5w head + what cab for nice lows ?

[agedhorse]

I learned from winding ferrite RF coils by hand, that of all the parameters involved to get high Q and adequate inductance in the smallest size, cost and weight, the turns count trumped all other considerations precisely because inductance goes up with the square of turns count. It's amazing how simple the analysis and design becomes the instant we do not ignore this.

Likewise, having an array of equal drivers wins, because it not only optimises SPL, but more importantly increases directionality, which counters the normal inverse square law reduction of amplitude over distance.

Anyone who ever doubts this should consider the design to propagate sound over events the size of the Monsters of Rock event at Donnington Park. It's the most impressive speaker array I ever saw, anyway.. As with laser beams, low divergence matters, a LOT more than originating beam power, to get a high power result at a distance, by reducing the impact of the inverse square law found in isotropic distributions.

An alternative way of managing directivity is horn loading and flair technology, analogous more or less to an acoustic transformer.

 

[Lostgallifreyan]

An alternative way of managing directivity is horn loading and flair technology, analogous more or less to an acoustic transformer.

I tend to forget horns. Probably because to do bass well they'd have to be big, but I have heard a few on ships and lighthouses (just fixed pitch there) and certainly they are the most efficient means of sound delivery I know of.

As a kid I used to like listening to Toyah's 'Sheep Farming In Barnet' and live LP's through a Goodmans Midax. The bass was lacking, but the loudness, clarity and stridency made it extremely exciting compared to a normal speaker, even a big one.

I just found this:
https://www.grc.com/acoustics/an-introduction-to-horn-theory.pdf
(Hosted on Steve Gibson's GRC.com site, of all places.
The maths goes over my head but the text descriptions are very good.
One of the implications is that the normally tinny quality associated with horns need not exist if the flare is formed in good materials with damping. I assume it's the air itself in the given space that couples from driver to ambient air, so damping material resonances is probably ideal.

I'm beginning to like the idea of those bass cabs with folded horns formed by braced wood panels, though I suspect that to get good LF at or below 40 Hz there may be no shortcutting the size, not that there is in a big array either.. I suspect the Donnington arrays may well have been arrays of folded horns, but my memory isn't good enough to be sure of it. Given the stack height (tens of metres), it may have been so, just to keep weight lower for the given output.

 

[agedhorse]

The challenge with horns, just like audio transformers, is that to extend low frequencies, it comes at the tradeoff of higher frequencies. Horns and transformers are limited bandwidth devices, and efficiency is part of the tradeoff. Give up some efficiency and you can gain bandwidth. It’s related to efficiency-bandwidth product.

For a folded horn, the external size appears smaller for a given throat length, the efficiency is typically higher over smaller bandwidth. Distortion also rises at the edges of the bandwidth faster than a straight horn.

In fact many of the electrical transformer equations have similarities to horn equations, just like sealed box and especially bass reflex boxes have similarities to electrical filter equations.

 

[Lostgallifreyan]

Simply not true and a gross generalization.

I have done pro gigs with an Ashdown LB30 (30W) head. Combined with either an Epifani UL410 or a Euphonic Audio VL210 (and once with an Ampeg 610AV) it got STUPID loud. I couldn't turn all the way up.

You are WAY over estimating how important Watts are in the volume equation.

Lots of people here gig with either that or an Ampeg PF50t (50W head).

I think JJ Burnel's first amp was 50W. A sound many call 'monster tone'. It's amazing how people never let these basics sink in. All other things being equal, it would take 500W to double the maximum loudness, and I think few if any instrument amps with valve outputs ever went beyond 400W.

I once worked on a strange open deck of aluminium that had 8 KT88's on it, that probably did, but I never heard it at full strength (I just fixed parts of its preamp). Last I knew, it was doing duty in the Star and Garter pub in St. Pauls, Bristol, playing dub reggae and whatever else DJ Derek played through it while he was still alive.

That deck was so heavy that picking it up carelessly threatened to rip it apart under its own weight, and the metal was already fatigued. Such amps very rarely exist outside of dedicated fixed installations.

For anything portable, the easy gains are in the speaker design, not the amp watts.

If we point these things out often enough, or tell tall tales of unnecessarily giant amps, will we become like Monty Python's Yorkshiremen, who no youngsters beleive?

 

[Lostgallifreyan]

The challenge with horns, just like audio transformers, is that to extend low frequencies, it comes at the tradeoff of higher frequencies. Horns and transformers are limited bandwidth devices, and efficiency is part of the tradeoff. Give up some efficiency and you can gain bandwidth. It’s related to efficiency-bandwidth product.

