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Power amp

D

Diegombass

Sep 19, 2012
566
417
Spain
#1
Hi, I am using a Crown XLS1502(1500W@4ohm) a bass amp, with a quiet, clean and flat digital preamp: Hx Effects to increase dB to input the Crown. Eq, compression or other effects when needed.

I love that sound, but sometimes the volume is not enough and I have fear of blowing the cabs (450w@8ohm the less).

I was thinking about real bass amps, they can get lots of volume thanks to a proper limiter. But I would like to control that matter. I would like to be free as a bird, until I get in the cab limit territory.

Does anyone know how to do that? Is there any bass amp that offers it?
Thanks!
 
#2
Are you using the amp to drive a single 450 watt 8 ohm cabinet?
Are you running the amp bridged or stereo?

In the amps set up menu there is setting for the input level, they are normally set to 1.4 volt you can change it to .775 volt, that would increase the level from the given output of your pre amp.

The XLS has a clipping limiter built in, depending on the cabinet / cabinets your using and the amp configuration you
possibly could still damage the cabinets before the amp would be clipping.

I would also use the XLS built in high pass filter function, maybe starting at 50hz.
 
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#5
Use amp bridged into two modern 410 8 ohm cabs and you should be good to go in any situation. Two 410 4 ohm cabs in stereo mode will give similar result even having bit less combined power.
 
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#7
Your XLS1502 is 300w per side at 8ohms. Add another 8ohms cab to get 600w.
You can bridge it and get 1050w at 8ohms but be careful with only one 450w cab.

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A bass amp will not gives you more.
 
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#8
Thanks for your answers.

Input sensitivity is set to 1.4v, and my HX Effects can even overload the input of the Crown. I don't think it is the problem.

And yes, more speakers would do the job... but it is not possible to bring more speakers to gigs. Moreover, I am sure my 2x 112 cabs could do it with another kind of amp.

The question is: is there an amp that is as pure, clean, flat and noiseless as my Crown, but as you increase the volume it would be limited to ~400w@8ohm in a way that a bass amp would limit?
Maybe a difficult question for my english level :roflmao:
 
#13
@agedhorse might be on to something with this angle. You have to use a Speakon NL4 speaker cable with the +1 and +2 pins connected on the amp end to actually use the bridging mode, regardless of the amp being set to bridging mode in the software. This is not a standard cable such as might be purchased from a retailer. If you're using a standard Speakon cable, you have only the output of Channel 1 connected to the speakers, so only half as much power is being delivered.

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#15
@Diegombass

The first step is to make sure you are wiring the amp to speaker connection for proper bridge mode operation. If you are using a standard speakON, you may only be getting 300W or even less. Using a proper bridge cable will raise the available power to 1050W.

While bridging the amp may sound like a good idea, you will have way more power available than your cab is rated for. If the cab is incapable of playing as loud as you need, bridging the amp just makes it more likely you will blow the drivers. If this is the case, the solution is either more cabs, or a different cab that can play louder.

The cab's 450W power rating may only be relevant in the mids, and its mechanical power handling below 100hz may be significantly lower. It depends on how the cab's power rating is derived. Many companies use the driver's RMS power rating, which relates to how much heat the voice coil can dissipate without incurring damage.

Mechanical power handling varies with how the cab is tuned. In other words, put the same driver in a different cab design and mechanical power handling will change. AFAIK mechanical power handling is usually less than the drivers RMS rating, and sometimes the difference is pretty significant. Unfortunately, most companies do not provide any data on their cab's mechanical power handling. So it's a good idea to be conservative with how hard you will push your cab.

Don't focus exclusively on how much power you have available. SPL is a function of power and how efficient the cab is at converting the power to sound.

We generally consider the smallest useful change in volume to be about 3dB. To get a 3dB change you need to double the power. So if your amp is already delivering 300W, it would need to deliver 600W to provide a useful increase in volume. This exceeds your speaker's 450W power rating, so it's not a solution.

