Quad Subs? - Page 2

What I'm questioning is your capability to utilize the tool properly. Based on your posts here and where you've posted graphs to date, I don't think anything viable is likely to be produced.

If you put two identical subs in different locations in a room, they'll have a different frequency response and different distortion curve relative to a given listening position. The differences can be very dramatic. I don't see how it would be much different than having two different subs. As a matter of fact, I would like to see a listening test whereby you have sub A in one spot and then put a level matched sub A, B or C in a different spot and see if you or anyone else can consistently tell if the sub is the same or a different model. I think many would fail the test.

Actually if you re-read that article you are posting it says that the left picture with the two subs got the best measurements.

Well all I can tell you is that I tried placing two different performing subwoofers in opposing walls of the room (I moved them around from both the middle of the wall to the corners on either side) and the second subwoofer (no matter where it was placed) made things worse with sub 30hz content (the lesser sub starts to rolloff around 35hz). I believe this is due to the subwoofer trying to keep up beyond it's limits where the other subwoofer sounded just fine.


For music, I don't think this would be nearly as big an issue, but with movies I found that I actually preferred only using one subwoofer with movies that have ULF content. Above 35hz or so up to 100hz both subs sounded pretty good together. If I had better EQ I would probably just highpass the lesser sub at 40hz and use it strictly for 40-80hz content.

But none of this matters now as I am building 4 identical subs and will have EQ.

 

Wow. You are really keen to learn aren’t you?

First, I would probably not suggest using 4 different subs that have different performance characteristics. In the case of the OP's situation, I would probably opt for using just the new XS-15's and re-purpose or sell the Velo's. The XS-15's have 2" of excursion, whereas the Velo's only have 5/8" of excursion. The Velo's will have a hard time keeping up with the PSA's. They'll compress and didtort long before the PSA's get close to their limits.

However, if he really wants to use them, I suggest he try the technique espoused by Earl Geddes: http://mehlau.net/audio/multisub_geddes/ This technique places the subs randomly and asymmetrically around the room, and uses the frequency response plot to set the levels of the individual subs. It *requires* measurement capability. It also requires judicious use of the Master Volume Control to ensure that you don't overdrive the lesser subs. Once the subs have been optimized with that technique, EQ can be added as the final icing on the cake.

BTW, I think the above technique is best suited for a "modest" volume, music oriented system. For an HT type system, where high output is a primary goal, the lesser subs will hold back the better subs, and limit total system performance. For ideal HT performance, identical subs, gain-matched, (not level-matched), is the ideal solution. The placement can be random and there is no significant need to time the individual subs to each other, as the response is more dominated by the room than by the interaction of the subs with each other anyway. This is the way I have my 3 Submersives set up. I described the whole process here: http://www.avsforum.com/t/759877/seaton-sound-submersive1/4500#post_19446901

Craig

You owe me a keyboard - mine is now full of the coffee I was attempting to drink

Excelent post Craig. Thanks for your insight, and even though I am sure I have read your process before, I will read it again.

Beeman up to his usual. Using his definition a hammer is an eq tool, as you can knock down walls to stop standing ways if you can visualize them. At least he didn't say 4 different subs, no problem just get an antimode. Passing along bad info and false information is not learning, its called blind leading the blind. What the heck is a pseudo (Adjective Not genuine; sham. Synonyms false - sham - spurious - phoney - mock - phony) room treatment. And now moving on to measuring driver break-in when can't set up a system. WOW really breaking new ground here. I would advise using the search function more than the submit post.

As usual good posts from Craig John. If utilizing measurement equipment it might be possible to integrate them but would be a guessing game without. It could be that gain matched running the velo's ~6-8db's down from the PSA's, and using them nearfield or as flanking subs could work as well.

http://www.avsforum.com/t/1380013/my-multi-location-subwoofer-thread-inspired-by-welti-devantier-geddes/150#post_22811159

Here are some good posts from Seaton I am sure some of you have seen utilizing gain matching, placement, delays, then eq.

http://www.whatsbestforum.com/showthread.php?7501-Seaton-Submersives-amp-Rockport-Arrakis-amp-Mira-Grands/page3

I have learned that it is much easier to just ignore someone that try to continue to reason with them.

 

Unbelievable. You really think it was everyone else who is wrong and you were 'misunderstood'. If you still think that a SPL meter is an Equalizer, or equalizes anything, then so be it. If you have your own private definitions for commonly understood terms and phrases, good luck with that...  Meanwhile the rest of us will continue to understand what a meter is, continue to understand what an equalizer is and continue to understand each other.

