Working bacwards

[Grant Bunter]

Sweet, and the reason for doing this is
1, to easy up the amp a little, because
2, if the corner freq of the box is x
3, it dont make sense to send lower freq to the driver, because
4, it cant reproduce it in said enclosure and
5, it can damage the driver
?????

Yes

Not trying to confuse you now, but:
If you get a DCX2496 you can use a LR48 slope set to 40hz because that's the largest slope available.
If you get a DBX driverack series, then the largest slope available is LR24.

So either is fine...

[Michael Murphy]

Ok so the DBX PA+ only has 24db, well I bought it already
http://www.ebay.com/itm/261185035743?ss ... 1439.l2649
and also
http://www.ebay.com/itm/130864283920?ss ... 1439.l2649
and looking at the QSC 2450 specs and what grant said before

"I can't find specs on the other QSC amp you mentioned, but I know you want 625W into 4 ohms to get 50V with 2 x T39 cabs parallel wired."

It seems the 2450 is perfect

lookin at this sucker!

http://www.ebay.com/itm/QSC-Audio-2450- ... 589e204393

but there are a couple others bidding now. Ill see how it goes

Hey I also see a GX7

http://www.ebay.com/itm/QSC-GX7-Stereo- ... 2c6d220631

massive power and only 15lbs I like

[kekani]

You fall in to the category a lot of us fall into, which is buying gear, some needed, some not, and continually upgrading, EXCEPT, you're asking for and getting advice along the way, which is great. Nice start with the PA+ IMHO - wish I started there instead of DBX231 eq first. BUT, I'm glad I have it as a backup if I need it, or if I ever need multiple aux mixes.

Question: Why the 1215? The Driverack will stomp on that, and unless you're doing multiple monitor mixes (which a 260 would do nice) which I don't think you are, seems to be unnecessary (did I miss something?).

I can't comment on setting limiters on the DRPA, but what I found interesting was how the dbxforum advises to set the gain structure (outside of what the DRPA does). Going back to one of the first posts in this thread, the DRPA won't allow a LP on your tops in a two/three way system, only HP. The HP/LP feature is only on the mid/low outs, so you'd have to set your tops on the mid channel, but you may already know this.

I'm still learning the DRPA, but once I learned to use the AFS, feedback is not an issue.

Gotta learn more once subs come into play. Have fun!

[Michael Murphy]

Hey kekani
The eq is to be used purely for that, you feel a track is missing something you can push up a notch. Im not a dj, I can run virtual dj just fine, we have sound clashes in my friends bar its fun pulling back the old tunes, clashes are usually dub related, its not dub step, its a style of reggae with tons of bass. I plan on uploading a play list because when I video record the next clash im sure ppl will be asking whats that playing. Heres a classic

http://www.youtube.com/watch?v=5DeDvGgBObg

And this dive into bfm designs is purley for my entertainment, when Im finished the build it will be for my use, possibly rent it, which is why its being set up how it is. And yeah it is fun!

[Michael Murphy]

I was just thinking of something, in my other thread

http://billfitzmaurice.info/forum/viewt ... =6&t=19652

bill metioned the whole voltage swing thing and what im thinking when setting voltage limits the amp does not know what load you are going to hook it up too. Say you set up your limiters as recommended, volt meter at rear 55v max under war conditions and just using my qsc 1400 as reference both channels 8 ohms is 200 watts and I jack in 2 T39's, 1 per side, I should be protected however if I parallel 2 to get 4ohms and jack it in its 300 watts am I still really protected due to the potential increase in voltage swing?

Which kinda makes me want to go with 2 bass amps instead of 1, in that case the GX5 fits the bill. How the logic going so far?

[Tom Smit]

As long as your limiter is set properly, and the last in the chain before the amp input, you'll be fine. The voltage will be limited to the same voltage regardless of the number of cabs. What changes is the amperes. The more cabs that you put on a channel (assuming that they are all in parallel), the lower the resistance which in turn means a higher flow of amperes. The higher flow can mean more heat, and potentially shorter life. This was discussed a few years ago, and someone said that the life expectancy can be reduced to just a few years (at 2 ohms) from a decade or longer (at 4 - 8 ohms).

[escapemcp]

I started to read the PA+ owners manual.

+1 for ANY electrical purchase!

It is in the manuals where you often find out about a devices weaknesses, rather than the sales blurb, where they only want to tell you about the +ives.
Yeah, I know it was a few posts ago that this was mentioned

[Michael Murphy]

Yup, I dont like to burden the forum by asking questions I can research myself, only when experiences on a particular item then ill ask. Glad theres a place to ask

[Grant Bunter]

Hey pumpsfast,

You've kind of nailed a tricky theoretical part lol.

