How many subs?

You may find this article helpful.  https://www.minidsp.com/applications/subwoofer-tuning/tuning-multiple-subs

There is one device that can configure them for you in the frequency domain and in the time domain with the push of a button: DSpeaker 8033, up to 4 subs. I sold mine when I bought an AVR that could configure 4 subs but regret that I did now. The DSpeaker is better. 

The answer is four.

Check this out: https://jamesromeyn.com/speakers/subwoofers/general-info-subwoofers/

Thanks for all the info.  I like the Debra system and the small magic box.

A sound guy worked in that room for hours moving 4 subs around and decided 3 was what is needed.  He used all the necessary gear to work it out.

Probably what I am liking when using only 1 sub is Rel's blending of sub with main speakers which are stand speakers.

The stand speakers are back to full range which also sounds better.  I just couldn't balance the mains with the subs when separating the frequencies sent to each.

I wouldn't use DSP if it had to involve the main speakers.  I have a very decent CD transport, musical R2R DAC and tubes at the front end of my amp.  Running that through digital and back again seems not the best idea.  But using DSP for bass?  I am using DSP - it is delays for 2 subs.  And the left sub never has gotten DSP.

The plan is to try the 3 subs again, but while considering the front left as the main one.  A combination of using Rel's preferred connection method for the left, running the stand speakers full range and less of the delayed subs might just hit the spot.

I don't know if I'd have 'gone so hard' with making a hifi room now knowing the difficulties with low frequencies.  But hey I'm here now so I need to get the best sound from it.

I have gotten further.

Front left - Rel high input using L and R as the main sub with stand speakers full-range - as I said I would do. The sub against the right wall (I think 3 ms delay), being nearly opposite the main speakers wasn’t doing it for me. Only having the back right (9 ms delay and 180) seems to work well with the front left.

I can hear ’a hole’ in the back left in bass. But it is a difficult room. 14 feet by 12.5 feet (that being the front wall) by 11 feet. The difficulty is a diagonal in the back left corner, amongst other standard difficulties.

I haven’t been using a low pass filter that is necessary as the 120Hz 4th order low pass on the Rel theatre inputs aren’t enough to remove higher frequencies. I want to sell a piece of expensive equipment that could take care of this. I know the driverack can create an appropriate low pass and I am hoping it can combine L & R to 2 mono outputs so I can properly test the 3 sub design. I am waiting on someone who can program it.  For the moment R is the input for it.

I can easily change it from L & R to all subs to L to the left sub and R to the right sub(s) by disconnecting a wire and removing a cable - once the driverack can accept L and R and make it mono.  I could buy a Radial Mix, but as I just sold 2 of those, I prefer the driverack to be able to do this.

I did a four subwoofer array in 2011. Two of the subwoofers, which I use today are equipped with fourteen onboard Auto and Manual subwoofer related parameters none of which is a delay. An older third subwoofer used nine parameters and the forth basic subwoofer was slaved by one of the newer subwoofers.

I positioned them in asymmetrical near corner locations within a vaulted ceiling open room. Playing the below 200 Hz Sweep Tone through the mains simultaneously and each subwoofer individually I ran the Auto Room Optimization which adjusts the subwoofer only.

I then played a very familiar Double Bass and Drums recording that I recorded and made some minor manual adjustments to taste and saved the results to the subwoofers preset  memory. The procedure took less than two hours to complete. The results were a stunning room lock and elimination on all the rooms bass modes. 

I'm a hack but I know what my Basses sound like. I've come to learn Optimization or DSP is for main speaker integration and not a panacea for improperly positioned subwoofers or poorly adjusted sub-bass speakers. 

I did find the HT receivers auto speaker distance delay very benificial until I rearranged the HT room, spacing the seven speakers equal distance from the listening position. 

As a Bassist I simply do not understand the benefit of delaying already long low frequency wavelengths. I still have my acoustic 360/361 which is another story altogether.

I had the big REL Studio III for a short time. You should understand that all REL products are simply sub-bass speakers Their -6dB roll off is so dramatic they simply do not excite a rooms bass modes which allows them to located most anywhere in a given room. 

I'd suggest that hunger for more your seeking can be found in most any -3dB actual subwoofer positioned precisely within the rooms multiple standing wave bass modes. Many manufactures provide quality phone support to assist in adjustments to your taste.

All the best. 

Thankyou m-db

I have a friend who is bemused about my attempts. He reckons he’ll come round and fix it without using delays, and with just 1 sub.

I know people are saying use 4 - but if it sounds artificial and I don’t like it, and I am determined to not use standard DSP - what can you do?

The driverack is for aligning 3 way stereo systems in large venues - or providing back delay onstage.

