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Upgrading to crown amps, help with choosing for my setup


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#1 theguitarfreak

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Posted 13 February 2014 - 11:15 AM

Hi i am currently planning to upgrade to Crown amps for the speaker setup that i have in my rental company. From what i understand power amp output rating should be 1.5 to 2 times that of the speaker's RMS rating. So going by that, this is the speaker viz a viz amp config i have made for my setup. Tell me if its alright or some things that i should consider.

1 JBL VRX932 1600W at 4ohms (2 cabs coupled) = 1 channel of XTi 6002 giving 2100W at 4 ohm (500W extra good enough?) or will a Macro Tech 5000i giving 2500W at 4 ohm be better?

1 JBL SR4733 1200W at 4ohms (1 cab) = 1 channel of XTi 6002 (900W extra good enough?)

1 JBL VRX932 800W at 8ohms (1 cab) = 1 channel of Xti 6002 giving 1200W at 8ohm?

We use XTA processors for the crossover points and other DSP but i can always bunk it and use the XTi's DSP if its good enough.

#2 dakos

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Posted 19 February 2014 - 11:34 PM

View Posttheguitarfreak, on 13 February 2014 - 11:15 AM, said:

Hi i am currently planning to upgrade to Crown amps for the speaker setup that i have in my rental company. From what i understand power amp output rating should be 1.5 to 2 times that of the speaker's RMS rating. So going by that, this is the speaker viz a viz amp config i have made for my setup. Tell me if its alright or some things that i should consider.

1 JBL VRX932 1600W at 4ohms (2 cabs coupled) = 1 channel of XTi 6002 giving 2100W at 4 ohm (500W extra good enough?) or will a Macro Tech 5000i giving 2500W at 4 ohm be better?

1 JBL SR4733 1200W at 4ohms (1 cab) = 1 channel of XTi 6002 (900W extra good enough?)

1 JBL VRX932 800W at 8ohms (1 cab) = 1 channel of Xti 6002 giving 1200W at 8ohm?

We use XTA processors for the crossover points and other DSP but i can always bunk it and use the XTi's DSP if its good enough.

From what you write I feel you lack a bit of basic knowledge about amps and speakers so I would advise you to read this:
http://www.crownaudi...490
You are matching RMS speaker power to the amps power and that's not how you're supposed to do it!!

Now, for the second part of you question, the more AD/DA conversions you have going on in your rig, the sound coming out of them will sound like it was converted to mp3. The maximum number of conversions recommended are:
Maximum of 1 conversion at 48KHz.
Maximum of 2 conversions at 96KHz.
Maximum of 4 conversions at 192KHz.
Since you can't shut down the DSP on the XTi and both are working at 48KHz, you might as well use the one on the XTi and gain some free sound quality.
Avi

#3 theguitarfreak

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Posted 20 February 2014 - 12:36 AM

View Postdakos, on 19 February 2014 - 11:34 PM, said:

View Posttheguitarfreak, on 13 February 2014 - 11:15 AM, said:

Hi i am currently planning to upgrade to Crown amps for the speaker setup that i have in my rental company. From what i understand power amp output rating should be 1.5 to 2 times that of the speaker's RMS rating. So going by that, this is the speaker viz a viz amp config i have made for my setup. Tell me if its alright or some things that i should consider.

1 JBL VRX932 1600W at 4ohms (2 cabs coupled) = 1 channel of XTi 6002 giving 2100W at 4 ohm (500W extra good enough?) or will a Macro Tech 5000i giving 2500W at 4 ohm be better?

1 JBL SR4733 1200W at 4ohms (1 cab) = 1 channel of XTi 6002 (900W extra good enough?)

1 JBL VRX932 800W at 8ohms (1 cab) = 1 channel of Xti 6002 giving 1200W at 8ohm?

We use XTA processors for the crossover points and other DSP but i can always bunk it and use the XTi's DSP if its good enough.

