Question for our experts - why aren't more amps designed for 2 ohm loads?

[Tassieviking]

When I see Markbass publishing 4x6" (equivalent to 1x12") cab 100dB/1w/1m and Ampeg 8x10" (roughly 5.5x12") publishes the same 100dB/1w/1m, I tend not to trust any figures

I think that these figures could be correct, they are mentioning the efficiency of the cabs and not the max SPL or max power rating of the whole cab.
With 1 watt input into the cab measured at 1 meter distance this is possible depending on the speaker drivers being used, that figure is like saying mpg for a car, not the horsepower or torque of the engine.
But then again they could be a pile of horse dung that someone made up as well.

 

[sokolasty]

I think that these figures could be correct, they are mentioning the efficiency of the cabs and not the max SPL or max power rating of the whole cab.
With 1 watt input into the cab measured at 1 meter distance this is possible depending on the speaker drivers being used, that figure is like saying mpg for a car, not the horsepower or torque of the engine.
But then again they could be a pile of horse dung that someone made up as well.

I never saw a frequency or frequency range at which sensitivity was measured. Is it 100Hz? 1000Hz? Average from 200Hz to 500Hz? Maximum value between 20Hz and 20kHz?
This, and other factors mentioned previously, make me distrust in sensitivity published. Only A/B on my own or by a reputable person in constant conditions.

 

[Hurricane Jimmie]

Sone of the older Peavey amps were 2ohm, like 400 Series amps from the late seventies.

I think some of the old Acoustic Amps might also have been 2 ohms.
Mine was 170 watts and could really honk.

 

[agedhorse]

I would be hesitant to agree with this, but that could be because I worked as an electrician all my life.
As an electrician I always work with constant loads when working out cable sizes, music is not a constant load.

Saying 14 gauge is ok for 2 ohm without taking into account the watts going into the 2 ohm cab or any other factors is a slight hickup for me, especially since that could refer to a 200 watt cab or a 1200 watt cab. (Yes I know who Agedhorse is and I do respect his opinion greatly)

If my mind is working today then an 800 watt amp going into a 2 ohm speaker would be close to 20 amps, I think 14 gauge wire is a bit too small for 20 amps even if the losses might not be too bad for a short run.
Cables will always be downrated by heat as well so if you are playing outdoors in full sun the black leads can get fairly hot just from the sun, there are many factors to consider.
Another thing to consider is the style of music, soft bass in a mellow jazz group or a bloke who is trying to smash his strings as hard and fast as he can playing his latest crazy doom sludge.

At least most modern amps usually have 2 speaker outlets, 2 separate 4 ohm cabs that have their own cable going back to the amp will make a 2 ohm setup, but each cab is still considered a 4 ohm run when working out the cable rating since the parallel connection is in the amp.
I would never recommend piggybacking one speaker from the back of another speaker when using high power amps, run a separate cable to each speaker from the amp if possible.

Doesn’t work that way if you do the math.

I never saw a frequency or frequency range at which sensitivity was measured. Is it 100Hz? 1000Hz? Average from 200Hz to 500Hz? Maximum value between 20Hz and 20kHz?
This, and other factors mentioned previously, make me distrust in sensitivity published. Only A/B on my own or by a reputable person in constant conditions.

Sensitivity for a bass cabinet really should be based on at least a majority of the bass guitar’s fundamental through the primary harmonics. I typically use the average sensitivity (over 50Hz-5kHz) for bass guitar speakers, even if the numbers are not as impressive as the marketing folks would prefer to see.

 

[Wasnex]

Hmmm....Not sure? It has a 4ohm/2ohm switch on the rear panel. Could have been a speaker compatibility thing. I was using Hartke Hy Drive 1x 12 cabs. 2 set at 8ohms and 1 set at 4ohms. Do you think that was the problem?

I checked the OM and it states 2 ohms minimum.

It's possible there is some problematic interaction between the amp and these particular cabs. The impedance rating of a cab is a nominal value, and actual impedance varies by frequency. The actual impedance at some frequencies drops below the nominal rating. You could try the amp with different cabs.

