questions about attempting full range surrounds.

[paul3221]

Hi,

I've been an audiophile for years, but only recently thought of trying to make my own speakers. I'm thinking of making surround speakers for my first project, since they should be cheaper, easier, and less important to the overall sound than a main front pair.
I was originally considering doing dipole/bipole surrounds, but after some reading, they seem to have been a passing fad, and more designed for Pro Logic than the newer discreet surround modes. Then I was thinking of of small, wall mounted, 2-way speakers, but I'm still trying to learn about crossovers. After reading on here, I hear a lot of people having great results with full range drivers, so I am now thinking of designing something along that line. Perhaps a smallish wall mounted enclosure, with the driver facing the listening area from above and behind. I was considering one of the smaller TB full range drivers. Possibly the 3" Bamboo cone driver (here ), or one of their other small full range drivers.

My Questions are:

IF I use a full range, single driver, do I need to worry about any sort of crossover?
If not, and I just wire them straight from the binding posts, do I need to worry about the input power being too high, and frying the driver at normal listening volumes? My receiver is 90W/ch. The drivers are rated for 12W.
Has anyone had any experience with this sort of setup? If so, how is the sound quality?

Any tips or advice would be much appreciated.

Thanks,
Paul

[chris661]

WRT the crossover - a high-pass filter set fairly low (40Hz ish) would protect the driver from over-excursion etc. This would be a simple cap in series with the driver.

Surround effects in movies etc are often fairly short, such as a bullet comming past (you get the idea), so it will be difficult to destroy the driver with signals that don't last. I've plugged 7W speakers into 100W before now. I let bass go through, lots of nasty distortion and smells. Turned the bass down and all was well.

The driver's high frequencies look a little rough, especially around 6-10KHz.

I'm assuming these speakers will be for movies only, but, if you were to do some listening with them as your mains, you might want to use a tweeter to smooth out the last few KHz.

Chris

[Godzilla]

http://www.zillaaudio.com/tb-1320-bamboo.htm

I built the above speaker but it's the 4" version. It works really well. I use it in my 'home theater' system with a 100 watt amp.

Godzilla

[GM]

Originally posted by paul3221

I was originally considering doing dipole/bipole surrounds, but after some reading, they seem to have been a passing fad, and more designed for Pro Logic than the newer discreet surround modes.

IF I use a full range, single driver, do I need to worry about any sort of crossover?

If not, and I just wire them straight from the binding posts, do I need to worry about the input power being too high, and frying the driver at normal listening volumes? My receiver is 90W/ch. The drivers are rated for 12W.

Has anyone had any experience with this sort of setup? If so, how is the sound quality?

Greets!

Not a passing fad, a requirement for best surround sound in Pro Logic mode in a typical HT app.

Not if you set them to 'small' and let the processor's bass management re-route any LF/lower mid-bass to the LFE system at whatever its XO point/slope is set to. This can mean bad news to smaller drivers, especially with those limited linear excursion even at the lower TV broadcast movie reference. If you live in an attached home this may not be an issue due to the need to keep the neighbors from complaining.

There's no such thing as too much power, only a point of diminishing returns and too high a gain setting for the app, i.e. the person controlling the volume decides when too much is enough, so if you have a knob to turn, best to protect it against little (and not so little) kids. WRT a remote, it's designed to move slow enough to hear the onset of potentially damaging distortion, though of course it too needs to be unavailable to the more irresponsible and/or hearing impaired folks.

Note that the 12 W is a continuous rating, so a music power rating will be somewhat higher (usually 2-3x for a typical 'FR' driver) since it's the transients that eat up power. For instance, a 90 dB eff. speaker may only need a watt to play at the loud 85 dB/listening position DD/DTS/THX cinema reference, but with a 20 dB dynamic headroom spec for all main, surround channels it needs up to an honest/low distortion ~101 W/channel to keep from clipping the amp on transients. Whether or not a 12 W speaker for sure can handle it would require testing, but I'm guessing not, though any decent quality 30-35 W, 90 dB/eff unit should have no problem with it.

I have and it can work very well indeed if the entire HT system (room layout, et al) is designed as a whole. That said, with today's incredible driver size/specs selection available compared to when I did some designs it shouldn't be too hard finding suitable units to work well in existing apps at reasonable cost.

