Re: Are 24 x T60-LAB15s Enough? ;)
Posted: Tue May 21, 2024 9:24 am
Price dropped on the K410's. 3 or more now $830 each. Saves another $100 on five of them.
Admark K410 at VIP Pro Audio
Admark K410 at VIP Pro Audio
Whew! Yes, great weekend! Productive weekend at the shop!
I see that I missed a lot of action on here!
Furthermore, more questions have come up!
Buckle up, fellas, this is going to be a long one!
@Bruce
Suggestions from the "old curmudgeon" are always, ALWAYS appreciated! Thanks so much for taking the time to help out us dumb burners! It really means a lot! This would already be a huge project if the conditions were typical. But because this is for the Burn, every little thing becomes way, way more difficult. Sometimes it seems exponentially so.
Audiences at the Burn are hard to pin down. There is the full spectrum of people out there, from every single slice of the population. You name a demographic, and they are out there. But, on average, I'd say burners lean more towards audiophiles than not. After all, if you don't like the system/performer you are listening to, you can just walk/bike a minute or two to the next one. Options abound!
Guessing the audience size is tough as well. Could be just the DJ, audience of one. It also could be a thousand or more. It's all fluid.
There are no volume limitations for our camp. This is because of our location along the edge of the city. If we were located in most other parts of the city, yes we would have volume limitations. The sound restrictions are relatively new. The rule is sound levels have to be at conversational levels (60db) at 100' out in certain areas. Otherwise, it's 60db at a border with a neighbor, or 60db in the middle of a street.
Budget is tough to say exactly. I think the absolute max is $8,000 though. (Originally it was much lower than that, but you swooped in and saved the day! Thanks, again!!!) The lower the budget, the better, of course, assuming there is no drops in sound quality. The higher the budget goes... well that means even more longer frugal living for me. Not ideal. At all. As in, I'd really, really prefer not to do that. So, a much lower budget is preferred. As low as possible, actually. That probably means inexpensive new amps, or great used amps. Either way, they need to perform flawlessly for a long, long time.
Given we have the Driverack 4820s now, we have the option of using amps like the Macrotechs or these Admarks without DSP, and not have to worry about being locked into a tight vs. wide deployment. Flexibility and options are a wonderful thing to have! Especially when we might have to McGyver something out there!
On that note, the tightest, most dense deployment it seems like we can practically do is 2 cab high (upright) x 16 wide, or 3 cab high (on their side) x 10-11 wide. So that would be about 62" (2 x 30" + rubber feet) or 5 ish feet high x 324" (16 x 20" + 1/4" spacing between cabs) or 27 ish feet wide for upright. Or 63"/5' high x 334"/28' wide on their sides. We probably don't have any need for delays or fancy stuff with those "tight" dimensions, correct?
The widest, least dense deployment would be either 54-ish feet wide with one row of upright cabs, or 80-ish feet wide with one row of cabs on their sides. It seems like those distances might need some delays, correct? Or not. I have no idea.
That said, we picked up the two used 4820s, so we have more options with deployment should things change. Which they always seem to do. But then again, maybe we got a little trigger happy on that purchase... Fancy hubcaps and all... Shit!
Good point on the X32! Thanks!
And man, thanks for the reality check on nature/physics sorting things out! It's nice for people to have options in how they want to experience the music!
And another great point on the amp shutdown/cooling cycle idea! As soon as I read this, I remember him saying that to me. That seems like a good safety measure!
Just out of curiosity, though...
Would it work just as well (if not better) to use a different cooling tactic? For instance, since the drivers cool themselves with movement of the cone, what if we took advantage of that? Instead of just turning them off, we could have a preset that is a much lower voltage and different bandpass? So that the driver has high excursion/movement at just the low frequencies, maybe 30-40Hz, and low power, maybe 10v. So maybe it would cool itself more than if it were just off? I don't know, just a thought I had.
Also, keep it simple... this is great advice! I think I should probably tattoo "KISS" or simply "Simple" on my forehead. I just get so goddamn curious! This stuff is really cool!
@Seth
Thanks for the wiring clarification using hots and no neutral! That opens up my mind as well as my options!
That said, though, I'm still puzzled on how exactly that humpy line-to-line wave is not humpy, and instead, a smooth sine wave.
