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How to pair large and small sub?

F

FreshJR

Member
I want new speakers for a 5.1 HT setup. I can't do large speakers in the front (depth > 5") or floor standing tower due to living room constaints. On the other hand I like DEEP bass, and want a large sub.

The issue with this is that large subs typically do the 20-80hz frequency well and that small speakers do 120hz+ well.

This means I will have a hole from 80hz-120hz.


Is it possible to run

large sub - 20-80hz
small sub - 80-120hz
small speakers - 120hz+

I think it is, but the problem is that I dont want the small sub also doing 20-80hz due to phase response issues between different subwoofer sizes cancelling out bass.

Is their a high pass frequency filter for 80hz that I can use with a RCA line input, that works well?

Is there anything I could do?
 
It's going to depend on the actually in-room freq. response. Also one must take care to avoid cancellation effects of two subs sometimes. In general, one sub is all one would need.
 
Having no idea what your fronts are capable of, or what your room layout is, I would say that you should:

1) draw up a floor plan
2) measure the existing in-room response

Multiple subs do serve a purpose, but for you, a single sub would probably do best.
 
Howard said:
Having no idea what your fronts are capable of, or what your room layout is, I would say that you should:

1) draw up a floor plan
2) measure the existing in-room response

Multiple subs do serve a purpose, but for you, a single sub would probably do best.
Click to expand...

I don't have any front speakers right now, but this frequency hole is not going to change no matter what room if I want to use a large sub.

Ultimately, I still want that low end rumble and no small sub can provide it.

I looked, but no fronts that are small and hit 80hz are available. The smallest depth to hit the 80 hz was an 8" depth with an 11" inch depth being the average.

From looking at a lot of sub frequency responses almost all 12 inch subs taper off after 80hz pretty quick.. I found this to be true even in the ultra high end subs.

When looking at smaller subs at an 8inchs, even the cheap subs, do 30-120 hz without any problems.


Since I will be missing the 80-120hz from the fronts/center, would using a high pass filter on a small sub fill the gap without interfering with with the other sub and causing cancelling effects.
 
Last edited:
FreshJR said:
I don't have any front speakers right now, but this frequency hole is not going to change no matter what room if I want to use a large sub.

Ultimately, I still want that low end rumble and no small sub can provide it.

I looked, but small no small fronts that hit 80hz are available. The smallest depth to hit hz with either fronts or centers was an 8" depth with 11" being average.


I looked at a lot of sub frequency reponses and most 12 inch subs do 20-80hz well, and quickly taper off. I found this to be true even in the ultra high end.

When looking at evn cheap subs, all smaller subs at an 8inch do 30-120 hz with no problem.


Since I will be missing the 80-120hz from the fronts/center as expected, would using a high pass filter on a small sub fill the gap without interfering with with the other sub and causing cancelling effects.
Click to expand...
You seem to know exactly what you're doing. Carry on.
 
As Howard was trying to say, speaker specs are completely different from in room measurements. Room acoustics pose severe challenges that, unless understood, render most considerations of just specifications irrelevant.

Because room acoustics is quite complicated in terms of considering a lay person, the best approach is to buy your speakers and set them up optimally within your room taking into consideration optimal listening position and reducing unwanted reflections from close surfaces. Once the listening position and speaker position are optimized, you have achieved pretty much most of what is possible in your room before considering acoustic products e.g. diffusers and bass traps and the like.

At this point, you can measure the effect of the room on the frequency response and you will be surprised with what you get. Rooms are quite different acoustically than anechoic chambers.

Adding a subwoofer to a system isn't just as easy as it sounds if you want good results. The bass below 150hz or so is extremely prone to room acoustical effects. This is ameliorated by very careful placement of the subwoofer within the room to minimize the resonate effects of room modes due to the dimensions of your room. Adding two subwoofers can make this task very challenging, even more so if the subwoofers are different from each other.

My point is this, even with two subwoofers you will never be guaranteed full spectrum sound. I have two speakers that can reach down to 30 hz and two subwoofers that are good from 18 hz to 150hz. It took me an entire weekend to set them up optimally within my room using acoustics software and a microphone with some sine wave tones. In the beginning prior to careful setup, I had no response at 40hz and 90 hz. This had nothing to do with my speakers or subwoofers specs and everything to do with room acoustics.

In the end if you still want to do things your way, be very prepared to put in the time to set it up otherwise you will be in over your head as to what exactly to do to fix acoustical issues. Hsu has a mid bass woofer in addition to full bass woofers. Some people have found success in using the mid bass woofer to fill in tiny speakers. This is a bandaid because you have an additional box in your room, going against any minimalist ideal that exists which forced yourself to use tiny main speakers in the first place. That additional box usually has to be placed in a conspicuous spot in the room in order to do it's job. In addition, you have the real subwoofer to contend with in terms of in room cosmetics and acoustics. This is a major thing to consider.

My fingers are tired to I have truncated my response. Do note that I haven't even talked about how to correctly size the subwoofers to your needs. It could be that your physical requirements on the subwoofer size to develop deep bass is already impossible...
 
a little more description of the house you are in might help. do you have an attic over the living room or basement under it? IB sub might solve your issue.
 
biostud said:
120hz as the lowest sounds a bit weird. What speaker system is it?
Click to expand...

