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Old 16th September 2008, 03:44 AM   #711
jdubs is offline jdubs  United States
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Nice! Thanks Earl! Glad to hear that simpler is better when it comes to subs. Also, I assume 24db slope is required?

Now, does anyone have any good leads on a trio of downward firing subs? I'm guessing these need to be on the powerful side to keep up with the spl capabilities of a pair of Nathans?

-Jim
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Old 16th September 2008, 06:05 AM   #712
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Jim, you can make just about any DIY sub down firing. You just have to check the driver will handle mounting this way - some will sag too much. There are formulas to work it out. It relates to things like xmax, stiffness, moving mass and how much sag will occur relative to xmax as a result.

As far as how much output you require, that depends on a number of things. Also, simply because your mains can handle 120 db doesn't mean your subs need to as well, especially if you are driving them with a valve amp. You also have to take into account your room and your preferences. You might have a lossy room, or you might have a room with very little damping at all.

So it's a bit like asking how long is a piece of string! Unless you have a more specific target. Even if you were to say that you want 6 db more output capability than the Nathans, the answer will be highly room dependent.

Case in point. I heard a 10" 200w sub in a local show room - very solid with concrete floor, relatively large in size, solid split face masonry walls on all sides and four bass traps. I was impressed with the impact, but also the accuracy. The driver had 18mm xmax. In my more lossy room it would be underwhelming. Despite being a smaller room, I use two 12" drivers with 18mm xmax and 370w each to get a similar result.

But now this is getting off topic ...
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Old 16th September 2008, 04:22 PM   #713
gedlee is offline gedlee  United States
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Quote:
Originally posted by jdubs
Nice! Thanks Earl! Glad to hear that simpler is better when it comes to subs. Also, I assume 24db slope is required?

Now, does anyone have any good leads on a trio of downward firing subs? I'm guessing these need to be on the powerful side to keep up with the spl capabilities of a pair of Nathans?

-Jim
I wouldn't bother with 24 dB LP slopes, 12 dB is fine and I can even see 6 dB working is carefully done. The subs need to overlap each other AND the mains so sharp transitions between them is not only not required, but undesirable.

Since there are three subs, they can be less efficient than the mains. I find that the mains almost always have more SPL headroom than necessary and subs don't need nearly as much headroom because of the limited bandwidth. Hence a sub that is about 3 dB less efficient than the mains will probably work fine as long as you use at least three of them. Use four and there is certainly no problem.

But then again, its not the efficiency that matter its the Max SPL, but this is hard to find in the marketplace. You can estimate it from the efficiency and the power handling, but both of these numbers tend to be exagerated in the same direction. Ideal is to match the MaxSPL of the total of all LF devices (include one main in this calculation) with the MaxSPL of the mains.
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Old 17th September 2008, 06:01 AM   #714
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Earl, I have read in an AES paper (forgot which one) that below 80 Hz the ear is incapable of hearing the location of a sound source, but above 80 Hz the ear starts being able to localize the source. This implies that if the crossover is going to be up in that region for a sub that will be positioned well away from the main speakers, then a steep-slope crossover would be desirable to prevent the ear from hearing the location of the sub from lower midrange energy that is insufficiently suppressed.

Am I missing something?

Also, seems to me the gradual blending you describe would be practical with main speakers that have a gentle rolloff, like your low-Q sealed boxes, but wouldn't one achieve a better blend with vented speakers using a steeper slope? Sort of like doing a crossover elsewhere in the spectrum, where we probably wouldn't want a first or second order acoustic on one side and fourth order acoustic on the other unless that was the best we could do.

Again, am I missing something?

Thanks,

Duke
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Old 17th September 2008, 07:20 AM   #715
Pallas is offline Pallas  Pakistan
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Originally posted by gedlee
I'll be honest - the simpler the better. Just three of the simple woofer facing down self powered subs work fine. I see these at Costco all the time and they are a tremendous deal.
Are you saying downfiring for sonic reasons, or is that an aesthetic preference?
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Old 17th September 2008, 07:28 AM   #716
col is offline col  Australia
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Default The Bottom End

This is a little off topic but why we are on the topic of subs and placement. I thought people might be interested in this radio show that was on the other night. At the end of it there is a sound engineer describing how he used subs in a figure-of-eight configuration to cancel out muddiness in a large outdoor concert.

