Upgrading to 2.1 System

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Hi,
I’m planning to build a subwoofer similar to the Madisound L26ROY kit with passive radiator. My main speakers are a pair of Seas A26 run from an Onkyo A9555 which I’m pretty happy with, the amplifier has ‘A’ and ‘B’ speaker outs but no sub out. Before finalising the spec for the sub I’m trying to work out the best configuration for the system (and where to spend my money), the way I see it is that I have a few choices to integrate the sub:

1. Use a plate amp like the Monaco SAM-2, connect the ‘B’ speaker outs from the amplifier to the sub’s high level input and adjust the Low Pass filter to pick up where the A26s roll off. This means I have a single volume control from the amp but I don’t know how smooth the crossover between mains and sub will be… this is my preferred option if it can work.
2. Replace the stereo amp with an AV receiver. This means I don’t need to worry about the crossover for the sub, can connect to the low level input on the sub amp and have a single volume control. But means I’ll be paying for 3 amplification channels that I won’t use (and maybe compromise the sound quality depending on how much I’m willing to spend).
3. Make/buy a passive pre-amp to control the volume, connect this to the low level inputs of the SAM-2 and feed the low level outputs to the amplifier for the main speakers. This means I use the high pass section of the sub amp and have a single volume control.

There are probably many other options but this is what i’ve come up with so far. The reason I looked at the SAM-2 amp is that it has a high-pass output that I can use for the mains, if this isn’t required then I have more options for the amplifier. I’ve opted for the L26ROY sub purely because I like the sound of the A26s, enjoyed making them and would like a sub of similar quality that would integrate well. Also I’m not that bothered about volume levels or room shaking bass, I just want to hear the lower frequencies in a system that I’m already happy with.

I’d really appreciate any advice on the pros and cons of the options suggested or any options that I’ve not thought of.
 
If you like what you have and just add bass, you may like the system less, unless you augment the treble too.

Hardly any way to proceed in an intelligent way unless you can measure where you are and re-measure upgrades along the way. REW software is free and the necessary mic is about $60. Lots of fun playing doctor.

There are so may "what-ifs" to your development, that you might start with the simplest paste-on subwoofer concept and see how you like it before diving into the sort of sophisticated systems most brothers and sisters on this forum love to recommend.

Ben
 
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Thanks for your advice bentoronto.
I have taken measurements of the speakers from the listening position in the room using Fuzzmeasure, applied treatment to address the key modes and achieved a sound which is good to my ear and shows an improvement (although I know a sub may excite modes that don't currently cause a problem).
I don't really want to augment the frequencies that I already have, just add the sub 100hz frequencies to the existing spectrum of sound. I guess what I'm asking is for the best way to add a sub without introducing humps or dips at the crossover point and how I should take this into account when choosing a design for a diy subwoofer.
 
I don't really want to augment the frequencies that I already have, just add the sub 100hz frequencies to the existing spectrum of sound. I guess what I'm asking is for the best way to add a sub without introducing humps or dips at the crossover point and how I should take this into account when choosing a design for a diy subwoofer.

Now you have to do the math to see where you are going. Specifically, you need sharp crossover curves to reduce the overlap you mention above. If you cross over at 100Hz, you can't be sending signals to your sub at 200 Hz which are just 15 dB down and likewise for the mids trying to handle 50 Hz input. Unlikely an A/V receiver has the full set of 18 or 24dB/8ave filters you'll need. A lot of folks use digital boxes with 48dB/8ave slopes (I can't imagine ever having a system - even a basic one - without DSP ever again).

I like the notion of putting as much core sound through a single driver (or carefully crafted pair) and have the bass and treble as "icing on the cake" rather than cross over in the middle, as is common.

You may find you need to sit an add-on prestige tweeter on top of your mids for the sound to seem right.

Ben
 
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A lot of folks use digital boxes with 48dB/8ave slopes (I can't imagine ever having a system - even a basic one - without DSP ever again).

Ok, thanks I'll look at DSPs.

You may find you need to sit an add-on prestige tweeter on top of your mids for the sound to seem right..

The Seas A26 use the T35C002 tweeter which is good enough for my ears.
 
