Bill Fitzmaurice

[quote name='MoonBassAlpha' timestamp='1402919831' post='2477834'] Speaker is Celestion bn200x, Thinking of making the cab taller than the previous trapezoid shape. I seem to remember the volume needed to be about 1 square foot, is this right? or different for sealed?[/quote]Have you modeled the driver using speaker modeling software to determine required cab volume, and to compare both response and maximum SPL of sealed versus ported? That is the first step in designing a cab.

[quote name='chriswareham' timestamp='1402850442' post='2477229'] in the case of the Vox Foundation they allegedly made the cabinets to the size they wanted (to match the AC50 head) and just bunged in a speaker without concerning themselves whether it was an ideal match. [/quote]In 1965 they had no way of knowing. Use of Theile/Small parameters was in its infancy, and was not widely known until a decade later. A modern 1x18 is about twice that net volume, and is properly ported.

Google 'schematic' for the amp, chances are it's out there.

Tilt the cab back, so that it aims at your head. You'll be able to hear yourself much better that way. If it's still not enough you need to investigate a better speaker, your head has plenty of power.

[quote name='discreet' timestamp='1402316668' post='2471988'] No, I believe Chris Squire and others did it years ago. I think he used two Fender Twin Reverbs at one point. Edit: This from his website: 'Chris’s rig…Marshall 100 watt head with a Marshall 4 x 12 speaker cabinet, two Ampeg SVT-2 Pro heads, two SVT- 8 x10 speaker cabinets, an SWR amplifier head for the Bass Pedals, and an SWR 2 x 15 speaker cabinet. Effects wise – a Samson stereo radio and receiver, a Sound Sculpture, which is a switching matrix to blend the effects together, a spare one, a Hush Unit, then the effects which are a Maestro Fuzz Unit, a custom built tremolo, an TC Electronics Chorus. On the bottom shelf we have a TC Reverb, a TC Delay, and a Mutron pedal from the 70's.' [/quote]He did use a Twin in the studio for the distortion on the first album. If I wanted that sound today I'd run a regular bass rig plus a 1x10 or 1x12 guitar combo.

[quote name='Balcro' timestamp='1402308063' post='2471833'] I've run it's specs through winISD, the first JBL I've checked, and it's the first unit I've come across that handles more than it's rated capacity and laughs at the amp power! It handles the full 150 watts all the way down to it's fundamental resonance @ 35Hz. I think that's it's thermal limit, but at the same time it never exceeds the mechanical "xmax" until the same low point. [/quote]It's certainly better than most vintage drivers, but today the 7mm xmax is about average. The main issue with it is the low (0.25) Qts, which chokes off low frequency response. In that respect JBL made it 'too good', as were most of the D, K and E series drivers, which were designed before T/S. Only after T/S came along was it understood that, while high sensitivity was in general a good thing, it could be overdone.

[quote name='davidlovellbass' timestamp='1402226374' post='2471094'] I was hoping to swap the JBL out for an Emience basslite C2515 but spending out for a speaker that could sound bad isn't very appealing [/quote]You need to go to the JBL Professional site and download their T/S spec sheet, then find a driver with similar specs to the E145. However, that only shows the low frequency compatibility, up to about 200Hz, not the midrange. You'd need to compare that on individual driver data sheets. The kicker though is that doing this only gets you something that's similar to the E145, it doesn't mean it's a perfect match to the Karlson, which the JBL may or may not be. Kep in mind that the Karlson dates to circa 1950, the E145 to circa 1970, so the Karlson was not designed using the E145 as a test driver.

[quote name='davidlovellbass' timestamp='1402165233' post='2470694'] Anyone have any ideas for a replacement speaker that isn't so heavy? [/quote]There are many, the problem is matching anything to a Karlson box. It's a seat of the pants design that can't really be software modeled to get a good driver match.