Also, I agree that if we can minimize amp draw on the power grid, that is a good thing. I am just saying that with our usual setup, using a Furman ASD-120 power conditioner, it won't really effect the rest of the grid whether we run 120v or 208v or 240v. This is because the Furman will take the 208v from the generator, and then split it into 6 x 120v/20 amp circuits. So the power delivered to the Furman will be at a higher 208 volt, and a lower amperage draw. I think that means the Furman and amp will create more heat within themselves as they work with the lower 120v instead of 208v. And maybe that is what Elliot's testing indicates - that 120v creates too much heat and that it has a harder time performing at full output. But, if we aren't running these amps anywhere near 116v, then using 120v/20amp outlets instead of 208v or 240v probably doesn't matter. Does that sound plausible at least?
I think yes. Until we load them up to a certain point, that is. The point at which too much heat is created from using the 120v, higher amp flow, vs the 208/240v lower amp flow.
What point would that occur at? I'm not sure.
Is it at 8 ohms (1 sub) per each of the 4 channels on the Admark (4 total subs)? I'd guess definitely not.
Is it at 4 ohms (2 subs) per 4 channels (8 total subs)? Probably no?
Is it at 2 ohms (4 subs) per 4 channels (16 total subs)? Maybe?
Would it be possible to push the amp lower than that, and still squeak by without tripping the breaker? My guess is no... but maybe if we turn it down to 40v or something? Or do some fancy series-parallel stuff?
Also, doesn't 32 x 250 watts = 8,000 watts, not 6,000 watts? And that's the limited 45v peak power, not the lower continuous power, yes? Dave Rat would say the actual continuous would be 32 x 80w = 2,560w. And the capacitors would handle the peaks, yes?
So 8000w/120v = 66.6 amps, and 8000w/208v = 38.5 amps. Again, those are limited peak at 45v. Continuous would be 2560w/120v = 21.3 amps, 2560w/208v = 12.3 amps.
Maybe, using all this, that means that two Admarks can run 16 subs each, with each Admark plugged into its own 20amp/120v outlet on the Furman... If any short blips can sneak through without tripping the breaker, and the capacitors in the amp can handle the 45v peaks, yes? Otherwise, using 4 Admarks on 4 outlets would be just fine, yes? Any more amps than that would just be further insurance?
Either way, upstream of the Furman, at 208v, there would be only 38.5 amps peak (12.8 amps peak per phase if perfectly balanced) through the main power cable from the genny/distro box. Continuous power would be a lowly 12.3 amps, 4.1 amps per phase.
That circuit has a 60 amp (per phase) breaker on it, and the cable has 6 awg copper THHN (per phase). The ampacity chart shows 75 amps (per phase) for that wire. Which should be plenty of headroom, even if we don't bury the cable and it sits on the surface and bakes in the sun. Granted, we will also be running maybe an additional 5000 watts for AC, the tops, and other stuff in that area. But still , plenty of headroom for all that as well. Yes?
Also, I'm not sure if I already said this, but our generator will have the capacity of about 150 amps per phase. I will balance the whole grid as well as I can. Sometimes it's tough to predict human behavior, and when they might be using their ACs or not. But even if things get really wacky, it shouldn't be too much of a problem. Famous last words...
To jump back out of the weeds, the question to answer is, would running these Admarks on 120v work in this situation? I think the answer is a confident yes if there are 4 Admarks? And a probably yes if there are 2 Admarks?
If the answer is no, maybe I could do something crazy like cut 2 cords coming off two different Furman outlets (with two different phases) to get 208v back from the 120v? Wire the two hots, merge the grounds and then wire them in, and just cap the neutrals and leave them out of it? That way we could get the 208v, and still use the other Furman outlets to power the other 120v devices?
Good point about the amp efficiency. I get the 3400w / 80% = 4250w. That's per channel, correct? Or is that coming off the wall? I think per channel.
As a complete system, though, at 250w per T60 and DR280, we'd be at 32 + 6 = 38 x 250 = 9500 watts, not 7500, correct?
9500w/80% = 11,875w.
11,875w/208v = 57 amps from the genny to the Furman. (Could be more with a little voltage drop and increased resistance in cable due to high temps. We'll crank the voltage up on the genny to compensate, though.)
11,875w/120v = 99 amps from the Furman to Admarks. (Need to use 5 x 20 amp circuits, 1 Admark per circuit.)
11,875w x 80% = 9500 watts from the Admarks to the drivers.
9500w/45v = 211 amps to drivers. (Just treating the DR280s the same as the T60s for math simplicity.)