It's also possible the amp has a problem. Contact DarkGlass.

I have no idea how common it is, but you are not the first to have problems running a DG amp at 2 ohms.

 

[Wasnex]

I never saw a frequency or frequency range at which sensitivity was measured. Is it 100Hz? 1000Hz? Average from 200Hz to 500Hz? Maximum value between 20Hz and 20kHz?
This, and other factors mentioned previously, make me distrust in sensitivity published. Only A/B on my own or by a reputable person in constant conditions.

I suggest taking specs as ballpark values. They are more useful when comparing cabs within a single product line. No guarantee a company will use the same measurement practices across product lines. And different companies certainly use different measurement practices.

 

[crguti]

My Ampeg Svt-8 pro with 1200watts at 2ohms is used for demolishing building.

 

[sokolasty]

I suggest taking specs as ballpark values. They are more useful when comparing cabs within a single product line. No guarantee a company will use the same measurement practices across product lines. And different companies certainly use different measurement practices.

This

There are two things I'd like cab makers would publish and measure in standard way:
- max linear SPL chart (because power is cheap and sensitivity IMO weights less and I can add bass with a knob on my amp within x-max limit)
- group delay, i. e. do I get punch or wool

Sensitivity chart is nice as well


Off Topic
I wonder how car makers measured HP and torque for marketing purposes before standards were implemented

 

[Wasnex]

My Ampeg Svt-8 pro with 1200watts at 2ohms is used for demolishing building.

SVT 8-Pro = 2500W a 2 ohms

 

[dbase]

When you see how loud you get be with a modern 2x12 @ 4Ohm and a 800W amp, who would need more?

 

[agedhorse]

This

There are two things I'd like cab makers would publish and measure in standard way:
- max linear SPL chart (because power is cheap and sensitivity IMO weights less and I can add bass with a knob on my amp within x-max limit)
- group delay, i. e. do I get punch or wool

Sensitivity chart is nice as well


Off Topic
I wonder how car makers measured HP and torque for marketing purposes before standards were implemented

Why manufacturers don't provide the two things you think you want?

1. Maximum linear SPL chart is a hard topic to explain to the average player, and the maximum linear (using the term generally) can be extracted from the average sensitivity and mechanical power handling. It's the product of sensitivity x mechanical power handling. If all you have is thermal or "wishful" power handling, you can make the assumption that mechanical power handling is 50% of thermal power handling and deduct 3dB from the claimed maximum SPL. None of this factors electrical and electro-mechanical power compression into the SPL value because that's a pretty non-linear term that varies with duty cycle. In the case of the Subway cabinets, the mechanical power handling is well within 1dB of the thermal power handling, so the maximum SPL based on rated thermal and mechanical power handling will be almost the same.

2. Group delay by itself has virtually zero impact on "punch" or "wool". In fact is has almost no value except as relative measurements to a designer to confirm appropriate tuning and matching of low frequency response across a family of cabinets or designs. It's a big marketing term in the audiophile community however, because it has no (useful) meaning it can be manipulated to however each manufacturer wishes, to attribute their own magical unicorn properties as required by the marketing department. Pretty much all cabinets within a usable tuning range will exhibit roughly 6-8mSec of group delay and a similar curve shape. Group delay is derived from the electrical high pass filter equations that the speaker response is modeled from.

 

[JimChjones]

Other than “I want to run two 4ohm cabs", is there actually any advantage in running an amp into a nominal 2ohms rather than nominal 4? All else being equal is there any observable difference between an amp rated at 400W into 2 ohms and one rated at 400W into 4 ohms?

 

[SunByrne]

Other than “I want to run two 4ohm cabs"

Isn't that enough?

 

[Jazzdogg]

I'm a bassist who has only purchased bass amplifiers that are 2 Ohm capable for two or three decades because that's how long I've been stacking two cabinets with a combined impedance of 2.67 or 2 Ohms; I don't like compromising which bass cabinets I can buy based upon the limitations of a bass amp.

