New Build - T30s and then Otops to follow

[Bill Fitzmaurice]

Since the resistor across the load in the plans is 30 ohm/10W, I might suggest putting 5) 6 ohm /2W resistors in series to make up the 30 ohm load. Connect the positive terminal of the tweeter array to the crossover common, and then connect the negative Piezo terminal to whatever tap at the junctions of the resistors you want for the desired attenuation. Technically this isn't an L-pad, but the piezos impedance is high enough that we can disregard the small change in resistance this creates. http://img.photobucket.com/albums/v354/ ... b82254.jpg

Not having a bunch of 6 ohm resistors on hand to try it I can't unequivocally say if that would work or not, but as the predicted dB drops seem to be predicated on the piezos offering an 8 ohm resistive load, I highly doubt it. I'd just lower the high frequency EQ.

[byacey]

I'm not sure why you mention 8 ohms; there's nothing here dealing with that value.

The calculations for voltage drop were done disregarding the piezo's high impedance as I mentioned in a previous post. They will add a slight additional load when paralleled across some point in the resistive divider, but not enough to get overly excited about in this particular application.

If you want to try a simple test, try it with the two 15 ohm resistors as I mentioned initially. This should realize close to a 6dB drop in output.

You could also use whatever combination of resistors you have on hand that will add up to 30 ohms. The values I chose were for easy calculations yielding a useful selection of attenuation values.

The whole point of tailoring the crossover is to avoid having to apply heavy handed equalization to make the box sound well balanced and natural. Most commercial manufacturers make something of an attempt to achieve this goal. My view is to minimize the amount of processing required to make the box sound good. In my experiences, if a box requires a lot of EQ to sound good, something isn't right.

I understand the concept of using lots of piezo elements in an array to minimize how hard they have to work, thus increasing long term reliability; that's a admirable design philosophy. However, if too much HF output is being produced by the over-designed array, (as the original poster is experiencing) something should be done to tame the output, keeping it in balance with the mid range component.

I should add - this resistive divider scheme will not work with a magnet / coil compression driver; the impedance is low and will load the crossover incorrectly causing the crossover frequency to change. In this instance a true L-pad must be used.

[escapemcp]

That's probably beyond the ability of the OP.

Thanks Bill for your confidence in me

Anyway, sorry for lack of posting recently, been very busy. The party happened last week and the speakers went out of the door with still-drying duratex on them! The party went well, I got several comments about how well the system sounded. I was having to use my home stereo for monitors though - a WH10 is next on the list methinks! I still felt that the PA needed a little EQ work, but that high frequency problem that you guys have been getting all worked up about wasn't anywhere near as bad as I thought it was once the system was turned up to a decent volume (as opposed to garage/workshop listening). I was at 3/4 power (on the volume dial - I wasn't measuring voltages) and the police turned up and asked us nicely to turn it down, which I did as I wanted to give the system a full (12-hour) test. It slowly crept back up and when they returned at 9 in the morning to let us know that they were going to get a section 63 (paperwork to shut us down), I decided to give it the full beans. Yeah, these things kick! They never came back so for 3 hours the system pumped it out Here's a pic from the night... but it's out of focus as I had the camera on my new phone on macro focus!



I did realize the next day that in the rush to get ready, I forgot to install both damping and the braces on the rear panel of OT#2. I will also be buying a DEQ in the next few weeks, so I can finally quantify the tweeter brightness and get the system sounding better than it did the other night (which was pretty good anyway!). Am loving the digital in of the DEQ. I will have a digital out from the mixer into the amp rack, and then take the aux out (pre-EQ) and feed that into an SD card recorder (Img Stageline DPR-110). Then take the processed signal and feed my working Behringer iNuke3000 DSP for the tops. My mixer also has a sub out which has already been mono-ed, so I will then use this (using a crossover point of 200Hz (the highest it will go)) and run it into the 2nd iNuke which will then do the 100Hz crossover. I don't want to use the one in the mixer, as I have no idea on what slope it uses - and it's very doubtful that it would be as steep as 48dB/oct.

