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opimax
10-28-2007, 08:43 AM
I am ready to do my center channel for my system and would appreciate any and ALL feed back

I have built my system based on music listening, not for movies or sports which I do some but music is #1! Think concert DVDs and standard 2 channel CDs. Southern rock, blues, classic rock, pop, jazz, some new age

I have a 7.2 system using 250ti w/CC TIBQ XO as my mains, 120ti for the surrounds, and a b460 and Velodyne 1200r for subs. I will biamp the 250s w/2 Perreaux 6000b (300 per channel) the center has a Perreaux 3000b (180 a channel or 400 bridged).The surrounds are fed by the Sony STR-da9000 receiver(130 -200 depending on which manual you read :( ) The b460 has an Adcom gfa555 bridged (600) and I have a Velodyne SMS1 to control the subs

I have thought of 2 108 woofers on the outside and a 44ti and 104 stacked in the center. It would look like an EC35. I have all the drivers. For XO I have a 120ti, a 250ti and my 1st choice 250tibq XO to work with. I don’t mind externally mounting the XO if needed

I thought either a 4 or 3 way depending on what makes sense.

1) 250tibq. 4 way speaker crossing the 108 at different points to match the XO. 1 would cross at 350 and the other at 1.2k. Additionally using this XO
a) I can biamp. Very strong preference to biamp
b) Copy the CC on my own and exact match to the 250s

2) Stock 250 XO. 4 way don’t see why I would use this over the TIBQ

3) 120ti XO. This was suggested by 1 of our members. Use this at a 3 way, change the XO by changing the LF cap/inductor to allow 4 ohm use ( Multiply the cap value by 1.414 and divide the inductor value by 1.414 ) and CC this set up

It has been recommended to build separate sealed enclosures for each woofer of about 1 cu ft but if someone who knows or will run the numbers and has something to add would be extremely appreciated


Current questions
1)Is it OK to cross the woofers at different points?
2)Any modifications for the XO since using a 108 on the bottom rather than the 14-3 with the 250tibq
3)Is it worth it to try to copy the tilted baffle and move the 44 forward to more closely match the 250s? if done how exact on the measurements?
4)Size limitations 9.5” to 10” high, 50” wide, 24” deep, 45lbs

Thanks much :),


Mark

opimax
10-28-2007, 09:09 AM
Found this for the box size help on the 108h

http://audioheritage.org/vbulletin/showthread.php?t=13744&highlight=108h

Re 5.5ohm
fs 75hz
Qts .39
Qms 2.80
Qes .45
Vas .5 ft
ref efficiency 1.3%
Sd .0218 m squared
Mms .021 kg
bl 11.0 Tm
Le .6 mh
Xmax 3.0 mm

Mark

oldsoundz
10-28-2007, 10:10 AM
I am afraid I can't answer any of the questions you have posed, but I would sure like to see the finished result.

Good luck with your endeavor.

Chris

sourceoneaudio
10-28-2007, 10:32 AM
Mark,
Here is a tid bit of information. Might be able to pull some area measurements from it. The enclosure in the 250Ti for the 104H is a cardboard tube 1/4" wall 5.75 id, by 3 5/8" deep.

http://www.audioheritage.org/vbulletin/showthread.php?t=3590&highlight=250ti+jubilee

Second, to get the area for the 108H I would just pull yours and measure.

Dwelling on the rest.

opimax
10-28-2007, 10:54 AM
Jeff that would work for the the 108h it was being used for the original purpose and for this, that would be if I make it 4 way and the high cross woofer thus having 2 different sized enclosures? that works I think

I have being doing yard work while thinking about this and decided against a 4 way biamped, that would put 1/2 the amp on just 1 of the 108s asking it specifically to do a little more bass then its design, probably a bad idea. :blink::blink:.

I don't really know which is why I am asking for input :)

Thanks

Mark

sourceoneaudio
10-28-2007, 11:11 AM
Need to find out the response curve of the 108H and see how low it can go. Yes a bigger box will yield more output in the LF region. Are you going to run it full range or start it at 80hz and up? In the 250Ti it starts at 400hz. I would guess running them if you are going to use two, 1.0 to 1.25 for each driver.

