a bunch of changes to argue with

[Pbassred]

finally getting arround to changing the 15inch drivers in my PA speakers - amongst other things.

Out will come my anon Chinese drivers 8ohm. In go Eminence Kappa15 4ohm. Apart from the obviouse efficiency of a higher quality driver, the impeadance change allows a jump from 275W to 425W (2db) (head room ). They are slightly more efficient than the Kappa Pro.

I usually only use these as part of a biamped system so the piezo tweeter is a passenger. So I will wire in a switch to bypass the crossover. Some people here would say that I could save another couple of db of losses.

When I bought these boxes I lined them with wadding. Having read a lot more on this forum I believe that it was a mistake so I might take some or all of it out.

I ran a simulation using WinISD and I get a 2db hump at around 60 - 90Hz fillowed by a trough of 1/2 db up to around 500Hz. Do you think that I will hear that in a live setting? By comparrason, I have no idea what the chinese drivers actually do.

The boxes are 160litres. Changing that would reduce the hump but cut off the low end by 10-20 Hz. In Win ISD the 2 x 70mm ports seem to make no change. I don't know what to do with them.

Well guys....... open invitation ... am I taking the right steps?

[kelticwizard]

ran a simulation using WinISD and I get a 2db hump at around 60 - 90Hz fillowed by a trough of 1/2 db up to around 500Hz. Do you think that I will hear that in a live setting?

You are worried about half a dB?

No chance of the slight irregularities you mentioned around 75 Hz and 500 Hz being large enough to matter in a PA setting.

[kelticwizard]

In Win ISD the 2 x 70mm ports seem to make no change. I don't know what to do with them.

The ports are 2mm wide and 70 mm long? Those have got to be the skinniest ports I ever came across.

I would think them quite useless for tuning a 160 ltr box.

These are the Thiele-Small numbers I got from WinISD, version a couple of years old, for the eminence Kappa 15:

Qts = 0.32
Vas = 208 ltr
Fs = 39.35
Re = 4.97
Le = 1.02
Xmax = 1.8 mm
Z = 4 ohm
Qes = 0.33
Qms = 7.55
SPL = 103 dB
Pe = 400 W
Bl = 17.37
dia = 15 in
Sd = 132.72 in²

If you are using a 160 ltr box, I would recommend tuning it to 40 Hz. This can be accomplished by using two 4" diameter ports, 4.5" long each.

A DJ friend of mine uses Eminence Kappas for his business, but in 80 ltr boxes. Half your volume. Not saying that your box size is wrong, for you will get more bass than he once your boxes are properly tuned. But you might be able to get away with smaller cabinets for DJ work.

[Pbassred]

LOL! I meant 2 ports 70mm (3") dia. 160lt was a guess and way off! I went and measured the cabs and yes they are 80lt, which is fairly standard I suppose.

It wasn't the 1/2 db that worried me as much as the 2db hump. However, with the smaller box it all goes away.

what about the other stuff?

[pinkmouse]

Definately go for the smaller boxes. They'll still be too big when you're humping them in and out of gigs!

[Pbassred]

Chatham! I'll be down there on the 6th. A friend of mine is playing a rock set in a pub. I offered my PA - so I might have to build it by then

Haveing looked at the "crossover" in detail I reckon that its a 20ohm and 4.7mF in series with the piezo. Standart faire I believe so that can stay. That leaves the coil.

How do I calculate the losses through a .33mH coil? or rather with a 4ohm driver I'd have to wind myself a .16mH to preserve the 4000Hz low pass ( Its never going to see anything above 500Hz though).

[kelticwizard]

The 0.33 mH coil will have an ohmage of 8.28 ohms at 4,000 Hz.

So I guess you will be down 9 dB from where you were before.

However, I think you have other things to look at.

Like a rather large peak at 1,700 Hz, according to Eminence.

You say that normally these things are crossed over at 500 Hz through an electronic crossover? And that you are just looking for something to get a friend by who wants to borrow the cab for his own gig, not using your electronic crossover?

Is that what we are dealing with here?

My friend who runs a DJ business-he has other people working for him as well as DJing himself-simploy says that he uses an 80 liter box, tuned to 50 Hz, with two Motorola, (CTS) KSN-1165's parallelled with each other.

His frequency response might not look good on a chart, lol, but the combo works and his employees use it in the cabs he gives them, as well. So in a pinch, that is one way to go.

Here is the frequency response according to Eminence. The 4 ohm version will seem to be more efficient because 4 ohms draws more power per voltage level. But Eminence says the response applies to the 4 ohm as well, I believe.

[pinkmouse]

Originally posted by Pbassred
Chatham! I'll be down there on the 6th. A friend of mine is playing a rock set in a pub. I offered my PA - so I might have to build it by then

Which pub? I might pop along and pass judgement!

As to your crossover question, I am slightly confused. I thought you were using an active one.

[kelticwizard]

Al:

He's not online now, so I'll answer to the best of my knowledge.

He said:

I usually only use these as part of a biamped system so the piezo tweeter is a passenger. So I will wire in a switch to bypass the crossover.

My guess is that he normally uses these with an electronic crossover, he's lending them to his friend in the band and his friend will use them full range. Then when his friend returns them, they go back to being biamped and using an electronic crossover. But he wants a passive crossover so he can forsake biamping and use the cabs full range when he wants to.

I think that is what he is saying.

[kelticwizard]

If you want to take that 1700 Hz peak down 10 dB or so you might want a parallel notch filter.

Offhand, I have some specs here of .13mH and 60 uF, parallel. But don't hold me to it-I'd like to see others agree on those figures before settling on them.

Of ocurse, if your rig has any equalizer circuits on it, and you have a control in the 1500 Hz to 2000 Hz range, by all means now is the time to use it.