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Author Topic: Need help with this...  (Read 6104 times)

Justin Lawless

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Re: Need help with this...
« Reply #20 on: June 09, 2005, 06:14:38 pm »

 im measuring at three diffrent points. eigth space, quater space, and half space. eighth space, i get just over 140db at max SPL levels between 1,100 - 1,300watt at one meter (10-30% over RMS rate). but my high db ratings are for, like i said the high SPL levels. normal between 750-1,000watt at one meter, i get anywhere from 130-135db. when i hockup 4 of these bad boys, at one meter with combined strangth im getting just above 150db running the horns at high SPL levels. at 750-1,000watt at one meter, i read just below 150db for 4 horns. this is all done at quater space (horns set near a wall). in eighth space i get a little bit higher, mabey +3 or 4db, for half space its about -2 or 3db.
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Michael_Elliston¶

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Re: Need help with this...
« Reply #21 on: June 09, 2005, 07:37:29 pm »

Justin Lawless wrote on Fri, 10 June 2005 10:14

  in eighth space i get a little bit higher, mabey +3 or 4db, for half space its about -2 or 3db.


Measure or model?
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Ivan Beaver

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Re: Need help with this...
« Reply #22 on: June 09, 2005, 07:46:02 pm »

Justin Lawless wrote on Thu, 09 June 2005 18:14

 im measuring at three diffrent points. eigth space, quater space, and half space. eighth space, i get just over 140db at max SPL levels between 1,100 - 1,300watt at one meter (10-30% over RMS rate). but my high db ratings are for, like i said the high SPL levels. normal between 750-1,000watt at one meter, i get anywhere from 130-135db. when i hockup 4 of these bad boys, at one meter with combined strangth im getting just above 150db running the horns at high SPL levels. at 750-1,000watt at one meter, i read just below 150db for 4 horns. this is all done at quater space (horns set near a wall). in eighth space i get a little bit higher, mabey +3 or 4db, for half space its about -2 or 3db.


At what distance and what type of measurement system?  Inside or outside?  How was the wattage figured out?  Did you account for the rise in the impedance due to the horn loading?  Did you measure the impedance?  And with what system?
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Re: Inductor wouldn't need to be too large
« Reply #23 on: June 09, 2005, 11:18:59 pm »

     None the less there is an iron core laminate inductor in the basstech 7 (I saw it when i had to change the phase of one of my new BT7's, and one of the employees at servodrive told me about it also).  I'm not sure if its parallel or series, I didn't see any capacitors in the circuit to make a notch filter.

    At 80Hz it would take a 7.95mH into 4ohms to be a 6dB per octave Low pass I do believe.  Using a core material can help keep your inductors small at the expense of hysteresis and lower saturation currents etc (Laminate cores being some of the best to reduce eddy currents and what not).

    Saying you have a 400Hz coil doesn't mean much since thats all relative to the load its designed to operate under.  At 8 Ohms you would need a 3.18mH and at 4 Ohms you'd need 1.59mH. A 14 or 12 gauge air core may be as large as a can of tuna or so.

    BT7 is still very flat in pairs from what I've measured with FFT.  Of course you get 3dB more sensitivity in 4's and double power handling.

    From everything I've heard from Mark Seaton and some of the other Servo/SPL staff past and present,  is that the horn coupling is not mearly aesthetic and that you would loose sensitivity if the flairs aren't coupled as an expanding horn or to a fixed boundary like a floor or a wall.

    I doubt you would achieve desired coupling and sensitivity with Labs or BT7's if you had four standing side by side with the flair opening to the ground and the flat end up top?

    Isn't the whole reason a bass horn has a higher sensitivity is because it increases directivity of the energy?  I'm not talking about pinpoint directivity.  If you took just the drivers sealed in a chamber with the throat opening into the air or infinite baffle what kind of sensitivity would you have?  Couldn't it be argued that a bass horn has more directivity at its low cutoff than a reflex cab at its low cutoff?

Sum-
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Ivan Beaver

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Re: Inductor wouldn't need to be too large
« Reply #24 on: June 10, 2005, 12:10:41 am »

I just asked Tom Danley about the choke.  It is simply in series to help the impedance of the transformer at higher freq from becoming to low.  It really does not act as a crossover or freq adjustment.
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Dave Rickard

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Re: Need help with this...
« Reply #25 on: June 10, 2005, 09:42:01 am »

Justin Lawless wrote on Thu, 09 June 2005 16:14

 im measuring at three diffrent points.