If you take your amps specs and, using maximum watts at 8 ohms, use a caculator such as:
http://www.rapidtables.com/calc/electri ... ulator.htm
to work out what the voltage would be at that figure, then do the same calculation with the 4 ohm specs, as Tom says, you will see amperage go up.

If you note your figures carefully, you will also see that the voltage has gone down some.
This is because amplifers under load are not linear in output, generally. Losses in energy occur, usually in the form of heat. Those approaching linear output tend to be more expensive.

Applying this to setting up your gear, if you really wanted the correct voltage reading, you would need to put a "dummy load" (look that up) across the outputs equal to the value of the cabs you are hooking up later. As an example, if you have 2 x T39's you plan to run in parallel, with 6 ohm drivers (lab 12's) in each, the nominal impedance of the cab is 8 ohms. 2 in parallel = half, so 4 ohms. So you would have to apply a 4 ohm dummy load to set correct voltage.

Having said that, in the real world, the voltage reduction occurring because of cabs in parallel really adds a little more safety margin...

[Michael Murphy]

ok a lil update, finally finished cab no 2. But before i get ahead of myself, I was running cab 1 off 1 side of the qsc 1400 and 2 6x9's in a box I use in my ford ranger for mids and hights off the other side, phone as source into gemini mixer then to amp, Turned up media volume on the phone all the way, mixer all the way and slider all the way up too and started turning up the gain on the amp for bass, clipping ever so slightly once in a while and guess what voltage I got, yup 34v piddly volts, but woah it was rocking! So played with it for a while and then installed the unbroken in driver in cab 2, (as you may recall im using the infinity reference 1260 as of now, waiting on the labs) fired him up and its sounds better and louder by a good bit, so I checked over cab 1 for leaks and found 2, fixed them, it got better but still cant compare to cab 2, any how moving on, after pulling in and out jacks comparing the 2 at different frequencys plugged in 2 ath the same time (second qsc 1400 running) and bass got lower, looked at my assistant you sure you wire that up right? Swiched over the wires in cab 1 and boom! If thats what doubling the db does with 2 cabs vs 1 I can just imagine what 4 v plated will be like. With a 40hz test tone and only 34v it blew away the lab horn, well not really only marginally and thats with my bias ears. Had my clothes vibrating. Taking the lap top to the shop to do some more tests. Ill report back and just for good measure reading ones owners manual can clear things up alot, excerpt from dbx1215 owners manual:-

Operation and Application Notes
The dbx 12 Series Graphic Equalizers are useful audio signal processing tools in situations where precise frequency
control is required across the audible frequency spectrum.
When used with an audio spectrum analyzer the EQs can tune any acoustical environment -- from the studio to the
concert hall -- to stop ringing, increase clarity, and flatten the overall frequency response of the environment. A
real-time spectrum analyzer or other types of audio environment analyzers are very useful in determining the
amount of equalization needed.
Insert the graphic equalizer between the signal source (usually a mixer) and the power amplifiers (or the crossover if
there is one). Adjust the level and equalization as required to yield the desired system response. The long throw faders
of the EQs allow very precise settings of the equalization for accurate equalization curves. For optimum signal-to-noise response, the gain structure of the sound system must be properly set up. Each component
of the sound system should be set at its nominal operating level, starting with the first element in the system,
usually a mixing console. Each element should be run at its nominal operating level in order to take advantage of
the maximum signal-to-noise properties of that element. Loudspeaker amplifiers, as the last element in the chain,
should be set only as loud as necessary, in order to avoid inducing unnecessary noise into the system.

[biggerrigger]

Yes 4 with a V-plate will ROCK

[Grant Bunter]

Hey pumpsfast,
Glad to hear you're at the stage you are.

You haven't mentioned a brick wall limiter at any stage in your signal chain.
Don't assume that just because your amp doesn't have the maximum voltage to suit your cabs that transients don't exist that are way above the maximum recommended voltage for your sub cabs.

Just saying, get/buy your limiter/crossover and set it up as well, and you'll not only protect your cabs from damage, but it will all sound even better...

[Michael Murphy]

Hey grant, yup im waiting on leyland to finish up the ot 12s to ship down the dbx pa+ and then I can set up properly and i think i know why cab 2 sounds better, When i Was rrackin up after testing i dropped à jack on the ground and When i bent over infront of the playing cab i heard the bass go up and realized i had it side by side with the lab Horn sticking out about 2ft and think i was getting some reinforcement from it. So When i fire them up again Ill move the labhorn. Recorded 108 db at 50 hz though

[Grant Bunter]

Temper your excitement mate!

Don't run your subs again without the limiting in place...

[Michael Murphy]

And soon the electronic media will be comming

https://www.dropbox.com/s/piwcac0wbcy8nla/VIDEO0019.mp4

http://www.trueaudio.com/rta_abt1.htm

trial version used also laptop mic not rta mic, just raw data at this point, (Loud raw data @ 34v pk)