I know that when Klipsch is using a double 8 configuration they do use one 8 for LF and one for Mid Bass on up.

http://www.klipsch.com/products/details/rc-7.aspx

johnaec
10-28-2007, 11:29 AM
I know that when Klipsch is using a double 8 configuration they do use one 8 for LF and one for Mid Bass on up.JBL does a similar thing with the dual-8" 4612B pro-sound speaker. One 8" goes all the way down, while the other has the low end rolled off: http://www.jblproservice.com/pdf/Cabaret%20Series/4612B.pdf

The 2118J is very similar to the 108, but 16 ohms, so the coil value wuld likely be different with 108's. I'm not sure what the rollover frequency is in the 4612B.

John

briang
11-01-2007, 10:44 AM
Mark,

I'm watching this thread.:applaud:

I'm planning on a similar center channel build.

104H, 044TI centered and in vetical array flanked on each side by an 8" JBL of similar vintage (probably two 116H-3 since that is what I have now).

I'll probably run the woofers in paralled (4ohm) across the same frequency range (no early roll off for one of them and each in its own ported sub-enclosure with identical port tuning.

Cabinet dimensions will yeild to the space available, and not necessarily to the optimal sound parameters.

opimax
11-01-2007, 04:42 PM
Brian,

originally was going to use the 116-1, from the 20t, t3 and 18 but was given a large hint not use them by one of the real old timers here. I am not familiar withe the -3 although I know it is an 8 and not the 6.5 I referenced. i am not sure how low the 108 can go effectively but I have enough of them and it should "match" the 250s sound.

So far I m still not sure of the better choice 3 or 4 way, still hoping for more thoughts, especially from some of the real old timers but I guess i would build the box (a friend will) and then hook up the XO and listen. Even if i go with the woofers doing 2 ranges I would put them in the same size box (1-1.25) .

I am still hoping someone will run the numbers for me here for the optimum size. If i had the space i would probably jiust use a 120, CC the XO but I have a gas fireplace that i still use that would be blocked.

Were you going to try to mount the voice coils in same plane? I don't have the space to mimic the 104/044 mounting but that would be cool to match the top of the 250. I thought about a template using the top 2 speakers but it is too much height for my box. I think it will end up just a flat front panel. Again waiting for moire opinions on that part.

John, thanks for the reference to the 4612b box. I can't tell if the woofers share the chamber of have their own. Don't they interfere if they share and even more so if they do separate frequencies?

Jeff, I think this box won't be able to go low enough w/o a sub crossed over, ear test will verify. the center will have no boundary reinforcement on any side either. Also, I am using TIBQ xo which are just a little different, 350, 1.2 and 5.5 k

thanks everyone , keep your thoughts coming :applaud::applaud:

Mark

Robh3606
11-01-2007, 04:44 PM
JBL does a similar thing with the dual-8" 4612B pro-sound speaker. One 8" goes all the way down, while the other has the low end rolled off: http://www.jblproservice.com/pdf/Cab...ries/4612B.pdf (http://www.jblproservice.com/pdf/Cabaret%20Series/4612B.pdf)


The high end is rolled off. There is an inductor in series, no caps at all.

Attached is what a 2118 and a 108 look like in vented cabinets. With that x-max I would be careful how hard you drive them.

Rob:)

opimax
11-01-2007, 05:20 PM
Rob,thanks much for the plots! :applaud:

Can the program (and will you please) do this for the 108 in a sealed box? or convince me I don't want sealed(what would the speaker like better)? and since i not familiar with the box design program I would guess this the optimal size box for 1 woofer using a vented design? I will use this box for each of 2 woofers do i get lower response, more spl or both?

I am hoping to get to a true 63hz (60)with out worry of overdriving but i will admit for no real good reason

Do you have an opinion of different frequencies for each woofer (3 or 4 way box)?

