Stereo Subs

David Ellis · « **on:** 7 Jan 2003, 01:28 am »

I heard a stereo subwoofers setup with some pipedreams speakers and Marsh amps. The setup did a wonderful job of reproducing stereo and the bass was NOT localizable. It works.

There are, however two considerations. First, the additional sub will obviously cost, er, more $. Second, the stereo subwoofers with th pipedreams setup were huge. I bet those things were 6 cubic feet internally. This is difficult in with most wifes and their living rooms.

Dave

rosconey · « **Reply #1 on:** 7 Jan 2003, 02:09 am »

have you ever heard the vmps large sub.mine is set up in stereo and the bass is so smooth.
there is a lot more depth and musicality with a stereo sub or subs.

David Ellis · « **Reply #2 on:** 7 Jan 2003, 02:44 am »

I haven't heard the VMPS subwoofer, but am certain that Brian Cheney implements his drivers quite well. I am sure his subwoofer is no exception. And yes, stereo subwoofers do sound nice.

Dave

Al Garay · « **Reply #3 on:** 7 Jan 2003, 02:52 am »

OK. I give. What do you mean by pipedreams? Do you mean sonotubes?

I can understand the preference for stereo subs. I like what Phil Bamberg does with the BESL Series 5 subs, http://www.bamberglab.com/series5.htm
The sub cabinets integrate nicely with his monitors. He chose to use the Peerless XLS 10" woofer with the 12" passive radiator. Phil claims this is lower distortion than a sealed sub. I'm still confused about the benefits (primarily for music, seemless integration with monitor, tight, ....) of sealed design versus a ported with passive radiator.

Of the few subs that I have heard (sealed versus vented, have not heard one with a passive radiator), the sealed had the best integration.

How have you guys implemented your SCC300? Sealed?

Al

jqp · « **Reply #4 on:** 7 Jan 2003, 02:58 am »

That I would like to hear!

Al Garay · « **Reply #5 on:** 7 Jan 2003, 03:09 am »

Oh man. I bet the designer is about 5 foot tall and drives a monster truck. Make that a semi. How else would you transport a set of these.

I guess I can show a picture of these to my wife and then the VMPS RM40 will not look so tall.

The venner looks beautiful.

Al

David Ellis · « **Reply #6 on:** 7 Jan 2003, 03:27 am »

Those are the pipedreams speakers I heard. The sounded very good.

dayneger · « **Reply #7 on:** 7 Jan 2003, 08:51 am »

How are stereo subs generally placed for best effect?

I've read of many systems where people make stereo subs and use them as stands for their monitors/stand speakers. This would seem to be no different than full-range speakers in 2 boxes instead of one box with 2 appropriately-sized internal chambers and cabling. Difficult to make attractive and eliminates the various purported advantages of stand speakers, such as having the serious base positioned less conspicuously.

Those pipe dream line arrays have a serious number of dome tweeters, don't they? Beautiful.

Judging from the photo the subs are set back a bit in this room. Helps to keep the pipes from seeming, well, imposing.

Just curious what the actual acoustic and design motivations/considerations are.

Dayne

doug s. · « **Reply #8 on:** 7 Jan 2003, 05:45 pm »

hi all,

i've been using a pair of vmps larger subs for ~8 years, now. w/a high-quality outboard x-over, (marchand or db systems are two that will work well), these give seamless, integrated, *real* bass response to pretty much any monitor you want. i have tried them w/several different speakers, & they all worked well. when i 1st got the sub system, my *monitors* were floor-standing thiel 3.5's, rated -2db at 20hz. the subs were a big improvement, both for low end response, & for the thiels' upper bass/lower mids, as its 10" driver dint see any frequencies <70hz, where before, they were stressed down to 20hz, along w/the thiels' active eq, which boosts the signals almost 20db at these frequencies...

regardless of whatever speakers i may have in the future, i cannot imagine ever not using my subs w/them... a pair of *real* subs w/active x-over is highly recommended, for anyone w/the space...

regards,

doug s.

David Ellis · « **Reply #9 on:** 7 Jan 2003, 07:22 pm »

The major advantage of a line source is the in-room response produced. The vertical response between the drivers loads, but when above or below the line source there is a serious drop in response. A taller line source will better accomplish this, but it is true with all line-type drivers. The result is little acoustic impact from the floor or ceiling. The 4 walls will still be an equally good player, but 2 of the walls (the floor and ceiling) are effectively removed from the acoustic equasion. This leaves only 4 of the room walls reflecting the music.