What make/model meter are you using?

Dave
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Re: Inductor wouldn't need to be too large
« Reply #26 on: June 10, 2005, 11:04:15 am »

Makes sense, but its going to act as a 6dB per octave crossover Not that the BT7 should or can be opperated an actave higher than 80Hz without killing it.  I though the Balist resistor kept the impedance in check?  But I'm sure Tom KNOWS! scince its his beasty.

Sum-
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Michael_Elliston¶

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Re: Inductor wouldn't need to be too large
« Reply #27 on: June 10, 2005, 08:21:55 pm »

sumsound wrote on Fri, 10 June 2005 15:18

   
    Saying you have a 400Hz coil doesn't mean much since thats all relative to the load its designed to operate under.  At 8 Ohms you would need a 3.18mH and at 4 Ohms you'd need 1.59mH. A 14 or 12 gauge air core may be as large as a can of tuna or so.


Yes mine was ~8ohm,home made.I wonder about the linearity of such coils,ive seen THD measurements that are horrible for inductors.

Quote:


    BT7 is still very flat in pairs from what I've measured with FFT.  Of course you get 3dB more sensitivity in 4's and double power handling.

Theyl be more reactive without enough mouth in halfspace.

Quote:


    From everything I've heard from Mark Seaton and some of the other Servo/SPL staff past and present,  is that the horn coupling is not mearly aesthetic and that you would loose sensitivity if the flairs aren't coupled as an expanding horn or to a fixed boundary like a floor or a wall.

Aesthetic,no way. Thats true,I never disagreed.
Quote:


    I doubt you would achieve desired coupling and sensitivity with Labs or BT7's if you had four standing side by side with the flair opening to the ground and the flat end up top?

Im not sure what you mean?
Quote:


    Isn't the whole reason a bass horn has a higher sensitivity is because it increases directivity of the energy?  I'm not talking about pinpoint directivity.  If you took just the drivers sealed in a chamber with the throat opening into the air or infinite baffle what kind of sensitivity would you have?  Couldn't it be argued that a bass horn has more directivity at its low cutoff than a reflex cab at its low cutoff?

Sum-

The directivity is only increased by 3-6dB on a large basshorn.The increase in SPL is largely due to the impedence transformation rather than DI.

Approximately 87-90dB/1watt/1metre with drivers on sealed enclosures.You can even model this in hornresp.

The horn will have slightly more directivity than a similarly sized reflex cab because of its mouth size which is similar to or larger than the wavelengths being produced.

Mike.e
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Antone Atmarama Bajor

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Re: Inductor wouldn't need to be too large
« Reply #28 on: June 10, 2005, 08:43:46 pm »

     I think a lot of the distortion happens in inductors with core material.

    Erse Rates their super Q inductors up to 3Khz at X amps of current before saturation.

    Their Laminate cores are rated up to 8Khz at X amps of current.  I think their inductance starts becoming much less linear up above those points.

    Putting a core material in causes lots of eddy currents and weirdness, hysterisis (kind of an over exaggerations of the opposition to the change in current flow I think) the waveform gets distorted in several ways.

Sum-  
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Justin Lawless

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Re: Need help with this...
« Reply #29 on: June 10, 2005, 10:23:33 pm »

  its using a model, i dont have the equipment to measure it for RTA. i do know this, with what it sounds like in person, i would say the model is close, its just using Hornresp so. but like i said, in person, i would say in personal opinion its modeling pretty accurate. at first i played it inside, and then after puting about 700 or 800 watts into the driver, i decided to take it out side because i decided the windows couldnt take much more. but we took it outside and i was able to get 1,200watts into it safely without damage. and ill tell ya, it was about the same as it was when it was inside at that point and it kicks hella hard. i would say it would be safe to say i could keep throwing 1,200watts maximume witch is 200watt over its rms. but ill keep it at or below the rms. witch reminds me, id like to make a LED power meter for this so i can measure the powerinput to the horn by the hundread to 1000. and then have a 1200watt LED and i want to try to get it so if it stays solid for too long, a braker or fuise goes off so it protects the driver from over powering. any thoughts?
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