From what you write I feel you lack a bit of basic knowledge about amps and speakers so I would advise you to read this:
http://www.crownaudi...490
You are matching RMS speaker power to the amps power and that's not how you're supposed to do it!!

Now, for the second part of you question, the more AD/DA conversions you have going on in your rig, the sound coming out of them will sound like it was converted to mp3. The maximum number of conversions recommended are:
Maximum of 1 conversion at 48KHz.
Maximum of 2 conversions at 96KHz.
Maximum of 4 conversions at 192KHz.
Since you can't shut down the DSP on the XTi and both are working at 48KHz, you might as well use the one on the XTi and gain some free sound quality.
Avi

Thats clear a lot of things up as definition. Now if you could follow it up with an example, say powering a coupled VRX932 at 4 ohms with a few different wattage amps like xti 6002 or MA5000i, what would be the differences in terms of RMS, headroom and all that.

#4 dakos

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Posted 20 February 2014 - 01:44 AM

OK, I'll give you an example of how I "do the math" for one speaker+amp combo so you can learn bit by bit to do it on your own. I'm here of course if you need more help with this.

The 932 has 800W RMS and 3200W peak power, at 8 ohms. As I wrote in the link I gave you before, we need to be able to feed the speaker it's peak power output while at the same time be able to control the continuous power so we don't go into power compression or damage our gear. In order to achieve this goal, we need to choose an amp that has enough power, yes that's 3200W for the 932, while at the same time we need to be able to restrain the amp from releasing it's high power continuously and thus ruin our speakers. For exactly this purpose limiters come in handy, with limiters you can set the amount of power the amp will be releasing, you can configure the limiter to be an RMS limiter by setting the attack and release times to be long or you can configure the limiter for peak limiting by setting the attack and release times to be very short.

The XTi series have only one limiter, so to get around this problem we will configure the limiter as an RMS limiter and choose an amp that has more or less as much as our speakers peak power spec. Now if we don't clip our amp then we sort of have a peak limiter and an RMS limiter.


How much amp power do we need? As sound technicians we only see as relevant what actually makes a difference in real life. To be able to hear a difference in SPL you need at least 3dB difference, that's twice the wattage. So if we take two 932's that need 3200W, and we A/B them, one of them we feed with a 3200W amp and the other with an amp that has just over 1600W, we will not hear the difference. To sum it all up, in real life condition, any amp with 1600-3200W will suffice.

So, which amp suits our needs? We need 1600-3200W at 8 ohm for each speaker, the 6002 has 1200W per channel at 8 ohm and 4200W at 8 ohm bridge. Obviously the 4200W is too much, and we see that 1200W is audibly less powerful then the maximum 3200W our speaker is capable of. Let's look at the 4002, it has 700W per channel at 8 ohms and 2400W in bridge mode at 8 ohms, could we have hit the jackpot with a bridged 4002 per speaker? The short answer is YES, the longer one is that the 6002 is less powerful but that might be acceptable for you. Lets also look at the 5000i, it has 1250W per channel at 8 ohms, so pretty much the same as the 6002. Let's look also at the MA12000i, it has 2100W at 8 ohms, it's just fine for us, but it has 4500W per channel at 4 ohms, that means you can load it up with up to four 932 and it will handle them beautifully. If you also need the DSP you might opt for the itech series rather then the MAi. You might also opt for used itechs, the 8000, which is the older version of the 12000, run at about $1800-2000 on ebay.

EDIT:
About your headroom, the difference in headroom between running the 932 with an amp capable of 3200W of peak power as opposed to running it on an amp capable of "only" 1600W of peak power is 3dB difference in headroom. That's only true if you need every last drop of power out of your rig. Your headroom will change in many situations, do you need curtain SPL at curtain distance from the speakers? What type of music do you play through your rig? Indoor or outdoor?
Avi

#5 dakos

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Posted 27 February 2014 - 12:30 AM

Added a comment about the headroom, was everything clear enough?
Avi

#6 greatzero

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Posted 27 February 2014 - 05:26 AM

Hi, I am planning to use iTech 8000 with 6 VRX932LA (3 boxes per channel) with HPF at 80Hz and use it in combination with 2 SRX728 (xti4000 bridged each).
I had no luck finding appropriate preset from Crown and JBL web, so I decided to create one myself.
As I am new in DSP amps, i need help first with limiters as not to make any damage to my gear.

