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Where do I install adjustable Lpad for Foamed Horn?

1285 Views 10 Replies 4 Participants Last post by cdy2179, Nov 9, 2010

cdy2179

Discussion Starter · Nov 8, 2010

I just ordered a 4" sheet of 30 PPI foam trom Swisstropics. I plan on installing it in the horns of my 3677s.

I know it'll attenuate the CD about 2-3db so I want to bypass the resistors in the Crossover and and use a parts Express adjustable L-pad (the same one used in the econowave Xover) to bring my Cd level back up level with the woofer.

I'm a Xover newbie and I've been reading up on it. I'm thinking I should remove R4, R5, R6 from the network and put my l-pad here. From what I gather these are the CD's attenuator resistors. R7 and R8 look like it may also be in that circuit. I probably don't need to remove them all.

But anyways am I on the right path here?

The Xover schematic is linked here.
http://www.jblproservice.com/pdf/The...eries/3677.pdf

Thanks.

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cdy2179

Discussion Starter · #2 · Nov 9, 2010

No crossover guru's on here today???

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Bill Fitzmaurice

· #3 · Nov 9, 2010

Quote:
Originally Posted by cdy2179 /forum/post/19456595

No crossover guru's on here today???

We're all over at the Parts Express forum where you double posted the same question.

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cdy2179

Discussion Starter · #4 · Nov 9, 2010

Quote:
Originally Posted by Bill Fitzmaurice /forum/post/19456897

We're all over at the Parts Express forum where you double posted the same question.

I'm picking the brains of both forums, why limit myself

There's smart guys here too!

And I double posted on parts express because another member thought I may get a better answer in the Pro speaker thread

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penngray

· #5 · Nov 9, 2010

lol

IMO, foam does not drop the response a constant dB across all frequencies at all so its not really an Lpad type solution

If you are thinking about using the 30 ppi foam, then just use it and listen. If you want to fix any response issues, you have to redo the XO or go active, there isnt an easy way to do it.

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cdy2179

Discussion Starter · #6 · Nov 9, 2010

Quote:
Originally Posted by penngray /forum/post/19458842

lol

IMO, foam does not drop the response a constant dB across all frequencies at all so its not really an Lpad type solution

If you are thinking about using the 30 ppi foam, then just use it and listen. If you want to fix any response issues, you have to redo the XO or go active, there isnt an easy way to do it.

Dang Penn, you sure know how to ruin a guys day

. Well it looks like R1 is the resistor I need to reduce if I choose to increase the CD level.

But about the response. I saw a few post of guys using the foam and posting before and after responses and it looked like the response was somewhat even in shape although reduced across the top end compared to before the foam.

My foam comes in tomorrow and I also ordered 75 feet of RCA cable so I can use REW again in my HT. I used to have a HTPC in the HT now I operate a PC that's actually in my study but I can use it in the HT as well, I just haven't been able to use REW since moving the PC to the study, I only used it for the sub and haven't really cared to again untill now. Now I'll be able to string the RCA cable through the house to get response info to my PC and see what going on.

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penngray

· #7 · Nov 9, 2010

I have not seen those measurements where everything was uniforum. I have my own and I know Augerpros effected lower frequencies more which is interesting because Geddes discussion on it had me thinking upper frequencies were effected more.

The only thing I concluded that ever single design needs its own measurement comparisons. It matters how much people use and that can vary. Some fill the throat to the entire mouth and beyond, some may not.

How are you cutting yours and will it fill 100% of the horn?

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kgveteran

· #8 · Nov 9, 2010

I was always thought it was right to leave the resistor in place.....

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cdy2179

Discussion Starter · #9 · Nov 9, 2010

Quote:
Originally Posted by penngray /forum/post/19459048

I have not seen those measurements where everything was uniforum. I have my own and I know Augerpros effected lower frequencies more which is interesting because Geddes discussion on it had me thinking upper frequencies were effected more.

The only thing I concluded that ever single design needs its own measurement comparisons. It matters how much people use and that can vary. Some fill the throat to the entire mouth and beyond, some may not.

How are you cutting yours and will it fill 100% of the horn?

Well what I saw wasn't perfect but it did seem to be more effected as the frequencies climbed. My CD are only good up to 12k (but it really hasn't bothered me).

Most of the time we don't hear any honk at all, the movies with good clean audio have no problems. We did watch the new Karate kid the other night and it was full of honk. I seemed to be something with the mix, although the music in it sounded great with no honk. Only vocals.

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cdy2179

Discussion Starter · #10 · Nov 9, 2010

Quote:
Originally Posted by penngray /forum/post/19459048

How are you cutting yours and will it fill 100% of the horn?

The foam is 4" thick. I plan on cutting about a 4" wide by 3" tall block and trimming it to fit all the way into the throat against the CD screen.

I'll then cut an arc into the face of it so that at any axis the depth of foam will be the same. The foam won't cover the horn as it flares out and faces the room. I don't see how it would do any good at these areas as HOMs can't bounce off the walls of the horn at these areas.

I may also experiment with only filling just the throat as since HOMS bounce off the walls of the horn this seems like where it "in theory" would do the most good and where the absorption happens.

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cdy2179

Discussion Starter · #11 · Nov 9, 2010

Quote:
Originally Posted by kgveteran /forum/post/19459184

I was always thought it was right to leave the resistor in place.....

If the foam doesn't screw up the response too much and does clean up the honk, I'll remove the R1 resistor and either replace it with another resistor or an ajustable L-pad.

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