[Seano]

from the redgum webpage:

RGSW8 Subwoofer Amplifier Plate
1500WRMS power output into 8ohm – 3000WRMS into 4 ohms - US$5990 each... and they kindly throw in delivery free

er...
correct me if I'm wrong, but there aint many complete commercial subwoofers that cost this much.... except for 'obscene $$' offerings like Krell's - but even then the Krell almost looks cheap at US$28k compared to the redgum amp... http://www.krellonline.com/html/m_MRS_p_MRS.html

Never at any time did I suggest that they were cheap/affordable/great value! I simply suggested they'd probably be quite good.

That said though that 1500W thingy a rather titanic plate amp.  Most normal homes would be happy with a sub capable of one-tenth to one-fifth of that output. To be fair, Redgum's 600WRMS plate amp is AU$1,100 and their 200W version is AU$750. Still not the cheapest of plate amps but not out of the league of ordinary gents who hanker for a head pounding.

If you want to be cheap, Jaycar do a 240watt into 8 ohm remote control plate amp for AU$379......plus delivery

But then Aaron do a complete 300W sub for AU$1,200 so where's the value in a plate amp?

Personally, I'd prefer to spend the extra cash for an average sub on boosting the quality of replacement main speakers rather than the sub but that must be just me.  

[Brownee]

Hi
Seeing as this thread is already talking subs I thought I would post here. I am after a DIY sub to go with my Aksonics/AKSA set up. It would have to double for HT but music is paramount. The Rythmik Audio DS350 DirectServo kit looks good but the shipping to OZ would probably push up the price. I think the AkSub is a fare way off (correct me if I am wrong Hugh), so can anyone give me some advice and a push in the right direction.

Thanks
Brownee

[DSK]

The Rythmik Audio DS350 DirectServo kit looks good but the shipping to OZ would probably push up the price.

I looked long and hard before going with the Rythmik kit. Yes, shipping and taxes add to the cost but it was still the best option in my view. For music, I can't think of an audibly superior sub under $5k. The speed, detail, lack of bloat and overhang are superb. Easily better than the M&K, Velodyne, Klipsch, B&W etc subs I've heard.

Hugh knows the sound of my system (with and without sub) very well and while I won't put words into his mouth I don't think I'm exaggerating when I say he was very impressed indeed with the performance of this sub.

[AKSA]

Brownee,

I would agree with DSK (aka Darren).  Absolutely entrancing sound, one of the most unobtrusive I've heard, yet with all the muscle of the best subs.  It integrates and beautifully fills the void left by the smallish woofer on the Ambience ribbon speakers;  I was extremely impressed.

It is a kit, and shipping is expensive, but much cheaper than the fully assembled item.

Cheers,

Hugh

[Brownee]

Thanks guys for the reply. I think I might bite the bullet and go with the Rithmik sub. Darren, could I ask what size your room is? I emailed Rythmik Audio and Brian mailed back that the DS350 might not be enough for my room size. (7.5m X 6m). Also did you have it shipped surface? If so how long did it take? (Air freight is twice the cost)

Thanks
Brownee

[AKSA]

Brownee,

See if you can get them to ship it US Postal Service, surface mail.  It's MUCH cheaper, but will take some time.

Cheers,

Hugh

[SamL]

Brownee,

See if you can get them to ship it US Postal Service, surface mail.  It's MUCH cheaper, but will take some time.

Cheers,

Hugh

I surface mail a 12in passive radiator from US and never see it. Seller is not keen to chase up the fright company as it was a few month old transaction. Not worth doing unless the seller has been using surface mail regularly.

Edit: BTW,  I did not get my money back. No reply what so ever.

Sam

[DSK]

Thanks guys for the reply. I think I might bite the bullet and go with the Rithmik sub. Darren, could I ask what size your room is? I emailed Rythmik Audio and Brian mailed back that the DS350 might not be enough for my room size. (7.5m X 6m). Also did you have it shipped surface? If so how long did it take? (Air freight is twice the cost)

Thanks
Brownee

Hi Brownee,

My room is 5.8m wide x 7.3m deep x 2.75m ceilings. One corner (behind listener's left shoulder) is completely open to a long hallway and also to an open staircase. So, the room volume is effectively much larger than the dimensions suggest. The sub has no problems in this room and is flat to below 20hz. I'll check the shipping details and PM you.

Cheers,
Darren.

[jules]

I have to support Hugh on the use of of USPS [as against UPS or other couriers]. Particularly if the cost of an import comes in below the $500AUD mark the savings are BIG. You can insure with USPS and items sent through the United States Postal Service come into Aus. through the Aus Post terminal which also helps [in either the case of airmail or surface mail]. I suggest you do a careful check of costs [customs and postal] cos it is complex but there is nothing inherently more relaible about couriers such as UPS or Fedex.

