Bill Fitzmaurice

[quote name='discreet' timestamp='1447541501' post='2908496'] Presumably if the tweeter level was set at, say, 50% or so as a precaution against the probability of burn-out, then it would take proportionately less extreme EQ settings to achieve the final tone. [/quote]+1. A 50% setting, which is down 4.5dB, shouldn't cause a heat issue. Where it's usually a problem is when it's turned fully or nearly fully off, and being a resistor all of the power going through it is burned off as heat.

[quote name='discreet' timestamp='1447534682' post='2908453'] [color=#282828][font=helvetica, arial, sans-serif]From what I can glean from t'interwebz, minimising tweeter activity with the LPad (the big potentiometer-type thing on the back which varies the effect of the tweeter) can produce a resistance in the circuit which manifests itself as heat in said LPad - it is possible to burn out the LPad [/font][/color][i]and [/i][color=#282828][font=helvetica, arial, sans-serif]the crossover [/font][/color][i]and [/i][color=#282828][font=helvetica, arial, sans-serif]even damage the tweeter/horn in the process. Allegedly.[/quote][/font][/color] [color=#282828][font=helvetica, arial, sans-serif]Assuredly. It's rare, usually the result of inadequate slope in the high pass filter and an LPad that's undersized, but it does occur. [/font][/color] [color=#282828][font=helvetica, arial, sans-serif][quote]I have read on TB and elsewhere that if you have a cab with a tweeter/horn you should run the cab with the tweeter ON and make subsequent necessary tone adjustments using your amp EQ. I have a cab with a tweeter and have recently started running it with the tweeters up FULL as an experiment - and it [/font][/color][i]is [/i][color=#282828][font=helvetica, arial, sans-serif]indeed possible to make the necessary adjustments at the amp.[/quote][/font][/color] [color=#282828][font=helvetica, arial, sans-serif]That's why they put those knobs and sliders on the amp. However, you might find it's best to use a combination of moderate lowering of the tweeter level with the LPad along with EQ. [/font][/color] [color=#282828][font=helvetica, arial, sans-serif]Most of this issue can be traced to the use of a horn loaded tweeter that has much higher sensitivity than the woofers, and could be avoided by using a midrange with sensitivity closer to that of the woofers. This also eliminates the typical response dip in the 2kHz-3.5kHz region between where the woofers leave off and the tweeters kick in. But they're more expensive than horn loaded tweeters, as are the required crossovers, so they're rarely employed. [/font][/color]

[quote name='Naetharu' timestamp='1447520620' post='2908308'] is it safe to just cut the connection to the tweeter and have done with it? [/quote]It's not. Depending on the crossover configuration doing so could cause high frequency oscillation in the amp, leading to amp failure. If it has a crossover it should be removed or bypassed.

If the horn hisses it's working. The source of the hiss isn't the tweeter, it's the amp. Speakers will only reproduce the signal that is sent to them. [quote] is this the intended functionality? [/quote]The intended function is reproduction of frequencies above the range of the woofer. The typical implementation tends to be flawed, as what's required isn't a tweeter that starts at 4kHz, it's a midrange that starts at 2kHz, if not lower.

[quote name='Ian Savage' timestamp='1447346462' post='2906942'] one of these should do it, right? [url="http://www.duramat.co.uk/checker-plate.shtml"]http://www.duramat.c...ker-plate.shtml[/url] [/quote]That may be of higher density than you want. Try kitchen supply stores for a resilient mat. Another option is a yoga mat.

[quote name='Ian Savage' timestamp='1447344307' post='2906910'] I'm getting some problems at high levels with my Laney Nexus bass head seemingly vibrating in sympathy with the matching 1x15" cab it sits on a producing a low-level crackling noise with the very lowest notes. [/quote]While vibrating cab panels won't cause a stage to vibrate, that would be the tail wagging the dog, they can cause a head atop them to vibrate. All you need to fix that is a piece of this, cut to size: http://www.homedepot.com/p/TrafficMASTER-Black-24-in-x-36-in-Anti-Fatigue-Vinyl-Foam-Commercial-Mat-60-571-0900-20000300/202015909 UK sources for something similar must exist. That said, vibrating panels suck away energy that should be going out to the audience as sound. Even a single brace connecting the middles of opposing panels will halve the energy lost.

[quote name='karlfer' timestamp='1447243926' post='2906016'] Anyway, just wondering what is the best way to stack them, photos 1,2 or 3. Basschat experts, your advice please.[/quote] This: [url="http://s1354.photobucket.com/user/Karl_Altdorfer/media/001_zpsuui24s2u.jpg.html"][/url] It gives the minimum distance between the tweeters while keeping them on the same vertical plane. It would be better to have the cabs mirror imaged, so that the tweeter would be at the top of the lower cab and at the bottom of the upper cab, both on the same vertical plane. That arrangement is specified in my DIY cab plans, but with commercial cabs you don't have that option.

