How many 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 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.

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.

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. 

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 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.

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.

The answer is four.

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

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. 

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