|   Dipole surrounds? | Zero27
Jul 29, 2002 8:36 AM | | I have a home theater set up in my bedroom, which is relatively small (12'6" x 12'8") and I am using front firing rear surrounds mounted on the side wall, above ear level, slightly behind the listening position. I was viewing some of the more expensive bipole/dipole surround speakers avaliable for purchase and had an idea. I have a pair of Linaeum Dipole ribbon tweeters lying around.
If I mounted them to the sides of each rear surround cabinet, leaving the original tweeter on the front connected as well, would I have essentially created a dipole surround? Would the surround effect be more enveloping? Or would it just be a pointless waste of energy and make the situation sound worse.
The surrounds aren't bad, I just think a bit more spaciousness in the rear sound field would be nice.
Any help is appreciated. |
| Suggestions for getting a more ambient sound from surrounds | Sir Terrence the Terrible 1
Jul 29, 2002 1:06 PM | | "I have a pair of Linaeum Dipole ribbon tweeters lying around. If I mounted them to the sides of each rear surround cabinet, leaving the original tweeter on the front connected as well, would I have essentially created a dipole surround?"
Not necessarily. The tweeters would have to wired out of phase with each other to get a dipole effect. This would also ruin the phase integrety of the original tweeter. Also it would drop the resistance of the speaker load to the amp to dangerous levels. The additional tweeter would probably send the ohms down to 4 instead of the traditional 8ohms
Check this link out for alternative placements in small rooms.
http://www.dolby.com/ht/Guide.HomeTheater.0110.html#s3.3
This ought to help give you some ideas on how to make your direct radiators more ambient sounding.
Sir Terrence |
| Suggestions for getting a more ambient sound from surrounds | Zero27
Jul 29, 2002 6:06 PM | | Terrence,
Thanks for the info! I tried changing the placement and found an area that really works. But, just on a random thought, mostly because i have these nice tweeters lying around, what if I disconnected the rather cheap tweeter in the rear surrounds (they dont even match my front mains anyway, timbre matching doesnt even matter at this point) and hooked up the linaeums instead? (The Linaeums are an all-in-one design, made specifically to be plugged in to the amp speaker level output, and then you run a feed from the tweeter into the bookshelf, so impedence problems are not an issue in this situation.) Would this perhaps give me some more spaciousness due to the design of the tweeter? or would this be a lot of wasted work?
Thanks for your time! |
| 4 ohm tweeters (or 4 ohm speakers) are rarely a problem | Richard Greene
Jul 31, 2002 8:36 AM | | TT sez:
"The tweeters would have to wired out of phase with each other to get a dipole effect. This would also ruin the phase integrety of the original tweeter. Also it would drop the resistance of the speaker load to the amp to dangerous levels. The additional tweeter would probably send the ohms down to 4 instead of the traditional 8ohms"
RG replies:
You've provided many good reasons not to add a supplemental tweeter but potential danger to the amplifier is not a good reason.
Very few amplifiers or receivers care whether they are driving 4 ohm or 8 ohm speakers. They'll usually run hotter driving 4 ohm speakers, but the probability of the amplifier overheating and temporarily shutting down is slim to none. My wild guess is 1 chance in 100.
I've used cheap receivers to drive 4 ohm subwoofer drivers with no problem. In fact, one of my bedroom systems uses the cheapest available ($139 at Best Buy) two-channel Sony receiver to drive two 4 ohm moderate efficiency subwoofer drivers with no problems. Even at high SPLs. Although I never read the owners manuals (real men don't need no stinkin' owners manuals) I know many of the manuals will say NOT to use 4 ohm speakers ... as I often do.
A problem is likely only if the 4 ohm nominal AC impedance speakers happen to have have a DC voice coil resistance under 2.5ohms (very rare based on my own measurements) or are very inefficient (under 86dB -- also rare these days). Even then, the most likely problem will be a hot receiver case -- the receiver probably won't shut down unless the speakers are inefficient, 4 ohm nominal impedance AND are played at high volumes with no subwoofer used (no high-pass filter to block deep bass going to the speaker).
I don't know of any good reason to hook up an additional tweeter unless you want to bypass the original tweeter... but two 8 ohm tweeters hooked up in parallel (4 ohm load)will not be a problem for any amplifier.
I suspect even two 4 ohm tweeters hooked up in parallel
(2 ohm load) would not be a problem, especially if the tweeters were different brands/models with different impedance curves ... (I've never done this and don't know anyone who has, so I'm just speculating).
The reason: Most sound energy goes to the woofers
in two-way speakers -- maybe 10-15% of the energy goes the tweeters -- so the impedance of the woofer is far more important to the amplifier than the impedance of the tweeter.
Two 8 ohm woofers hooked up in parallel (4 ohm load) will rarely be a problem ... but if they are the exact same brand/model they will have virtually identical impedance curves ... and that means the impedance may get very low at some frequencies. That could be a problem for the amplifier. This "rule-of-thumb" also applies to hooking up two 8 ohm speakers in parallel (4 ohm load) to one amplifier -- there is less risk if the speakers are different brands/models whose low impedance points are at different frequencies.
The real problem here is many speakers are rated 8 ohms nominal for marketing purposes. The engineers who designed the speakers might not agree but no one is asking them! Many speakers should be rated 6 ohms or 7 ohms nominal rather than 8 ohms. Consumer Reports has pointed out this "impedance inflation" problem for decades. Some speakers rated as 4 ohms nominal should be rated as 3 ohms nominal -- these can be a problem for many amplifiers.
In my opinion the best way to estimate the nominal
impedance of a speaker is to evaluate a chart of impedance versus frequency. An easier alternative is to measure the DC resistance across the + and - terminals of the speaker and multiply the DC resistance by 1.333 for a fair estimate of nominal AC impedance. I've been doing that for almost three decades -- only speakers whose DC resistance is under 2.5ohms are likely to shut down an amplifier (I've probably measured the DC resistance of over 50 pa |
| |
