Mid bass modules anyone?

[kevinm]

I've been reading up on people using mid-bass modules (bass bins?) to provide that extra oomph in the 50-150hz range. I was gifted an RSS265HF-4 and RSS390HO-4 to play around with from a friend. After looking up builds using the RSS390HO's, I found engr_dave's thread on his quad sealed RSS's (https://www.htguide.com/forum/showth...-Assault-on-SQ). He mentioned in his post that he noticed there was a lot of bass coming through the left and right front channels rather than the LFE channel - something I've noticed too.

The GF and I watch movies and listen to music fairly evenly split, but we like watching concert blurays the most. I noticed a lot of these mixes also put a lot of bass emphasis on the left and right channels. While we definitely lack nothing on the LFE channel, I feel like I could improve the mid-bass on the left and right channel - missing that chest vibrating feeling you get at live concerts (kick drums, gun shots, etc...).

I currently run ported Statements for my LCR, but am going to switch to sealed for the new boxes which I am going to start in the next few weeks. This got me thinking, if I build the smaller sealed versions that need stands, would it be worthwhile to use sealed mid-bass modules/bass bins as the stands? Thinking I could use an active crossover to split each channel into 2, one for the MBM and one for the speaker crossed maybe around 150hz with a really steep slope.

If I'm on a constructive track, I was looking at the RSS series subs since they are the SW brother to the RS225's. Thoughts?

[5th element]

Hmm, the chest hitting/thumping bass that you really feel isn't that low, although it is within 150hz. I think it's more centred around 80Hz if memory serves? The statements should be pretty good with this and actually have excellent authority down pretty low. I mean going sealed and adding in dedicated modules to take over below around 100Hz would help give you more dynamic headroom, if it's needed, but beyond that I am not sure if it will do much more.

One thing is for certain though, to really feel bass you need to crank it way up otherwise there simply isn't enough energy being produced for you to feel it properly.

[kevinm]

Well that's where I am at right now, I am by no means disagreeing that the Statements have nice bass authority. In 2 channel, I am in heaven and for the majority of my content, everything sounds amazing. But with 4 subs and tactile transducers installed in the couch, I can help but noticed that it sounds (shall I say feels?) off-balanced. More of a room for improvement rather than necessity scenario.

I've also been following a thread at AVS for the Savoy Theater where the OP uses MBMs and it was pretty much all everyone talked about from the get together - so my interest is peaked. That's why I was wondering if 4 subs in two small sealed cabinets placed under the L&R would be optimum at boosting these areas?

[JonMarsh]

I'd be curious how a setup with those MBM's actually measures... I mean, we ARE doing this for fun, but how much coloration do you want to build into your system to achieve specific effects? An On/Off switch might be cool...

I wouldn't call this sort of thing a sub; your implementation concept is OK, but the needed frequency range is about 50Hz to 150 Hz. Might be hard to do in an HT situation. This is analogous to the bass hump JBL had built in to the old L100 "Century 100" book shelf 12" three way.

[kevinm]

Jon, why do you think it would be hard specifically in HT? Because of the type of drivers?

Maybe I am looking at this wrong. Maybe using them as subs for their respective channels (1 under the left speaker and 1 under the right speaker) to cover the low end with a boost in the 50hz-80hz range as 5th mentioned would cover what I am looking for. It might not even be necessary to cross at 150hz, might be able to get away crossing lower - around 80hz.

This would probably make 2 channel listening really pleasant. If I run sealed Statements, I'll need something to fill the bass anyways.

[kevinm]

Here is an explanation I found for the use of MBMs in the Savoy Theater I mentioned previously. Anyone have any thoughts?

I posted this info on the JTR thread a couple weeks ago. It explains the background into why David is using MBM's so I thought I'd post it here.

