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How do company's determine frequency response?

Discussion in 'Amps and Cabs [BG]' started by reel big bassist, Sep 1, 2000.


  1. reel big bassist

    reel big bassist

    Mar 27, 2000
    Maryland

    How do company's determine the frequency response
    of a speaker? I recently looked at ampeg's webpage
    and I checked out their SVT-15e.
    Here are the specs it listed concering frequency.
    Frequency Response (-3dB): 40-3kHz
    Useable Low Frequency(-10dB: ) 28Hz
    What is the difference between
    frequency resonse and usable low freqency.
    I thought frequency response was the range,
    of frequencies a speaker could cover.
    So if it can only go down to 40hz,
    how can you use it to 28Hz.
    Also, Why does the frequency response have
    a (-3db) before it, and the usuable low frequency
    has a (-10db). This is really confusing me.

    Also I was checking out the GenzBenz website,
    and looked at their specs for their bass cabs.
    http://www.genzbenz.com/gb_specs.htm
    Specificly I was looking at their cabinet named
    the GB 115B. The GB 115B has a frequency response of
    55-4Khz. I may be mistaken but I thought
    open "E" was 50 Hz. And if the frequency response
    doesn't go down to 50 hz that means, it will be
    playing the 50hz harmonic not the note, correct?
    Does Genz Benz rate their frequency response
    different from ampeg. Also, on the spec sheet,
    the collum heading for frequency response reads "Frequency +/-3db." Maybe that has something
    to do with it. It's just confusing me. check out the links
    if anything I said was unclear.

    Thanks,
    Gregory P

    Link for ampeg: http://express2.expressivetek.com/ampeg/basscabindex.html


    [Edited by reel big bassist on 09-01-2000 at 03:29 PM]
     
  2. john turner

    john turner You don't want to do that. Trust me. Staff Member Administrator

    Mar 14, 2000
    atlanta ga

    they use a device called a real time analyzer. in conjunction with a microphone that the unit has been callibrated for, a real time analyzer can measure the output power of each frequency band within the frequency spectrum.

    they pump either white noise (equal power output per frequency) or pink noise (equal power output per octave) or some other test frequency, and then read the results. by comparing the results with what they know that they are feeding the speaker, they can tell how the speaker is performing.

    there are also complex mathematical equations which describe the electrical, mechanical and acoustical responses of a cabinet based on measurable quantities like the size of the cabinet and the speaker, the amount of insulation within the cab, the resistance and inductance of the speaker, the Q factor of the speaker suspension, and others. these equations can be used to design a cabinet, and then the RTA (realtime analyzer) measurements can be used to fine tune the cabinet.
     
  3. Well, that's what they should do, but in reality, I think what they use is something called a Marketing Department.

    For instance, Eden Electronics lists the following specs for their D-210XLT cabinet:

    "+/- 2db 48hz to 14khz"

    Anyone who has ever played through Eden cabs is familiar with the tremendous low-mid hump they have. That spec makes it LOOK like they used an RTA, but your ears will tell you they used a Marketing Department.
     
  4. The -3 dB point is used because it means the point at which the power level of audio out of the speaker is half of what it is at the 0 dB point, which is usually taken to be midrange. Because the human ear is swanky as hell, a decrease in power of 50% sounds like a barely noticeable decrease in volume. A drop of 10 dB, which is actually 1/10th the amount of power measured at 0 dB, sounds half as loud. Crazy old human hearing. You have to increase your power by a factor of 10 just to double your volume.

    Anyway, a speaker's low frequency limit is not a hard stop. If a speaker is down 3 dB at 40 Hz, then you can still hear 30 Hz, just it will be much lower. In the above case, 28 Hz will sound half as loud as, say, 100 Hz. 40 Hz will sound slightly less loud than 100 Hz.

    Chris
     
  5. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    When you play your bass, most of what you hear is the harmonics and overtones, not the fundamental. That is why even if a cab's frequency response isn't listed as going all the way down to low E or low B it still sounds normal. I think Joris can explain this better.
     
  6. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    OK, reel, here's the answer you're looking for. In an ideal world, a cabinet would have the same volume level across all frequencies, say from 10 hz to 30k hz. The problem is that physical constraints make this nearly impossible. So the cabinet manufacturers try to optimize the frequency range to the application for which the cab is intended. In the case of a bass cab, you'd like to have even response starting down at about 30 hz for that B string, and up to say, 10k hz or so. (Not that you're going to be playing notes in that high range, but you need the overtones for fabulous tone.)

    But even that overall range is a stretch, so they try and keep the volume level constant across as much of the range as they can. Still, the volume starts to fall off at the low and high ends. So what they're saying when they say -3 dB at 50 hz is that, by the time you get that low, the signal has dropped 3 dB from a flat response. When they say that 28 hz is still usable at -10 dB, that means that the speaker will play it, but its volume will be 10 dB lower (half as loud) than the flat portion of the response. Clear as mud, eh?
     
