Bill Fitzmaurice

1 hour ago, Jaybeevee said:

I think in this case it does. 

Most assuredly it does not. Power output depends on a number of factors, starting with the voltage output and frequency response of the bass, ending with the actual impedance of the speakers, which isn't a constant. It varies with frequency. This is a plot of the power output of an amp across the frequency spectrum into a typical 8 ohm twelve in a ported enclosure, driven with 28.3v, which is nominally 100 watts. There's nothing linear about it. This, BTW, is why loudspeaker engineers don't deal in watts. We deal in volts, which are a constant into any impedance load.

I didn't miss it.

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If being where you were also put the cab on axis with your ears as it always should be the mids and highs would have been louder and more clear as well.

2 hours ago, Huge Hands said:

 I believe what I was hearing (or not) could have been down to comb filtering effects caused by having mismatched driver sizes.  

That wouldn't be caused by the different driver sizes but by different phase responses. At frequencies where they differ at or close to 180 degrees apart they cancel. This scenario is one reason why well engineered systems never use different drivers in the same passband. Comb filtering is a related effect. It's when wave fronts from multiple sources meet at or near 180 degrees apart causing cancellation notches that alternately occur and disappear as one goes across the sound field. The primary cause is placing drivers side by side. The easiest cure is don't place drivers side by side. If you must do so the fix is to low pass one driver, or one side of a 4x,6x or 8x cab, so that they only work in tandem in the lows where comb filtering doesn't occur, and not in the mids and highs where it does. It's a simple inexpensive fix, known as an x.1 alignment, that's been used for at least fifty years by PA designers. AFAIK the only bass cabs that use it are Barefaced.

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What really opened my eyes, and ears, was a gig in a stall venue before Christmas, where a couple of ladies from the audience wanted to sing, so I sat on a stool in front of my rig and played,  the difference in what I could hear was pleasantly staggering.

What happened there was you had a boundary reflection sourced low frequency cancellation zone on stage, where you were close to boundaries. Out in the audience away from those boundaries you don't have those cancellations, so the lows are louder there. If being where you were also put the cab on axis with your ears as it always should be the mids and highs would have been louder and more clear as well. The cure is to do your sound check listening out in the audience, adjusting both volume and EQ accordingly. Whatever that results in on stage you live with.

4 hours ago, Phil Adams said:

firing straight at my bum!

That's why you can't hear it. Why do you think the monitors are tilted upward?

1 hour ago, Jaybeevee said:

This particular amp is made or fitted with linear pots. Where as most amps deliver more power in the early part of the volume sweep, and much less in the later, this amp delivers a linear power based on the pot adjustment.

Seems like a good idea, but our hearing isn't linear with respect to power. It's logarithmic, requiring ten times the power to sound twice as loud. That's why logarithmic taper pots are used for volume controls. They may not be linear, but they sound linear.  

1 hour ago, JPJ said:

Sorry Bill, 

I should have been clearer in my post. I have several preamps (both pedal and rack mount) that I tend to run into the return of my amp, hence thinking of a built-in poweramp in a single cab solution.

In that case...there's Powersoft if you've won the lottery. Otherwise just search. Just be sure it's full range, not a low passed sub amp. Sub amps are very inexpensive, as they don't need low THD specs and other attributes because they don't operate where they're an issue. 

IMO a better option is to make the cab an airhead, with an integrated space for a rack mount amp that are abundant.

1 hour ago, JPJ said:

“is there a simple plate amp module including power supply suitable to build into a bass cab”? 

Not that I know of. Those I'm familiar with don't have a pre-amp and tone controls that are suitable. You'd still need that in a separate package or pedal.

Even worse, multiple sources playing low frequencies may cancel each other. Besides, what you don't need from monitors is lows. You need mids and highs, especially if your backline isn't aimed at your ears and the mids and highs from it are passing you by below the belt.

1 hour ago, Jaybeevee said:

Thanks, that's something new for me. Unfortunately, not supplied with a manual, and the manufacturer is not answering me specifically on this point.

You can find third party sources for manuals for most amps. Google ' *** amplifier manual'.

It depends on where the lamp is wired to the circuit. Clipping can take place at every stage of amplification, from the input to the output. The manual should say. In general minimal clipping takes place when the master is on full, with the pre volume low.

The only people with any interest in your rig are other bass players. 😉

Aside from an old spare for emergency use, which of course I've never had a need for, I've never had more than one amp. You'd think I'd have a shed full of speakers too, but I don't. I've never had more than two on hand, most of the time only one. I've never owned more than one bass at a time either. The one I have now I made 25 years ago. I'm comfortable with what I have.

He may, he may not. When I do my initial sound check in a smaller room without major PA support I do it from out on the dance floor, adjusting my volume and tone for the best result there. Whatever that ends up sounding like on stage I live with.