There is a reduction of SPL caused by deconstruction interference between the direct sound of a speaker and the reflected sound. This cancellation is called Speaker Boundary Interference Response (SBIR) or Allison Effect. It is discussed in the Acoustical Treatments Master Thread, at GIK Acoustics, and elsewhere. Since the effect is based on the speaker's position, the cancellation occurs regardless of where you sit.

SBIR's effect can be calculated by the following formula: Speed of sound (1130 ft/s)/distance in ft X .25
The formula can be simplified to 282.5/distance in ft
This is 1/4 wavelength and can also be calculated using the calculator at Real Traps and viewing the 1/4 wave frequency.
For a speaker 2 ft from the front wall, the cancellation occurs at 141.3 Hz (285.2/2).

For most people, SBIR causes issues with their midbass since the cancellation ranges from 80-200Hz.

There are several ways to reduce/eliminate SBIR:
1. Use a baffle wall. This eliminates reflected sound.
2. Use absorption on the front wall. It takes a lot of absorption to reduce reflections at the midbass frequencies.
3. Position sub(s) and speakers so they each have interference at different frequencies. Set the crossover around the 1/4 wavelength frequency. This will help get a little overlap. The problem is that many use subs with lots of excursion for low frequencies. Some of these rolloff early above 80 Hz or have lots of distortion (IMD). If playing below 40 Hz, you don't want the sub playing above 150 Hz.
4. Use an MBM in a different location and overlap the midbass frequency range. For example, you can use a 200 Hz low pass on the MBM and a 80 Hz high pass on the speaker. They will then overlap in the problem frequency range. To correct the SPL, you use a high or low shelf filter.

#4 is basically the same as using flanking subs as advocated by Wayne Parham. In order to get the maximum midbass coverage, the driver of the MBM should be a different distance from both the front wall and side wall than the speaker. I think Wayne recommended no more than 4 ft away, though, so their aren't audible timing issues in the frequencies. The MBM under the speaker changes the speaker to floor distance, but the other two are the same unless you rotate the MBM so it faces a different direction.

Below 1/4 wavelength the direct/reflected frequencies couple and you get bass reinforcement.
The MBM's will be used like #4 above. However, now that there is a baffle wall SBIR is less of an issue and the MBM's will be placed below the speakers. The floor to driver distance is still different for speaker vs MBM so these cancellations will be mitigated.

I started a thread in the DIY Speakers and Subs forum documenting the MBM's:
Acoustic Elegance PB18H+ Sealed Build x 4

Source: http://www.avsforum.com/forum/19-ded...-savoy-22.html

[JonMarsh]

Jon, why do you think it would be hard specifically in HT? Because of the type of drivers?

Maybe I am looking at this wrong. Maybe using them as subs for their respective channels (1 under the left speaker and 1 under the right speaker) to cover the low end with a boost in the 50hz-80hz range as 5th mentioned would cover what I am looking for. It might not even be necessary to cross at 150hz, might be able to get away crossing lower - around 80hz.

This would probably make 2 channel listening really pleasant. If I run sealed Statements, I'll need something to fill the bass anyways.

It depends on how you have your subs and LFE setup crossover frequency- if you have big mains, and can run them down low, then adding in the midwoofers shouldn't be a problem.

What I often see, is that people want more "punch" in that area, but the real problem (or a significant one anyway) is that they're getting boundary reflections which are causing dips or notches in the response. My experience is that things either work best in a studio style flush mount to wall, or in a Cardas style well out from the wall- things in between have issues of one sort or another.

[kevinm]

It depends on how you have your subs and LFE setup crossover frequency- if you have big mains, and can run them down low, then adding in the midwoofers shouldn't be a problem.

How low are you thinking?

[kevinm]

So I've been playing around and doing a little more research. Using a Minidsp to set a crossover, I could use these as the subs for music and added "oomph" during movies. Not sure one crossover points, but I'm thinking 70-100hz would probably work best...have to play around with it. The Pre/Pro would see the speakers as full range, but these would effectively act as the subs in a 2.1 system.

