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Discussion Starter #1 (Edited)
Just curious, wondering what sort of results one can expect with a single 21" bass driver for a subwoofer?

I have noticed a few while looking for my budget drivers, though expensive do they offer more than a pair of 15" or 18" drivers? How does a 21" sound? Is it slower with less slam, any sort of signature sound?

Still trying to work out what direction may be best in a few months time if the budget twin 15" doe snot meet requirements in the 60/80ft room.. Tuba HT is another consideration still in my mind for later if the DIY bug goes well..

As an example what sort of results could be expected with this £400 drivers spec?


Description LOW FREQUENCY WOOFER
Size (in.) 21.0
Nominal Diameter (mm) 530
Standard Impedance (Ohm) 8 Ohm
Power RMS (Watts) 600
Power Program (Watts) 1200
Sensitivity 1w/1m (dB) 97
Basket Material Die cast aluminum
Cone Material Paper
Poles Material 1008 Cold Roll Steel
Magnet Material Ferrite
Voice Coil Material copper+fiberglass
Voice Coil Diameter (in.) 4.0

Fs (Hz) 31.3
Re (Ohm) 6.2
Sd (sqmt) 0.166
Qms 8.31
Qes 0.35
Qts 0.33
Vas (lt) 355.81
Mms (gr) 283.84
Bl (T/m) 31.39
Xmax (mm) 7.5
Levc20 KHz 2.06
Hvc (mm) 25.0
Hag (mm) 10.0

Cheers,
Steve
 

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Discussion Starter #3 (Edited)
Well I modelled it 500L cab tuned to 20hz, 111db at 20hz, power limited to 300w to keep cone excursion down, If I use a fourth order HP I get 108db at 20hz and much safer cone excursion.

This I guess is another reason to avoid large PA drivers, as it shows the characteristic downward slope from 100hz down to 20hz any lower usually results in a freefall response in frequency.

It was a P-Audio P210 21" driver which I may be able to get for half price (RRP £400) but I think I would rather have something with a flatter responce.

I Guess I would be better off saving for one of the RE Audio SX18 D4 or D2 18" bass drivers (£300)?
 

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That driver is not designed for low HT bass. Tune it to 35Hz - 45Hz and it probably gives more SLAM faster, louder, than any normal dual 15" HT sub. :)

If you want 21" try Eighteen Sound 21NLW9600. 200l and tune to 23Hz and you will get >120dB from 24Hz and up. 20Hz scores 117,5dB.
 

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Most of those sentiments come from the car audio field. I have found that large woofers back even in the late 90's were considered slow and sloppy.

However most large woofers had heavy cones, and were rather inefficent. But as cone materials became lighter, and new amplifier circuitry produced faster switching amps this problem was eliminated through more efficent redesigns.

Also alot of old 15's or 18's needed 3-8cuft for a sealed enclosure and most people did not have that type of room to dedicate to them.
 

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I built a DIY eighteen sound 21lw1400 subwoofer in a 250L cab tuned to 30hz slot ported. I get solid response down to about 22hz in room powered by a behringer ep4000 amp. I have yet to reach the limits of this thing. I use it with a pb-13 ultra, I am not too sure what people mean by slower or faster sounding but yes the bass sounds very clean and responsive. Sound quality is about the same as the ultra, if not better when pushed to loud volumes. A couple of times I pushed it to 125 db at about a meter away and it still sounded clean.
 

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I built a DIY eighteen sound 21lw1400 subwoofer in a 250L cab tuned to 30hz slot ported. I get solid response down to about 22hz in room powered by a behringer ep4000 amp. I have yet to reach the limits of this thing. I use it with a pb-13 ultra, I am not too sure what people mean by slower or faster sounding but yes the bass sounds very clean and responsive. Sound quality is about the same as the ultra, if not better when pushed to loud volumes. A couple of times I pushed it to 125 db at about a meter away and it still sounded clean.
*hint* Fast or slow means they don't really know what they're talking about.
 

