Bill Fitzmaurice

MDF is fine, for home hi-fi cabs. It's gosh awful for anything intended to be portable. Put the blame on using MDF, particle board and worse on Electro-Voice, who used what they called Road-Wood back in the 80s-90s. They said it was 'a structural material made of layered and selectively oriented wood strands'. Translation: OSB! They started using it during a period when plywood prices were high. Ampeg used something similar for a while when it was run by St.Louis Music. It wasn't as heavy as MDF, but it was no more durable either. No engineer worth his salt would ever specify MDF or OSB. That decision would have been made by Bean Counters. 🤔

They all look OK at a small signal level on-axis. Where cabs differ the most is in maximum output and off-axis response.

27 minutes ago, sandy_r said:

a 100W True RMS amp, can apply up to 200W (True RMS) into its usual load - hence advice to use speakers with higher power rating than the amp

I never said it couldn't. But if that happens and as a result the the driver is blown it's not because it was underpowered, it's because it was overpowered. Too much ado is made about clipping, but it's just another complex wave form, which is what all musical tones are. The sine wave versus square wave comparison lacks any validity, as with the exception of some synthesizer patches neither are present in music. Even when that's the case it does nothing to bolster the myth that clipping kills drivers. If it did the name Robert Moog never would have been known outside of his family and friends.

He seems legit, his post wasn't old stuff copied and pasted.

Keyboards work better with a FRFR speaker for their reduced coloration, but otherwise you're good to go.

2 hours ago, agedhorse said:

I do this regulatory stuff every day as part of my design work.

+1. By the same token I do this loudspeaker stuff every day as part of my design work. 😉

3 hours ago, sandy_r said:

So, the power density of the signal to the woofer IS affected (as by clipping)

Not so. Power density is highest at the lowest frequency of the woofer passband. Go up one octave it's down 3dB. Go up another octave it's down 6dB, and so forth. No amount of clipping will cause the power density of harmonics anywhere within the woofer passband to even equal the power density at the lowest frequency of the passband, let alone exceed it.

The bass isn't actually deeper, it just seems that way due to the reduction of midbass boom. The mids are smoother as the internal reflections back to the cone have been eliminated. From a technical standpoint what you accomplished was to lower the speaker Qa, which tames boomy midbass. The same thing happens when you fill the box with polyester pillow stuffing.

49 minutes ago, sandy_r said:

Amps overdriving the speakers into clipping (presenting as distortion) is an indication that the speakers will suffer thermal damage if exposed to continued power in excess of their rated power handling

Only when those drivers are tweeters and the occasional midrange. The increase in power density {look it up} only occurs in the harmonics, not the fundamentals. That being the case woofers are unaffected. It's different with respect to tweeters and some midranges. The power density of a normal clean signal drops by 3dB with each octave increase of frequency. That's why pink noise is used to test speakers, as it also drops in power density by 3dB per octave increase in frequency. For this reason the actual thermal capacity of a tweeter rated for use in a 100w speaker will seldom be more than 10 watts. Clipping upsets the apple cart by delivering more high frequency content than normal, so said 10w voice coil may receive 20w or more. That's why clipping can thermally kill tweeters. The power density of the signal to the woofer is unaffected, so clipping doesn't affect them at all. This goes to the Myth of Underpowering, a myth long ago debunked, but like most myths it refuses to die the death it deserves.

6 hours ago, Gypsyfolk said:

Octave and distortion pedals seem to cause speakers to let go more than loud clean IME

Only in the sense that when you use them they can mask the distortion that results from pushing drivers past their linear excursion limit. The distortion doesn't affect the drivers at all, if they did guitar players would be swapping them from gig to gig, if not from set to set. But guitar drivers have far more leeway between when they reach xmax and when they reach xlim (look up those terms) than bass drivers. https://speakerwizard.co.uk/thiele-small-parameters-what-are-they-for/

One could do three 2x10 vertical, but the additional sensitivity of three versus two cabs wouldn't amount to much.

You may not need an amp. An emulator pedal or preamp with a number of presets direct to the board will be more versatile. One of the most prolific bass players of all time, James Jamerson, was always recorded direct at Motown. He had an Ampeg B-15, but that was only for monitoring.

The Barefaced can probably handle as much power as the pair of Ampeg before reaching the driver mechanical limits, but you'd need at least a 400w amp for that to be a concern. As mentioned when you're power shy you need sensitivity, where four drivers will probably be better than two.

2 hours ago, sandy_r said:

 

I suppose it's worth emphasising, as mentioned in with the graphs above, that these are not swept-frequency spectra, they show the accumulated peak levels at frequencies stimulated by the individual notes played and their accompanying harmonics. 

They're still very useful. In part the results are speaker and amp derived, but they also reflect the fact that by no means does the fundamental define the tone of the instrument, it's defined by the harmonics, and that starts with the bass itself.

