[dwr]

Turkey, I totally agree with you, I would buy the Nathans in a heartbeat over the Orions, As for the upgraded parts, cujobobs explanation says it all. It is just a matter of what the cost would be for the parts as opposed to what you will gain from that cost.

[turkey]

but my guess is that some crossovers are more efficient than others, at least this is what Steve Deckert (Decware) and Israel Blume (Coincident) led me to believe.

Horses for courses. A crossover is simply something you use to get a final acoustic response. Depending upon the drivers used and the overall speaker design, you will need different crossovers to get the desired result.

You should first look at what you want to accomplish with the speaker design, and then select the parts to get the job done.

It's not very useful to decide on some crossover topology and then try to design speakers around it. (Although there are indeed some that have taken this approach.)

[turkey]

Turkey, I totally agree with you, I would buy the Nathans in a heartbeat over the Orions, As for the upgraded parts, cujobobs explanation says it all. It is just a matter of what the cost would be for the parts as opposed to what you will gain from that cost.

While I'm sure I would like the Abbeys better than my Nathans, cost was an issue since I don't have an unlimited budget.

As for the crossover parts, I don't see that I would gain anything by switching to boutique parts. I also don't like supporting snake oil, and unfortunately the magic parts industry is rife with this.

[jtwrace]

I wonder what Dr. Geddes response to upgraded crossover parts would be...I still question whether changing a few caps would really net a worthwhile result.   

[turkey]

I wonder what Dr. Geddes response to upgraded crossover parts would be...I still question whether changing a few caps would really net a worthwhile result.   

He would just say they're not cost-effective.

[poseidonsvoice]

He would just say they're not cost-effective.

Exactly. If you are going to play with crossover parts then you are on your own, as I was. And to be honest, I asked him about tolerances of parts. It didn't have to be 1% or something ridiculous like that as far as he was concerned. He stated that the room would change the response far more than small crossover intolerances. Still, I got 1% tolerances on my parts. And as I have stated earlier, I do not think that the difference in performance was comensurate with the amount of money I spent. It was the first time I have ever had this occur in my system, it just goes to show you that the Abbey is a damn good design stock. Tells you a lot about controlled directivity, waveguide design, and optimization of the directivities between the woofer and tweeter at the crossover point. Earl has got it set.

Anand.

Anand.

[jtwrace]

Exactly. If you are going to play with crossover parts then you are on your own, as I was. And to be honest, I asked him about tolerances of parts. It didn't have to be 1% or something ridiculous like that as far as he was concerned. He stated that the room would change the response far more than small crossover intolerances. Still, I got 1% tolerances on my parts. And as I have stated earlier, I do not think that the difference in performance was comensurate with the amount of money I spent. It was the first time I have ever had this occur in my system, it just goes to show you that the Abbey is a damn good design stock. Tells you a lot about controlled directivity, waveguide design, and optimization of the directivities between the woofer and tweeter at the crossover point. Earl has got it set.

Anand.

Anand.

Methodical approach with science usually doesn't lie.   

I know you are very aware of that.   

[TRADERXFAN]

HI, thanks - not sure how I missed that, but it doesn't explain the theory -

What I'm looking for is those details.

[Edit - just saw you added some info - will look at those.]

So the white paper is the "why", the theory.

This is a summary of the "how" ( and it is Geddes approved)
http://mehlau.net/audio/multisub_geddes/

Is that what you are looking for?

-Tony

[JohnR]

Hi, thanks, but there's no theory in the white paper you linked to... from the procedure it seems to be a very heuristic trial and error approach, where one plonks the next sub down somewhere and fiddles with the gain, phase, and lowpass until the response looks better. I just thought there would be a more precise approach.

[JoshK]

John, it is probably in his book.  Then again there might not be a precise method.

[jtwrace]

John, it is probably in his book.  Then again there might not be a precise method.

I wonder if you get the book free with the purchase of some Abbey 12A's.    

[TRADERXFAN]

I think the theory IS there. You are just either expecting to see something that isn't there, or not realizing it...

