Bill Fitzmaurice

An old story, so forgive me if you heard it:

A 9,000 seat outdoor venue near me was being threatened with closure over noise complaints, low frequency noise in particular. They hired a 'professional' company to come up with a solution. Said solution was a cheap PC with sound level software, with a mic that measured the level in the FOH.  An alarm light lit if the level they'd hit exceeded the standard that they assured would not be too loud in the area. For a full season the light never lit, yet the complaints increased with every concert. For this the venue paid them $25,000. 🤥

Just before the start of the following season, on the threat of being shut down, they hired me. The first thing I noticed about the gear they had and the standard that was being used was that the levels were being measured with 'A-weighting'. They were upset to say the least when I told them that 'A-weighting' doesn't measure low frequencies. 😄

The main problem is PA subs that go an octave lower than bass cabs. The cure is to high pass the bass channel strip around 60Hz. FOH guys who are also bass players or recording engineers known this. But those who aren't usually don't.

That rarely happens. Most sound men make it what they think bass should sound like, and they're usually wrong. My number one complaint about concert sound is pounding deep bass that has no resemblance to what players want for tone, at levels that drown out the rest of the band. 

Alex is correct insofar as what he talks about, which is frequency response. As to whether by looking at charts you can tell what a speaker sounds like, you can. But that's 'charts' in the plural. A waterfall chart will tell you most of what a frequency response plot doesn't. Then there's THD, polar response, power compression and a half dozen more. Speaker emulation devices adjust frequency response, some high end studio plug-ins can adjust some other parameters, but none can do it all. The main thing they can't do is to vary all of the various parameters as a function of the volume that the speaker is being played at. If your charts are going to be truly accurate they have to be measured at various power levels, because they will change at various power levels. Even if you had software sophisticated enough to duplicate all of the charted results at one given power level it wouldn't be able to do so at any power level without an unaffordable level of processing, along with the necessary interface to tell the software at what power level it's operating at any given moment. That would require something with capabilities similar to Klippel analysis. It would be less expensive to run six different speakers.

Speakers reproduce the signal that's sent to them by the amp. In this case the amp is sending hiss. You don't hear it through the woofer because woofers don't respond to high frequencies.

There are professionals, in that they get paid for what they do, and there are professionals, in that they know what they're doing. This bunch doesn't know what comb filtering and power alley are, let alone how to prevent them. They had both, with not only poor sub placement but also side by side tops. 🤥

The LPad can't hurt, but since you have dual woofers at 4 ohms that will even things out a bit. You usually have to reverse wire the tweeter with a 2nd order/2nd order crossover, another reason why I never use them. But it doesn't hurt to run a 2kHz tone through the system before you button it up, trying the tweeter wiring both ways, going with whichever is louder if there is any difference.

On 26/07/2023 at 14:07, BassmanPaul said:

As the OP last visited on December 01 2021 I'm afraid your query fell on deaf ears. Sorry!

 

As did two more replies after you posted this. 😄

I always mic drums, and for that matter all of the instruments. It's not about volume, it's about dispersion. The only instruments that don't have a problem with dispersion are the bass and keys, and then only below 200Hz or so, where their speakers are omnidirectional. To prevent them from being too loud down low I high pass their channels as required by the venue acoustics.

5 hours ago, Happy Jack said:

 

Bill, my bands play very few gigs where placing our subs 15 meters apart is an option.

Then don't. Keep them together.

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A big central bass zone and either side your low notes have the bottom drop out

Although the name 'power alley' makes it seem that way you don't have a big central power zone. You have alternating power zones and null zones across the room. A more accurate description is low frequency comb filtering, as that's what it is.

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Probably best to side by side them in front of the stage for best effect.

That can result in a total cancellation frequency where the distance from the subs to the wall behind the stage is 1/4 wavelength. Side by side or stacked to one side of the stage close to the wall eliminates that possibility. And no, they won't be heard as being to one side. You can't localize long wavelengths. The perceived location of low frequency sources comes from the harmonics produced by the mains.

On 23/07/2023 at 20:10, Stub Mandrel said:

 two huge The Box 2x15 cabs.

Old school. Use them for now, but when the time comes to invest you don't want anything of that sort. A pair of 1x10 or 1x12 mains will work far better in the mids and highs, while a pair of 1x15 or 1x18 subs will work better in the lows. In the smaller gigs where you don't need the subs leave them at home. Self powered is the way most are going these days, although the more experienced still prefer passive speakers separately amped.

