Subwoofer advise

[Primare Knob]

Hi,

 

I am planning and gathering bits for my yet to build home cinema, and I am trying to get an idea about subwoofers. How many, which type and how to set them up for movie playback.

 

I do have a pair of Martin Logan Montis, which have a powered (200w) 10inch woofer in a closed cabinet. This woofer is crossed over at 340Hz where the panel starts to take over and are rated to go down to 29Hz +/-3dB.

I also have a single Paradigm Ultracube powered (650W) 12inch subwoofer with 2 x 10inch passive radiators. This subwoofer is claimed to go down to 19Hz DIN.

 

The new room will roughly be 3.4 x 5.5 x 2.5m (46 cbm). The recommendation is to use more than 1 subwoofer for a better bass response.

 

I can't really count the Montis woofer as subwoofers, since I have no control over them separate, and they still have to play up to 340Hz.

The Paradigm does have their PDK software for bass response control so going with another Paradigm or Martin Logan would make integration easier. But should I go for a twin pair of subwoofers, or can I mix and match?

 

What other options can I use to integrate the lower end into a smooth and powerful response, and would a 15inch sub be a good addition or more of an distraction. There is a fair chance that all of this is will be sitting behind an acoustical projection screen.

[Bunno77]

Mixing subs isn't usually recommended.

If you're happy with the supercube adding a second will give more impact and be better balanced. 2 subs does sound better than a single positioned to one side and 2 smaller can equal or better one larger. 

If you want a lot more impact and room shaking then a bigger more powerful 12 or 15 but can get costly quick.

If putting behind a screen and if you can position it centrally then you don't really need 2 and going a higher spec larger sub might be an option.

PBK helps and your avr or processor if it has room correction use that as a basis. If not happy can fine tune it from there

The bigger JL audio, Paradigm, Martin Logan and SVS subs are all good.

[Sub Sonic]

@I'd be going with a pair (or more) of the same subs, which should help smooth out the in room bass response.

 

Recently I have been playing around with a Rythmik sub from Paul Spencer (Red Spade Audio), and have been very impressed. A second unit is also on it's way. These subs are in a different league to most.

 

@Paul Spencer (Vic) also offers a measurement service which would help you work out the best subwoofer positioning and could make some recommendations re types/brands of subwoofers.

 

Regards,

 

SS

Edited November 28, 2016 by Sub Sonic

[Primare Knob]

I haven't got a change yet to test the combo Montis-UltraCube 12 but in my previous and smaller room the Ultracube 12 wasn't giving me the oomph. Although this was in a smaller part of a very large room with an open filled up bookcase as a divider. The new room will be completely sealed off. From memory the Ultracube 12 was never there, which might be a good thing. I don't want the sub to be overpowerd or claim all the attention.

 

It should not be a problem to mount a sub underneath the center speaker.

 

What I am going to do with room correction I don't know yet. I have never been a big fan of using the AV included one. The PBK seems like a very capable one and gets good reviews. I might also work it out at the source on a powerful HTPC.

[Paul Spencer]

On 11/28/2016 at 7:36 PM, Primare Knob said:

 I am trying to get an idea about subwoofers. How many, which type and how to set them up for movie playback.

 

It's a good question but it's also impossible to answer well without in-room testing. Generic advice is very hit and miss here. One has to ask the right questions as well to give a definitive answer. The right placement and calibration are critical. Done wrong you may find two subs can be inferior to one.

 

One of the key questions is how are you arranging your seating? Will you have rows and where are the seats you consider prime located? If you have just one or two prime seats next to each other then that can often mean less subs are needed - often only one or two in the right positions. Two rows tend to mean the rear will be comparatively bass heavy. The more seats you want to optimse, the more difficult the challenge and the more likely you are to need more subs.

 

Quote

What other options can I use to integrate the lower end into a smooth and powerful response, and would a 15inch sub be a good addition or more of an distraction. There is a fair chance that all of this is will be sitting behind an acoustical projection screen.

 

 

All else being equal, a 15" sub provides more output than a smaller sub. A quick rule of thumb is that where one sub has twice the physical volume, it will provide around 6 dB more output, which will sound twice as loud. If you compare both and they are correctly calibrated and working within the limits of the smaller sub, if all else is equal they will sound very similar. In that specific situation, the larger sub will have lower distortion but it won't be a very significant difference. The decision would be more about size and price. In a real world comparison, all else isn't equal, so you are dealing with many other factors.

 

If a sub is "distracting" then something is wrong. A good sub set up correctly should disappear completely.

