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In Reply to: RE: EQ and subs? a continutaion from K-Bob's learning. posted by Timbo in Oz on May 04, 2017 at 00:27:08
Here is my take.Over the years I have set up lots of budget systems, sometimes using things for pre-amps and amps most 'philes would not consider (or tolerate).
The 6000C seems to be a decent choice for running (2) four ohm subs in stereo. 500WPC into 4 ohms stereo and at 55 pounds, one can probably assume this amp has some good damping factor characteristics (aka, good size supply rail capacitors and transformers, which are important for Class AB amplifiers like that. (Class D amps can weighing 10 pounds can delivery 1000W..)
The push pull amps use 10" drivers and are 88db 1w/1m sensitive?
What is the impedance of each driver in the box and how are they connected?If you provided the specs (or at least model) of each driver, someone could better help getting the most out of that specific combination of amps and boxes.
To figure this out you want to try and estimate the maximum power output of each box and how much input power is required to get there. This will help you decide which amp to run on which boxes.
The HK is a good amp, but remember that 60A peak power (likely total, and not per channel else they would have said so) at 8 ohms is 240watts per channel peak. Not as impressive sounding... This is not rated for four ohms (no specs given) but is four-ohms capable.
So what's the plan here? Put the larger amp on the more efficient boxes to maximize output? Or put the bigger amp on the less efficient box to try and have some sort of level matching this way? The HK probably does about 150W/ch at 4 ohms... maybe 175. It won't double with a damping factor of 150. You need to get into 750+ numbers to do that. (Also, this damping factor could be averaged over a range of the spectrum... this is often done. An amp with a damping factor of 500 at 250Hz can be below 100 at 50Hz.)
Next calculation is to see, for each connection option, which unit bottoms out first in each case. I bet the 6000C could drive either pair of subs to full excursion, possibly without even clipping. In the case of the HK, I would bet the amp starts to suffer first, with the PS rail voltage getting dragged down considerably during heavy bass power surges. This can lead to the kind of distortion that can cook woofer coils, or cause excessive heating in the amp, but worst of all, distorted uncontrolled bass. The opposite of tight, clean bass. (Once you've heard super-powered amps and high quality woofers that don't "thump" but can actually pound and *hit*, when you hear loose distorted bass it makes your skin crawl.
There is really one question here: given the type/nature of each sub box and each amp, is there a way to best match them up, OR is using both pairs and both amps not going to be an optimal solution anyways?
Do you have separate circuits to the room? If both sub amps are on the same circuit, I would not have the HK and the less sensitive box dragging down the AC supply voltage if only delivering a smaller chunk of the over-all SPL.
I suppose the "multiple subs for smoother response" will be a factor in this, but I have a feeling the HK amp will be a limiting factor and possibly even do more harm than good depending on how your audio room is circuited.
Cheers,
Presto
Edits: 05/07/17Follow Ups:
With push-pull you are looking at -3db so actually 87db/w. These may need an Rb enclosure.The 12s are 93db/w and 8 ohms, 23Hz. So sealed p-p gives around 90db/watt.
The big rb Sub is an old design but IIRC is about 90db/w, 8 ohms, and ran happily off a 100 watt amp with hard use.
Its partner will use a new Canton 26cm woofer which is 3.5 ohms and 91db/w, and can handle 100watts. Similar box size and port.
I'm hoping that both Rb subs will get down to their Fbs without needing heaps of power and that's why I will use the HK 870 for them, to start with.
I will be sitting down with a box-plotter for all three box builds and make sure I'm getting down low enough before the EQ is added. I do have all 5 driver's TS's to do that with.
The room does give room gain > ing as f falls, but it's not a concrete room!
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 05/08/17
Timbo:
I think you should try the HK as you have planned and see how it goes. See how "tight" the bass seems... of course, there is more to it than just response. Just look for signs the HK is struggling... one is distortion the other is excessive heat.
I read your other post... you have lots of copper going into that room so voltage drop should not be too much of a problem. Running big amps on their own circuits is always a good move. I suppose it could be fun to switch amps and boxes to see how things sound. It is tempting to put more power behind the drivers that have higher xmax... but it's also important to know if there are any potential issues with "unloading" of the sub driver, aka where a subsonic filter should be used. Super-lows just rob amp power and move the subs voice coil out of it's sweet spot, as far as it's B-L curve is concerned.
I am not aware if you have a preliminary plan for placement. There are theoretical "optimal zones" to put subs in multi-sub applications for the flattest response (most even excitation of different room modes).
For two subs, I think it was one in a corner and one on the center-line of a given wall. My understanding is that mirror image location of subs is *not* necessarily an optimal layout.
Cheers,
Presto
One is used to power the sources and pre-amp.So that leaves 4,800 watts of mains power available to run:
i) the Fostex SS amp OR the 40wpc strapped LEAK St20s, and
ii)the two stereo sub amps,
iii) active HP filter and
iv) the two Eqr's.Even with the slight inefficiency of SS circuits, and even with the valve amps draw of 200watts each in Winter - I don't think those two circuits will sag.
Feeding panels across the entire roof space there are two redundant 2.4KVA heating panel circuits. Some professional work would be required to redirect their cabling, and remove their timers on the mains power breaker box.
I would then have 4 x 2.4 KVA circuits to feed the power amps with!
Given all that spare capacity I have thought about going with balanced AC mains.
But I would prefer to do that first for the sources and pre-amp, using the existing 240V 10 AMP unbalanced circuit. It may be that an isolating mains transformer that also does balanced AC might be the best solution for the system's front-end.
Then there would be the task of dragging two or more big traffos into position under the house, and re-cabling to the wall outlets. Special wall outlets to meat safety laws and special wall sockets and differing plugs.
LBNL the various systems in that room have never been prone to mains-borne noise. Maybe I'd hear a lower noise floor but would it be worth > $Au2k?
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 05/07/17 05/07/17
I will have to suck it and see.
There may be a 6000B around.
That would be ideal.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Used this amp to drive two built in 10" drivers, would rattle my neighbors windows lol. Stable into 2ohms, rated 300watts/channel 8ohms, 400watts/4ohms, doubles down when bridged making 800watts, this amp never breaks a sweat and will run any load BWAAAAAA HA HA HA HA HA, he laughs his evil laugh.Martin
Edits: 05/07/17
;-)!But, I will keep hanging out for a Perreaux 6000B or C!
Lots of power and individual-channel gain controls.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 05/08/17
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