As an experiment, seek out some Newform R630s or Magneplanar 1.6s. Listen to them in a sitting position. Then stand up. There will be a serious drop in the response (if you are tall enough). This is due to the line loading from the vertically spaced line-source drivers and the gross lack of response when above or below the line. The same is true to a lessor extent with the taller ribbon drivers such as the Raven R2, but it is much less obtuse.

The flip-side of this is that real instruments and voices don't come from a line-source. A violin certainly doesn't project acoustic energy like a line source. It projects acoustic energy like a point source. This model is much closer to a traditional (i.e. non-line source) speaker with respect to in-room reproduction. Maybe reflections from all 6 room surfaces are better? I don't really know.

But... all of this is just theory. There is certainly some testosteone factor involved when stacking drivers from floor to ceiling. It also sounds good. It would take roughly 13 W18's ($142each) and 23 OW1's ($75 each) to go from floor to ceiling for a single line array with good drivers. Multiply this x2 and the number is EXTREMELY expensive. I am sure the sound would be nice, but it would not warrant the expense. It would be opulence.

Dave

rosconey · « **Reply #10 on:** 7 Jan 2003, 10:01 pm »

line arrays are nice.
i amost made a linnus array but it looked too big for a first time project.
seems most diy kits are going with ribbons instead of domes.like gr research -alpha ls and rick craig linnus and excell array's.
some one from parts express did one with full range drivers.
i might try some with a b@g 48" or 50" someday when my cabinet skills improve

David Ellis · « **Reply #11 on:** 8 Jan 2003, 02:12 am »

I thought about this too.

Have you ever auditioned a large BG ribbon?

Dave

rosconey · « **Reply #12 on:** 8 Jan 2003, 01:18 pm »

the old carver amazing(i think thats what they are called)
a friend had some years ago

JoshK · « **Reply #13 on:** 8 Jan 2003, 02:34 pm »

Dave,

First off, don't take my questioning the wrong way. I have read a lot about your design and your feedback on forums and I respect what you think and you are a bit easier for me to understand than some. This is why I ask.

I get your point on the cost being overdone for the benefits of a line array. The question I have, is, if you were to build a high end line array would you really need to use such expensive midrange drivers? It completely makes sense to me why you want to use the best drivers in a monitor "point source" type speaker. In a line array given that SPL decreases linear with distance away from source, rather than the square and given that you have so many drivers working, it seems that no driver is forced to work too strenously. It also seems--and I could definitely be wrong here--that a lot of properties of the highest quality drivers are really needed when the driver is worked very hard. Am I way off base? I mean I am not advocating cheap drivers, certainly ones with still very good characteristics but maybe not so expensive exotic materials are to be needed.

Just curious. I know Danny Ritchie uses a less expensive paper cone mid-woofer in his line array and argues why it is sufficient in this design.

Josh

audiojerry · « **Reply #14 on:** 8 Jan 2003, 03:33 pm »

When using multiple drivers, how do you solve the impedence problem when wiring either in parallel or in series? Aren't you either going to get a very high total impedence or a very low total impedence?

doug s. · « **Reply #15 on:** 8 Jan 2003, 08:13 pm »

jerry,

w/line array's, there is usually a mix. ie: w/six drivers, ya can parallel two series of three, or three series of two, depending on the specific driver impedence...

doug s.

David Ellis · « **Reply #16 on:** 8 Jan 2003, 08:44 pm »

Very good questions - especially the one from Josh!

Josh...

When considering the effects of a line array and drivers I think the easiest/best way to consider this is in terms of the motor and the cone. With respect to the motor, Josh is right on the $. The major advantage of a good motor system with shorting rings (i.e. Scanspeak or SEAS Excel) is the very linear X-Max region. Motors that don't have such rings in their motors will have a shorter linear region within their X-Max. This is because the flux field is strongest when the voice coil is centered on the pole piece and decreases as the voice coil moves toward the limits of X-Max. John Paulsen (SEAS) explained this to me at CES. Soooo, when applying all of this goop to the concept of a line array there isn't much need for a good motor because that cone isn't moving very far. The voice coil will remain almost dead centered in the gap between top plate and pole piece.

The cone is another issue. If the cone flexes under stress at 3000hz then it will still flex under stress at 3000hz. 3000hz remains 3000hz no matter what.

There are two other issues that are fair to address here. They are the specific design of a cone driver for a line source, and the relationship between a smaller cone and cone flex. It is theoretically possible to get 30hz from a 4" cone. The reason this is not done is that the level of air displacement necessary to move 30hz at an acceptable level is substantial. With many of them it might be possible to get enough air displacement, but then there is is the issue of driver suspension. Driver dampening is normally setup for a certain frequency range. It just isn't possible for the suspension for a driver to perform ideally at all frequencies.

