Speaker watt rating

[JohnH]

A 1 watt speaker is not going to cut it for a guitar amp...

No worries there - in this case I'm really just noodling around for my own educational purposes rather than building guitar gear!

[Simon Barden]

I have a forum mate who used to work for Blackstar. The only speaker brand he actually trusts for their ratings are Celestion. Anything else he'd match with an amp rated at half the speaker rating.

A lot of valve amps are rated around the point the THD exceeds 5%, i.e. when they still sound clean, but can put out a lot more power when really driven hard. A 100W Marshall amp can put out between 180-200W if really pushed. Transistor amps normally have far less headroom at this point and put out very little extra power if driven hard.

But as Marcel said, the average power level when playing a guitar is a lot lot less. All those gaps between the notes, plus the level dying away after the initial attack really lower the average energy level. I asked Celestion about the 90W rating of the speaker in my 100W Mesa Nomad and they said it was fine.

But until recently there hasn't been a universal standard for testing and rating speaker wattage e.g. at what frequency or mix of frequencies, how long the test went on for and what (if any) level of 'damage' was acceptable. There is now an AES standard, which does give a figure very close to most normal RMS watts figures, but it is a set test with known program material and a set duration.

[Simon Barden]

And one other fact I didn't know until recently, was that the reason that it's not a good idea to play bass through a valve guitar amp, is not due to the speaker, but to the output transformer. Most guitar amp OP transformers aren't big enough (low enough inductance) to cope with frequencies below 60Hz, so the power valves see a near short-circuit at those frequencies and can redplate, maybe burn themselves and/or something else out, or hopefully pop a fuse. At low volumes you are probably going to be OK. but turn it up and especially if using a 5-string and you could be in trouble, even if you are using a valve head into a bass cab.

[Marcel]

A sad but educational story....

Back in the late '80's a friend borrowed my Wharfdale cabinets for a party... He also borrowed my NAD 100W RMS stereo power amp....all in exchange for an open bar tab and a place to crash.... Anyway, it was a great party, lots of girls, I got rotten drunk, and soon as the very loud music stopped I closed my eyes and suddenly it was morning...or afternoon... or whatever...

I thought "I'll put some music on".. and only farty-fart-fart noises came out of my beautiful seriously expensive for the time Wharfdales... I was not impressed and after getting them home I sought out replacement 12" drivers. I had bought these speakers when I had a good job that paid lots of money, but at the time of failure I was essentially jobless thus couldn't afford to buy recones or replacement drivers yet I did find where I could get them...

Months latter I bought the two replacement 12" drivers.... To my surprise the packaging said they were rated at 25W each.... but the originals had lasted over 8 hours connected to a 100W RMS per channel amp at 'party volume' for over 150 people. So I investigated further and found the old drivers hadn't actually blown but the voice coils were overheated and had melted enough to cause binding to the magnet housing. There was a lot of other damage so I felt justified in getting full replacement speakers...

With the knowledge gained from my experience above I had little fear a year or two later in hooking up a newly acquired amp to my Wharfdales... Through a lucky stroke I scored a Jands 920 power amp for a very reasonable price... 450W RMS per channel... I knew what I was doing. I knew what I was risking if I turned it up, and I was in a small flat with a lounge room barely 25sq m in size..... My mistake was not to pull the fuse when I left my flatmate alone with my enhanced "home stereo"... It took her about a month to find the master volume control, and I found out the same evening that she had found it with the comment "There's something wrong with your stereo... I turned it up and it was all right for a while, then it started making weird sounds, so I turned it off".... And sure as hell I remember I found the Master volume set at 8.

So the Wharfdales got packed away, as did the NAD amp. The 920 got sold to a PA hire company.... And about 5 years ago I bought yet another set of replacement drivers, both the LF 12" and this time also the HF horns. Watching movies and the occasional DVD or blueray for an older couple like us is a walk in the park when compared to a party for 150 twenty-somethings...

[wazkelly]

For what it is worth I played 4 string bass through a 1970's Marshall Super Bass Valve Head into a quad box loaded with 4 x 12" Green Back 25 w Celestions. Never had a problem with bottom end reproduction, even when I played the Riccy 4001 in Stereo through both 'inputs'. The amp was ridiculously loud and rarely played past 1 as it didn't have a master volume control, and any higher just drowned out everyone's stage sound plus front of house. Fiver's weren't around back then so not able to comment on how that may have sounded, but seriously, if using a DI stage sound is only for your own benefit as signal would also be pumped back through foldback monitors for others to hear, including yourself.

[MrZhdens]

I tried figuring out what was going on once with my speakers and I nearly electrocuted myself Ever since then I knew that I was a real clutz when it came to electricity and in general the technical stuff. Every time I am doing a gig or playing at an event I have been hiring a company that provide me with both lighting and speakers for a gig. I have been looking for a good company that would be able to provide a good speaker hire that would not have unreasonable prices. i found one that I liked and they have been helping me out ever since. They are really good. They also provide services that are good for major events like weddings or a big birthday or something.. So yeah they are always top notch

[Simon Barden]

And transistor power amp clipping is far more damaging to HF tweeters than main drivers. HF drivers aren't making the long low frequency excursions that the larger drivers make which provide airflow across the coil for cooling.

[JimC]

Also that typically and especially in bass rigs the tweeters aren't specified for the full rated power of the cab because in normal circumstances they will only see a fraction of the total. That's a bit two sides of the coin though with Simon's point because typically its heat dissipation that limits the power rating.

[Simon Barden]

The heat dissipation capability defines the power rating.