HELP!!!! :Bass Guitar Cabs

[sangram]

Open E on a standard bass guitar is 40 Hz.

You will need to be flat at least upto here, if the boxes can go lower it's better.

PA and bass speakers are constructed differently from hi-fi drivers. Excursion is smaller and the setup is very, very stiff - ever driven a competition vehicle, then compared to a road car?

I do not think over excursion is that much of a problem. As you will see repeated many times on the board, it is the HF harmonics and clipping power that destroy a driver. There is of course a potential issue of having adhesives melt if you're running a speaker at 3x its rated power, but I guess if you're not deaf you will be able to hear the distress that the woofers are in.

Over excursion is much more of a problem with tweeters. It is difficult to hear LF products being passed on to the tweeter and since the tweeter cannot dissipate that energy as sound it disspiates it as heat. Tweeters are also built with little or no venting near the VC gap, so you have a cycle which gradually builds up heat and destroys the poor tweeters.

I hope that addresses the questions in your earlier post.

Yes, I use a 10 ohm, 15 watts fusible wirewound ceramic resistor in series with the horn. A small VC to vary the volume needs to be of impractically high wattage rating, though wirewound pots may be available. I know some of these pads have a couple of transformers for signal attenuation using impedance matching, not sure of the exact schematic but I have some amount of idea about what it could possibly be.

The horan may be very sensitive, but you have a lot of bass speakers. I had to pad mine because the rig had a single 8" speaker. The horn was the only thing you could hear when it was direct, without the series R...

[Le Basseur]

The horn regulator you're talking is not a simple pot,but a so-called "L-pad".The construction of this device is a little different regarding the average potentiometer;it's a low-ohmage wirewound device (4 or 8 Ohms),and has two wired resistances for high-power handling (up to 100W). Among the various models I recomend the ceramic ones (it has better thermal-disipation behaviour).Any average pot installed as an atenuator will burn out after a few seconds because of the power wich can't handle.
About the other topic,in my opinion,the lenght of the woofer's excursion is a very important issue!Aside of the aspects mentioned by sangram,there's another one,ignored most of the time by the manufacturers.It's named " the Doppler effect" and it affects the most part of the bass drivers.Personally,I vote for a woofer having the minimum possible diafragm excursion,having in mind this parameter before others.

[moose54]

Okay buggered if i can get a response that loosk reasonable from Kappa Pro 10 especialy at a volume of around 140L.... If anyone can give me some decent numbers to work with i'll have a go at it... otehr wsie i'll stick with the gamma 10's.... i know they arn't cast frames but i'm an engineer.... so i need to trust the numbers before i build it

can anyone help???

please

thansk for the horn info i think i'll give it a shot

[moose54]

hmmm back at the horn and i guess sangram you would be the best to answer this... and maybe you allready have but i dont quite understand. It's in reagards to the resistance of the cab.

Would i be safe in saying that the overall resistance of the cab would still be 8 ohm (if thats how i wire the woofers) if i added a horn with out a crossover on the woofer section. I'd assume that as only a small amount of frequencies would be heading to the tweeter.... basicaly my amp will only run down to 4 ohm. running two 8 ohm cabs in parallel will do this, and i want to know if adding a horn in that fashion will cause my amp to be overdriven and blow up!. By my logic i dont think it will but i may be missing something really obvious... hmmm

[Le Basseur]

Originally posted by moose54
hmmm back at the horn and i guess sangram you would be the best to answer this... and maybe you allready have but i dont quite understand. It's in reagards to the resistance of the cab.

