Two subwoofers for two different and narrower subbass ranges

[Balmer]

I am considering substituting a subwoofer for the range below the LaScala in the Khorn range as a substitute for the BIG Khorn bass box. Then use another subwoofer for the sub Khorn range. I have found from my experience that one subwoofer covering the full sub LaScala range doesn't work well. It seems that subwoofer volume levels drop off quickly within the first 10 dB. If I want to hear organ notes in the sub 30 Hz level on par with the LaScala, then the subwoofer volume levels above 30 Hz are too loud and unnatural. If I had two subwoofers while using an active crossover, I could set the first one from the threshold of the LaScala to 32 Hz. which is the Khorn range, and the second subwoofer below that to the limits of the room. Each subwoofer could have it's own amp and volume control so the frequency range could be more linear throughout the entire bass and sub bass ranges. The Khorn box is an eye sore aesthetically, but replacing the Khorns with LaScalas and putting two subwoofers in the rear of the room would solve that problem. However, I will not do this unless the Khorn bass sound can be substituted convincingly. What are your recommendations?

Presently Iam using Khorns with two TacT passive subwoofers each with a range down to 13 Hz. The avtive crossover is set at 32 Hz.

[wuzzzer]

Hsu has done this with their MBM-12 module. Its low end is 50Hz and you can adjust the top end from 80 to 150Hz. You can then use another subwoofer for 50Hz on down.

It worked great for the old SVS PC-Plus 16-46 that I used to have. The 16-46 was awesome for deep bass but didn't have the slam factor.

Only reason I sold that combo was my CS-Ultras provide both mid-bass slam and deep bass extension.

[Islander]

Why would you place the subs at the rear of the room? You know what works best in your room and it would make sense for movie explosions and the like, but for 2-channel music at least, all the sound, including bass notes, would come from the area of the main speakers at the front of the room.

[Balmer]

Why would you place the subs at the rear of the room? You know what works best in your room and it would make sense for movie explosions and the like, but for 2-channel music at least, all the sound, including bass notes, would come from the area of the main speakers at the front of the room.

Islander, the upper sub woofer will cover a half an octive range from 50Hz to 32Hz which is the frequency range of the Khorn up to the lowest point of the LaScala. The full wave length of these frequencies is from 24 to 32 feet, or the half wave length which is enough room to hear the notes is from 12 to 16 feet. Since the listening room is 13 by 20 feet, these frequencies are omnidirectional. This means you could put these woofers anywhere in the room (front, side, rear) and you couldn't tell the original location of the sound. The second subwoofer will cover a full octive below that from 32Hz down to 16Hz. The full wave length of these frequencies is from 16 to 64 feet. I doubt if 16 Hz will even be developed at all in the listening room.

[DrWho]

these frequencies are omnidirectional.

Omnidirectional means the sound sprays in every direction from the source. Just because it is omnidirectional does not mean it is not localizeable. While bass frequencies certainly become increasingly more difficult to pinpoint, they can still be rather localizeable...

I doubt if 16 Hz will even be developed at all in the listening room.

The size of the room does not determine the lowest frequency that is able to be reproduced. The best example is headphones....you can hear low frequencies through headphones, despite the fact that the acoustical space (or "room") that the headphones is firing into is the sapce between the headphones and your ear drum. Using your assumption, low frequencies should not be audible in headphones. However, it turns out that they are...

That said, low frequencies take longer to rotate through their phase (that's kinda the definition of low frequency), so when the room is small enough, the reflections in the room tend to be short enough to still be in phase (or really close) with the driver making the sound. This in turn increases the coupling of the driver to the air in the room and increases the amplitude of the signal.....creating what is commonly referred to as room gain.

As far as running two subwoofers over two bandwidths....that's fine and all, but is kind of a waste - especially if you're using two of the same subwoofer. You will have lower distortion, possibly better modal response, and more headroom using two identical subs to cover the same range.

If you're having trouble blending your subwoofer with your mains, then I would suggest that you simply don't have things dialed in correctly. I'm not quite clear on the whole configuration and the equipment you're using, but I would try to get the most out of your configuration before spending money. But if you're really set on your propose plan, then I would certainly encourage finding out for yourself. Just try to keep time and phase alignment in mind....especially when dealing with horns.