 

Quote

What I am going to do with room correction I don't know yet. I have never been a big fan of using the AV included one. The PBK seems like a very capable one and gets good reviews. I might also work it out at the source on a powerful HTPC.

 

 

MiniDSP 2x4 units are very good. They provide plenty of EQ capability as well as the option to use high and low pass filters. You can increase the headroom of your subs with an appropriate rumble filter and more options with the low pass is also a good thing. It requires a manual process, measurement equipment and knowing what you are are doing.

 

I've tested the correction of various automatic systems, both stand alone units, in-built units and the correctly applied by AVRs. In each instance, I've found some have poor if not questionable results. 3 results I've seen:

 

1. An appropriate correction

2. No correction applied at all

3. The correction introduces problems

 

My suggestion is to verify any correction with acoustic measurements.

[Primare Knob]

My suggestion is to verify any correction with acoustic measurements.

That is the idea at some point. Get the bare room ready, start measuring it and take it from there. From a design point of view, what physical treatments are there to treat the sub frequencies. I have been given some pointers towards a bass trap riser.

 

Is there a way to calculate theoretical SPL levels for subwoofers? THe Ultracube 12 I have, doesn't state anything about efficiency, or does this not mean much with a subwoofer?

[Paul Spencer]

On 12/5/2016 at 6:42 PM, Primare Knob said:

That is the idea at some point. Get the bare room ready, start measuring it and take it from there. From a design point of view, what physical treatments are there to treat the sub frequencies. I have been given some pointers towards a bass trap riser.

 

There are basically 3 types, only one of these well suited to DIY:

 

1. Broadband

2. Tuned

3. Hybrid

 

Broadband traps are suited to DIY and they must be big.

 

I've tested all types, both DIY and commercial versions. The results are sometimes surprising.

 

Quote

Is there a way to calculate theoretical SPL levels for subwoofers? THe Ultracube 12 I have, doesn't state anything about efficiency, or does this not mean much with a subwoofer?

 

You can calculate it but I find that these calculations are mostly only useful for comparing one option against another. They aren't very useful for deciding how much is enough.

 

One simple way to compare subs is based on their physical volume. In the bottom octave, the maximum output of a sub is pretty closely tied to the physical volume. This tends to apply across the board, whether you are considering sealed, ported, passive radiator, bandpass, quarter wave or horn. If you have a horn sub that takes up the volume of 8 sealed subs, then that one horn will do the work of 8 sealed subs. This rule of thumb works better than you might expect.

 

When comparing similar subs, such as sealed subs of the same size, or porte/PR subs of the same size, then output comes down to total piston area, xmax and power.

 

In a HT, you might be interested in the output in the bottom octave most. Sensitivity might not be very useful. Above 40 Hz, things shift. Now it's about sensitivity and power. We're less concerned about the volume of the box and the excursion. This is where a sub with a sealed box and a pair of drivers can leave behind a ported sub with a single driver. Both are about the same size. Both have about the same bottom octave output. But the pair of sealed drivers has twice the power (the drivers do at least) and 3 dB extra sensitivity.

 

Short answer. With a bit of guesswork, you could estimate the SPL of a particular sub by modelling something similar. I do this kind of thing where a client has a requirement for more output than what they currently have.

[Primare Knob]

 
You can calculate it but I find that these calculations are mostly only useful for comparing one option against another. They aren't very useful for deciding how much is enough.
 
One simple way to compare subs is based on their physical volume. In the bottom octave, the maximum output of a sub is pretty closely tied to the physical volume. This tends to apply across the board, whether you are considering sealed, ported, passive radiator, bandpass, quarter wave or horn. If you have a horn sub that takes up the volume of 8 sealed subs, then that one horn will do the work of 8 sealed subs. This rule of thumb works better than you might expect.
 
When comparing similar subs, such as sealed subs of the same size, or porte/PR subs of the same size, then output comes down to total piston area, xmax and power.
 
In a HT, you might be interested in the output in the bottom octave most. Sensitivity might not be very useful. Above 40 Hz, things shift. Now it's about sensitivity and power. We're less concerned about the volume of the box and the excursion. This is where a sub with a sealed box and a pair of drivers can leave behind a ported sub with a single driver. Both are about the same size. Both have about the same bottom octave output. But the pair of sealed drivers has twice the power (the drivers do at least) and 3 dB extra sensitivity.
 
Short answer. With a bit of guesswork, you could estimate the SPL of a particular sub by modelling something similar. I do this kind of thing where a client has a requirement for more output than what they currently have.