I know I ask too many questions...and take people's time :blah::blah:

thanks again

Mark

johnaec
11-01-2007, 06:52 PM
John, thanks for the reference to the 4612b box. I can't tell if the woofers share the chamber of have their own. Don't they interfere if they share and even more so if they do separate frequencies?Damn! 'Just typed a whole reply then forgot to "Submit" after "Preview". :banghead:

Anyway, to repeat, (to myself :( ) - the 2118's in the 4612's do share the same cabinet space. I doubt interference is too significant it the range they play, and the second 2118 might even act as a sort of passive radiator at the low end... :dont-know

John

Robh3606
11-01-2007, 07:08 PM
Vented is your best bet. Here's a link to WinISD. Give it a try these programs are very user friendly and come with a large preloaded driver database. The 108's are not woofers in the traditional sense more mid bass drivers. You might want to consider different drivers like 115H or 116H's.

http://www.linearteam.dk/default.aspx?pageid=winisd

Rob:)

opimax
08-08-2009, 09:36 AM
Please any comments are helpful for a beginner such as myself!

Bringing this back up as I think i getting closer to this build, the 108h are being reconed, the 044 is getting coated and rebuilt with a new kit :applaud::applaud:


I have I believe the optimal box size from the previous post (thanks again Robb, you are always very helpful!). It seems small but that is a good thing.
1) Is there anything to make go lower? and do the 2 together "help" or make it just louder? I am Ok with what is posted just asking...

If I go with the box design of (2) individual boxes for the 108's the center compartment will house the 044 and the 104h
2) Does the 104 need a "doghouse" as in the 250 for an enclosure or is it not needed since there won't be any woofer interference?

I would like my box builder to match the front slope and the tweeter ring bringing it forward.
3) Is this critical or should we do this this just for appearance (at least the tweeter ring )and no slope since it is going to be a short front baffle?

The 44 and 104 will be much closer together due to space limitation,almost not worth asking about, just no height room available
4)Is it a deal breaker? any othe comments on this?

The 2 108s, should they be as close to the tweeter/mids as possible and ports on the outside? or another suggestion?
5) Is there an ideal shape for the 108 boxes, ratio thing? the left and rt outside wall of the whole cabinet will match the slope of (2) 250s put togther (for appearance only) and the lowest height we can make it are the limitations

External XO so I will deal with this later but since the idea to match voicing (my biggest use is music/live concerts) in a perfect world I would think the XO points should match the TIBQ XO in the mains of 1.2k and 5.5k for the upper end.
6) Is that a critical factor?

this is the 1st speaker box for me that isn't a car subwoofer


Thanks for your input!!:applaud::applaud::applaud:

Mark

hjames
08-09-2009, 08:29 AM
Okay, so my vision of what you're talking about is a long box that would lay on its side (probably on a shelf/table/stand to get the height right) under the TV, with a mid-bass driver at each end and a HF and tweeter in the middle, with the ti tweeter on a built up section of the baffle (like the 250tis have) to get the time align thing right. You know, if you are doing a 4-way like the 250tis, you could probably put the LF woofer in its own large box and set the other cabinet on top of that, kind of like I did with my DIY 4 ways back inna day ...
Kind of a modified 250ti for the center ...?

Or have you just considered just buying an LC2 for the center? :applaud:




Please any comments are helpful for a beginner such as myself!
this is the 1st speaker box for me that isn't a car subwoofer

Thanks for your input!!:applaud::applaud::applaud:

Mark

duaneage
08-14-2009, 09:45 AM
The midrange to low crossover needs to be developed. A 104H driver can easily go to 750 hz with a 3rd order network. The crossover point needs to be carefully chosen to give good polar response with the three drivers. The best way to do this is with off axis testing of a mocked up baffle.

rdgrimes
08-14-2009, 10:07 AM
Or have you just considered just buying an LC2 for the center? :applaud:
I know from experience that the PC600 is an extremely close voice match. It has dispersion unrivaled by any other center. Currently available at HarmanAudio, but not cheap. What's your time and drivers worth? Those 108s are worth a small fortune re-coned.

