GedLee Abbey's Feedback Wanted!

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TRADERXFAN

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Re: GedLee Abbey's Feedback Wanted!
« Reply #320 on: 11 Oct 2010, 06:12 pm »
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).

The pdf white paper I linked had been rewritten from one posted earlier. Maybe that is the one you are thinking?
Also there is chapter 4 of the home theater book available for download from his site. That has more info about damping, but not anything to add to the multiple subs concept than what you would see in the other 2 places. I have the book and there isn't any more about it, as far as implementation process, in the book than this.

-Tony

poseidonsvoice

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Re: GedLee Abbey's Feedback Wanted!
« Reply #321 on: 11 Oct 2010, 06:13 pm »
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.

Earl hasn't published something like what Welti has done. I think its just a matter of time to be honest. He has been busy with the new speaker business, etc...so it's low in the priority scale. He will need to answer other questions like, why 3 subs instead of 30, etc...using 3 subs instead of 4 is a savings, and his placement is asymmetrical which can be advantageous in many rooms compared to the symmetrical approach of Todd Welti/Floyd O'Toole. Not all rooms are perfectly square. I respect them both and I am happy they divulge their techniques for us all to enjoy, literally for free. To be honest, Markus Mehlau's description is all one needs to implement the technique. But the theory is yet to be published in a peer reviewed journal to my knowledge. White Papers are getting bad raps, because historically, they seem to be just another avenue for spreading marketing propoganda, although Earl's White Papers are anything but.

Thanks TraderX for the links, it was a nice refresher course for me.

Anand.

JohnR

Re: GedLee Abbey's Feedback Wanted!
« Reply #322 on: 11 Oct 2010, 06:14 pm »
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.

That's about it - thanks ;)

J

TRADERXFAN

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brj

Re: GedLee Abbey's Feedback Wanted!
« Reply #324 on: 11 Oct 2010, 06:44 pm »
Here is a link to the Harmon International white papers, including relevant multiple subwoofer papers from Welti and Toole that several have referenced:

http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/WhitePapers.aspx?CategoryID=White%20papers

DWR, I don't think anyone is trying to complicate things.  Many people reading this thread, and AC in general, simply like to know how things work, and many of them have very technical backgrounds.  Wanting to understand the math and physics does not in anyway minimize the enjoyment of the end result.

As for modeling the room directly, rather than measuring its acoustic response, the technology exists today to do this surprisingly well.  It isn't simple or common, however, and requires, as TRADERXFAN indicates, very accurate physical measurements of all room dimensions and features.  Acoustic engineers like Jeff Hedback have such modeling tools and have consulted on room design for AC members to roaring success.  (Rives might as well, but it has been a while since I looked at their approach.)

An example, in which only physical measurements of this room, not acoustic, were sent to Jeff prior to the design implementation:


Relevant quote:

http://www.audiocircle.com/index.php?topic=72137.msg726236#msg726236

TRADERXFAN

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Re: GedLee Abbey's Feedback Wanted!
« Reply #325 on: 11 Oct 2010, 06:49 pm »
Well for Art's room, I really wanted to see the "after"... he hasn't showed the freq response so I don't really know if it "just sounds really good", or has acheived a flat freq response. [I mean no criticism here. No intent to disparage him in any way. Just wish we could see measurements.]

brj

Re: GedLee Abbey's Feedback Wanted!
« Reply #326 on: 11 Oct 2010, 08:16 pm »
As of a few weeks ago, at least, Jeff hasn't seen the room in person to measure it and neither has Art.  I do know, however, that Art hosted one audiophile interested in his system that brought a handheld measurement unit and reported that it was the flattest room he'd ever measured.

(I was lucky enough to spend 3 hours listening to Art's system from the sweet seat several weeks ago during a visit to Fort Worth, and I had heard various "pre-Jeff" incarnations many times before.  "Wow" does not even begin to describe it.  I've been a firm believer in room treatments as the single biggest impact on a system for a while now, and my interest in waveguides and controlled directivity speaker designs haven't changed that.  They definitely help minimize certain room interactions, but do not eliminate them.)