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Very large subs have a wow factor, but there is a strong argument for multiple smaller subs. Have you heard about the Geddes Multisub approach? It's related to room modes and getting the best in room bass, typically with 3 subs.

I have nothing against large drivers. Actually, when comparing a single subwoofer, I'd say bigger is usually better. However, in my audio blog I've written a post suggesting multiple subs as an alternative to a single huge sub.

You might find it interesting:
http://redspade-audio.blogspot.com/2009/08/why-two-subs-isnt-enough-part-1.html
 

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What about multiple very powerful subs...:demon:


I have one issue with multiple subs scattered around the room. What about time alignment with each other and the mains?
 

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Ricci, I like your thinking!!!!!

I have experimented with "time alignment" using ultracurve, adding different amounts of delay. I have to say, you need to add a lot of delay before you can really hear a difference. The kind of delay which relates to much greater path difference than you find in any room with multi subs.
 

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I have experimented with "time alignment" using ultracurve, adding different amounts of delay. I have to say, you need to add a lot of delay before you can really hear a difference. The kind of delay which relates to much greater path difference than you find in any room with multi subs.
In order for the delay to be heard as a distinctly different sound, then I agree, but as little as 6ms (6ft) can introduce a huge swing in the frequency response. The effective group delay effects aren't going to be completely inaudible either....

I'll have to dig up the link, but there is a very creative way to array a series of subwoofers to actively cancel out room modes. I would be far more inclined to pursue such an approach before doing just a single box solution.
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Dr Who, I don't believe trying to cancel room modes is the best approach. What can happen is that the remaining modes become more pronounced. Above the Shroeder frequency, room modes still exist, they are just so closely spaced that the result is a much smoother response. The idea which makes the most sense to me is multi subs placed to excite more modes, not less. This is the idea presented by Harman as well as Geddes.

It's also discussed in a few threads online:
http://www.diyaudio.com/forums/showthread.php?threadid=134568
http://www.avsforum.com/avs-vb/showthread.php?t=1124011

I should probably avoid getting too much into this side of things, I don't want to hijack this thread.

I'll just add this. The multi sub approach doesn't rule out larger subs. In fact you may still keep one uber sub, then augment it with two smaller subs to smooth out the mid to upper bass range.
 

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Ya, I'm familiar with the approach of maximizing modal density, but the approach I'm referring to used an array of subwoofers that coupled with the room boundaries to create a plane wave. There is no accentuation of any single mode - it's guaranteed by design.

I believe the guy that actually build one "only" had 4 subs on the front wall and 4 subs on the rear wall. The driver-to-driver and driver-to-boundary (wall, ceiling, or floor) spacing was something like around 3ft, so it was very effective up to around 80Hz or so. The subs on the rear wall were delayed the length of the room and then had the polarity flipped, so almost no sound reflected back towards the listening position.

The downside is you don't get any room gain, but I think room gain sounds unnatural anyway...

Btw, one of the downsides to making the diaphragm of your driver larger is that it lowers the frequency where cone breakup occurs. Generally you want it to be well above the highest frequency you plan to operate the speaker at, since our hearing is more sensitive to ringing than it is distortion. The other downside is that rocking of the cone becomes more and more of a bigger concern the larger/heavier the diaphragm gets.
 

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When you say that room gain is unnatural, how do you know that is what you were hearing? It can be challenging if not impossible to actually isolate just one aspect.

Regarding large drivers there are many things to consider together. Cone breakup is one of the issues, but I don't expect it to be make or break. One of many things that can be allowed for in the design. Another issue came up in one of those "fast bass" threads addressing the question of small vs large drivers for SQ. Someone linked some info on why large drivers are better. It dealt with issues like efficiency and in particular the linearity of compressed air. You can make small or large drivers appear superior depending on which aspects you focus on. But how do you take all the factors, correctly weight them according to perception and then come up with a winner?

