1st Order High Pass on Compression Driver?

[Mr. Widget]

What was confusing me was everyone on AA and elsewhere were saying I could destroy the TD4003 diaghram - and I couldn't understand that!

The active crossover by the way is an XVR-1 by coincidence. Superb unit. And it does allow me to adjust the Q of the 1st order slope which I have set to medium. I use low Q on the 3rd order LP.

I certainly wouldn't count on getting very much good advice from "everyone" on AA. That said, I wouldn't blast those drivers with the network that you are using... I doubt that you ever would really blast them in a domestic setting though... the damned things are so efficient that I am pretty certain they'll send you running for cover before you give them very much juice.

Your setup sounds quite interesting... I wish the pond wasn't quite so deep.

Widget

[Ian Mackenzie]

Okay,

I now see what you are saying. I will insert my comments below for clarity. I would not normally edit a quote but have inserted reply for clarity

Sorry Ian you are losing me totally I'm afraid - I suspect we may be a crossed purposes. I am just trying to confirm the effect the series protection cap has on the roll of in the stop band.

A capacitor in series results in a 6db per octave attenuation below a set frequency as I have always undertood it.

Yes in theory that is correct..but in the real world it may measure differently due to the variation on the impediance of the compression driver mounted on the horn.


Therefore, if a signal comes in an octave below the F3 point and that signal was originally say 100db, it will be attenuated to 91db. Is that correct? Again in theory that would be right.

Now if that signal was really originally 109db but has been attenuateed to 100db by an active filter an octave higher before the capacitor sees it, it's still going to end up at 91db isn't it?

Merlin, This is difficult to discuss and I will simulate the voltage drives later in the day for you and post the cascaded attenuation into a simple 8 ohm load. Technically the attenuation will sum negatively at any point at the capacitor -3 point and below at 6db per octave

And that would be a total attenuation of the music signal of 18db.At a particular point on the curve yes.

My goal is to use a first order slope - specifically in the octave around the crossover. There is always going to have to be a protection cap an octave lower isn't there? Yes.

So it's only a first order slope in the crossover area itself. Correct

Another reason is it sounds shootloads better than using 3rd order. It can do depending on the overall design.

I see Pass Labs recommend the lowest possible order too. In my case, the horn/compression driver starts to roll off at 6db per ocatave acoustically below 900hz, whilst the bass unit, a 1500AL has a rising response above 500hz of 6db per octave. I'm therefore trying to use a third order slope on the 1500al and a first order on the horn, resulting in matching second order slopes at the crossover point. I hope that makes sense!

I understand.

Put another way, in trying to answer my quandry, if we follow guidelines and insert a series cap 1 octave below the crossover point, does that not mean that a 1st order slope becomes a 2nd order slope below this lower point, and that a 2nd order would become a third order and 3rd a fourth?

Yes in additive terms but not in terms of the filter shape (with a qualification in theory). Your overall voltage drive will look a bit like an inverted riaa curve..with steps.

It would seem you have a Passlabs XVR1. If you need technical support you can email the factory. AS mentioned above I will try and simulate the voltage drive and amplitude response and post here when I get some time.

Your project and equipment is impressive and I am pleased to see your are looking outside the square.

Ian

[Ian Mackenzie]

I certainly wouldn't count on getting very much good advice from "everyone" on AA. That said, I wouldn't blast those drivers with the network that you are using... I doubt that you ever would really blast them in a domestic setting though... the damned things are so efficient that I am pretty certain they'll send you running for cover before you give them very much juice.

Your setup sounds quite interesting... I wish the pond wasn't quite so deep.

Widget

It only a hop, a skip and a jump!

Ian

[merlin]

I have it on good authority that Ian certainly does!

Coming from Down Under, I doubt they'd let him out of the bloody country if he didn't

Something to do with their reputation overseas I think.

Ian, thanks for the kind comments and I look forward to seeing your calculations, that would be really helpful.

[merlin]

That said, I wouldn't blast those drivers with the network that you are using... I doubt that you ever would really blast them in a domestic setting though...Widget

I reckon I might drive them to 106db at 1m if I really raised the roof. That would be as loud as I've ever gone without ear plugs. What would the power requirement be at that level Widget?

Your setup sounds quite interesting... I wish the pond wasn't quite so deep.

I'll get there I think. If you and your good lady ever fancy a trip to the mother land I'm sure the LH Europe division would make your stay both enjoyable and informative. Provided you like a beer of course....

[Mr. Widget]

I reckon I might drive them to 106db at 1m ... What would the power requirement be at that level Widget?

~250 whopping mW!


Widget

[Ian Mackenzie]

Coming from Down Under, I doubt they'd let him out of the bloody country if he didn't

Something to do with their reputation overseas I think.

Ian, thanks for the kind comments and I look forward to seeing your calculations, that would be really helpful.

"Do you enjoy a beer at all?"

Is the Pope a Catholic?

I will try and re install SE tonight and run some sims and see what's happening.


Looking deeper into the issue it ultimately depends on how well the horn loads the driver below the primary crossover point. If you are using flea power I doubt its a real issue but be careful if you are out to impress foreigners...

[Ian Mackenzie]

Merlin,

Unfortunately I cant run the software at the moment as there is a bug. I will try and get a fix this week if time permits.

Ian

[merlin]

Hi Ian,

no worries and thanks for trying. It would be interesting to see the resultant slope though at some point - just for curiosity I think!

[richluvsound]

[QUOTE=Ian Mackenzie;177043]"Do you enjoy a beer at all?"

Is the Pope a Catholic?


The Pope would'nt know what faith he is after 3 pints of Furkins "DOG BOLTER" what say you in Windsor ?

Rich