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HI Folks,
My post presenting my Pocket Rocket 805 system generated interest concerning subwoofer integration. I’m writing this in response to that interest and because I assume that others are facing the same issues. I’m making this a new post because I think it will be more accessible here rather than hidden in the other thread.
I have definite opinions on this subject so be warned. I will try to be clear when I stating fact or opinion. Not everybody will agree with my ideas. Feel free to contribute.
This is a big subject and I want to do it as right as I can. So I have decided to write it in sections. This will give me a chance to answer questions, make corrections, and see if I’ve generated understanding or total chaos. This first section will deal with the most important issue; selection of the main speakers and subwoofers.
Moderators: If you think this article is too long, too ambitious, or misplaced (or flat out wrong) let me know. I will accommodate your ideas and needs.
What is subwoofer and main speaker integration? It is the method used that results in the presentation of a unified sonic structure from the highest highs to the lowest lows produced by a speaker system that consists of a main full range speaker and a purpose designed subwoofer. Ideally, the subwoofers presence should not be detectable as separate from the main speakers. It should sound as if you have a single super speaker that produces the entire frequency range that is completely seamless. Often, the sound of the sub is audible as separate source from the main speakers. Worse, the subs and mains can overlap and produce very boomy bass at the crossover frequency that is very fatiguing and irritating. Another case is the sub and mains don’t overlap at all producing a hole in the frequency response and causing the speakers to appear obviously separate. Good integration takes these and other things into consideration and makes appropriate corrections to achieve a seamless joining. The effort to do so is worth the trouble.
Here we will explore methods to maximize integration to get bass to die for. I will concentrate on music reproduction because I know more about it and if you solve the problem for music it will also work for theater systems. However, systems used primarily for theater often are composed of different components which reflect theater priorities. These can be more difficult to integrate for music.
The most important first step in integration is proper selection of the speakers. Here I impose my opinions. Be warned; I will do so throughout this essay. I think it is easier to integrate a main speaker that has limited bass extension. More important than bass extension is how the speaker behaves in its bottom octave. Let’s examine a hypothetical speaker that has a low frequency cut off of say -6 dB at 50 Hz. That means it is outputting ½ the sound pressure at 50 Hz than it does at 1kHz, a common 0 dB reference. A further reduction of frequency results in lower output. The speaker is at its bass cutoff frequency where bass rapidly becomes inaudible with lower frequencies.
In order to stretch the usable bass as low as possible, the enclosure is often (always?) tuned to give an increased output in the bottom octave before the cutoff frequency is reached. Ported boxes are common violators. This is known as reflex sound. Ideally, the speakers output would remain constant until the cutoff frequency is reached then roll off smoothly. This is rarely (never?) the case. What you are after is a bottom octave that exhibits little or no rise. Careful listening to bass instruments should reveal the best performers. Also, male spoken voice can reveal lumpy low bass. Smooth, no boom; that’s the goal. Don’t worry too much about bass extension. I feel 50 Hz is plenty with the right sub.
Don’t forget other normal good speaker characteristics especially solid box construction. Rap on it with your knuckles. It sound like a solid block of wood not like a dry wall construction. This is Very important and also rare.
Now we can select the sub. Subs with built in amplifiers and crossovers will be assumed. Here is where things get complicated. There are very many different sub designs and they all have different strengths and weaknesses. There is no silver bullet, only tradeoff’s. Here are some basic ground rules: Bigger is better for any given room. 8” drivers are a joke meant for computer speakers. 10” is still not serious. 12” is getting there but you better have a small room. 15” can do a good job. 18” should be used for large rooms and can do a fine job in smaller rooms. Dual matched subs are always better than a single sub. There are several reasons for this but most important is they give double the driver cone area. People don’t seem to realize the enormous amount of air that must be moved at low bass frequencies. That’s why you need large and/or multiple subs.
Next, down firing drivers are the most difficult to integrate. These are common because they are relatively efficient at very low frequencies. However, because they are slot loaded around the floor opening, they have an increasing output as the frequency rises. This is very difficult to compensate for. I don’t like them but they can give very impressive lowest octave performance. Many subs place the driver cone in a closed servo loop that compares the cone motion with the input signal and corrects the output to match. This can work but it’s very tricky. Others drive the cone directly with an equalized signal from the onboard amplifier. These are probably sonically best but they usually don’t give as much extension as other techniques. The bottom line is sub selection is very difficult without extended listening and experimentation and a solid set of sonic priorities.
For this reason I recommend buying a sub made by the same manufacturer as your selected main speakers. Definitely do this if you are forced to buy without listening (not a good idea). But this is not a silver bullet either. One would hope that a makers subs would be designed for easy integration with their own mains and still give good bass performance. It’s often not true. The problem is expense. Really good subs are expensive (it’s a cosmic law); often out proportion to the cost of the mains. So quality is sacrificed to bring the price down. So, you may have to make a decision whether to change to another maker of the mains to get a compatible sub. That can be tough decision. But remember, we are putting together a system and it is the total performance that concerns us.
I’m going to close this section with a reminder. Do a lot of listening. Putting together a well chosen main/sub system can seem daunting but your ears will reveal the truth. You will learn as you go. Make it fun and not work. Take your own recordings to the listening sessions. Make VERY sure you always do your serious listening at the same volume. This so important that I recommend that you run down to Radio Shack and buy a Sound Pressure Level Meter and use it to calibrate every listening session. They are not very expensive when you compare the cost to the cost of your audio investment.