The acoustic engineer studied how to manage low frequencies in a room - so I don’t understand why his method of using delays would seem to be not at least an option.

The subs I have are Rel S/510 - it was what was recommended for my stand speakers which now people might be curious about - B&W 805D3. That was a good choice of main speakers for my room. I know some people don’t like B&W tweeters, but it would be boring if everyone liked the same things.

I also have an AVAA (I have more but selling them). Their party trick seems to be to lessen the time a sound bounces around the room. This is below approx 150Hz.

@bilateral No need for any delay in such a small room! If your 'acoustic engineer' thinks otherwise, fire him- he's doing you no favors.

Here are some facts to consider: at 80Hz, the waveform is 14 feet long. It takes a full cycle to pass the ear before the ear can tell its there; it takes a few more to tell what the note actually is.

By this time the bass has bounced all over your room. This means the bass is 100% reverberant.

For that reason you can use a mono bass signal in most rooms except those that are very large. The subs need not be anywhere near the main speakers as long as their output is kept below 80Hz so as not to attract attention to themselves.

The problem you run into in a room like yours is something called a 'standing wave', which can cause bass to cancel. Cancellation can't be corrected by bass traps or digital room correction since that would simply ask for more amplifier power which would get cancelled. To break up the standing wave you need multiple subs which are asymmetrically placed about the room. This isn't the sort of thing that 'takes hours'.

For this you need 4 subs to be the most effective. This technique is called a 'Distributed Bass Array'. It will breakup any standing waves and will take care of 95% of the room's bass problems. Only after they are installed should you try bass traps and/or room correction, which can do the other 5%.

End of 'facts to be considered'; now for the anecdotes:

My speakers at home are flat to 20Hz. I had a significant standing wave. So I needed two subs to break it up. One is to the left of my listening position and the other is behind me and to the right. This worked a treat and literally took a few minutes to set up.

Audiokinesis makes a sub called the Swarm for this purpose. Its designed to be set as close to the wall as you can get it. In my room, I have the drivers actually facing the wall so as to be certain its inside the room boundary effect. By so doing, the Swarm subs are also flat to 20Hz. A single, inexpensive subwoofer amplifier recommended by Audiokinesis drives the two subs.

For my system I do use 4 JL-F-113 subs. My room size is 17’ x 25’.

The subs have a calibration mic that I use to set up each separately in the chosen location.

After all are calibrated, I use 45hz as the crossover point. Everything blends beautifully and extended.

Though each sub has a delay feature I don’t use it. Try to not make this too complicated.

ozzy

@bilateral  I don't think there is a standard for Digital Signal Processing. Its not the answer for you anyway.

I'm aware that some companies rely on matching their products to speaker brands. Of course this is absurd. Actual subwoofers are adjusted, not matched to the speakers. 

-6dB@20Hz is hardly, if any, 20Hz output at all. 

You're looking for that delicate extra low +2dB@20Hz feeling coming from many modern recordings. If a dealer did that matchmaking, demand a refund or a store credit toward some actual subwoofers. You'll be amazed.  Take care,

to be safe, build the back wall from subs. You have never heard anyone say

I built a wall of subwoofers and I so wish I hadn't

Cheers everyone.

Everyone knows I'm going to still give the delays another go - even just to better understand I don't like it.

From my engineer:

"The method I used for setting up the three subs wasn’t with all subs at the same loudness (in my opinion it isn't correct due to different distances from the listener and other factors...). I used a method, which slightly varies the dB levels between each sub to achieve a smoother in-room response. This approach focuses on reducing peaks and nulls caused by room modes while maintaining overall balance."

The original subs I chose were lesser Rel subs.  I gave instructions to where I bought them is I cannot have the deepest bass due to neighbours.  I am already aware that they can hear what is happening.  I want to have some hope of being able to play music.

It is Rel that paired their choice with the speakers.  The S/510s are needed to keep up with the 805s.  They insisted that TX7s or whatever I chose weren't good enough.

I installed just over 3 inches of acoustic treatment along the party wall in the hallway, lounge and kitchen - 4 layers, including 3 layers in "acoustic-board" specifically designed to reduce vibration.  With the double brick, I estimate (and because I can no longer hear the neighbours) I might have achieved close to Rw + Ctr of 60 dB.  But that won't stop low frequencies - nothing can completely stop them unless we go with "in space, no-one hears your subs."

The room is separated from the hallway by a brick wall with plaster on each side.  The front window got a double glazing upgrade using a material that isn't glass and with a large distance between them.  Then theatre blacks - 95% wool curtains.  This is the front wall.

Acoustic treatment (above ~200Hz) around all walls which surprised me how much it quietened noise from outside.

With the acoustic door - that room is sealed tight.  Acoustically and thermally.

Even with all this - I can't have subs that properly do 20 Hz.

