[jtwrace]

Is there anywhere online where Dr. Geddes recommends running the mains full range?

Post #21 here http://www.avsforum.com/avs-vb/showthread.php?t=1099840

"The mains are played full range and overlap the subs over a fairly large range. This is quite unique to my approach. Different subs are better than three or four identical ones, because the subs resonance is basically the same thing as a room mode. We go to great lengths to not have several coincident room modes and its a good idea not to have several subs of identical tunings. But the sub modes do tend to be well damped and this means that modal coincidence for them is not as critical as it is for room modes."

__________________
Earl R. Geddes
GedLee

[Watson]

Post #21 here http://www.avsforum.com/avs-vb/showthread.php?t=1099840

"The mains are played full range and overlap the subs over a fairly large range. This is quite unique to my approach. Different subs are better than three or four identical ones, because the subs resonance is basically the same thing as a room mode. We go to great lengths to not have several coincident room modes and its a good idea not to have several subs of identical tunings. But the sub modes do tend to be well damped and this means that modal coincidence for them is not as critical as it is for room modes."

Thanks for that. I notice in the same post that Dr. Geddes says his speakers have no baffle step compensation, so it does make sense that one would have to run the mains full range. That also probably explains why some earlier posters said they feel his speakers sound thin without multiple subs.

[DougSmith]

I've taken the liberty of cutting out your frequency response and comparing to my most recent measurement on roughly the same scale. I'm told that my system is bass-heavy! On the other hand I could see/hear that I might prefer more a bit more of a down-slope a little earlier. Perhaps some overall eq experiments will yield some insight into the differences here.

Looks great.  Who told you that?  I bet it was someone with a bass-light system!

[poseidonsvoice]

Thanks for that. I notice in the same post that Dr. Geddes says his speakers have no baffle step compensation, so it does make sense that one would have to run the mains full range. That also probably explains why some earlier posters said they feel his speakers sound thin without multiple subs.

Sorry for this digression. Since his overall philosophy IS to use multiple subs with his loudspeakers it does make sense. All his speakers roll off in the low end, my Abbeys are about -3dB at 65 Hz. That's not too low for a 12 inch driver loaded in a sealed enclosure. You should always use subs with his speakers, period. It's assumed. If you don't, you'll feel like something is missing, and that's a foundation to the music.

Anand.

[jtwrace]

you'll feel like something is missing
Anand.

You'll feel that because you ARE missing something.   

[Phil A]

I actually use 4 subs in my set-up (all Rels).  Most often I am just using two for stereo listening and they are crossed over very low (22Hz for music) with my Thiel 3.7s.  Using my one third octave RTA the bass is flat from 25-80Hz.  The room is treated.  I have a sub on the center and a sub on the surrounds.  I don't hate multi-channel music but prefer stereo most of the time.  The crossovers are adjust to fill in the low bass where the speaker drops off.  In the secondary bedroom system, my Marantz receiver has a mode where you can use the sub for movies but not for music and that's what I use as it sounds better that way to me.  For a bit in the bedroom, I did have one of my Rels in there and I did prefer a sub that way using the high (speaker) level input with its flexible crossover.

[Quiet Earth]

The California Audio Show is coming up soon . . . . July 15th through 17th in Burlingame (south San Francisco). It could be a wonderful opportunity to hear a multi subwoofer system properly demonstrated by one of our Audio Circle Manufacturers.

Who's in?

[JohnR]

"Different subs are better than three or four identical ones, because the subs resonance is basically the same thing as a room mode."

That's ... a bit hard to swallow. If a sub performs well then you don't see any "resonance" in the (anechoic) frequency response. If it's peaky anechoic then wouldn't it just be better to buy (or build) better subs - ?  What did I miss

[JohnR]

The California Audio Show is coming up soon . . . . July 15th through 17th in Burlingame (south San Francisco). It could be a wonderful opportunity to hear a multi subwoofer system properly demonstrated by one of our Audio Circle Manufacturers.

Who's in?

Duke would probably be the only one and I think he's a long way away.

[DougSmith]

That's ... a bit hard to swallow. If a sub performs well then you don't see any "resonance" in the (anechoic) frequency response. If it's peaky anechoic then wouldn't it just be better to buy (or build) better subs - ?  What did I miss

You missed nothing, as long as the sub(s) cover the range from 20 to 130 Hz or so.  Earl recommends having two that are tuned higher and one that is tuned lower.  He also prefers bandpass subs. With available drivers and conventional designs it not possible to make one that covers that whole range, but a combination of two different bandpass can do it very  well. There are plenty of other options that would work well, however, without using different types of subs.