I haven't bought the speakers yet, but I actually was looking at energy classic speakers due to their 4" depth.

The room is pretty big, 25' x 25' that's why I would like a bigger sub than the one that comes with the energy speakers if possible.

I attached a picture of the room.

If you look at it, the reason I can't have large fronts/center is because the TV is mounted on a wall next to an opening door and a common walking area. Any speaker that protrudes further than 5" looks really off, so its really a big aesthetics vs performance trade off, where I'm trying to regain the performance.

setupz.png
 
Your main listening position is up against a wall. This is the worst possible acoustic position for all frequencies including bass due to the reflections off of the wall competing severely with the source sound. You will be unable to recapture your lost bass by buying more subwoofers alone without relocating your listening position. Also from your picture, it looks like the likely spot you would place the subwoofer is in a corner which is away from foot traffic. Corner location subwoofers exacerbate all three room modes to a maximal extent which renders the main listening area even worse off. "One note bass" effects would render your experience intolerable and even headache laden. I hate being Rhee barer of bad news but physics is physics 🙁
 
I'd move the TV to the door side where the couch is before i invested any money in audio equipment. I'd move the big couch so the back faces the island. Even that isn't a perfect configuration, but at least then you can have decent sized speakers up front.

Without that, you have what Tiamat says. You're screwed by physics.
 
the room is what the room is.

I can't really do anything about that. I was thinking of putting the sub against the left raer of the small couch in the rear of the picture.

If that didn't work then against all the way to rear left cornefof the room with the sub facing the coach.

Some sub is better then the micro speakers in the TV. does anyone have any ideas even if its not optimal
 
Yes you can run the two subs that way. There will be some bleed between them and depending on room characteristics there could be a bit of a dip between the mains and the smaller sub. It's not a bad idea to be honest, running differential subs. It really all depends on the room. Placement obviously is key and with subs if you can, always try them out in the room before settling on what you want.
 
Most better in-wall brands come with in-wall cabinet options. It's preferred if you have cheaper drywall or sheetrock. Actually I'd say with the bracing options it provides it's probably preferred in every situation. The wall will still offer resonance but it's severely reduced by having this option. It's a decent choice if you want the speakers out of the way. Just make sure to buy speakers with pivotable tweeters, and if possible a cutoff/boost function. Even with cabinet options it can help with off center placement.
 
I'm surprised no one has offered this advice, but what you want to do is actually very simple. Just run your front speaker outputs to the speaker-level inputs on your small sub, then plug your front speakers into the pass-though. Set the crossover on the small sub to 120 Hz.

Then run your large sub from the LFE output of your receiver.

In your receiver settings, set the LFE crossover to 80 Hz.

Now you will have the large sub play 0-80Hz, the small sub play 80 Hz-120 Hz, and the fronts play 120Hz+
 
thomsbrain said:
I'm surprised no one has offered this advice, but what you want to do is actually very simple. Just run your front speaker outputs to the speaker-level inputs on your small sub, then plug your front speakers into the pass-though. Set the crossover on the small sub to 120 Hz.

Then run your large sub from the LFE output of your receiver.

In your receiver settings, set the LFE crossover to 80 Hz.

Now you will have the large sub play 0-80Hz, the small sub play 80 Hz-120 Hz, and the fronts play 120Hz+
Click to expand...

You assume the sub has speaker level inputs connected to an internal crossover and step-down circuit.
 
thomsbrain said:
I'm surprised no one has offered this advice, but what you want to do is actually very simple. Just run your front speaker outputs to the speaker-level inputs on your small sub, then plug your front speakers into the pass-though. Set the crossover on the small sub to 120 Hz.

Then run your large sub from the LFE output of your receiver.

In your receiver settings, set the LFE crossover to 80 Hz.

Now you will have the large sub play 0-80Hz, the small sub play 80 Hz-120 Hz, and the fronts play 120Hz+
Click to expand...

I've never cared for the loss in sound quality you get doing it that way. I don't care for the impedence hikes, frequency slope hit, or potential for thermal runaway. The possible strain on the amp that results means the potential to trip the protection circuit is increased.

To answer the original question, MK used to make a 80hz filter that worked very well. The problem is finding one. It's been years since I've seen it.
 
There are other options, but all come with headaches. Duel subs have issues all to themselves. Remember that crossovers are not hard frequency stops. It isn't that sound that is 79Hz works on the sub, but 80Hz is played on the speaker. There is typically a two octave range that a crossover effects (an octave is a doubling of the frequency, so one octave above 80Hz is 160Hz, one octave below 80Hz is 40Hz). A typical 80Hz crossover means that a sub will still be playing a 160Hz frequency, just 12db softer than the speakers. That means your multiple subs and speakers will be playing the same frequencies (just softer depending on the frequency), which means you now have to deal with phase-shift due to distance differences and room reflections which will create all kinds of frequency peaks and valleys depending on your listening location in the room (even different from your left ear to your right ear!).

An external crossover would help you get the right frequencies to the right sub, but you still have to fix the placement issues to resolve the constructive and destructive wave interference that will occur when a frequency that is played on both subs (and in this case, potentially both subs and the speakers). This can be a nightmare. The best you can attempt to do is force the interference bands to be in height by stacking the subs.
 
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