looking to upgrade the 6.5" driver in a home theater tower speaker

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dualblade

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i've got a pair of polk rt20p speakers. they've got (2) powered 8" bass drivers, a 6.5" for mids, and a 1" tweeter. they sound pretty good but i was wondering if i could pick up a good set of 6.5" drivers (and maybe new 1" tweeters) to make them sound even better. i know it's alot cheaper to buy drivers than it is to buy speakers, so i thought this might be a cost effective upgrade. also, there's enough space on the towers that i could use another 6.5" driver if i wanted to.

i figure that i can either get 1 8ohm or 2 4ohm drivers. i don't mind cutting/modding the speaker cabinet and if the sound would be better with a pair of 6.5" auto speakers wired together to create an 8ohm load, i'd go that way.

i know this forum is for computer audio so this question might be a bit off topic, but i'm sure some of you guys are audio guys in general and will have some good suggestions.
 
just look at either
www.partsexpress.com
www.madisound.com

there are tons of brands out there.. one combo that is used a lot in high end diy bookshelves is this:
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=297-305
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=277-030

i don't think either speaker is shielded though.. and those vifa mids will cost you $100 alone..

and once you get to that point, you would have to redo your crossover anyways..

you could most likely go with the same configuration (being an 8, 6.5, tweeter).. but i don't know how much improvement you will get.. your mid driver(s) are going to be very dependent on the enclosure..

play around with winisd to figure out what drivesr will work in those polk enclosures you have now.. http://www.linearteam.org/winisd.html..

i cna't find pictuers of the exact model you have.. do they have 2 8 inch bass drivers in each tower? and then 1 mid and 1 tweeter?
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=297-305
 
yes, there's 2 8's towards the bottom, powered by an amp built into each tower. the 6.5" and 1" tweeter are powered by the receiver, and are farther towards the top. the speakers are 44h x 9.5w x 14d (in inches).

i've got no qualms about modding the speakers to allow for a different size driver, but i thought that 6.5" was a decent size for midrange. i think i'll put a cap of around $200 for both speakers, so whatever's a good buy in that range would be ok with me. i'm not looking to throw away money, as there's nothing really wrong with the current drivers. my thinking is that i have a good size and nice looking enclosure, and the 2x8" drivers provide good support on the upper bottom end (i have a separate sub for the low stuff). i've heard stuff in stores that sounds better (more of that crystal clear sound) and i figured that if i was a driver upgrade away from better quality sound then i would go for it. if the drivers in my price range are more on the level of replacement than upgrade than i'll be perfectly happy with what i have. these speakers are not new so i figured that a few hundred bucks and new technology might change my listening experience. i'm supplying the speakers with 100watts rms from an onkyo home theater receiver

is it important to change the crossover? can i not assume that the stock crossover point is ok?
 
when i first was typing.. i didn't really understand what kind of speakers you had.. i thought you had some kind of old school 3-ways..

the top half with the 6.5 and tweeter is probably seperated from the subs.. at least it should be...

the question is, what about other speakers did you think sounded better, and waht kind of speakers were they?

i don't know a whole lot about crossovers, but supposedly there is more to them than just mere crossover points.. sound is real subjective though.. most peopel i know, think that distortion sounds good.. and they crank the shit out of the speakers till they distort before they think they are loud.. not realizing that they were really damn loud already...

really, what it depends on is what other speakers you heard that you like.. then try to get something that will create the same kind of sound characteristics.. from what i have seen, the speakers you have already are good speakers..

there is no real techology that your drivers are lacking that others have, that i would know of.. speakers are pretty simple tech, and haven't changed a whole lot in the last 50 years other than build materials, higher excursion, and such..

so really.. before i start repeating myself too much.. figure out what speakers you like.. and why you like them.. maybe they are bright.. maybe they are accurate.. there are peopel out there that will know what specific drivesr are in the speakers that you liked and heard.. and might be able to point you to them...

theoretically that vifa/morel combo is just plain great.. but it might not be what you want..
 
i think the last speakers i heard and thought sounded pretty good were a pair of infinity home theater towers. my speakers sound slightly muffled. i have a pair of infinity speakers in my car and i think they sound very clear. i also have a pair of sennheiser hd600 cans for quiet listening on the pc, and they seem to bring out more in music than my towers do. i guess this is not a huge surprise, as the hd600's are pretty well known as quality headphones. maybe the best way to describe it is that if i'm listening to an orchestra, i hear the orchestra in my towers and the individual instruments in my headphones. the headphones are better able to fully represent and separate different sounds so everything is clearer. i don't really know the audio buzzwords, so i don't know what this is called, but i know i like it.

