Impedance and Crossovers? 8ohm or 1000ohm - I'm confused!

[Pbassred]

You haven't got anything wrong. ProSoundWeb have a forum dealing with live sound. They talk a lot about Front Of House (audience) sound. They dont have the depth of knowledge about individual components as DIY audio. They discuss propritry Amps and speaker (wild generalisation. They ain't stupid, just focused).

 

[lucpes]

My reckoning is to design the speaker around a premade crossover, all in one tall case with a 12"-15" Sub crossing @800Hz to a 10-12" Mid crossing at 4kHz (ish) to a tweeter(s).

Hi, 10-12" is too big for midrange, 5" or so would be more appropriate.

I'd also set the bass-mid crossover point differently, ~350-400Hz is more than enough and the 4kHz for the tweeter would be ok.

 

[Pbassred]

Hmm.... This is almost exactly what I want to do, except a more powerful twin cab system. The Yamaha Sound Reinforcement Manual ( price £20, weight 1 Kg). Suggests 15" and 10" and compression split at 500 and 2K or 4K depending on the driver. There are a few 8" out there too.

However, you will get better performance if you Biamp because the bass tends to drag the system down and you loose highs. A crossover before the amps is regarded as being more efficient. 2 advantages are that you don't need to bin your old amp , and if one fails at a gig you still have some sound . Make sure you get those high drivers above the audiences heads to make it travel
Dx

 

[imix500]

There are lots of highly effective and proven systems out there with 10's and 12's for mids. I think the JBL HLA rig uses a 14" if memory serves. A 5" would be fine for smaller cabinets, Meyer's smaller UPM series boxes use them and they sound very nice, but for larger rigs they probably wouldn't be quite enough.
That Yamaha manual is one of the bibles for live sound, it's used in the US as course material in many universities including the one I went to for sound design. It's suggested crossover freq's are pretty much in tune with the rest of the pro audio world, +/- an octave. 800htz is a bit high to cross a sub. Most sub cabs will probably have a horrible response curve up there. 4k is also a bit high for a 3-way system. Usually, the mid driver only handles around 120 or 200 or 250 -to- 800 or 1.2k or 2k (the actual crossover freqs used vary quite a bit out there) and the tweet handles the rest. The critical mid band requires a large amount of energy to be reproduced faithfully, so the less that driver has to deal with the better- within reason.

 

[Ovation]

Hi, 10-12" is too big for midrange, 5" or so would be more appropriate.

I'd also set the bass-mid crossover point differently, ~350-400Hz is more than enough and the 4kHz for the tweeter would be ok.

The problem with 5" is that they're fine for low power, refined Hi-Fi but I can't find any cones that are smaller than 8" with an RMS rating of >100W
Okay, so I could use several of them to achieve the power, but I think that any more than two smaller cones would make the front of the box look 'busy'.

Incidentally, If the boxes end up reasonably tall, I'm considering fitting them with an attenuated horn/tweeter that points backwards at the DJ to try and reduce the need for a monitor.

Posted by Pbassred

Make sure you get those high drivers above the audiences heads to make it travel

I assume we could build a pair of subs to stand on the floor and then have an extendible pole from the middle of those subs on which a detached box with middle and tweeter could be raised or lowered?

 

[Swedish Chef]

Lets be systematic here...

1.

Make sure you get those high drivers above the audiences heads to make it travel

I could not agree more.

I assume we could build a pair of subs to stand on the floor and then have an extendible pole from the middle of those subs on which a detached box with middle and tweeter could be raised or lowered?

This is definitely what I would do - for many reasons. It is much more flexible. Hauling huge cabs around is something I can do without. You can upgrade parts of the system independently. You can tailor the system to suit a wide range of venues by adding a couple of extra bass bins for large settings and leave them resting at home for small.

2.

However, you will get better performance if you Biamp because the bass tends to drag the system down and you loose highs. A crossover before the amps is regarded as being more efficient. 2 advantages are that you don't need to bin your old amp

This is also exactly what I would do. There are so many advantages of biamping that I could not possibly state them all here... Basically, NOT biamping is a very bad idea IMO.

3.

Hi, 10-12" is too big for midrange, 5" or so would be more appropriate.

I disagree. Any good 10'' or 12'' pro driver would be pretty ideal. I would not run them as high as 4k however. I would use a compression driver and horn above 2k. (I would probably horn-load the 10'' or 12'' cone driver too).