This would also allow me to cross the LFE channel lower (50hz?) where they sound the best. If they ended up not working that way...I can always use them to replace the subs on my LFE channel no harm no foul. Thoughts?

The enclosure ended up being 3.7ft net after driver displacement, bracing, etc...right about where WinISD Pro recommended for a QTC of .707. Is there an problems with using a dual-opposed configuration underneath the L&R channels with a driver facing the wall and one facing the front of the room?

[5th element]

My main thoughts would be that the more low frequency sources you have in a room the better the bass is from a modal point of view. Having the main subs playing up to 100Hz and over lapping with the bass modules in the mains would be a very good thing.

The LFE channel is always talked about as being the unique entity that should be crossed over the mains to minimise overlap and to prevent the mains (via a high pass) from seeing too much bass content. It is absolutely vital to make sure that the mains aren't being over loaded, but beyond this you should absolutely use them to their full capabilities if possible. If this means having them working down to 30Hz, with the main LFE channel working up to 100Hz then so be it. One of the main aspects of a multiple sub type arrangement is having the ability to EQ each source differently to create a spacially flat average about the room. With so many sources covering the same bandwidth it actually reduces the demands placed upon any one of the drivers and if you've got a miniDSP at your disposal it makes even more sense.

[---k---]

Do you think your Statements woofers are not keeping up with the mids and tweeters? Do you think your Statements are not flat with the frequency response?

I think the Statements are a well designed speaker and have good size woofers that will remain flat for quite high volume levels.

Unless your room positioning is causing destructive interference with the bass from your Statements (very possible), and your Statements are constructed correctly, and you use the mini DSP to maintain a nominally flat frequency response, I don't think adding mid-bass modules will make a huge difference. But, there is nothing wrong with adding mid bass modules and cranking them way up for that happy fun club feeling.

Don't discount room causing bass problems. Bounce back off the rear wall, depending on where you have them located is probably well in that region your questioning.
But, people also just love the feel of heavy bass. I do. I run my subs hot. Push the sub crossover up and turn up the sub and it can get real fun.

Try playing some bass heavy club music and see how it sounds... is it bass heavy?

I think Blue Man Group "Audio" DVD is a most excellent demo disc for proving that speakers like the Statements and my Khans can deliver great impactful bass when it is in the source.

[kevinm]

5th, if I understand your response, I am in total agreement Plus, this will allow me to move the LFE subs around the room in search for better displacement, although the GAF might come into play...she's pretty understanding, but maybe not that understanding. Haha

From my quick and dirty graphs a few months ago, I wasn't seeing an major dips in the lower frequencies from the Statements that were concerning. I think it's more that I like my house curve really hot on the low end

I did a lot of testing on Friday and I found I like the sound of the mains running full with no extra stuff routed to the LFE channel other than what's below the LFE crossover point. I would just like more 100hz and below volume from the mains.

Ryan, like you I like the low end hot. My EDM music is bass heavy, but it could have more authority. I'm thinking 4 Dayton RSS390HO's would give me plenty of clean, low distortion bass with lots of headroom for the L&R channels.

[5th element]

You can't just overlap the LFE with the mains without some sort of compensation going on, otherwise you will simply have too much output over the ranges that they are all covering - this is where the DSP comes in with lots of tweaking and measuring.

I too like the bass run hot, but this is fairly common, most people do. Earl Geddes, a pioneer, one could say, of multiple sub implementation, found this to be true, pretty much, across the board., He designs a rooms inherent response to be flat, but then has a bass boost control to allow you to dial in whatever extra you want.

[Jim Holtz]

Guys,

FWIW, here's what my Statements II system looks like. All of my speakers including the rear Statements Monitors run full range. The subs are used for movies only and are rolled in around 50 - 60 hz. using a Behringer EP4000 and a 24 db active crossover for power. The Statements are designed to be as accurate as possible for music. Movies are a different subject where more is better since there's no reference for explosions, trains etc.

