better to under or overpower cabs?

[bass_ferret]

[quote name='Catalin' post='251988' date='Jul 31 2008, 12:39 PM']So a distorting tube power amp can damage speakers just like a clipping solid-state power amp ?[/quote]
yes. Ampeg developed the 8x10 cab because it was the only way to get enough drivers to cope with the 300 watt SVT.

[alexclaber]

[quote name='bass_ferret' post='252083' date='Jul 31 2008, 02:56 PM']yes. Ampeg developed the 8x10 cab because it was the only way to get enough drivers to cope with the 300 watt SVT.[/quote]

Though with modern technology it would only take two 10" speakers voice coils to dissipate that heat without suffering damage, which I believe is due to higher temperature resistant materials. You could clip an SVT all day long into a modern neo 2x10" without hurting the woofers - survival of the tweeter would be much less likely, though hopefully there'd be some kind of bulb or polyswitch protection that would blow or trip to prevent it burning out.

However, crank up the bass knob on the amp and slap some B-string notes and you could easily drive the woofers into suffering mechanical failure from over-excursion, which is by far the more common failure mode for bass cabs.

Alex

[NickS]

On alt.guitar.amps there was recently mention of "hang time" in relation to driving speakers, the idea being that with a square wave into a woofer it would be possible to have the voice coil stationary for most of each half cycle, and that excessive power would be dissipated in the relatively low resistive load (?) of the stationary voice coil. This may be where the idea of DC came from, along with the suggestion that direct-coupled amps are more likely to produce a perfect square wave at low frequency than transformer-coupled amps.

[Bill Fitzmaurice]

[quote name='alexclaber' post='252092' date='Jul 31 2008, 10:10 AM']Though with modern technology it would only take two 10" speakers voice coils to dissipate that heat[/quote]It wasn't the heat, it was the excursion. The original 1969 SVT drivers were guitar drivers, with perhaps 1mm xmax. It took two of the 8x10 cabs to handle the 300 watt head clean. Longer xmax drivers were introduced in the early 70s and since then only one cab was required.

[quote]On alt.guitar.amps there was recently mention of "hang time" in relation to driving speakers, the idea being that with a square wave into a woofer it would be possible to have the voice coil stationary for most of each half cycle, and that excessive power would be dissipated in the relatively low resistive load (?) of the stationary voice coil.[/quote]Complete utter total piffel. That never happens. Said post was not made by a competant transducer engineer. Railroad engineer, maybe.

Edited July 31, 2008 by Bill Fitzmaurice

[Protium]

I am still going by the argument that the speaker does not care what shape the waveform is, as long as the mechanical limit (Xmax) of the speaker is not exceeded.

[Bill Fitzmaurice]

[quote name='Protium' post='256141' date='Aug 6 2008, 07:05 AM']I am still going by the argument that the speaker does not care what shape the waveform is, as long as the mechanical limit (Xmax) of the speaker is not exceeded.[/quote]
Exceeding xmax doesn't bother anything, it just makes for a dirty/compressed tone. Guitar players get their tone by exceeding xmax, and being able to do so in the midrange is why guitar drivers have small xmax values.
Exceeding xlim OTOH has disastrous consequences.

Edited August 6, 2008 by Bill Fitzmaurice

[Protium]

[quote name='Bill Fitzmaurice' post='256372' date='Aug 6 2008, 03:18 PM']Exceeding xmax doesn't bother anything, it just makes for a dirty/compressed tone. Guitar players get their tone by exceeding xmax, and being able to do so in the midrange is why guitar drivers have small xmax values.
Exceeding [b]xlim[/b] OTOH has disastrous consequences.[/quote]

This value is probably what I meant the shape of the waveform does not matter.

[Bill Fitzmaurice]

[quote name='Protium' post='256462' date='Aug 6 2008, 11:50 AM']the shape of the waveform does not matter.[/quote]
Not a whit. BTW, what happens when you push a driver past xmax? It creates clipped waveforms, in exactly the same fashion as do over-driven amps, or stomp-boxes.

[KiLLaGoD]

Maybe I've got the wrong idea here but I've always been told that where possible you should use a power amp matched to the speaker cabs wattage exactly. So a 1000w speaker cab should be driven by a 1000w power amp. Then you should keep the power amp turned up full and control the volume with a pre amp just like you would do with a PA system only it would be a mixing desk rather than a pre amp.