211 amps divided by however many channels... let's say 5 Admarks, 20 channels total... that's about 10.5 amps per channel.
These are all "peak" numbers.
If the Admarks can do 2890 peak watts per channel at 60v (which is the standard rating voltage, correct?), then 2890w/60v = 48 amps per channel.
10.5 amps/48 amps = 22% of capacity
...so...
Easy peasy, lemon squeezy! 120v all day long with 5 amps, right?
And if shit hits the fan, we can McGyver 208v off the Furman 120v outlets, and really load up the Admarks.
Point taken on how the impedance is different at different frequencies. And sorry, I should have clarified - the only reason I said 1kHz is because Crown uses that as a reference point in their "guaranteed minimum" and "maximum burst" power ratings for their amps. Maybe other companies do that, too. I'm not sure.
If Corona Operator had 800w peak, which would average to 100w peak per cab, then we'd have 32 + 6 = 38 x 100w = 3800w, right?
But I also feel like he could have his cabs turned way down, because he is likely indoors?
Overall, for this application, it seems like an advantage of modern class D amps, versus class AB, is more efficient continuous wattage handling. (No surprise, there. I'm just rehashing old conclusions.) They can meet that continuous demand using less power. That's great! If the difference between class D at 80%, and class D at 60%, of 80 watts per LAB12, is a 20% difference of 16 watts per amp... 32 x 16 watts = 512 watts of additional efficiency loss, aka heat. So running the old AB amps would be the equivalent of having a 500 watt heater going all the time. If we go class D, we skip the 500w heater. More specifically, 512 watts x .293 = 150btu/hr. Huh. I don't know. My gut tells me that my math is probably wrong (again), and I'm probably underestimating the extra heat output of the AB amps...
But also, and probably more importantly, the advantage of modern class D amps have higher peak capacity, yes? My guess is that they have more/better capacitors, and all of that good stuff, inside that can provide the higher peak capacity. Does this seem correct? Plus, if they have integrated DSP, all the better. But really, if they have one single major advantage, it's really all about the peak capacity, correct? Because music reproduction and amplification is so inherently transient? Meaning continuous ratings fall more in the category of fancy hubcaps?
Unfortunately, 208v/240v air conditioners seem to be twice the price or more than 110-120v air conditioners. They are much higher BTU, but are also pigs, like 120lbs or more. A pain to move around, and a pain to support when installed. I already curse all of our little 5000btu units that are maybe 30lbs or so. It's an awkward, poorly balanced 30 pounds. But, gripes aside, it would be doable. And we'd probably only need only one or two. But now we are in the same argument as with the amps. What if one fails? Plus, I hope I have made the case that we have the amperage to spare to run the cheaper 120v ACs. So power draw isn't a huge issue.
That said, it might be cool to go the mini-split AC route! They have the higher 208v ability. Plus, they would give a lot more flexibility in where we can place both the main unit and the secondary unit. We could have the amps buried inside the booth iwth the secondary unit (shorter cables!), and run the insulated cooling lines into there from the main unit located outside, which we could place in the shade. By contrast, the window ACs would need to be on a wall. Hmmm... Oh, but what if mini split unit goes down? Hmmm...
On a separate note, I guess I fundamentally do not understand the difference between the advantages/disadvantages of series vs parallel wiring.
General concepts that I get...
Both circuits use the same amount of energy. Or close enough, anyway.
To have enough juice to power multiple cabs on a series circuit, you gotta have higher voltage because there is more resistance. Your power source better be good, otherwise further down the circuit you get, later cabs will be quieter. Also, if something goes wrong at a single link, the whole chain is down. You get to save on wiring, though. Lower over lengths, and probably smaller diameter compared to parallel. Maybe that's not a big deal in this application, though, especially if we already have bigger speakon cables.
With parallel, you don't need the higher voltage ability. But you better have the ampacity. If a single link goes down, the rest of the chain survives. But you need more and thicker wiring, yes?
If that is correct, series can be appealing because it doesn't need as high of ampacity. That can be a big deal, because the smaller amount of materials, and the space they take up, and the weight they have, can lead to smaller and lighter-weight equipment. Or maybe more drivers per channel. Maybe. That's a little foggy.
Amplifiers that can crank in parallel need to be burly. More amperage flowing through, requiring larger materials and all that vs series.
Overall, the concept seems similar to why power transmission lines run at high voltages and low amperage, yes? Overall, more efficient given the same size of amps/materials?
