A driver has both a mechanical suspension and thermal losses. Until you can overcome the majority of losses in both of those areas via increased drive levels, the driver itself won't be running in the region where it has the greatest linearity. At the same time, driving the speaker harder will eventually go beyond the sweet spot of operation, causing dynamic compression due to saturation of the mechanical suspension and / or thermal losses.
In effect, a driver is no different than any other type of device. They all have a region where they operate most linearly. Above and below that, they still work, just not as linearly. This is why various speakers sound better at certain spl levels i.e. don't come alive until cranked up or sound worse as they are driven harder. Bass alignment also comes into play here as a higher Q design will sound "fuller" at lower volumes, but becomes bloated and tubby as drive levels are increased. This is why speakers are the most specialized component in the system i.e. they vary the most in terms of room interaction / placement, listening style ( spl ranges, seated listening position, etc.. ) and personal preferences in terms of tonal balance, transient response, etc.. Sean
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Sean...Other than compression at some high level of SPL, I can't think of a reason for a low SPL "knee" in driver sensitivity. Can you provide any further info/references?
Equalization that is SPL-dependent is another one of the tricks that the ubiquitous Behringer DEQ2496 can do. I haven't tried it yet, but I have hopes that it might provide the "Loudness" function which my preamp lacks. |
I have had alot of experience with both, DD-15/DD-18 and ended up with the DD-18s each time.
I ALWAYS run subs in pairs. Aerial SW-12s, Velodyne F-1800R's, HGS-18's, HGS-18II's, DD-12's, DD-15's, and DD-18's. I had a pair of DD-18s, sold them to go back to the Aerial SW-12s.
Now, these are the only subs I like personally. The SW-12s did better at all volumes/material than did the HGS series of subs. I preferred the 15s over the 18s from the HGS series, as the 18s didn't have enough power to keep up with the driver, so it was slow and needed volume/room to 'catch up' to my mains, but was quickly overpowering even set at about 2. Then the DD series emerged. Again, I got into the 18's, and was shocked at the presence at low to mid level volumes and the spectrum they can cover. I know Velo told me they increased the output by 2DB, which normally isn't a big deal, but in subs it is a HUGE deal, and mid level volume is where I noticed it most. No, wait, maybe that was because I was finally able to dial in the room with the built in spectrum analyzer?
No wait, maybe it was the increased servo speed of the DD versus the HGS? No wait maybe the spectrum? No wait, maybe..........anyway, you get my view.
The change between the HGS and DD was a huge step. Now, 15 versus 18s? I doubt VERY much at normal / moderate listening levels anyone is to notice differences between the 15's and 18's. Anyone unless trained professionals with perfect rooms and ears. As you probably know, the room will change the sound more than anything else, so probably no reason to get hung up on the sound differences between these two at normal levels. My bet is they will act / sound the same.
The big differences kick in as the volume levels increase and you start to walk away from the mid-low bass of the 15s and start getting into the quick, deep push of an 18. There is nothing, imo, like a correctly powered 18" sub driver, actually 2, in a system for 2 channel. Just incredible. I have someone that has a full scale ORGAN (like 100ft tall, 200ft wide) that bought 2 DD-18s for reproduction of sound in the hall! And home theater, well, suffice it to say, if it is good for 2 channel, it is great for theater. I don't think there is a better sub for 2 channel or theater, low to high levels of output as the DD-18s. I definitely feel bass is directional, despite what many others say, and in stereo, dialed / spectrumed (is this a word?) in there is no better.
Alot of folks in the 18" game look into Bag End. They never had enough power for my liking, which led to weak/anemic tonal control of the driver. I am not a huge fan of ported subs, as the Aerial SW-12s are. The had to be to achieve volume but the mass air push on my legs during huge passages was quite annoying despite their nice presence at normal levels. Servo's of the DD series are so much more advanced than those of the HGS series (alot of hum, buzz, etc.) and seem to get bass right.
Now, again, this is all my experiences, my opinions, and you know what they all say about opinions? Like asshol_s, everybody has one. But, that being said, I am not a dealer, I don't 'represent' any lines, have no affiliates, and have had the ability to try / demo many subs (powered and not - passive like Snell 18's, JBL 18's, and some older Kinergetics) and have landed 100% into the DD line. If space (physically) isn't an issue, go 18's, you will not be disappointed!
For what is it worth, I am running 2 pair of JBL K2S9800SEs, matching center, Levinson 33's, Meridian 861/800 for theater, and the Conrad Johnson Premier 8A's and the CJ ART in 2 channel. Oh yeah, a trio of DD-18s, stereo pair in front, single in back (for theater - as if really needed).
