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Twinning speakers but retaining imp ohms. (1 Viewer)

Chris PC

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Is it possible to take a pair of 6 ohm speakers and alter them such the two speakers only present a 6 ohm load to the amplifier? The only way I was thinking this could be possible would be to alter each speakers imp to 12 ohms each so that connecting both speakers would result in 6 ohms. Connecting two speakers to the same output would halve 6 ohms to 3 ohms and my receiver could not handle that, or, at the very least, run hot and risk fire! Yes, I know I could power the second set with an amp, but that would require a y-cable on my pre-outs, and also, I want to avoid using outboard amps.

The idea is that I am wondering if I could run two pairs of front speakers in a bipole fashion. One facing the listener, and the other facing the wall.
 

Robert_J

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I agree with Clinton.

The only way you could do this is disassemble each driver (thereby destroying it) and unwinding the voice coils to half the impedance. If you could do that without destroying each driver (impossible) you would then have to re-design the crossover and the cabinet since you changed the electrical portion of the driver's Theile/Small parameters

If you want bipole mains, then get the Loudspeaker Design Cookbook. It's a must read for any speaker builder.

-Robert
 

Leo Kerr

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Um, can't you just use an out-board speaker-mult box that actually does more than just short the wires together?

Depending on your amp and how it works the A/B speaker selector, it might do that for you. I know my older Yamaha amplifiers do impedance control so that the amp still sees the same load if you run both outs together.

That, and my DSP-A1 has the option to shift its configuration for 4-ohm loads...

Leo
 

Chris PC

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Hmmm, I don't think so. The speakers are 6 ohms each. parallel = 3 ohms or less. Not possible. Receiver is a Marantz SR9600.

Ok, the bipolar idea isn't a good one, but, I was sort of thinking of using the second set of T55's as subwoofers. Just two woofers playing 500 hz and below, or even 200 or 100 hz and below.

What I want, is a speaker that is as high as the PSB Image T55 but that has the same bass response and efficiency as the T65. I played around with dimensions, and if I could make a T55 cabinet 1.5" deeper, and fit all drivers that the T65 had, then the newer T55 would be as big externally as the T65. Not sure if that would make the volume equal or not.

What if I did something like this:

Take the drivers and crossovers of a T65 and put the upper two woofers in the T55 cabinet, then wire the last woofer into another cabinet like a B25 or C60 cabinet? That would work electrically and give my all the woofers. Trouble with using C60 cabinet's, the overall volume would be larger, unless I could somehow use the two woofers.

Or perhaps I could bite the bullet and try this:

A pair of T55's running off of the receivers amps.
A pair of frankenspeakers built like this:
C60 cabinet's with no tweeters and 500 hz crossovers instead of the centre channels normal 2500 hz crossover. So essentially, I'd have two subwoofer-ish cabinets.
Run the C60 woofer speakers off of separate amps.

The idea would be shorter height but the same bass or better response as T65's. Although it's weird, it may work because I'm using the same drivers and crossovers.
 

Robert_J

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Again, not a good idea. There is a LOT of science behind speaker design and most of it has to do with the way sound eminates from the driver's cone. Moving them around and putting them in different boxes changes everything and usually not for the better.

What are your goals of this experiement? What is lacking from your current speaker?

-Robert
 

Chris PC

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Ok, I went off a little with the first post without fully explaining myself. Let me try to start again.

My home theatre is in a basement that has great dimensions for sound. I have plugged the numbers into the calculators you find on the net, and they love my room dimensions. The room is 17 feet long by 11 feet 4 inches wide by 7 feet 3.5" high. Quite un-square. This is good for acoustics and I notice. Particularly the bass is smooth. My previous room was 14 x 12 x 7. More square. Not terrible, but not as good as this room. Ok, so that's the acoustics of the room. How about for home theatre? The problem I am having is that my front tower speakers which I love so much for their balanced two-channel (and multi-channel hi-rez audio) sound are 39.25" tall. 87.25" - 39.25" = 48" high for a screen. This limits my screen height. I was hoping for a larger screen. Another issue is that you can't just use the 48" above the speaker, as you must then make sure your head is above the top of the speaker or you miss the bottom of the screen.