Frankly, before spending time and money on a custom center for 250tis, I'd take a good while trying them with "phantom center" mode. they really are capable of running with no center.

opimax
08-14-2009, 02:55 PM
I am attempting to make it look "factory" is why to build it. the 108 recones are currently paid for, allthough I could sell I would keep them for spares anyway. I guess "Just Because" is also a factor

Once the physical box is built Duane has "beaten" me to death to let him build my XO which I will happily do. I had bought some spare 120, 250tibq and maybe another (have to check inventory) XO thinking i would get help to modify 1 of them for this but I will sell the ones I don't need for potential spares (probably) to help pay for this.

I am currently using a beat looking but accoustically sound l250 converted to Ti for this but it blocks the view of the fireplace and breaks up a pair(although not being used anywhere), I was using 2 18Ti laying on thier side tweeter to tweeter , sounded OK at best,looked a little funny haveing 2 speakers where 1 should be too

please keep the comments coming :applaud:

Mark

JBL 4645
08-17-2009, 09:30 AM
I’d match up the frequency signature as close as can be within a few db± otherwise the tone from left and right matching speakers won’t match the centre and you’ll have holy mess on your hands.:banghead:

Even if you have matching speakers the tone in someway shape or another due to location in the room will still play havoc with the tone.

It needs to be EQ either by lazy mans Adyssey because there are those who can’t be asked or manually EQ which can take days to perform.;)

You’ll need matching EQ for LCRS and a lot of tolerance as well as it can take days, to get done right. Well maybe not right just so that the frequency is within a few db of each other with no dramatic drops or peaks so that a single speaker will show more than the others. They should have equal tonal quality. its then down to how the mix is created.

I’d personally stick additional EQ in so that you can make custom adjustments without affecting the primary room EQ frequency response.

rdgrimes
08-17-2009, 09:55 AM
I am attempting to make it look "factory" is why to build it. the 108 recones are currently paid for, allthough I could sell I would keep them for spares anyway. I guess "Just Because" is also a factor

Once the physical box is built Duane has "beaten" me to death to let him build my XO which I will happily do. I had bought some spare 120, 250tibq and maybe another (have to check inventory) XO thinking i would get help to modify 1 of them for this but I will sell the ones I don't need for potential spares (probably) to help pay for this.

I am currently using a beat looking but accoustically sound l250 converted to Ti for this but it blocks the view of the fireplace and breaks up a pair(although not being used anywhere), I was using 2 18Ti laying on thier side tweeter to tweeter , sounded OK at best,looked a little funny haveing 2 speakers where 1 should be too

please keep the comments coming :applaud:

Mark
There's nothing wrong with "whim" as a reason to do anything.

So keep the drivers the same and keep the crossover points as close to the same as is possible. Personally I think the 108s are over-kill in a center, but they will lend some voice match in the low midrange. The critical matching will be in the 104, and it should be crossed over at points very near the 250ti points of 1400 and 5200. The 104 should have it's isolation box the same size as the 250's. I assume that having 2 108s in one box will alter the ideal volume of the box and possibly the XO as well. Since the 108s run in the limited range of 400-1400 in the 250, changing that range by removing the lower XO will significantly alter the required volume and XO tuning. The isolation box in the 250 is tuned for the lower limit of 400Hz. With that in mind, the 108s aren't really providing any significant voice matching, and a pair of 6" drivers might be easier to manage.

opimax
08-18-2009, 03:58 PM
I believe the design for the 108 is an individual box for each woofer with its own port,think 3 seperate chambers, 1 for each woofer and center with the 104 and 44 vertical in the middle.

the 104 will have either a calculated area the size of the dog house from the 250 or an actual dog house from a 250.

Since it is a (most likely) 3 design the XO points will be the same as the 3 top drivers of a TIBQ XO currently in the 250. The XO will be external so the box will just have the drivers and speaker connections and can worked with at any time

original plans were to use 2 of the 6.5" woofer from the 18Ti but It was highly recommend not to and to use the 108s

I think the only issue left is the driver placement on the front. most of this will be driven by available space while trying to keep them as close to each other possible. I also believe while talking to Duane that he would have some input to that while testing for XO.

Mark