Thanks Paul, I'll take that into account and see what I can come up with. I am still a long way off before finalizing.

Sent from my HTC_0PKV1 using Tapatalk

[Primare Knob]

Found this info as well. Not sure how to take this. How would you need more Subwoofer SPL for bass managed speakers?

 

For 5 bass managed speakers an additional 6dB and for 7 bass managed speakers an additional 8dB of output may be required from the subwoofer channel.

[jamiebosco]

21 hours ago, Primare Knob said:

Found this info as well. Not sure how to take this. How would you need more Subwoofer SPL for bass managed speakers?

 

For 5 bass managed speakers an additional 6dB and for 7 bass managed speakers an additional 8dB of output may be required from the subwoofer channel.

 

Because  the Bass (usually under 80hz) from the other 7 channels  is being redirected to the subwoofer. So the subwoofer has to handle this + the LFE track (which is completely separate to the other 5-7 discrete tracks) Which it is why it is said that at reference level, in a worst case scenario, the subwoofer needs to be able to handle 123dB peaks (115dB LFE track + 8dB for redirected bass from the other 7 channels)  

[Primare Knob]

I am trying to hide a sub by having it sitting inside a cavity and firering through and opening in the wall.



I got a respond from a different forum telling me this.

suggest you place a subwoofer on the couch and crawl around to find out if the spot you want to place it is one of the best. Usually, the longest wall of the room has better bass than the wall that has shorter lengths of the room. Even though bass is omnidirectional, the spot you picked in the picture can be used for a subwoofer and probably not the best spot.

Martycube with Ultimax 18-inch woofer will have very high delays. This will make integration a pain and will sound muddy. I suggest the following.

Dayton Audio 18" Reference Series HO Subwoofer and Cabinet Bundle (Parts Express #300-7094)
2 Dayton Audio RSS390-PR 15" Passive Radiator
2 Plywood sheets cut to attach inside the box where passive radiators are mounted
1000 watt amplifier or Dayton Audio SA1000 (technically 950 watts)
4th-order Linkwitz-Riley highpass filter set around 18-19 Hz (depends on passive radiator tuning)

If you want loud bass or bass output of 120 dB, use three weights on each radiator and set the high pass filter to 19 hertz. If you want lower bass extension, add all seven weights to each passive radiator and set the high pass filter to 18 hertz. The total delay is 40 milliseconds. This makes it easier for the AV receiver to integrate the subwoofer with the speakers. This design bass extension depends on the weights. Using three weights, it can achieve 25 hertz. If using seven weights, it goes as low as 22 hertz. These are not in room response. I haven't built it because I don't have the money. I have built Dayton Audio Ultimax 10-inch Subwoofer and 1.25 cubic feet knock-down flats. It's able to produce 20 hertz without bass boost which is much lower what Parts Express describes in their description in my room. My room is similar size as yours. This 18 inch subwoofer will easily go much lower than 20 hertz in 1220 cubic foot room.

What suggestions would you guys have, and is it a reasonable option to place a sub in that position?

[Primare Knob]

Are there any big concerns to be aware of if I want to use/build shallow depth (height) down firing subwoofers and place my front speakers on top of this?

[Guest thathifiguy]

If you're running a single sub, it is usually advisable to run it on the front wall.

[Guest thathifiguy]

Here are a couple of handy links with regards to subwoofer placement.

 

Digital Trends

SVS

[Primare Knob]

I am looking to do 2 subs, underneath the front speakers. Front speakers sitting roughly in the front at 1/3 of the room length, roughly 1/5 of the room width.

Sub wise it doesn't seem like the worst position, but how is the interaction going to be when I literally place a front speaker on top of this low profile sub woofer.

[Guest Peter the Greek]

One big on, in the middle at the front and one small balancing sub, middle-ish on the side wall. You may find you need up to 4 to get it right (mid points), depending on the construction of the room (and bass traps)....and then you need to pay Paul et al to calibrate them all for you.

 

Paul could build you a tapped horn to go in that room, but I dont seem to like subs behind me, even when well calibrated I just dont seem to like it

[Guest Peter the Greek]

PS, that room at the back is huge, valuable real estate IMO. I'd can it. Put the projector in a hush box and a rack in a silent cupboard (ventilated) near that. 

 

Could be a good place for a variety of bass traps too. Specifically this sort of thing:

 

 

 

[warweary]

If you're willing to fill one cavity with a subwoofer anywhere is better than no where hey. I like the idea of a pair at the front down low and a pair in the ceiling at the rear. Will the walls shaking and vibrating upset anyone?