It's easier to break down a subject and talk about narrower areas, but I think at the end of the day, you can get a great result with small subs, medium subs, big subs, huge subs. But if you really want to get accurate bass, you have to seriously think about your room acoustics, and not just the driver.

I actually think that if there's one setup that would please most people in here, at least based on performance alone, then it would probably be this. One large and very power subwoofer in a corner - as big as you need to get the wow factor, covering as low as you want to go, up to about 50 Hz ... and then two modest but good quality subs very carefully placed and set up with measurements covering 50 - 120ish.

If we could all get together and try out all the options and evaluate them all blind, that would be my guess as the winner.

Feel free to disagree. I'm sure plenty will disagree with me. Such is the nature of this hobby.

The nice thing about this approach is that you are still free to satisfy the urge for the monster sub, but at the same time you can deal with those difficult room modes and get better bass than music only systems.
 

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When you say that room gain is unnatural, how do you know that is what you were hearing? It can be challenging if not impossible to actually isolate just one aspect.

Regarding large drivers there are many things to consider together. Cone breakup is one of the issues, but I don't expect it to be make or break. One of many things that can be allowed for in the design. Another issue came up in one of those "fast bass" threads addressing the question of small vs large drivers for SQ. Someone linked some info on why large drivers are better. It dealt with issues like efficiency and in particular the linearity of compressed air. You can make small or large drivers appear superior depending on which aspects you focus on. But how do you take all the factors, correctly weight them according to perception and then come up with a winner?

It's easier to break down a subject and talk about narrower areas, but I think at the end of the day, you can get a great result with small subs, medium subs, big subs, huge subs. But if you really want to get accurate bass, you have to seriously think about your room acoustics, and not just the driver.

I actually think that if there's one setup that would please most people in here, at least based on performance alone, then it would probably be this. One large and very power subwoofer in a corner - as big as you need to get the wow factor, covering as low as you want to go, up to about 50 Hz ... and then two modest but good quality subs very carefully placed and set up with measurements covering 50 - 120ish.

If we could all get together and try out all the options and evaluate them all blind, that would be my guess as the winner.

Feel free to disagree. I'm sure plenty will disagree with me. Such is the nature of this hobby.

The nice thing about this approach is that you are still free to satisfy the urge for the monster sub, but at the same time you can deal with those difficult room modes and get better bass than music only systems.
Excellent post paul. I like the evaluation method you mentioned too :)
 

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Well I modelled it 500L cab tuned to 20hz, 111db at 20hz, power limited to 300w to keep cone excursion down, If I use a fourth order HP I get 108db at 20hz and much safer cone excursion.

This I guess is another reason to avoid large PA drivers, as it shows the characteristic downward slope from 100hz down to 20hz any lower usually results in a freefall response in frequency.

It was a P-Audio P210 21" driver which I may be able to get for half price (RRP £400) but I think I would rather have something with a flatter responce.

I Guess I would be better off saving for one of the RE Audio SX18 D4 or D2 18" bass drivers (£300)?
If this is of any help, I have heard a P audio 21 (single sub) running with a pair of coaxials.

To this day, prob one of the most awesome scary bass experiences I have had. The thump and kick in the chest was unbelievable.

And, this was in a huge warehouse! A couple of points, the box for the driver was basically 'smaller' than the packing case it came in. We eq'd it to do what we wanted. Amp power is cheap, real estate is not. The 'box' was circular, just wide enough to mount the driver, and just deep enough to house the driver.

Doubt it would have been fifty L, let alone 500!! (assuming that they do not have more than one 21 model BTW)

I never saw any measurements of the thing, so do not know how low it went.

As you are on this forum, I presume you are not against eq in the bass region? If so, then if you have enough power maybe you can get it to do what you want. (be the boss over the driver ha ha)

I run two 18 PHls at home, and they are excellent and certainly give the slam and speed, but to this day I still not have experienced slam like that 21.

Oh, slow is another audiophile myth when talking about big drivers. So, don't listen to audiophiles yeah?
 
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