Bill Fitzmaurice

Beaming is a product of the cone diameter. It has nothing to do with sealed versus ported, which only affects response below roughly 120Hz. The cabinet shape doesn't matter either. What the cabinet shape, specifically the baffle size, does affect is the baffle step frequency, below which the radiated wave wraps around the speaker rather than projecting forward. It begins where the baffle is one wavelength in dimension, rolling off forward response as you go lower, to a maximum of 6dB. With a  baffle dimension of 60cm, for instance, roll off starts at roughly 550Hz. It's the reason why when standing behind your cab you'll hear the lows but not the mids and highs.

I wouldn't put a lot of stock in ChatGPT. From what I've seen its accuracy rate is no more than 50%.  Artificial it may be, but intelligent not so much.

Frequency gaps aren't the issue. Uniformity of off-axis response is. The higher you go with the woofer the narrower the dispersion angle, eventually resulting in full out beaming. Most bass cabs cross over to the tweeter in the 3.5kHz to 4kHz range, which is where even a ten will beam. Crossing over at 2kHz to 2.5kHz is much better. Doing so without worry of blowing the tweeter requires a high order crossover, preferably with a 24dB/octave high pass. No manufacturer I'm aware of does so. Barefaced might, but their literature doesn't say.

Send the line level out to a power amp, or the effects return of another integrated amp.

2 hours ago, BassBunny said:

 you really need to take each driver out and test. There is a crossover of sorts in the cab which could have gone. This would then effect all 4 speakers in the way the OP has described.

Not necessarily. First, you're not looking to hear a pop or click, although you might. You're looking to see the cone(s) move. Even a 1.5v battery will do that. If they don't something isn't right. If they don't move then you pull them to test them individually. A crossover won't affect the result for woofers, as low pass filters allow the DC of a battery to pass. High pass filters on tweeters block DC, but you wouldn't see a tweeter diaphragm move anyway.

I believe they were designed for 2 ohm loads. Peavey gained a reputation for being bullet proof. One reason why is that they assumed that they'd be abused, so they were over-spec'd. They were abused for sure, but handled it well. Keep in mind that they were made long before the internet came along, and reading manuals was (and still is) considered an assault on one's manhood, so concepts of acceptable impedance loads were pretty much unknown. I had one just like that in the picture until just a year ago. I'd stopped using it only because it weighed more than I wanted to deal with anymore.  

If yours is a 15L then going to a 3015 would give better lows, mainly due to it's longer excursion. At only 3.3mm the EVM is limited to only 100w through much of its range. But don't do the 3015LF, as it is a subwoofer driver that doesn't have much in the mids. It still may be necessary to lower the tuning on the Mesa cab. Given the exact internal dimensions we can calculate what the tuning frequency is now.

TL606-606DX%20EDS.pdf

1 hour ago, Jaybeevee said:

It's a 15L in my cab. Ribbed cone as apposed to smooth.

Somebody goofed there. The 15B goes lower. The 15L goes higher, but I never found my 15B lacking for highs.

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 According to TB...

Go to the horses mouth. The EDS shows a later version, loaded with the DL15X, a later iteration of the 15B.

It's more likely to have a 15B.

Ampeg speaker power ratings are conservative, so I wouldn't be concerned.

What I can't do with four strings doesn't need to be done. 😉

1 hour ago, Shaggy said:

The EV drivers were mostly what raised the MB Diesel cabs a notch above everything else. 

True, but that was 30 odd years ago, when very few mainstream manufacturers used premium drivers. JBL, Altec and Gauss were in the same league, hardly anyone used them. EV and JBL both made cabs back in the 70s, perhaps into the 80s, which were far superior to Fender, Ampeg and most others. They never sold well, so they were eventually discontinued. That's because back in the day you never bought amps and cabs as separates, you bought them as a matched set. Mesa was one of very few that sold an amp and cab set loaded with premium drivers. Sunn was another.

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The TL606 isn't very big but built like the proverbial brick outbuilding

The TL606 was good in its day, but it was optimal with 55Hz tuning, which gave a 60Hz F3 and 45Hz F10. The step down option lowered the Fb to 40Hz, which lowered F10 to 40Hz but it raised F3 to 70Hz, so it didn't work all that well.

Low end response is 1/3 driver, 2/3 enclosure. If the enclosure won't support deep bottom no driver will give it. BTW, the Kappalite 3015 response isn't much different from the 15B. The 15L is weaker in the lows, being optimized for guitar.

Usually hiss is created early in the signal chain, so gain amplifies it, making it worse as the gain is increased. If it's there no matter where the gain is set then it's taking place further along the signal chain. That could indicate a fault in the amp, perhaps something as simple as a broken PC board trace or a cold solder joint on a component. That's something that could have occurred when it was shipped. I'd call around to see if a nearby store has one that you could compare yours to. That way you'd know if yours is within spec.

9 hours ago, Marcus Cornall said:

Hi Downunder,

Yes  a Barefaced Big Baby.And yes, sorry it is termed a 'compression  driver '

 

A compression driver is a type of tweeter.

