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blown 6"

M

Matthijs

Supporting Member
Jul 3, 2006
2,247
1,154
Amsterdam
#1
I should have known better. Went to a small outdoor gig with just one of my diy 12/6/1 cabs, should have taken both. This was a big band gig that asks for a big bass sound from my DB. The crowd wasn't that big (small opening of a medical center) but I still needed to compete with al those horns. Close to the end the alphalite 6 cbmr went without any warning. This surprised me because it is filtered 12 db at 1600 hz and with a spec of 100 watt in a 500 to 4k frequency range I didn't expect it to be the weak link. The amp was my eden wt300, that's not an overkill on wattage too. The alpha 6 is paired with a deltalite 12" that had no audible problems at all. Maybe this was due to a loud transient from a slap on the fingerboard?

Anyway I'm hesitating about what to do: put in a steeper filter and always take two cabs outdoors, or go back to the drawing board an turn both 12/6 cabs into one 'compact' 2*12/2*6/1 so I will never be tempted to leave a cab at home again?
 
#3
and one is even easier ;)

They are not extremely small and I might be able to design a 2*12 with a bit less low end that's just a tad bigger. It will weigh a lot more though.

I guess you're right. Maybe it's best to replace that 6" and bring both cabs more often. That was the idea behind building them anyway. Pity I can't think of a better way to protect that 6".
 
#5
Muziekschuur said:
On-off switch. U didn't need the 6" outdoors...
Click to expand...

Might work, but it would need to bypass the filter as it's a three way crossover. Also I did not build it as a 12/6 only for reasons of dispersion only. The 6 reproduces the upper register of the double bass much prettier. Might be sensible to install an extra input after the crossover though, for those gigs where it's better to suck up my hifi ambitions and I just need to be heard.
 
#8
Matthijs said:
I've toyed with lightbulb fuses before but found it hard to determine the right values. Do they alse work for short peaks of power?
Click to expand...

Yes, seen may "My cab is lighting up!" threads. As the driver compresses (increase in Back EMF) the waste power is used by the lamps. Might try two 12 volt in parallel as a starting point as the the 6" is more capable than a tweeter?
 
#9
Hey Matthijs,

You don't want or need the lamp idea with a mid driver. At best it's excess baggage for midrange, and often ends up being a liability for anything that sees much power - unless the designer is really proficient. You need good mid drivers and good crossovers that match the drivers well. You might already have both in your design (though I personally think from working with them that the CBMR versions are cheesy).

After reexamining the crossover design for flaws you might also consider that just because a driver blows does not ALWAYS mean that something was wrong with anything else - other than that particular driver sample. That happens sometimes.
 
#10
Thanks Greenboy, what would you recommend as a mid together with a deltallite 12? I selected them based on the efficiency graphs matching, and on a positive comment from Billfitzmaurice somewhere on TB. The crossover is a off-the-shelf unit that might not be the best solution, but I thought I wasn't running any major risks as I was crossing over at more than twice the resonance frequency.

Might very well be neither the speaker nor the design is to blame, as I was pushing stuf pretty hard and a double bass can cause a lot of high-mid transients.
 
#12
Matthijs said:
Close to the end the alphalite 6 cbmr went without any warning. This surprised me because it is filtered 12 db at 1600 hz and with a spec of 100 watt in a 500 to 4k frequency range I didn't expect it to be the weak link.
Click to expand...
There's no way that it blew from over-excursion or overpowering unless it was being sent a severely distorted signal. This assumes the crossover is properly configured, though with a 1.6kHz knee it would have to be totally botched to be the culprit. As a for instance, if the crossover is an off the shelf for an 8 ohm driver it's not going to work correctly as the impedance of the driver at 1.6khz is 12 ohms. In any event I would not use a 2nd order/2nd order crossover due to the phase issues it creates, as well as the lessened protection factor.
 
#13
O.K. Thanks Bill, if I read the chart in the pdf on the eminence site correctly the impedance at 1600 hz is well above 10 ohms, might even be 12 ohms. I guess I was a bit lazy thinking I could get away with a ready-made crossover.

I'll try and figure out a new crossover and replace the alphalite.
 
#15
qts said:
Hey Matthijs, keep me/us informed about the project.
I'm planning to build another 2 way crosover for my D12LF+La6 CBMR.
Mine is crosed over at 800Hz, which is a bit low i think due to harsh sound at high levels.
Click to expand...

I will, if only to sollicit for free advice from Greenboy and Billfitzmaurice :)

I did the calculations for a 18 db highpass filter for the alphalite 6 cbmr at 1200 hz (impedance at 1200 db is approx. 12 ohm) and a 6 db lowpass at 1200 for the deltalite 2512. I hope to achieve a level response around 2000 hz as there is a small dip in the response of the alphalite around 2 khz.

What I always find hard to do is determine the voltage ratings for the components. Is there an quick and easy rule to calculate those?
 
#16
Matthijs said:
I will, if only to sollicit for free advice from Greenboy and Billfitzmaurice :)

I did the calculations for a 18 db highpass filter for the alphalite 6 cbmr at 1200 hz (impedance at 1200 db is approx. 12 ohm) and a 6 db lowpass at 1200 for the deltalite 2512. I hope to achieve a level response around 2000 hz as there is a small dip in the response of the alphalite around 2 khz.

What I always find hard to do is determine the voltage ratings for the components. Is there an quick and easy rule to calculate those?
Click to expand...
Metalized Polyprop caps are ok at 250 volts for this application, though of course 400 volt is better.
:bassist:
I think you need more power because you must be clipping your amp lots, if the driver melted its voice coil? its because the passive crossover failed to send a suitable proportion of the high frequency information, as it will read square wave as potentially three or more close coupled peaks and send this to the midrange unit.
So this is all part of the myth of under powering, Actually its where the myth originally came from, you cant destroy a woofer with square wave but you sure as hell can a midrange unit, the crossover frequency should be lower for an efficient 6" mid 800 seems far more real, as long as its attenuated back to flat and its getting clean power it will sound better.
 
#17
Matthijs said:
What I always find hard to do is determine the voltage ratings for the components. Is there an quick and easy rule to calculate those?
Click to expand...
Ohms Law. For good measure run the caps at twice the voltage required. With a 500 watt 8 ohm nominal system the maximum input voltage is 63 volts, so the minimum cap rating would be 125 volts. And make the woofer low pass 2nd order, otherwise it won't roll off fast enough to prevent destructive wavefront interaction.
 
#18
billfitzmaurice said:
For good measure run the caps at twice the voltage required.
Click to expand...

That was the quick and dirty tip I was looking for.

With "destructive wave front interaction" do you mean phase cancelation in the overlapping freq area because of the phase shift caused by the crossover? Should I avoid multiplications of 12db/octave in the total amount of seperation? (does that make any sense?).

I've got a general grasp of the underlying math concerning all this, but I realise that's not enough to do it right.
 
#19
Bassmec said:
I think you need more power because you must be clipping your amp lots, if the driver melted its voice coil? its because the passive crossover failed to send a suitable proportion of the high frequency information, as it will read square wave as potentially three or more close coupled peaks and send this to the midrange unit.
So this is all part of the myth of under powering, Actually its where the myth originally came from, you cant destroy a woofer with square wave but you sure as hell can a midrange unit, the crossover frequency should be lower for an efficient 6" mid 800 seems far more real, as long as its attenuated back to flat and its getting clean power it will sound better.
Click to expand...

It was not a melted voice coil and there was no audible clipping going on.
 

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