Dumb Question? maybe but could some one explain.

[pat_staunton]

Hi
I recently decided on building a pair of 3-Way speakers, but had no idea there was so much detail into it. However I started off, but in the wrong direction. I purchaced a ready made cross over network (commercial kind) and thought all I had to do was connect the speakers, but I now see that it's much more than that. The specs. on the crossover are:

Power handeling capacity - 50 Watts ( Max)
Cross over Frequency - 1000 - 6000 Hz / sec.
Attenuation - 6 db/Octave.

Now what does that mean??

I know it was a kinda stupid thing to do, but could some one please help me here...

I was planning on using a 12" woofer , 8" midrange and a 1" Tweeter.

[SY]

Now what does that mean??

Absolutely nothing.

Crossovers must be purpose-built for a specific set of drivers to be at all effective. "Universal" crossovers aren't, as you've found out. If you can detail out what your driver specs are, someone may be able to help you put together a rough crossover. But to do it right is going to take some pretty hard work and a lot of measurements.

[BillFitzmaurice]

Your best options are to either get a good book on DIY speakers or buy a kit. Otherwise you'll most likely spend a lot of time and money on something that probably won't sound good.

The crossover you purchased, for instance, is virtually worthless with its low power handling and 1st order slopes. Also, combining a twelve inch woofer with an eight inch mid is a mismatch. Don't waste any more money before acquiring the requisite knowldge to make an informed choice.

[pat_staunton]

Thanx a ton Bill,

But could you explain why is the combination of speakers a "miss match"? 1.What would be a good combination of drivers? And ,
2.what does -Crossover frequeny-1000 - 6000 Hz mean? and, 3.what does - Attenuation 6 db/ octave mean?

This will help me understand what this crossover of mine is..

[BillFitzmaurice]

First, a twelve is generally OK to about 1kHz for response and dispersion. A matching mid should be large enough to take over where the 12 leaves off but still as small as possible to go as high as possible. 8's are generally run from 100 to 4kHz; a better match with a 12 is probably a 2" dome mid made to operate from 800Hz to 8kHz or so.

1000 and 6000 are the frequencies where the crossover from woofer to mid and mid to HF takes place.

6dB refers to the amount of attenuation offered by the crossover, and 6dB is the minimal value available. High quality crossovers will usually have 18 to 24dB slopes. Judging by the wattage and slope your crossover is very cheap. The crossover is the most esoteric and critical part of a loudspeaker design and there is no such thing as an 'off the shelf' crossover that will give top level performance. That's why a kit is a far better proposition for a newbie than scratch building; a kit will have the correct drivers and crossover and a tested design.

[Andy G]

... but understand there will be a LOT of generalisations !!


Ok... I don't know what combo I would ever cross at 1k and 6k.. ever !! but I guess it could be for say a 8", 4" and a low powered 3/4" tweeter, maybe if I was desparate !!! Your pre-built x-o also has shallow roll-off on the mid and tweeter, which isn't always good.. depends on the drivers used !!!

Problem is that a 12" hifi driver will start "beaming" well before 1000Hz (ie get very directional) and should generally be crossed below, say 350Hz.. the 8" gets directional around the 1.5-2k region.... most people here would not generally cross an 8" much higher than about 2k.

in general a 12" needs to cross to a 6" or 5" then a beefy 1" tweeter with an Fs of below about 1k, crossover points generally about 300 and say 2500-3000

a 10" generally is ok crossed to a 5" or 4" and a 1" or beefy 3/4" tweeter, maybe cross at say 350 and 3500.

All that being said, a pre-built crossover doesn't take into account any of the driver characteristics.. yours is almost certainly based on drivers with an 8 ohm nominal impedance... which drivers never actually have !!!

The other problem is that the main vocal fundementals and a lot of instrumental fundementals and the ears highest sensitivity all fall in the 300 - 3000 range, so putting a cross-over point in the 1000Hz area generally isn't a good idea, unless you really know what you are doing.

so you see, basically everything you are looking at doing is basically against any logical combination of speaker units and, as a speaker that will produce "good" sound, is almost certainly doomed before you even start.

The whole thing in speaker design is a very fine balancing, but you have to learn to crawl first, then walk for a while... first try should always be a 2-way, because 3-ways can be a real pain to get right, even with lots of experience and knowledge.

If you want to build your own speakers, my advice is to do a whole heap of research and learning first. Maybe head to doing a well designed kit.

[Andy G]

ya went and posted while I was typing !!

how's it all going ?

[pat_staunton]

Ive allready baught the drivers Is there any way in which I could make a cross over for these drivers? Since These are crappy drivers as well there are no Specs. to them. Any suggestions here Bill? Should I scrap the drivers too?
Could you give me some basics on Cross over construction here Bill?

[pat_staunton]

Thanx there Andy,
Could I build a crossover with cut off points at 400 and 2500Hz? Would that make any difference? And just for information- JAMO has a range of side firing speakers, Does'nt that effect the time allignment and direction of sound waves of these particular speakers?

[Andy G]

.... there was some info on the drivers you bought, maybe something almost workable could be cobbles together... way better than that pre built x-o !! but without knowing the drivers and what problems they might have, and things like frequency curves, sensitivities etc etc.. its basically impossible.

As to the side firing woofs, it is likely they are crossed in very low, (maybe around 100Hz or below.. guess). Below this frequency, bass is basically omni-directional..... and maybe Jamo have considered the time alignment in the cross-over... or maybe not !