[JoshK]

You still need absorbers or you won't affect decay time.  Just because you have more even response throughout the room doesn't mean you affect physics.  There's still going to be boominess caused by ringing.  Show a decay plot with and without absorbers, and you'll see what I mean. 

You definitely hit upon my sole reservation with multi-subs.  It smooths the in room response but doesn't prevent or treat modal ringing or excessive decay.  Right now, this is just a question.  I have no opinion and I probably wouldn't trust the opinion of someone else who hasn't actually tested it. 

[JohnR]

You missed nothing, as long as the sub(s) cover the range from 20 to 130 Hz or so.  Earl recommends having two that are tuned higher and one that is tuned lower.  He also prefers bandpass subs. With available drivers and conventional designs it not possible to make one that covers that whole range, but a combination of two different bandpass can do it very  well. There are plenty of other options that would work well, however, without using different types of subs.

Oh I see, thanks Doug - I did miss that bandpass subs are implied.

[jtwrace]

Oh I see, thanks Doug - I did miss that bandpass subs are implied.

...and I can say that using two bandpass subs wtih my two Aluminum Rythmiks is awesome!

[gedlee]

You definitely hit upon my sole reservation with multi-subs.  It smooths the in room response but doesn't prevent or treat modal ringing or excessive decay.  Right now, this is just a question.  I have no opinion and I probably wouldn't trust the opinion of someone else who hasn't actually tested it.

It is of course better to damp the room at LFs, but thats far more difficult than "using room treatment".  (You basically have to damp the structure, you cannot just add-on absorption, thats not very effective.) Room treatments seldom do much if anything below 100 Hz, which is where the biggest problems are, and they do far too much at HFs.  So it goes withot saying that a better damped room at LFs is going to work better.  But multiple subs don't aggravate this situation and in fact do a lot to help it by smoothing the response.  So I do not think that your "reservations" really say anything about using multiple subs or not.

I used to make full range mains, with ports and the like, before I dialed in on the use of multiple subs.  But after using multiple subs you will never go back to mains only.  Think about the "typical" situation, and I'll use mine as an example because it is quite typical.  The mains are placed for the best HF positioning for good imaging etc.  In any symmetrical room this is almost always going to be symmetrical to the room and the seating area.  Two in phase sources symmetrically placed in a symmetrical room are equivalent to a single source in a room 1/2 as large (a perfectly reflective wall in between).  This is not a good situation, you are just asking for trouble, damped room or not.  It would be ill advised to move the mains to improve the bass only to degrade the image.  So, to me, full range mains was simply not a good choice.

Once you conclude that multiple widely spaced subs is actually a requirement, for any setup, full range mains or not, then it makes no sense to push a design for extended LF response, its simply not a good tradeoff.  Hence, I deleted all the ports on my designs from that point on.  For the bigger systems running them full range with no HP is not a problem since my woofers are always large - for their HF directivity NOT to get better bass.  They are closed box and well damped and there simply is nothing to be gained from HP filtering them.  For the Harpers (8" woofer) HP filtering should always be used and perhaps the Nathans (10" woofer) might benefit by this if they are played very loud.

My approach to LF design in rooms has evolved considerably over the years, and this is from tried and true theory, implimented numerous times in practice and proven out through countless reviews of dozens of people.

I do need to do a write paper on this someday.   

[Quiet Earth]

I don't want to read another paper, I want to hear a demo.

Cal Audio Show in July, RMAF in October. Bring your gear, I'll bring my ears.

[jtwrace]

I don't want to read another paper, I want to hear a demo.

Cal Audio Show in July, RMAF in October. Bring your gear, I'll bring my ears.

   I highly doubt he will be there.  Your best bet is to go to someones house and listen.  You might have someone close by with a nice setup...

[Quiet Earth]

If the multi sub method really is da bomb, then someone with a vested interest should be willing to do a demo.

[jtwrace]

If the multi sub method really is da bomb, then someone with a vested interest should be willing to do a demo.

If you want to go to MI Dr. Geddes will demo his system for you.  Otherwise, you can find someone else that may be closer.  Duke sometimes shows his multi sub approach (which was learned from Dr. Geddes) so that is an option too.

[werd]

Hello folks

What is the purpose of these multi sub apps? Is it just for room ambient LF info, or are we getting more instrument resolution and clarity ?

[sts9fan]

it evens the response out around the room