Do a thread search about driver replacement and you'll find reference after reference that you can't just plop a driver into a cab and get a good result. They must be matched. As for not seeing bass dedicated eighteens, that's because with the driver technology that's existed for the last 15 years or so you can now find tens that have higher output and lower response than vintage eighteens, while eighteens have poor highs and virtually no dispersion in the mids. In short, we no longer use eighteens because we don't have to. Chances are your cab is undersized for an eighteeen anyway, and would work better loaded with a twelve or fifteen. Exact internal dimensions would be required to determine what would work best. The driver you linked to is, frankly, a POS. Don't even think about using that.

[quote name='Roland Rock' timestamp='1401279967' post='2461944'] Thinking about it, I have a vague memory of Dave Marks demonstrating an EBS head, and his description of the 'notch' control sounded similar to this. [/quote]A parametric works very well, you set it for a narrow notch and simply sweep the frequency until the boom-boom goes bye-bye. It's the best tool for the job, but seldom seen on bass heads, as most bass players tend to be intimidated by such high tech tools. Parametrics are ubiquitous on good PA consoles.

[quote name='Roland Rock' timestamp='1401265026' post='2461707'] If I were to create say five '100-250hz room' presets, what settings would you suggest? [/quote]Usually the issue is midbass boom, which you need to notch out. I'd make the filters all -6dB cut, each at a different frequency, say at 80Hz, 120Hz, 160Hz, 200Hz and 250Hz. Then you can scroll up through them to find the right one for the room you're in. If your cab tends to run on the boomy side anyway you might want to make it a -10dB cut. Most guys like a tone that's fat in the lows and the mids, and getting it as often as not doesn't mean boosting the lows and mids but rather taming the midbass that can mask them.

[quote name='Dad3353' timestamp='1401235619' post='2461615'] ...which will be constantly changing for many of us as folks come in and leave. [/quote]Out in the room, to some extent. Not on the stage, where the main determinants of midbass response is the distance between the amp, the nearby boundaries, and you. Upper mids and highs aren't affected much, as those frequencies are too directional. Deep lows aren't affect much, as the wavelengths are too long. The non-directional midbass of medium wavelengths are very much affected, and as the distance relationships between the amp, nearby boundaries (both walls and ceiling), and you vary greatly from room to room so does midbass response.

I EQ for every room, because every room sounds different. The main differences in rooms tend to be in the midbass, 100 to 250Hz, so that's where I usually have to adjust for the room, leaving all else alone. That means you need an EQ capable of working within that bandwidth alone, a graphic or parametric. 3 or 4 band EQs typically don't give you the adjustment accuracy that you need to account for room acoustics.

[quote name='thebassman' timestamp='1401141367' post='2460593'] Would this change with different pa set ups? Just curious as I have never had the problem before, with the same amp/cab, but different pa. [/quote]It can, depending how their inputs are wired. Not all are as they should be. This explains: http://www.rane.com/note110.html

Symptoms are those of a ground loop. The amp should have a chassis ground lift switch to prevent that.

[quote name='Thurbs' timestamp='1400830457' post='2457274'] For a cheaper option than buying loads of new gear, grab a screw driver, take out the old driver and then do some googling for a new driver with the same or compatable ohms as your existing one. You could "upgrade" your cab to somthing louder for not much money at all... (< £100) [/quote]Driver swapping is a far more complicated affair than just inches and ohms. You must consider all of these factors: http://www.members.shaw.ca/loudspeakerbuilder.ca/thiele-small.html Where low bass output is concerned the main limiting factor here is the size of the box, not the driver that's inside of it. Google 'Hoffman's Iron Law'. You can get around the low sensitivity issue with a small cab by using a very long xmax driver (which you won't find for < £100) and an amp with sufficient power to drive it, but in the OPs case that means replacing the entire rig anyway.

[quote name='dincz' timestamp='1400863939' post='2457737'] I normally run with the filter switched on anyway. For limiting LF driver excursion, wouldn't 75Hz be even better? It's 12dB/octave by the way. [/quote]At 12dB/octave it would, and partly explains why you don't hear it all that much. Most high pass filters are 18dB. [quote]Bill do you focus on the low end roll off or making the 80-160Hz range sound good? [/quote]Where the low end is concerned I go for about a 50Hz corner, where tone is concerned mids are what matters.