So maybe I do understand the differences?
If yes, for this application, where we are way out there on the moon, it's nice to have backups and redundancies. So it seems like parallel is the way to go. As is having more smaller amps than fewer large amps. Same for ACs.
All that said, I am puzzled by how the series-parallel harness would work. As in, if I make a harness myself, how exactly would it work, given the T60s will be wired in parallel? Or would it be easier to take off the speakon dish and adjust at the terminal blades? I feel like once I see the answer, it will seem so simple, and I'll just shake my head at my own stupidity!
Also, what is the advantage of running mono vs stereo for the subs?
Is it that if, in the event there is strong panning from one side to the other, that one side would be dormant, while the other is overloaded? Also, is there a lot of stereo content with panning in those low frequencies in the musicks that the kids like these days?
If there is content, maybe stereo bass could be a cool effect? But only if you're in the middle to experience it? Assuming we have a 5' high x 27' wide cluster of subs, where might the middle effectively be? Where would the audience need to be to experience that stereo effect? How far off to one side or the other would make stereo useless? Or undesirable?
Back to driver temps and sun exposure for a bit...
The cabs in the center will be shaded. So, if we go for a tall/narrow deployment, they will all be shaded.
If we go short/wide, several might be in direct sunlight all day long.
But will the shade in that location be much more beneficial? Maybe, maybe not.
It's likely that we will do 2 rows of 16, upright (not on their side). If they are all tucked in a nook underneath the DJ booth, they will be out of the sun. Good. But there will not be great airflow... Bad. Maybe sixes inches above the top of the top subs, a quarter inch or something between subs. Potentially much more room off the sides, but still it would be a nook. Maybe we open up the sides of the nook for better airflow...
Anyway, the point is that airflow can make a huge difference in temperature, for sure. Is it better to be in 100 degrees, full sun, and 10 mph wind? Or 100 degrees, shade, no ventilation? Maybe we should try to have a few box fans in the nook? As well as leave the sides open?
By the way, I love the idea of wireless thermometer! I think I'll get a couple if the price is right! I would be great to monitor in real time! And make adjustments if necessary!
Oh, and no worries, I didn't read your post as bossy/absolute! I really appreciate the amount of time and effort that you have put into our project! We are learning and making the system better, and more reliable in the process! Yay!
I get the concept that the line-to-line sinewave is a product of the voltage potential difference at any given point. I just don't get how it would be another "pure" sinewave, instead of a highly modified, humpy kind of sinewave. I'm not disagreeing with the concept, I just don't understand how it can be the case. At the points of highest differences, the red and blue are parallel. That would create a flat-top hump, yes? Not a smooth parabola? Maybe the hump vs. parabola doesn't matter, as long as there is 208v available?
Okay, now that I am somewhat caught up with your guys' posts... I have more questions!
T60 Orientation
Given this application, does it matter whether these cabs are on their side, or even upside down?
Would there be any danger of driver sag, or something like that, if they are playing almost nonstop, for a week straight?
In other words, is there any reason not to only have them upright?
We are planning on mounting the drivers with wood screws. I've had a gander at charts with shear strength, and withdrawal strength, and it seems like we'll be just fine from those perspectives when securing the driver frame to the cab. I am just not sure about the the rest of the driver components. Will yes be okay good okay?
Also, after agonizing about where to put the casters and feet, we finally made a decision! So that we can easily change the configuration of the subs, we ultimately decided to do NO casters, and only rubber feet.
This is because the recessed casters we have would be too wide to put in the long sides without cutting into the horn path. I don't think it would be a big deal if we installed them, they were airtight, and we kept them there always and forever. But, if we ever wanted to change it up, which seems very likely, it would probably be a pain to reposition the casters and plug that hole. Well, maybe it wouldn't be that bad for one or two cabs. But 32... man, that's just so many!
Also, surface mount casters either can't take the weight, or would be too tall. And outrigger casters would create way more work - we'd have to put them on to move them out of storage, and then take them off to tetris them in again.
I tried just using a regular ole dolly to move around one of our T60LAB15, and it was just fine. A mere mini fridge. So we'll just use regular ole dollies. The side benefit of that is we don't need hand hold cutouts. I suppose we could go without them even with the onboard casters, but meh. The point is, that several of the cutouts in on our old T60s have split/cracked because of people dancing on them or lifting them onto the trailer. Plus, if we flip the subs on their sides or upside down, and there are no cutouts, then there are no trip hazards at all in any of the orientations.
