Amp head and speaker mach

[jaysgr]

Hello guys,
I could use a suggestion on this:
I have a SWR Bass 350 amp and a cabin that can hold a 15" woofer.
The woofer needs to be changed and I would like to be sure that I will do things right.

The swr specs are
450 Watts @ 2 Ohms
350 Watts @ 4 Ohms
240 Watts @ 8 Ohms.

The previous woofer was an 8 Ohm/200 Watts.

I am thinking now to replace it with a 4 Ohm/300 Watt, because as far as I can understand, it will be a little louder (won't it?), which is what I want.

The question here is, if the best choice is a speaker with a little less Wattage than the amps output.

Any help would be very much appreciated!
jay

ps. all watts in RMS

[Resonator Guy]

Any speaker change won't really make much difference in loudness. You could try one with greater sensitivity than your current one, but again it won't make much difference.

[tedmich]

should work:
Eminence Delta Pro-15A, 101.6db/1w at 1m, so 256w = 125.6 db crazy loud
or Eminence Kappa-15LFA
might work:
Celestion TF1525
Peavey Pro 15

you'd need to tune box to be sure you got the real low stuff represented, is it closed or open?

[jaysgr]

Thanks for your answers.
But still don't get it..

Resonator, why any speaker won't make a difference in loudness? If a speaker has more Watts rms, doesn't it mean that it will be louder?

Tedmich, the speaker you suggest are 8 Ohms, and the Eminence Kappa-15LFA is 600Watt. Will that work fine with the amp that has an output of 240W@8Ohms?

[Enzo]

If you double the power into a speaker, it will get only 3 decibels louder. Not much. So moving from 200 watts to 400 watts nets you 3db. Your amp was going to go from 240 watts to 350 watts. That is less than a 50% increase, so you would net maybe 1db, if that. Imagine turning the volume up less than half a number on the dial. Now of course that assumes everything else about the speaker is the same. It rarely is.

Speakers have efficiency ratings in decibels. That is what this meant above: 101.6db/1w at 1m. 1 watt at 1 meter is the standard, so the higher the decibel count the louder it will be. But the same formula applies. If one speaker has 3db greater efficiency, it is like using the original speaker at twice the power. But 3db is 3 db.

Tedmich suggested that speaker because at 101db it is a high efficiency speaker.

[jaysgr]

Thanks Enzo,
I'm about to get it. But what about the Watts? A 600 Watt speaker, when driven from a 240 Watt amp, doesn't mean that the speaker doesn't operate correctly?
I guess that the power isn't enough to make it move as it should, am I wrong?
Also, is it ok for the Amp itself?

[Mick Bailey]

There are a number of considerations that are worthwhile getting to grips with;

The rated outputs of your amp into different impedances are nominal RMS ratings into a test load. That load could be just a resistor and that doesn't make any sound at all. Those figures just mean that the power amp will deliver that amount of power into each specified load. If I had your amp on a bench for repair, I'd connect up one of those loads (as a dummy resistive load) and run a signal generator into your amp. Then I'd measure the RMS output to see if it made near enough what the manufacturer claimed. But it wouldn't make a sound.

So, the RMS rated output isn't how loud the amp is going to be, it just tells you the power that can be delivered into the speaker load.

Then we need to translate that power into sound. So the driver (speaker) efficiency comes into it. The more efficient the speaker, the greater the movement of air for each watt of power delivered, and the greater the volume. That efficiency is measured in how much sound pressure is generated at 1 Metre distance with an input of 1 watt. Now, that efficiency isn't throughout the frequency range that the speaker can handle, so every manufacturer produces a response graph to show the peaks and troughs. You can see where the speaker is at its most efficient, and where the upper and lower ranges tail off.

Further to this, the actual cabinet size, construction and venting play an important part. All of these modify the frequency response and overall efficiency of the speaker.

A speaker has a limit on how much power it can take before the coil burns out, so the manufacturer also provides a maximum rating for the power handling. Generally its a good idea to ensure that when the amp is turned right up the speaker can continue to handle the power. So a 300w amp may be coupled to a 400w speaker. Going higher with the speaker's power rating gives a better safety margin. It doesn't relate in any way to how much volume the speaker will produce with a given amp, though some speakers with very high power ratings can have a low sensitivity, but that's a different matter.

We can hear a pin drop in a quiet room at tens of feet. Equally we can hear a gunshot at five feet. So the ear has a vast dynamic range. Think of it like a set of scales that can weigh a speck of dust or a 40 tonne truck and anything in between. To accommodate that range the ear is progressively less sensitive to louder sounds in a logarithmic response. Therefore to give the impression of something being twice as loud, that sound source takes a lot more power - a 100w amp is only twice as loud as a 10w amp. The resultant acoustic energy can either be created through brute force - pushing more power into a speaker - or it can be done by increasing the efficiency of the speaker and not having to drive it so hard. So for example, for a 3db increase you can double the power going into your speaker, or use half the power into a speaker that's 3db more efficient. Either will give the same output.

[jazbo8]

Emience has a good article on the subject - why the speaker driver has to have a higher "music power" rating.

