Double Bass iamp200 and infrasonics

Well, last night was the first time I had my new iamp200 and Wizzy out with "the band." Naturally, I had it cranked higher than I did when I was fiddling with it at home. I noticed that if I grab the E-string and wiggle it, the speaker cone moves with large excursions in response. That is, the cone was following movements of 3-5 Hz or so. Okay, so I don't wiggle my strings when I play but this very low frequency response manifests itself as substantial cone movement each time my finger is placed on a string in the natural course of playing.

John at EA confirmed that the iamp has no infrasonic filter. He suggested I use the lowest band of EQ to cut the very lowest octave. That won't do as I use that band for slight boost!

By the way, I tried a similar test with my old Behringer BX-1200 bass workstation. No such cone movement occurs.

Can any of you recommend an outboard infrasonic filter?


FYI-- I am using the Revolution Solo pickup

P.S.-- Yes, "infrasonic" which refers to those frequencies below those in the audible range (sound) as opposed to "subsonic" which means below the speed of sound.

bolo said:

I just bought an LR Baggs Gig Pro, because I wanted to try a high pass filter. I chose the Gig Pro based on comments from Adrian Cho and flatback in their review of the Vektor pickup here:

http://www.talkbass.com/forum/showthread.php?t=198970

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Indeed! ...just got off the phone with Brian at L.R. Baggs. Nice guy. The Gig Pro seems just the ticket and I ordered one at Music123 for $85 and free shipping.

I must say that after spending all the $$$ on the EA system, I'm a bit miffed that I have to spend even more $$$ to tame the iamp200's response at 5 Hz or so.

Mike Dimin said:

It is our natural inclination to boost frequencies rather than cut. But I would recommend, getting your tone by cutting other frequencies rather than boosting the bass. It is a bit of a paradigm switch but works exceptionally well with the iamp. Then boost the overall volume. Don't try to add volume through the EQ.

Mike

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Mike, I agree wholeheartedly with the spirit of your comment but, with respect to this, I am (literally) a pro. When I say a boost, I mean 3-4 dB or so in a limited band. Cutting other filters to effect this will result in a ragged frequency response owing to the nature of the overlap and filter-Q's of the remaining bands. Thus, cutting a series of bands is less desirable than a modest and judiscious boost to a single band. I know many people over-use equalizers. I am certainly not one of them.

fdeck said:

I would say, this is a problem that EA should be notified about. It may be a repair issue.

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I did notify them. John simply said that there is no infrasonic filtering on the iamp and that he tells double bassists to cut the lowest frequency band on the circuit in order to tame the wild cone excursions. That's a poor solution. Gee, about $0.25 worth of parts would have been required to effect a useful high-pass filter that would have solved this. I think EA missed the boat on this one, especially when you consider that they tout the amp as being compatible with piezo pickups.

bolo said:

I bought the Gig Pro primarily to see if it would help me get more mileage out of my Series I Contra. The Contra seems to try and reproduce many of those dastardly infrasonics you mentioned. To me this seems to "spread out" the sound of the Contra in an undesirable way when you push it beyond a certain volume limit.

And the bass shelving control ain't cuttin' it (pun intended).

None of the other gear I own contains a high pass filter. Hence the Gig Pro.

Yeah, boy, one more piece of gear ... Man oh man.

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Yep, same experience with how the sound of the EA gets corrupted. I'm really surprised that the high-pass filter on your Contra doesn't "cut it." It is of the same slope as the high-pass filter on the GigPro. Hmm. In all event, I'm glad to hear that the GigPro does the trick.

By the way, are you using a piezo pickup?

bolo said:

Actually, there is no high-pass filter on the Series I Contra, unless I am all wet. When I said "bass shelving control" I meant the bass EQ knob on the Contra. Sorry if I wasn't clear on that earlier.

That's really what's behind my decision to try the Gig Pro - I'm really buying it just to try the high-pass filter.

Oh, for my pickup I have a Rev SOLO.

