Making a center speaker

meljr

I currently have a pair of RT8T speakers for my A/V setup. (I might switch them out for a pair of 10a's or SDA's) So I want to make a center channel to match. There is a pair of Monitor 10's on CL for cheap and was thinking of maybe using one to make it, using just the 2 woofers, tweeter and crossover and building an enclosure. I'm pretty handy with all, but not sure of problems that I might encounter, so here are my questions

Do I have to match the same inside volume as the 10 or would it be smaller because of no PR?

If it can be smaller any guess on what size? I can't find any specs on these speakers.

Do you think there would be enough bass with no PR or should I try my hand at porting it? I have enclosure software, but with no specs on the speakers I'm lost.

If you can think of any other problems that might arise, let me know.

Thanks for the help
Martin

deronb1

The best match for a.pair of rta 8Ts would be another 8T. They are a great all around speaker for both music and HT. Simple xovers and easily upgradeable. 6 ohm but fairly sensitive at 89.5 so you dont need a ton of juice.

teekay0007

Hey meljr, check out this thread by westmassguy, he's been down the road you're thinking of traveling.

http://www.polkaudio.com/forums/showthread.php?150760-My-Center-Channel-Project

He's also a very good source of info on this type of thing.

westmassguy

Thanks teekay007. meljr, I'd be happy to help you with your project. Are they RT8Ts or RTA-8Ts, big difference

meljr

According to polk pictures they are RTA-8T. They just say Monitor 8T on the back.

Well I just picked up a cheap pair of 10b's . All the mids move when PR is pushed. He said one tweeter is blown, but I only need one any way. I will be taking them apart tonight to check them over and find out what drivers they are.

BTW thanks for the help.

meljr

First off let me thank Westmassguy for posting his build of his center speaker. It gave me a place to start.

So I have my donor 10b with the sl2000 tweeter and MW6503 woofers. I'm getting a new TV soon and will be building a cabinet to go under it so I was not to concerned about the size of the speaker box.

I borrowed a copy of Bassbox 6 and used the cubic ft. of the 10b as a starting point. I liked the idea of using the 6" PR like Westmassguy did, but Polk told me they don't sell them. I was thinking of using the 10" from the speaker, but it would have to fire either up or down and wasn't sure if this would work so good. (let me know your thoughts on this ), so I went with a ported box. This is what I came up with.

Box size - 9.5" H x 31.5" W x 15.39" D 1.929 cu ft.
2 - 1.5" vents I'm using 2 to balance out each side.
It said to use minimal fill ........ I could use some input on as it's tough to get a definite answer on. Is it 1-2" all around or on just 2 walls? let me know.
F3 - 49.78
Fb - 36.38
Not sure what these numbers mean, but I assume it has to do with where the bass rolls off and it seemed the lower the better. Again........let me know.

I'm going to be rebuilding the x-over and finalizing the box soon. I'll start building the box in a week or so. It's going to be all paint grade to match the rest.

I'll be posting the build with photos as I go...

I would be appreciate any and all input on this.
Thanks

Nightfall

Passive radiators off of Monitor 5's or 7's can be found on Ebay quite often. I have one off of a Monitor 5 (just one) but the rubber surround is torn. You're welcome to it if you'd like to try and repair it.

Nightfall

westmassguy

meljr wrote: »

First off let me thank Westmassguy for posting his build of his center speaker. It gave me a place to start.

So I have my donor 10b with the sl2000 tweeter and MW6503 woofers. I'm getting a new TV soon and will be building a cabinet to go under it so I was not to concerned about the size of the speaker box.

I borrowed a copy of Bassbox 6 and used the cubic ft. of the 10b as a starting point. I liked the idea of using the 6" PR like Westmassguy did, but Polk told me they don't sell them. I was thinking of using the 10" from the speaker, but it would have to fire either up or down and wasn't sure if this would work so good. (let me know your thoughts on this ), so I went with a ported box. This is what I came up with.

Box size - 9.5" H x 31.5" W x 15.39" D 1.929 cu ft.
2 - 1.5" vents I'm using 2 to balance out each side.
It said to use minimal fill ........ I could use some input on as it's tough to get a definite answer on. Is it 1-2" all around or on just 2 walls? let me know.
F3 - 49.78
Fb - 36.38
Not sure what these numbers mean, but I assume it has to do with where the bass rolls off and it seemed the lower the better. Again........let me know.

I'm going to be rebuilding the x-over and finalizing the box soon. I'll start building the box in a week or so. It's going to be all paint grade to match the rest.

I'll be posting the build with photos as I go...

I would be appreciate any and all input on this.
Thanks

I think you're better off with a ported design for that application. Trying to mount the 10" PR on the bottom for example, is a no-no.
Did you use the T/S parameters for the drivers with Bassbox, or just copied the internal volume of the 10 cabinet? The cab for the 10s was designed with a passive radiator in the mix. A ported design using the actual T/S parameters will be more accurate.
The reason I was able to use those 6" PRs, is because I switched to 4 ohm drivers that have half the VAS of the 8 ohm drivers you're using.

meljr

Thanks for the offer Night, but I would need 2. I did input numbers from a Dayton 8" PR, but the box size was getting too big to get low numbers.

meljr

I did use the T/S parameters I found here for the MW6503. I liked your design and how you went about it, but I'm trying to keep it simple. Changing X-over design is way above my head at this time, but I'm learning........

westmassguy

meljr wrote: »

I did use the T/S parameters I found here for the MW6503. I liked your design and how you went about it, but I'm trying to keep it simple. Changing X-over design is way above my head at this time, but I'm learning........

Sounds like a plan!

markamerica

Meljr,

It looks like we're working on similar projects. Good luck to you!

Face

westmassguy wrote: »

I think you're better off with a ported design for that application. Trying to mount the 10" PR on the bottom for example, is a no-no.

Big no no! A PR doesn't have a magnet to keep it centered in the gap, so it will sag, offset the tuning and have much more limited travel.