[J M Fahey]

Nice article

He gives you the grand tour but in the end he stays with the thermal rating , because in Musical Instrument land we can never count either on amplifier not clipping or on average level being 10dB below peaks, both assumptions valid in Hi Fi home music land.

Besides mechanical disintegration, which comes from an improperly made cabinet (or no cabinet, such as an open back combo) or getting tons of low frequencies below the cabinet loading area (typical of DJ and those stupid Ashdown bass amps with built in sub octave generators ... what were they thinking ?? ) , the main speaker killer is cooked voice coils or thermally softened adhesives which turn the VC wires into a knitting wool ball clone after the cats have been playing with it.

There is a JBL picture showing the different types of voice coil failures so reconer can identify what actually broke the speaker, whether it was DC at the output, low frequency overexcursion (happy DJ syndrome) , plain overpower toasting (headbanger or insufficient PA for a large space), etc.

I´ll post it when I find it but if somebody finds it sooner, please be my guest.

Here´s Rod Elliott´s version, very good as always.
Speaker Failure Analysis

Here´s a little horror pictures gallery:
https://www.google.com/search?hl=en&...25.MlLEwXVuoAA

[Leo_Gnardo]

Thanks Enzo,
I'm about to get it. But what about the Watts? A 600 Watt speaker, when driven from a 240 Watt amp, doesn't mean that the speaker doesn't operate correctly?
I guess that the power isn't enough to make it move as it should, am I wrong?
Also, is it ok for the Amp itself?

Efficiency counts - a LOT! Make the most you can out of every watt. Not necessarily meaning the speaker with the highest figure is going to be what you want to hear, tone wise. But there are plenty in the high 90's and into the 100+ dB/watt range. I happen to like the tone of the Eminence Kappa-Pro's. It's BASS, not treble. Whenever possible get a look at a frequency response curve. If there's good response above 1000-2000 Hz you can predict you'll hear some clank out of that speaker too not just wooly bass. Caution: the JBL D or K or E-130 15 inch speakers sound good at low volume, but die a quick death if overpowered by watt-happy players. I've done it. They have screaming-high efficiency figures, about 102-103 dB/watt. Please don't sacrifice any. Same for Altecs. OTOH ElectroVoice 15's take a lot of punishment and keep going for years. They just cost a fortune now compared to the Eminences. Funny thing, now most EV's are made at the Eminence plant. Hmm......

Just going by power figure is a beeeeg mis-steak. There are plenty of fancy and expensive car boomer speakers with ratings in the low 80's. Takes an enormous amp to drive 'em but that's what that crowd wants. Not good tone, just something to boast about, and cost a fortune to replace when wrecked. If you want super power handling, get a toaster, they're cheap and handle over a thousand watts. Oh you want to hear something? Stick a big magnet on your toaster, you'll hear something all right but it won't be pleasant.

[tedmich]

Q "loud, like LOUD! I mean really L O U D ! which speaker to use?"

A "...and then solving for total system Q, approximated by spherical speakers in a vacuum, while paying particular attention to pages 4-7 of Thiele's classic proof..."

[jaysgr]

Thanks again for your answers.
But, to be honest, I'm starting to getting more confused..
The article that jazbo8 posted says that the speakers must have more Watts than the amp.
This guy here says the opposite
Pro Audio 101: Matching Amps To Speakers And How Not To Blow Them Up. - YouTube
Any opinions?

[überfuzz]

See it as an insurance. If the speaker copes with higher watts the risk of busting it is lower.

Just fiddle around with speakers until you find a speaker that sounds great.

[Mick Bailey]

The scenario he's referring to is uprating the speaker power handling in order to deliberately push an amp into distortion. When a power amp distorts the peaks of the waveform begin to flatten off, because the amp can only amplify to the +/- limit of the power rails. As the input signal continues to increase, the waveform can go completely squared off. This creates additional heat in the speaker coil, because whilst the cone excursion is governed by the voltage (assuming this is less than X-max which gives the limit of mechanical movement), the amount of thermal energy is greater in a square wave than if the waveform was an undistorted sine wave. So whilst the speaker doesn't generate any more volume once the amp starts to clip, the voice coil has to handle the extra heat.

If the voice coil had enough thermal headroom though this wouldn't necessarily be catastrophic.

Now, if you were to match exactly the power handling of the speaker to a clean-running amp, then there wouldn't be a problem. But occasionally you may run into clipping if the amp is turned up a little bit to high, say when you're playing finger style and then start some slap & pop. That's where you need the assurance that the speaker has enough thermal safety to cope. Or maybe you've got a drive or sub-bass pedal. Both of those can increase the thermal energy in the waveform.

Interestingly, I replace far more bass drivers than those for guitar, and many of those busted speakers are OEM and are rated very close to the amp's output.

[gui_tarzan]

No love for EV? I've got a pair of 1975 EV SRO 15" for my rig, each in separate cabinets built from EV documents for that speaker. I get nothing but good comments from other bass players that play through my rig at open mic nights. It's got so much tight bottom end it's ridiculous.