 Blame Leo Fender. Good engineer, but a notorious skin flint. Telephone switchboard 1/4" jacks and plugs had been used for electric guitar leads probably from day one. When Leo came up with separate heads and cabs he used 1/4" because he had them on hand. In his defense there wasn't much to choose from, but still when Leo had a chance to save a buck he did. The same applied to his instruments. He didn't set out to build a better guitar, he set out to make a cheaper guitar, and the bolt on neck was how he did it. By the same token single coil pickups were cheaper than hum bucking, which were around since 1932. Fender was able to sell his guitars at 2/3 the price of Gibson. It was pure serendipity that they also sounded very good.

Obviously there are no glaring differences between those charts. Note the deep notch they all have at 90Hz. That's the cancellation caused by the distance from the cab baffle to the wall behind. There's another around 150Hz. That's probably from the distance between the mic and the floor.

I figured you meant 1 meter to the front. 1 meter to the back would push the baffle even further from the wall, lowering the cancellation frequency. When dealing with hi-fi or PA where you have separate subs and mains the subs should be placed close enough to the wall so that the cancellation frequency is above the sub passband, while the mains should be placed far enough from the wall so that the cancellation frequency is below their passband. You can't accomplish that when the mains are mounted above the subs. For that reason the only time one should do so is if there is no rear wall, which is to say outdoors.

1 hour ago, warwickhunt said:

The cab was located 1m from the nearest rear wall.

That will result in a response cancellation notch centered around 80Hz. It wouldn't affect the comparison, they'd all suffer equally, but unless you're trying to reduce boomy response due to an 80Hz response peak you don't want a cab that far from the wall.  I won't venture an opinion on which is which, knowing that driver size alone only affects off-axis response.

3 hours ago, chris_b said:

The size of a speaker means nothing. The sound depends of something like a dozen different parameters and the box.

Pretty much. There is one factor that's almost entirely related to speaker size, that being midrange dispersion. The smaller the speaker the wider the dispersion angle. That's why midranges are smaller than woofers, and tweeters are smaller than midranges. But all else is determined by the Thiele/Small specs of the driver and the engineering of the cabinet.

The range of power usefulness is 4:1. With a 200w cab amps ratings of between 50 and 800 watts is appropriate. Frankly if you blow a bass cab it's entirely your fault, because it will severely distort long before it will blow.

A good 1x12 or 2x10 should suffice.

4 hours ago, Chienmortbb said:

Much of what you say is true but as you know, using 2.83V for all cabinets will give  the impression that the 4R cabinet(s)  a. 3dB advantage. To put us another way, 2.83V gives 1 watt at 8R and 2 watts at 4R.  

True. However, there's a benefit to testing with the same amp settings. Power doesn't define how loud a cab goes, voltage swing does. While power varies with the load impedance voltage swing does not. So if your intent is to see which cab will go louder with a given amp you test them with the same voltage input.

Quote

Halve the voltage. Job done.

Halving the voltage results in one-quarter the power. Also, in most cases otherwise with identical drivers save one is 8 ohm and the other is 4 ohm the 4 ohm driver actual impedance is usually more than half that of the 8 ohm driver. There are too many variables involved to truly know how much power the cab is actually being driven with. When you use voltage as the benchmark there are no variables. For this reason testing is never done with a specified power, as there's no way of knowing how much power is being applied. It's different at every frequency. Testing is always done with a specified voltage. When the result is called 1m/1w that's a calculated figure, and not a particularly accurate one. For instance, this charts the power into an 8 ohm speaker at 2.83v. How many watts? There's a thousand answers, one for every frequency.

You'll be surprised how loud 2.83v is at 2 meters. BTW, you can't accurately measure pink noise with a volt meter as it will bounce quite a bit. Get it close and leave the amp set at the same volume with each speaker. If you want to calibrate the result you'd do that with a 1kHz sine wave at 2.83v. Measuring at 45 degrees is simple, just rotate the cab.

First and foremost do the testing outdoors, well away from any buildings or walls, otherwise at least half the result will be from the room. Some years ago there was a much ballyhooed  'subwoofer shoot out' where the results were totally useless, as the room response dominated the results. Second, don't place cabs near each other. An unused cab acts as a bass trap. It's best to leave the mic in one spot and then place each cab in the same place one by one. The mic should be at least two meters out from the cab location, preferably more. 1m/1w is how the charts are shown but that's an extrapolated result. Danley Sound Labs, for instance, measures at 10 meters with 100 watts, which is the equivalent of 1m/1w. Finally, measure on axis and 45 degrees off-axis. Off-axis is where differences between various configurations will be most evident.

A more accurate statement is that it shouldn't be more than just tickled when you play your heaviest.