Bass/Guitar through a h ifi amp

[JungleVip]

I was hoping to have some light shed on this. I can understand how hi-fi speakers can be blown by bass or guitar because there construction can be less sturdy but what about amplifiers?

How could a bass signal blow an amp? Is it something that happened in older equipment or certain types? Is it a misnomer or is it a myth?

[Steve Conner]

As far as amps go it is a myth. Some old, cheap, nasty hi-fi amps might have no protection circuits, undersized transformers and heatsinks, and might blow, but these could just as easily be destroyed by cranking the hi-fi too loud at a party.

The problem with the speakers isn't so much the construction, as the sensitivity. A hi-fi speaker can be 10dB less sensitive than a musical instrument one. So to get the volume you want, you will crank the amp right up and ram 10 times more power into it. Lo and behold it goes up in smoke.

Musical instrument speakers are more robust because they are more sensitive- your ears start to hurt before the speaker burns out.

Sensitivity, bass extension and physical size are a three-way tradeoff, which is one reason why hi-fi speakers are insensitive, and why a surprising number of bass guitar cabinets don't bother to maintain a flat response down to the low E at 42Hz, let alone the 33Hz B on a 5-string.

[kg]

i agree with steve.. a properly designed amp should have no issue with any program material you could throw at it.

in fact, for years i used a crest vs900 power amp in my rig... not a "hi fi" amp per se--more of a sound reinforcement amp--but it worked just fine in that capacity.

[JungleVip]

This is the story so far:

[JungleVip]

So far I have two subs as shown, but I think they are hi-fi speakers. Its ok with a bass through a pre-amp and ok with a mp3 player. But not great at either...

So the plan is to put some full range speakers on the rear(magnet to magnet) and turn it into a mini boominator, run the amp at a higher wattage with 2 x 8ohms in parallel per channel giving 4ohms(I think?)

I think this will do the mp3 player well but are there any things like:
High/Low pass filters
Dynamic Noise/Audio limiter

In various (switchable) configurations that would improve it as a bass guitar amp.

JV

[J M Fahey]

The difference lies in the designer's expectations , and their influence on the actual physical design.
A Home use Hi Fi amp will normally be run at no more than continuous 10% of its rated output , meaning a 100W amp will be usually run at no more than 10W continuous (which is a quite loud home volume) , because good music sounds very clean and realistic with that 10:1 ratio to accomodate its dynamic range.
And if music is just a background when you work or do something else, you might be using it at 1W continuous, which still is more than the power of an annoying, blaring table radio or kitchen TV.
Then the regular Home Hi Fi designer takes that perceived market and designs a (cheaper/competitive) product which, in fact, will last years of home use .
Which 100W home system will get to Wal Mart shelves?: a 150$ one which satisfies 99% customers or a similar 250$ one that goes the extra mile?
See it from another point of view: you can have a 5W, 50W or 500W RMS per channel amp, your neighbours will kill you if you use it at over 5W all day long, and will accept, say, 60W RMS some Friday or Saturday nights but it'd better be a Birthday or equivalent party.
Now, you have a 100W musical instrument amp, you use it at 40/60W at least , even in a garage, if you want to compete with the drummer, and for long hours, practically non-stop.
A DJ will also drive his amp hard.
And, kg, I wouldn't consider

a crest vs900 power amp

the typical (Home) Hi Fi amp we are talking about ... although it would doubtlessly excel in that use.
In a nutshell: I wouldn't consider that old Sansui 100W amp I got for $20 at Salvation Army shop a proper "100W" guitar or bass amp although it might *electrically* supply that power.
Or I would add a small fan plus a couple strategic ventilation holes.
Original heat sinks are often small and/or inside the chassis, with some small vents cut in the chassis.

[teemuk]

Really depends, though... My early 1980's Sansui (2x50W) has the typical heatsinking configuration of the day: Four TO3 transistors bolted to the chassis, which is about 3mm thick aluminum. It would likely suffer a horrible death if cranked. Then again, my mid 1990's Pioneer amp (2x75W) has bigger heatsink and PT than any similarly rated guitar amp I've ever seen, the sink actually takes a good 1/4th of the chassis space. More output transistors in parallel too. It also "chimneys" the air from below the chassis to top, as both bottom and top panel are equipped with ventilation holes.

As for speakers for domestic audio and PA/MI, the issue goes beyound "sensitivity": The robust speakers for MI/PA are designed for abuse, because they had to be. This means higher temperature withstanding materials are used in things like voice coil winding insulation and all kinds of adhesives. The coil itself usually has a passive cooling arrangement and it is most likely thicker. Domestic audio speaker can on the other hand cope with thinner voice coil, which makes easier to build speaker with better linearity. PA/MI speakers are usually also designed for greater cone excursions (eg. voice coil winding supports that, cone materials support that), which again is a design choice that sacrifices linearity but makes the speakers more robust. Overall, its easier to develop a speaker with good linearity but poor heat dissipation and tolerance of over excursion (good for domestic HiFi), or poor linearity but good heat dissipation and tolerance of over excursion (good for PA/MI duties). Combining all the three is damn near impossible.

[J M Fahey]

Combining all the three is damn near impossible.

Yes, real world is "compromise world"
Depending on target you optimize one variable and try not to loose too much on others.
That's why there are so many different versions of what's functionally the same product.

[Zipslack]

intrustment vs. hifi speakers

Here's an excellent explanation of why hifi speakers would not cut it as high-volume instrument amplifier speakers, complete with pretty pictures and graphs. In a nutshell, amplifier speakers are made to temporarily handle being pushed past their limit, while the demands of hifi mean that the speaker will be damaged by being pushed past their limits.

GM Arts - Guitar Amplifiers