Time to move on and focus on the intent of the OP"s thread.

An "EQ tool" is an equalizer. Since you thought he "didn't have a sound meter," you thought he didn't have an "EQ tool" aka "equalizer."

The first thing I said to you was that you need to be more precise with the vocabulary. I reiterate that you need to be more precise with the vocabulary. The OP said "The only EQ tool I have is Audyssey". The correct response to that would have been: "OK, you have an EQ tool. Do you also have any calibration equipment, such as an SLP meter?"

Then we would have only had to correct you when you advised him to use the SPL meter to check and reset the speakers and subwoofer levels set by Audyssey, which I did in Post # 25, and which you unfortunately stopped reading before you gained anything useful from it.

Sooooo, to get back on topic, the question the OP posed was:

The correct response to that question is that it depends on the model of SPL meter you have. There is a "sticky" in this forum that discusses many different SPL meters and the correction files for them: http://www.avsforum.com/t/505236/spl-meter-correction-tables Most SPL meters are not linear devices, and they have differing responses at low frequencies. The correction tables in that thread show how much roll off different SPL meters have at low frequencies. I haven't reviewed the thread in a while, but my recollection is that the digital meter is among the worst in this regard. This is yet another reason not to use an SPL meter to check and reset the levels set by Audyssey. The Audyssey mic may have some non-uniformity between mics, but each mic is linear at low frequencies.

Craig

Whoa, really?

How low does the Audyssey mic hear? How low does Audyssey apply filters?

They have been measured and have shown differences. It has been discussed some in this thread.

http://www.avsforum.com/t/1328136/measurement-mic-shootout-emm-6-wm-61a-rs-33-2055-audyssey

Some of the multieq have been shown to boost down low and cause problems with headroom and especially with bass reflex enclosures below tune. It is supposed to not eq below the -3db point and seems they have fixed this with xt32.

Here you can see how notnyt's differences between xt and xt32, of course he doesn't have a problem with a bit of extra boost and liked xt on the subs and adds the boost manually with a minidsp.
http://www.avsforum.com/t/795421/official-audyssey-thread-faq-in-post-1/51990

Chris Kyriakakis from audyssey
"It is MultEQ that is in charge of creating the filters and it will look all the way down to 10 Hz. If it finds usable response down there then it will apply correction down to 10 Hz."

https://audyssey.zendesk.com/entries/20953442-subeq-ht-vs-multeq-xt32

Wow, that's a great link. Thanks for that!

 

I've been debating on upgrading to XT32, but have been afraid to do it because XT in my setup, boosts me 10db at 5hz. In my room, that's exactly what I want! I do have an external EQ, but it can only EQ down to 10hz. Audyssey puts me flat to at least 5 hz, and I certainly wouldn't want to lose that boost by switching to XT32!

Flat to 5hz. You crazy!

Luke: thank you very much. I'd never have guessed any of that stuff. Users like you are a valuable resource.

Thanks guys, I lurk around a lot I guess.

Thats a lot of boost dominguez1 as 10db boost is 10x the power! Its easy to see how that could be troublesome for less robust systems. I have followed your systems subwoofer journey and its always a good read. It may not be worth it to you to get xt32 then as it most likely won't boost that much. I have seen where craig john and others have commented on the improvement in the bass in the modal region above the subwoofer crossover with the additional filters in the sats. I am going to be trying xt32 and four of the SI 18" in a few months and will be measuring and will start thread and report my findings. Might wait for in room response before I make a decision on what eq to get.

Thanks Luke.

 

I went back to my OM files and it looks like Audyssey is only boosting 8db at 5hz. At 8hz, it looks like it's 12db!

 

 

 

A fellow AVSr in town recently upgraded to XT32. His curve has never looks so flat! He runs ported and sealed like me as well. Audyssey right out of the box got it right with XT32. It's pretty amazing actually what XT32 does with the increase in filters. He also raves about what it did to his surround channels. He's do for a review on AVS...laugsbach, you reading this? 

 

I'll probably will eventually end up going there at some point. I know it would flatten out my curve more....the dip around 65hz is annoying to look at. 

 

 

I'm confident XT32 would fix that but at the cost of boost below 10hz. Hopefully I'll be able to cut a large frequency range, essentially boosting 10hz and below if I ever do move to XT32.

 

Looking forward to your SI build! What are you thinking about? Dual opposed? Don't you have VTF-15H's now? Are you planning on integrating those as well?

