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edd9000

Exakt Design Beta impressions

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4 hours ago, edd9000 said:

Looking at the above the amps will be at full voltage swing with 1v or so, about 8db less than 2.5. Since pretty much every cd hits digital peak these days it seems about 77 minus any boosts is the volume limit.

You may get a bit higher than that.  Remember that any peak in a digital file will most likely have quite a few frequencies contributing.  These will be spread across the amplifier channels depending on the crossovers you have applied.  Either way, the amps will clip before you reach digital clip.

Phil.

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3 hours ago, Philbo said:

You may get a bit higher than that.

No harm erring on the side of caution :) I'm not worried about damaging anything, I Just like to know what's going on in terms of the gain structure (An all too commonly misunderstood topic).

Edited by edd9000

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Still getting to grips with exakt design, but a few tweaks to the roll off behaviour of the mid and the roll on of the horn later and:

linn%202_zps05ioyw3k.jpg

I also discovered the exaktbox-I can do high processing, MOAR TAPS!

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Nice work Edd, out of interest, what is causing the dip and phase shift at 660Hz?  Is that a crossover point or just the room? 

2 hours ago, edd9000 said:

I also discovered the exaktbox-I can do high processing, MOAR TAPS!

When playing around I tried the high and normal processing options but it didn't make any difference as I hadn't run out of taps.  9_9

Any thoughts on how it sounds compared to the previous way you had it set-up?  I'm interested to know how loud you can play using the amps in the ekatbox-I, or whether you are using external amps for the bass. :)

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1 hour ago, rv295 said:

Nice work Edd, out of interest, what is causing the dip and phase shift at 660Hz?  Is that a crossover point or just the room?

Probably just the mic placement, 660hz is about 0.5m and I was measuring at about 1m.

1 hour ago, rv295 said:

Any thoughts on how it sounds compared to the previous way you had it set-up?  I'm interested to know how loud you can play using the amps in the ekatbox-I, or whether you are using external amps for the bass. :)

I keep changing things so its hard to say if more taps sounds different, other than it allows me to manipulate the bass more but I'm really just looking at mostly flat with as little manual correction as possible. The above has a manual baffle step filter and a notch on the tweeter. Once I get to that point I listen and decide if I need to change anything.

At the moment one of my compression drivers is misbehaving, I think it might have been for a while and DRC was masking the issue :(

I'd estimate about 90-100db average without clipping depending on the source material, but it depends on how much boost I settle with, and the louder you play the less bass you actually need, but anyway, loud. Ill measure it when I buy a battery for my spl meter.

I usually only use  100w on the bass, I did have the 240w crown, but that's only 3db or so louder.

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That makes sense, I didn't think you'd be running your 18's that high or your horns that low.  Sorry to hear about your compression driver, I hope you get it fixed or find a cheap replacement.

90 to 100db would be more than sufficient for me, if that's at the listening position.
Glad to hear you're coping with the available power.

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5 minutes ago, rv295 said:

I didn't think you'd be running your 18's that high or your horns that low

Crossover is 200hz and 1200hz. Crossover to the horn is based on where the 10" mids dispersion narrows to 90 degrees where the fixed 90 degree dispersion of the horn kicks in for smooth off axis.

It was a $30 driver, no loss, I can get replacement diaphragms too.

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Quick non scientific test typical compressed music, 60 on the dial is about 80db A weighted, I have 6db boost on the bass so using the above about 71 on the dial is safe and that was reading 90-95db. C weighting reads about 8db higher, but is rather skewed by bass response.

Id estimate that allows peak volume at about 105db, which is what I usually aim for.

The mid is being ran some 6db Lower, and its 16 ohms, so about 12w peak ish, and the horn some where around another ten db lower so maybe 1w ish. Of course music isn't flat, it rolls off more like pink noise so chances are the horn is seeing even less.

Edited by edd9000
Numberwang

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Cheers for the reply Edd. :)

Do you know how many watts the exaktbox produce at 16ohm or more importantly at 12ohm?  I presume the Ekatbox-I amps are 100watt at 4ohm as that's how other Linn Chakra amps seem to be rated. I may be wrong here but from memory, I think the other 100w Chakra amps I've seen were 56w at 8ohm.  I guess that's around 30w at 16ohm. 

