October 27, 2010

List of active crossovers

The range of active crossovers now available seems to be expanding very quickly. Here is a list of some of the options available. If you know of any that I've missed, please let me know via the comment section below.


MiniDSP > (Low cost flexible PC controlled solution)
Behringer Ultradrive DCX2496 >
(Popular pro choice for a stand alone box)
Ashly Protea 3.6P> (Similar to DCX, other crossovers available)
DEQX > (The ultimate solution)

Hypex AS2.100 >

CAD Audio DSP modules >


DIY analogue (ESP) >
Marchland >

PC based

Bodzio Sound Easy >
Thuneau Allocator >

So what do they do and how are they different? See my summary of active crossover options or jump to which one is right for me?

October 21, 2010

How to connect a subwoofer

For any given system, there are a number of ways you can do it. This generally applies to conventional subwoofers that have a plate amp. If you have a sub with an external crossover, the situation may be different.

High vs low level inputs

High level - are speaker level signals coming from an amplifier that would normally be connected to the speaker terminals
Low level - are preamp level signals

Always choose low level inputs first. There are two reasons for using high level inputs:

1. Low level inputs aren't available (typical with an integrated 2 channel amp)
2. Low level inputs don't provide enough gain

Subwoofer outputs

Subwoofers vary in whether they provide outputs or not. Where provided, they usually feature filtering at a pre-determined point such as 80 Hz.

Preamp > Subwoofer low level input >
> Subwoofer low level output (bass filtered out) > Power amp > Speakers

A separate power amp, or power amp inputs are required. The advantage is extra headroom both for the amp and speakers. The amp will use less power where bass is filtered out, and the drivers will use less excursion. However, this may not always give the best integration and it's better where possible to have more control of the filtering. It's preferable to have control of both the low pass on the subwoofer and the high pass on the mains. In some cases, overlap might integrate better. Also consider that the slope of the electrical filter will be added to the acoustic response of the driver. The final response will be the two combined and will often not be quite what you expect.

Normally the outputs are a filtered version of the input provided. So if you use low level inputs, you can only use low level outputs if required. The high level outputs could not be used since no signal is being fed into the high level inputs.

2 channel integrated amp

Check if you have pre outs and amplifier inputs (often marked "main in" and right next to the pre outs).

If so, use low level inputs. Two options:

1. Use a splitter on the pre outs. One set of interconnects to the sub inputs, the other back to the power amp inputs.
2. Pre outs > subwoofer inputs and low level outputs > power amp inputs

In the second option, the sub provides filtering of the signal sent to the power amps.

If you only have pre outs, then you need an external power amp to use low level inputs since your power amps inside won't get an input. Or you might have to consider high level inputs.

If you have no pre out at all, then your only choice is high level inputs.

Surround receiver

With a receiver, it's simple. Connect the sub pre out into one of the low level inputs. You will have bass management settings on your receiver that can be used. Depending on the options available on your sub and receiver, you may choose one or the other to control the settings.

Common problems

"My sub won't play loud enough when the volume is turned up."

You have a gain problem. Check the settings on your receiver. Another solution can be to use high level inputs. This can also happen to those who have used an external power amp with no dedicated preamp/crossover. In that case, an external crossover which includes variable gain should be added.

"Auto turn on does't work."

Same problem - the gain isn't high enough to activate the switch. See previous.

"Bass sounds boomy on some notes, absent on others."

There are two potential problems. One is incorrect setup with the main speakers where you might have a dip in between the sub and the mains. The other is that the room acoustics are causing peaks and dips. Most rooms have this problem and it is not easily solved.

The best solution to both problems is to set up the sub with measurements. You will need a basic measurement setup and some patience to learn how to use it. The cost is not high, you might enjoy the learning process and you will certainly enjoy the result.

More about getting a measuring setup >

Two steps

1. Nearfield measurement - put the mic close to the cone of the sub and mains to isolate the sound of them from the room

This will help you set them up correctly so that you don't have dips.

2. Farfield measurement - put the mic in your listening position, then measure speakers + sub as well as showing the impact of the room

This will help you find the best placement of the sub.

This process will take some time but give you the best result.

Here is an example of the kinds of results you will see:

An example of subwoofer integration with measurements >

October 13, 2010

Subwoofer transient response

Does transient response in subs really matter? Are sealed subs better for their superior stop on a dime bass? It turns out that the answer in most rooms is "no" in both cases.