I ended up with this limiter settings:
Peak Lim. : SQ Root (9600W * (8/3 Ohm)) * (SQ Root 2) / 2 = 160V * 0,707= 113V  attack = 0,01ms  release = 1s
RMS Lim. : 2400W / 4 = 600W  attack = 4s release = 6s (rated (nominal) = 8 but i don't know anything about this parameter..)

Will you please confirm that what i set is right? Thank You

#7 dakos

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Posted 27 February 2014 - 12:14 PM

I kinda asked many things so I'll answer your questions within the text...

View Postgreatzero, on 27 February 2014 - 05:26 AM, said:

Hi, I am planning to use iTech 8000 with 6 VRX932LA (3 boxes per channel) with HPF at 80Hz and use it in combination with 2 SRX728 (xti4000 bridged each).
I had no luck finding appropriate preset from Crown and JBL web, so I decided to create one myself.
As I am new in DSP amps, i need help first with limiters as not to make any damage to my gear.
First, I have to say that the XTis (1000/2, 2000/2, 4000/2), despite them being great amps at great value, don't excel at subwoofer duty for a number of reasons. I would much prefer you sell those 2 XTi 4000 and get another i-Tech 8000 for those 728, you will have a great upgrade and not invest that much in it (400-500$).
Second, i-Tech amps were optimized for 4 ohm loads, since you have three 932 per channel (2.6 ohm total per channel) you are getting less performance from the amp but I'm not sure what impact it has on the overall performance.
The third issue I need to tell you is about speaker protection and limiters. First, when setting a limiter you only protect the biggest driver connected to the limiter, you will not have any problem frying the HF driver even with the limiter so you still need to keep your ears open for any distortion and back the knobs/sliders a bit. Second thing you need to remember is that the more you slam into the limiters the more RMS the signal has so If the limiters have engaged, back up as well.

View Postgreatzero, on 27 February 2014 - 05:26 AM, said:

I ended up with this limiter settings:
Peak Lim. : SQ Root (9600W * (8/3 Ohm)) * (SQ Root 2) / 2 = 160V * 0,707= 113V  attack = 0,01ms  release = 1s
This part (Peak setting) is correct.

View Postgreatzero, on 27 February 2014 - 05:26 AM, said:

RMS Lim. : 2400W / 4 = 600W  attack = 4s release = 6s (rated (nominal) = 8 but i don't know anything about this parameter..)

Will you please confirm that what i set is right? Thank You
As for the RMS limiter, I see you devided the RMS speaker spec by 4, do you only need 12dB of headroom? What type of music do you play through your rig?
Avi

#8 greatzero

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Posted 27 February 2014 - 04:15 PM

Thank You for your advice.

1. xti4000
I know that this amps are not the best choice for my subs and will look for some better amp in the future. Until then I have to stick with my xti's..

2. iTech8000
As I am a technician in low budget company, this amp is a top gear.. I hope you know what I mean.. Never the less I would like to get from my equipment as much as possible, especially when it is equipped with such a gizmo as DSP..

3. RMS limiter
Mostly i play mastered music through my system. When doing live gigs I usually work with jazz bands and acoustic bands in smaller venues  for max. 500 listeners.. What headroom is appropriate for this kind of audio signal?

There is one thing I have to mention. I use only digital mixing console (Soundcraft Si compact 24).
Do you have advice on how to set up input sensitivity on iT8k (gain structure) according to fact that i will not feed it with overloaded signal from mixer as I will make sure to limit the output to 0dB. (consider my knowledge as very very low in this subject)

If you think that my iT8klimiters are not set well, what should I change? If I can stick with my settings, then I would like to move to EQing my speakers.
Or should I consider Bi-Amping my 932s to protect my HF drivers from frying?

