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Do all bass heads high pass at 30Hz or so?

Discussion in 'Amps and Cabs [BG]' started by remo, Mar 22, 2006.

  1. remo


    Jan 15, 2005
    You can set most high end power amps (QSC, Crown etc) to high pass at about 30Hz 40Hz because there is very little use for pumping that freq. into a speaker.. most speakers (apart from subs of course) can't go that low anyway and all it's doing is robbing amp headroom and putting the speaker cone through unnecessary excursions in a vain effort to reproduce the Hz..

    Now what I'm wondering is do bass head manufactures (Eden, Aguilar, SWR, Trace etc) put some sort of HP filter in the signal path of their amps or do they all just run them at full range?

    Personally, I think it's a crazy waste of amp headroom and exercise in futility to pump 20Hz or so into a 4x10...

    … and for people who think it does affect the sound most speaker and specs only rate down to 50Hz and even THAT is a big push IMO.

  2. dadodetres


    Dec 19, 2004
    In my SWR grad prix (pre) you can choose wether the highpass is on or off.... i use it woth a yamaha power amp, so maybe the yamaha has already the high pass on.
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not per se, but since these amps aren't intended for high fidelity use they tend not to have the wideband response that a quality power amp does. Putting 20 Hz into a 4x10 would be a waste, but unless you've got some serious drop-tuning going on there's no source of a 20Hz signal going into the amp to begin with, and the amps passband is designed accordingly. Getting an amp to work flat to 5Hz costs money, and bass amp manufacturers aren't going to spend what it takes to do so unnecessarily.
  4. Except for a fad that went on in the 70s for "DC-coupled" hi-fi amplifiers with flat frequency response down to 0 Hz, the overwhelming majority of amp designs used commercially today have at least one (normally more) coupling capacitor between stages that creates a high-pass rolloff in the frequency response. Even if this is not necessary, it's usually included to prevent the amp from amplifying the DC offset of a not so well designed source and frying the speakers. Many amps have this DC-blocking cap at the very input.

    Since the cut-off frequency is inversely proportional to the cap value, the manufacturers will choose the smallest cap (highest freq) adequate for each specific application. For hi-fi amps, you have to be able to quote a reasonable +/- dB figure for the 20-20000 Hz frequency band, so you may choose a -0.5 dB point @ 20 Hz (so your figure will be +/- 0.25 dB) and work out the value of the cap or caps from there. For bass amps, you want the fundamental of the B string to go through with negligible attenuation, so you may choose for example a -0.5 dB point at 30 Hz. I haven't actually measured any bass amps but I bet you'll find this high pass response in most of them and I wouldn't be surprised if among the most respected ones you found -3 dB points @ 30 or even 40 Hz, since, as you said, very few bass cabinets go that far down anyway.

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