Subs aren't as different as you think

When you look at actual subwoofer measurements, they aren't as different as one might expect. Most of them, whether high quality or cheapies, measure about the same except at the low end which is less critical. A vented subwoofer will ring around it's tuning point, but as with many cases, if tuned around 20 - 30 Hz, this will have no effect on music. It will tend to influence low frequency effects which are artificial in nature.

Here is one example:

JL Audio fathom >

Scroll down to the spectral decay. You might like to look at some of the other measurements and you will see that most of the subs measure the same above about 30 Hz.

Sub tests >

Look at the spectral decay in the first example. It's a top notch sealed sub, and at 100 Hz you get 6db of decay in the first 40 ms. That's about as good as it gets, and with low frequencies, things get worse.

Now lets look at a room measured by Ethan Winer:

Look at the first chart and you see that it takes about 100ms to achieve the same amount of decay due to modes in the untreated room. In the next chart with treatment, the subwoofer range is virtually the same and it's only about about 80 Hz that signficant improvement is seen. At this point the room now decays faster than the subwoofer, but only outside it's passband.

Of course, each room is different.

Looking back at those measurements, the best performing sub I found out of the lot seems to be an REL, one which measures very poorly in every other way:

REL storm >


So what does all this mean? There are a lot of things to worry about in setting up a sound system, but subwoofer transient response isn't one of them. Even a treated room will ring out longer than the sub itself, except for LFE content. The subwoofer transient response can't be considered in isolation from the room - the two are combined together and the ear can't distinguish between them. The ear is also not quite so sensitive to time domain issues in the sub range, certainly not as much as many of us have been told.

The lower midrange deserves more attention, but gets strangely ignored. Room modes cause ringing there and this can be treated effectively with bass traps. EQ will have no effect on ringing there, but we can flatten the inroom response with multiple bass sources.

The key point I'd like to make is this - ignore what you can't fix and what doesn't need to be fixed - in this case subwoofer transient response. Instead, focus on what you can fix and what does need to be fixed. This is the reverse of what many choose to do. Those that haven't figured out what needs to be done have a habit of tail chasing. Rather than find real problems to fix, they chase after imaginary ones.

October 12, 2010

White Van speaker scam

"Hey mate, want a pair of speakers?" It usually starts like that. Next comes the story which has many versions, but always it's shady and suspicious and you immediately sense that something is dodgy. You're not sure if they really are clearing excess stock sent by mistake, or if they are trying to unload stolen speakers quick. It's a clever trick designed to get you to make a decision before you have a chance to realise what is going on. They count on the fact that some people are opportunistic enough to go for it and part with their money. The fact that some may think they are getting stolen goods only enhances their game as it works as a distration from the truth. The reality is, these speakers are worth very little. They certainly aren't worth thousands.

If you meet the White Van guys ...

Don't believe a word they say about their value. Some have bargained them down to a very low price. I've heard one case where they were sold for $50 at a service station. If you want some cheap party speakers, or workshop speakers then see how low they will go. Offer them $100 then walk away.

So what is the scam?

It's simple - they are dirt cheap el crappo speakers often sold for more than they are worth to people who get excited by the chance to pick up $6k speakers for a grand. In reality they are worth much less than that. They make a quick sale and run on pretty low overheads. The scam has been around a long time because it works. Even if only one in ten bite, it doesn't take long to drive around in a truck and find 10 people.

So what do I do now?

Think of it this way - you've just paid for an education. It wasn't quite as rewarding as you'd hoped but you can redeem the situation. In fact, you might be able to improve these cheapies. Here are some suggestions you could try:

1. Knock on the box - is it hollow and resonant or reasonably solid and dead? You might consider adding some braces internally.

2. Remove a driver and see what kind of lining is inside the box. You might consider adding lining if there is none. That can clean up the sound a little.

3. Find the crossover. Take a photo of it and see if you can make a schematic of it. Chances are they use cheap rubbish parts and a crossover that is so lean on parts that the drivers have little chance of working properly.

4. Listen to the treble. Does it sound exaggerated? If so, find the tweeter impedance and add an L pad. I've described how to do this in my blog. Use the search function above (sorry I'm being lazy with the link).

5. Consider measuring the response. I have a blog post about what you need - search for "basic measurement setup" in the search box.

This is the start of a good education! You've already paid the entrance fees, why not sit in on the lessons?

Or you might consider an entry to the world of DIY. The surprising fact is that with DIY, you actually can come up with something that matches the deal they promised you. $1k can be enough to put together a $5k speaker.