Ok, so what can I do? I live in a condo, so I cannot alter the concrete floor. I looked at the joists to see if I could sneak the screen up into the joist space like I did at the last place (I gained 4" in screen height = going from a 94" diagonal screen to a 102" diagonal screen). I cannot use the joist spaces here in the same way for several reasons. There is a cross-brace at one side of the room due to a window, and this cross-brace reduces the horizontal space for my screen. To make matters worse, I am using CIH with a 2.37:1 screen. Also, the more I look at it, hacking into the ceiling is just a messy thing that wrecks the basement, so if I can't do AT or use shorter speakers, I will probably just have a smaller screen. Trouble with that is the projector I am going to use it at it's limit of zoom for screen size and going with a smaller screen is trouble-some. So what I am going to do with the ceiling is, I am going to simply patch back up the investigation holes I made, or possibley re-build the last few feet of the drywall ceiling such that the drywall is not below the joists. I save a whole 1/2" ! Lastly, I am planning to put down dark red carpet in the theatre, but at this end of the room, I will use thinner underpad, or no underpad at all. I cannot eliminate carpet completely as I believe it will mess up the sound. The sound in this room with my receiver and speakers is already very bright. I need acoustic absorption tiles too.

Ok, so that is the history lesson, here is a review of what I want:

1) I want a screen that is higher than the 47 to 48" that I presently have to work with.
2) I cannot, nor do I want to alter the ceiling or floor to gain any useful height.
3) I love my main tower speakers because they are very efficienct and have great smooth low bass extension. I don't want to lose any of that at all, in fact, if I changed anything, it would nice to get a bit more bass.

Using the 6.5" woofers for bass does work, because the T65 and T55 speakers use the 6.5" woofers for this already, in a 2 and a half way system, using 500 hz crossovers. In fact, the previous generation 7PT used a pair of 6.5" woofers and an amp as a sort of subwoofer up to 200 hz.

I could use a subwoofer, but it never sounds as good as the T65's sound alone.

The best idea I have come up with is to take the T65's and build a shorter cabinet, keeping the front baffle driver alignment the same. I could reduce the speakers height by 3 to 5 inches. This is not easy, and I'd have to make a really nice tight cabinet in order to minimize any changes in the sound quality.

The reason I suggest using a set of T55's and then supplementing with woofers in another T55 or C60 cabinet is that I would cross-over those additional woofers at 500hz or 200hz, so the midrange shouldn't be negatively affected. This option could still work. In fact, one idea I have is this: Take a pair of T55's and use those as main speakers. Get another set of T55 cabinets and put only woofers in the cabinet crossed over at 200 hz. Then use an amp like the 7PT did.

Any more thoughts? Sorry for the confusion. I can't find links to the older 7PT, but the newer stuff is here:

PSB Speakers - Product Comparison

Just pull up the C60, T55 and T65.
 

Robert_J

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Then you didn't correctly set up your sub. A 6.5" woofer can't hold a candle to a true, quality subwoofer that has been set up properly. Some might say I'm a bass nut with a 2,400w amp and dual 15" subs but they are integrated seamlessly into the rest of my system. Those consist of DIY speakers made with 6.5" woofers and silk dome tweeters.

If you are going to the effort of rebuilding cabinets, then why don't you go completely DIY? There are hundreds if not thousands of designs all over the web. But if you don't want to do that, then spend the time and money that you would put into your rebuilding or DIY and buy a quality sub. Properly integrated you will do much better than your franken-speaker your are proposing.

-Robert
 

Chris PC

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I have a Mirage BPS-400 and I originally had 6T's in my other room. The room wasn't a very good shape. This new room is better. Now I have the Mirage BPS400 and the T65's. I haven't tried my best to integrate them. I just liked the sound of the T65's themselves. I know they can't match the sub for low bass volume, but they do go to 30 Hz - 3db and they sound good. The T65 towers each have a volume of 65.8 L so I think with their three 6.5" woofers and 3 ports, they do a good job, about as good as most towers can.

I have a 50-100 hz crossover in the subwoofer and my receiver can use a 60hz crossover on the towers, though that seems a waste. I also have a BFD1124 I can play with. My home theatre isn't quite together at the moment. I'm deciding on whether to go with a smaller screen, shorter front speakers, or an Acoustically Transparent screen.
 

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