The key to understanding (accepting?) the whole approach is that it is a statistical problem. It isn't something you can pre-calculate. You have to use the in-room results, and do some trial and error to optimize them.  The damping factors and modes are estimated by certain calculations, but anything deviating from the assumption to those calculations will skew the results ( a window, a doorway, a void space behind drywall, a closet, concrete behind your wall, actual rolloff of subs, etc) and therefore you can't computer model an optimum setup -if that is what you seek?

In realtime there are curves and cancelations going on all over the place.

Geddes does have an algorithm where [as a service to his customers if you buy his subs] he will calculate and set a dcx unit for you.  But you have to record results of test tones taken in your room with his subs and he will tell you the setting for your subs in the behringer dcx.  This is a little less optimal as the sub locations need to be firmly set for that, so you lose that degree of freedom in your optimization.  You can't experiment with moving them to new locations to get a little better.

-Tony

[JohnR]

Is it true that I don't see how it's a statistical problem. Three subs and a few sparsely-distributed modes...

[dwr]

Why are you guys trying to make this so difficult. The multiple sub theory is nothing more than this, get your room frequency response as close to flat as possible under 200Hz....thats it, there is no voodoo involved here, using mulitiple subs makes achieving this much much easier,but you do have to take room frequency response readings using software like REW or HOLMPULSE that Earl uses. I agree learning how to use the REW software can be a PIA, once you get your readings you then either move the subs around taking measurements before and after the moves. You also set the phase and delay times and do the same measurements. This multiple sub theory is nothing new Toole believes in the same thing. And I will say that since I went to the multiple sub approach, I have the best bass response I have EVER had in my system and room. The big thing that Geddes stresses in his theory is that EVERY room is different thats what makes the measurements a requirement.

[dwr]

Oh yes and the nicest thing about the multiple sub approach is that it works for ALL types of speakers not just Geddes speakers.

[jtwrace]

Oh yes and the nicest thing about the multiple sub approach is that it works for ALL types of speakers not just Geddes speakers.

This is what I think is so great!  I come to A.C. to learn and feel that I've learned something no matter what I decide to do.   

[turkey]

Yes, Toole has mentioned similar things, and there is also Welti's paper.

However, Earl hasn't published anything so comprehensive as Welti's paper on his variant of the multi-sub approach.

It would be interesting to see it given the "full treatment," and I assume this is the kind of thing JohnR is asking about.

I've got the impression that Earl's approach is more of a practical thing. He has observed things over the years, knows what _doesn't_ work, and came up with something that does work and can be done inexpensively.

He's given us the basics of it for free, and it does work. I was able to find enough info on it to implement it in my listening room without much effort.

[TRADERXFAN]

Is it true that I don't see how it's a statistical problem. Three subs and a few sparsely-distributed modes...

Well what I am trying to get across is that it is statistical in that you are averaging sound levels in db -as opposed to linear in that 1+1 =2. This may not be your conception, but sometimes people are misunderstanding to think that adding subs is just adding db output (which they are not).

At each frequency, each source (sub) relative to another source will experience constructive and destructive interference from other sources and boundary reflections. You are attempting to flatten average spl at all bass frequencies of all of this interaction by adjusting phase and sub position relative to the listening area [not limited to a "sweet spot"].   Does this part make sense?

Perhaps you could further explain what you see as the issue with the approach?   

[dwr]

I think thats about as clear as you can make it Traderx, also guys there used to be a white paper written by Dr Geddes available on his website pertaining to the multi sub approach, that white paper is no longer available from his site. I am not sure as to the particulars of why that is but I am sure there is some type of proprietary reasoning behind it. Ticks me off too I had read it when it was still available but never downloaded or printed it (nice job on my part huh).

[TRADERXFAN]

Also may help to think of modes as simply the result of the boundaries rather than some separate entity. Each boundary acts as a "phantom source" in that it is a reflection of the sources. [-But, for some, adding that wrinkle may actually make it more difficult to conceptualize.]