[Islander]

the upper sub woofer will cover a half an octive range from 50Hz to 32Hz which is the frequency range of the Khorn up to the lowest point of the LaScala.

I've found that La Scalas (mine, at least) start to roll off at around 90Hz, and I get the smoothest bass response running the sub all the way up to 150Hz. The sub's upper-end rolloff seems to be sort of gradual, so it blends well with the La Scalas with that setting. My room is 18' x 19', opening on one side to a vestibule, hallway and dining room, so it's sort of like 18' x 30', if that helps.

Posted specs and in-room performance can be quite different.

Have you tried using an equalizer with your sub? I was getting a very irritating peak at 32Hz and a dip at 60Hz, even with the sub in its optimum location (I tried several other spots first), and the EQ helped a lot. I didn't completely EQ out the peak and dip, but I was able to make them less noticeable, so that was worth it to me. I used an old 10-band stereo EQ that I hadn't used in years, connecting only one channel of it.

[Balmer]

As far as running two subwoofers over two bandwidths....that's fine and all, but is kind of a waste - especially if you're using two of the same subwoofer. You will have lower distortion, possibly better modal response, and more headroom using two identical subs to cover the same range.

If you're having trouble blending your subwoofer with your mains, then I would suggest that you simply don't have things dialed in correctly. I'm not quite clear on the whole configuration and the equipment you're using, but I would try to get the most out of your configuration before spending money. But if you're really set on your propose plan, then I would certainly encourage finding out for yourself. Just try to keep time and phase alignment in mind....especially when dealing with horns.

DrWho, thanks for the clarification. It's never too late to learn new tricks. As for using two subwoofers dividing up one and a half octives, I'm trying to keep the sound levels as flat as possible throughout the 50 to 16Hz range. I am able to to get the sound level of the subwoofer in the 32 to 16Hz range the same as the LaScala. However, while using only one subwoofer to cover the full 50 to 16Hz range, the 50 to 32Hz range is about 10 dB louder than the 32 to 16Hz range. I was thinking of using a separate amp and attenuator to lower the 50 to 32Hz range down to the same level as the others. Will this work? What do you mean about time and phase alignment?

[Balmer]

the upper sub woofer will cover a half an octive range from 50Hz to 32Hz which is the frequency range of the Khorn up to the lowest point of the LaScala.

I've found that La Scalas (mine, at least) start to roll off at around 90Hz, and I get the smoothest bass response running the sub all the way up to 150Hz. The sub's upper-end rolloff seems to be sort of gradual, so it blends well with the La Scalas with that setting. My room is 18' x 19', opening on one side to a vestibule, hallway and dining room, so it's sort of like 18' x 30', if that helps.

Posted specs and in-room performance can be quite different.

Have you tried using an equalizer with your sub? I was getting a very irritating peak at 32Hz and a dip at 60Hz, even with the sub in its optimum location (I tried several other spots first), and the EQ helped a lot. I didn't completely EQ out the peak and dip, but I was able to make them less noticeable, so that was worth it to me. I used an old 10-band stereo EQ that I hadn't used in years, connecting only one channel of it.

It sounds like we both are having the same problem, however, my problem starts at 32Hz and gets progressively louder as the frequencies increase. I have not tried an equalizer. I used an analog equalizer thirty years ago and was disappointed with the distortion. I guess the quality of the equipment has improved since then. I had no idea that I would have to start the subwoofer at 150Hz! This is a whole new ballgame. I wonder if there are digital equalizers or room correction processors that will serve that purpose?

[Islander]

I'm using an old analogue equalizer for the sub only. I wouldn't use it for the main speakers, since it has a slight veiling quality, but I reasoned that would be much less noticeable at the sub frequencies and it is. It tamed the two problem areas in the low-end response, which may actually be room-related, rather than sub-related.

There are more modern and more accurate ways to correct room response and Dr Who is very knowledgeable about the pros and cons of doing this. I just used a unit I had on a shelf and it's good enough for my purposes.

Although it's now considered to be old-school and not the very best way to go, you might want to get yourself an SPL meter and a test CD or other test sound source and see what your speakers' in-room low-end response actually looks like. It's never as simple as the specs would imply.