I have built a flightcase for the CDJs and mixer as well, and I'm also using a Chord rack bag for my amp. It makes such a difference being able to sling your amp rack over your shoulder, rather than something that weighs as much as the boxes that they are driving!! By using digital outs and a few other ways to simplify wiring, I have worked out that I will have an amp rack each side of the decks. The first will be for the tops, so I will have power running from the plug into this via powercon, and then a digital in from the mixer. I will then daisy chain the power into the mixer/cdj flightcase and out into the second amp rack. The second amp rack will also need a connection for the subs and one for the monitor. All this pre-wiring of flightcases and amp racks and my simplified wiring means that my whole system will be rigged by chucking 3 boxes on the table, placing speakers and connection of 10 leads (3 power, 3 signal and 4 speaker) - all vital for when I need to set up double quick!

[Grant Bunter]

Um, sorry, but in this post ^ above I can't see any mention of a limiter????

[escapemcp]

Um, sorry, but in this post ^ above I can't see any mention of a limiter????

Don't worry... it's in the iNuke DSP... Limiting, crossover and EQ all in the amp The subs are set to -0.5dBFS (=about 45V). Tops to about 34V (-3.0dbFS). Not sure that if I set the limiter to 0dB for the subs, whether it still engages, as that would get my 50V exactly. The limiter light still seems to come on at the right point if set limiter to 0 (with sine wave and voltmeter), but with -0.5 I KNOW that the limiter is engaged - the light may have just been coming on as the amp had nothing left to give with a sine wave... with music's higher crest factor, you might get transient peaks higher than this. Any thoughts? Any way to test (thinking burst tones, but really not sure!)

[MissileCrisis]

I'm guessing by the grin on your face and the recurring cops that the event was a great success. How was the bass?

[byacey]

I still felt that the PA needed a little EQ work, but that high frequency problem that you guys have been getting all worked up about wasn't anywhere near as bad as I thought it was once the system was turned up to a decent volume

Welcome to the world of Fletcher Munson curves!

[escapemcp]

I'm guessing by the grin on your face and the recurring cops that the event was a great success. How was the bass?

The bass was good, they pumped it out all night without complaining (although my mate did say they had a rattle, but by the time I got to them to check, there was nothing.. and I kept checking throughout the night and they were fine). I did have the tops turned down to balance them out with the subs though... the V-plate is in the garage awaiting for completion tonight, so that should make the whole system more balanced. Add to that the fact that the next gig is inside in a old concrete bunker, and I am going to have some serious cabin/room gain going on when compared to the last outdoor party

Yeah, it wouldn't be a free party without the joining us at some point. They are just another problem to manage! Overall very happy with the first outing. Everything ran like clockwork and the system didn't even flinch. Can't wait to get my broken amp back. The first iNuke that I had just stopped working - it was a B-stock item, so may have been a unit with a fault and it got 'repaired' - except they repaired the wrong bit and the fault remained. From what I have read about those amps, they are pretty good, with few reports of them doing what they did with me, so hoping I just got a duff one Then I can run the whole system (well, the tops) in stereo off one amp and the subs and monitor off the other. Then I have redundancy if an amp does go south. I am hoping that they chuck my one in the bin and give me a new one... then I can use the 5 year warranty on my new one on both of the amps

[Grant Bunter]

Apologies, should have tweaked with the mention of the inukes.

If the limiter section of the amp is set at 0 (basically off), then you're not stopping transients.
Technically the amp can go more than 50V, even if only for brief periods.
It's in the plans!

So I would engage the limiter with the lowest possible increment in the inukes settings.
Sure, you may not get 50V any more, but your drivers are protected...

[escapemcp]

Apologies, should have tweaked with the mention of the inukes.

If the limiter section of the amp is set at 0 (basically off), then you're not stopping transients.
Technically the amp can go more than 50V, even if only for brief periods.
It's in the plans!