  7. VicDamone

    VicDamone

    Jun 25, 2000
    In the Hi-Fi world one of the first things you learn is that loudspeaker system specs are a very vague guidline as to the systems ability. The only truly usfull specs are the physical diamentions, weight, and the most important sensitivity. The good news is that the sensitivity given by the manufacture is usually fairly close to the actual sensitivity. This will help you match your speaker to an amplifier who's power rating is almost as vague as the speaker's frequency responce figures. Did I mention that those 4 and 8 ohm ratings are rounded off just a bit? Then you gotta ask yourself what's the deal with this hall or room your playing in?

    It becomes a black art very quickly if your reading specs and not listening.

    Getting back to your question. Yes, your E string vibrates at a fundimental tone around 40Hz, but the pluck of the E string along with the harmonics of the instrument go well bellow 30Hz. If you want to reproduce these harmonic frequencies at the same volume or greater than your cabnits -2dB@48Hz roll off point your going to need a subwoofer. If you were to scrape a round wound G string quickly with a pick or a fingernail you may reach a very high 19kHz. The question is do you want these extreams as a part of your sound? Maybe your interested in hearing the tonal differences of different instruments much more clearly.

    Whatever your looking for, you and everyone here owe it to yourselves to demo a full range system. A subwoofer capable of supporting the 20-90Hz range. Not just one of those 18" blubber boxes but a true subwoofer and crossover. I don't know what it is but the sub realy helps to tighten up the rest of the frequency range.

     
  8. reel big bassist

    reel big bassist

    Mar 27, 2000
    Maryland
    Thanks everyone,

    You really explained this to me well.
    VicDamone you made a very good point
    about how you need to listen and not just
    rely on specs. I knew that I had to
    listen to the cabinet and not rely on the
    specs. However, I was curious what they meant,
    and you all explained them to me very well.
    It's great when you start to understand something.

    Another question: So If I had a subwoofer that
    could go down to 20hz(the cuttoff for human hearing right?)
    I would not only hear the harmonics and overtones of my E
    String but also the Fundemental. Could you explain the difference between the three?

    VicDamone you said a true subwoofer, not just a flabby 18.
    Is their a brand you could suggest? I'm thinkin a genz benz
    18. http://www.genzbenz.com

    Again thanks to everyone this really helped.

    Sincerely,
    Greg P
     
  9. VicDamone

    VicDamone

    Jun 25, 2000
    To be honest Reel Big I don't have a heck of a lot of experience with amplifying the electric bass. I have been amplifying my fiddle with an Acoustic 136 100W 1x15 folded horn for far to long, so I upgraded to my current system (profile). I do have alot of Hi-Fi knowledge which proved very usefull with my bass system purchace.

    What is amazing is how few manufactures are producing a subwoofer system. I only know of two, Bag End, and, mentioned in Bass Player September 2000 page 54, Eric Wilson uses a Meyer Sound 650-P 1,600 watt 2x18 powered subwoofer.

    It would be nice if somone made smaller powered systems like the Home Theater industry makes. In particular the True Subwoofer by Bob Carver, an 8" driver 8" radiator, 2400 watt amp/crossover all in an 11" cube.

    I first purchased the Bag End cabinet hopeing to use the crossover built into the Navigator preamp. The results were not that impressive. Installing the ELF-M processer made all the difference in the world. I wasn't able to audition this system befor buying it which was kind of scarry which is why I've been responding to posts such as yours. I'd like to spread the word about subwoofers and bass amplification.
     
  10. Okay, let me tune in here. But first let me say this: I pretend to know everything, but I could just as easily be wrong :D


    Vic, the harmonics of a note NEVER go below the root frequency, that's why they're called overtones. The proper word would be superharmonics, as opposed to subharmonics. So, a 4 string bass low E consists of 41.2 Hz and 82.4 and 123.6 and 164.8 Hz, etc. etc... The root frequency is 10-30% of the signal (my educated estimation). But when you play close to the bridge over the bridge pickup (if you have one) there's almost no fundamental in the signal. Yet you can hear the difference between a low E and a one-octave-higher E.

    Here's the deal: the human ear can detect the distance between adjacent harmonics. The above low E has a distance of 41.2 Hz between every harmonic. The brain substitutes the fundamental frequency accordingly, even if it's not there to begin with. The high E has 82.4 Hz between every one of its harmonics and so you hear it as a one-octave-above low E....

    This is called psycho-acoustics. How do you quickly tune your bass string-to-string? You play a harmonic at fret 7 on the first string and on fret 5 on the next. You should hear the same frequency. If one of the strings is not exacty in tune, you'll hear a wavering. This is the psycho-acoustic fundamental frequency your brain substitutes as a result of the slightly different string tuning. The distance of the two strings' frequencies is the frequency of the wavering.

