Bill Fitzmaurice

On 21/10/2025 at 08:34, synthaside said:

Buy a cheap  DB meter on amazon 

Most cheap dB meters only have 'A' weighting. They don't measure bass. You need 'C' or 'Z' weighting. 

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"I havent ever titlted it or put it on a stand off the floor as many say dont elevate it as you lose the bottom end." 

True, if it's lifted by a meter or more. Less than that and there's no loss of bottom end. If you don't tilt or lift it the highly directional mids critical for the perception of loudness are passing by your knees, which can't hear them, rather than by your ears, which can. 

Mixed subs might not make a lot of difference to the sound, as it will end up being a blend of the sources. But due to the often wide differences in response between different subs it's a lot more difficult to get the best result when they're not matched. Looking at the SPL chart for the SWA1501, which is about as flat as the Matterhorn, I can see it being a challenge to get it to play nice with another sub. https://www.fullcompass.com/common/files/2965-SWA1501SpecSheet.pdf

Since the room affects everything in the PA you want to adjust the GEQ. 

You wouldn't hear much, if any, difference if the tops aren't reproducing sufficient lows. However, they're still receiving the low frequency information, so the amps are producing low frequency power and the drivers are taking that power, which stresses both the amps and the drivers, while the THD of the tops will be higher than if high passed. You've got nothing to lose with high passing, and potentially much to gain with respect to amp and driver headroom and lower THD, so it should be done.

Knowledge is like good food and drink. It's best when shared. ☺️

One would be sufficient. ☺️

Steel is highly unlikely, tinned copper is common. 

If not identical you can have one coasting while the other is stressed. 

3 hours ago, ossyrocks said:

Please have a look at the speaker frame. This speaker mounts into the cab from the front, so I would have thought it would have had some kind of gasket around the rear edge of the frame. 

When the D140F was introduced front mounting was rarely use, so they didn't come with a gasket. IMO that driver pre-dates the cab, so it probably wasn't a factory installation. The fact that it was reconed adds to that opinion. In any event yes, you should clean it up and use a new gasket or 2mm neoprene gasket tape. 

3 hours ago, Jackroadkill said:

 

I have, however, come up with a plan for the connection of the drivers - tin the cables up, run them through the spring connectors and then heat-shrink them (carefully) into place.

Don't. Spring connectors work by deforming the copper wire, which prevents it from vibrating out. If tinned it's too stiff to deform. I've been using spring connectors for at least 30 years, have yet to have the wire pull out. 

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some of the Speaker Cable tomfoolery defies credits. And Power cables.

Victor Wooten lost all credibility when he started endorsing huge, and hugely expensive, power cables that don't do anything. I'm surprised he doesn't have a Shakti Stone atop his amp. Maybe they can't afford him? 😮

Neither do audiophools who spend a fortune on oversized cables that don't do anything other than depleting their bank accounts. 😉

1 hour ago, Jackroadkill said:

 This is the wiring; do we reckon it's up to the task?  

It's far larger than the wire in the voice coils. 😎

I haven't used Tolex since the 1990s but if I did I try this to keep it looking good, it works wonders for my car: https://www.amazon.com/dp/B01AAZ1OAE

That is a possibility, impedance rises with temperature, but it would take a very sophisticated DSP to incorporate that feature. 

Thermal protection only applies to the amp. 

The only method of driver protection that really works is limiting the voltage output of the amp. It's SOP in touring pro-sound. The voltage is limited so that neither the driver Pe nor Xmax is exceeded. Outboard DSP can incorporate it, as can onboard. Whether or not a given powered speaker has it or not you can probably determine from the owner's manual. If it has it they'll say so. If they don't say so it likely does not. 

Since the dome is paper it was probably re-coned with a 2226 kit. Not ideal, but it still works. As to the wife, a man should have as many amps as his wife does shoes. 

Judging by the vintage if loaded with JBL it's probably an E140. If you don't see a 10cm diameter aluminum dome it's not JBL. 

According to Fender: Compact and lightweight (16 pounds) sealed enclosure with removable grille. Given the size and power chances are it's an inexpensive high Qes driver, so there wouldn't be any point in porting it. 

Thanks. Celestion hasn't been known for PA drivers for DIY but they're getting very strong in that market.

They're very light, as they are built from 12mm plywood and the drivers are neo. The exact weight depends on the plywood species, but they're going to be lighter than most commercial offerings. Like any sub they should cross to the mains between 80 and 120 Hz. 

Celestion hired me to design compact lightweight enclosures for their TSQ 1845 and 2145 drivers. They're now posted on the Celestion site as free PDFs with youtube videos. 

https://celestion.com/blog/build-this-18-inch-bass-reflex-enclosure-featuring-the-tsq1845/

https://celestion.com/blog/build-this-21-inch-bass-reflex-enclosure-featuring-the-tsq2145/

1 hour ago, Davy said:

@Phil StarrWe use in ear monitors which sound sooo different to the main PA sound

They shouldn't. The room affects the PA of course, but standing close enough to the PA to take the room out of the equation your in-ears should sound very close to the same.

3 hours ago, Al Krow said:

 

Seems to be the key point here, thanks. Please remind us why that is Bill - sound reinforcement from the walls?

Allison Effect, the cancellation from the reflection off the rear wall. To prevent it the subs must be close to the wall, the mains far from it. When both are the same distance away it's unavoidable. 

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I suspect 8/10 pub / bar bands in the UK put their tops on poles above their subs due to space limitation issues. But if the only downside is directionally locatable frequencies and bands aren't fussed about the losing the ability to put subs anywhere, then no particular problems crossing over at a higher frequency than the usual 100Hz when using a bass combo as a sub?

See above. Since you can put the sub anywhere that relieves some of the space concerns. By dint of using a bass combo as a sub it is a sub, and the same placement rules apply. 

7 hours ago, Al Krow said:

 

It's an interesting one, 'cos there's an argument that tops are completely fine with going down to 60Hz? So why cross at 100Hz?!

Because the sub probably has more available output from 60-100Hz than the tops. Crossing lower than 100Hz with tops that are on stands also brings floor bounce cancellation into the equation. 

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crossing over at 150Hz (because the bass combo can easily handle up to this) would be more beneficial than 100Hz.

No, as that results in directionally locatable frequencies coming from the subs. Then you lose the ability to put the subs anywhere, which should never be below the mains unless there's no alternative.