200 watt Marshall amp into 2 650 watt cabs...

[jcburn]

Hello everyone.
Now before I don the flame retardant suit I need everyone to realise I've read the "Underpowing Cabs" sticky, and I guess because I have a specific question I couldn't really find an answer that I was happy with.
I recently tried a Marshall DBS 7200 (200 Watts RMS at 4 ohms, 2000 Watts peak) through my 2 Ashdown ABM cabs(650 watts RMS @ 8 ohms each, 900 watts peak). It sounded incredible to me - just the sound I am after.
I did have the input gain cranked fairly high(but only typically so that the clip light flickered here and there), and to get the volume I wanted I also had the master volume at about 3 o'clock. With FOH support I may not need to go this high but on this occasion I did need this level of volume.
Now at no stage did I experience any speaker distortion, but I am concerned that I am underpowering the cabs and possibly melting voice coils.
I did read in the sticky a comment by Bill Fitzmaurice, who I respect for his opinions, saying that matching amp output ratings to cab ratings is flawed as promoted cab ratings are usually a maximum power handling, and that to operate a cab safely and efficiently they only need a fraction of this.
And yes - my question is should this be safe to operate, and what signs should I look for to say things might go pear shaped? I will have the chance to try the amp again in a band setting. Also even if the speakers dont distort could damage be done to them by underpowering that isn't obvious?
Thanks all - I realise this is covered all the time, I guess I am after some advice to my specific question, not just a general one about underpowering cabs.

[Jim Carr]

Assuming you are not using distortion—either as an effect or as a by product of over-driving your preamp or power amp—you should be able to hear whether or not your speakers are distorting. When they sound distorted, turn down and or reduce the lows until the tone is clean. Your speakers will be safe.

[dincz]

Originally Posted by jcburn

Also even if the speakers dont distort could damage be done to them by underpowering that isn't obvious?

If you disconnect them and leave them in a corner unused for 20 years, they will deteriorate - but not from underpowering.

[Downunderwonder]

Originally Posted by jcburn

Marshall DBS 7200 (200 Watts RMS at 4 ohms, 2000 Watts peak) through my 2 Ashdown ABM cabs(650 watts RMS @ 8 ohms each, 900 watts peak). It sounded incredible to me...

Read the underpowering sticky again?

I realise the sales pitch of the DynamicBassSystem implies you can put 2000W temporarily through your speakers. So you would be overpowering them briefly by 100W each. I find the 10:1 peak to RMS power claim kinda unreal myself.

No distortion, nowhere near the rated thermal power unless you give it a real slam, happy as a clam.

[CL400Peavey]

Originally Posted by jcburn

Now at no stage did I experience any speaker distortion, but I am concerned that I am underpowering the cabs and possibly melting voice coils.

How is less power going to melt a voice coil when more wouldnt?

[jcburn]

Originally Posted by CL400Peavey

How is less power going to melt a voice coil when more wouldnt?

I have limited understanding but the way I see it is that if I am driving the amp to clipping by cranking the gains and volumes in an effort to produce more volume, then sending this signal to the cabs can cause them to perform ineeficiently, causing heat and damaging voice coils. Some please chime in if this is incorrect.
I am just wondering - how different does a clipping amp signal sound from speaker distortion? How would one describe these sounds?

[basscooker]

distortion and overdrive have a very familiar sound, and if you hear it and you aren't doing it on purpose, adjust something. that's the way i see it as far as amps go.

now, speaker distortion, as i understand it, is literal. you are DISTORTING the driver's design with too much power, typically this is VERY evident, described typically with the highly technical term "farting".
as far as burning up voice coils, i know nothing, and i accept this. unless it's a combo amp, or designed for use with an amp, i just stick as close as possible to the 1/2 power "rule" : 300 watt amp needs 600 watts overall driver rating, and so on. newer drivers, tho have been challenging this.

[Downunderwonder]

My trace preamp distorting sounds like ass to my ears, similar to what some guys like in a "fuzz" pedal. If your power amp was doing that it would be very very evident to your ears.

Flapping my 15" speaker is something I studiously avoid but it's more organic and comes on slowly. You aren't getting any of that so you don't have a thing to worry about.

Overpowering kills speakers, not underpowering, rinse and repeat.

[Downunderwonder]

Things to look for:

Audible distortion
Volume going down over time can indicate you are heating up your speakers.
Deafness, 2 900W 4x10 full blast is going to deafen you quickly, wear earplugs!

Most guys on here would flay them with a 500W amp, minimum, they would have a lot more to worry about and perhaps a 3dB edge on you. Depending on how often you dig in hard the "2000w" boost system might keep up just fine. They would have no edge on you.

Dynamics and punch are dependent on headroom and the speaker's ability to give more. Too much punch flaps the speakers. If the bass is all blah blah blah blah loud with no dynamics because headroom has already been used up the risk is cooking speakers from over powering, not underpowering.

With your setup it seems the dynamic punch is satisfying you. The amp is only rated 200W RMS coninuous, 1/10th of the speakers, happy days.

[jcburn]

Originally Posted by Downunderwonder

Things to look for:

Audible distortion
Volume going down over time can indicate you are heating up your speakers.
Deafness, 2 900W 4x10 full blast is going to deafen you quickly, wear earplugs!

Most guys on here would flay them with a 500W amp, minimum, they would have a lot more to worry about and perhaps a 3dB edge on you. Depending on how often you dig in hard the "2000w" boost system might keep up just fine. They would have no edge on you.

Dynamics and punch are dependent on headroom and the speaker's ability to give more. Too much punch flaps the speakers. If the bass is all blah blah blah blah loud with no dynamics because headroom has already been used up the risk is cooking speakers from over powering, not underpowering.

With your setup it seems the dynamic punch is satisfying you. The amp is only rated 200W RMS coninuous, 1/10th of the speakers, happy days.

Thanks mate - that answer makes sense to me. My concerns were that I may be "underpowering" the cabs, creating coil heating issues but your response makes sense. On occasion I will have to have the output volume cranked a little (i.e. 3 o'clock-ish) and I was concerned that I may be doing speaker damage without being able to hear it. I guess as long as the sound stays clean and I cant hear any distortion then all is good yeah?

[CL400Peavey]

Please read the FAQ at the top of the forum. There is no such thing as underpowering a speaker.

[jcburn]

Originally Posted by CL400Peavey

Please read the FAQ at the top of the forum. There is no such thing as underpowering a speaker.

Sorry - yes I do realise that - I guess I just used the term "underpowering" cause everyone understands what I'm getting at.
Suffice to say I think the setup I'm suggesting will be safe, and that I shoukld use my ears to judge if there is anything going wrong.

[Clammy]

Before getting my current VBA 400, I ran old Marshall Super Bass amps (100W), into 4x12 and 2x15 cabs with a combined rating of 1200W (400W for the 4x12 and 800W for the 2x15). I ran the amp hard, with plenty of distortion, and in 10 years never had any speaker issues (or amp issues).

Cheers!