    A lot of cabinets with 10" drivers have a -3 dB point between 60 and 80 Hz. Hardly a subwoofer. But they can sound really fat and warm. As long as you emphasize the proper harmonics, by playing a certain style or twiddling your EQ in the right way.

    Furthermore, when a manufactorer rates a cab (which is measured in an anechoic room), say, 80-4000 Hz at -3 dB, the influence of a real life room will improve the low end drastically. It adds like 25 dB at 25 Hz. This means that in real life conditions, the cab has a -3 dB cutoff of (say) 60 Hz, and still has only (say) -15 dB at 40 Hz. The smaller the room, the more low end.

     
  11. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    I think this is the heart of the problem - I read some incredibly involved technical discussions in amps and think - is this anything to do with bass playing? I don't admit to understanding half this stuff and even when I started to get an idea through reading some of the stuff put up here by people like Joris, I find that it only served to confuse me more in terms of what you expect and what you actually hear.

    But I still think I know what a good amp or cab are - and the only way to do this, in my experience, is to try them out. Play your bass though as many amps and cabs as you can and listen.

    The problem is of course, that most people who seem to come on TalkBass are doing so mainly becuase they are buying mail order without trying the stuff out first because they don't live near a dealer or whatever.

    So people are looking at specs on websites and in catalogues and trying to decide what to buy - I think it's just impossible and of course the manufacturers must be aware of this situation and are going to try to convince you that their product is the best for what you want.
     
  12. VicDamone

    VicDamone

    Jun 25, 2000
    Reel Big Bassist I apologise for my remark, "It becomes a black art very quickly if your reading specs and not listining". Of course your listining. If I had taken the extra time to reread my own drival I would have rewritten to say, if you are unable to audition a cabinet and all you have are specs to read etc.

    Whats worse is that it goes to the heart of the matter I am trying to convey. I live in the San Francisco Bay area and none of the stores had a subwoofer system to audition. To spend $1-2000 on a somthing you haven't heard is frightning. Bottom line is if your looking for tight and louder low end then a subwoofer system is one way to get it. If you go with Bag End and your not happy with it in your bass rig you can hang it on your stereo with no problem.

    Thanks to Bruce Lindfield for pointing out that my comment to Big sounded like a snip. Boy it sure did and once again my apologies to Reel Big.
     
  13. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    Actually Vic, I was sort of agreeing with you. I always want to say in these discussions, that people need to try these things out in a shop and that no amount of talking will help. Sort of like "a picture paints a thousand words" - listening to 10 -12 amp/cab combinations in a shop with the bass you are most likely to use, is worth a million words in TB, IMO. ;)

    Buying a cab or amp by reading specs or other people's opinion is just a futile exercise, in my experience. I remember buying a Trace Elliot combo because a lot of people rated them and I needed something quickly; but this was the worst mistake I ever made. It was virtually unusable to my ears. Hated the sound and it had a fan that was louder then the output! What was worse though, when I tried to trade it in for something else I was told that TE had just dropped the prices, so I only got a fraction back of what I paid! :mad:
     
  14. Matthias

    Matthias

    May 30, 2000
    Vienna, Austria
    I agree with Bruce.
    But I also think that specs and recommendations can help you to sort things out or to get hints what to look for. (Not everyone has a mega-shop next door where you can compare all and everything...)

    Two examples:

    Many people say that Acme cabs are excellent but power hungry - 800W plus for the 2x10 (and specs seem to say the same).
    I will not even try to find one to test it, because I will definitly not buy a new head zo meet the demands of this cab. There are tons of other good quality cabs...

    I'm interested in 2x12 cabs, because I hope that I find one wich gives me a good compromise between power and portability. I will not even have a look at the Marshall MR7212 because I can read from the specs that it's even heavier than my current 2x15 cab (besides I'm not a Marshall fan, but this is just an example).

    So try to get the 'best of both worlds'!

    My 2 cents

    Matthias
     
  15. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    I agree that the weight and size specifications are very useful. I wouldn't consider a cab over 60lbs for example, because I know I would damage my back by trying to lift it on my own regularly and I don't have any roadies (!) and can't guarantee that I will get anyone to help me lift it up stairs at a gig.

    I suppose I just mean about "sound" which is after all the most important thing! Somebody might describe something as warm and rich sounding, but then when I hear it, it just sounds muddy and ill-defined! I think all these other figures are just a sort of "smokescreen" that hides the fact that you want something that sounds good.

    I realise that people don't have great shops next door - neither do I, but if I'm paying out £1,000 for amplification, then it's got to be worth spending £20 - £30 on a train ticket to go to the place where they do have all the best amps/cabs and spend a day trying them out.
     
