Questions about the Polk SRS1.2TL - diyAudio
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Old 25th April 2004, 01:46 PM   #1
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Default Questions about the Polk SRS1.2TL

My brother has a set of these speakers and I am a little curious about the design. A picture and specs are found at http://www.polkaudio.com/home/produc...5aba4cbc56165e

The two major factors that impress me about these speakers are the imaging and the lack of comb filtering that takes place from the small number of drivers. The speakers sound great both on- and off- axis, vertically and horizontally.

Does anyone have any information about the crossover design needed to pull these speakers off before I rip one open? I am not trying to clone them, but I would love to know what technology is in there. The crossover is all passive, but there is a wire (2 conductor, I think) that is connected between both speakers. We disconnected this wire and the imaging shrank considerably.

I guess this isn't the quintessential crossover design to end all designs, but I can hear sounds all around me when I listen to the speakers.
Thanks for any input
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Old 25th April 2004, 08:46 PM   #2
Ron E is online now Ron E  United States
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Based on their blurbs, I would guess that these speakers use perhaps 1/3 of their driver complement on each side to drive a difference signal. There would be two actual crossover networks per box and on the left side, the drivers produce a L signal and a L-R signal. On the right side, a R signal and a R-L signal is produced.

You can do this with a separate speaker system on top of regular speakers. The circuit "surround with phantom center channel" at the site below is the one you want to use. You place the speakers on top of or even beside the normally-connected speakers.
See:
http://kantack.com/surround/surround1.html
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Old 28th April 2004, 04:05 AM   #3
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Those speakers (with the required crossovers) are designed to cancel inter-aural distortion caused by sound from the left speaker reaching the right ear and vice versa. The mids on each side are separated by a distance that's about the same as the distance between human ears. That presumably gives the correct delay to the cancelation signal. Today the DSP in a home theater system could easily get the same effect without the extra speakers. In fact, a year or two after the Polk speakers came out, that Carver guy came out with an electronic box to do the trick. He called it a "sonic hologram." I owned one. It hummed something awful.

To get the full effect, get a binaural recording if you can find one, and sit with your head exactly on the center line. But some regular recordings work pretty well. Back in 1979, it was pretty amazing to listen to a stereo and hear sounds off to the side or behind you. Now we are quite used to such magic.
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Old 28th April 2004, 04:22 AM   #4
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Quote:
Originally posted by Ron E
Based on their blurbs, I would guess that these speakers use perhaps 1/3 of their driver complement on each side to drive a difference signal. There would be two actual crossover networks per box and on the left side, the drivers produce a L signal and a L-R signal. On the right side, a R signal and a R-L signal is produced.

You can do this with a separate speaker system on top of regular speakers. The circuit "surround with phantom center channel" at the site below is the one you want to use. You place the speakers on top of or even beside the normally-connected speakers.
See:
http://kantack.com/surround/surround1.html

You're right on the first part, except maybe the 1/3 number. However, I don't think one speaker on top of another would work as well as side-by-side. The side-by-side arrangement delays the right side cancelation signal so it reaches the right ear at the same time the sound from the left main speaker does.
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Old 28th April 2004, 07:53 AM   #5
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1. the polk SDA and SRS series are meant to be close to the rear wall and 3 ft from the sides.

the inner woofers get teh L / R signal. the outer woofers get a L-R / R-L signal.

the tweeters are also progessively rolled off. only 1 tweeter operating above 14k, then 2 above 10k etc...how this helps reduce comb much is beyond me.

i think polk is trying to replicate bose's marketing not that they dont make decent speaker though.
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Old 29th April 2004, 01:44 AM   #6
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Thanks for all the info.
The truth is, I have not been impressed with any other Polk speakers I have heard. My summer plans include a line array design, so I figured if there was anything to learn from the Polks, I want to find out now before I start cutting wood
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Old 29th April 2004, 07:13 AM   #7
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a long long time ago i decided to test the polk sda 1. must have been mid 80s.

my test was simple.

my benchmark was a bass reflex MTM using 2 8" Focals and a 1" Morel.

i took a bunch of fav cds, a cd player, a carver 1.0t, a ADC eq with analyser, and a dbx compander and aa radio schack SPL meter.

i played various rock music (who, pink floyd, alan parsons, etc...) and some classical mostly tchaikovsky (1812, swan lake, sleeping beauty) and some andrew lloyd weber (phantom of the opera).

while the music was playing i boosted the bass 6db at 30Hz and increased the expansion control on the dbx. the dbx controlled dynamic range and could expand and compress the same.

i found the MTM out perfromed the SDA1 which had 4x6" + a 12" passive by over 10db.

at a later date i tried to replicate the spl levels i was getting with the MTM. I bought 8 Peerless TP165R (rubber surrounds) and replaced the polk woofers with the TP165R. It involved makig a new baffle too as the TP165R were not a perfect fit. Still I could not meet the SPL levels of the MTM but the results on the SPL front were a bit better execpt that the balance of the speaker had now changed.

finally i sold the SDA1.
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