multi-driver sub question

[taylor]

Hi, I have decided to build a narrow footprint sub, either a BR or TL to replace my large cube subs. I am going to use either two 8" or 10" drivers and would like to know what the best placement for them would be. I can either mount both on the front baffle(my last choice), opposite each other (front/back or left/right), or at 90 degrees (either one front/side or one front/bottom firing). This last option is the one I would prefer. Both drivers will be identical so I should be able to wire them in series and just adjust the VAS (2x)while using all the other T/S parameters for just a single driver right? Any help will be much appreciated. Im an industrial designer and not a very good engineer. Thanks Taylor

[Super]

Not sure about your other questions, but remember that when wiring in series, you're going to have to drive them harder than you probably did with your old subs, since you're going to have an 8-16 ohm load. Can you wire it in parallel? And yes, all that you should have to worry about if driving them in mono is the vas (to the best of my knowledge). I would suggest going with the 10 inch drivers (at least), and not mounting them to the same baffle. You'd be losing a lot of strength, and you'd be increasing the footprint. If your main concern is size, I have some other ideas that you can try (if your not fixated on a TL or BR sub). Subwoofers don't have to be cubes, they can be taller and narrow, or as I prefer, SonoSubs

[kelticwizard]

If you are going to wire them in parallel, they should be 8 ohm woofers. If each woofer is 4 ohms, you'd better have a very fine amplifier capable of driving 2 ohm loads.

When you wire in parallel, you divide the impedance in half. When you wire in series, you double the impedance. If you have a fairly inexpensive amp, then I would go with hooking them up in series. It is better to have impedance slightly too high rather than too low.

If you plan on having one woofer firing in front, having a second one above it will not increase the footprint any. If the speaker is wide enough to fit one, it will be wide enough to fit the other.

I agree with Bryan about encouraging you to go with the 10" woofers. Reason? There are a lot of very good 10" subwoofers around. There are not so many 8" subwoofers to choose from that can go really low.

One more thing. There are some 10" subwoofers, such as the Dayton Titanic, which have a very very long excursion. The whole idea of a subwoofer is to move air, and two woofers can move more than one. But they take twice the volume. The Dayton Titanic, (as well as others), can move two or three times as much air as most other woofers-very long excursion. So in a sense it is like having two or three woofers in one.

If you keep the volume the same as for two woofers, but install just one, then that woofer will give you half an octave extra bass-a significant amount.

But before we go any further, would you care to tell us

a) how large you would like to build your cabinet,

b) what amp do you have driving the subwoofer?

[GRollins]

Taylor,
Is there some reason you want the drivers at a 90 degree angle?

Grey

[taylor]

Thanks for the info gentlemen. To elaborate further, I suppose I should have given you more info. I would like to use dual subs as pedestals for my satalites (braun L200s or dyi scan speak mtms) or in the corners of my living room. I would like a footprint of 12" square or less. With 1" thick cabinets I felt that two 8" or maybe a 10" would supply similar or better LF than my old M & Ks and be far easier to "decorate" with (recently married) I am driving them with bridged Hafler DH200s which I am going to replace. I thought that series wiring would yield a higher impedence that would be easier to drive for a single amp. My days of high spl are over and I'm more concerned with tight controlled bass. I would like to use a single amp to drive the sats and the subs. Simple is now becoming better. As far as the height goes, if they support my sats, 26" is about it but if I use them in the corners, anything up to 9' will fit. What do you think? Thanks Taylor

[taylor]

PS The 90 degree thing was to keep both drivers closer together for a TL design. I thought a down firing and a forward facing configuration would keep them low and close together in the cabinet and help minimize the length. Taylor

[kelticwizard]

Taylor:

Thanks for the info. Things are much more clearly in focus now.

If you use the subs for stands at 26" high, with a footprint of 12" square, and using 1" thick material, then you have an internal volume to work with of 1.38 cu. ft.per channel.

If you go with one amp for both the satellites and the sub, you will not be able to use an active crossover. Passive crossovers that cross over at 200 Hz or so get expensive, but you can still do it.

I have never built a transmission line. But you mentioned that you might decide to put the subwoofers in the corner, and that they can be 9' high if you do. Assuming that the internal height will be 8', (you want to leave some space between the top of the sub and the ceiling), then a single internal barrier will give you a line that is 16' long. That is approximately one quarter wavelength of a 17 Hz tone.

Sounds exciting. Very few people in the world, I imagine, can boast of a transmission line that long, or which goes that deep. But I will leave transmission line advice to those who have experience with them.

[Edited by kelticwizard on 10-05-2001 at 09:26 AM]

[kelticwizard]

Taylor:

I think I might have found a 10" subwoofer that goes down to 25 Hz. in a 1.4 cu ft box. Didn't think I would, but there it is. I have to check something on it first. Will get back.

[taylor]

Kelticwizard, I checked out the Dayton Titanic 10" and it looks pretty impressive. At 90db and an Fs of 25.8, I think a single driver will be sufficient. I will have to relocate the site but I found a plan for the 12" version that was used in a 12 x 12 x 48 inch cabinet to be hidden behind a couch. Very nice design and performance. I'm going to abandon the speaker stand idea unless a driver does exist that can perform at 25 hz in < 1.5 cf. So corner columns are now my focus. If I can design it right, a TL should be able to drop the f3 to under 20hz and be close to a 12 x12 footprint although it will be quite tall. Im also now looking at combining my mtm w/ the sub. This might make an excellent full range speaker. Thanks again for the help. Taylor

[kelticwizard]

Taylor:

I found at least one woofer to fit your speaker stand enclosure perfectly. It is the Audiomobile EVO 2210 S4. It will go into a 1.4 cubic foot box and be 3 db down at 24 Hz or so-extraordinary. Frankly, I thought you would have trouble finding a subwoofer to go down as far as 30 Hz in such a compact box.

It is $169 plus shipping-just a tad more than the Dayton Titanic. It is rated at 86 db sensitivity, but I would wager your satellites are probably about 88 db or so. You will never hear the sensitivity difference, and the bass extension is outstanding.

Here are the specs: http://www.audiomobileinc.com/main.htm
Here is the price list: http://www.audiomobileinc.com/main.htm

Another possibilty was the Cupric 10 by Ultimate Sound, which still remains a possibility. However, it was a dual voice coil, and I wanted to check how they rated the sensitivity of the subwoofer-different dual voice coil hookups give different sensitivities. http://www.ultimate-sound.com/ProFrame.htm

Overall, the Audiomobile looks the best overall choice right now.

There were other subwoofers that would fit into your 1.4 cu. ft. box and go down to 25 Hz or so, but they were all over $200. Usually well over $200.

A 3" diameter port of 21.5" should tune the box to 24 Hz, which will be your cutoff. This will require an elbow in the port-easy to do, and the price you pay for getting a woofer that goes so low in a small box. You will get a slight dip of 1.5 db at 30 hz or so, but I have never found such a dip to be audible. Don't split hairs-the speaker fits the box!

PS: In no way do I intend this post to discourage you from the transmission line corner subwoofer, (which I still think sounds like a great idea!), or the behind-the-couch enclosure. I just posted to let you know that IF you decide to do the speaker stand idea, you have a woofer to do it with.

PS: Just checked the efficiency of the MTM's. It is 86.5 db @ 2.83V compared to the Audiomobile's 86. Nice match.

[Edited by kelticwizard on 10-07-2001 at 10:07 PM]