How many watts is too much?

[lownote]

I am running an Ashdown MAG 300 Evo II through two Phil Jones cabs, a 47 and 27.  The head is rated at 325w RMS. The bigger cab is rated at 300w, but its baby sibling only 200w. Are there out there any cab experts who can tell me if I'm risking the health of the 27 by running the amp at full power?  I see from the Barefaced site that their One10 is 250w but can take 500w, which surprises me.    It's not yet proved necessary to go beyond mid way wick on the amp with my current band, but I just wondered where the 'do not exceed limit' might be on the 200w cab.  

Edited December 14, 2020 by lownote12

[BassmanPaul]

You need to tell us what impedances are in play here.

Amp: 325W into what impedance?

Cab 47: What impedance?

Cab 27: what impedance?

[BassmanPaul]

Having looked on-line both cabinets are 8Ω therefore 4Ω when run in parallel. the Amp will supply 325W into that impedance. Split equally between the cabinets each one will see 162.5W. Your baby cabinet will be fine!

Edited December 14, 2020 by BassmanPaul

[Bill Fitzmaurice]

1 hour ago, lownote12 said:

I just wondered where the 'do not exceed limit' might be on the 200w cab.  

If it distorts turn it down. The power required to do that is moot, as you have no way of knowing how much power you're pushing anyway.

[bazzbass]

best advice is to test it without the other band members,turn the volume up gradually,listening to the cabs for farting. I doubt you'll have any problems.

[lownote]

15 hours ago, BassmanPaul said:

You need to tell us what impedances are in play here.

Amp: 325W into what impedance?

Cab 47: What impedance?

Cab 27: what impedance?

Amp is 300, not 325 as I said earlier.soz.  300@4ohms.

Cabs are both 8 ohm.

I am running them daisy chained: amp -> cab1->cab2

[Beer of the Bass]

If both cabs are the same impedance but one has two drivers and the other four, the drivers in the 27 cab will be working harder than in the 47. That's not necessarily a problem, but I'd put the 27 on top to increase your chances of hearing it if it does start to complain.

[Dan Dare]

Bill's right. Power output figures claimed by amp manufacturers tend to be over-stated. An amp may produce its stated maximum power output over a few milliseconds at, for example, 1khz into a resistor, but it will be very unlikely to be able to sustain that. You will hear distortion if you are pushing a speaker too hard. Most speakers can handle short term bursts/peaks above their rated power, anyway.

[Phil Starr]

14 hours ago, BassmanPaul said:

Having looked on-line both cabinets are 8Ω therefore 4Ω when run in parallel. the Amp will supply 325W into that impedance. Split equally between the cabinets each one will see 162.5W. Your baby cabinet will be fine!

This is correct and in all probability you will be safe.

'all probability' is a scientists answer of course. You will almost certainly be safe. The doubt comes because speakers and amps aren't rated in the same ways. Amps are essentially rated on how much electricity they can pour into your speakers. Speaker limits are measured by how much heat they can take before they burn out, a thermal limit. Heat and music aren't the same thing. the heat limits are measured with a continuous signal and the bass filtered. Music isn't continuous so the speaker has chances to cool down, that's why Barefaced and nearly everyone else give a music rating for their speakers twice the heat limit. They are assuming that most of us won't do anything stupid and most of the time won't blow our speakers.

The second factor is that the test for speakers filters bass and bass players sometimes boost bass. The reality though is that if you use the rule of thumb that 200W into a 200W speaker is OK you are going to have to do something really silly to damage your speaker.

[lownote]

30 minutes ago, Phil Starr said:

This is correct and in all probability you will be safe.

'all probability' is a scientists answer of course. You will almost certainly be safe. The doubt comes because speakers and amps aren't rated in the same ways. Amps are essentially rated on how much electricity they can pour into your speakers. Speaker limits are measured by how much heat they can take before they burn out, a thermal limit. Heat and music aren't the same thing. the heat limits are measured with a continuous signal and the bass filtered. Music isn't continuous so the speaker has chances to cool down, that's why Barefaced and nearly everyone else give a music rating for their speakers twice the heat limit. They are assuming that most of us won't do anything stupid and most of the time won't blow our speakers.

The second factor is that the test for speakers filters bass and bass players sometimes boost bass. The reality though is that if you use the rule of thumb that 200W into a 200W speaker is OK you are going to have to do something really silly to damage your speaker.

Many thanks.

Edited December 15, 2020 by lownote12

[Japhet]

The strength of the signal going into the amp will make a big difference too. An active bass and a hot signal would create a load more volume whatever the wattage being supplied by the amp.

[Bill Fitzmaurice]

I'm afraid not. With no changes to any of the amp controls a hotter input signal will result in increased power output.

[Japhet]

1 hour ago, Bill Fitzmaurice said:

I'm afraid not. With no changes to any of the amp controls a hotter input signal will result in increased power output.

Thought that's what I said (presumably not very well).

