Homebrew Center channel speaker

[speakerdave]

Pair of properly refoamed 122A's on ebay, $175 BIN. (I've no knowledge or connection with this seller--the usual caveats.)

http://cgi.ebay.com/Pair-JBL-Vintage...QQcmdZViewItem

David

[grumpy]

one could consider laying whatever mid/bass driver back flat, or nearly so, and
reflect or poorly horn load it or them to lower the profile further. Sort of an Aquarius notion,
but less than 180 deg spew... driver would have to be of the type that is happy in a
horizontal load position regarding worries about sag (I don't have that list) -grumpy

[northwood]

The way my center channel is wired, I can use the 2235 woofer as the center speaker's woofer (with a 175/075), or in parallel with the W15GTI used as a sub mounted in the same cabinet (but separated). I use it in this configuration on occasion when using some of the Yamaha surround sound settings that do not use the center channel. (Talk about some thump!)

If I switch to DD and forget to reset the combined sub to the center speaker position, the sound is obviously weird and you would not want to listen like this.

I think you will need to strike a balance, and a 15" woofer may be the only really good way to do it. Besides, the center channel is the most important channel for movies. Why short change yourself there?

I noticed this one long time ago,I like it,it's the best of the best of the best center speaker

[Fangio]

So - I wouldn't want to look for a pair of 2122s?

Dang!!

Guess I'll have to put them aside for now, until I get around to making up some 4345s ... sigh

Heather, thanks for bringing this up - great advice assembled above, aplenty of info on issues from soo many knowledgables - particularly about the 8 ohms 2122H in a 16 ohm alnico environment..................

Interesting thread and project. There is some overlapping with mine - going to follow further considerations with attention.

[hjames]

Yes - the set is a 34" Philips HD with CRT - big ol heavy picture tube thing!

Thanks to everybody for all the good ideas!

Ah well - all I can do is try and see what I can bear to live with. To be honest, even with the little JBL center speaker I still enjoy the sound of movies in 5.1 dts or DD format - I'm just not likely to watch many movies in stereo after experiencing Private Ryan or some other films in surround.
Now I need to build the crossover and hook up the horn and slots and see what I have ...

Okay - I have the raw speakers in place - feeding my JVC receiver front center audio to the Giskard 3133 equiv network. Horn and slot seem to work fine tho its a bit bright on shows like NBCs Heroes in HDTV ...
not much bass feeding the LO side of the xover to the old center speaker (pretty much what we all expected) - but thats just a temporary placeholder until I find something better and figure what to do for a box (next month ...)

Meanwhile, the 2123s are on the way ...
now - how to integrate them into my 4320/4333clones?

[Earl K]

Meanwhile, the 2123s are on the way ...
now - how to integrate them into my 4320/4333clones?

- Were these 2123s purchased as an add-on to your 4320s ?
- What impedances are these 2123s ?
- If you're wanting to make your 4320s into a 4way / then download the 4344mkII network schematics. This schematic represents a good "study" of how JBL used network design to integrate the ( 8 ohm ) 2123H .
- Physical integration ? I believe you're pretty MUCH stuck with placing your 2123s in their own sealed enclosures / sitting outside of the main enclosures .

[Earl K]

Okay - I have the raw speakers in place - feeding my JVC receiver front center audio to the Giskard 3133 equiv network. Horn and slot seem to work fine tho its a bit bright on shows like NBCs Heroes in HDTV ...
not much bass feeding the LO side of the xover to the old center speaker (pretty much what we all expected) - but thats just a temporary placeholder until I find something better and figure what to do for a box (next month ...)

FWIW ; I think a slot tweeter is superfluous to the needs of a center speaker.
- It's quite easy to take the le85 out to 12.5K / which / IMO / is more than high enough .
- Just my opinion / and you know I don't do H.T.

- The 3133 network was meant for use with the 2312 ( H92 ) horn / not the 2307 ( H91 ).
- I'd use a variation of the N200 which uses a 3-pole bump filter to reinforce the anemic performance of the 2307 ( that one octave just before cutoff ) . Zilch has done some relevant work to that circuit / for use with or without the 2405.

[Robh3606]

FWIW ; I think a slot tweeter is superfluous to the needs of a center speaker.
- It's quite easy to take the le85 out to 12.5K / which / IMO / is more than high enough .
- Just my opinion / and you know I don't do H.T.

Hello Earl

That would be a big mistake.There is a lot more than voice in the center channel and more importantly you will hear it with any pans across the front speakers.

Hello Heather

I hope you realize those 2123's are unshielded ferrites

Rob

[hjames]

Hello Earl

That would be a big mistake.There is a lot more than voice in the center channel and more importantly you will hear it with any pans across the front speakers.

Hello Heather

I hope you realize those 2123's are unshielded ferrites

Rob

Yes - my long term plan is to use the 2123s with my corner speakers, the 4320s - (currently using all AlNiCo components) ...

From all I've read, I really doubt I'd use them in the center -
but they'll be good to save for the day I start mocking up a pair of 4344 clones from the existing 4320s... (yes, I know I need better than my existing 2215s to do that right).

I gather they would be good as a MidBass driver, just above the main Low Bass drivers (15s) which would handle say ... 35 or so to 300Hz, and under the 2420s which would be the HF ...

