KEF Coda 9 - what to do?

[the-real-mandak]

Hey there, I found a pair of these for cheep and thought to give them to a friend of mine. After bringing them home I hooked them up in my own system for a little listening and found that the bass has problems with resonance from the box. The sound of the speakers in general is what it is and I think it will be hard to do much about it, but the box seems to be possible to fix.

My own thought was to make the sides a little more stiff (just a little wood, glued to the side "cutting" the surface in half) and ad Bitumen on all the sides.

BTW. There is not much info on this speaker anywhere, KEF only has the Coda 9.2 in there history section and that is a different design.

But here the Q: What would you folks suggest as an easy (and cheep) fix to improve this speaker?

 

[audiomagnate]

I have a pair of Coda 7s I use for surrounds, and yes, the boxes are shockingly cheesey for a Kef product. I think the sevens use the identical driver/baffle/crossover/back panel as yours in a shorter box the same size as the back panel. Your ideas sound fine. The worst thing about these is the box. I ordered mine over the internet many years ago and was shocked to find out how lightweight they were.

 

[the-real-mandak]

To me it looks as if the Coda 9 is the Coda 8 with a woofer added underneath and made into a 3 way system. But this is just assumptions, I have no real info.

The tweeter I think is the same in just about all the Coda line (25mm soft dome), but the bass unit is different.
The Coda 7 uses a 130mm bass driver.
The Coda 8 uses a 160mm bass driver.
The Coda 9 uses a 160mm mid drivers and a 160mm bass driver.
The Coda 10 seems to use the same drivers as the Coda 9, but in a new design - here the crossover is done at 85Hz and 3kHz.

All the plastic crap is the same

 

[audiomagnate]

Looking at your pictures - I've never had mine apart - it looks like a pound or so of Mortite stuck to the inside of that cheap plastic baffle might do wonders.

 

[OvenMaster]

To me it looks as if the Coda 9 is the Coda 8 with a woofer added underneath and made into a 3 way system. But this is just assumptions, I have no real info.

The tweeter I think is the same in just about all the Coda line (25mm soft dome), but the bass unit is different.
The Coda 7 uses a 130mm bass driver.
The Coda 8 uses a 160mm bass driver.
The Coda 9 uses a 160mm mid drivers and a 160mm bass driver.
The Coda 10 seems to use the same drivers as the Coda 9, but in a new design - here the crossover is done at 85Hz and 3kHz.

All the plastic crap is the same

I remember reading years ago in several British hi-fi magazines that that's exactly what the 9's were: extended-box 8's.

In December 1997, Hi-Fi Choice said about the 8's, "Outstandingly well-balanced, bass is deep but a little vague", and as much as I love mine, I agree. The 9's? "Uneven budget 3-way floorstander with poor bass definition". The 8's lowest bass available was 28Hz, the 9's, surprisingly, was 30(!)Hz.

The 8's were recommended, the 9's were not. What I think you're hearing is why.

My first thought is to glue some wood along the longest part of the side walls so that they would be stiff and have less resonance.

 

[sealy]

Don't put too much absorbent material in the box. Keep in mind it is ported, not sealed. As long as the walls are lined with bitumen, you should be ok. That is sufficient. I have the same setup in my Rogers Studio 1's, which are superb speakers. Regarding the resonance, I would put at least 4 braces in the box with a hot glue gun, 2 front to back and 2 more bottom to top, all evenly spaced. That should calm down the boominess somewhat. It wouldn't hurt to put one of the braces behind the tweeter connected to the rear of the box. That will stiffen the entire structure considerably.

For braces you can use 1 x 1 in. nailing strips, which are usually cedar. You can find them at any building supply store in 4 ft. strips for about a quarter each.

 

[the-real-mandak]

My first thought is to glue some wood along the longest part of the side walls so that they would be stiff and have less resonance.

Exactly what I was thinking about.

sealy: I will not put any absorbent material in the box, maybe a bit on the plastic but that's it.

 

[audiomagnate]

This helped quite a bit.

 

[the-real-mandak]

What is this material?

And did you close the port?

 

[audiomagnate]

I used rope caulk from Home Depot. I used a whole roll for each speaker so the total cost was under $10.00. I have sealed the port to increase power handling and reduce coloration. I have to run these full range because of a bug in my Blu-ray player's firmware. Bass response is not important because that is supplied in spades by my ADS L1530's up front.

