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[Eugen Jeličić]

We bought 4 used home made "Mini H scoops" loaded with paudio C15-600EL drivers for a club i work in. We are really happy with the boxes, i was suprised by the SPL and frequency response they have considering they are 15's.

But i have a problem, we run them using 2 yamaha p7000s amps, one sub on each channel.
This means about 750w peak since this is the 8 ohm power rating for this amp.

Still it seems to me that when pushed very hard with bass heavey electronic music like drum'n bass, they seem to hit thermal compression.

I didn't run them up to the clipping point and they allways sound great, but they tend do start smelling a bit after 30 minutes of constant sub torture and the amps sometimes start hitting the clipping point wihouth me pushing the gain.

So we are at a constant level, the amps are not clipping during the first few minutes but after the coils warm up, they begin peaking into clip.

Also, i can't figure out why do they have a slight burning smell when pushed hard. They are rated at 600W continuous, they have been sitting for a few years so this might me some dust on the coils or it's too much power?

[Scott Holtzman]

We bought 4 used home made "Mini H scoops" loaded with paudio C15-600EL drivers for a club i work in. We are really happy with the boxes, i was suprised by the SPL and frequency response they have considering they are 15's.

But i have a problem, we run them using 2 yamaha p7000s amps, one sub on each channel.
This means about 750w peak since this is the 8 ohm power rating for this amp.

Still it seems to me that when pushed very hard with bass heavey electronic music like drum'n bass, they seem to hit thermal compression.

I didn't run them up to the clipping point and they allways sound great, but they tend do start smelling a bit after 30 minutes of constant sub torture and the amps sometimes start hitting the clipping point wihouth me pushing the gain.

So we are at a constant level, the amps are not clipping during the first few minutes but after the coils warm up, they begin peaking into clip.

Also, i can't figure out why do they have a slight burning smell when pushed hard. They are rated at 600W continuous, they have been sitting for a few years so this might me some dust on the coils or it's too much power?

Search term of the day 'power compression'

[Paul G. OBrien]

Any processing inline with these? Limiter or compressor? And if so are you constantly engaging the limiter or compressor during these runs?

[Eugen Jeličić]

Scott, i meant thermal compression, the coils get hot, impedance changes, more power results with more heat, not SPL.

Paul, yes there is a dbx2231 in the line, it has a brickwall limiter, but we try not hitting the limiter, if i see it touching red, i turn the signal down.
However this is very bass heavey music, so at moments there are very long lasting sometimes compressed sublines

[Ivan Beaver]

Scott, i meant thermal compression, the coils get hot, impedance changes, more power results with more heat, not SPL.

Paul, yes there is a dbx2231 in the line, it has a brickwall limiter, but we try not hitting the limiter, if i see it touching red, i turn the signal down.
However this is very bass heavey music, so at moments there are very long lasting sometimes compressed sublines

Axctually-power compression means LESS power is going to the drivers.

When they get hot, the impedance rises.

For the same given input voltage, the POWER is actually less going to the driver.

The "compression" in the term means the output level is dropping.  At that point, people often turn it up to get the same loudness, and kill the drivers.

When they are going into power compression, they are at their limit.

[Eugen Jeličić]

Axctually-power compression means LESS power is going to the drivers.

When they get hot, the impedance rises.

For the same given input voltage, the POWER is actually less going to the driver.

The "compression" in the term means the output level is dropping.  At that point, people often turn it up to get the same loudness, and kill the drivers.

When they are going into power compression, they are at their limit.

That's right, and it seems to me that is what's happening here, event with the amps away from the clipping point.

But they do tend to start hitting the clipping point when i run them at a constant level for long enough with very bass heavey program.

Can thermal compression be the cause of this?
How does the amp respond to coil overheating/impedance rising. I understand the total output power of the amp will drop, but can this make it hit the clipping point earlier then when it's running a cold coil?

[Rob Spence]

That's right, and it seems to me that is what's happening here, event with the amps away from the clipping point.

But they do tend to start hitting the clipping point when i run them at a constant level for long enough with very bass heavey program.

Can thermal compression be the cause of this?
How does the amp respond to coil overheating/impedance rising. I understand the total output power of the amp will drop, but can this make it hit the clipping point earlier then when it's running a cold coil?

The amp doesn't care.
It is a voltage source. If the impedance rises, then there is less current (Ohms Law).

The amp clipping point is likely either the input stage or when you reach the max voltage the power supply rails can do.

You basically do not have enough subbage for your type of gig. You need either more, or better subs.


Sent from my iPad using Tapatalk HD

[Don T. Williams]

+1 for Rob's comments.

[John Roberts {JR}]

The smell is "pre-smoke" ....

JR

[Eugen Jeličić]

The amp doesn't care.
It is a voltage source. If the impedance rises, then there is less current (Ohms Law).

