Sub crossover freq for MMGs?

[Mike Anderson]

My amp (Musical Fidelity A3.2, an integrated amplifier) has a preamp (line level) out. I'm assuming it's the same signal that goes into the main amp section. Obviously, I'm running that into the RCA line-level input of the subwoofer.

But I'm confused about a couple things.

First, although I'm using my ears instead of a meter, it sounds like my MMGs have a fairly flat response down to about 55hz. So why would I set the crossover as high as 80hz? Wouldn't this necessarily create a hump in the 55-80 range?

Perhaps my problem is that I don't know the slopes of the rolloffs for the two speakers, so I'm having a hard time picturing this all in my mind. Perhaps I should just bite the bullet and get an SPL meter. Is a $50 digital Radio Shack meter going to be more accurate than my ears?

I experimented with a large range of crossover freqs, and found that anything as high as 80hz made it really boomy on any recording with substantial bass; if I then back off on the subwoofer gain to eliminate the boominess, it becomes difficult to tell that there is any subwoofer at all. No matter what I do, it seems like I still get a dip at 65hz, which makes me think it's a room problem.

I will say that at 40hz, I'm still having a hard time getting a good rock and roll punch.

[Mike Anderson]

"MMG's do not have a lot of surface for the bass. Consequently the roll off is in the area that smaller bookshelves usually have. In any case, I don't think you bought MMG's because of their prodigious bass."

I don't know if you've tried out the MMGs, but you might be surprised: if you drive them with a sufficiently powerful amp, it makes a big difference. I don't know what bookshelf speakers do, but I'm definitely getting good bass down to 55hz or so.

[JoeE SP9]

<quote>"MMG's do not have a lot of surface for the bass. Consequently the roll off is in the area that smaller bookshelves usually have. In any case, I don't think you bought MMG's because of their prodigious bass."</quote>

I don't know if you've tried out the MMGs, but you might be surprised: if you drive them with a sufficiently powerful amp, it makes a big difference. I don't know what bookshelf speakers do, but I'm definitely getting good bass down to 55hz or so.

I have owned Maggy's in the past. Several of my friends currently own 3.6r's, 1.6QR's and some old Model 2's. I have owned MG1's, MG2's and MG3A's. So, I am familiar with the bass characteristics of the breed. What musical selections are you using to gauge the low end? Bear in mind that a large percentage of popular music doesn't really have any low bass. I agreed that 80Hz was a good place to start. I would consider it an upper limit. The reason I can use 80Hz is because I use an electronic crossover that sends everything above 80Hz to my panels. By getting everything below 80Hz away from my panels I get around the boom. I have found an external active crossover to be much more flexible in adjusting frequency and level than the ones built into most subwoofers.

[Mike Anderson]

What musical selections are you using to gauge the low end?

Not music -- using Wavelab, I generated a series of pure sine wave test tones, starting at 30 hz and increasing in 5 hz increments.

Here's how it works with the MMGs only: I start at 160hz, and step down. I notice a slight dip right around 65-70hz, and then it's loud again at 60hz. A very slight decrease at 55hz, and at 50 hz the dropoff is substantial.

Adding the subwoofer obviously increases level in the 55hz and below frequency, and I can get levels in that range to match a level in the 80hz range if I set the crossover somewhere below 60hz and fiddle with the gain repeatedly. But there's always a dip right around 65hz, no matter what I do; there must be a room-generated node at this frequency.

Again, this is using nothing but my ears, no meter.

A problem is that once I set it using the test tones, the music is all over the place.

Using a well-recorded jazz piece with lots of acoustic bass (e.g. Diana Krall's "Stop This World"), there's loads of bass, and in spots it's boomy. If I then go to a rock album (e.g. Foo Fighter's "Colour and the Shape"), there's not much at all below 80hz or so, and it has no punch unless I really jack up the gain on the subwoofer. On the other hand, with something like a modern electronica/house recording, the bass is just too boomy and dominating.

Optimally, I'd have a remote control for the subwoofer gain, I suppose, and adjust it to the music.

[Mike Anderson]

I have found an external active crossover to be much more flexible in adjusting frequency and level than the ones built into most subwoofers.

Well I guess I'll just have to go buy one of those then! Perhaps you can explain this all to my wife.

Anyway, I'm being quite picky here. Once I fiddle with it enough, I've generally got things where I want them. I find it best to back off on the subwoofer gain a bit, and that usually keeps things from getting too boomy. Seems the ears can tolerate a slight absence of bass better than an abundance of it.

[JoeE SP9]

Well I guess I'll just have to go buy one of those then! Perhaps you can explain this all to my wife.

Anyway, I'm being quite picky here. Once I fiddle with it enough, I've generally got things where I want them. I find it best to back off on the subwoofer gain a bit, and that usually keeps things from getting too boomy. Seems the ears can tolerate a slight absence of bass better than an abundance of it.