On a related note, the design of Art's room specifically accommodated the radiation pattern of his line arrays.  Pseudo point-source or controlled directivity speakers would benefit from some minor tweaks, primarily to the ceiling, I believe.  They've also talked about subwoofer placements, as Art plans to experiment with some Rythmik subs.  The last I heard, he is testing only two subs at the moment rather than the 3 or more Earl recommends, but I know the discussed placements were asymmetrical to even out room modes along the lines that Earl and others have discussed.

JohnR

Re: GedLee Abbey's Feedback Wanted!
« Reply #327 on: 12 Oct 2010, 01:55 am »
... but I know the discussed placements were asymmetrical to even out room modes along the lines that Earl and others have discussed.

The thing is, modes are modes, and they're either excited or not excited. The only way (that I can tell) to reduce excitation of a mode that's already being excited (e.g. by a corner sub) is to excite it at a different phase angle - a different point along the mode, phase shift, delay. It would be interesting to see the settings (and positionings) that people have used on their subs that achieve the flattest response - would anyone be willing to post theirs?

WGH

Re: GedLee Abbey's Feedback Wanted!
« Reply #328 on: 12 Oct 2010, 02:33 am »
There is another paper by Todd Welti and Allan Devantier that is not included in the Harman link above.
I keep adding new white papers as they show up.

Low-Frequency Optimization Using Multiple Subwoofers
http://www.audiocircle.com/index.php?topic=58304.msg516580#msg516580

"At low frequencies the listening environment has a significant impact on the sound quality of an audio system. Standing waves within the room cause large frequency-response variations at the listening locations. Furthermore, the frequency response changes significantly from one listening location to another; therefore the system cannot be equalized effectively. However, through the use of multiple subwoofers the seat-to-seat variation in the frequency response can be reduced significantly, allowing subsequent equalization to be more effective."

Wayne

JohnR

Re: GedLee Abbey's Feedback Wanted!
« Reply #329 on: 12 Oct 2010, 05:20 am »
There is another paper by Todd Welti and Allan Devantier that is not included in the Harman link above.
I keep adding new white papers as they show up.

Low-Frequency Optimization Using Multiple Subwoofers
http://www.audiocircle.com/index.php?topic=58304.msg516580#msg516580

Great paper - I'd printed it out last night but only read it today. It actually answers a lot of the questions I had. One thing I wonder about is why subs out from the walls were not considered, as in slide 40 of the earlier "Subwoofers: Optimum Number and Locations" presentation. I don't know whether that's to keep the problem size under control, or whether they feel it's not relevant. Somebody above mentioned use of dipole subs, so out in room would be particularly relevant in that case.

It's occurred to me that a miniDSP would (might?) be a great tool for multiple sub configuration, whether using the Geddes method or trying to emulate manually what the SFM algorithm does in the Welti and Devantier paper. One in, four out, with gain, delay, and eq on each. Here's an article I wrote on eq'ing a single sub - a dedicated unit for subs looks really interesting:

http://www.hifizine.com/2010/09/subwoofer-equalization-and-integration-with-the-minidsp-2x4/

Anyway - thanks, I've learned a lot the last day or so  :thumb:

poseidonsvoice

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Re: GedLee Abbey's Feedback Wanted!
« Reply #330 on: 12 Oct 2010, 11:16 am »
Great paper - I'd printed it out last night but only read it today. It actually answers a lot of the questions I had. One thing I wonder about is why subs out from the walls were not considered, as in slide 40 of the earlier "Subwoofers: Optimum Number and Locations" presentation. I don't know whether that's to keep the problem size under control, or whether they feel it's not relevant. Somebody above mentioned use of dipole subs, so out in room would be particularly relevant in that case.