[JBLnsince1959]

Hello Earl

That would be a big mistake.There is a lot more than voice in the center channel and more importantly you will hear it with any pans across the front speakers.

Hello Heather

I hope you realize those 2123's are unshielded ferrites

Rob

exactly.....Rob knows what he's talking about....

[Earl K]

Hi Heather,

Once you get your 2123 midrangers you may want to play around with them.

- ie ; You may decide to try to make them work as drivers for a center channel .

- So; apart from the fact that the magnets are unshielded, there's another issue. That is , they are pretty "light" in the lower midrange area below 300 hz. I use these in some custom designed SR enclosures and they do require EQ below 300 hz to make them usable for even just a "balanced" voice sound .

- I've prepared a PowerPoint pic of some comparitive FR studies for various JBL 10 inchers. Unfortunately, the official "public" FR study for the 2123 is pretty optimistic / whereas the 251J and 2122H will be closer to the truth .
It would be nice to see a CLIO workup on the 2123 / measured close in / housed in a larger enclosure , such as .75 cu' or so .

- If you are going to attempt to make them work ( the 2123 ) then you'll need to get very creative in the design of the lowpass section for any crossover you buildup. I've included one creative solution ( designed by GT I assume ) for a driver that in balance, has a lot more lower mid than the 2123h. I included the 2122H for the sake of more comparisons.

[Earl K]

- The 2123 can be put into a larger enclosure and ported / but it still won't "tune up" very well.
- It'll still need very creative network design to get a relatively flat response, from 80hz to 800 hz .

- I find that it's impossible to get flat response down to 100 hz (for the 2123 ) with any sort of alignment.
( OTOH, the 2012 is easier to tuneup into a more reasonable response . )

- Here's an alignment quite similar to what I presently use in my small cabinets ;
- The acoustic boost, occuring between 100 hz and 200 hz still won't completely flatten the 2123(s)' lowmid response, ( "in real life" ) .
- Note ; I've used JBLs' older ts parameters for this sim and the sim is done using software that is pretty iffy with my present operating system .
- Acoustically, I know the response is still droopy below 300 hz / even with this type of "boost" alignment .

[JBLnsince1959]

-

That is , they are pretty "light" in the lower midrange area below 300 hz. I use these in some custom designed SR enclosures and they do require EQ below 300 hz to make them usable for even just a "balanced" voice sound .

I find that it's impossible to get flat response down to 100 hz (for the 2123 ) with any sort of alignment.


-

I have a pair of those and I've play with them for years and you are dead on. In fact I never cared for them much below 400, but that's a personal thing, just to "thin" for me ( I love the 2202 )

trying to use the 2123's around 80 to 300 would be more trouble than it's worth and still they may not sound right. If she had the room a pair of 2206's may work pretty good. But then space ( or the lack of) is the real issue.

BTW, love those graphs....

[Earl K]

CLICK HERE ! to see some "Bucking Magnets" available from Parts Express'

- If I was serious about making a center channel out of ferrite magneted drivers / I'd want to invest in a handful of these things,( even if just to try them out ) .
-Thankfully , these are quite inexpensive .
- Considering how much magnetic weight JBL uses in their drivers, I believe only the largest available from P.E. would come close to offering the needed CRT protection . I wonder if one can double-up these things.
- Being able to deal with Ferrite magnets should open up a broader range of possibilities by using JBLs' newer/smaller ferrite offerings ( maybe 4, 116h-1 or 127H-1s, wired in series/parallel - to get that sensitivity figure up ) .

BTW, love those graphs....

Thanks ! Also, don't take the sims that I run as gospel. They're done with software that is flakey at best with the operating system that I'm presently using. Others should run their own sims on BBP6 to check for themselves .

trying to use the 2123's around 80 to 300 would be more trouble than it's worth and still they may not sound right. If she had the room a pair of 2206's may work pretty good. But then space ( or the lack of) is the real issue.

It'll be some trouble for sure. Too much ? I don't know.
- I never want to underestimate the inventiveness of the "motivated" .
- I know from experience that 2123s can be used ( as mentioned, with EQ ) in a 2-way SR box, quite successfully ( as long as a sub is present for all the VLF duties ). I have clients who prefer this "sound" compared to what one is able to achieve with more "full-range" 2 way designs using 12s or 15s .

- "Inventiveness" could mean adding some weight to those 2123 cones ( ie; 10-20 grams of added cone weight, maybe aquaplas or some standin ). For sure it'll mean some "inventive crossover design" in the lowpass section ( ie ; extreme manipulation of the 2 drivers' FR curve / & very likely, utilising one 10" as a "helper woofer" for what little LF can be derived from it ) .

[JBLnsince1959]

It'll be some trouble for sure. Too much ? I don't know.

Well, I was speaking from my respective . Someone with your knowledge and experience could work it out I'm sure.

Everything I tried never worked to my likeing, so I'm planning to use them in my next "Super Center Speaker" incarnation. personally once below 400 I find the sound to "thin" for my likeing, but that's a personal taste. Other people didn't mind...

great idea, I never thought about adding mass , but then I'm not that smart on buiding stuff and as far redesigning crossovers I'm brain dead...that's where I would personaly draw the line

I hope she gets something that both fits and matches in sound..