[lownote]

Phil Jones themselves have had the last word on this.  Just got an email to say they've run the Cab27 with an 800w head.  So clearly, that's all right then!

It's amazing what 7 inches will do.

Edited December 15, 2020 by lownote12

[BassmanPaul]

As long as you don't get a volume surge above 200 odd watts! You can run a 5W speaker from a 1KW amp as long as you don't drive it past that 5W rating! 

[bumnote]

I have been using Phil Jones stuff since 2011. [8b,6b,12B, 2xC4,.

I have at times given them serious abuse and they have never let me down.

 

[Balcro]

Lownote12 is daisy chaining his two 8 Ohm speakers. Series?

For the impedancely challenged like me, what is the resulting impedance shown to amp?

Is the input power equally distributed across the 6 drivers?

What is the overall power handling of the speaker pair?

 

[BassmanPaul]

Daisy chaining, amp to speaker 1, speaker 1 to speaker 2 is still a parallel connection. The result is 4Ω.

[agedhorse]

19 hours ago, Phil Starr said:

This is correct and in all probability you will be safe.

'all probability' is a scientists answer of course. You will almost certainly be safe. The doubt comes because speakers and amps aren't rated in the same ways. Amps are essentially rated on how much electricity they can pour into your speakers. Speaker limits are measured by how much heat they can take before they burn out, a thermal limit. Heat and music aren't the same thing. the heat limits are measured with a continuous signal and the bass filtered. Music isn't continuous so the speaker has chances to cool down, that's why Barefaced and nearly everyone else give a music rating for their speakers twice the heat limit. They are assuming that most of us won't do anything stupid and most of the time won't blow our speakers.

The second factor is that the test for speakers filters bass and bass players sometimes boost bass. The reality though is that if you use the rule of thumb that 200W into a 200W speaker is OK you are going to have to do something really silly to damage your speaker.

Except that most bass speakers fail from exceeding their mechanical limits not their thermal limits. 

The mechanical limits of a speaker can be as low as 1/2 the thermal rating, and when you exceed the mechanical limits you cumulatively cause damage to the suspension components and reduce their lifespan. Also, mechanical power handling decreases as frequency falls below ~100Hz on most speakers.

Generally, when you match the amplifier power (in RMS metrics) with the speaker rating (in RMS metrics) you will be reasonably well matched. This is a rule of thumb that’s holds up pretty well in the real world IME.

[Phil Starr]

3 hours ago, agedhorse said:

Except that most bass speakers fail from exceeding their mechanical limits not their thermal limits. 

The mechanical limits of a speaker can be as low as 1/2 the thermal rating, and when you exceed the mechanical limits you cumulatively cause damage to the suspension components and reduce their lifespan. Also, mechanical power handling decreases as frequency falls below ~100Hz on most speakers.

Generally, when you match the amplifier power (in RMS metrics) with the speaker rating (in RMS metrics) you will be reasonably well matched. This is a rule of thumb that’s holds up pretty well in the real world IME.

@lownote12 this above is all true IMO.

@agedhorse hence my comment about filtering bass, and what the player does about boosting bass. I did think about going into mechanical limits but wanted to keep it simple and stick to talking about how the ratings were made, so I kept comments to thermal limits which were quoted in the original post. I think this is a question simply asking 'is my speaker safe'. As we agree matching speaker ratings to amp ratings is a generally good rule of thumb for real world bassists.

[lownote]

Well, from what everyone says I think if I keep the gain down to under 12 oc and the volume very little more I should be alrighty.  Phil Jones speakers are pretty top quality, so if Alex's BF 10" can take 500w, even though rated at 250w, I'm sure Mr Jones' finest 7 incher (ooer missis) can cope with 300w. 

[Bill Fitzmaurice]

Seems logical, but the position of the knobs doesn't limit the output of the amp. All you can say with any certainty is that with the gain set at 4 it won't be as loud as when it's set at 6. How much power either will result in one can't say, as it doesn't account for the other half dozen or so variables. What one can say with certainty is that if you hear the drivers straining to handle the low notes you're approaching mechanical failure, so back off on the gain or volume or bass EQ or instrument output or all of the above.

[itu]

3 hours ago, lownote12 said:

Well, from what everyone says I think if I keep the gain down to under 12 oc and the volume very little more I should be alrighty.

Adjust the gain so, that the input is not distorting. Check it with low volume level. This way you amplify the signal, not the noise!

Gain is just an adjustment. It has to do with good and good quality signal level. If it has to be at 3 o'clock, be it so. 

[Bill Fitzmaurice]

You can use the gain to add some edge and grit to the tone. Set it with the master volume low at first, then bring the master up. The sound with a bit of overdrive is related to the sound of drivers being pushed too hard, but it's not the same. Overdrive sounds the same no matter where the master is set. Over-excursion distortion gets worse as you turn the master volume up, disappears when you turn the master volume down.