Bill Fitzmaurice

9 hours ago, itu said:

Neither is superior, both can be designed well - and not so well. They are a bit different, but both are complicated to design.

Sealed designs are simple compared to ported. The advantage to sealed is that they're hard to mess up, so long as the drivers used have the right specs for sealed. It just so happens that the right specs for sealed are high Qts, which are what's usually found with inexpensive drivers, so if you're going to use an inexpensive driver just stick it in a sealed box and you're good to go. Ported cabs work best with lower Qts drivers, which also tend to be more expensive, so if you have a more expensive drive it probably needs to be in a well designed ported box for best results. Ported goes lower than sealed when done right. What you don't want to do is to put an inexpensive high Qts driver in a badly designed ported box, as the result will usually be a boom box. When you hear people complain about ported speakers being boomy it's usually because they had a cheap driver in a bad box.

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A generalisation is that sealed enclosures have a more contolled/attenuated low end response. It's a characteristic that can mean sealed cabs are a good partner with amps with a lower damping factor, such as valve amps.

Like most generalizations it's not true. The Ampeg SVT, for instance, was made sealed because that's what gave the best results with the high Qts drivers that they used. They could have made it ported and probably would have if they were able to find low Qts 32 ohm drivers, but none were to be had in 1969.

Damping factor is a non-factor other than in extreme cases that are very rarely seen.

http://www.cartchunk.org/audiotopics/DampingFactor.pdf

You're not wrong, but also not entirely correct. Most of what's heard form electric bass is midrange harmonics, not low frequency fundamentals, exaggerated as the ear is most sensitive in the midrange. Therefore the comb filtering is happening where it's most audible. Then there's the matter of horizontal dispersion, which is halved when drivers are so placed compared to vertically aligned, and here again that halved dispersion occurs primarily in the midrange that's critical to intelligibility.

9 hours ago, Chienmortbb said:

If we assume that both amplifier amd speaker are substantially linear, then the correalation between watts and SPL is also linear.

The problem is that assumption is incorrect, in a few ways, the most obvious being that speaker impedance, and as a result current and power, isn't a constant with respect to frequency. That's why neither amperes nor watts are used in SPL computations. Volts are, being unaffected by the load impedance, and being linear with respect to cone excursion.

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Yes but amplifiers supply WATTS to an impedance. 

See paragraph above.

Try plugging your headphones directly into the SansAmp. You 'll need a stereo to mono converter plug to get it in both ears.

Players, not necessarily. But speaker designers should know better. Sadly not all do. 🙄

1 hour ago, Stub Mandrel said:

 

Interested to know more! The linear array attaches to the top of the woofers by built in sockets., Similarly on the other PA you can stick a rod in the top of the bass bin and balance the other speaker on top, if space is limited.

For best results the mains must be out front, lest they feed back into the mics. The subs should be close to a wall, for boundary loading and to prevent boundary reflection sourced cancellations. If you have two or more subs they should be placed either together or at least 16 meters apart, to prevent phase sourced cancellations. This also isn't new by any means, but it is almost universally unknown by consumers, and therefore ignored by consumers and manufacturers alike.

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Why don’t they mount speakers in a cab angled up ?? 

The detracts from the interior volume of the cabinet. Not a good idea when most commercial bass cabs are undersized as it is.

2 hours ago, pburrows said:

 If my understanding is correct.... both cabs 8ohm, sending each side of the 1600w power amp to 8ohm give 800 per side @ 8ohms, so the cabs do not get their full capacity?

Once again, with feeling:

The watts don't matter.

Mains should seldom, if ever, be mounted above subs, but that's a PA issue, not electric bass.

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Leo got it..... Wrong?!

Leo was a very skilled machinist, but acoustic engineering wasn't in his wheelhouse. He did recognize the need for tilt back legs on his cabs, though, a feature curiously absent on other brands.