Dan |
Bag End's are designed COMPLETELY different from ANY other subwoofer made. As such, they will respond differently. The one thing that will be consistent with Bag End's regardless of size as compared to other subs is that they will require more power to achieve the same level of volume. This is directly related to the design choices that they made when building these products.
Other than that, all drivers have a "knee in the output curve", just like all semiconductors do. The subs using a servo system can take this into account whereas those without some type of active equalization / monitoring system can't. I'm quite certain that the Velodyne's have this factored in. The Bag End's also vary bandwidth as spl is varied i.e. the lower the spl's, the deeper the sub goes. As spl is raised, the active EQ system reduces the boost applied at the extreme low frequencies. While this occurs naturally with ALL woofers to some extent, the Bag End's do this not only acoustically, but also electrically. Like i said, they are kind of a novel design. Sean
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To follow-up, I called Bag End and the sales guy told me that there was no difference in quality between the Infra 12" and 18" at low volumes (I said I heard a large difference at any volume between 12" and 15" with B&Ws, and he said, "well, not with ours"). This was also quite different from what the Velodyne guy told me, which was that anything 12" and below is basically a 'toy' and that the move to a 15" is a dramatic step up at any volume. The Martin Logan guy gave me the opposite advice- that the smaller Depth may have an edge in clarity and response over the Descent at lower volumes, because of its agility.
Three different manufacturers, three different basic responses...bigger is better, no difference, and smaller is better..... |
Eldartford: I probably didn't state things very clearly. You are correct, it's not really inertia in the classical sense, rather it's the amount of current needed in the voice coil to get the driver moving in the first place. You have to overcome that intial friction. I've been told by speaker manufacturers that this is an issue for larger drivers. To move them properly with good control you have big magnets and big voice coils and this can become an issue playing at low volumes. (A speaker manufacturer is probably better to comment on this than I am) You are also correct about the perceived loss of bass at low volumes, this is the work done by Feltcher and Munsen, that shows how our ear sensitivity drops off in the lower octaves and that it is a non-linear phenomenon and becomes a greater discrepency at lower volumes. Lastly, with regard to your comments about the servo. You are probably right too, though some servos are better than others (I've measured some that weren't too hot), my guess is that Velodyne has been doing this for so long that there's is probably pretty close to spot on--but having never measured it I don't know for sure. Keith Yates did a few articles on subwoofers and some very extensive measurements. I don't think they published the low level data, but he may have it. Now I'm curious and will likely ask him. |
Rives...good idea. I called Velodyne and the guy told me that for a 4000 cubic foot room, he would recommend two DD-15s or one DD-18 (he said these are equivalent, as are four DD-15s and two DD-18s). When I mentioned cost wasn't an issue, he recommended DD-18s, and said that there was absolutely no downside to getting a larger subwoofer, as far as low-level playing and neighborly relations. The DD-18 can always be adjusted to a lower volume and match any low volume DD-15, and in fact at low volumes one would be hard-pressed to tell the difference between the two boxes. |
Rives...I don't understand your comment about "inertia". The effect of cone mass does not have any threshold to be "broken". If the parameter were "friction" what you say would make sense, but a cone driver has no friction, just mass.
If sensitivity diminishes at low power level something other than inertia is at work. I, like every other audiophile, have the impression that this occurs, but I am of the opinion that it is the human ear sensitivity that is diminishing rather than the speaker output.
Because it is servo controlled, I would expect a Velodyne to perform well at low volume. If there were any nonlinearity of the driver at low SPL the servo would counteract it. As you suggest, Velodyne should have something to say about this. |
Your question is now much more difficult. Since cost is not an issue, go with 2 subs. Now which sub is not so easy. It depends on the volume of the room, the size of the cone, and the subwoofer design itself. The first two are pretty easy. Suffice to say, if your room is 22 x 30 with 9 foot ceilings (big volume) you should go with the 18 inch. If you have a small room, you may actually be better off with the smaller cone, particularly since you've already indicated that you want to play at low volumes. Some drivers need enough power into them to really break the inertia of the voice coil. I have not demoed, nor do I know about the low level performance of the Velodyne's. This might be a case that Velodyne may be no good at all for low level playing, or they may be great--I have no idea there.
Why not call Velodyne? That might sound crazy, but they want you to be happy too, and you are talking about buying multiples of their subs. Most people would say--of course they will try to sell you the big sub. But I'm not so sure, someone in corporate will want you to walk away as a happy customer and tell other people you are happy. If you explain your situation, it would be in their best interest to tell you which one would work best for you. |
http://www.velodyne.com/velodyne/products/specs/DigitalDrive.html
Look at the specs. |
My dilemma at this point is not about 1 vs. 2 subs. Should I get two larger 18" subwoofers then? Would larger subs would hinder room placement in my case? The difference is about four hundred dollars from my dealer between the two sizes, and I can afford two 18" models - cost is not an issue in the case.