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Since my old head is 30yrs old SS , thought the hiss sitatuion would have improved. Is it because it's a real tube?

Back in the early days of SS they were much noisier than tubes, but I'm talking 50 years ago. Tubes aren't inherently noisy.

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I did t realise that essentially then the ampeg is limited to old sounds only in that way.

I wouldn't say Ampeg is limited at all.

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I would've expected to hear talk of hiss issues in online discussions,but have not.

That's because it's not an issue.

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One of the reasons for a control on the tweeter/compression driver is to be able to remove that ultra high frequency hiss without really affecting your tone. The cab cannot generate hiss, it can only let it through.

Quite right. Other steps for minimum noise is to turn down the gain, turn up the master, and turn off the ultra high switch.

The Bravo 112 cabinet volume is perhaps half that required for good results with electric bass.

It may not, the loop could be on the back side of the input stage but before the gain control. The manual should say.

The mass of the steel of the frame is dwarfed in comparison to that of the top and bottom plates, so it's a minor concern.

Cast aluminum baskets are used for two reasons. With heavy ceramic magnets it's to be stiff enough so that the frame doesn't flex. With neo magnets it's to act as a heat sink. Steel is OK with lighter weight ceramic magnets, and with lower power neo magnet drivers that don't require much heat sinking. Eminence uses steel for their 150w Basslite series, cast aluminum for the 250w and higher Delta Lite and Kappa Lite.

Where frame stiffness is concerned there are two requirements for very high sensitivity. One is a high flux magnet, the other is a tight magnetic gap. If the magnet weight causes the frame to flex it can cause voice coil rub with a tight gap. That was a problem with the 1968 Electro-Voice SRO 15, later re-badged as the first generation EVM. It had a cast aluminum frame, but with only four spokes, so it would flex under the weight of the 16 pound magnet structure. The second generation EVM cured that by going to an eight spoke frame. 

There's very little difference in the sensitivity of different cabs, but a lot of difference in their response and mechanically limited power. The only way to be sure of a good match is with identical cabs.

9 hours ago, Old Ozzie Guy said:

Hi all, anybody had much to do with Fender rumble 2x10 ? Any idear what their sensitivity is? In other words are they efficient, volume wise?

There's not much sensitivity difference between different drivers. Where going loud is concerned that's a matter of excursion/displacement, which is pretty much a matter of price. Longer excursion/higher displacement drivers cost more than shorter excursion/lower displacement drivers. The only manufacturer I'm aware of that reveals displacement is Barefaced, which doesn't aid in making comparisons, since you don't know the displacement of other brands. But suffice it to say that no other brand exceeds Barefaced, and very few, if any, equal it. 

Download the manual. It may have a thermal switch.

A good example. Xmax of the Greenback, and for that matter most guitar drivers, is very short. The result is high distortion at moderate power levels. This relates to us in the form of the original 1969 SVT. It was loaded with short xmax musical instrument drivers, as there were no long xmax tens in 1969. Even eight of them couldn't run clean with the 300w SVT head. The cabs were rated at 240w thermal, while the mechanical capacity was at best 120w. That's why those who could afford them used the Ampeg recommended two cabs.

8 hours ago, Downunderwonder said:

If we accept that Ampeg are selling us a bass cab and not a mid cab then I don't think it's wrong to infer SPL from sensitivity and power handling by assuming the xmax is available.

In most cases the xmax isn't available. The mechanical power limit of drivers averages around half the thermal limit. Some are higher, some are less. Some even have a mechanical capacity equal to or greater than the thermal. But those are high cost premium drivers that are seldom seen in electric bass cabs. Here again don't take my word for it, verify it yourself with speaker modeling software. As a for instance, the Eminence Deltalite II 2510 is the most popular neo ten inch platform. The thermal rating is 250w. The mechanical limit in the critical 80-100Hz region is 100w. And the 2510 is better than most. The most popular ceramic ten platform is the Eminence Beta 10. The thermal limit is 250w. The mechanical limit is 60w. 

No doubt Ampeg is one of the more honest manufacturers. Their power ratings are conservative. But the fact remains that without xmax or Vd one simply cannot calculate max SPL. Try it yourself, using any of the common loudspeaker design programs, leaving xmax/Vd out of the parameters. You can calculate response, impedance, phase, group delay, port velocity, but when you go to the max SPL chart it's left blank for the lack of the required specs.

This isn't picking on Ampeg by any means. AFAIK Barefaced is the only manufacturer that provides that critical bit of information.

A rig of that sort will only sound as good as the crossover allows it to. That means having sufficient high pass slope to prevent over-excursion of the midranges. It also means low passing the woofer cab, otherwise the woofers and midranges will fight each other where they're operating in the same frequencies. MIdrange drivers are a good idea, but as is the case with all good ideas it's the execution that determines success versus failure. If the bright box doesn't have a jack to send a low passed signal to the woofer cab the execution was flawed. If they didn't do that then the high pass filter, if it has one, is also likely to be inadequate.