[quote name='Skybone' timestamp='1447160956' post='2905355'] The decibel scale is based on a Logarithmic scale, not a linear scale. .[/quote]True, and that's why 10dB is perceived as a doubling of volume. 3dB is a doubling of radiated power, not perceived volume.

[quote name='Happy Jack' timestamp='1447100195' post='2904914'] That's cheating, that is. Them's [i][b]valve [/b][/i]watts which are a whole nother thang. [/quote]A watt is a watt. If you want to do the same with 100w SS as you can with 100w valve use a compressor. [quote]Surely a Jack cabinet with a 200W amp and you are good to go Bill. [/quote]I only run 160w into mine.

[quote name='bonzodog' timestamp='1447089978' post='2904762'] I appreciate watts is not a good way of measuring volume but think its clear most 500w amps would be louder than 200w [/quote]By 4dB to be precise, which isn't worth the bother. As equally valid a question is what is the point of 500w amps? If I manufactured amps I'd make the size differential between models at four times the power rating, say 50w, 200w, 800w.

[quote name='Jono Bolton' timestamp='1447014006' post='2904199'] As the screw holes of the speaker overlap the screw holes in the baffle (but don't line up), what would be the best way to secure the speaker in place? [/quote]Pull the driver, fill the old holes, rotate the driver position 30 degrees, drill new holes.

[quote name='Jono Bolton' timestamp='1446929549' post='2903635'] One of the screws connected the bottom driver to the baffle wasn't tight and the screw holes on the speaker don't match the holes in the battle so it's not got a full compliment holding it in; as a result almost the whole left side of the bottom driver wasn't secured. [/quote]That would be problematic to say the least. The driver frame could vibrate against the baffle, with the same effect as rapidly whacking it with a hammer.

[quote name='shizznit' timestamp='1446986886' post='2903900'] they behave quite differently.[/quote]The particular neo drivers you have may behave quite differently from the particular ceramic drivers you had before, but that has nothing to do with the magnet material. Flux is flux, no matter the source, be it neo, ceramic, alnico or field coil. If there was a characteristic neo sound, or ceramic or alnico, then all neo driver would sound the same, as would all ceramic, etc. That's no more the case than all tens sounding the same, or all twelves, or all fifteens. [quote]Swapping drivers in a cab has always struck me as an illogical thing to do since the cab has to be designed around the driver, most likely outcome is that you end up something that sounds worse and is worth a lot less money than what you started with. If you want a lighter neo loaded cab then buy one[/quote]+1. Besides, not only do all neo drivers not sound the same, they don't all weigh the same, nor do all ceramic drivers. For instance, Orange uses Eminence Beta 10 ceramics, which weigh 3.1 kg. The most common neo ten is the Eminence Deltalite II 2510, which weighs 2.1 kg, so with four you'd only save 4 kg. OTOH there's the Kappalite 3010MB, and it weighs 3.2 kg.

[quote name='Ghost_Bass' timestamp='1446736503' post='2901885'] I think that any type of base (not just gramma pad) with such a low height won't do anything to isolate the cab. There's a bit of height needed to "decouple the bass from the ground", i use an amp stand and lift my cab about 1 metre from the ground, this works! [/quote]What you're referring to is acoustic decoupling, which is a real phenomenon. Full boundary loading occurs when the speaker baffle is less than 1/4 wavelength from the boundary. At 1 meter 1/4 wavelength is 85Hz, so you'll lose boundary loading above that, which can be effective taming boom, as that typically occurs in the 80-160Hz octave. [quote]I only see one use for those isolation foams, it's when you play on a hollow and flimsy stage and dial enough lows on the amp to make the entire stage vibrate (vribation of the cab being transmited to the stage) [/quote] A cab that flimsy is defective. Even in that case all that's required to 'decouple' the cab is rubber feet. If what decoupling devices claim is true then a drummers sticks left atop his kick drum or the snare wires beneath the snare drum wouldn't vibrate when you hit a note, since the cab isn't even remotely close to being in contact with the drum heads. Stages vibrate for the same reason as drum heads do, in sympathy to the sound that the speaker creates, not any vibrating of the cab walls.