T60 Orientation and Deployment
I've gone through the "Rules for Subwoofer Placement and Stacking"
https://billfitzmaurice.info/forum/viewtopic.php?t=398
I have a few questions.
My first question is a dumb one, so please don't rip my head off...
Do these rules apply to all subs? Not just the Titans pictured? The answer is yes, I'm pretty sure. But I can't explain why.
I see that in the Titan plans, the triangular "V coupler plate" is included right in there, in the plans, towards the end. However, in the T60 plans, there is no such mention. Only references to boundary loading, cancellations, corner placement, etc.
Why is the V coupler not in the T60 plans? My guess is because if we put them all in a row, they already couple, yes?
But can't we also do that with the Titans?
So is there an additional advantage of doing the V coupling? For an extra 3db for free? Or would you only bother with the V coupling if you only have a few subs, and don't have, I don't know, 32 or so cabs?
If you can gain the 3db, is it an option that we can consider the V coupling with the T60s? Is an extra 3db for free possible in this situation?
What if we can build our DJ booth, and position the T60s, in a way that effectively creates a mega V coupler and/or elongates the horn? We could build our own kind of corner placement, or maybe even better than a corner, with V coupling as well? Generally speaking, maybe we could build what amounts to a further extension of the horn path in the T60? Or would that matter at at all, given that the 20" max width cabs would already horn load all the way down to 28Hz (or however far, I forget)? Does all this sound just plain dumb dumb stupid? I'm like 50/50 on it. Or maybe 80/20. 80 being that it does sound dumb dumb stupid. 20 being it's sounds only dumb stupid.
Also, what exactly is considered a boundary? My guess is it would be something capable of reflecting all the sound energy, rather than allowing it to reverberate and pass through. What enables that? High density/mass?
And I'm also guessing that the definition of a boundary is different depending on the frequency... lower frequencies need more boundary-ness, yes?
For the sub 100Hz range, would a shipping container count as a boundary? Would a plywood wall/reflector count? Linking this back to the V coupler questions above, can we be clever with the subfloor design of our DJ booth to create even more horn loading?
Our First Option of Deployment (as of now, anyway) - "Max Output"
If you go back to the pretty picture of the gold standard art car, we figured we'd use that as inspiration for our "max output" configuration.
We talked at length about doing something more dense, such as 4 high (on their sides) by 8 wide, for a roughly 7' x 20' cluster. (How crazy would that be, btw? A whole wall of T60s!) However, it just doesn't seem to fit with the vibe of our camp. Maybe we can be persuaded otherwise, but it will need to be a compelling case. For instance, Seth, going back to your 3x5 and 1x15 models, it seems like our 5'x27' would be close enough 7'x20' (the max 3x5 model) without giving up too much output, yes? Maybe only 1-2db?
Okay, okay, I know. I hear you. This whole time I've been saying sound quality over aesthetics, and I'd like to think I've stayed the course, even when difficult. But, I think we've reached the limit on this front. Having the DJ be up 8'+ off the ground is just too much for us. At least too much for now. I've floated the 8'+ idea, and there have been strong objections. We need more "accessibility" to the DJ. I know it's just 2' of difference between the 6' and 8'+, but 2' can be a lot, right? Especially during smaller parties? Just think of a guy that is 2' taller than you. Damn near breaks your neck to look up that high, right? Also, doing this will put our DJs at the same height as the gold standard guys. Having experienced it, I can say that 6-6.5' height is plenty high for a DJ focal point for the audience, as well as experiencing low frequency output. The difference is that the top of their subs is at 6', because the deck of the vehicle is about 2.5' off the ground. Our subs will be right on the ground and come up to 5'. That probably doesn't make a whole lot of difference, but I thought I'd mention it anyway.
They have basically a 4' high x 24' wide array of subs, that is about 2.5' off the ground. Their J-arrays are just on the outside of that, with the lowest edge of the lowest cab at about 6.5-7'. This is a proven, gold standard concept.
The big difference, of course, are that they are using 18" drivers in dual bandpass cabs, not 12" drivers in horn cabs.
Now, I know we have already done the subwoofer comparison game. Bill was nice enough to model T60s vs B-2s. Both are about 112db in that 30-60Hz range.
I'm not looking to rehash that...
...But maybe I am a little.