Flemke, I have no plans to crank my subwoofer(s) either, I will play at low volume at least during the next year in this apartment. My question is whether the DD-18 can be played at an equally low volume as the DD-15, and achieve better effect musically. Unfortunately, I won't have a chance to demo both in the showroom. |
Get the DD-15. I have mine set at 4 and have no plans to crank it up any higher. |
If it is a question of 2 smaller subs vs one larger one, I absolutely agree with Rives. The recommendation for large cone area assumes that cost is not the deciding factor (which I admit may be unrealistic unless you are building the subs yourself). Velodynes don't come cheap.
The loss of low frequency at low volume is mostly the result of human hearing characteristics, rather than actual reduction of SPL from the speaker system. Corrective action for this is the "Loudness" control that used to be a common feature of preamps. |
I'm going to recommend something entirely different. Get 2 lesser subs rather than one big one. You can place them in such a way to cancel out certain room modes and get a much more even response throughout the listening room. I also think those with parametric eq built in is very useful, you can fine tune the one mode (floor to ceiling) that you usually can't do much about based on positioning. The Harmon Group wrote a great paper on number of subwoofers. There's a link to it on our resources page. There's also a paper we wrote on speaker placement, which includes subwoofer placement. |
Thanks for your responses so far. I will audition Bag End and Martin Logan, in addition to Velodyne. Up to now, I am inclined towards Velodyne because of the easy built-in room correction features. I'm not sure that Revel is available in Hong Kong, where I plan to make the purchase. I will also look into the Aurios and Auralex Gramma, recommended from a previous posting.
I guess I have a very basic question..before getting into differences in speaker design, if possible. That is, is it possible for a large subwoofer (or several smaller subwoofers in one enclosure) to be effectively played at an equally low volume as a small subwoofer? I'm really not concerned about large volume sound for the medium-term, and want to achieve the best possible sound, i.e. bass extension, resolution/clarity, and fullness, at extremeley low to low volumes. All other things being equal, should i just get the largest subwoofer (or largest total cone volume, for those who advocate using several smaller cones) possible? I guess I don't understand the physics involved..
my Velodyne dealer recommends the 18" over the 15", independent of room size (mine happens to be about 14 x 35 feet), placement issues and price. he said the main reasons people would go for the smaller subs is because of price and lack of physical space for the cabinet, and that inside this subwoofer line, volume/neighbor issues are a total non-factor, since i have control over the volume. is this true at low levels, or is there a "minimum" effective volume threshold for the 18" which is higher than for the 15"? |
Eldartford you make a good point. I know some don't understand the concept of multiple subs in a system.
I think you hit the nail on the head. This is why I have went this route.Blind folded it will be nearly impossible to point out the subs in my system. |
I asked Tyler acoustics for a quote on a custom subwoofer with the following design parameters:
purpose is to use with single ended tube amps and very efficient speakers....the sub must be "quick" enough to keep up with demanding bass passages and the mid/hi frequencies.
dual 8" drivers arrayed vertically
one speaker input straight to the drivers
one speaker input with a quality passive crossover (cut at 60 to 75hz)
non ported design
high efficiency so can be driven by a tube amp if desired (intention is to build a mono tube amp that will only operate in the bass frequencies and opimtized for bass duty)..output control on the amp would control the level
Tyler quoted me a price of 450 for a basic black ash woofer based on these specs and estimated the bass output would go to 30hz or slightly below.
An AudioAero dual 8" sub which supposedly hits 20hz recently sold very cheaply locally. I missed it by a couple of days.
This is supposed to be an excellent product but that is only hearsay. |
I have one Bag End Infra 18. It will shake the pictures on the wall. I recently purchased (2) conventional 12" powered subs from a local Phoenix dealer (Celestial) to augment it.
The Bag end goes low, I want to have more fleshed out bass above 20 Hz. The Celestial subs have the often used 12 NHT driver.
I also have a B&K REF 30, which is very underatted, in my opinion. This processor has very excellent bass management that allows you to notch filter & boost the bass, for your room. Anyone who owns this processor & doesn't appreciate the bass management, hasn't used it to it's full potential.
(I still have a dealer friend who tweaks mine with the on screen adjustments - whenever I make a room/system change). |
I think that for LF, and especially for SW, the more cone area the better, although, as Sean says, there are other imnportant considerations. The large cone area is not to play louder. It is to play with the proper loudness without need for extreme cone excursion. A small subwoofer must be very loud one foot in front of it because the sound pressure must spread out to fill the whole room, with the SPL falling off rapidly with distance. If people used multiple 15" subwoofers (one for each speaker system) there would be less chatter about the difficulty of locating SW in the room. |
Before you buy, check out the Revel Sub 30 system. You will get parametric equaliziers, a 1,000 watt amplifier, 15inch woofer with additional 15 inch dual-layer metal dome acoustic radiator.