[quote name='bassman7755' timestamp='1446705176' post='2901549'] Well speaking as someone with amateur interest in electronics (and therefore not really and "expert"), a pure square wave requires infinite signal bandwidth to amplify accurately and most audio signal chains have various filters which will attenuate the extreme high and low frequency content so what arrives at your speaker probably wont look much like a square ware.[/quote]Correct. First and foremost of those filters are voice coils, which are inductors, and as such function as first order low-pass filters. [quote]The clipped signal still contains more energy for a given amplitude though than a clean signal and so yes you will have to make some allowance for that. [/quote]Close. At the fundamental frequency the power density of a pure sine and pure square wave is identical. It's only in the harmonics where power density of a square wave is higher, and that's why tweeters and the occasional midrange can be vulnerable to the higher power density of a clipped waveform, while woofers and subs are not. That's one reason why guitar amps don't use tweeters, and why if you're a bass player running distortion pedals you shouldn't unless you roll off the high frequency EQ on your amp to compensate for the high frequency boost that most pedals create. The exception, and there are always exceptions, would be a bass specific pedal that has internal EQ compensation to tame the highs.

I suppose as far as placebos go they're cheap enough, but they're still placebos. I've never been able to find a single bit of objective data from any of the makers of either isolation or coupling devices (and you really should wonder why there are both) so I obtained my own. The results are posted here: http://billfitzmaurice.info/forum/viewtopic.php?f=10&t=19112 BTW, since hockey pucks are a high density material if they did anything it would be to increase coupling to the stage, not reduce it.

[quote name='alexclaber' timestamp='1446651008' post='2901157'] This article that I read years ago was what first got me thinking about it: [url="http://www.meyersound.com/support/papers/amp_power.htm"]http://www.meyersoun...s/amp_power.htm[/url] [/quote]Referencing the link, here's the issue: [i]Recently Meyer Sound measured a well-known dual 18” subwoofer system that came with a power amplifier. The amplifier’s power supply rail when it was not being driven sat at 160 volts. Using this rail voltage, we could calculate the instantaneous peak power for a 4 ohm (resistive) load to be: [/i][i] E[sup]2[/sup]/R = 160[sup]2[/sup]/4 = 6,400 watts per channel[/i] That's not how one measures amp output. The correct method is to feed the amp pink noise, turn up the volume until THD reaches the design spec into the specified load impedance, then measure the output voltage. Anything else is smoke and mirrors.

[quote name='Jono Bolton' timestamp='1446496506' post='2899874'] assuming that the cab is completely empty inside, would the vertical rods need to run the full height of it? I would have thought that that length of rod would have license to oscillate from the vibration. [/quote]With rods, and they can be square or round, of an inch diameter oscillation isn't an issue, as there are no forces in that direction, it's all tension and compression. FWIW I only use 1/2 inch plywwod, even with concert grade subs, and they don't vibrate. This illusltrates why: Using only the single red brace to connect opposed panels the vibration resistance of a 1/2" plywood panel is the same as a full inch of unbraced plywood. Using the blue braces as well increases the stiffness to the same as two inches of unbraced plywood. Commercial cabs tend to use thicker materials with inadequate or even no bracing, as that greatly reduces labor costs, and when corners are cut it's usually inside the cab, where it can't be seen.

[quote name='garyod7' timestamp='1446500800' post='2899920'] The stuff was 2 months old by the way just when you mention how long stuff lasts or doesn't! [/quote]At 2 months old it should be under warranty.

Nothing lasts forever. I'd only suspect a problem if you'd blown all four drivers. But don't assume that the knob positions have any relationship with the amp output. All that 12:00 indicates is that it's more gain than 11:00 and less than 1:00.

[quote name='dincz' timestamp='1446486503' post='2899773'] Their rated powers are measured differently. [/quote]No, a watt is a watt. A valve amp and SS amp of the same power will both deliver the same voltage and current into a given load. A valve amp can sound louder than an SS amp even though the delivered voltage and current from the valve amp is less because of the alteration of the waveform by the natural compression that valves impart. This begs the question as to whether you can duplicate the effect with SS by using a compressor, and the answer is yes.

[quote name='Jono Bolton' timestamp='1446472357' post='2899565'] Is it worth running a brace from top to bottom? Would I need one running width-ways across the middle to support it? [/quote]This is what the interior of a well made cab looks like. Few do.

[quote name='Jono Bolton' timestamp='1446455545' post='2899401'] My head is an Ashdown ABM 300 which is reasonably small and lightweight, when I got the cab I tried it out with a Mark IV which may have weighted the cab to stop it vibrating. [/quote]A heavy head would be less likely to vibrate atop the cab, but nonetheless the cab panels should not be vibrating in the first place. A well braced cab won't even cause a pint to vibrate off. That's how I test my cabs. Of course, you can't take the results of only one test as valid, only after a dozen or so pints can you be sure.

[quote name='Japhet' timestamp='1446458986' post='2899428'] why is it that a 200 Watt valve amp outperforms a 600Watt class D? [/quote]Signal compression. Valves do, SS doesn't.

Bracing in older, and for that matter many newer, cabs is often inadequate, if not missing entirely. That's what I'd check first.