Next, just because a cone is smaller doesn't mean that it will be stiffer at 3000hz. I corresponded with Sigfried Linkwitz on this issue and he conveyed this truth. It was quite simple, but escaped me prior to that correspondence. I though that a smaller cone would always be stiffer because its outer edge is closer to the voice coil. This isn't always true. It is possible for a larger cone to have a stiffer cone than a smaller cone. I have a hunch that this might be true between the SEAS W18 and W15 cones, but am not sure. I certainly though the Joseph Audio RM40 (now called the Pearle) sounded nicer than the Joseph Audio RM33 in the midrange. There could be other factors with these specific speakers, but examination of the SEAS page indicates a strange rising distortion in the W15 at 2khz that is not present in the W18. I am guessing (again, not 100% sure) this could be due to cone flex. It is certainly true that the W18 and C95 cones are darn stiff at 3000hz. This isn't true with many/most smaller drivers.

Tweeters are another story. I don't believe that a cheap tweeter could ever sound good. I don't know as much about tweeters, but believe a few things. First, a cheap tweeter sounds mediocre no matter what volume level it is played at. This is a SUBJECTIVE opinion. I have listened to many some $25 tweeters. The all sound, well, like $25 tweeters. The difference between a $25 tweeter and a $75,$200, $300 seems quite nebulous, but there are differences. This leads me to the next point.

Second, I can speak with some degree of authority on the motor and dome of the Hiquphon tweeters. I will cite Osakars words as accurately as I remember them. When discussing the matter of "why the Hiquphon tweeters sound good" I really expected that he would tell me something really special about the motor structure. I figured there were shorting rings or something of the sort - nope. Oskar did spend about 10 minutes of telephone time addressing his attention to voice coil concentricity, and the tolerance between the voice coil and the pole piece. He maintains .07mm gap between the voice coil former and pole piece. He maintains .1mm gap between the voice coil and the top plate. He further explained that getting a very good magnetic linkage required a very tight tolerance and that such tolerance is not possible when using stamped driver materials. Opening up this tolerance allows the use of cheaper stamped materials, but also reduces the solid magnetic link between the voice coil and the top plate. Opening the gap increases distortion. This is obviously undesirable.

The second issue Oskar addressed was the dome. He said that most fabric domes are sprayed/doped, then pressed into shape. This creates an undesirable dispersion of the doping material on the dome. Then ferrofluid is added to damp the travel/overtravel of the dome. Oskar's domes are pressed first, then triple coated (OW1) with different coatings at differnt places on the dome for proper strength and dampening of the dome. Oskar conveyed that the SS Revelator tweeter and the Dynaudio Esotar also use this method of dampening. Oskar said that this method of doping a dome is very effective, but also very time consuming and therefore expensive.

Given what I know about tweeters (relatively little), I don't think (?) that it is possible for 20 low quality tweeters to have a sound quality equal to 1 high quality tweeter. I dunno though. This is obvously all theory. I didn't have the opportunity to a/b the pipedreams line source and the 1801, but recall that the pipedream speaker sounded very nice.

The problem of parallel/series isn't very difficult. You just hook up the drivers in a mixed series/parallel configuration and aim for about 8 ohms nominal. Given 4 8 ohm drivers the solution is simple. Hook two pairs in series, then hook those pairs in parallel. The result will be 8 ohms nominal. given 6 drivers, I'd probably hook 2 triplets in series, then hook those in parallel. This would result in 12 ohms nominal.

There are probably other issues to.

Hopefully this all makes sense. There is considerable rambling contained herein.

doug s. · « **Reply #17 on:** 8 Jan 2003, 09:25 pm »

hi dave,

i was told by someone familiar w/the mfr of the pipedreams that $20 was about right for the cost of their tweeters, fwiw... perhaps their more recent iterations are more $$$...

regards,

doug s.

David Ellis · « **Reply #18 on:** 8 Jan 2003, 09:31 pm »

About $20 could be the price. This is on the more expensive end for a tweeter built in Southeast Asia. This would seem about right.

Agian, the pipedreams speakers were very far from bad.

Dave

JoshK · « **Reply #19 on:** 8 Jan 2003, 09:34 pm »

I happen to totally agree with you on the tweeter, Dave. Actually I was just talking about the mids, and your explanation added a lot of insight as usual. Its great when someone who has done a lot of research and tried a lot of things actually is willing to explain stuff to you without a marketing propaganda perspective.