ABC: Into The Music

The Bottom End

http://www.abc.net.au/rn/intothemusi...08/2338883.htm
rtsp://media1.abc.net.au/rn/mod/itm_06092008_2856.rm

Join Cathy Peters as she searches for the low down on low sound from night clubs and car shows to university sound laboratories and CD mastering suites. The 'bottom end' permeates most aspects of music these days; whether it's the vibrating car next to you or the rumble of your neighbour's new sub woofer, you just can't escape it.

Offering all you ever wanted to know about low frequency, high density sound waves, this program explores the good, the bad and the ugly effects of the 'bottom end'. Speakers include acoustician Densil Cabrera, audiologist Chris Whitfield, mastering engineer Steve Smart, sound theorist and practitioner Eliot Palmer, ABC Classic FM recording engineer Jim Atkins and acoustic bass player Lloyd Swanton. First broadcast on Into the Music in 2007, this program won a silver medal at the 2008 New York Radio Festival awards.

Produced by
Cathy Peters

Sound engineer
Louis Mitchell
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Old 17th September 2008, 03:02 PM   #717
gedlee is offline gedlee  United States
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Quote:
Originally posted by audiokinesis
Earl, I have read in an AES paper (forgot which one) that below 80 Hz the ear is incapable of hearing the location of a sound source, but above 80 Hz the ear starts being able to localize the source. This implies that if the crossover is going to be up in that region for a sub that will be positioned well away from the main speakers, then a steep-slope crossover would be desirable to prevent the ear from hearing the location of the sub from lower midrange energy that is insufficiently suppressed.

Am I missing something?

Also, seems to me the gradual blending you describe would be practical with main speakers that have a gentle rolloff, like your low-Q sealed boxes, but wouldn't one achieve a better blend with vented speakers using a steeper slope? Sort of like doing a crossover elsewhere in the spectrum, where we probably wouldn't want a first or second order acoustic on one side and fourth order acoustic on the other unless that was the best we could do.

Again, am I missing something?

Thanks,

Duke
I wouldn't agree with the 80 Hz number for localization. I think that its much higher. And what do we mean by "localization" in this context? Do we mean where the source sounds like it is coming from? Or do we "hear" the location of the sub? These are completely different things.

If I am listening to a bass guitar it will have harmonics well up above the LF region that the subs act in. The listener will tend to hear the location of the player bassed on the HF localization cues from the mains, as long as there aren't any contradictory cues at LF. So it is important to keep the sound from the subs above their LF passband as low as possible which is why I use bandpass subs (acoustic LP).

If you can actually hear or physically place the location of the subs, then quite simply, it is too loud. Only the mains should ever provide any localization cues for a bass instrument.

As to your question about "crossover" for subs to mains that are ported, well I don't do this and don't recommend it. So your question is really "I'm not going to do what you recommend, so then what should I do it?" - to that I don't have an answer (except maybe "Block off the ports"?)

Quote:
Originally posted by Pallas


Are you saying downfiring for sonic reasons, or is that an aesthetic preference?
It's a practical solution based on marketplace availability that is neither sonically prefered (IMO, I prefer true bandpass designs) or that aestheticly pleasing (to me). The downfiring will tend to lower the HF content from the sub which is desirable for the reasons stated above.
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Old 17th September 2008, 03:12 PM   #718
soongsc is offline soongsc  Taiwan
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Regarding localization, if you only listen to single tone signals, then probably 80 hertz is about right. However, if you are listening to a musical instrument the extend from higher frequency into this range, you will notice shift between clear focus and lose of location focus as the instrument is played, which makes the musical instrument sound unnatural if below 80Hz is not treated as normal stereo signal.
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Old 17th September 2008, 03:19 PM   #719
gedlee is offline gedlee  United States
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Its been a long time since I listened to pure tones - music is so much more entertaining.

I don't agree with you statements. Mono LFs is the standard in virtually all CDs and works fine in all the rooms that I have built.
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Old 17th September 2008, 03:32 PM   #720
soongsc is offline soongsc  Taiwan
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Most people have not listed to live performances with unamplified instruments for a long time as well. But I do agree there are difference in preferences.
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