And BTW, I just ordered the Gig Pro earlier this week. I haven't received it or tested it yet. Sorry if I wasn't clear on that either in my previous posts.

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It was I who did not read carefully enough to notice that you said Series I Contra. I have a Rev Solo as well. It is really the piezos that seem to cause this. In fact, I chatted with Gary Upton this afternoon and he mentioned that the particular crystal they use has a rather extended response. There's no excuse for building an amp with no infrasonic filtering. Gee, have I said that enough?


I just ordered my Gig Pro today. Should ship today or Monday.

Passinwind said:

You may not want (or now need) a DIY solution, but here's one anyway in case someone else wants to roll their own:
Link Removed . You'd need to be running a preamp into this if you're using a piezo pickup, so just getting a preamp with a high pass filter probably makes more sense for many of you.

Lack of control of very low frequencies was the one thing I disliked about the iAmps I've owned. It never caused me any practical difficulties when I used the amp with an EA speaker though. Personally, I'd much rather have an infrasonic filter than a CD input, if it's a cost issue.

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Thanks for the great info! You are correct that, for me, it makes more sense to just go with the pre-amp-- although I have built such filters in a past life.

The Wizzy cone really goes through huge excursions as a result of the extended low-f response. Not good-- no sir.

Thanks again.

Well, it seems I have two choices. Given the infrasonic response problem, I can use the iamp200 with the Gig Pro (so I have a high-pass filter) OR I can return the iamp200 (and the Gig Pro) and wait for an AI Clarus.

Thoughts?

Mike Dimin said:

First, what you are talking about is subsonics not infrasonics. Infrasonics are created by large scale events like Earthquakes - not your DB.

Secondly, By boosting the bass on your iamp, you are creating more bass, not less. Although it sounds obvious, you are complaining of too much bass, yet continue to boost the bass. If you have too much bass, then you should cut the bass, not boost it, seems like common sense to me. As I said earlier, cut frequencies, especially those around 40hz. The fact that the Iamps EQ section has some overlap will allow you to create the sound you need WHILE cutting the frequencies that offend you.

Third, we used to build amps with sunbsonic filters. Filters with a very steep slope below 40hz - guess what - nobody liked it. Perhaps it only costs .25 cents, but if it sounds like crap, then we don't make them!

fourth, as a DB player, it amazes me that you would want to boost the bass, as every DB player I know is trying to get away from that large "footprint"

Mike

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Well, Mike-- first of all, I AM talking about "infrasonics." "Subsonics" is an incorrect term. Infrasonics refer to frequencies of vibration below those that are audible (sound). "Subsonic" refers to being below the SPEED of sound. Don't believe me? Look it up. Gee, I ought to know...

Second, I wish to slightly boost the lowest audible bass frequencies, around 40 Hz or so The frequencies I wish to remove are the infrasonic ones. Even with the EQ set flat, I have the infrasonic response problem. The last thing I want to do is to cut the octave around 40 Hz in order to rid myself of the response at 5 Hz! Hello! I am NOT complaining of too much bass. I am complaining because the amplfier responds to infrasonics.

Third, I don't know who "we" is but removing infrasonics beginning at 40 Hz would not be suitable either. One can easily build a filter to roll off below 15 Hz and get rid of undesired infrasonic response. People would not complain about that because you'd be removing what they cannot hear and relieving the stress of reproducing those frequencise from the amplifier and the speaker. Just because someone built poorly designed infrasonic filters that people (rightfully) did not like does not mean that well-designed ones are a bad idea.

Fourth-- you don't get it. I boosted the lowest octave by about 3 dB because that sounded the best to me at the time. Of course, this only aggravates the infrasonic response-- but that should not be there.

Let me make this very clear. The iamp200 responds to very low frequencies well below the audible range. These are called infrasonics. They are, indeed, created by a double bass fitted with a piezo element. When you place your finger on the string, you create a broadband impulse that includes VERY low frequencies. They are NOT produced by the natural vibration, i.e., harmonic motion of the string. There is no reason that these should ever reach the output stages of the amplifier or the speaker.