I don't listen to techno or pipe organ. However, everything I listen to has great bass that is tight and more than ample. (4) RS225's will move a lot of air and go down to the low 30's.

Jim

[kevinm]

5th, are you saying its a bad idea to run (4) 15in subwoofers and (4) 12 in woofers at maximum?!

Jim, that is a monsterous set of subs you have there! What are you running?

[Jim Holtz]

5th, are you saying its a bad idea to run (4) 15in subwoofers and (4) 12 in woofers at maximum?!

Jim, that is a monsterous set of subs you have there! What are you running?

Those are Exodus Audio Tempest X2's each in their own sealed compartment. They aren't near as crazy as most that hang out here. I'm much more concerned about 20 hz on up than I am below 20 and they have the ability to get as loud as needed and pound your chest when things go boom. 8O

As I said, I only use them for movies but if your taste runs to super strong bass in music, it'd be easy to roll them in for music too.

Jim

[5th element]

5th, are you saying its a bad idea to run (4) 15in subwoofers and (4) 12 in woofers at maximum?!

Haha, no not really, what's important is that the subs blend together well. If the main pair are flat down to 35Hz and you turn on a sub to extend from 35Hz and down, then things will carry on being flat. If however you add in the sub and use it up to 100Hz, you're going to get a lot of overlap between 35-100Hz, but only the mains above that and only the subs below. You will not have a flat frequency response any more. You need to provide a degree of filtering on the subs and the mains so that everything sums flat. I did this using lots of shelving filters.

The idea of having all those bass drivers covering 100hz and below actually excites me If you configure it all properly it should sound amazing. Oh and if you can, put one of the main subs in say the corner behind the left hand side loudspeaker as you listen to them. Then place the other sub in the corner behind the right hand speaker, but instead of it being behind the right hand speaker put it behind YOU, in the corner against the back wall along the right hand side.

[kevinm]

Jim, those seem like some nice transducers from what I've heard. The amount of rubber sure looks like they can move a lot of air because of their xmax. I prefer sealed subs as well. With me switching to the sealed statements, I'll need subs. So I think RSS390HOs should blend nicely.

5th, what are you using to put the shelving filters in your chain? And don't worry...I'm already warming the GF up to exploring sub locations. I've always wanted to try them behind the couch...good way to scare people

[jim1961]

One thing to keep in mind here is directionality. Directional queues are picked up by the ears from about 80hz and up. Much of the range from 50-150hz is therefore directional. I would be careful where I put units adding in this range.

[5th element]

5th, what are you using to put the shelving filters in your chain? And don't worry...I'm already warming the GF up to exploring sub locations. I've always wanted to try them behind the couch...good way to scare people

It's a self built DSP.

One thing to keep in mind here is directionality. Directional queues are picked up by the ears from about 80hz and up. Much of the range from 50-150hz is therefore directional. I would be careful where I put units adding in this range.

Nothing directional happens when the room is still largely modal, you can easily go up to 100Hz without any trouble in this regard. The trouble comes in with filter steepness. If the filter is too shallow then you're going get bleed through of a lot of higher frequency stuff and it is this that gives away a subs position. I actually run my subs up to 150Hz and don't have any issues with localising them. It's all about the implementation.

[jim1961]

Nothing directional happens when the room is still largely modal, you can easily go up to 100Hz without any trouble in this regard.

And a room where modes have been tamed?

I do agree with you that high sub XO points that use shallow filters (2nd order) are more a problem than those with lower XO points with steeper filters (4th order).

[5th element]

And a room where modes have been tamed?

Room modes aren't tamed, they are controlled. Even if you manage to get a flat frequency response within a rooms modal region it is STILL modal. The modal region refers to an area where the waves travel around and interact with the room in the certain way and is dependent on the wave length of the sound vs the rooms dimensions, you cannot change this.

[kevinm]

Well, this weekend I shall get to start cutting wood on the sealed Statement cabinets - yay! This means I need to get serious about my bass bins/MBMs for stands.