So I would engage the limiter with the lowest possible increment in the inukes settings.
Sure, you may not get 50V any more, but your drivers are protected...

Thanks that's basically what I was after Am glad those iNukes have 0.5dB steps

On the whole subject of limiting, the best practice (from what I have picked up here) is to open up the amps, and then limit the signal to the subs & tops. Now if I do this with an XLR input, I easily hit the limit when the volume dial approaches 2 o'clock. If I then leave my dials fully open (which I thought was the recommended BFM way, but now I am not so sure), it means that the limiter is almost always engaged. This then leads to worse sound if you are always bouncing off the limiter. I thought the idea was to run it with the amp attenuation always fully open, but is this JUST for setting the limiter and then you dial in the volume accordingly? From my (limited) knowledge of gain structure, I thought you wanted to keep the signal as hot as possible for as long as possible, which then reduces your noise floor. So I suppose the question is... should I be turning down the amps once the limiter is set to ensure cleaner audio?

This is a bit of a moot point once I get the DEQ, as I can use the setting in the menu to dial back the signal getting sent to the amp (I forget what it was called... I think it is the 2nd option in the 1st config menu - maybe 'Gain adjust' or 'offset' something like that) I can also use the subwoofer/output 2 gain on the mixer to adjust the volume hitting the sub/monitor amp, so it shouldn't really be an issue when I get the DEQ in a couple of weeks.

Managed to complete (bar a bit of routing and duratexing) the V-plate last night. I didn't want to have to drill holes in the sub to attach it, so I am using handwheels to clamp a bit of wood I have underneath the v plate to the subs. It seems pretty solid, but maybe at 48V it may jiggle, so I will keep the weatherseal handy. The handwheels are to reduce the need for tools (which I could well lose at a free party if I have to use them!) They look something like this:

[sine143]

run amps full open.... turn down mixer so they dont hit the limiters... if you are hitting the limiter at 2 o clock on the input attenuators, then its likely you're clipping the hell out of the input stage of the amp anyways before you even get to the output stage. dial back!

[escapemcp]

A couple more pics. 1st is of my new flightcase that I built with my new wooding skills (thanks for those Bill ). 2nd is just a gratuitous porno shot of my amp rack - when I get the DEQ and the SD card recorder, then the connector panel will be transferred to the rear rail. At the moment the rear of the amp rack just has a couple of 2U grills attached to stop anyone's fingers getting in there!

[escapemcp]

run amps full open.... turn down mixer so they dont hit the limiters... if you are hitting the limiter at 2 o clock on the input attenuators, then its likely you're clipping the hell out of the input stage of the amp anyways before you even get to the output stage. dial back!

I am running XLR into the amp with the mixer barely hitting 0dB... surely it should be able to cope with that? I suppose I should check the output of the Behringer DDM4K against the input of the iNuke to ensure that they are similar.

[sine143]

doesnt matter if its barely at 0 db on your mixer. if its hitting the limiter (almost always), then your input is obviously too hot. the only thing the knobs on the front of an amp do is attenuate the *input* signal btw, so you are achieving the same thing as turning your mixer down.

[Grant Bunter]

The trick is to set your gains to (roughly) 0dB (or clipping, whichever comes first) on your mixer or whatever, before the (in this case) the inuke(s).

You have to set the limiter with the attenuation on the amps fully open, simply because, if you don't and "someone" turns up the attenuators, your drivers are going to get more than your driver protecting voltage.

If this means you need to turn down (or adjust the gain of) the output of the device prior to the amp, so be it. Lock the settings in your memory!

It's not exactly moot when you may introduce something like a DEQ, as any variable can possibly be changed. Not by you.

You have to know your system inside out to protect drivers, and set up up against people who might try to "help".

If some drunken idiot comes up to you and somehow pushes everything to max, that is the point at which you have to know the limiter is set correctly, and none other.
Much more so for your subs than your tops...