FYI: The decibel difference between 450W and 300W

Log(450/300) x 10 = ~1.8dB

If you add a matching cab, then the sensitivity goes up about +3dB. If you double the power to 600W, you also get +3db from the increase in power. So adding a cab and doubling the power gets you ~+6dB, which is a very usable increase in volume.

If you there is not space for a second cab, then you need to consider a different cab that can play louder. The specs for many cabs include a sensitivity rating. If this rating is expressed at 1W/1m then you can use the following formula to estimate how loud the cab can play.

Calculated SPL = [Log(Usable Power) x 10] + Sensitivity Rating

The first part of the formula (in the brackets) calculates the change in SPL produced by raising the power from 1W to the usable limit. So if you have a 1050W amp and a 450W speaker, then the usable power is 450W. The second part of the formula simply adds the 1W/1m Sensitivity Rating.

Let's assume your cab can handle 450W and has a 97dB 1W/1m sensitivity rating. This sensitivity rating means when 1 Watt is applied, 97dB is measured at a distance of 1 meter from the cone.

Calculated SPL = [Log(450) x 10] + 97 = 123.5dB

Now lets add a matching cab. Usually the connection is in parallel so the impedance will be cut in half, the power handling will double, and the sensitivity will go up by +3dB

Calculated SPL = [Log(900) x 10] + 100 = 129.5dB As you see the SPL is 6dB higher than one cab

Now lets consider a cab that is rated for 300W but has a 103dB 1W/1m power rating. Lower power rating and higher sensitivity rating.

Calculated SPL [Log(300) x 10] +103 = 127.8dB **

** Notice the last example is way louder than our first example, even though the usable power decreased by 150W.

Something to keep in mind: The way specs are derived is not standardized across the industry; so Calculated SPL should be considered a ballpark estimate. Comparisons across brands will have the lowest efficacy, because different companies are likely to use different measurement practices. There can even be differences when comparing two product lines under the same brand. Comparisons across one specific product line should be pretty accurate.
 
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#16
Diegombass said:
Thanks for your answers.

Input sensitivity is set to 1.4v, and my HX Effects can even overload the input of the Crown. I don't think it is the problem.

And yes, more speakers would do the job... but it is not possible to bring more speakers to gigs. Moreover, I am sure my 2x 112 cabs could do it with another kind of amp.

The question is: is there an amp that is as pure, clean, flat and noiseless as my Crown, but as you increase the volume it would be limited to ~400w@8ohm in a way that a bass amp would limit?
Maybe a difficult question for my english level :roflmao:
Click to expand...
If you have two 8 ohms 112 cabs you will get 300W per cab in stereo mode that is total 600W. I would not put much more than 300W into typical 112 cab anyway. Be careful in bridged mode while 1050W at 8 ohms and 1500W at 4 ohms is more than many cabs and combinations of them combinations can handle in practice. 1002 is safer model when using bridged mode, and 2500 is good in stereo mode, but bigger, heavier and more expensive.

If you think using your amp in bridged mode and feel it is not enough, then probably your Speakon cable is not wired correctly and you are using it only in 300W mode (single channel at 8 ohms). That amp eats your cab alive when set bridged and using correctly wired cable.
 
#17
With the rig you have, assuming the Speakon cabling is correct and you have set the right output level on the HX to drive the Crown amp properly, I'd forget bridge mode, and run stereo one cab off Ch A and one cab of Ch B. This would give you all this combination will give, and a margin of safety not running them in bridge mode.
 
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#18
I have a proper speakon cable for bridge.
So, what I can read on all your answers is that I am not going to get better volume feel with a dedicated bass amp 400w@8ohm with a dedicated bass limiter than my Crown in bridge mode.

I usually get enough volume from my rig, but when the venue has bad acoustics, I change the Eq and have fear of blowing the cabs, and because of that I don't turn up the volume. Maybe, with a 400w@8ohm I would feel more confident.

FYI, my cabs are a GreenBoy F112 450w@8ohm and a Barefaced BB3 800W@8ohm.
 
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