It's occurred to me that a miniDSP would (might?) be a great tool for multiple sub configuration, whether using the Geddes method or trying to emulate manually what the SFM algorithm does in the Welti and Devantier paper. One in, four out, with gain, delay, and eq on each. Here's an article I wrote on eq'ing a single sub - a dedicated unit for subs looks really interesting:

http://www.hifizine.com/2010/09/subwoofer-equalization-and-integration-with-the-minidsp-2x4/

Anyway - thanks, I've learned a lot the last day or so  :thumb:

That's why I gave you the positive feedback that I did. I think its an excellent article you wrote and a must read to be honest.

Anand.

jtwrace

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Re: GedLee Abbey's Feedback Wanted!
« Reply #331 on: 12 Oct 2010, 12:20 pm »
That's why I gave you the positive feedback that I did. I think its an excellent article you wrote and a must read to be honest.

Anand.

+1 

JohnR

Re: GedLee Abbey's Feedback Wanted!
« Reply #332 on: 12 Oct 2010, 04:44 pm »
Thanks :)

jtwrace

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Re: GedLee Abbey's Feedback Wanted!
« Reply #333 on: 12 Oct 2010, 04:52 pm »
It's occurred to me that a miniDSP would (might?) be a great tool for multiple sub configuration, whether using the Geddes method

It could be as long as Dr. Geddes method is followed.  The main speakers are run full range (preamp > amp > GedLee Speakers) and the subs are the only items that are eq'd.

If this is done, then the mini DSP can be used to follow the Geddes method.  In order to do this you just need to split the signal from the pre output to the amps that are driving the mains and the other to the DSP.   :thumb:

cloudbaseracer

Re: GedLee Abbey's Feedback Wanted!
« Reply #334 on: 12 Oct 2010, 05:07 pm »
Do these splitters reduce the sound quality at all?  I would think that someone with expensive cables and power cords (this is not me) would not be interested using an inexpensive splitter on the signal.  This questions is posed whether talking about the impact on the high frequency OR the low.  I know some say the low frequency is not as critical.

Thanks,

James

JohnR

Re: GedLee Abbey's Feedback Wanted!
« Reply #335 on: 12 Oct 2010, 05:09 pm »
It could be as long as Dr. Geddes method is followed.  The main speakers are run full range (preamp > amp > GedLee Speakers) and the subs are the only items that are eq'd.

Won't the measurements tell you whether you need to highpass and/or eq the mains?

DougSmith

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Re: GedLee Abbey's Feedback Wanted!
« Reply #336 on: 12 Oct 2010, 05:16 pm »
Earl recommends no EQ on the mains.  Personally, I use a little bit - mainly in they modal region below 200Hz.

jtwrace

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Re: GedLee Abbey's Feedback Wanted!
« Reply #337 on: 12 Oct 2010, 05:43 pm »
Won't the measurements tell you whether you need to highpass and/or eq the mains?

Not being a GedLee customer / user I can't comment with certainty.  I'm sure one of the users will though.

BUT, in reading all of Dr. Geddes papers and emailing him the subs need to be blended in with the mains NOT the other way.  Right customers?  Aren't I correct in that? 

jtwrace

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Re: GedLee Abbey's Feedback Wanted!
« Reply #338 on: 12 Oct 2010, 05:47 pm »
Do these splitters reduce the sound quality at all?  I would think that someone with expensive cables and power cords (this is not me) would not be interested using an inexpensive splitter on the signal.  This questions is posed whether talking about the impact on the high frequency OR the low.  I know some say the low frequency is not as critical.

Thanks,

James

Please don't turn this thread into a cable debate.  I will say this...

If you believe in science and this speaker approach chances are you are not buying into the 6" (max) cable extension degrading sound quality. 

Many cable manufacturers will make you a "high end" Y if you so incline out of your favorite cable.  I know my cable guy does. 

Also, many preamps and buffers have dual outputs so it's a non issue.   :thumb:

poseidonsvoice

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Re: GedLee Abbey's Feedback Wanted!
« Reply #339 on: 12 Oct 2010, 05:53 pm »

Also, many preamps and buffers have dual outputs so it's a non issue.   :thumb:

Bingo.  :thumb:

Anand.