Multiple Small Subs - Geddes Approach - Page 146 - diyAudio
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Old 7th May 2011, 01:55 PM   #1451
djn is offline djn  United States
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Quote:
Originally Posted by tb46 View Post
Hi djn,

From the link in Post #5:

"Subwoofer setup after Earl Geddes (GedLee LLC)

The multisub setup described on this page has two big advantages over other methods: only three subs are needed and you don't need to put the subwoofers at specified locations. Nonetheless there are some basic rules that have proven to yield best results:

Put one sub in a corner close to the mains. The second sub is a lot more flexible as to its location, but it should not be in a corner. Side wall or back wall, near the midpoint is a good idea. Put the third sub wherever you can that is not too close to the other two. It's a good idea to get one of them off of the floor."


If you read through the thread you'll find additional information on placement, and number of subs. After the initial corner-loaded sub you have a great deal of placement flexibility, end tables may be just fine. It comes down to the calibration procedure.

Could be your wife knows the best spot for the subs after all.

Regards,
She has been right before. In the new room I do have two corners on the wall where the mains will go, so I can put one or both into the corners.

Quote:
Originally Posted by dolphinamica View Post
Just a word of caution on those PE/Dayton plate amps. I bought a Daton 250 wt plate amp and it hums and buzzes like a huge pissed off bumble bee. I know, this is a lame post because I donít have the model number, but I bought it to play in my system up in my cabin. I got it at home, took it to the mountains a few weeks later where it is now, installed it in the speaker box, hooked it up and it hummed so bad that I couldnít use it for music. Dayton knew about the problem because they enclosed an instruction sheet warning about it. I did everything the sheet suggested, switched from speaker wire in to RCA plugs, reversed phase, AC to a different outlet, ground wire to the amp, ground the amp and all the sources, even grounded to the outside copper ground stake, nothing. So much time went by that I couldnít return it. Itís OK for loud movies, but for music, anything short of loud rock is out.

The auto on/off sensor does not work consistently, but no problem there, with all that noise, I sure donít forget to turn it off before I go to bed.

I would suggest you talk to a tech guy at PE about returns/problems/complaints before you purchase a Dayton plate amp.

Donít get me wrong, I think PE is great and Iíve bought a lot of good stuff from them over the years, but this plate amp is not one of them.
Good luck, Dolf.
The BASH 300 amps are dead quiet and never heat up. The other amps are bottom of the barrel but have not given me problems yet. I got them from a friend so I have no recouse but to toss them if they give out.

Quote:
Originally Posted by bentoronto View Post
I see that tb46 has replied with what might be called a "doctrinaire" formula from the Gospel of Geddes. After reading Toole's exhausting discussion of multiple subs (another place where he and Geddes differ??), my impression is that many kinds of mix-and-match solutions work well and it really depends on which room or speaker deficiencies you are addressing.

Radiation resistance, if I recall Olson, becomes a factor when driver diameter is small compared to sound wave-length. So I think it comes home to roost below 250 Hz. I hope better informed people will correct me since I can be all wrong on that. But the idiocy of shaking large masses of cardboard in thin air to generate sound is true at all frequencies: you want the resistance of the air to be as relatively important as possible, not the mass of the driver.

It is widely agreed that balance of treble and bass (400,000 Rule) is important. Changes to either end need to be compensated by changes to the other. Rather easy today to create a little super-sub-woofer somewhere in the room to supplement very low bass, even if you are leaving behind a super woofer when you move. I have downsizing moving ahead of me too - at least it is some long time before I get to the headphone listening stage when in a nursing home.
Behind one wall of the new space is a laundry room and behind another wall is a 4" tall storage space as big as half the house. We were over there last night will a friend and he thinks IBs on each wall would work well too. That would be 6 subs in a 20 x 20 room. A little over kill if you ask me.
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Old 18th May 2011, 10:07 PM   #1452
graaf is offline graaf  Poland
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hi to everyone!

perhaps it's a silly question but how can I connect multiple small subs to one preamp line out socket? I am talking about 8-10 subs - how can it be done? Can I just use multiple Y-splitters without risking damage of my preamp?

regards!
graaf
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Old 18th May 2011, 10:25 PM   #1453
badman is offline badman  United States
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Quote:
Originally Posted by graaf View Post
hi to everyone!

perhaps it's a silly question but how can I connect multiple small subs to one preamp line out socket? I am talking about 8-10 subs - how can it be done? Can I just use multiple Y-splitters without risking damage of my preamp?

regards!
graaf

You could use a series resistor in line with the pre-out, then parallel all sub inputs, if you want.
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Old 18th May 2011, 11:32 PM   #1454
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by graaf View Post
perhaps it's a silly question but how can I connect multiple small subs to one preamp line out socket? I am talking about 8-10 subs - how can it be done? Can I just use multiple Y-splitters without risking damage of my preamp?
If your preamp has a cap or (less common) transformer coupled output, you can't damage it even with the output shorted. But you have to remember that your input impedance for the subs will be the impedance of all 10 in parallel. Say the subs each have an input impedance of 20k, the combined impedance will be 2k. Likewise the input capacitance will be the sum of all 10. Unless your preamp has an unusually low output impedance, you will see increased distortion. If your preamp doesn't have a separate buffered output, you will need a buffer. An op amp designed for this application is a simple way to go.