But, bassists who will pay for a 2-Ohm-capable bass amplifier comprise a very small percentage of a very small market. Many companies don’t offer this because their target buyers don’t know they need the capability.

If there's not enough demand to make it worthwhile for a manufacturer to incorporate a feature, recover their sunk cost, and make a profit, they won't do it.

Manufacturers who add these kinds of "unique" features tend to attract a relatively small segment of the market, without enough annual sales to support more than a few manufacturers. Acoustic Image (RIP), Mesa, and Bergantino come to mind.

If enough bassists become willing to pay for certain features, and manufacturers start to notice the growing market demand, they might consider it a feature worth incorporating. But manufacturers who add special features "on spec" may be gambling with money they can't afford to lose. In my experience, no matter what a manufacturer produces or how well it performs, the percentage of the buying public that "get's it" is pretty small, and a small pool of prospective buyers doesn't typically attract manufacturers unless doing so is profitable.

 

[Tassieviking]

Doesn’t work that way if you do the math

Would you be willing to explain this further keeping it simple for an old bloke who takes a bunch of crap medicine daily that can screw with his brain ?
What is the difference when calculating cables used in audio compared to domestic cables, I am truly curious as I try too keep my noggin functioning by keeping it active.

Why manufacturers don't provide the two things you think you want?

Now that information I find really useful, that is a great way to show data on a cab so a basic person can understand it in layman's terms.
If only all cabs had that information available to the buyer. Thank you.

 

[Panek]

When you see how loud you get be with a modern 2x12 @ 4Ohm and a 800W amp, who would need more?

Exactly right!

 

[Redbrangus]

What is the difference when calculating cables used in audio compared to domestic cables,

...music is not a constant load.

I think you already answered your own question.

At my house, I have a air conditioning unit that draws 93+ amps per leg (two 120-volt 'hot' wires) at startup, but it's only serviced by a 50-amp circuit and the wire is sized accordingly. Duration/duty cycle is a factor. Typically, inside a cab, even a big one, the wire size is pretty small -- #16 or even #18 AWG.

Note I'm not asserting that long cables don't need to be sized up appropriately, but few bass rigs incorporate 50' or longer cables.

 

[agedhorse]

I think you already answered your own question.

At my house, I have a air conditioning unit that draws 93+ amps per leg (two 120-volt 'hot' wires) at startup, but it's only serviced by a 50-amp circuit and the wire is sized accordingly. Duration/duty cycle is a factor. Typically, inside a cab, even a big one, the wire size is pretty small -- #16 or even #18 AWG.

Note I'm not asserting that long cables don't need to be sized up appropriately, but few bass rigs incorporate 50' or longer cables.

Correct, for thermal calculations the average power dissipated in the wire is based on 1/8 rated power (voltage squared divided by the total resistance). Since the wire is so short, the resistance is very low even with smaller gauge wire.

For power loss it’s the current squared times the resistance. Again, for short lengths, the resistance is low therefore the power loss is low.

 

[Tassieviking]

I think you already answered your own question

Exactly right, but it does not explain how I should down rate a cable for a bass amp.
I was hoping for an answer with a ratio or a percentage or something similar.
I can work out wiring for a domestic air conditioner, or even a small 11kV substation for a factory as I have done it in the past. (A long time ago)
Is there a formula for working it out ? It is a genuine question.

Edit: never mind, Agedhorse said 1/8 in the above post. Thank you.

 

[Tassieviking]

I guess my current speaker cables should be ok for most amps then as I always used 2 core 1.5mm2 flex heavy duty extension lead cable I have a 100m roll of, I have another roll of flex 1.5mm 4 core as well which I will start using if I make leads with 4 pole speakon plugs. I only use them at home. (16 gauge = 1.31mm and 14 gauge = 2.08mm)

I love reading posts that teaches me things, even when I am too stupid to heed the good advice given.