You must remember that most popular music is mastered for playback on gear that is no where near as good as what you use. Using test tones will get things close. The ear is the final arbiter. I think a lot of what you are hearing is just plain poor mastering. Once you get good equipment you have to get used to lousy mastering. Actually the differences in bass quality and quantity are normal. Some recordings sound good and quite a few don't. As far as absolute bass level is concerned use your ears! By the way, I have owned a RS SPL meter for more than 20 years. They do come in handy and are a good thing to have around. I have found if you have the bass level high enough to actually hear it, it is probably to loud. Remember most rock albums don't have any real bass while something like a well recorded Diana Krall does. If you set your rig so Diana Krall sounds right you are probably very close to the correct settings. I know this may make a lot of popular music sound bass shy but that's the price you pay for good gear.

[Mike Anderson]

If you set your rig so Diana Krall sounds right you are probably very close to the correct settings

Yes, that's basically just what I did: After tuning with the test tones, I put on Krall and a few other high-quality recordings, and set the subwoofer gain so that it's about as loud as it can get without being boomy.

Thanks for the feedback though, it helps me know I'm on the right track.

[Feanor]

...
First, although I'm using my ears instead of a meter, it sounds like my MMGs have a fairly flat response down to about 55hz. So why would I set the crossover as high as 80hz? Wouldn't this necessarily create a hump in the 55-80 range?
...
I will say that at 40hz, I'm still having a hard time getting a good rock and roll punch.

The reason you don't get the punch form the MMGs is that they just can move enough air at the lower frequencies. That is the "loudness" issue I mentioned earlier. It's also the reason that you will be better off with a higher crossover point, say 80Hz. That way your sub does more work and you will get more punch. I owned MMGs for awhile and try the various settings. 80Hz is your best bet, IMO.

As you observed yourself -- the MMGs have flat response down to about 55Hz so you will get a bit of a hump between 50 and 80Hz (or whatever high-pass frequency you use) unless you limit the signal to the MMGs in that range. This is best done with an active crossover between the preamp and the main amp that feeds the MMGs. I used to use a Paradigm X-30 active crossover unit, although a few subs have built-in high-pass, line-level filters that work at a suitable frequency.

Unfortunately the Musical Fedelity 3.2, (while it has "pre-out" connectors), doesn't have "main in" connectors. This makes it basically impossible to send a high-pass-only signal to the main amp. There is no handy solution to this problem that I can think of.

[Mike Anderson]

The reason you don't get the punch form the MMGs is that they just can move enough air at the lower frequencies. That is the "loudness" issue I mentioned earlier. It's also the reason that you will be better off with a higher crossover point, say 80Hz. That way your sub does more work and you will get more punch. I owned MMGs for awhile and try the various settings. 80Hz is your best bet, IMO.

I've experimented with it quite a bit, and I think what you say is true -- particularly if I'm looking for extra punch in rock and roll type music.

However, most of my music collection doesn't require the extra punch, being either: 1)music that is already mastered with a fair amount of bass, such that the hump would be really obnoxious; or 2) the style of music that just doesn't need it.

So for now, I think my solution will be to simply turn up the crossover freq on those occasions when I want to rock out, and at all other times I'm leaving it around 55-60.

Unfortunately the Musical Fedelity 3.2, (while it has "pre-out" connectors), doesn't have "main in" connectors. This makes it basically impossible to send a high-pass-only signal to the main amp. There is no handy solution to this problem that I can think of.

Yeah, I figured that out at some point. It's OK though, I think I'm quite happy with things now - I'm done fiddling and I'm just going to sit back and listen for a while. (Although I reserve the right to change my mind about that!)

[Mike Anderson]

BTW, just out of curiosity: What if one were to split out the signal before sending it to the pre-amp and filter it there, i.e. sending everything above 80hz to the integrated amplifer that feeds the MMGs, and sending everything under 80Hz directly to the subwoofer?

Ignoring the possible degredation of the signal that may occur by inserting extra components in the signal path, is there some reason this wouldn't sound good? Does the signal going to the subwoofer "need" to be pre-amp'd to blend properly with the signal going into the MMGs?

[Feanor]

BTW, just out of curiosity: What if one were to split out the signal before sending it to the pre-amp and filter it there, i.e. sending everything above 80hz to the integrated amplifer that feeds the MMGs, and sending everything under 80Hz directly to the subwoofer?
...

The issue, of course, is volume control, that is, you would want a volume control ahead of the crossover device so the volumes of the amp and sub volume can be controlled together. Some degradation is inevidable, however with a decent volume control device, (in effect a preamp), the degradation is likely to be unnoticable.

My own amp, (the Bel Canto), doesn't have a "main in" either. However my MG 1.6's inherently have much less of the "loudness" problem than the MMG's, so I just set my sub to 50Hz which is just above the 1.6's roll-off in the mid/low 40's. Integration is pretty good.