i do not like distortion, and am not a loud listener. i find it's actually easier for speakers to sound good loud as long as the amp isn't clipping: it's when you quiet them down that you can listen more critically. now i know that my room and the amplifier have alot to do with the way sound sounds, but if i could get the clarity that i have in my car, i'd be really happy with that. it may be that the car is a very small space (i have a miata) so no sound is lost or wasted, and this clarity is not reproducable in my room. if the way to go to duplicate this sound is just to get a set of infinity reference car speakers, that's fine with me. i could get two pairs for the price i'm looking to spend, and mod the speakers so that i can put another 6.5" driver in each (so that the impedence is 8ohm).

about the vifa drivers: they say .35 to 1cubic foot, but i have much more space in my enclosure than that. do i want to get a different driver that can better use the available space?

this pic should give you an idea of what the speaker looks like. i didn't see any good pics on the web so i took one:
rt20p.jpg


thanks very much for your help so far
 
DON'T DO IT!

*ahem*

Now that I have your attention... crossovers are matched to the drivers that are used. Not only that, but quite often the drivers used in a speaker are matched to have a somewhat similar sound quality. If you want a sonic upgrade, sell your old speakers and buy new (Or, if you really like the DIY route, look into some kits, say from Adire Audio [very well-respected DIY brand], which tell you what to use for components, what size to make things etc. so that you wind up with a good sound for your labor).

Changing out the driver would most likely sound WORSE than it does now. Not only that, but you would be butchering the cabinets most likely to make room. Not. Worth. It.

*bow*
 
Heh, was just about to say the same. Learned a while ago that you cant just slap a driver in there. You'd either have to create a new crossover or modify the existing one.
 
You can do it, just first calculate the volume in the cabinets, then find a suitable driver by working it's calculations, paper cones tend to have a more vocal sound you may like if you don;t like the Polks now. Higher sensitivity helps, find a new set of tweeters that have the same sensitivity ratings as the mid bass drivers you are replacing.

This will allow you to eliminate the lossy polk crossover and use a simple 3db/octave crossover and not have unnatural harshness.

I personally think the Polks are too flat sounding, no transient response (which, in comparison, Infinity is fairly good at). I base this on the SDA's my father in law has and listening at show rooms as well.

I would say you definitely want the highest sensitivity quality speaker you can find. Madisound and Parts Express are excellant sources.
 
BBA...nice ideas...but...if you are going to be replacing the drivers, rebuilding the crossover, measuring the interior of the cabinet etc, quite possibly bracing it (I don't know about polk's build quality on that speaker)....why not just do what I mentioned earlier and go with a proven design / kit?

There's a lot of work to woofer/tweeter selection. Trust me, I've done it. And crossovers, (I've never heard of a 3db/octave as you were saying, first order are 6db/octave), are fairly complex things to work out also. You have to map out the best frequency to cross over, decide what quality of components you want to use for each inductor and then, after all that, try to cram it into a small space without harmonic disturbance. It's really not as easy as you make it sound.

I'm not saying it can't be done or isn't fun to try, I'm just saying you should be aware what you're getting yourself into.

By the way, BBA, please don't take offense. I just want to make sure he doesn't get in over his head.
 
I agree you have to be aware of what your getting yourself into.

Your right, 6db/octave is a simple cap inline with tweeter and coil inline with low freq driver. Also a cap and coil in series with a midrange driver.

If you look at some of the better speakers, you would be surprised at how many highly regarded speakers have 6db crossovers, it's is a sign of proper driver matching.

The easy way is to look at the response curves of each driver, find a good crossover point where each speaker overlaps, preferably above the fs (resonance) freq of the tweeter (hate shrill sounds) and chose the cap, then go about 200 hz lower for the upper corssover of the midrange and chose the coil for that crossover. (instead of a 200 Hz gap, you could take the common way of revers phasing the midrange driver, but that really puts humps and dips in the response and hurts imaging) You do have to take into consideration the impedance of the drivers at the crossover frequencies you chose, because it will effect the crossover values. The impedance curves are usually listed in the drivers specs.

Your challenge is to get matched sensitivity drivers and a selection of crossover components to experiment with.

There are many books and resources on how to find the right values...in book stores and on the internet.

It is a challenge to get it right but when you do, you get what you really wanted in the end, and thats something most of us can't afford to just go out and buy.
 
Oh, I know. Vandersteen is one of the companies that solely uses first-order crossovers, if I recall. They have some superb speakers.

Anyway, I just wanted to let the guy know that he would have a fair bit of research to do...it's not drop in and go.
 
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