The amp clipping point is likely either the input stage or when you reach the max voltage the power supply rails can do.

You basically do not have enough subbage for your type of gig. You need either more, or better subs.


Sent from my iPad using Tapatalk HD

So then somehow a more powerfull signal got into the amps and pushed them into clipping,

if the smell is "pre smoke smell" then it means these p7000s are too much for these drivers. They tend to start smelling even with the amp away from the clipping point if the program is continuously rich enough below 100hz.

That's weird. 750-800W peak shouldn't be too much for a driver rated at 600w continuous AES.

[John Roberts {JR}]

So then somehow a more powerfull signal got into the amps and pushed them into clipping,

if the smell is "pre smoke smell" then it means these p7000s are too much for these drivers. They tend to start smelling even with the amp away from the clipping point if the program is continuously rich enough below 100hz.

That's weird. 750-800W peak shouldn't be too much for a driver rated at 600w continuous AES.

The heat comes from average power not peak...

JR

[Mark Wilkinson]

The heat comes from average power not peak...

JR

John, in over my head here...but is it possible this is a case of apparent power becoming more a function of real power (due to rise in coil resistance), than of reactive power when voice coil is cold?   ala 1.7 in this powersoft note http://www.powersoft-audio.com/en/downloads/technical-notes/804-how-to-setup-limiters/file  ?

Limit light's could look the same, but with even more heat going to coil ??

[Ivan Beaver]

That's right, and it seems to me that is what's happening here, event with the amps away from the clipping point.

But they do tend to start hitting the clipping point when i run them at a constant level for long enough with very bass heavey program.

Can thermal compression be the cause of this?
How does the amp respond to coil overheating/impedance rising. I understand the total output power of the amp will drop, but can this make it hit the clipping point earlier then when it's running a cold coil?

I HIGHLY doubt the amp is changing anything because of the speaker changing impedance.

If anything, (if the clip light was actually looking at the output vs input signals-like old Crowns-but not most amps) the clip light should be going on early and then not as much with a higher impedance load.

I SUSPECT that the program material has changed (unless you are running the same material (meaning the same song the whole time) and is putting out a higher drive voltage-EVEN IF you are not changing your fader levels.

Here is one other "possible" answer (but I don't think it is right-but just throwing it out there).

Let's say that the clip LED is for a specific output voltage.

When the driver is cold, the impedance will be lower-possibly pulling down the available output voltage.

When it heats up, the impedance is higher-so the amp can swing more voltage.  So the LED turns on.

This is a typical indication of a "sloppy" power supply.

I installed quite a few P7000s years ago.  I found the sound to be very "loose" on the low end.  Especially when compared to a Crest CA amp of similar power.

The Crest were A LOT tighter sounding and had more impact.

This was using the same full range speakers, but in different rooms.

But the results were the same each time.

[Paul G. OBrien]

That's weird. 750-800W peak shouldn't be too much for a driver rated at 600w continuous AES.

Actually the data I see says that driver is 1200w AES but go lookup what the AES standard is. They don't use sine waves for these test standards anymore it's a bandwidth limited noise signal with 6dB crest factor which is the difference between the dynamic peak of the signal compared to the mathematical average level. That means the driver can really only handle around 300-400w of continuous tones for any extended period of time so yeah a P7000 is more than capable of melting the drivers with the right program material. The solution is to use better limiters, maybe a DSP processor with both RMS and peak limiting.

[Eugen Jeličić]

Ivan, so your theory is that since the p7000s has a sloppy power supply, when the impedance is lower the power supply becomes a limiting factor so the amp never hits the voltage clipping point, but when the impedance goes up there is no need for the power supply to push that much current into the amp so the output voltage will be able to go up (the PSU is not a limiting point anymore) and that will cause clipping?

Of course it might simply be that i didn't test the system with enough different program material to see will the amps really clip.


Paul, you have been looking at the V2 of this driver. This is the first version, it's rated at 600W AES.

So yes, it seems like the p7000s is too much.
That's not really a problem i just need to turn it down a bit. But got used to having amps not powerfull enough for the box so i always see the clipping point as a warning sign.

I do understand that clipping is not what melts a coil, heat is. So, too much unclipped power can melt the coil too.

Ivan, yes i can agree, the p7000s is terrible for subwoofers.

[Ivan Beaver]

Ivan, so your theory is that since the p7000s has a sloppy power supply, when the impedance is lower the power supply becomes a limiting factor so the amp never hits the voltage clipping point, but when the impedance goes up there is no need for the power supply to push that much current into the amp so the output voltage will be able to go up (the PSU is not a limiting point anymore) and that will cause clipping?

I said it was a possibility-but not really a "good" possibility.

The better idea is that the level coming out of your mixer was louder later on, even if you didn't turn the faders up.

Most likely due to the program material being louder

[ProSoundWeb Community]