Would i be safe in saying that the overall resistance of the cab would still be 8 ohm (if thats how i wire the woofers) if i added a horn with out a crossover on the woofer section. I'd assume that as only a small amount of frequencies would be heading to the tweeter.... basicaly my amp will only run down to 4 ohm. running two 8 ohm cabs in parallel will do this, and i want to know if adding a horn in that fashion will cause my amp to be overdriven and blow up!. By my logic i dont think it will but i may be missing something really obvious... hmmm

Even though it seems you choose another DYI mate to answer to your (numerous) questions,there you have my explanations:
1.You don't miss anything,you're just a little confused...
When you're insisting so much on the overall impedance of the cab,please don't mix two different things:the DC resistance of a resistor (driver coil) and IMPEDANCE (wich is freq.dependant).
2.Having understood the above-mentioned difference,here's the practical solution:
-wire your woofers in order to get the desired nominal impedance (8 or 16 Ohms).Don't build a high-cut passive crossover for them,as we're already conclusioned that's pretty useless and totally unpractical.
-build a 3rd order high-pass filter for the tweeter,choosing the cutoff freq.according to your taste.Eventually,put a "L-pad" BETWEEN the filter and driver,in order have a "volume control" for the tweeter itself.
...and you're done!
One last word:if you choose to build a 3'rd order filter,you'll have a 360 degree phase rotation,so the wiring stays as one could expect (+on+,-on- all along).
If you choose a 2nd order crossover,you'll have a phase rotation of 180 degrees;this means that,for the most correct response's sake,you'll have to invert the polarity of the tweeter AFTER the L-pad.However,this is subject of testing,since you'll maybe like more how the cab sounds with the tweeter out of phase.
Once more,no matter of the choosen crossover network,the overall IMPEDANCE of the cab is 8 Ohms (since each individual component:woofer tandem,tweeter has an nominal impedance of 8 Ohms),and not 4 or less.So,you don't have to worry on frying the amp.
Cheers

[moose54]

thanks La Basseur! sooo are the roumors true???? are you really french????

Thanks for the help man thats exactly what i wanted to hear... started the construction phase of my 15" cab this weekend.... cut all parts yesterday, and started the gluing today..... should be awesome when i get it done.... so looking fwd to get these babys pumping.....

good luck on the tweeters..... hows that all going by the way?

[sangram]

Moose let us know how it turns out after you're done.

Thanks for the answer, Le basseur. I wasn't in town for the last few days - so good that Moose can start work...

Moose, as the frequency rises, the impedance of the woofer also rises, and it is able to put out less sound as the power to it is less. A tweeter takes over from there, and at any point, the impedance should ideally remain constant. This is of course a subject of great debate, and the winner is usually common sense - the tweeter has to take over the job once the woofer starts to droop off, so the crossover must be appropriately designed - else at certain frequencies the amplifier will be driving a lower impedance of two speakers in parallel, almost.

Also keep in mind that the frequencies in question are not that often encountered when playing bass, and when so, they are usually low energy components. Therefore your poor amplifier will not have to endure too much hardship.

[moose54]

Yeah thanks sangram..... looks like this tweeter shouldn't be too bad after all.... a bit of tweaking will be necessary but shouldn't be too much drama...... I'll defiantly let you guys know how they go. will take a little while for me to complete them as I spend a heap of time with basketball commitments.... but now that I got the cutting out of the way I’ll be able to do some work during the week.... but to finish them completely will take a while.... I like to take my time so things are right and look pro.... I spent ages on my ht sub to get it not just sounding nice but looking awesome too...

I got a dig cam so I’ll post a pic or two of them when I complete them on here and let you guys know how they went.... probably revive this post by the time they are complete...

o I’ll stick a pic of my ht sub on here too.... just because I’m wrapped with how it finished up and pretty proud of it.... yeah its only a sealed sub but it was my first go at a speaker box of any type and I’m wrapped with what I got.... maybe one day when I not living at home and wont have people complaining about the space I'll pull out the Shiva driver and build a ported enclosure...

Thanks again all...

btw did anyone have a look at a reasonable solution for the Kappa Pro 10's in a volume of 140L+ ???? prob not but doesn't hurt to ask

[moose54]

the 15" cab begins

[22pauld22]

Hey moose .. since you got a labsystem bass head have you thought of going the lorantz 10 inch that labsystem put in their own 4 10 .. they are quite the bargain and made in melb ..

go have a look melmusic.com.au .. nice guys there .. and if you rip one a recone is as cheap as ..

just an idea .. but I don't think you would be dissapointed

cheers Paul