4. Sub crossover point. 800 Hz is way too high for most bass bins. I would keep it below 300 Hz, probably around 200 Hz assuming that you bi-amp the subs and use a 10'' or 12'' cone driver for the mids.

This is quite a good link dealing with the basics. http://quadrasub.netfirms.com/

Also, check out the bass horns from Bill Fitzmaurice http://www.billfitzmaurice.com . He frequently writes on this forum and has a wealth of knowledge about pro audio and could probably help you out better than any of us dirtbags here.

Cheers
/Magnus

 

[Pbassred]

I assume we could build a pair of subs to stand on the floor and then have an extendible pole from the middle of those subs on which a detached box with middle and tweeter could be raised or lowered?

I have noticed an odd use of terms BTY. "Subs" are very low drivers often run in mono through a Low pass filter set between 150 to 80 Hz. the speakers that WE are talking about are "bass". The pole idea is used by several reputable manufacturers ( and again, part of my plan too).
I couldn't find a 5" driver either, which is why I mentioned the 8". (225W)
http://www.bkelec.com/Professional/Loudspeaker%20Drivers/Eminence/eminence_page.htm . Eminence also Make a compression driver for 3.5kHz and up.
But hang on here ..... We started talking about your EXISTING 12"+ comp cabs. Why can't you just mount THOSE over a bass cab? Like I said, If you're in North London.........We each own the complementary halves of a system.

 

[Swedish Chef]

I have noticed an odd use of terms BTY. "Subs" are very low drivers often run in mono through a Low pass filter set between 150 to 80 Hz. the speakers that WE are talking about are "bass".

That is absolutely true and I feel guilty for having added to this confusion . I shall hereafter say bass bins for bass bins and subs for subs...

Anyway, adding bass bins to your existing cabs is indeed a great idea that would yield a substantial improvement pretty cheap. How about a pair of these http://www.speakerplans.com/page12.html bass horns loaded with Eminence Kappa LF's (the cheapest of the recommended drivers)? Add an amp and an active crossover and you're all set to go.

 

[Ovation]

I hadn't really though of using the existing speakers!!!

I could certainly do that - but we might want to build something more powerful overall....

The zomax cones currently in the speakers are far better suited to bass than midtone IMO (Range: 35Hz - 5kHz).

I would imagine that something like this Celestion cone (TRUVOX 1218TC 50Hz-8kHz) would be a good 'drop in' replacement for the Zomax:
http://custom1.farnell.com/cpc/prod...pc+catalogue&category_name=&product_id=276234

And then we could use the Zomax cones in the bass bins.

I'd like to take on the project of building an active crossover - it'd be a great chance to learn more electronic theory (I know almost no mathematic principles) - I assume there are some good sites about building one of these.

Now - Wattage!
If I have a Speaker running Midtone + Tweeter from a 100W Amp and I have a Bass Bin runnign off a second amp @ 100W or more, I assume I then have the equivalent of a 200W system ?????

So I'm going to build a bass bin (let's suppose). I want to be able to use the original speakers on their own, or bi-amped with the bins:

If the original speakers now have the celestion cones (or another) and the lowest freq. is 50Hz - Is this low enough for reasonable bass?

At present we still only have one KSN-1141 Horn per speaker and there's only space to add perhaps a small round bullet tweeter for extra oompfh! Is that going to work?
http://custom1.farnell.com/cpc/prod...pc+catalogue&category_name=&product_id=260512
http://custom1.farnell.com/cpc/prod...pc+catalogue&category_name=&product_id=260528
http://custom1.farnell.com/cpc/prod...pc+catalogue&category_name=&product_id=260527
http://custom1.farnell.com/cpc/prod...pc+catalogue&category_name=&product_id=260530

If I add extra tweeters - How do I wire them? Juat in Parallel?

If I choose a really excellent tweeter but it only 50W can I use two of them some how to cope with a 100W of power between them?

We also want a monitor of some kind - as we're near the speakers could this be a satellite with a horn fed from the left and right speakers? (This *must* have an attenuator and be very compact.)

Am I going to add a passive crossover for my Mid/Tweeter box, or just give it the 300Hz and up feed from the Amp and let it cope as it does now?

