Help With Dual Subs and Proper Phasing

[Mike Cason]

I'm looking for advice from some of you more experienced HT guys and audio pros......

I'll have my second Soundsplinter dual sub finished in about a week and have a technical question of being in or out of phase.

My two subs will be in each corner of the front of my living room HT and I am running the top of the line Rotel receiver/amp with dual subwoofer pre-outputs. I'll be using each pre-out to each sub's QSC 1450 amplifier. Rotel has no information about phase control in the owner's manual or online, and there are no adjustments in the receiver's set up menu for subwoofer phase control.

I've heard that sometimes if the phase is not set correctly, one subwoofer may actually cancel out the other or reduce the bass you would expect by having two subs in the system.

Do these high end receiver/amps take in consideration that with two sub outputs, there should be a built in phase difference, or is it even necessary? Some conventional (brick & mortar & DIY) subs have a phase control built into the plate amp on the sub, but the custom DIY subs using rack mounted amps don't have this capability to adjust for phase differences.

If there needs to be some phase control in place, what piece of electronic equipment would fit the bill for such an application. I'll have a total of 4 active RLP-15's and 8-15" passive radiators, two amps, and would like to full advantage of the twelve drivers in my subwoofers.

Many thanks in advance for any replies or comments.

Mike

[saramac]

If by, both in front you mean (left and right of the main speakers) Phase should not be an issue. I run 4 subs, and the rear two I mess with the phase to get the most output at the seating positions. With just the front two. I never found any benifit in it. Now if your room is an odd shape, or your listening positions abbynormal you might benifit from experimentation. Every room/speaker interaction is different. Just have fun with them.

[imbeaujp]

Yes you could have phasing problems when you try to match the sub with the mains like I did RoomEQWizard is a nice tool to check that. I got the RSP-1098. There is 2 sub out but in fact, this is the same output. Nothing more than a splitter. Rotel does not provides phase control but you can do the same with the sub delay. Try to change de distance (delay) in the DELAY menu I think this will help.

JP

[Mike Cason]

saramac,

I think I have the ideal "shoebox" living room dimensions, retangular. 18' x 24' with 9' ceilings. My intentions were to move the TV & equipment rack further to the left and place the subs on the outside of the mains, corner loaded & about 1.5 feet from the wall, using the walls to help with the sound.

I did manage to find some other posts a few minutes ago and a couple of long time posters were talking about co-locating the two subs, ie, stacking them on top of each other. (yuk)

I've managed to keep the WAF at 99.5% and by stacking the subs, it would look horrible. I got that dirty look a minute ago when I went in to measure for stacking. I have spent a lot of time to make the system look elegant in the LR, so I really would like the corner placement.

I'll go ahead and put them there and see what happens.

imbeaujp, Thanks for the Rotel tip.....I do have a delay option so I can play with that too.

I appreciate both of your inputs!

Mike

[Mike Cason]

Well, I've finished up an indentical sub to my original dual RLP 15 with 4 passive radiators. I got it in the home last night and hooked it up. The system sounds better with only one sub turned on. I didn't move all of my equipment to the left and corner load the new sub yet, but had it close to the right side of the living room equipment set up.

I'm running QSC 1450 amp briged to each subwoofer with an 8 ohm load so they are getting about 800 watts for each sub. My Rotel doesn't have a delay for my subs. I have an Arts Clean Box coming in next week, but that's only going to help my impedance matching and provide some gain for the amps, but is not going to solve my "Phasing" problem.

Does any one know a source to check to help with the phasing.

I'm leaning toward the "stacking of the two subs" to co-locate them, but that's going to give me a 7' tall subwoofer with a line array of forward firing woofers and side mounted passives. Would this be an even realistic solution to my problem?

Any constructive information would be appreciated. I would be interested in some type of "phasing box", if someone makes such an animal.

[Mike Cason]

This is what makes the DIY so much fun! My finished system is what I've been looking for!

I spent about 4 hours researching multiple sub locations and proper phasing and testing. There was one extreme to the other on suggestions, but the most mentioned with good reason, was the co-locating of the two subwoofers. Reports indicate that there is a 6 db gain with this placement, and I'm a beleiver. Joe Satriani has four bass guitar quads stacked on both sides of his sound stage for a reason. I just figured out why. I stacked them on top of each other and there is a tremendous gain resulting in this configuration with all of the drivers working together instead of cancellations from each other if they were to be located on different sides of the living room. The living room is 18' x 24' with 9 ft. ceilings and opens up to the kitchen and dining area. I've also got a nice clean corner location for added room gain.

I now have 12-15" active and passive drivers working together in the same corner and I'm at the point to say I think I could have too much clean bass now. I have reduced the gains on my amps, reduced the db gains in the Rotel set up program, and the output is extremely more pronounced. I've bumped the crossover point up to 60 hz and the mains are producing cleaner sounds than I've ever heard. They are not having to carry the 40 to 60 hz range which is quite a load. The QSC amps are blowing out cold air meaning they aren't working as hard. I've cut them back by 30%. This will also save my drivers as they don't need as much power as before.

