Narrow 3-way with sidefiring woofer?

[Landroval]

Hi,

My friend is starting a new project which includes 3-way WMT mains and probably 2-way center and surrounds using the same drivers as the mains MT. A designer friend of ours recommended to do a tall but narrow (~5"-7") speaker with some cool finish, and I think that's what my friend is going to do.

My question is about the sidefiring woofer. What needs to be taken into consideration when selecting the drivers? How should the sidefiring driver be measured? What would be the differences in the crossover between side- and front-firing woofer?

We have thought both, plate-amp driven active woofer, and a normal 3-way with passive crossover. Any other benefit from going semi-active than efficiency?

Any help is appreciated.

[Jed]

Here is an interesting interview on this topic. I'll paste it below:

Several of the larger Audio Physic speakers have two woofers mounted low on each side of the speaker. Gerhard explains that this is done to get a low-range response with better phase behavior.

- We invented this system because we wanted an in-phase signal in the bass. I have always tried to avoid the double signal pass that you usually get from conventional systems; with one pass going directly from the membrane, the other over the floor and the ceiling. This placement near the floor also gives you approximately 3 to 6 dB gain. So one of the advantages is that you can use lower mass in the woofer and stronger magnet systems. But from 200 or 300 Hz you run into problems. You get a resonance. The magazines say that you shall not put the woofer to the floor, because it gets boomy. But we found that the problem in fact is in the deeper midrange region. So if you make a very low crossover frequency, say 125-180 Hz, you can avoid this problem and have the advantage of the room gain. Also, you benefit from the fact that the center of the gravity is very low. The system is push-push, so the energy inside is canceled, and the loudspeaker gets pneumatically stabilized. And the effective baffle is large, because the woofers "see" the side of the speaker. So you have tremendous advantages. The only problem I have found, is that the crossover has to be very steep to get rid of the boominess.

- How crucial is the localization near the floor?

- Very crucial! In the Virgo, we found that from the floor to the middle of the woofer, 40 centimeters was ideal. But place the woofer 5 centimeters different, and you get a totally different result. I would encourage people to build a simple box, fasten it on a string or something, and then raise it and lower it while listening and measuring from the listening position. Maybe you will find some interesting results!

- What part of the frequency band do you find most difficult to tune?

- Oh, the midrange! Of course. The ear sensitivity is at the best there, and you are in a wavelength of between 10 to 30 centimeters, which also is the dimensions of the baffle. So you get dips and peaks. Also, when you measure the energy in natural music, you will find a peak at 100-800 Hz.

- What solution do you have to get enough energy in the octaves between 80 and 320 hz?

- First and foremost, this is a range where you really can hear the advantages of harder cones, because of the demanding dynamics in these octaves. But I try to cover this with a regular midrange driver, with a crossover frequency at maybe 150 Hz. I find this better than trying to let a larger driver, maybe a 8", cover it. Because then you usually have to cross it over higher in the midrange, and that is very difficult. I find simple things so challenging that I see no reason in going into even more complicated things. First I have to master simplicity, Gerhard says.

[Landroval]

Thanks, that's very interesting. I'll have to see if I can find a sufficiently shallow woofer so that we can put one on each side.

[derekbannatyne]

http://yellow.mynethost.com/~bv126368/shop/catalog/product_info.php?products_id=51

What about that one right there?

[Landroval]

Yes, the SL-10 might be good. Although it's very low efficiency and needs a lot of power. That means a huge (and expensive) plate amp and wider enclosure. I'm not entirely happy with that.

[cjd]

Why narrow?

A narrow top cabinet and a wider base cab (even widening - trapezoid) may open up some possibilities. Something like the RS150 MTM I've done with more of a sub module below crossed actively (RS265HO may fit the bill quite well) - possibly even using a receiver's built in XO, could provide everything you want. If 100-120Hz can be done, the sealed version of my MTM would be ideal.

C

[Landroval]

Narrow because of looks. A wider base structure is not pretty, and in this project looks are as important as sound.

The construction will probably be made with Kharma Exquisite-style piling of carved plywood. The target is quite close to Penaudio Serenade which can be seen in the attached picture.

If we go active with the woofer(s), I think Peerless SLS8 or XLS10 will be the choice. If passive, then something different.

[ThomasW]

Narrow because of looks. A wider base structure is not pretty, and in this project looks are as important as sound.

People wanting their cake and eating it too run into trouble when the real world of physics raises it's head. Hoffman's Iron Law

Take your pick, smallish woofer, small box needing high power or an larger driver and a bigger box requiring less power. Pick one.....

Don't plan on anything close to 'realistic' SPL with a design like the Penaudio Serenade. It will be fine for chamber music and quiet Jazz. It will be destroyed if it's used for home theater...

[Landroval]

I don't want both. Narrow enclosure with one or two 6,5"-8" for the bass will be just fine. One XLS10 will also be ok, they work very well in ~15 liter sealed.

Edit: No need for realistic SPL's here. So far I've been happy with a single 6,5" + 1" coaxial driver per channel, and my friend who is building these has currently some low-fi Yamaha floorstander TMM's with two 5", so I think high SPL isn't really required.

Edit2: Hmm, so how big should the speakers be in order to produce satisfying SPL for home theater also?

[ThomasW]

Narrow enclosure with one or two 6,5"-8" for the bass will be just fine. One XLS10 will also be ok, they work very well in ~15 liter sealed.

You already know what you want, so have fun....

Edit2: Hmm, so how big should the speakers be in order to produce satisfying SPL for home theater also?

There's simply no replacement for displacement. High SPL means lot's of air needs to be moved...

Small 5"-6" drivers run into radiating resistance (compression) and create high distortion when one attempts to drive them to high SPL. So one need bunches of them (line array) or bigger drivers.

Smallest system I've ever used for HT is a pair of 8" MTMs augmented with dual 15" subs. Now I use these with a 12-12" driver IB subwoofer.....

[Landroval]

Lol, I see what you mean by displacement. Nice idea for the sub by the way.

[cjd]

A wider base structure is not pretty

I disagree with your opinions on design. :P

But, as they are your speakers...

C

[Jed]

Alright, I have an idea. How about an MMTMMW setup using 5" or 6.5" Ms and a sidefiring woofer? The Ms and tweeter would be 2.5way so a 3.5way total. At least you should be able to get a bit more power handling out of it, plus they should fit in a smaller room. I'd love to have speaker's like Thomas has, but us mortals sometimes don't have the space for a system like that. ;x(

RS150, RS180, or peerless 883 or 882 would work nicely. Woofer would cross in at around 175 HZ or so. Could even go semi active for the woofer/ mid crossover.

Jed

[Landroval]

Zaph has been designing MMTMMW's for quite a long time, but I dont think that's what we're looking for. Too complex I would say. A MTMW or MTMWW could be ok, but I dont see the benefit from those extra M's. Preferably TMW's. Some of the Audio Physics models are actually quite nice, e.g. Tempo and Virgo.

cjd, care to show pics or something what you mean by the wider base? If there's a good idea, my friend might be willing to change plans.

[Jed]

The benefit is greater dynamics, SPL, and easier amplifier load with the extra Ms.

[JoshK]

I actually think these are pretty cool looking.

[kejolly]

http://www.salksound.com/gallery-avail.html

I like the HT3s....not the price!