@bilateral  Considering your living arrangement concerns the -6dB sub-bass speaker suggestion is understandable...but no. 

A subwoofer with a modicum of frequency response control would be a far greater advantage while maintaining the ability to go low if or when the opportunity or circumstances change. Ultimately, a subwoofer with customizable presets would allow you situational flexibility and convenience. 

I purchased my first subwoofer in 1967. Living in wood framed and floored ranch homes most of my life and annoyed by the travel of those filtered bass frequencies. While my little studio is substantially treated the HT room isn't and only first reflections are lightly addressed in the two channel room. I'm not a fan of closed in treated rooms. 

My two twelve inch subwoofers rest on simple to build DIY dollies. I used these soft rubber plate casters attached to twelve layer Baltic Birch (any 3/4" plywood) followed by old Boogie board closed cell foam and topped with four inch heavy latex, foam store foam.            

https://www.castercity.com/product/5-super-soft-gray-soft-rubber-plate-swivel-caster-3/

Decoupling, suspending and the twelve inch hight increase required resetting their settings. The resulting improvement in bass presentation was very noticeable. Unknowingly, the transmission of resonant frequencies throughout the dwelling structure were stunningly reduced. No more rattling and buzzing, gone, except for preset #6.   

@m-db

The Rel subs have to be on the floor - another disadvantage.  I tried platforms and it really sounded much worse.

Subs that can be decoupled from the floor, with proper bass extension, and ability to knock some lowest frequencies out of the mix when playing particularly annoying bass heavy music, looks like a good solution.

The sound track to Blade Runner - CD (probably all formats) has some excellent bass moments.  It would be great to hear that with fully capable subs.

I like that there is a preset - 6 - that is too much.

You always need a preset that risks causing an earthquake.

Iam using three 2 pioneer sub modified by a guy who sold Teajay the pioneer modified. I heard them at his house pre pandemic with the ps 12. One sub Iam using  denon. I used three because of my room configuration.Atmasphere is right audiokinesis does has swarm set up, that I considered but I decided to do 3.

@jayctoy any number of subs is good - I just got the 3 sub system going with some outrageous hardware. It sounds fantastic.  Not the lowest bass - I don't want that (yet).

Delays with a Drive Rack. Low pass filter for the right subs with a CR1 - nothing spared.

I need some tweaks to get it right.  When you hear a Tyrannosaurus Rex on S/510s - you will run.

Everyone will be pleased that the experimentation with delays for subs 2 and 3 is done and it is a fail.  It takes a few sessions and many tweaks of levels to hear what is happening.  To get the sound so subs 2 and 3 don't noticeably interfere with the main speakers is a very low level.  I turn off output 1 on my amp and listen to only output 2 which feeds the 2 delayed subs.  Really not a lot happening.  Not worth it.

@bilateral  Just a thought.

Saturday January 11, I filled in on Bass at a benefit held in a medium sized hall. After the sound check I noticed the front of house equipment rack included a 1U spaced component called DBX Drive Rack (something). 

The tech had left after the check. He was still working after I left that evening so I was unable to question. 

I think it might be a more recent Auto EQ system for both stage and / or front of house EQ. Just how this would function using REL's preferred speaker/high level connection without also affecting the mains? 

Front of house or FOA sound is a whole other world of audio. You might want to get clarification as to what the intended use of this DBX Drive Rack model is designed to control. Don't give up on your low frequency reinforcement. 

@m-db  the drive rack was not used for purpose, it was what it could do.  I wanted a balanced product that could give delays up to 10 ms (not including latency).  When the Acoustic Engineer said 3 ms delay there and 9 ms I got someone else to program it because we could not work it out.

I cannot use Rel's preferred method of connection for sub 2 and 3 due to the delays so it is the 0.1 input or whatever it is called.

Then the problems with the 120 Hz 4th order low pass filter on the subs - it is worth mentioning again - this is not the filter for hi-fi.  Too much higher frequencies.  I have the JL CR-1 to fix that.

Is today today?  Good it is.  3 days for suggestions for testing.

The MP-40 Lyngdorf processor in our system allows subs to set up several ways. I have four in the system. You can choose Stereo, or LFE. You can do Stereo Up Front and LFE in the Rears. Or Stereo all the way around. Or All LFE. For my ears, I like ALL LFE. Each is different in their own ways, but I like to listen to video concerts (Eagles @ Melbourne etc.) and for music, all LFE is the ticket. If I was a movie geek possibly I would have chosen Stereo. Movies are still fine on all LFE with Movies, but I believe the sound stage is a little wider when I tested Stereo set ups. 

@bilateral sorry to hear of your day.