Since these are Kefs, I tested the treated vs untreated speaker with BBC news via NPR. The improvement is audible but not earth shattering. According to Kef, "The Coda Series, particularly the Coda 7 continually outsold competing brands throughout the world." I might beef up the rest of the cabinet this weekend with some added MDF panels, some cross bracing and some ice guard. The baffles and back panel are very dead now when you tap them, but the cabinet itself is still quite live.

 

[the-real-mandak]

Darn glue gun, it died on me in the middle of fixing the first speaker

 

[audiomagnate]

Darn glue gun, it died on me in the middle of fixing the first speaker

At least you're keeping it "authentic." Raymond Cooke, founder of KEF, would probably roll over in his grave if he saw how these things were put together.

 

[the-real-mandak]

LOL - yes. If you look at the pic of the bass driver, you'v see that the glue was added after the driver was mounted!

And maybe Mr. Cooke was the one who sabotaged my glue gun, in the spirit of - don't try fix it, get some real ones

 

[the-real-mandak]

A little update.

I finaly finished treating bough speakers with 4mm Bitumen and stiffend all sides with wood (about doubbled the weight of the speakers), hooked them up to a Yamaha M-85 driven by a Yamaha CD-5050 (same as the CDX-1120) straight into the amp, also did a run with a Sony BDP-S373 (blu-ray player).

In general the entire sound spectrum cleaned up, especially the high became much more leaned back and smooth. It do seems like some of the width of the soundstage has become more narrow but also deeper. It's a bit hard to tell due to ½ a year has passed since I did the listening to the un-treated speakers, so judgement is out of old memory.

But anyway, the speakers lost a lot of the low mid and bass resonans comming from the box and reveal much more detail. Not that all problems has gone, there are just less of it. They are still a bit moddy and boomy and the low do not seem in level with the high, if Bi-amped I would gain the low down a bit for better balance.

The highs has become much more pleasent to the ears but also seem weaker, this is properly due to less distortion. The feeling of the highs reminds me of the B&W sound but more colsed, it lacks some 7-8kHz and up. Witch again is why they sound a bit closed, the reverb dossent really open up and the sound tend to stay between the speakers.

But all in all, it did improve the speaker to a much more pleasant encounter.

And yes, the cheap blu-ray player did get smoked by the old Yamaha CD-P

 

[OvenMaster]

Not bad, not bad. So would you say that your efforts were worth it in light of the so-so results?

Now that I think of it, one time I did an experiment with my stand-mount 8's. As music was playing, I put one hand on each side of the cabinet, and squeezed them together. I immediately noticed a difference in the sound: a substantial bit of bass boom was gone. I'm guessing that the resonance of the thin walls of the cabinets was intentionally left in to help bass response.

 

[the-real-mandak]

Yes it was worth it, if they wher to stay in my home I would do even more to make the 2 plastic sides more stiff and heavy - especially the front I would reglue and make much more stiff. The crossover would properly also do well with some better components, but here you have to make an entire new crossover since the one inside the box is flodded with glue.

The really positive thing about the speakers are the "missing" highs and soft/smooth sound, if they are used in a rather lively room they do not become unpleasent, this I like about them.

About the walls you are propperly right, but it also tend to mud up the sound, not a good solution. I did not do anything to the lowest compartment in the speaker, since it was really difficult to access (bass unit was glued to the wood and hard to reach down there). so only the mid and top compartment was treated.

 

[lurch31]

hi all .
I also found a used coda9 pair .
missing filter and original tweeter ..
Is anybody has filter values?(sp2241) I can rebuild it ..

Low speaker (6ohms)is filtered at 85Hz
crossover between High speaker (6 ohm) and tweeter( 8 ohm) is 3KHz .

 

[lurch31]

or a bottom view of PCB ??

 

[lurch31]

Found !
(thanks to Kef France..)

https://docs.google.com/file/d/0ByrZLZLxcLtAcmMtWDFqU2ZGOUU/edit?usp=sharing

 

[baco99]

FYI, The KEF museum now has information on this line of speakers from the 1990s.

Note, the PDF manual is located at the bottom of the page.

http://www.kef.com/html/us/explore/about_kef/museum/1990s/Coda7_Coda8_Coda9/index.html

The speaker used a bass reflex enclosure for the top and what they call "coupled cavity" for frequencies below 85Hz. Coupled cavity was basically a fancy term for bandpass. One sure way to clean up the mid bass would be to firm up the upper enclosure and/or make the volume of the upper enclosure smaller by adding some kind of ballast (a brick maybe?).

I know this is an old thread, but figured the link to the KEF site was important for the lurkers.