T24's should be used in multiples of two.
By and large, that's because the temptation is to keep turning up. You wouldn't want to flog one to death.

What's the application mate?

I only ask, because 300W/8ohms is 42V and that's the spec in my Jands 920's as well. If the 402 is similar, that will be 450W/4ohms, and, it turns out, that equals a limiter setting of -6dB on the DCX for a result of 35V, perfect for the budget line of speakers like the BP102...

Grant Bunter wrote:Dan,
There's a few things to consider going this way, ie bridging.

1. Don't bridge wherever possible, unless it's the only way to get the required voltage swing.
At least one of the main reasons for that line of thinking is that, if an amp non bridged is capable of transients 10 times the RMS output value, then the same amp is also capable of 10 times the output value when bridged!

2. Limiting bridged output. IIRC the DCX can limit by up to 24dB. That should allow the 30V reduction in output you require when bridged, BUT, you don't want to end up with a situation where, because of a large amount of limiting required to reduce voltage adequately, the system ends up hitting the limiter constantly (vs not just occasionally). You can have to much amp!
Hitting the limiter constantly sounds terrible.

3. In the plans it states that T24's should be used in multiples of two.
By and large, that's because the temptation is to keep turning up. You wouldn't want to flog one to death.

What's the application mate?

I only ask, because 300W/8ohms is 42V and that's the spec in my Jands 920's as well. If the 402 is similar, that will be 450W/4ohms, and, it turns out, that equals a limiter setting of -6dB on the DCX for a result of 35V, perfect for the budget line of speakers like the BP102...

The proper way to deal with an amp with too much power is to reduce gain after the limiter, and set the limiter with the reduced gain structure necessary for it to sound right. Some dsps have this option, but dcx doesn't. You can do it at the amp trims, but thats risky. The few times I've done that, I've put a tamper cover in place to prevent problems.


One of these days I'm going to make a comprehensive video on gain structure and system tuning. When I get a roundtuit.

Here ya go!

Hey Brent,
Thanks for chiming in.
I wish you would use Tom's roundtuit because I would love to see how you're achieving this.

What's getting in the way of fully comprehending (inside my head) is:
The limiter should be the last thing in the chain.
That way, whatever anyone does, your drivers survive.

Now you're saying to alter gain post limiter, and, protective cover or no, in my world, some clown would work out how to totally mess that for me because they have a leatherman in their pocket...

Grant Bunter wrote:What's the application mate?

I only ask, because 300W/8ohms is 42V and that's the spec in my Jands 920's as well. If the 402 is similar, that will be 450W/4ohms, and, it turns out, that equals a limiter setting of -6dB on the DCX for a result of 35V, perfect for the budget line of speakers like the BP102...

We are beefing up his home stereo, which currently consists of 2 old wharfdale floor-standing 2 or 3 ways with crackling woofers. I figure once crossed at 100hz ish the floorstanders will sound better/go louder without breaking up (if not, we'll replace the woofers, then they will sound better). He likes to play vinyl records and is planning to start learning how to mix with vinyl on 2 turntables, although he only has 1 at present for listening duties. The T24 will be corner loaded 95% of the time, and also most of the time only be used at relatively moderate volumes. The exceptions being the odd party here and there. This is why I suggested to him to build just the one cab for now. He wanted something relatively small.

I suggested the T24 with the premium driver because of the temptation to turn up; it can go a fair bit louder with the 3010LF than the BP102. That, and it just makes sense to put the absolute best driver in something that has had so much time and effort put into it

The BP102 is no slouch. My 1 shakes the house before full tilt. Build it as wide as possible and use the appropriate amp for the job. Used amps always pop up on CL or other places.

jimbo7 wrote:The BP102 is no slouch. My 1 shakes the house before full tilt. Build it as wide as possible and use the appropriate amp for the job. Used amps always pop up on CL or other places.

Thanks Jimbo, this is good to hear, and confirms that we've made the right choice by going for the premium driver as we're considering about 18-20 inches width due to room constraints.