Hi simonra,

While DSP is definitely a good idea, I would run the A26s in full range, and add only to the bottom end using as close as I can get to the Geddes multiple subwoofer approach: http://www.diyaudio.com/forums/subwoofers/134568-multiple-small-subs-geddes-approach.html ; also, take a look here:
GedLee LLC

Either way you will need some kind of measuring equipment, and follow the procedure linked to in Post #5 in the above reference.

I can see no need for hundreds of watts in subwoofer power to augment a pair of A26s, but individual level control on the subwoofer amp(s), 0-180° phase control and control over the HP and LP of the subwoofer will be needed as in your choice of the Hypex (an inexpensive example is the The Apex Junior Subwoofer Amp .)

Regards,
 
Swap out the Onkyo as a test

Hi Simonra,

I know you mentioned being happy with the Onkyo but I really think you might consider swapping in a different amp as a test. My experience has been that the majority of Japanese integrated amps just don't get the bass right. You might be surprised what those speakers can do when powered by an amp that's got significant horsepower and more importantly, has been designed for good, solid bass response. Based on what you wrote, I searched and found the review below on your amp. The reviewer noted that when compared to the PS Audio amp, the PS Audio had more extended bass response.

Usually the design flaw in integrated amps is the power supply. They are built to a price point or are constrained by space and often the power supply is where corners get cut. While on paper everything looks fine, when listening you find things just like the reviewer did where the bass isn't as extended as other amps.

http://www.stereophile.com/integratedamps/907onk/index.html#wSaqHlruj8gfT4CQ.97

Find yourself another amp to compare against. Even if it's older, I'm betting you will find it will sound better. If you can afford it, perhaps a Pass Labs, Threshold, Coda, Nakamichi PA-5 or PA-7, Parasound, or PS Audio, amp & preamp. I have a hunch they will hands-down smoke the Onkyo and you might find you don't need a subwoofer after all (unless you just want it for movies).

And no, I'm not trying to be insulting at all regarding the Onkyo as it looks to be a nice unit. I just have a hunch you might be surprised at what you will find that's all.

Just my $.02.

Kind regards,

Steve
 
Thanks Oliver, I'll do some reading on the multiple sub approach it looks like an interesting alternative to room treatment. I've put quite a bit of effort into room treatment and (more by luck than judgement) have dealt with some pretty nasty low frequency lumps and bumps although I'm sure more will reveal themselves when I introduce a subwoofer into the mix. I understand that placement is going to be key. I'm glad that you suggest running the A26s full range as I really didn't want to risk degrading the sound by introducing a high pass filter for the mains. The Apex amp looks interesting, I'll look at the possibilities of shipping to the UK.
 
Hi Steve,
Thanks for your reply, I think you raise a good point. I've only ever up-graded and don't really know what I'm missing if by not going a step further... auditioning another amp is definitely a good idea. If the several hundred pounds I'm going to spend building a subwoofer would be better spent on a new amplifier I'd rather know now. I'll take a look at the options you suggest and see if I can get to try some out.
 
Quick update

Just a quick update in case anyone's interested.

I took most of the advice given here although I couldn't make the multiple sub option work given the layout of the room. This is what I ended doing:

I built the sub as per Madisound design and started with the Monacor 300D plate amp - I think there may have been something wrong with it as it sounded awful (hf buzzing). So I swapped that for a BK Electronics BSBP 275 plate amp - that got me the sound I wanted from the sub. The controls on the plate amp allowed me to get a pretty good blend with the mains but exposed some pretty nasty room modes.

So in comes the MiniDSP 2x4 HD & measurement mic - after a lot of experimentation I found that running the A26s full range with no eq or crossover sounded most natural so I used REW & eq to flatten out the sub a bit and to take over phase and crossover (LR 24dB/oct @ 95hz) duties from the plate amp.

What with the amplifier, dsp, phono pre-amp & HDMI audio extractor the mess of wires was getting to me. So I bought a 3u rack case and a pair of Hypex Ucd180 amps & SMPS and put the whole lot in one box with one mains cable connector going in. So the Onkyo can be used for something else now.

The whole thing took me a few months longer than planned and quite a bit more money. But I can now fully appreciate the low e of a bass guitar and the weight of the kick drum so it all seems worth it.

Thanks for advice and all the valuable information on this forum... just need to save up some money while I think of the next project.
 
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