Sheldon
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Old 19th May 2011, 01:38 AM   #1455
Okv is offline Okv  Norway
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Default How does it perform - a simple test

Well, how does the Multiple Sub approach perform?

I measured to verify what can relatively easily be achieved by using 4 small subs located using a simple and fast method.

The blue line is a set-up with 2 smaller subwoofers located in the front, close to the mains.

The black line is where I added two Even Smaller subs, located to try fill in the 60Hz null.

Click the image to open in full size.


As you can see, there is a significant improvement, even though the response is yet far from flat.

The brown line is with 2 Even Smaller subs only.

Click the image to open in full size.


I listened to this set-up only briefly now, but the improved preformance in the mid bass especially is very noticeable, as bass drums now has much improved attack, and the bass sounds more balanced.
Listening impressions will however always be very subjective, so you should not rely to much on what I think I am hearing - trust the measurements instead.


Location Method for Additional Even Smaller Subs:

I placed one sub in the LP, 60Hz sine on, real-time spectrum anayser, and then took a trip around the room with the mic in my hand, searching for spots where the 60Hz was strong.
You could do just as good using your ears, as there is a clearly audible difference between the bad and the good locations.
This way I found that the front left corner and the rear left corner were good locations with spare room to accomodate an even smaller sub.


Further improvements:

Obviously one could try to improve the room by adding bass absorbers and resonators, you can also see from the measurements that then additional subs did little to remove the peaks and the dips - they only lifted the weak area between 50-100Hz.

Also I think there may be potential in having dedicated DSPs on each sub.
Here I would first remove everything below 40Hz from the Even Smaller.., that could make the response flatter, and it would gain headroom as those too small subs would be relieved.

Hmm.. may be I should try this some day, the DSP is readily available..
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File Type: png 4x sub test freq resp 2.png (91.8 KB, 995 views)
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Old 10th June 2011, 05:53 PM   #1456
Pallas is offline Pallas  Pakistan
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Some more data in favor of Geddes' approach. (5-point spatially-averaged measurements)

Three subs' individual raw responses, with mains (120Hz crossover), but no EQ:
S1 (front-left corner)
Click the image to open in full size.
(The notch at the top of the graph is from the mains' floor bounce, which from other measurements is centered at about 230Hz. You'll see it in the rest of the graphs, too.)

S2 (~25% down the right wall)
Click the image to open in full size.

S3 (~70% down the left wall, practically nearfield)
Click the image to open in full size.

Of the three, the nearfield-ish S3 by itself has the smoothest response, followed by corner-loaded S1 and then S2. But it's still pretty bad, thanks to the ~80Hz null. And you lose A LOT of low end, as you can see by comparing S2 and S3. (They are identical subwoofers, just placed differently.) S2, which is closer to a room corner, has a significantly lower corner.

So... any one of those alone...no thanks! Even with massive EQ. But add them together using Geddes' method, and:

Summed response S1+S2+S3, after just optimizing levels and delays on the miniDSP, prior to application of any EQ
Click the image to open in full size.

I think most people could live with that, honestly. It sounded really good as it stood. BUT:

Summed response S1+S2+S3, after Audyssey calibration (MultEQ XT on, DynamicEQ off) and three bands of fairly mild EQ cuts
Click the image to open in full size.

Icing on the cake!

Last edited by Pallas; 10th June 2011 at 06:13 PM.
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Old 11th September 2011, 03:37 AM   #1457
xyrium is offline xyrium  United States
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Sorry, I'm late for this party, but how far from the three drivers was the combined measurement taken?
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Old 11th September 2011, 05:01 AM   #1458
Pallas is offline Pallas  Pakistan
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Listening position. Obviously, varying distances from each driver.
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Old 11th September 2011, 01:35 PM   #1459
xyrium is offline xyrium  United States
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Thanks. Any distance at the listening pos. less than 1M?
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Old 11th September 2011, 02:57 PM   #1460
Pallas is offline Pallas  Pakistan
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Quote:
Originally Posted by xyrium View Post
Thanks. Any distance at the listening pos. less than 1M?
No. The closest is S3, which is 2.5m away, give or take a bit. S1 and S2 are significantly farther way.
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