How do you determine crossover settings for home audio?

September 23, 2005 2:11 PM

I'm setting up my first home theatre system, and I keep hearing and reading about crossovers, which have me a bit confused...

I guess I understand the basics, that each speaker has a range of frequencies that they can produce, and that the crossover is the range of frequencies that more than one speaker will be responsible for producing. So, what I need to know is do you want small ranges of crossover, large ranges, or is it all a matter of preference?

To be specific, I am running a Pioneer A/V receiver (model # escapes me at the moment), Boston Acoustics CR67 for the left and right channel, and a Velodyne DLS3500R subwoofer. Eventually, I'll add the center channel, move the CR67's to the surrounds, and buy something fancy for the left and right channel.

posted by WinnipegDragon to technology (10 comments total)

Is the crossover on your subwoofer? If so, I'd suggest the following: check out the specs on the CR67's and find out how low they'll go. Set the crossover to that point. Call that "standard operation", and then mess around with the crossover point while playing either music you love or the latest Micheal Bay movie.
posted by hammurderer at 2:36 PM on September 23, 2005

The main application for a crossover in home theater is to segregate the really low tones (~ 80hz and below) and send them only to your subwoofer, which is designed just for low notes. That control is probably buried somewhere in the menus of the receiver.

Your Boston Acoustics main speakers also likely have a crossover circuit built into them (probably not adjustable however) to drive the individual speakers with the appropriate frequency range.

BTW the HT wisdom I have heard is that it's a good idea to have the left / center / right set match. The center is quite important for movies since that's where the dialogue is. The Paradigm line of speakers has good sound (to my ears at least) at a wide variety of price points.
posted by omnidrew at 3:11 PM on September 23, 2005

Assuming your Pioneer receiver is semi-modern (say, 5 years old or newer) and has a dedicated subwoofer-out jack, it will handle all your crossover needs. If your subwoofer has a crossover disable switch, activate that. Otherwise, turn its crossover all the way up so that it doesn't get in the way of the Pioneer's crossover.

So what is a crossover? Basically, it's a circuit that determines how to split audio frequencies. For an individual speaker, such as your CR67, the internal crossover determines the range of frequencies that the tweeter plays and the range of frequencies that the woofer plays. In your Pioneer receiver, the crossover setting determines the point around which the receiver starts diverting audio signals from your speakers to your subwoofer. (I say around which because the crossover is not a hard cut-off, but a gradual slope.) Typically, this crossover point is somewhere in the 60Hz to 150Hz range. I always try to keep the crossover point below 100Hz unless the main speakers can't play that low.

Your CR67s are rated to play from 62Hz to 20kHz. Your subwoofer can handle 34 to 140Hz. As you can see, these ranges overlap. Your goal is to find the crossover point which makes the best use of both the sub's and the CR67's capability. This point in not at 62Hz, as hammurderer suggests. Toward to low end of a speaker's frequency response, the loudness at which it can play starts dropping off significantly as compared to the loudness at which it can play higher sounds. You don't want to leave a gap in your overall system response, so choosing a crossover well above that is essential.

I would set the crossover point at 80Hz to begin with, but definitely experiment with higher points to see where it sounds best.

Also, if you can tell me the exact model number of your Pioneer, I can give you more detailed info.
posted by pmbuko at 3:11 PM on September 23, 2005

Also, since you're in the market for speakers, I highly recommend Axiom. They are Canadian-made (like Paradigm), and sound as good as comparable speakers from Paradigm's reference line.
posted by pmbuko at 3:15 PM on September 23, 2005

Does your receiver have just a crossover for the sub or one that can cover the entire frequency range?
posted by shoos at 4:31 PM on September 23, 2005

So, what I need to know is do you want small ranges of crossover, large ranges, or is it all a matter of preference?

The 'range' of the crossover is determined by its slope, measured in dB/octave. A steeper slope will result in what you would call a narrower range. So say you have a 6dB/octave crossover and the crossover point is at 100Hz. If you were to hook the crossover up to a magical, perfectly flat, DC-to-light bandwidth speaker and play a 100Hz sine tone through it at a given reference level, then swept the pitch down an octave to 50Hz, it would be 6dB quieter.

Your understanding that a crossover controls the range of frequencies that is shared by more than one speakers is generally correct, but the terms, etc., make more sense when you realize all a simple crossover can do is make a tone get quieter when the pitch goes down (high-pass) or make a tone get quieter when the pitch goes up (low-pass). Everything else is a combination of those principles.