  16. reel big bassist

    reel big bassist

    Mar 27, 2000
    Maryland
    Hello,

    I have read your replies and have thought on them.
    The reason I posted the thread is because I am interested in
    techinal stuff like that. I don't think I could buy a cab without testing it, that's why I probably wouldn't buy direct from carvin.

    I do agree with you when you said "Buying a cab or amp by reading specs or other people's opinion is just a futile exercise, in my experience." Buying anything by just what other people tell you is foolish in my opinion. I also agree
    that a
    cabinet sounds different to everyone.
    The reason I ask about sound is because I am interested in
    knowing what people think about a certain product.
    What they think it sounds like. I'll admit peoples opinion do influences
    me a little, but their opinion by itself doesn't determine my purchase. If someone says a cab sounds warm for example,
    I'll play through and try to see where their coming from.
    Ultimatly, However if I don't like the sound I'm not going to buy it. It's that simple.

    When you stated "I read some incredibly involved technical discussions in amps and think - is this anything to do with bass playing? I don't admit to understanding half this stuff and even when I started to get an idea through reading some of the stuff put up here by people like Joris, I find that it only served to confuse me more in terms of what you
    expect and what you actually hear. "
    I'll admit this can confuse me to. But I think what people like joris write has a lot to do with bass playing. Without people like joris that understand frequency,amplification,etc. Their would probably be no electric bass or amplifiers. We'd be playing eveything acoustic their is nothing wrong with that by the way. I like upright. Besides, frequency & harmonics that he talks about have a lot to do with bass playin' you hear them everyday. I think people like joris who are good at technical stuff are just as important as awsome bass players. My understanding is that if you know the rules, you know how to bend them. Just like musicians know which notes (frequencies) will go together and sound good,but if they know theory they can mix different notes and it will still sound good. People like joris could probaly make a real good amp system because he knows all the techinal stuff. I don't know if you are but I don't like people putting down people like joris, because #1 what he knows is important to bass playing. and #2 I really respect him.

    I know I'm comming off strong but this is how I feel.

    Showing how I really feel,
    Greg P
     
  17. Bruce Lindfield

    Bruce Lindfield Unprofessional TalkBass Contributor Gold Supporting Member

    I wasn't rying to put Joris down - on the contrary, what I was trying to say is that I know nothing really about the technical stuff and even when I do learn a bit more, it just makes me realise how much I don't know.

    I admire anyone, like Joris, who actually **understands** this stuff and I have asked questions before on technical questions and have been very grateful for the knowledgeable answers that I have received.

    I doubt however that the majority of pro musicians know much about this side of the equation. There's not time in the day for everything! So I was just saying that it's not actually necessary to know what all this means in order to be a good bass player, but it's certainly necessary that such people are out there developing new ideas and better cabs! We all benefit from this and of course we should pay homage to those who do contribute to building a better cab.
     
  18. reel big bassist

    reel big bassist

    Mar 27, 2000
    Maryland
    You are right, you don't need to know this stuff to be a good bass player. I thought you were puttin people like joris down, i was mistaken. That's the problem with writing, it's not as clear as when your face to face with someone. Unless you have a tremendous amount of skill.

    Sincerely,
    Greg P



    [Edited by reel big bassist on 09-07-2000 at 12:13 PM]
     
  19. Skip

    Skip

    Mar 22, 2000
    Bronxville, NY
    Just my $.02 :D

    Remember that specs are given as +/- 3dB usually. This means you can have a 6dB hump and be considered "flat". It won't sound flat. Dips and spikes like that usually due to poor design and integration of drivers and ports. That said, bass amps and cabs differ from audiophile amps and speakers in two very important ways.

    First is mobility. If you're a pro (I'm not) your equipment has to move and be built to move. That means no 120lb. amps or 300lb. speakers for most of us.

    Secondly, and more fundamentally, is the purpose for which they're built. Audiophile equipment is built to most faithfully reproduce the recorded medium. Your gear is not always built to be flat - if it was, we wouldn't have tone adjustments on the bass or the amp. There would be no reason to have most effects. You don't buy an old Fender or Ampeg or Marshal head because they're so flat - you buy them for the tonal changes they cause. So the frequency range is not that important except as a gauge of how low the cab will go - and as Joris pointed out, you may not have as much need for those low tones as you think.

    That said, the guiding rule here is: whatever is good for you is good for you. :) You have to be happy with your tone. Try everything you can get your hands on, feel free to try stuff that you wouldn't assume is right for you. Only by knowing what the tonal possibilities are can you make an informed choice. Good luck finding your tone.
     
  20. Matthias

    Matthias

    May 30, 2000
    Vienna, Austria
    Excellent post, Skip!!
    Matthias