[Bill Fitzmaurice]

[quote name='KiLLaGoD' post='314511' date='Oct 25 2008, 09:19 AM']Maybe I've got the wrong idea here but I've always been told that where possible you should use a power amp matched to the speaker cabs wattage exactly.[/quote]
Been told by whom? Certainly not a quailfied engineer. Anywhere from a 2:1 to a 1:2 amp power to speaker power rating is well within the useble range in most cases. A 2:1 amp power to speaker power ratio won't hurt speakers, assuming one has enough sense to turn the volume control down if the speakers distort, while a 1:2 ratio is usually adequate to drive the speakers to their full output capacity, as that capacity is determined by the excursion limit of the cones, not the thermal power rating.
The only immutable rule is that there is no immutable rule.

[bass_ferret]

[quote name='Bill Fitzmaurice' post='314546' date='Oct 25 2008, 03:22 PM']snip................
The only immutable rule is that there is no immutable rule.[/quote]
yes there is: [b]You can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur[/b]

[alexclaber]

[quote name='bass_ferret' post='314565' date='Oct 25 2008, 04:06 PM']yes there is: [b]You can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur[/b][/quote]

My general guideline works in 99% of cases. The cases where it might fall down are when a bassist is using a deliberately nasty sound and thus can't tell good nasty from bad nasty or where the amp power vs thermal power handling ratio is so large that thermal damage occurs before the onset of mechanical damage - I've heard of this happening once when bridging a large power amp into a single Acme Low-B2 2x10" and EQing down the bottom to get maximum output, the result being a melted voice coil. That takes some doing though!

Alex

[Stag]

Quick query on this then :

I have a Trace 300w 4ohm min load head. If I drive my Ampeg 4x10 (400w, 4ohm) on its own, I get 300w straight through it... right?

If I daisy chain my Trace 15x10 (300w, 8ohm) into the equation via the Ampeg, I actually only get 100w through the Ampeg, and 200w through the Trace cab, due to the ohmage?

My simple question is : the two cabs will certainly be louder than one. Why? Is it not better to just dump all that power into one cab? Im a bit of a beginner at this electronics business.

[Merton]

[quote name='Stag' post='336590' date='Nov 25 2008, 08:13 PM']Quick query on this then :

I have a Trace 300w 4ohm min load head. If I drive my Ampeg 4x10 (400w, 4ohm) on its own, I get 300w straight through it... right?

If I daisy chain my Trace 15x10 (300w, 8ohm) into the equation via the Ampeg, I actually only get 100w through the Ampeg, and 200w through the Trace cab, due to the ohmage?

My simple question is : the two cabs will certainly be louder than one. Why? Is it not better to just dump all that power into one cab? Im a bit of a beginner at this electronics business.[/quote]
Noooooooooooooooooooooooooooooooooooooooooo, don't do it. You'll be making the load 2.66ohms, wich is below the rated 4 ohms. This is a Very Bad Thing for solid state amps and will cause the output devices to fail.

[Stag]

Ummm - in plain English then, should I just be using one cab, or two? The thread at the top of the forum refers to [url="http://www.duncanamps.com/technical/impedance.html"]http://www.duncanamps.com/technical/impedance.html[/url] - ive had a shufty at that, and that infers that id be doing 12ohms total impedance, so ummm..... oh I dont know!

And if I cant just use the head and the Ampeg alone- why not? They are both rated at 4ohm... so that would be ok?

Sorry to sound daft, but, i am when it comes to this! Basically - both together, or not?

Cheers peoples

EDIT - is it just daisy chaining that is the issue... could I run each cab from separate outs on the amp?

EDIT 2 - so, basically, according to [url="http://www.about-guitar-amps.com/speaker_ohms_calculator.html"]http://www.about-guitar-amps.com/speaker_o...calculator.html[/url], I cant really ever really use any combination of 4ohm cabs at all with my amp, because it's min load is 4ohm?

EDIT 3 - sorry, will stop editing soon. Sooo... [url="http://www.britishaudioservice.com/inst/SMC.PDF"]http://www.britishaudioservice.com/inst/SMC.PDF[/url] is my amp. Now that has REALLY confused me - the pic of the backplate states (as I said before) - "Min load 4ohms" but the Tech Specs page has completely befuddled me as there are about 6 difference impedance values. Hellllllpppppp!!!! (lol)

Edited November 25, 2008 by Stag

[Protium]

[quote name='Stag' post='336590' date='Nov 25 2008, 08:13 PM']Quick query on this then :

I have a Trace 300w 4ohm min load head. If I drive my Ampeg 4x10 (400w, 4ohm) on its own, I get 300w straight through it... right?