It occurred to me over the weekend that, even though we have the advantage of horns, in the end, it probably doesn't matter. This is because in practice we won't be listening to either system at 1w/1m. The T60s will be limited to 45v, 253.125w. That means we gain about 24db, by increasing the power from 1w to almost 256w. However, the B-2s are not limited to 45v/253.125w. That's a big, big deal, yes?
I'm not sure how hard they can be pushed. For output in that 60Hz and below range, which it seems there can never be enough, the B-2s might have a significant advantage. Since they don't have the high pressure and demands of horn cabs holding them back, that means they can crank the power levels way, way, way up, correct? To what limit without risking over-excursion, I don't know. I'm not sure what 18" drivers they are using in the B-2s... Let's use the Eminence 18" as a placeholder, yes? They can do 1600w continuous, 3200w peak. So, if they can do 3200w peaks without over-excursion or distortion, that means they can do 160v instead of 45v. Let me say before going on, that I don't even know if that's possible. But, if I don't a little thing like "what's possible" or "I'm so, so wrong" stop me, then I can continue. If they have the amplifiers and all that that can handle it, a full 160v is probably still not realistic. So, let's take that down to say 128v. That would be 8 ohms, 128v x 16 amps = 2048 watts. Comparing 2048 watts to 256 watts, that's a 9db difference, correct? So the B-2s are about twice as loud in that "feel it" range than the T60s. If we were talking about higher frequencies, in which the extra decibels would be of no benefit, then forget it, it doesn't matter, because there is easily such thing as too loud. But we are talking about the low stuff, here, below most human ears, in which there can always be more, yes? Especially outdoors. That said, B-2s win, and they win very easily. However, it takes way, way, more power to do it! 24 drivers x 2048 watts = 49,152 watts. Versus 32 drivers x 253.125w = 8,100 watts. 49,152/8,100 = just over 6 times the power...
Does all that seem right? I hope it doesn't come off sounding like I'm super confident in it. I'm not. I just had a thought, and am trying to see it through.
Okay, so, even though horn loaded cabs can take a little power, with little drivers, and make a big boom, no matter what, they have a tough time competing with the big boy modern trends, yes? This is because guys can just slap huge drivers in reflex-style cabs, give them a shitload more juice with much improved amps, and completely overpower any advantages that the smaller horns would have, yes?
Side note, wouldn't it be something to see what an appropriately sized horn cab for these bigger drivers (18", 21", or more) can do? Assuming the drivers could survive the pressure? First of all, how big would they be? And how would they feel? I imagine it could be something crazy like rotor wash from a helicopter. That level of output probably isn't super desirable in practice, but it's kind of fun to think about, isn't it?!
Also, maybe servo style drivers can help with the demands of a horn cab vs magnet ones? I don't know. Dave Rat is using M-Force 30" servo drivers at Coachella, 10,000 watts continuous/20,000 peak. In reflex style cabs it looks like, though. Anyway, if he's able to run them at 16,384 watts... that's another +9db from these high and mighty 18" drivers at 2048 watts... Or +18db from the T60s! Holy smokes! Rotor wash!!!
Now, I know that a properly designed horn can have better/flatter overall response curve using less energy, but if you're only focusing on that 60Hz and below range, it seems like a higher-priced, higher-powered, bigger driver in a reflex cab, coupled with an adequate amplifier, is the best way to get there? Maybe! I don't know!
Thoughts?
Note, we're still building the T60s, staying the course. I'm just curious if this theory from the rookie sounds plausible... Does it?
Another difference is that they have more cabs in their J-arrays. And their V12s have a 120 degree dispersion. Versus the 90 degrees of the DR280s.
The V12s in their J-arrays:
https://www.dbaudio.com/global/en/produ ... hnicaldata
Any chance we dare compare 6 x DR280s to their 20 x V12s? And maybe use this to help place our DR280 arrays? How far apart, how far forward/back, how much delay (if any), etc.?
They obviously can cover a much longer distance with their V12s, much more than we'd need for our DR280s. It would just be interesting to see how the quality might compare in that first 10, 50, 100, 200 feet. Coverage beyond that, beyond 200' feet for sure, that doesn't matter to our situation at all.
Oh, also, note that their DJ monitors are 8 x V8s. 2 stacks of 4, rotated 90 degrees on the deck, on each side of the DJ. What do you think of that?
Amps
We are really starting to lean hard into the newer class D amps. Here's why.