A major consideration is the surround channel's directivity. Too small a driver and you'll have unwanted output comb filtering with the mains and other surround channels (an all too common problem). Conversely, with too large its beaming won't cover all the listening position with adequate output. Note this also applies to the mains and of course using the DD/DTS/THX recommended positioning scheme as much as practical is a good plan.

GM

[paul3221]

Thanks guys for all of the input so far. I appreciate it. The in-line filter to protect the driver is a good idea. I'll definitely do that.

I agree that a 2 way may be a better plan to get the full range, but like I said, I still have to learn about crossovers. These are going to be strictly surrounds for the 7.2 setup. They'll have to be smallish, and very aesthetically nice to keep the wife happy... ;-) She's already a little tired of my multiple amps and speakers sets around the house.

If someone has suggestions for a smallish, nice looking, full range driver that may work better, I'm all ears. I've also considered the non-bamboo TB driver Here , but I'm not sure how I would cover that ugly, bare metal flange to make is still look nice.

Thanks,
Paul

[GM]

You're welcome!

One more time, A major consideration is the surround channel's directivity.

If you take this out of the equation, then driver selection is reduced to finding the cheapest 'FR' driver able to handle at low distortion the ~100-7 kHz ~flat BW that the vast majority of movies are limited to. IOW, anything > ~4" or even smaller if it has more Xmax than the typical 'el cheapo' 'FR' driver. Placed at the wall/ceiling juncture and you can probably get by with one or two small, high Q drivers/channels scrounged from discarded TVs and/or car audios mounted on a small OB, not to mention get a bit of vertical plane directivity. Use high aspect ratio oval drivers oriented with the long side horizontal and you get a bit of horizontal directivity to boot.

GM

[paul3221]

OK, at the risk of sounding thick, what do you mean by directivity? I plan on having the surrounds mounted on the wall, with the driver baffle part facing down and toed in towards the listening position. Should that work well, or is there something else I need to consider?

Thanks,
Paul

[chris661]

I speaker with lots of directivity will put sound mainly to one place. If it has little directivity, the speaker will radiate sound into the whole room. For surround apps, you'd want the second one, as it will blend sound together with your other speakers more smoothly.

For example, driver A has lots of directivity. You are watching the Matrix, and a bullet goes past you. It will sound like the speaker goes from your mains, then teleports to the surrounds, with nothing in between.

Driver B isn't very directive. When the bullet goes past you, driver B makes it seem like it goes all the way past you, smoothly from the front to the back, because it radiates sound into the space around it, not just at one place.

Chris

[maxmercy]

I just came across this thread, and here's what I am planning to do for full-range surrounds, with the 2" Peerless that are on sale at PartsExpress..



JSS

[GM]

Originally posted by paul3221
OK, at the risk of sounding thick..........

No risk, though as a 'long time audiophile' I did assume you had at least a basic knowledge of how sound radiates from a speaker and how to control it. Ditto the basics of how we hear, so hadn't planned on doing any in-depth tutorial or would have refrained from posting due to self imposed time restraints.

WRT general speaker placement, DD/DTS/THX reference applies, but they assume a certain amount of controlled directivity. This info is found at their respective websites in one form or other and regurgitated all over the net with seemingly endless pro/con discussions.

I imagine the prosound web has a directivity tech article or FAQ and books such as Don and Carolyn Davis's SOUND SYSTEM ENGINEERING are a 'must have' reference for the 'serious' among us.

WRT point source driver/horn directivity (DI, aka Q), there is (was?) a complete on-line acoustics engineering class worth of info on the under both the 'directivity' and 'polar response' headings. Ditto human hearing research. 'FR' drivers in particular though, not so much for a variety of reasons, but once one has a good understanding of the basics combined with analyzing a few high resolution response and matching polar plots should allow you to visualize how they will change with different radiator, dust cap and/or whizzer size.

Anyway, just to answer your Q.............

You want the surrounds somewhat above seated head height and somewhat behind the mains's focal point as per DD/DTS/THX reference. How high normally depends on how wide the listening area to be covered is and how many seating rows there are, but with no DI considerations there's no set height beyond the acoustic one of using a golden or acoustic ratio offset, so focusing them to the main's focal point seems a good starting point to find the best overall toe in compromise, ergo a swivel mount is your friend here.

GM