When you get to this point know that the most popular way to set up is with the mains pole mounted above the subs. It's also the worst way. Subs work best when they’re placed either close together for mutual coupling, or spread very wide to cover large areas. The basic rule is to have them either less than a quarter-wavelength apart or more than two wavelengths apart for their pass band, which for 40 to 100 Hz means less than one meter or more than 15 meters. Boundary loading should be used whenever it’s practical to do so. Having subs next to a wall gets you 6dB of additional sensitivity, and putting them in a corner an extra 12dB. In most cases you’ll have best results aiming the subs towards the wall or corner from about a foot away. The wags will tell you that's all wrong, but that's why they're wags. The mains are pole mounted for proper projection and to prevent feedback, but not above the subs.

Aside from playing golf I've nothing else to do. 😄

That only has a 2nd order high pass, which is totally inadequate. 3rd order is the minimum acceptable for pro use. The 4th order I use reduces the power to the tweeter an octave below the knee frequency by an additional 12dB compared to a 2nd order. That makes the difference between clean and distorted, as well as between functioning and blown. 

2 hours ago, nbaptista said:

And a Fender rumble 40 watts?

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To make a change worthwhile you need 50 watts into a ten, minimum.

With bass cabs I use the Eminence BGH25-8. It's rated at 25 watts, because that's all there is above 2kHz with 500 watts program. There are few, if any, off the shelf 4 ohm crossovers, but off the shelf crossovers aren't very good. I design my own. This is an 8 ohm 2kHz 4th order high pass filter, which you can't buy from anywhere in the UK. The capacitors are poly or mylar, rated for at least 100 volts. The coils are air core, of the smallest available wire gauge with no more than 0.5 ohms DCR. A plus/minus 10% tolerance of the component values is permissible.

This is a 4 ohm 2kHz 2nd order low pass filter. The capacitor is a non-polar electrolytic (NPE), rated for at least 50 volts. The coil may be solid or air core; what’s critical is that the DCR (resistance) of the coil for a 4 ohm system be less than 0.2 ohms. A plus/minus 10% tolerance of the component values is permissible. Being 4 ohms you can't buy one of these either.  

I always build my filters on separate boards, it's too easy to get confused with the layout and wiring putting them on the same board.

If you want to go twice as loud you need to increase power not by a factor of two but by a factor of ten, so going from 15 to 30 watts is futile, especially if you don't increase the speaker size. To make a change worthwhile you need 50 watts into a ten, minimum.

Ports can go anywhere, as their radiation pattern is omnidirectional. But most players, let alone people in general, aren't aware of that, so they tend to avoid cabs that don't look conventional. Being well aware of this commercial cab manufacturers tend to avoid breaking out of the cookie cutter mold. What's the first comment you see about a new product? It's almost always about how it looks. Too bad we don't hear with our eyes. 🫢

Bottom porting is perfectly feasible. It doesn't lower the tuning all that much, maybe by 3Hz. It acts more like a flare than an extension of the port. You just have to use cabinet feet at least 2.5cm high.

If they were on the dimmer circuit the low voltage would have been a major problem, so that probably wasn't it. But inexpensive dimmers create RFI/EMI that radiates through the air, which can cause what you experienced.

Offhand I'd say it's a 3012LF magnet structure judging by the depth of the recess in the mushroom.

44 minutes ago, Jaybeevee said:

Many thanks, confirmed it as a kappalite 3015LF 👍

Not if it's a 12. It could be a 3012HO, could be a 3012LF, which has a deeper rear 'mushroom'. Or it could be an OEM version of either. TBH neither the HO or LF are ideal for electric bass. An OEM with specs midway between them, along with the longer voice coil that the extended mushroom allows, beats them both. I've worked with a few of those designing commercial cabs.

24 minutes ago, Phil Starr said:

 

Does anyone have strong feelings about 18mm v's 12 mm ply

A single brace connecting the middles of two 12mm panels gives the same vibration resistance as using no brace with 24mm panels. That's why I don't use 18mm in any of my designs, while some use only 3mm and 6mm, with no vibration issues.

On 11/07/2023 at 05:32, Downunderwonder said:

To be clear, the most you would get from the extra 30w amp, ie twin amps one on each cab, is a measly 3dB.

+1. Doubling the power isn't worth carrying the second amp around. At the very least you want to double the voltage swing capability, which translates to four times the power.

Since they have much lower EMI than standard transformers tightly packed components is one reason for using toroidals. One of their characteristics is they don't have stray magnetic fields caused by the ends of the cores, because the cores have no end. Whatever EMI they do radiate travels in all directions. They're also smaller and lighter, but are much more difficult to make, so they cost more. Why you had your result is puzzlement. 🫢

OP, you may find this of interest. Scroll to post # 33 https://www.talkbass.com/threads/eden-toroidal-transformer-buzz.391552/page-2