See ya later, Sparky
My post presenting my Pocket Rocket 805 system generated interest concerning subwoofer integration. I’m writing this in response to that interest and because I assume that others are facing the same issues. I’m making this a new post because I think it will be more accessible here rather than hidden in the other thread.
I have definite opinions on this subject so be warned. I will try to be clear when I stating fact or opinion. Not everybody will agree with my ideas. Feel free to contribute.
This is a big subject and I want to do it as right as I can. So I have decided to write it in sections. This will give me a chance to answer questions, make corrections, and see if I’ve generated understanding or total chaos. This first section will deal with the most important issue; selection of the main speakers and subwoofers.
Moderators: If you think this article is too long, too ambitious, or misplaced (or flat out wrong) let me know. I will accommodate your ideas and needs.
What is subwoofer and main speaker integration? It is the method used that results in the presentation of a unified sonic structure from the highest highs to the lowest lows produced by a speaker system that consists of a main full range speaker and a purpose designed subwoofer. Ideally, the subwoofers presence should not be detectable as separate from the main speakers. It should sound as if you have a single super speaker that produces the entire frequency range that is completely seamless. Often, the sound of the sub is audible as separate source from the main speakers. Worse, the subs and mains can overlap and produce very boomy bass at the crossover frequency that is very fatiguing and irritating. Another case is the sub and mains don’t overlap at all producing a hole in the frequency response and causing the speakers to appear obviously separate. Good integration takes these and other things into consideration and makes appropriate corrections to achieve a seamless joining. The effort to do so is worth the trouble.
Here we will explore methods to maximize integration to get bass to die for. I will concentrate on music reproduction because I know more about it and if you solve the problem for music it will also work for theater systems. However, systems used primarily for theater often are composed of different components which reflect theater priorities. These can be more difficult to integrate for music.
The most important first step in integration is proper selection of the speakers. Here I impose my opinions. Be warned; I will do so throughout this essay. I think it is easier to integrate a main speaker that has limited bass extension. More important than bass extension is how the speaker behaves in its bottom octave. Let’s examine a hypothetical speaker that has a low frequency cut off of say -6 dB at 50 Hz. That means it is outputting ½ the sound pressure at 50 Hz than it does at 1kHz, a common 0 dB reference. A further reduction of frequency results in lower output. The speaker is at its bass cutoff frequency where bass rapidly becomes inaudible with lower frequencies.
In order to stretch the usable bass as low as possible, the enclosure is often (always?) tuned to give an increased output in the bottom octave before the cutoff frequency is reached. Ported boxes are common violators. This is known as reflex sound. Ideally, the speakers output would remain constant until the cutoff frequency is reached then roll off smoothly. This is rarely (never?) the case. What you are after is a bottom octave that exhibits little or no rise. Careful listening to bass instruments should reveal the best performers. Also, male spoken voice can reveal lumpy low bass. Smooth, no boom; that’s the goal. Don’t worry too much about bass extension. I feel 50 Hz is plenty with the right sub.
Don’t forget other normal good speaker characteristics especially solid box construction. Rap on it with your knuckles. It sound like a solid block of wood not like a dry wall construction. This is Very important and also rare.
Now we can select the sub. Subs with built in amplifiers and crossovers will be assumed. Here is where things get complicated. There are very many different sub designs and they all have different strengths and weaknesses. There is no silver bullet, only tradeoff’s. Here are some basic ground rules: Bigger is better for any given room. 8” drivers are a joke meant for computer speakers. 10” is still not serious. 12” is getting there but you better have a small room. 15” can do a good job. 18” should be used for large rooms and can do a fine job in smaller rooms. Dual matched subs are always better than a single sub. There are several reasons for this but most important is they give double the driver cone area. People don’t seem to realize the enormous amount of air that must be moved at low bass frequencies. That’s why you need large and/or multiple subs.
Next, down firing drivers are the most difficult to integrate. These are common because they are relatively efficient at very low frequencies. However, because they are slot loaded around the floor opening, they have an increasing output as the frequency rises. This is very difficult to compensate for. I don’t like them but they can give very impressive lowest octave performance. Many subs place the driver cone in a closed servo loop that compares the cone motion with the input signal and corrects the output to match. This can work but it’s very tricky. Others drive the cone directly with an equalized signal from the onboard amplifier. These are probably sonically best but they usually don’t give as much extension as other techniques. The bottom line is sub selection is very difficult without extended listening and experimentation and a solid set of sonic priorities.
For this reason I recommend buying a sub made by the same manufacturer as your selected main speakers. Definitely do this if you are forced to buy without listening (not a good idea). But this is not a silver bullet either. One would hope that a makers subs would be designed for easy integration with their own mains and still give good bass performance. It’s often not true. The problem is expense. Really good subs are expensive (it’s a cosmic law); often out proportion to the cost of the mains. So quality is sacrificed to bring the price down. So, you may have to make a decision whether to change to another maker of the mains to get a compatible sub. That can be tough decision. But remember, we are putting together a system and it is the total performance that concerns us.
I’m going to close this section with a reminder. Do a lot of listening. Putting together a well chosen main/sub system can seem daunting but your ears will reveal the truth. You will learn as you go. Make it fun and not work. Take your own recordings to the listening sessions. Make VERY sure you always do your serious listening at the same volume. This so important that I recommend that you run down to Radio Shack and buy a Sound Pressure Level Meter and use it to calibrate every listening session. They are not very expensive when you compare the cost to the cost of your audio investment.
See ya later, Sparky
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