So, back to slope. Our theoretical 6 db/octave crossover is going to share a large range of frequencies between two speakers. We've gone down a full octave, from 100Hz, which is right around the low A on a guitar, to 50Hz, the low A on a bass, and we're only down 6dBs (that's actually a lot to the ear, but that's another discussion). Perhaps our subwoofer sounds like crap when reproducing signals closer to 100Hz, or, working the other way, we need to protect delicate tweeters from low bass. We need a steeper crossover. There are number of reasons why you would want to keep the range of frequencies covered by a given speaker small, but primarily, the motivation would be that it is easier to build a speaker that works well over a small range of frequencies. So, yes, small ranges=good.

You'll often see crossover specs quoted with an 'order' like 1st order, 2nd order, etc. These are the multiples of 6dB/octave that the crossover's slope is. For example, 4th order = 24dB/octave. There's no reason to get into the reasons behind this unless you want to build crossovers, which is a fool's errand. But the takeaway from here is large ranges=good.

Unfortunately, there's a tradeoff, and it's not so much a matter of preference (inasmuch as preference can be taken to mean "I like to use only two speakers, he likes to use nine.") as a matter of balance or design. Actually, there are a number of trade-offs. Crossovers of various designs (and slopes, and Q's which we didn't get into but are also something to consider) will exhibit different artifacts such as ringing, messing up phase (particularly important with regard to your subwoofer), etc. This is why speakers are normally sold with integrated passive crossovers. The crossover, and its integration with the drivers and box (which also functions like a crossover), is an integral part of how the speaker will sound.

So, that's the beginning of an answer to your question, inasmuch as you actually want to know about crossovers, but if you just want your subwoofer to sound good during movies, just use the crossover output on your receiver and it'll probably sound fine.
posted by jeb at 4:52 PM on September 23, 2005

This is why speakers are normally sold with integrated passive crossovers. The crossover, and its integration with the drivers and box (which also functions like a crossover), is an integral part of how the speaker will sound.

Of course this is just as true for the crossover in the sub as it is for the crossovers in the speakers. So in principal relying on the receiver to do the filtering (crossovers are filters) isn't really the correct advice.

In reality you have to put a lot of effort in to optimize your system at that level, and even then the room and the placement of subwoofer/speaker within the room probably matter at least as much as the shape of the subwoofer's built in crossover. So, if you really want to learn about this stuff lets all have a long talk, otherwise the advice to use the receiver's crossover is fine.

I find jeb's use of the word range to describe the roll off of a filter a little strange, but except for the semantics his answer seems pretty good, so...
posted by Chuckles at 7:33 PM on September 23, 2005

Wow, great stuff folks... This is why I love MeFi!

To answer the specifics on the reciever it's a modest one but brand new, a Pioneer VSX-C302. It has a dedicated subwoofer out (an LFE port) and two subwoofer related settings, one that seems to be the crossover point and can be set to 200Hz, 150Hz, 100Hz and 'PLS' which is a 'bass boost' according to the manual. The second setting is an LFE attenuator, that can be set at no LFE, 10db attunuation and no attenuation.

To clarify, the sub has a dial for it's own internal crossover that can range from 40Hz to 200Hz. Having read the information here so far, it sounds like I should set the receiver up as 200Hz and no attenuation, dial the sub to roughly 80Hz and then just fiddle until I reach my own preference. I'm thinking this since the crossover in the receiver is limited to only four settings and I think I want a little more control than that.

As far the replacement main speakers and centre channel, that's a little while in the future. I'm going to save up my money and hit my local B&W dealer. I'm hoping I bought a sub that won't disappoint when paired with a higher end brand like B&W.
posted by WinnipegDragon at 9:58 PM on September 23, 2005

no no no! You want to dial the sub up to its max crossover setting (taking it out of the equation altogether) and the receiver to 100Hz -- the lowest it will go. If you do what you just said -- set the sub to around 80Hz and the receiver to 200Hz -- then you'll have a gap in your frequency response and nothing will be responsible for handling 80Hz to 200Hz. Gaps are bad. You need overlap, and the best way to assure an overlap of equal slope is to only use the receiver's crossover.
posted by pmbuko at 1:42 PM on September 24, 2005

Oops, I realized what I wrote was not what I intended. I meant setting the receiver to not crossover at all (i.e. send all frequencies to the sub) not it's highest setting.

Having read your comments about slope though, I see your point. I'll set it to that and see how it sounds.

Thanks for the advice!
posted by WinnipegDragon at 9:25 AM on September 25, 2005