Bill Fitzmaurice

[quote name='JTUK' timestamp='1416387778' post='2609567'] I think boom is a problem of the cabs, mostly... [/quote]Some cabs are prone to boom, but so are some rooms, where you'll get boom no matter what cab you have.

[quote name='Beer of the Bass' timestamp='1416397504' post='2609709'] Yes, I think most manufacturers do it. I have a small 1x10" which the manufacturers claim has 102dB sensitivity, 126dB max SPL and a usable frequency response down to 45Hz. I don't believe any of those for a moment! [/quote]Technically all of that is possible. It could have a midrange peak at 102dB sensitivity, it could reach 126dB in the midrange, and it could have useable response to 45Hz, meaning that it's down 10dB from average at 45Hz. But that's all specmanship. There are specific rules set forthe by the AES as to how speaker measurements are to be made and quantified. Virtually every manufacturer ignores them. One honest manufacturer is Ampeg, so they can be condsidered as the spec benchmark. When you see sensitivity and/or frequency response specs that are more than a couple of dB or Hz off from what a similar Ampeg product is rated at you can safely assume that the claims are bogus.

I do the same with my Superfly, each preset with the same EQ save for one filter that I set at -9dB, at six different frequencies. When I encounter boom I can scroll up through the presets until I find the right one to suppress the boom in that room. Then I can tweak the other sliders to get the final tone that works best, though I seldom have to do much once the boom frequency is notched out.

[quote name='Musky' timestamp='1416355308' post='2609447'] A few years back when Alex pointed out that the specs quoted for a cab made by a respected manufacturer couldn't possibly true, said manufacturer did the decent thing, apologised and amended the specs. In mitigation they said they did it because all their competitors were lying as well... [/quote]Aguilar, if I recall correctly. Eden was well known for blatently lying about their response and sensitivity specs when still being run by Dave Nordschow, and Nordschow continues to do so with his DNS line. Old habits die hard.

[quote name='FuNkShUi' timestamp='1416318496' post='2608974'] So Bill, sorry if this is a slight derail, if you wanted a Amp with the most volume "out front", what measurement would you be looking at? SPL? [/quote]SPL is what you hear, not watts. There is no direct correlation between power and SPL. One can calculate the maximum SPl that a given amp and speaker combination will deliver if you have the required data, but no speaker manufacturer that I know of provides that data. If you know the T/S specs of the driver being used and have detailed cabinet dimensions you can calculate both the frequency response and maximum SPL of the speaker, but most speaker manufacturers won't tell you what the driver specs are.

[quote name='skidder652003' timestamp='1416316514' post='2608929'] doesnt the wattage have to be 10 times as big to just double the DB level, [/quote]It does. More accurately, it takes a 10dB increase to be perceived as a doubling of volume, which requires a tenfold increase in power.

[quote name='LukeFRC' timestamp='1415800503' post='2603903'] and would I be right in guessing that your ultimate cab wouldnt be a bass reflex either? [/quote]I play a bass reflex cab, a Jack 12 Lite. But it's also horn loaded.

[quote name='LukeFRC' timestamp='1415776932' post='2603566'] I mean it's common in PA land- just not bass world yet. [/quote]So is line array technology, midrange drivers, crossovers and cabinets that are actually large enough for the drivers that are contained within. To be frank, the engineering used by most electric bass amp and cab manufacturers is archaic, but as long as they sell they'll continue to be made.

There is no simple answer. There is another point to ponder, though, that being equal loudness. The lower the frequency the harder it is to hear, so to compensate for that you might use EQ. EQ eats up headroom like nobodies business, both in terms of driver excursion and amplifier power. For that reason I'm hesitant to sacrifice either excursion capacity or speaker sensitivity in the 40-50Hz range, where one is most likely to apply EQ, in favor of above 60Hz, where you're less likely to boost EQ.

[quote name='Ruds' timestamp='1415631525' post='2602139']. Maybe I'm just overthinking, and in practice this is not important, or I'm overlooking something. [/quote]It's not that xmax isn't important, it's that you don't have to consider it along with the thermal power rating, frequency response and sensitivity in a juggling four specs scenario when the maximum SPL chart wraps it all up in one neat package. It also helps to know that you don't need for a cab to have consistent maximum SPL down to the lowest fundamental. Where you run into a compromise situation with respect to a design that anyone can use is not knowing if the end user has a four string, five string or a drop tuned six string.

Any of my 2x12 designs would suffice. They're made from 12mm plywood, so they're light weight. They've also withstood falling off the back of a pickup truck at 60MPH with only scraped paint to show for it. I'd venture that barefaced are just as durable. What you make a cab out of is of far less importance than how you make it.

[quote name='owen' timestamp='1415563197' post='2601516'] One speaker firing out of the front and one out of the back (presuming out of phase with the front one)[/quote]That would result in their cancelling each other. They would have to be in phase/polarity. For best results the rear driver would have to be low-passed, probably around 250Hz, where the rear radiation pattern is omni-directional. Some will suggest that having the rear driver full range would give good dispersion, but the result would be severe comb-filtering, with the cab sounding different at every possible combination of both the cab placement and the listener position, as the front and the reflected rear waves meet at constantly shifting degrees of phase based on the wall distance and listening position.

[quote name='Ruds' timestamp='1415547203' post='2601329'] But, if I know the cab is going to be used mostly for electric bass, and I know something about this signal, wouldn't it be more precise to use this information to estimate the limits of the enclosure on a more practical situation? [/quote]I don't. I look at SPL, Maximum SPL and port velocity charts. I don't worry about excursion per se, as it's just a means to the end that's seen in the Maximum SPL chart. Looking at the excursion chart shows only one dimension of a three dimensional result. The main benefit to looking at the excursion chart is in learning how it fits into the overall result, including how tuning affects excursion, but after a few decades of designing speakers that's second nature.