The use of a sub, particularly with a 55, looks like a great idea. The power of the Aksa in concentrated where it's needed and the power of the sub compliments it perfectly.

jules

[pauly]

I have been looking at the oaudio bash sub amp as SamL mentions.
imput impedance is 20k. Is this O.K with the GK-1R?
Rhythmik also looks very good
I will build 2 subs for my 780sq. ft. room.
Just shortlisting all the online choices.



Paul

[AKSA]

Yes, Paul,

20K is OK for the GK1-R.

Hugh

[DSK]

I have been looking at the oaudio bash sub amp as SamL mentions.
imput impedance is 20k. Is this O.K with the GK-1R?
Rhythmik also looks very good
I will build 2 subs for my 780sq. ft. room.
Just shortlisting all the online choices.

Paul

Hi Pauly, 20k is fairly typical for subs and some are as low as 10k. From memory the Rythmik is 37k. This was important to me as I drive the sub and the AKSA 100N+ from the GK-1.

[pauly]

Thank-you for your replies.
Are there any advantages to the higher r plate amps?
Some amps I've seen are as high as 43k
Has  anyone heard the o audio sub?  http://www.oaudio.com/500W_SUBAMP.html


Darren,
you seem very happy with the rhythmic subs.
mabey it's the better choice.


Paul

[jules]

The more I look at subs the more sense they make. The lowest note on a piano is 27 HZ and an organ can manage 16 Hz [is it a coincidence that Hugh's sub can do this figure   ] so without even attempting to analyze what the resonances of a hall etc might be it's clear that most "audiophile" systems are woefully inadequate in a very important zone. Apart from the fact that a 6" speaker rolls off dramatically below about 70 Hz, even a 12" speaker in a 100W system isn't going to have the power necessary to produce a full bodied 20 Hz tone. As I understand it, a drop in frequency from 40 Hz to 20 Hz requires a fourfold increase in power to achieve the same output. So I have to say that rather than buy a 1,000W amp and a matching 3 or 4 way speaker system for maybe $150,000, a sub looks rather good value   .

I would like to ask a question [of Hugh or others who know such things]:-
A sub such as the Rythmik servo, can be adjusted for it's highpass xover but when a sub is added to an existing speaker system you are still left with the soggy cardboard thwock of the low end to remove somehow. What is the beat way to deal with this? Would first order RC attenuation installed on the input of an AKSA power amp be appropriate or problematic in some way?

jules

[andyr]

A sub such as the Rythmik servo, can be adjusted for its LP xover point but when a sub is added to an existing speaker system, you are still left with the soggy cardboard thwock of the low end to remove somehow. What is the beat way to deal with this? Would first order RC attenuation installed on the input of an AKSA power amp be appropriate or problematic in some way? ...

Hi, Jules,

As I understand it, it depends on how soggy your cardboard woofers are and how low they go ... and the sound you like.  

If you leave your "mains" full range then maybe your subs only have to come in very low?  However, if you think that chopping off your "mains" would be a good idea (because they sound bad at the lowest notes they can go to) then you have to decide how you are going to chop them off ... and the frequency.  This will then relieve your "mains" - and the AKSA powering them - from the really heavy work of reproducing these lowest frequencies ... so the "mains" should sound cleaner/better as a result.

I understand the -6dB point of the sub/woofer crossover point should ideally be set no higher than 80Hz, to avoid male bass voice from being reproduced by the sub.

You then have to decide how to implement the (80Hz) HP -6dB point for the "mains":

1.  a suitable cap on the input to the AKSA (first order).  The Butterworth equation gives you the -3dB point so you'll have to estimate what -3dB point will give you an 80Hz -6dB point - then you can calculate the required cap value.  I make it 27nF (for 43Kohm).

However, I believe 1st order is too shallow a slope - it will be quite a few 100Hz before the slope is asymptotic, so you may be impacting the woofer LP crossover point in your "mains" (depending on how high this is).

2.  an active HP crossover ... say 3rd/4th order.  Of course, unless you have organised your "mains" crossovers properly, this means that all of the signal going to your "mains" has gone through this active HP filter on the bottom end!  Ideally, only the woofer signal should have gone through this, so your tweeter (and mid-range, if you have one) are "untarnished"!!

Regards,

Andy

[jules]

Andy,

thanks for the help including the useful little details such as the matter of the deep male voice! I am still in the position of being able to tailor my speaker box to the situation so rather than designing it to get the most out of the bottom end of the range of my drivers I will tune it to avoid any heroics down there.

After that, if there's any soggy cardboard thwocks left I feel armed to deal with them though I think I should do some reading on crossovers.

jules