Functionally a send and an active DI should be essentially the same. They may differ in whether they're pre or post EQ. The amp block diagram would reveal that. 

At the very least either lift the cab or tilt it back to aim the drivers as close as possible to your ears. One of the reasons why the 8x10 gets so much love is its height allows you to hear the mids and highs.

Google 'boundary sourced low frequency cancellation'. You get it when you're close to boundaries. It goes away when you move away from them.

On 17/01/2023 at 09:25, Mykesbass said:

I'm sure one of the speaker experts on here will correct me if I'm wrong, but my back of an envelope calculation shows that the surface area of the PJ cabs is very small - a couple of 112s will be significantly larger and give you a lot more movement of air.

That. The cone area of a five inch cone, Sd, is around 100 square cm. Four of them is around 400 square cm. An average twelve is 530 square cm. Just as significant is the excursion limit, xmax, which combines with Sd to give displacement, Vd. Vd defines how loud a driver may go. An average five inch Vd is 50cc, making it 200cc for four. An average twelve Vd is 300cc, a high end twelve Vd is 500cc.

There are a number of other factors which impact how low a five can go. They can go as low as larger drivers, but to do so they sacrifice sensitivity, which means less output per watt of input. I'm a big fan of fives myself, in the right context, which IME is as a midrange driver used in conjunction with a larger woofer.

6 hours ago, fretmeister said:

Silly question about gauges. I see on some sites that a chunky gauge should be used with amps that are about 1000W, but up there ^ 18 gauge has been suggested as ok. So what's the deal? And why do some sites use mm measurements rather than gauges?

You need sufficient gauge to handle the current without overheating and not cause voltage drop. At 1 meter it doesn't take much. Wire gauges are typically used in the same locales that use inches and feet, mm where they use metric, for the same reason. This is a must read if you don't know anything about cables. It's aimed mainly at the hi-fi crowd, as they tend to be more easily scammed by cable mountebanks than professional musicians, but the physics still apply. http://www.roger-russell.com/wire/wire.htm

I have no issue with buying rather than making your own, even though it's a ten minute job. But at least buy something that's reasonably priced, twenty quid tops. The reliability factor is determined by the quality of the connectors. Those I linked from Blue Aran are as good as it gets.

28 minutes ago, three said:

 Amazon have the EA Siren 3' at about £72

That's an insane price for a one meter cable. As for all the claims they make, they're piffle, the entire lot. A pair of these, along with a meter of zip cord from a local hardware store, is all you need. https://www.bluearan.co.uk/index.php?id=NEUNL4FX

Just be sure to get Neutrik, not an imitation. The knock-offs have been known to cause problems.

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So I could order the parts and then have to find some time to assemble it and then be paranoid that I’ve done it wrong and I’ll cause a fire or something,

You're a bass player. You're supposed to be the smart one in the band. 🙄

When you've got four identical woofers sharing the same airspace you're not going to get a significant difference in response from each pair even if you were to bi-amp them, let alone dual amp.

The BN10-200X is displacement limited to 120 watts, so a 500w/8 ohm amp would have no problem driving four of them to maximum output. If you can't find one rated for 2 ohms rewire them to series/parallel for 8 ohms. BTW, you didn't bi-amp if you didn't have an electronic crossover. You were dual amping.

You might not need as much power as you think, nor dual heads. I may be able to confirm it knowing what drivers you have.

Actually it's small, low and sensitive. Money does enter the equation, as longer xmax drivers capable of going low in small boxes tend to be more expensive, but they still can't get around the sensitivity, so to go loud requires more power, which means a more expensive amp as well.

1 hour ago, Balcro said:

The BN300S that Bill mentioned is 4-5 dB louder than the Celestion Pulse 12 from 400Hz & upwards, but the Pulse has a very strong thump around 80-140Hz - see Celestions' own frequency response graphs.

That has nothing to do with the magnet material. A higher Fs and other factors give the BN300S higher sensitivity in the mids, but also result in less low frequency extension. One of the highest sensitivity drivers ever made was JBL D130, which had an AlNico magnet. It also had very poor low frequency response, but that was an acceptable trade off in 1948, when 25 watt amps were state of the art. It was also designed some 17 years before the advent the Thiele/Small specs. Only after that did designers realize that the main way to get higher sensitivity, more magnetic flux, doesn't increase sensitivity linearly across the full audio spectrum. It tilts it to the mids and highs. Where electric bass is concerned you want to compare sensitivity where it matters most, 50 to 80Hz. You can't do that with manufacturer data sheet charts, as they are measured with the driver mounted in a wall, and don't show the results in an enclosure. You need to use speaker modeling software to do that.