It's the maximum SPL chart you should be looking at, not the excursion chart. Maximum SPL accounts for sensitivity, excursion and thermal power. With a 5 string tuned at B your maximum demands lie at the 2nd harmonic, 62Hz. However, obtaining maximum SPL at 62Hz will come at the cost of sensitivity, and therefor output, below that, so you must compromise to get the best overall result. In 56L 55Hz tuning gives maximum SPL of 121dB at 62Hz, but only 104dB at 40Hz. 48Hz tuning still gives 118dB at 62Hz but with a much more useful 110dB at 40Hz.

[quote name='yorks5stringer' timestamp='1415011014' post='2595501'] How do you get on with the right hand drive and UK registration plates in New Hampshire..... ? [/quote]That's my spare that I keep garaged in St.Andrews, for when I visit to play a few rounds.

[quote name='88reaper88' timestamp='1414358999' post='2588655'] I'd rather have the van [/quote]So would I, when I was 23 and on the road. But to paraphrase an old movie scene, "BMW. It's a little too small to get laid in. But you get laid the minute you get out". And we all know from sad experience it's not the bassplayers who get the women, it's the drummers.

[quote name='88reaper88' timestamp='1414348980' post='2588526'] ...not gain a masters degree in acoustics. [/quote]If you do you'll have something to fall back on when your playing days wind down. When I played bass five nights a week this is what I drove from gig to gig: I don't gig much anymore, but I play golf seven days a week, and this is what I drive to and from the course:

[quote name='Chienmortbb' timestamp='1414325852' post='2588211'] I was really excited when I first looked at the SM110. I have just done a quick winisd plot of the SM110. It has a great frequency response in a 40L box but xmax is exceeded in the at very low power (approx 75 watts) . This means that it is 3-6dB down at 70Hz. I will recheck later but at the moment the Fane 10-300 looks. a better bet [/quote]Good call. One cannot look at a sensitvity plot alone. Below are shown the Celestion (red) compared to the Eminence 3010LF (green), both in 45L. If all you look at is the top sensitivity trace then there would seem no real advantage to be had with the 3010LF. Looking at the middle maximum power and lower maximum SPL traces reveals a very different story: While you're at it model the Eminence BP102. [quote]If only I could make two cabs and test them out![/quote]Theile and Small rendered that necessity obsolete circa 1970.

They would not be my first choice. The 73Hz Fs is too high. Assuming that you don't know what that means, required reading: http://www.eminence.com/support/understanding-loudspeaker-data/

[quote name='Kevin Dean' timestamp='1413982999' post='2584377'] Everything was fine until the drummer who is also the singer decided he liked having the Sub behind him & I must admit the bass drum does sound good compared to what was coming through the monitors . [/quote]That's all well and good, but what does it sound like where it counts, in the audience? Having subs (and you need more than one unless the room is tiny) on stage is not the best placement where driving the room is concerned.

[quote name='lefrash' timestamp='1413967770' post='2584056'] Has this gaping hole totally knocked the balance off the sound of the cabinet? [/quote]It has. Cover it.

[quote name='xgsjx' timestamp='1413972882' post='2584156'] The difference between 4 ohm & 8 ohm cabs (if they're the same, such as 2 MarkBass 2x10s), is @ 3 decibels. [/quote]The difference is 3dB higher sensitivity for the 4 ohm cab with the same voltage input. The difference in maximum output is zero, because that's limited by the driver excursion, which is the same.

[quote name='Kevin Dean' timestamp='1413933262' post='2583909'] the only thing is I'm not getting all of that power out of my Abm 400RH [/quote]Going to a 4 ohm cab probably won't make any difference. Speaker output is limited by the driver excursion capacity, and that's not affected by impedance. Very few tens will take much more than 100w before they reach maximum excursion. The SICA drivers in your cab, for instance, max out in excursion at 100w each in the low end, so a larger amp won't make any difference either. Bottom line, you can only get so much out of a 2x10.

[quote name='chris_b' timestamp='1413801390' post='2581961'] The boom you hear might be localised to your corner of the stage and won't be heard out front. The problem with EQing out of it is that by the time you get a sound on stage you'll have changed the sound out front to the point that it might not be what you want. [/quote]True, but seldom if ever is the tone you hear on stage the same as what's heard out front. Ideally out front is covered by the PA, controlled by a competent sound guy who knows what you're supposed to sound like. If you're not in the PA then you adjust your EQ during soundcheck using wireless or a long cord to stand out front, and live with whatever it sounds like on stage. [quote]Ports are omni directional though & unless the ports on the cab is less than a few inches from the wall, I believe they have no affect on sound regardless of where they are on the cab.[/quote]Correct. [quote]My (inexpert) opinion would be that the problem is to do with reflections coming off both wall and floor as having speakers positioned in corners is known to cause problems with bass frequencies. Maybe raising the cab up some may help.[/quote]Also correct. Lifting the cab by a meter or so can reduce midbass boom, while making it easier to hear the mids and highs, which will mask a midbass boom.

[quote name='leroydiamond' timestamp='1413717615' post='2581090'][color=#141414][font=verdana, geneva, lucida,] Previous experience of doing this with a rear ported cab, resulted is excessive boom that could not be controlled with EQ.[/font][/color] [/quote]Boom is easily controlled with a parametric EQ. Set the Q to medium width, set the gain to -10dB, sweep the frequency until the boom disappears. Then tweak the Q and gain to taste.