For a folded horn, the external size appears smaller for a given throat length, the efficiency is typically higher over smaller bandwidth. Distortion also rises at the edges of the bandwidth faster than a straight horn.

In fact many of the electrical transformer equations have similarities to horn equations, just like sealed box and especially bass reflex boxes have similarities to electrical filter equations.

That's useful. I can almost cope with filter calculations at need, so that's a way in if I need one some time. That efficiency vs bandwidth compromise explains to me why foghorns have a single narrow and distorted frequency.

I'm aware that op-amps often have a parameter called gain-bandwidth product, though I'm not sure if this is the same kind of principle.

A very odd and possibly related observation to the distortion at edge of bandwidth... Several years ago, when I was reading and posting on alt.lasers (usenet) I claimed to be able to detect when a red diode laser was being pushed close to its safe limits, and maximise power without destroying it. It took a while, but early scepticism was changed when a few people replicated the observation. I saw it as a kind of pastel shade that slightly blurred an otherwise highly specular monochromatic output. (To optimise drive I'd back off till that pastel shade returned to a strong clean specular light.) I assumed that this pastel quality was a simple broadening of the bandwidth, but what you say about horns suggests that there was also some kind of extremely high frequency distortion there, breaking up the coherence of the laser. I couldn't have known then, I have never had any way to measure something like that. Those who did were amazed that it could detected by eye just by looking at an oblique projection onto dark paper!

 

[agedhorse]

There are types of limits that are based on the product of two variables. Gain x bandwidth is one, if you half the gain you double the bandwidth (or some proportion like that, based on the device).

With some LEDs, the color can shift with current, so your observation seems reasonable on the surface.

 

[Gizmot]

I am not suggesting anyone consider the power increase in isolation. SPL is a result of both available power and the cab's sensitivity. You have to consider both. So I totally agree that focusing solely on optimizing the amp's output tend to be a fool's errand....this is exactly why I suggest doing the calculations for the amp/cab combinations under consideration.

I also agree that a cab's calculated max output is not going to be accurate. A big factor is something called power compression. The harder you push a driver the more it compresses. So real world measurements will always be lower than simple calculated figures. With a 5W amp pushing a large cabinet with a high power rating, I would expect the calculated figure to be fairly close to the real-world measurement. A big sturdy cab will not experience a lot of power compression with 5W.

Some higher-level PA companies actually publish max SPL measurements. Not sure if any bass cab makers do.

Power compression is caused by the rise in impedance that occurs when a speaker is pushed hard and it can’t dissipate all the heat. Certainly a 5 watt amp shouldn’t be a problem unless it gets pushed into high distortion

 

[Lostgallifreyan]

There are types of limits that are based on the product of two variables. Gain x bandwidth is one, if you half the gain you double the bandwidth (or some proportion like that, based on the device).

Right. 'Product' does imply a strictly linear proportion.

With some LEDs, the color can shift with current, so your observation seems reasonable on the surface.

I've seen them do that, but I suspect it's a wavelength shift with temperature, (it's tough to get heat out of an LED). It would depend on the direction of shift too, I think red go long as they get hot, blues likely go shorter. They do with laser diodes anyway, and the materials are often similar. I think the laser noise observation is different though, and could be seen independently of temperature, but I have no idea if the same effect exists with blue and green diodes. It might be specific to the materials, (was my assumption) but what you said about distortion at edges of the band suggests it might exist for all laser diodes regardless of materials. If I ever go back to working with them I'll try to look for it (very carefully, they are dangerous beasts these days, they've grown teeth and bad attitudes).

 

[Lostgallifreyan]

Power compression is caused by the rise in impedance that occurs when a speaker is pushed hard and it can’t dissipate all the heat.

Wouldn't it reach a form of compression from mechanical limits before it got to that point? During major excursions, running out of magnet to push against, combined with greater resistance from cone support, might do it.

 

[agedhorse]

Wouldn't it reach a form of compression from mechanical limits before it got to that point? During major excursions, running out of magnet to push against, combined with greater resistance from cone support, might do it.

Yes, there are 2 forms of power compression, mechanical (electro-mechanical) and thermal.

 

[Smokey P]

Yes, when it comes to running low watts but getting a good return on volume a super efficient cab is the key. My revsound 112 can get wildly loud with 100 watts, thinking about going down to 50 so I can just bring a pedal board and a cab to small gigs/rehearsals.

 

[Super_Knack]

I'm the end I got 200w TC electronic 208 cab + Bam200 amp

 

[Super_Knack]

Of course will try my 5W head too

 

[msb]

I have a Hotone , but use it as a headphone amp , with the aux in I can plug in a tablet. I actually use it a lot. I have other practice rigs I use with cabs …