Lighting! My untouched 1959 formica covered ranch house has hanging brass fixtures right out of the Jetson’s. Regardless of their mid century cool the homes lighting is a nightmare. I sure could use your chops.

You take care.

I have a friend who is bemused about my attempts. He reckons he’ll come round and fix it without using delays, and with just 1 sub.

I know people are saying use 4 - but if it sounds artificial and I don’t like it, and I am determined to not use standard DSP - what can you do?

I'm not a fan and not able to use 4 subs, so that whole argument doesn't work with me despite the cult-like following the 4 sub array fan boys have.

Placement and bass traps can go a long way but measurements to properly config your speakers and a little EQ on the bass can do marvelous things.

Also, if your main speakers are ported, put a sock in them and try.  :)

Check the AM Acoustics Room Mode simulator btw, it can help you with placement.

You might want to start by reading this. https://www.acousticsciences.com/wp-content/uploads/2024/11/Soundoctor-Barry-Ober-sub-integration.pdf

My guess is that your acoustic engineer was adding delay to your subs so they would be in phase at the listening position.

To my knowledge, all powered subs have some type of e.q. circuitry in their design which also creates a delay of a few to several milliseconds depending on the model, coupled with the delay caused by normally placing your subs further away from your listening position than your mains, you could start getting a significant delay between your subs and your mains, so I am surprised he didn’t say anything about delaying your mains since he was concerned with a 3 ms delay between your subs.

Your driverack is primarily a 3 in, 6 out active electronic crossover with DSP, that also gives you a 30 band,1/3 octave e.q. along with an 8 band parametric e.q. on each input. On each output you will have both low and high pass filters with selectable slopes. 8 band parametric e.q, driver protection and driver alignment delays. It is a pretty powerful piece. There is also software that you could download onto your laptop that would allow to to operate the driverack from your listening position. You would also use the driverack to set the volume balance between your subs and mains so one doesn’t overpower the other.

Your CR-1 gives you an active crossover with either a 2nd or 4th order Linkwitz-Riley slope. You can also control volume balance between subs and mains and both units will give channel muting capabilities.

If you do not use either unit you would want to set the low pass filter on your REL’s around 34 Hz, not 120.

I would not rule out using DSP on your mains until you have at least tried it. If done correctly the positives should be far greater than the negatives.

the drive rack was not used for purpose, it was what it could do.  I wanted a balanced product that could give delays up to 10 ms (not including latency).  When the Acoustic Engineer said 3 ms delay there and 9 ms I got someone else to program it because we could not work it out.

@bilateral unless your room is enormous you don't need any delay at all unless your subs are active at higher frequencies. But most speakers will go well below 80Hz; that's sort of the 'magic number' in most rooms; if the subs do not put out information above 80Hz they won't attract attention to themselves. Since all the bass at that frequency and below is reverberant its easy to get them to blend.

I now have only 1 sub. No delays. No DSP. It is in the front left corner and 180 degrees out of phase. It uses Rel’s high level input from both L and R.

I found whatever I did, multiple subs interfered with the sound from the main speakers.

It sounds great - that is what counts.

What has become apparent, is my floor.  Vibration through it.  A timber floor with construction involving stumps. I have plans (that will likely be never done) of removing the carpet, ripping up the floorboards, removing the structure, levelling the ground and then preparing it for a concrete pour. No formwork is needed as the brick foundations of the walls will provide that.

I haven’t looked into if it actually needs rebar, but I’ll go there and have fun making it up as I go along. After watching a 5 minute video on YouTube of course. In addition to what might look sensible, I’m going to incorporate an immature shape into it and know it is there.

I have a couple of friends that can weld - they would find my plans funny. Both know about concrete foundations so I don’t need to waste 5 minutes on YouTube.

Then open up a window, get the 2 (?) concrete trucks and pour concrete through.

Floorboards back on top and carpet. It will likely still need a lesser form of joists between concrete and floorboards - or I ditch the elderly floorboards and use something else.

I could lower the floor which makes the possibility of tripping into the hallway at some point likely which I approve of and I think everyone else would too.

I found whatever I did, multiple subs interfered with the sound from the main speakers.

@bilateral In that case they weren't set up correctly. The most common problem is crossing them over too high!

Here's a  tip for your sub. Point it at an angle towards a wall; imagine bouncing the bass wave off of the wall in a manner similar to a cue ball in pool. This will allow the bass to be more able to not form standing waves and might sort the room out nicely.

My main speakers take a nose dive at around 58hz as designed (test CD used to verify this, Heresy III with titanium mid and tweets, better sounding than IVs with poly mid and no horn throat...I tried 'em, IIIs sounded much better). I have 2 older RELs, both kick in at 58hz and work amazingly well. I don't recommend bouncing a cue ball off the wall as it could be bad if you stepped on it in the dark..