3 hours ago, BassAdder27 said:

I do think a vertical designed cab ( still wide enough for a standard amp head ) has a lot of advantages

The loudspeaker engineering community has known this since the late 1940s. Neither Leo Fender nor Jim Marshall were loudspeaker engineers, so the blame for poor electric instrument speaker designs that persist to this day can be attributed to them.

4 hours ago, Hammer_ said:

one amp is a gt1600fx

 

Isn't that a dual channel amp?

Run each cab off its own power amp. I won't bother getting into the whys and wherefores but the watts don't matter.

Maybe she preferred Entwhistle? Or Sir Paul? 🙄

Crossing above 80Hz is usually the better option with all but high end PA, as typical portable PA tops don't go much below 100Hz, if at all. There's no reason for subs to go below even 35Hz with music. Below 30Hz is home theater territory.

At what frequency to cross over to the subs depends on how low the tops go before dropping off in response and/or output capability. Finding out where that frequency is usually requires experimentation, as it's not a spec provided by most PA manufacturers. 'What other folk are doing' should not be a consideration.

I doubt if you need a sub based on your audience capacity. Home audio subs won't work, they lack the sensitivity/output to work for PA.

It does not, at least where maximum volume is concerned, which is usually limited by the driver excursion. With no changes to the knobs the four ohm cab will be perhaps 3dB louder. However, all it takes to get the same excursion, and therefore the same output, from the 8 ohm cab is a slight twist of the volume knob. If the amp is rated well below the power rating of the speaker, like by half, then you might, might, get 2 dB higher maximum output from the 4 ohm rig. It might even be slightly audible, but that's it.

11 hours ago, MattW said:

 I wish the BB was 4ohms though as it would give me a bit more headroom as a single cab.

That's a common misconception. You do get higher output per volt, but there's no such thing as a free lunch. You also lose current headroom in the amp. People tend to look at the higher amp power output into 4 ohms as opposed to 8 ohms and assume that's a good thing. It's not, because that higher power output is obtained at the cost of higher current draw.

1 hour ago, bassman7755 said:

I think were both right but just arguing over the semantics of "signal" which to me means voltage and current since to transmit the signal we need some current to flow.

You can't have the one without the other, but in this case the current level is far too low to be of any consequence and has no influence on the result.

While on the subject: The reason speakers are very inefficient, on average only converting 2% of the electrical energy they receive into sound, is impedance, specifically the impedance of air, which is very low. 8 ohms doesn't sound like it's a high impedance source, but it's a lot higher than air, so nearly all of the energy put into a driver is lost as heat. A horn loaded speaker acts as an acoustical transformer, just like the output transformer in a valve amp. The horn raises the impedance of the air mass that the driver operates into, increasing efficiency as much as tenfold.

Current doesn't determine the signal level, voltage does. Input impedance doesn't affect the signal voltage flowing in the cable. Losses occur when the amp input impedance is too low, not when it's too high. When the amp input impedance is less than some ten times the output impedance of the bass what's known as loading occurs, which results in signal loss. https://www.electronics-lab.com/article/input-and-output-impedances-of-amplifiers/

This being the case the higher the source impedance the higher the input impedance must be. Power amps tend to have an input impedance around 10k ohms, because the consoles that plug into them have an output impedance of 600 ohms or less. Instrument amps have an input impedance of 100k ohms or more, because passive pickups have an output impedance of 5k ohms or higher.

You don't need a new cab, you need new wheels. 😊

Those sites are useful, but they only scratch the surface of speaker design. They're the equivalent of the first day's lecture in a four semester course at University of Salford.

Even with identical drivers a sealed cab and ported cab will have totally different low frequency response and displacement limited output. You may be able to get a useful result, if you've got the engineering skill to pull it off, but otherwise it's a shot in the dark.

If they don't have a crossover that assigns different pass bands to different drivers they weren't truly designed to be mixed, advertising claims notwithstanding. I've yet to see definitive objective data that says otherwise.