[quote name='dincz' timestamp='1400855692' post='2457618'] My current preamp has a 75Hz high pass filter. Initiallly I got all fired up about modifying it for 40Hz, modelled the required component changes in Spice, and then after hearing the minimal audible difference the standard filter makes to a bass, decided I can't be bothered. [/quote]Do it anyway, not for tone purposes, but to limit driver excursion below the useful frequency range and cut down on thump noise.

The f3 of a Fridge is 58Hz, and few complain about lack of lows. With drop tuning you might need as low as a 40Hz f3. Those who are aware of the fundamental frequency of their lowest note often think that they need a speaker capable of going that low, but that's not the case, as most of what's actually in the signal is harmonics. Most players who don't have any training in acoustics will be off by a full octave between what they're hearing and what they [i]think [/i]that they're hearing. Raggae has the deepest tone of mainstream genres, and to hear it one might conclude that most of its energy is in the 40-80Hz octave, but actually it's in the 80-160Hz octave. In concert the 40-80Hz octave might be more present than in a recording, but that's due to the contribution of PA subs and a heavy hand on the PA console EQ.

It's almost impossible to damage an amp by over-driving it. Were it otherwise guitar'd players would be replacing amps weekly. Damaging the driver with too much low end is common, especially with combos, where the cab is much too small to deliver deep lows and the drivers tend to be lower end models.

Qts higher than 0.5 is best. Find out for sure by modeling some drivers in WinISD. You will lose a lot of low end going sealed. You shouldn't be experiencing the issues that you are, probably due to a design that's not quite right.

[quote name='Conan' timestamp='1399964397' post='2449298'] If you couldn't see the speakers through the grille, and there was no identifier on the cab itself; I wonder how many bass players could plug into an anonymous "black box" cabinet and be able to identify the size of the speaker(s) inside just from how the cab sounded? My guess is that it wouldn't be very many - especially if the speakers were decent quality. [/quote]+1. No one would be able to do so with any more accuracy than calling the flip of a coin, in this case one with three sides. It would be even more interesting to have three examples of each, loaded with different drivers that would give different results. For example, one with an Eminence 12, one with a Beyma 12, one with a Celestion 12. All would sound different, despite being the same size. To further befuddle the 'Golden Ears', how about a horn loaded Eminence Kappalite 3010LF versus an EVM15B in a 1 cu ft sealed cab? There are some things where size matters. Electric bass drivers isn't one of them. OTOH, like another tool, what matters isn't the size of the driver, what matters is what you do with it.

[quote name='Michael J' timestamp='1399707372' post='2446795'] Stuffing can make quite a difference to low end extension by making the box "appear" (to the driver) internally larger than it really is - [/quote]Stuffing a cab lowers the speaker Q, which can tame a midbass peak, but it does not give any additional low end extension. If your cab has boomy response stuffing may help, but if it doesn't go as low as you want that can only be fixed with a larger box. This chart shows response of a driver in a small box with 0.9 Q, the same box stuffed for a 0.7 Q, and a larger box also with 0.7 Q. Lowering the Q of the smaller box with stuffing does not give better lows, but making the box larger does. This chart shows the results with an HT subwoofer, with an electric bass driver the same effect would occur, but about an octave higher.

[quote name='redstriper' timestamp='1399679909' post='2446733'] Another question -Is it likely the drivers will come to any harm by being in the wrong size cabs? [/quote]Only in that since the cabs are undersized the drivers can't produce what they're capable of, and in the quest for deep lows you might over power them.

[quote name='redstriper' timestamp='1399676332' post='2446700'] I wonder if I could get more deep bass extension and possibly more volume level by adding a larger port(s) in a similar way to this post: [/quote]Probably not. Deep tone is more than just the cab tuning, it's also the size of the cab. A 3015LF needs at least a 4 cu ft cab, not counting the driver and port volumes, for best results in the lows.