Grant Bunter wrote:2. Limiting bridged output. IIRC the DCX can limit by up to 24dB. That should allow the 30V reduction in output you require when bridged, BUT, you don't want to end up with a situation where, because of a large amount of limiting required to reduce voltage adequately, the system ends up hitting the limiter constantly (vs not just occasionally). You can have to much amp!
Hitting the limiter constantly sounds terrible.

Grant, I was looking around for an appropriate amp and it occurred to me that it might be a cheaper option for him to go with an amp that had lower output but could be bridged to get to where one would need to bring full noise with the 3010LF. I have already purchased the driver (got a cracker deal too).

If the bridged 402 is not optimum (but at $180 it's certainly well priced), could you recommend something that would be appropriate, and not cost over $AUD500?

Most pro amps I've looked at either don't have enough at 8 ohms (and if they do, they're creeping up towards $1k), or have way too much in bridged mono 8 ohms. I'm going round his house this week to have a look at his pioneer 5.1 AV amp, it may be enough for now anyways, I just don't think it'll be rated more than 120W ish at 8ohms. Enough for listening but he'll want more especially since he knows the cab can take more.

The other side of the equation is that I only know the setup that I have. This means I can only recommend a passive system with an active crossover, for anyone: pro sound or home user. Should I be recommending the DCX / DBX + amp combo or is there another combo that I could be considering that might be cheaper, yet achieve what these active crossover units can do with limiting, parabolic / graphic EQ, delay, routing etc?

I also note that a brand new Crown XLi 800 does 600W bridged mono 8ohm, which is only 69V. Is this a more realistic figure for the DCX limiter to handle? At $AUD459 brand new, it's alot more expensive than our 2nd hand $AUD180 option, but also is newer/has warranty etc. Hmm what-a-to-do!

The last generation Crown XLS series would be a good choice. You should be able to pick up an XLS1000. In bridge mode, it would be about the right power and they are going cheap.....don't know if you'll be able to find any where you are.

OUCH!!!

Just tried finding the XLS in AU. The sites I saw are still trying to get over $600 for 'em. You can pick 'em up here for $159 on Amazon.....

Yeah man, we get ripped off 'ere down under. You can see why I bought all my amps from the US. XTi4002 is (brace yourself) $2300 here. Ridiculous eh?

Another question regarding bridging. I see with crowns there is no speakon for bridge mode (there is on the crest amps). Do you make an adapter with speakon on one end and bare wires on the other to put into the bridge ports of the amp? Seems a bit crappy to me. I hate bare wires with a passion.

commander_dan wrote:Yeah man, we get ripped off 'ere down under. You can see why I bought all my amps from the US. XTi4002 is (brace yourself) $2300 here. Ridiculous eh?

Another question regarding bridging. I see with crowns there is no speakon for bridge mode (there is on the crest amps). Do you make an adapter with speakon on one end and bare wires on the other to put into the bridge ports of the amp? Seems a bit crappy to me. I hate bare wires with a passion.

In bridge mode, Ch 1 serves as the output.

That said, I use the binding posts on all my amps.....that's because they are in a rack with a rack panel on the back - the connections at the amp are NEVER touched....speakon nor xlr input. Stuff doesn't go wrong when you keep your hands away from the back of your gear. Build it right once and enjoy trouble-free operation from now on.

Now to mention that setup time is much faster.

Yeah, I know this doesn't really matter much in a home setup - more important to those setting up and tearing down.

Ok, channel 1 serves as the output. How do you go to bridge mode? (sorry for the noob question but I've never bridged before, just assumed you hook into the bridge binding posts on the back of the amp!)

commander_dan wrote:Ok, channel 1 serves as the output. How do you go to bridge mode? (sorry for the noob question but I've never bridged before, just assumed you hook into the bridge binding posts on the back of the amp!)

Timeout......

I'm sorry, I thought you were talking about the XLS drivecore series....are we discussing the old XLS 402?

The drivecore amps have DSP, so all you have to do is set it for bridge mode and use channel 1

On the old style xls 402, you must use the two red binding posts for bridge operation.