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SWR IOD - 4w Speaker out experience

Discussion in 'Amps and Cabs [BG]' started by thejohnkim, Sep 22, 2004.


  1. thejohnkim

    thejohnkim

    Sep 30, 2003
    NYC
    Wow, this thing sounds great plugged straight to a cab from the tube power stage.

    I moved into a smaller apt, and decided that I didnt want to deal with my rack when I'll mostly be practicing for the next year without gigs since i've become a student again. I set up my IOD as the head, and praticed tonight.

    First of all, it maybe 4 watts, but this thing is a really loud for 4 watts! Now i can totally relate to that review that mentions it being loud. I don't know if it would hold up in a loud rock practice, but i can definitely see it holding up fine for acoustic practices with room to spare. Maybe i'll try that out one day by bringing the 1/4" speaker cable.

    Second of all, it sounds much different. It has waaaaaaaay more lows like this. I know that some people have found the SWR IOD to be 'thin' sounding and lacking those deep lows, and maybe now i have a real taste of why they think that. The lows i get through the direct out, and my Eden 210XST are much deeper and satisfying. And mind you this is flat, since there are no tone controls availible, only the tube gain control, everything else is bypassed/not in the signal chain, and my bass does not have active controls, so this is flat across teh board in terms of settings.

    This leaves me wondering where these lows go. Something with the design keeps them from getting through the tone control section when the preamp-outs are used. Thats too bad. I've switched back and forth by plugging in my poweramp and trying to compare, and there is a difference, its not astoundingly huge, but its there, and not hard to discern, immediately noticble i'd say. Not to say that the lows are lacking in normal use for me, but the idea that this experience put in my head, is how nicely my cab would sound with a tube head, especially since its pretty sensitive, and probably would get very loud very quickly.

    Just thought i'd chime in with this, as i think there are still a few of you with the IOD and might take interest in this if you havent tried already. :eyebrow:

    on yeah....and the thing is dead silent when using the power from teh tubes. no noise at all.
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    First, 4 watts can be enough power to drive a speaker system to 115dB levels- with a 109 dB sensitive speaker, that is; more to the point, 4 watts is only 18dB softer than 250 watts, which makes it plenty even with inefficient speakers for home practice or recording work.

    To the crux of your question, I'd venture to say that somewhere in your amp's circuitry past where the 4 watt tap comes out there is a high pass filter than is intended to roll off the bottom end so that the amp output doesn't overtax factory made speakers, keeping in mind that the average factory made box seriously rolls off below 90-100 Hz. Alternately, perhaps there is an EQ boost circuit on the 4 watt tap, designed to deliver at 4 watts a bass heavy tone that once again your speakers would not tolerate at full power. Whichever the case is could be easily determined on looking at a schematic of the amp. The teaser is that with the 4 watt tap you're hearing what your bass could sound like if you had a true subwoofer on stage.
     
  3. Soulfinger

    Soulfinger

    Sep 20, 2004
    Houston, TX
    I have an IOD and I like the speaker out too. I think it would be great for recording, especially if you could send it to a high-quality 10" speaker in a sealed box.
     
  4. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    I agree with your post overall, but 109 dB sensitivity????
    That's a lot! Check the sensitivity charts on eminence.com. You can see that even the most efficient drivers (such as some of the 50 watt guitar models) *peak* at 109 dB in the upper midrange and are 10 dB down at the low end. And you're not going to find those drivers in a bass cab where low end and high power are the typical goals; more likely, you'll get something that averages 100 dB across its usable range.

    So more likely a 4-watt amp might get you 106 dB. Which is still plenty loud :) From http://en.wikipedia.org/wiki/Decibel#Acoustics we can see that that's roughly halfway between "pneumatic hammer at 2 meters" and "accelerating motorcycle at 5 meters".
    In other words, loud :)

    Agreed!
     
  5. if you can understand it, check out the schematic here. the speaker output is pre tone controls, whereas the preamp output is post tone controls. (the DI out is pre EL 84 power amp.)

    there's very little in the signal path that would degrade the low end significantly enough to hear the difference, but i guess there's enough that it could exist.

    robb.
     
  6. Bill is talking about one of his horn loaded cabs at 109 SPL sensitivity.

    If you don't have one of those, drive a JBL loaded cab with your IOD. Mine will make plenty of noise with an E-series JBL.
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Sure. Driver SPLs are measured with a standard baffle and reflect what you can expect to get from the driver so mounted. Horn loading gets you on average 10 to 12dB higher SPL than baffle mounting.
     
  8. winston

    winston Supporting Member

    May 2, 2000
    Berkeley, CA
    Maybe a load device (like THD Hotplate or Marshall Power Brake) or a direct box that accepts speaker-level signals run from the 4 watt speaker out would capture the sound better. Never tried one, but they seem to be advertised as devices that can get the "working power tube sound."
     
  9. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    Ah, good point.