If I daisy chain my Trace 15x10 (300w, 8ohm) into the equation via the Ampeg, I actually only get 100w through the Ampeg, and 200w through the Trace cab, due to the ohmage?

My simple question is : the two cabs will certainly be louder than one. Why? Is it not better to just dump all that power into one cab? Im a bit of a beginner at this electronics business.[/quote]


You can only use one cab at one time otherwise you'll be running less than a 4ohm load (connected in parallel).

Running more speakers can push more air = more volume.

[xgsjx]

So if I set my input level on an amp in a combo so that the clip lights just blip on the hard notes of an active bass, should I in theory, be able to turn the output level all the way up without fear of doing any damage or is it the initial "pop" from a note (either slapped or picked or whatever) that puts the drivers at risk?
Obviously turn down if it sounds bad in reality, but just trying to get a feel for what is & is not possible as I still get scared by how much I'm moving the drivers, but it does sound clean enough.

[Stag]

me again...

So, basically, I can only ever use one 4ohm cab with my amp? Thats a bit sh*te! Why arent all cabs made at 8ohm?

Second thing... if I wired them in series (Is that basically daisy chaining?) would that be OK as per [url="http://www.tunemybass.com/bass_amps/how_to_hook_up_heads_and_cabinets.html"]http://www.tunemybass.com/bass_amps/how_to...d_cabinets.html[/url] , because the load would be 12ohm rather than 2.67ohm (if I wired in parallel using both outs on the amp) ?

Im such a noooob! haha!

[Protium]

[quote name='Stag' post='336737' date='Nov 25 2008, 11:01 PM']me again...

So, basically, I can only ever use one 4ohm cab with my amp? Thats a bit sh*te! Why arent all cabs made at 8ohm?

Second thing... if I wired them in series (Is that basically daisy chaining?) would that be OK as per [url="http://www.tunemybass.com/bass_amps/how_to_hook_up_heads_and_cabinets.html"]http://www.tunemybass.com/bass_amps/how_to...d_cabinets.html[/url] , because the load would be 12ohm rather than 2.67ohm (if I wired in parallel using both outs on the amp) ?

Im such a noooob! haha! [/quote]

You can only ever run a 4ohm [i]minimum[/i]. TO do this you can run one 4ohm cab, two 8ohm cabs or four 16ohm cabs. You can also run a load higher than 4ohms, but never less.

If you wired the two cabs in series you would have a 12ohm load but would require a specialist cable to be able to do it.

[Stag]

hmmm... starting to think I shouldnt have invested in a 4ohm cab then, as it renders my other cab pretty useless... unless I get a 2 ohm head in the future. Oh well... shame I got confused with all the maths

[Protium]

To be honest there aren't many situations where you need that size rig to be heard. I've never had volume issues with a 300W head + single 4x10" 8ohm cab.

Edited November 25, 2008 by Protium

[Stag]

I doubt ill have issues to be honest, that 300w will get heard pretty clearly out of an Ampeg 4x10 400w cab, probably better than out of my poor old custom built 2x10 and 80's Trace cab - just would have liked to have the whole caboodle all together to look proper raaawwwk! Hehe. At least the missus will be happy because ill only be carting one big cab around with me now...

...still a b*gger about 4ohms tho innit? Seems odd to make them like that if you could make them all at 8ohm and everyone would be as happy as Larry.

Does give an excuse to blow some serious dosh an an SVT 2ohm head at some point though - lol

[Stag]

...and thanks for your help Protium, you've explained something quite foreign to me that I might just remember now!

[Protium]

No problem
I think the 4ohm option is available so you don't have to lug around two 4x10's. I do agree though, nothing beats a giant bass stack!

[Stag]

If only the Ampeg had been 8ohm I would be pushing one hell of a lot of air at my next gig - very very loud indeed, deaf audience, 5 x10's and a 15 ! lol !

Although from what you have been saying and what ive been reading, I should a hefty sound at 4ohms from the 4x10 on its own anyway, no power going anywhere else but into one cab... look forward to it.