Loads of ideas I know, but I'm excited about this - It sounds like a really neat solution to have optional bass bins and various lengths of speaker pole up to the top units. No Tripods!!!
(I assume that the usual top-hat plus pole idea will be sufficient)

Magnus - You're a genius, and I value you're opinions!
(and thanks also Pbassred)
Cheers
Jonathan

 

[Swedish Chef]

There is something to be said about the usable range of cone drivers here. When manufacturers specify the frequency range of a speaker they have used the general definition for all electrical engineering. That is, the frequency range (or bandwidth) is specified as the outer limits where response have dropped by - 3 dB. Take the Eminence Kappa 12 as an example http://editweb.iglou.com/eminence/eminence/pages/products02/speakers/kap12.htm. The stated "usable frequency range" is 40 Hz - 4 kHz. A quick look at the graph confirms that response has indeed dropped about 3 dB (from a hypothetical horisontal line) at 4 kHz, right after the big "bump" in response which peaks at 103 dB.

Does this mean that this driver should be operated up to 4 kHz? - No. I really mean NO! The frequency response graph says NOTHING about distortion. This "bump" (which looks great doesn't it - hey 103 dB sensitivity!) is actually due to a breakup mode of the cone. Breakup means that the cone is no longer acting as a piston but rather is bending and rattling like mad. This creates massive distortion = really bad sound

No driver should be operated in breakup territory unless you intend to make a religion out of bad sound. As a general rule of thumb this means that the average 10'' or 12'' pro driver should never be used above 3k. Personally I would never go beyond 2k (I have the Kappa 12's myself). For pro audio this isn't a problem because just about any 1'' titanium compression driver would go down to 2k.

Regarding that Celestion driver, I would not spend my money on it in this case. Is was designed to be used as a fullrange driver (that little double cone takes care of the highs) and response up to 8k is not necessary in this case. In fact, the Zomax driver isn't all that bad for a midbass/midrange driver (that is what it was designed for). Just don't operate it too high. If you hooked it up with an active crossover set to 2k (where the KSN-1141 takes over) you would most probably notice a great improvement in sound quality. This is what crossovers are for and proper crossover design and driver matching is a great deal of what you pay for in a readymade brand speaker.

Although it probably would work I would not use the Zomax drivers for dedicated bass bins. You would probably want to use at least a 15'' driver here and anyway you would want drivers specifically engineered for bass duty (the Eminence Kappa 15LF for example).

Now, wattage. If you biamp two 100W amps together im fact you get more than 200W! (That is one of the beauties of bi-amping, for more info see http://sound.westhost.com/bi-amp.htm).

But you would not use two 100W amps for bi-amping. Simply put this is because bass reguires much more amp power than the mids and highs. Rather you would more likely use say a 300W amp for the bass bins and a 100W amp for the mids and highs.

If you choose an efficient tweeter you don't have to worry about tweeter power rating. The bass bins and mids are going to go out of steam long before the tweeters.

For DIY crossovers and such, take a look at http://sound.westhost.com/index2.html

 

[Pbassred]

I'd like to take on the project of building an active crossover - QUOTE]
Er... yeah.... IF your aim is a project, or to practice soldering. The design is a done deal and in any event not to be messed with if you are using it to dive your prized rig ( well, I'd be scared). It looks like £30 to make the board plus your box. plus connectors and sundries, plus PSU. I'd guess all up - £60. You can buy a new Behringer for that. It not great quality but its vairiable, pretty, lights up
As you probable gussed, I'm not a hobby/project guy. That's just me. I apologise for raining on your parade

 

[Ovation]

I don't know - You 'wannabe' DIY audio enthusiasts with all your speil - that don't want to pick up a soldering iron

I know project stuff is often too much like an effort, but I was looking at plans for a Linkwitz-Riley Active Xover and it didn't look too painful (bear in mind I already have a few project boxes and Powersupplies - So it's only components and a board I need).

I might have a bash at doing this - Given Jane's AMP and speakers are probably worth <£100 I wouldn't go so far as to call them 'my prized rig'

I've also got reasonably good soldering skills and I quite enjoy doing fiddly jobs like this.

 

[Pbassred]

I understand what you are saying. That's why I said it would be fine if you were looking for a project.

As for me, I'm a Production Engineer in the electronics industry. I could use some design experience but not practice. As a hobby, I'm a bass player ( see the link) so my reason for being here is to support that. I'm only building things to use for that. If I was rich I would just buy and have done with it.

Its just bangs for bucks really. Speaker cabs yes. Also understanding amps. Spending the next 6 weeks making something that I could buy - when I could be playing instead - no. I don't knock anyone for doing it. Its interesting, but just not my prime motivation.