I was fairly set on the RSS390HO, but am piddle-paddling a little bit - wondering if it's too overboard to use four of these

So, assuming I can work with up to a 3ft ^3 cabinet (after bracings and such) under each speaker, I have been looking at the following drivers:

RSS265HF

http://www.parts-express.com/dayton-audio-rss265hf-4-10-reference-hf-subwoofer-4-ohm--295-460

RSS315HF

http://www.parts-express.com/dayton-audio-rss315hf-4-12-reference-hf-subwoofer-4-ohm--295-464

RSS390HO

http://www.parts-express.com/dayton-audio-rss390ho-4-15-reference-ho-subwoofer-4-ohm--295-469

The RSS265HF's would allow a substantially smaller box - which would be aesthetically pleasing. But I do max out at about 120db with my amp - still more than I need. On the opposite end of the spectrum, I can use the RSS390HO for pretty ridiculous output capabilities, but I do have a fairly large box - as seen above. Plus, a 15in under the Statement cabinet might be too overwhelming - especially next to my new beasts.

Using the RSS265 or RSS315 also allows me to use the HF version....thoughts anyone? Recommendations?

[Jim Holtz]

This is a picture of a Statements/Sub design similar to what you're thinking. The subs are 15" TC Sounds. My friend Chris built two pair plus a center for his system. It's quite awesome! 8O

Jim

[kevinm]

That is some beautiful wood grain and wood working skills! I'm very jealous!

I've decided after modeling to go with (4) RSS265HFs. Should give me plenty of clean bass in a nice small cabinet. CAD drawing to follow soon!

[---k---]

Fun.

[kevinm]

Alright, here is what I came up with.

Each cabinet is 2.3ft^3 net internal volume - leading to a Q of .694 for the two drivers. Here is the maximum SPL chart for 1 of the cabinets



Here is a CAD drawing of what I am building







The cabinet height is 18 inches, so with the 20in tweeter height on the sealed Statements, that should put the tweeter height at about 38 inches. With the 1-1.5inches for the feet, that should put the tweeter height just about perfect!

Now, which wood veneer/stain should I use?

[5th element]

Well you're certainly not going to lack for any bass in that room of yours!

[kevinm]

Update time:

I have all the wood cut, braces glued and baffles router. However, my braces ended up being a smidgen too wide, so it caused my side+brace+side total width to be wider than my bottom/top. So, I needed to trim some material off the brace edges.

In order to make it a little easier for myself, I build a guide out of wood that I could use to guide my router bit as I took 3/16in of an inch off.

First, the jig/guide. In order to keep the router tipping/toplling over, I need a decently sized surface area for the base to run on. From my experience, even my small trim router is too wobbly when using only (1) 3/4in board as a guide. Therefore, I ended using two and a 3/4in MDF gap. This allows the router to be supported on both sides of the edge and even use the sides as guide. It'll make more sense when you see the pictures below:



When clamped on, it looks likes this:



To ensure that I was trimming exactly 3/16 of an inch each board, I would level the guide on the board that was to be trimmed. I'd then adjust the router (and router guide) so the flush trim bit was barely touching the edge that was going to be cut. This is PRE-any trimming:



I'd set the guide on the router to 0:



Then lowered the bit to 3/16in:



Now, you're ready to trim!

It worked very well for me. My top bearing flush trim bit just bounced off the sides of the guide, so I had plenty of control. Additionally, having a piece of MDF on either side of the board I was trimming made sure my router wasn't wobbly.

[bostonmurf]

outstanding work Kevin, and can i also add amazing photography!!! it nice to see the build THIS close, shows how much care and effort you put into your projects.

[kevinm]

Thanks! It's actually just the new iPhone. It still blows me away at how nice the pictures turn out.

[kevinm]

I'm going to merge this with my other thread. If anyone is reading this and wants to see more jump on over to this thread:

https://www.htguide.com/forum/showthread.php?42064-Sealed-Statements-2-0-Center-Channel