One thing that has changed since I last posted, is that we attempted a A/B comparison of the Macrotech 2400 and the Itech 5000 amps that we have. Emphasis on "attempted". You might remember that we only have 2 working T60LAB15s from our once mighty count of 12. So, we hooked up one on each channel of each amp.
First, we took a multimeter to the output of each amp to set the limiter, so that it would be roughly 55v. (The plans say max 60v, and we backed it off a little just for a safety margin.) This process felt very clumsy, though. The meter jumps all over the place. That makes sense because it is producing a sine wave, yes? So we tried to dial it in by splitting the high and low values that would flash on the screen. We figured seeing 60 ish volts on one flash, and 50 ish volts on another meant we were close enough to a 55v average. We decided that we should get an oscilloscope to make that process more exact. Thoughts?
Once we got the limiter set for each amp, we plugged in the speakons to the T60s. We made sure only one amp was plugged into the speakers at a time. We disconnected the other amp completely.
We then listened to a continuous 50Hz sine wave on repeat, walked all around, and tried to get a good impression of the sound quality, while changing volume levels from low all the way up to clip. Then, we stopped, unplugged the speakers, plugged them into the other amp, and listened again. Back and forth a few times.
We realized that it's tough to get a really good comparison without an immediate switch back and forth, like Dave Rat did in his amp comparison video. It's hard to tell by memory alone! The only thing that really stood out was volume. It seemed like the old Macrotech was quieter. That could have been due to a number of factors, though. Like maybe we didn't have the limiters set exactly the same, to deliver the exact same voltage from both amps. Maybe the Macrotech was sending slightly lower voltage, and that accounted for the lower volume. Also, we didn't have a decibel microphone. It was just noticeably quieter.
The other interesting thing was that at clip, the Itech was much cleaner. Didn't even flinch. The Macrotech, on the other hand, started giving a distinct "wah wah" sound when near or at clip. Is that what harmonic distortion sounds like? It didn't sound good. Maybe it's just the case with this one amp, and doesn't speak for the group as a whole? Either way, it made me really glad we tested. It wasn't just a audiophile level of subtlety, either. It was VERY obvious.
Anyway, based on our shitty test, the Itech wins hands down.
We are hoping to do a better test this weekend. We will use a dbx microphone this time. (We forgot it last time.) The hope is that if we can make sure each amp is producing the same decibel level, we can get a better feel for if there is any "color" that old Macrotech has vs new Itech. See what this whole "rolling bass" vs "punch" might actually sound like. And if so, whether it is desirable or not. Also, maybe we need to play actual music instead of just a continuous 50 Hz sine wave.
Do you guys have any suggestions on this process?
Maybe any clever tricks to get that instant switch back and forth between amps, so the difference would be immediately heard, rather than relying on short term memory?
Other Questions
What exactly is "usable frequency range"? This is a spec I've come across in the data sheets, and it has puzzled me. This is because the line on the charts always goes past what the usable range is, and it seems just fine in a lot of cases - pretty flat, no big drop offs.
https://eminence.com/pages/support__und ... eaker-data - "This is the frequency range for which Eminence feels the transducer will prove useful."
When considering going below the range, it seems a little subjective maybe? They think it sounds good until that low point? Or is it based on a hard line, like damaging the driver?
Does being in horn cabs like the T60 and the DR280 change the usable frequency of a driver, extending it to the downside? Is that what the whole lower extension thing is about? Does having multiple cabs change it as well? If yes, is it because the horn loading and/or additional cabs allow a lower amount of energy to produce the frequency, meaning less strain on the drivers?
https://eminence.com/products/asd_1001b#specifications
For instance, in the Eminence ASD1000 sheet, it has a usable frequency of 2,500-20,000 Hz. It's frequency response chart clearly shows decent output below 2500Hz, all the way down to about 1500Hz, where the line starts dropping hard, and where the impedance line spikes around 1200Hz or so. But using the 18db/oct slope, the plans call for a 2,000Hz crossover. I'm feeling around in the dark here, but using a 12db/oct slope would mean that driver would go from 104db at 2kHz to 96db at 1kHz, yes? 96db just happens to be what the chart shows at 1kHz. So using the 12db/oct slope could work, but it would be riding the line? Risky business, yes? The 18db/oct ensures it is under that line the whole way, helping to protect the driver, yes? And also probably sounding cleaner, less distorted. Does that seem right?