The reason I ask is that I have 4 bass drivers to use but I'm currently just using 2 of them as they dip to 6.1ohm at the point where I'm using them.  I didn't know if it would be safe to run two in parallel as the exaktbox amp would see 3.05ohm.  I'd rather not run them in series due to back EMF and the loss of watts being 12ohm.  What would you do with these drivers? (apart from throw them in the bin) They are specified as 8ohm average but that's only true higher up in the frequencies compared to where I'm using them. Sorry for the off-topic question.

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I was just going by the voltage mentioned earlier, 29v rails is pretty much 100w into 8 ohms, obviously its not all that simple, the outputs can rarely swing the full voltage, and it depends what THD the rating is at and how many channels are being driven etc.

The current limit mentioned was 12 amps, That seems plenty even for 3 ohm loads but that's really a question for Linn, as I don't know how many channels that limit is for. (20v into 3 ohms, is 130w and 6.6 amps for example)

Any 8 ohm driver will have a dc resistance of around 5-6ohms, which usually correlates to the lowest impedance the amp will see.

Typically a 16 ohm driver will halve the power seen as few amps usually are not current limited at 8 ohms, unlike most of them at 4 or below. So if its 50w into 8, its very likely to be 25 into 16.  I'd just try them in series first, if its not loud enough, try parallel assuming the amps are happy with 3 ohms. Not sure why you are worried about back emf, in fact the damping factor would be better wired for 12 ohms than 3, though once its above about 10 it doesn't matter much anyway, and id imagine the output impedance of the amps is nothing to worry about.

What I'm really getting at here is watts don't really matter, its not all that useful. Amps function as a voltage source trying to maintain a voltage with a fixed gain of the input voltage, the power and current required then depends on the impedance of the driver at a given frequency. Knowing what voltage is available and max current is more useful.

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Thank you for the info Edd, I hope you didn't mind me asking, I thought you'd be a good person to ask seeing as you build amplifiers.  

I follow what you are saying, but in the meanwhile I tried to dig a little deeper and find out if anyone else is using any load below 4ohm without an issue.  The only relevant info that I found is that the Exkatbox-I amps are rated at 100w in to 4ohm.

http://docs.linn.co.uk/wiki/index.php/Majik_ExaktBox-I

Copied from the link above: 

Specification
Power output: 8 x 100W into 4ohms

I'll try them as a 12ohm load and see how I go with the volume.  It's probably fine at the moment but I haven't added any bass eq yet. 

Edit: I tried wiring them as a 12ohm load but instantly felt it sounded bass shy, then the obvious hit me...  I'm only running a 3-way so I have 2 spare amps.  I can run them as a 4-way and keep them at 6ohm which is better all around and means they are all included in the time of flight adjustments within the space optimisation part.

Edited by rv295

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It would sound bass shy as you will lose 6db in volume, you would need to turn up the gain to compensate. 

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9 hours ago, edd9000 said:

It would sound bass shy as you will lose 6db in volume, you would need to turn up the gain to compensate. 

I wasn't quite expecting that much difference, I thought, half the watts would be closer to 3db loss but I'd gain the extra SPL back from having 2 extra drivers, one of which, almost touches the floor so I also expected that to bring extra reinforcement from the floor.  Running them as a 4-way works really well. I should have done that to start with.

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Ah a bit lost now, I thought you meant from 3 ohms in parallel to 12 ohms in series. 4 way sounds like the best solution.

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Just now, edd9000 said:

Ah a bit lost now, I thought you meant from 3 ohms in parallel to 12 ohms in series. 4 way sounds like the best solution.

No sorry Edd,  I was only running one pair of the 15" drivers to start with and they are roughly 6ohm each.  My option was to either add the second pair of 15" drivers in series or parallel so I'd end up with each pair at 3ohm or 12ohm. 

At 12ohm it sounded bass shy to me and I thought about running it as a 4-way before I even got the mic out.  I haven't tried wiring them up to produce a 3ohm load due to fear of cooking the amps.  So basically, I went from one driver at 6ohm to two drivers at 12ohm and felt it was giving me less bass which isn't what I'd expect to happen.  Either way, a 4-way works brilliant. B|

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