For a review go to http://www.avrev.com/equip/revel_sub30/index.html
or Harman Specialty Group
If you want are interested contact Adidadi. |
The Bag End Infra Sub 18 is the most musical sub I have heard. However it does not have the output of a Velodyne for HT applications. Since this is not an issue with you (as you prefer a lower volume/output)the Bag End is the way to go.It is extremley accurate and at low volumes is quite amazing.As far as the fallacy of an 18" sub being slow and innacurate that is just not true of a well designed unit. In fact an 18 " woofer has to move a fraction of the distance as a smaller woofer to provide the bass desired. Trust me you cannot go wrong with the Bag End Infra Sub 18.Hope this helps. |
There are too many other design factors to consider than just cone area, especially in your "limited use" situation. This is why we have Thiel-Smalle parameters as it describes most all of the aspects of the driver. Once you know all of those factors, then you consider cabinet rigidity, volume, bass alignment, etc...
Other than that, driver size has nothing to do with efficiency or cabinet volume. It is quite possible to have a 12" that needs a bigger box and requires more power than an 18" driver. This all depends on the above mentioned factors and the over-all design of the product.
I can't really point you in any specific direction as i stopped looking at subwoofers a while ago. Most are ridiculously priced and under-designed. After all, a passive sub is basically a woofer, a cabinet, some stuffing, binding posts and some feet. How they think that this costs as much as multiple drivers, complex crossover networks, etc... I don't know.
The one thing that i would suggest would be to try and listen to / compare some sealed designs to vented designs. The one advantage that vented designs offer is that they will play louder. Since this is not a major concern of yours, you can take major advantage of the improved transient response, increased damping, lack of overhang and ringing, slower resonance, more controlled output at resonance, etc.... of a sealed box. You'll also get less "bloat", which means you probably won't annoy the neighbors as much. Whether or not you prefer the sonics of this type of design is a personal matter, but i thought i would mention it. Sean
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If you go BagEnd you need to buy the 18" the 15" wasn't rated a very good value compare to the minimal extra cost of the 18". But the acoustical shaping that the DD's provide will definitely outclass the uncorrected BagEnd. You will need to use a Berinhger or Audio Control Richter Scale or other EQ to correct for the room accoustics and placement to truely compete with the DD's.
if you want your neighbors to have a chance float your sub with a decoupler like the Aurio Pro's (that's what I use on my Velodyne 18") and then mass load the top of the sub with 25lb back of #6 lead shot to tighten the response.
I am also considering the Velodyne DD15 and DD18 since I have an older F1800X without correction (which I will keep to use with the DD15). In my research I am going to go for the DD15 because the only thing different is the size of the enclosure and driver, and I don't need more max output. The other option is to do a pair of bagend 18" (commericial)with a Crown K2 amp and a Tact or Berinhger digital correction system, but I haven't been able to figure out whether I can actually hide 2 18" enclosures behind my couch. |
It is time to start believing the tales told to women. Size (in this case) does not matter. A larger woofer will move lots of air and make deep bass. However, it is difficult for an amplifier to do this with any accuracy. How much air do multiple small drivers move? Lots of air with more authority and precision. Check out the Martin Logan Depth (three 8" drivers) for small to moderate sized rooms and the Martin Logan Descent (three 10" drivers) for small to huge rooms. These are three spun aluminum (light and easy to move) drivers positioned in a triangular array (directly opposing each other to cancel out internal cabinet vibrations). They are also servo controled which means that they start and stop when they are supposed to. This is a big problem with larger woofers. They have more mass and air resistance to their movement which increases the lag-time between the time that the amplifier tells them to start/stop and the point in time that they acctually do this.
Another big consideration is tweekability. The ML subs give you a high level of adjustability as far as phase, crossover point, and low level cut/gain. There is an adjustment knob centered at 25Hz that gives you up to 12db of cut/gain. THis can help smooth out common room modes that give you boomy bass. Every room has peaks and nulls. There is little that you can do about these without tearing down a wall. By moving the sub around the rooom you can find a position that doesn't excite peaks too much and through phase adjustments you can demphasize the nulls. An equalizer that does not mess with the mid-bass (this 25Hz knob) can also be most useful.
Two cents. |
Find a Bag End dealer and audition one of the best. Go review their site; think they may offer both sizes. Great product, rarely found used. |
