Stonking Centre Speaker for <£75 ??

[Ovation]

After a fantastic first experience in this forum asking about impedance and horns and upgrading disco speakers, I thought I'd come back for a second helping :-)

My home cinema sound system currently consists of:
Denon AVC-A11SR AMP (http://www.denon.co.uk/startpage.htm --> Products --> Discontinued Products)
2x Kef Model 105 Speakers (http://www.kef.com/history/1970/model105.htm)
A pair of old Wharfedale Diamonds as my main rear channels
Some really unnecessary and rubbish little wharfedale 'things' for rear centre channel

And then:
Wait for it.......
A Bose 301mk1 as my centre channel!!! (See http://members.aol.com/KDresch/301.html )

I have no sub as I dislike them and the KEFs provide sufficient bass.

The 301 is perfectly acceptable to me as a centre channel, but it's old and it's ugly and I've been looking at some sleek black little numbers which are too expensive for me.

I don't know what range a centre speaker is meant to handle, nor how to 'match it' with my KEFs.

What experiences do people have here with Centre channels - they seem a bit odd to me - I only ever use surround sound for movies and I really can't judge what's good or bad in a centre speaker.

I think I need to design one that's long and thin with an impedance of 8ohms, and one that will produce a similar frequency response to that of a THX certified speaker (as my amp is THX certified, I guess I might as well try and follow their standards).

Can you all point me towards box designs, cones, tweeters, crossovers and anything else I may need to make a ££££'s worth of equivelent speaker for <£75 :-)

Many Thanks
Jonathan

P.S. Okay - So my budget could probably stretch a bit further if you can give me a good excuse :-)

[Kittle]

Ovation,

Heres my experiences with center channels..

I went from no center channel to a little cheapo I picked up at circuit city one evening -- nice improvement in my sound.
Then while visiting one of my local high end audio places I heard a REAL center channel -- made by McIntosh, and realized what a piece of junk I had. But it was half the size of my refridgerator, and cost $5k. So buying it was out of the question.

I searched this forum for center channel designes & experiences, but came up with nothing -- at least nothing useful to me. So I went back to the same store & eventually bought a Klipsch RC-7 Center channel. Its VERY loud compared to the rest of my system and a bit larger than I planned. But overall im pleased with the result.

For reccomendations? ... well cheap drivers are available for those willing to spend the time searching, and the rest is just standard DIY fare... time spent in the garage behind a saw.

[RobWells]

The perfect centre channel for your system is a single kef 105.

""" (as my amp is THX certified, I guess I might as well try and follow their standards).""

If you want to do the THX spec then you need a sub whether you like them or not

The THX 'thing' is to have 5 main channels that roll off naturally at 12dB/octave @80Hz . this rolloff is added to an electrical one from the amp that is also 12dB/oct @ 80Hz. This gives a 24 dB roll off that matches the amps xo for the sub. ie : the bass from all 5 channels are sent to the subwoofer *plus* the LFE effect channel..

Cheers,

Rob



btw, for home theatre you -do- want a sub . honest.....

[Ovation]

I didn't know that was the case with THX :-0

The reason I don't like Subs is that I always feel that they're an excuse for speakers that cannot handle smooth bass. Everytime I've been to Hi-Fi exhibitions I've always experienced Subs as very untamed bass and usually painfully loud.

I assume all this talk of octaves and rolloff basically means that the speakers drop their output by a cumulative total of about 24dB when they get down to 80Hz, and the sub starts pumping out the bass at that point?
What exactly is an octave - it is the same as the musical definition?

I did consider getting some of those rocker things that you connect to the sub channel so that I could make the floor vibrate without actually hearing the bass! No Flames Please!

My father recently bought a £200 all-in-one Panasonic system (against my better judgement). As I predicted, it sound like a pair of gnat's testicles wrapped in a wet paper bag being hit with a dead catfish
That's the kind of experience I get with Subs at the moment.

I guess the problem is that my preference falls greatly into the upper middle range. Jane, my fiancee, is always moaning at me in the car because I have the treble up a bit and the bass down a bit. I guess that kind of defeats the object of home cinema..

My only *real* arguement for not getting a sub is simply: If I put on a LaserDisc of the film 'Event Horizon' and turn the volume up, the rumble of the space ships (not that sound is possible in space - duh!) is so intense that I have to turn it back down again. If the KEFs can produce enough Bass to cause me pain, do I need a sub? (Answers on a postcard please).

Anyway - we're now Waaaaay off topic.
If anyone can pursuade me about Subs - I'm all ears.
On the centre channel story, as much as I'd like to invest in enough KEFs for the front Centre and all of the backs as well, I don't have the money or the space
Anyone got an other ideas about what constitutes a good centre speaker and how to design one??

[richie00boy]

I agree that your ideal centre is another one of your mains. I have a Kef Q-series setup and use the dedicated centre from the range as I can't accomodate another floorstander for the centre.

If you are going to buy, pick something from the Kef upper ranges as it will sound similar. Check out ebay for second-hand stuff.

If you are going to build, see if you can find a pair of Audax AP130Z0 drive units in your local Maplins. They had these on clearance half-price a month ago and would be ideal. The warehouse has none left. Add a TW025A0 tweeter also from Maplins and on clearance, but not reduced price.