While you are certainly correct that different placements will yield different responses, that is simply not germane to this discussion. We are talking about integrating dissimilar subs with each other. Let's take an extreme example. Let's say you have one sub that can produce 115 dB @ 20 Hz and another sub that can only do 90 dB @ 20 Hz. That's a 25 dB difference. If you level-match those 2 subs, and then calibrate the system with both subs, when you send them 20 Hz content, you'll need to keep the Master Volume Control at -25 to keep the lesser sub from distorting. You'll be wasting the 25 dB of extra output you paid for in the better sub. Or, if you do turn it up to take advantage of the better sub, you be BADLY distorting the lesser sub, and potentially damaging it.

And it actually gets worse... If you calibrate the subs together, each sub will be set 3 to 6 dB lower than it would have been set if used alone. That means the extra LF output of the better sub will be 3 to 6 dB lower than it would have been if the better sub would have been used by itself. That really LF stuff is where the *fun* is, and turning it down wastes the potential you bought the better sub for.

Now, there are some things you can do to offset these issues, Geddes technique being one of them. In addition, placement, EQ and a HPF of the lesser sub can also be beneficial. However, it's not likely you'll ever get to use the full potential of the better sub without distorting/compressing the lesser sub, and the entire system will be limited by the lesser sub.

You might be right if you used similar, but not identical subs for your listening tests. However, if you used the two subs in my example above, anyone who couldn't tell those two apart shouldn't be on the subwoofer forum.

The bottom line is this: If you use very similar, but not identical subs, (subs with similar LF extension, output and roll off), it is possible to integrate those subs pretty easily. The larger the disparity between the subs in those parameters, the more difficult it becomes to optimize the "system", and the more compromise there will be of the final result.

Craig

More germane to this discussion is the fact that Welti used *identical* subs and they were all sent the same signal. Also, the applicability of Welti's results is limited to rectangular, sealed rooms with the seating in the central area. If you have one of those, Welti's recommendations are great. If you don't have a rectangular, sealed room, or if your seating is against a wall, you'll need to try other placements. You can start with mid-walls or corners, but it's likely some other distribution of multiple subs will work better.

Craig

I have integrated dissimilar subs in my setup successfully to where I'm maximizing the capabilities of both sets of subs, IMO. I have 2 sealed cabinets that house a 21in driver powered by ep4000 (~2000w RMS) up on my front stage. Together they yield 79db with the test tone. I also integrate a ported 15in driver (600w) with the FV15HP. This is placed in the rear of the room right behind my main LP. I have calibrated this to 67db with the test tone. I run the entire sub system +7db hot. When playing at reference, all subs are playing very cleanly. It's quite the tactile experience. 

 

Frequency response of the system are a few posts up.

^^^ This would fall under the paragraph you *didn't* quote:

"Now, there are some things you can do to offset these issues, Geddes technique being one of them. In addition, placement, EQ and a HPF of the lesser sub can also be beneficial. However, it's not likely you'll ever get to use the full potential of the better sub without distorting/compressing the lesser sub, and the entire system will be limited by the lesser sub."

You've set the level of the "lesser" sub 13 dB lower than the main subs. You've placed it nearfield, and you have a HPF built into the Servo Control of the lesser sub. Finally, you've EQ'd the system with Audyssey. I didn't say it couldn't be done, but to do it properly takes some effort, some knowledge and the ability to measure the response. You obviously have all 3.

Craig

Right. I was stating that four subs is not always the optimum number in a home theater. I think it was the same guy that posted this in another thread and keeps saying the same thing.


by the way......good luck to your Packers

Good point.  I was distracted with your negative tone and glazed over what you said about the potential ways to integrate dissimilar subs (which is exactly what I did to make it work). 

 

And yes, it wasn't easy to get them to play nicely and I certainly couldn't have done it without measurement gear and know how.

 

My recommendation is always to buy the same subs, unless there is a particular reason why you can't or don't want to. I am a big fan though of not tossing your incumbent subs, and trying to integrate nearfield.

You know, one thing we haven't yet suggested to the OP is that he try co-locating his pair of Velo's, either by stacking them or placing them right next to each other. Co-locating two identical subs causes them to mutually "couple" yielding 6 dB of increased output at all frequencies. The co-located pair could then be used as a "third" sub with his pair of PSA subs. It would still take some work and the ability to measure the responses to optimize such a system, but that would give him the best chance at integrating them with his PSA's.

Craig