Peter

#9 dakos

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Posted 27 February 2014 - 06:02 PM

Dear Peter,
I more then understand what it means to be restricted by low budget, but it will make you learn many aspects of sound engineering to maximize the gear you already own.

For this type of music you don't need much more then 12dB, but since we divided the peak limiter by 0.707, we also need to divide the RMS limiter by the same value, so here is the correct calculation:
RMS Limiter: (2400W/4)X0.707 = 424W

Your console has 20dBu on its output section, and yes, you should never clip anything in the signal chain, not just the amp.

Gain structure, many have written about it better than I ever could, here is a good, but long, article about gain structure:
http://www.prosoundw...gain_structure/
Another good article about it:
http://www.rane.com/...el_Controls.pdf
Also many youtube video tutorials about the subject.

Now for EQ'ing, I would suggest you start with the IT8000 with factory presets for your speakers, you can download them from here:
http://www.jblpro.co...t/vrx900-series
After that it's all about your ears.

Biamping, there is no bulletproof rig, a bad operator would always be able to ruin things somehow. Having said that, biamping and using limiters will protect your HF drivers better.

Hope I got everything :)
Avi

#10 greatzero

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Posted 01 March 2014 - 07:54 AM

Thank you again.

1. I made correction to my RMS limiting, thank you for your advice
2. Read articles, you suggested, thanks for this links
3. Gave up bi-amping so far.. :)

EQ'ing:

I searched for suitable preset for some time before I joined this forum and found nothing but a simple one with crossover setting, but no eq, no limiting..

So i decided to use EQ from iTech HD presets. No luck as this factory presets are locked and don't show neither eq nor limiting. So i decided to use eq for XTI2 amps.
I suppose once considering the same speaker, there is no difference in EQ presets for various amps. Limiting set with Avi's kind help.

Can someone please explain to me, what are bandpass gains used for? Are they used to match both channels outputs (for example match sub on channel 1 and top on channel 2, or are they used also for gain correction when boost in eq is set???

Peter

#11 dakos

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Posted 01 March 2014 - 08:36 AM

Dear Peter,
What software do you use to configure your amps? Did you have problem loading the presets I gave you in the link?

Factory presets are usually made to smooth out the speakers frequency response, that includes the transition from subs to mains and vice versa.

If you are using the EQ feature, try as much as you can, to use it for cutting rather then boosting.
Avi

#12 greatzero

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Posted 01 March 2014 - 05:27 PM

Dear Avi,

i use System Architect 3.40 and have downloaded VRX900_Series_Tuning_Files_11192008 earlier.

The thing is, that in factory preset for "3xVRX932 stereo made for iTech8000" there was only crossover setting but no equalization for this speakers. That's why i created my own preset using crossover settings from that factory preset and copied EQ from preset made for XTI2 amplifiers.

I am about to "build" my PA next week. I hope that this will give me a picture of what should i focus on in the next step.

When using my master EQ provided by Soundcraft Si console I never boost anything, but I suggest that EQ in DSP presets is set such as to make frequency response of certain speaker as flat as possible which means cut and boosts.

Thank you for your advice again

Peter

#13 dakos

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Posted 02 March 2014 - 10:06 AM

I've looked again into the preset files I gave you a link for, and please correct me if I'm wrong, but I clearly see EQ settings in the attached pdf file along the xover data. Can you verify what I'm seeing?

I'll attach a screen shot later since I'm on my mobile at the moment...
Avi

#14 greatzero

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Posted 02 March 2014 - 03:17 PM

Do you mean file "VRX900_Series_Tuning_Files_11192008/VRX932LA & VRX918S DSP Tuning Files/Crown ITech/VRX932LA ITech-tunings table.pdf"?

#15 dakos

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Posted 02 March 2014 - 04:03 PM

Yes, I marked in red the relevant sections:

Posted Image