Go for a sealed box in MTM configuration. The bass-mids are shielded, but the tweeter isn't. If you get picture distortion on your TV, add a thick sheet of steel to the side of your box nearest the TV.

Search the forum, recently somebody posted (I think in the AP100Z0 thread) a link to a website with crossover designs for Audax on. I think also on this website is a centre speaker using the AP130Z0.

[Ovation]

Originally posted by richie00boy

If you get picture distortion on your TV, add a thick sheet of steel to the side of your box nearest the TV.

No Problems there - I've got a projector

Thanks for that advice - Sadly, I've got little chance of getting near a Mapins store. It's just vaguely possible that I might make it to the one in Stevenage this weekend, but I'm not ready to build these boxes yet (I'll go an look when I can anyway).

Does anyone know what range these things should cover? Are we talking something like 800Hz - 27kHz or is the band narrower on the centre channel?

Cheers
Jonathan

[Kittle]

Originally posted by Ovation

Does anyone know what range these things should cover? Are we talking something like 800Hz - 27kHz or is the band narrower on the centre channel?

from what ive seen (someone jump in if my off base here), is the center channel is primarly for vocals, so it sould be at its best over the range of 100hz to 1500hz -- which is roughly the human vocal range. the greater the range the better of course.
But make sure you have a listen to the drivers before you go all out & make purchases.

----------------------------

As for the subwoofer subject..........
I got along for close to 7 years with no sub in my system, as my 4 mains were designed to be 'good' down to 40hz. but theres only so much a 6" cone can do with low frequencies
I made myself a sub a while back which turned out to be nothing more than an exercise in carpentry (it was useless). Recently I got my act together & built a better sub. The difference has been INCREDIBLE! you have to hear (and feel) the difference.
Now I also had the same problem with the bass being Way to loud. So I grabbed my SPL meter, and put a 100hz tone through my system, measured the level on my mains, and then adjusted the level on my subwoofer amp so it matched. Problem solved

[richie00boy]

Knowing now that you use a projector and seeing your main speakers, I think the 5.25 inch cone of the AP130Z0 would probably be on the small side for your requirements. You may also prefer something that goes a little deeper, venting the box would be the way to go possibly if you stuck with AP130Z0s.

My opinion is that you can quite easily get away without a sub with those main speakers. I believe that the woofers in your speakers are sealed. If this is the case and you need to get really low, a Linkwitz Tranform for left and right between pre and power amp would do the job just fine.

[Ovation]

Originally posted by Kittle

the center channel is primarly for vocals, so it sould be at its best over the range of 100hz to 1500hz -- which is roughly the human vocal range. the greater the range the better of course.

Thanks for that. The only thing that puzzles me is why centre speakers need a tweeter - Surely this is within the range of and mid-range speaker??

Now I also had the same problem with the bass being Way to loud. So I grabbed my SPL meter, and put a 100hz tone through my system, measured the level on my mains, and then adjusted the level on my subwoofer amp so it matched. Problem solved

Okay, that sounds like a sensible idea - How big is your sub, and how is it amplified??

Originally posted by richie00boy
Knowing now that you use a projector and seeing your main speakers, I think the 5.25 inch cone of the AP130Z0 would probably be on the small side for your requirements.

I was considering something around the 6" - 8" mark. I quite like the look of these speakers:
http://custom1.farnell.com/cpc/produ...ct%5Fid=260393

These might be okay also:
http://custom1.farnell.com/cpc/produ...ct%5Fid=276161

http://custom1.farnell.com/cpc/produ...ct%5Fid=260406

http://custom1.farnell.com/cpc/produ...ct%5Fid=260394

This looks like a nice monster of a tweeter:
http://custom1.farnell.com/cpc/produ...ct%5Fid=260515

My opinion is that you can quite easily get away without a sub with those main speakers. I believe that the woofers in your speakers are sealed. If this is the case and you need to get really low, a Linkwitz Tranform for left and right between pre and power amp would do the job just fine.

I'm sure you're correct about that - they look sealed. However, if I attache a Linkwitz Transform, surely that'll have an impact on my Mid and Upper speakers?!?! (They're not biamped).

Isn't there a risk that one of these devices is going to cause a loss in sound quality - given that this is meant to be the dog's wotsits when it comes to amplifiers.

Thanks
Jonathan

[Kittle]

Sorry for the confusion there.

To answer your questions:

The center channel needs to be at its BEST in the 100-1500hz range.
meaning thats where it should shine ... but having it limited to ONLY those frequencies is probably not a good idea.
The larger the range it can handle, the better off you are.

My sub is a sealed box, 3.5 cubic feet with a 300w plate amp driving a NHT 1259 driver. (12" driver). Outside measurements are 22.5 inches W, 22.5 inches Deep and 20 inches tall, and VERY heavy.

The main problem I had was that my mains are only 88 db sensitivity with 125watts into each channel from my receiver, whereas the sub is 90 db efficency with 300watts of amp power. Higher efficency and almost triple the amp power translated to overpowering low end before I cranked the volume down.
But if I turn it up - I can rattle myself while sitting in my office chair on a carpeted floor whith the sub on the otherside of the room

But if your satisifed with your sub output - then dont change anything right yet. Go visit a local high end audio store & listen to some of their stuff.