    I rarely see too many bassists using horn-loaded cabs these days though... except for the occasional old Acoustic folded horn sitting under a 360 head!

    Probably not popular anymore because you need a lot of space to build a horn that does much for the low end... from what I've heard, you need at least 1/4 of your lowest wavelength, so if you want to go to 50 Hz you need something like 5 feet! Even in a folded horn that's a pretty big cab. With the availability of compact high-power amps, it's easier to carry a less efficient cab and still get plenty of volume, so maybe people don't want to bother with the bulk.

    On the other hand, plenty of people don't mind carrying around those SVT fridge-sized cabinets... so much for that theory :)
     
  10. thejohnkim

    thejohnkim

    Sep 30, 2003
    NYC
    hehe well this discussion went one direction i didnt anticpiate, but i feel pretty happy with the sound as it is right now, so no need to check out one of those DIs...thanks for everyone's input
     
  11. you won't need a special DI to connect a 4W signal. the 4W is using an assumed 8Ohm load. the equation is P = V^2 / R, where P = 4W and R = 8Ohms. that means V = 5.4V, which ain't much at all. inside the preamp, the 4W signal is routed directly into a TL072 op-amp, which isn't exactly the most rugged device in the world. you'd be fine feeding the speaker output to an amp if you really wanted to.

    just to clear things up.

    robb.
     
  12. thejohnkim

    thejohnkim

    Sep 30, 2003
    NYC
    ahhh, thanks for the clarification. I think i'll go ahead and try that into my trusty DPC and see how that goes. much appreciated!
     
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That was true until I invented folded horns that are actually smaller and lighter than less sensitive 'traditional' bass cabs. Manufacturers did get away from the horn when watts got cheap and labor got expensive. Supply your own labor and beat the system- and get better sound than any commercial cabinet can deliver no matter what the cost.
     
  14. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    I just checked your homepage Bill, interesting stuff.
    If I was putting together a PA and had the time I would definitely give 'em a try!
     
  15. As a student of horn technology since the 1960's, I'm curious how you got around the laws of physics, where Fc = lambda, and mouth perimeter = lambda.

    Every measurement I've seen published so far cannot sustain horn coupling when the length is less than lambda. Choppy response is a consequence of diminshed mouth area where the perimeter is less than lambda.
     
  16. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    the other possibility re: the tone difference is that the power tube and the speaker are interecting with each other changing the sound somewhat

    i recall when the unit was released that swr suggested running a speaker off of the 4 watt output while using the unit as a preamp to drive a poweramp and other speakers. They stated that the tone of the preamp would change due to the the interaction of the poweer tube and the speaker plugged into it, resulting in a different tone being sent out of the line outs (and maybe di) of the iod
     
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I didn't get around them, I redefined them. A law is only a law until someone comes along with something else that works even better. Ever heard of neutrinos, quarks and dark matter/energy? Ruthorford, Curie, Einstein and Bohr never did.

    You haven't been reading Speaker Builder 1997-2000 or AudioXpress 2001-present.
     
  18. No, I have not been reading speaker builder.

    I was looking at a response chart on your web site. It is a bit difficult to discern the X-Y axis labels, but the Tuba 24 appears to have a 10dB drop from 80 to 50 Hz. This is the type of rolloff one would expect when the horn runs out of length.

    You associate yourself into some pretty lofty company, eh?

    As for redefining... the physics that operate the universe are established. It is our understanding of them that is constantly refined.

    I'm not digging at you, but this discussion did get turned away from the IOD and focused on your product. I'm just curious about how you redefined the laws of physics. All horns have a cutoff point. Do you have any response plots other than a bar chart?
     
  19. You should never let the horn run out of length because the impedance of the air presented to the cone is too low below x-frequency. Due to this there is a high possibility of the driver in the box suffering over-excursion and it killing or at least damaging it. The length of the horn is entirely critical to the cutoff of the box... If been driven hard, it should come with a hipass filter of at least 18dB/oct...
     
  20. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It's supposed to do that. As part of my position as a consulting audio engineer to a 6,000 seat venue I've compiled an extensive data base of RTAs of major national/international touring acts. Using that data the Tuba 24s frequency response was tailored to deliver the best possible combination of SPL/Response Bandwidth/Size and Cost for the real-world needs of the average working band's electric bass,keyboard and PA speakers. The Tuba 24 doesn't run flat below 80 Hz because it doesn't need to. It delivers it's highest output where it's required the most: from 80 to 120 Hz. For that reason the horn path was kept to 5 feet.

    As for the physics aspect, I've been hearing for ten years from various experts, both the real and the imagined so, that my designs can't work because some 60 year old formulas and pre-conceptions say so. According to those 'rules' tubas, trumpets and clarinets can't work either. Since the field of musical instrument design pre-dates that of loudspeaker design by a few hundred years I decided to take my cues from the real masters in the realm of sound, and my horns are designed accordingly- and most assuredly do work quite well.