It's all a win win situation, but I'm going to have to live with a tall subwoofer. I'm leaving the grills off the lower one until the upholstery shop finishes covering my frames for the top one so it won't look funky in the mean time.

I now think I have the ultimate sub setup. The WAF has not been affected. When I told her I was going stack it, she said to get some help. When she got home, I reminded her of the don't ask and don't tell policy. Each subwoofer weighs 235 lbs. It was a chore indeed to do by myself. I had to take the picture down behind the sub, but she will find a place to move it.

The output is absolutely stunning, clean, undistorted, loud (if needed) and very low. Thanks for the support from the forum members, especially to Mike P. who figured the tuning frequency which came out to 23.5 hz with WinIsd. I tested it and got a good reading of 23hz using Vance Dickison's instructions. It gets much lower than 23 hz. though!! I used a Granite Audio bass test CD. I am sold on the passive radiator design because of its clean undistorted and lack of a resonant sound that can sometimes be heard in a ported system. You pay dearly for the design though.

Mike Cason

[Mike P.]

Glad you found a placement solution for your subs, and that you're happy with the output. It's nice when the solutions end up being simple. Now for your build thread!

[Mike Cason]

Mike,

Do you want me to revamp my Photobucket site and use it as the reference URL, or resize all my photos and post them here in it's own thread?

Thanks,
Mike

[Mike P.]

Copy the image tags from Photobucket and paste them in the build thread.

[eyekode]

Just to throw in my 2 ct... I have 2 subs that serve as speaker stands for my mains. They are Paradigm passive subs (whimpy... look'n to upgrade ). I had nasty deep nulls in my response.

So I measured them individually. Each one looked more or less reasonable. Turns out one was out of phase. Simply swapping the speaker leads drastically improved the summed F/R.

The moral of the story is to measure each speaker individually. If the curves are good, but the combined is bad then indeed you do have a phase problem. Otherwise you probably have a room problem (er... if you have an untreated room you _also_ have a room problem). Note that phase can be the result of either electrical differences or path length differences. This is why moving the speakers around has an affect on the interference frequencies. Because you are changing the path lengths between you and the speaker. Note that moving speakers closer together generally moves the interference nulls/peaks to a higher frequency. Stacking them as you found out effectively eliminates phase differences in 2d space (there is still vertical lobing but at these wavelenghts and room dimensions it is just academic).

Phase problems can be fixed by either electrically or physically modifying the system. The simplest thing to try that is available to everyone is to swap the speaker + with the -. More difficult is to move the speakers around (which you seem happy with ).

You can also add delay to the signal. For 100$ elemental designs has an interesting product: http://www.edesignaudio.com/product_...roducts_id=657

This is a sub eq with continuously adjustable phase from 0-180. Note: I have never used this product, just looks well thought out.

[SoundSplinter]

Impressive, I don't think the stacking looks bad at all!

[Sonnie]

Looks good to me as well.

I would love to see some REW response graphs.

[Mike Cason]

Hi again Sonnie and Mike and thanks for the compliments...

Mike P. asked me to post a build thread so I did at:

http://www.hometheatershack.com/foru...or-design.html

I've not figured out to use the REW yet as I've been too busy with two jobs, but I have posted some "ear" test results at the above thread. The Michael Murray's organ appeared to hit the 18hz bottom end with no difficulties at all. It is incredibly low and smooth and with dual subs, it seems to have much more room gain. I've pulled them out to about two feet from the corner and am using the side walls as reflectors. I did politely ask my neighbor on the next street over and down two houses whether it bothered him....

I'm used to the 6.5' tall sub set up now and wouldn't place them anywhere else due to the increase in performance...the WAF has remained the same!

Thanks Mike & Sonnie

[Mike Cason]

Update on the performance...

I bought the Reckhorn B1 equilizer from CSS, turned off my QSC's 30 hz filters, (options are 30, 50, or none and didn't want to blow the drivers) and left their clip limiters turned on and what a huge difference this product makes!

It is made in Germany and the controls feel like they are very high quality, as well as the fine machine work and the overall finished box's looks. This is a splendid piece of engineering. It is also heavy for it's size.

I've set the bass boost frequency at 20 hz (with little cone excursion) and have the boost set for about 50% with the main setting at midpoint. This little box really bridged the gap between using home and pro audio equipment allowing them to blend together so well, ie impedance matching and the extra bass control.

I had the Arts Clean Box and it didn't work for my system at all, so I pulled it out ten minutes after modifying it and installing it to test it out.

The Soundsplinter drivers just got better!

Both subs stacked are acting as a single unit and with this location and are performing flawlessly!

I've read some posts and lots of guys are suggesting transducers under all of the chairs or seating areas. You probably won't feel them with this system cranked up and the output I'm getting now! It's kinda neat to watch the curtains dancing with the music.

Thanks to all for your inputs, especially noting all the help from Mike P....

Mike Cason