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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Subwoofer FUD Forum Archive => Topic started by: Aaron Kovacik on May 27, 2008, 10:20:55 am

Title: Sub impedance
Post by: Aaron Kovacik on May 27, 2008, 10:20:55 am
OK, a few questions. I just built one of these (yes its a D&B copy) just for shits and giggles (i know it wont sound like the D&B box). My questions are mainly about impedance. Will this design change the impedance of the drivers. Its loaded with two 8ohm drivers, but does the amp see 4ohms? I know some cabs (LAB etc) that are not front loaded have an effect on the impedance, but I'm not sure about this design since its not a true horn design. If it does affect the impedance, how would I go about finding what the overall impedance of the cab is?
Title: Re: Sub impedance
Post by: Marjan Milosevic on May 27, 2008, 05:10:30 pm
D&B B2 is a band pass sub. So unlike the front loaded horn it wont affect the impendance.
What speakers did you use?
Be aware that bandpass boxes dont load the speaker as well as the reflex or horn boxes so be careful with the excursion.
B2 from D7B is massively processed when used with the recommended D&B amps.
How did it sound?
Title: Re: Sub impedance
Post by: Aaron Kovacik on May 27, 2008, 10:47:52 pm
I put two cheap drivers i had laying around in there to test it, since i had no idea what would make it happy. They are madison warrior 18s. I have to say that for being loaded with cheap drivers it sounded really good. Very high sensitivity and good low end extension, maybe some day ill get measurements but with some sweeps etc the usable range was roughly 27 hz-80hz. It rocked that range, but had a huge peak in the 90-200 stupid large, all you heard were low mids if you crossed the box above 80. all in all im pretty happy. Ill try some other drivers in it when i have money/time and see how that goes, but right now as long as you couple it with a couple of boxes to pick up the 81-120 range it kicks pretty hard....oh, it was also underpowered in tests, but still rocked hard enough for 200ppl easy.
Title: Re: Sub impedance
Post by: Aaron Kovacik on May 31, 2008, 12:05:29 am
Any suggestion on things i should look for in driver to go in to this kind of box?
Title: Re: Sub impedance
Post by: Mike {AB} Butler on June 03, 2008, 10:48:38 am
It's a little hard.. just having a photo to go on. I have no idea as to your dimensions here, as well as your expected goals from this box. If we knew a bit more about what you want to do, it's a whole lot easier to get an answer. My first question - why are you so concerned about impedance? Is it because you want to know about how much SPL the box will generate.. or you don't want to overpower the driver.. or are you trying to get a box that will do X amount of SPL, or weight and size not to exceed X?
Anyway, the more we know, the better the likelihood of an answer, here..
Title: Re: Sub impedance
Post by: Aaron Kovacik on June 03, 2008, 08:30:42 pm
I was wondering about impedance because the amp clipped pretty hard during testing, but the drivers played clean (powered of one side of an xs 900). So I wasn't sure if i was running less than 4 ohms. Now I know i just need more head room. as for the box dimensions, they are those of the D&B B2. (3'x3'9"x1'6") As for goals, id like to see it match the D&B specs, though i doubt that will happen. High SPL is a definite plus. (the drivers that are in it right now are 99 @ 1w/m). response is ideally 90 down (within reason, i know i wont hit 20 hz with this box). Basically I'm just looking for anything that would excel in this kinda band pass style box.
Title: Re: Sub impedance
Post by: Elliot Thompson on June 06, 2008, 12:35:15 pm
When building your own enclosure, you need to measure or simulate the response to find the impedance plot.

No one can tell you by a photograph or cabinet dimensions.

It's like judging someone's intelligence based on first appearance without a word spoken from the individual.

Best Regards,
Title: Re: Sub impedance
Post by: Aaron Kovacik on June 06, 2008, 10:35:16 pm
I understand that, but since it is a copy of the D&B B2 subwoofer, I was wondering if anyone had any general ideas(possibly from experience with the D&b box), primarily whether the nominal impedance would drop due to the manner in which the drivers were loaded. I had wondered because I know the impedance can be altered in certain, primarily horn loaded subs (for ex. the LAB sub). My second question was, are there characteristics of woofers that would preform well in a band pass enclosure of this type. For example, drivers in horns are generally better off with a high EPB, and high BL. I know no one will be able to give me an exact answer, but this is my first venture into Band pass enclosures, and I was just looking for some general ideas. I know it wont ever sound like the D&B box its designed from, but I like to tinker, and I look at this as a great way to learn out band pass enclosures.
Title: Re: Sub impedance
Post by: Elliot Thompson on June 07, 2008, 07:50:09 am
As you stated, "it is a copy of the D&B B2 subwoofer" so, the characteristics will be different.

Here's a tip about speaker building. Unless you are using the same speaker (Model Number) and can guarantee the dimensions are exactly as the original, it is a replica. It may look like the original but, it will never perform like the original.

If you designed that box using a sheet of paper (blueprint) with only the cabinet dimensions, your guess is no better than anyone else on the impedance plot. All speaker enclosures alter the impedance curve of the driver based on frequency when sitting in the box. Whether it be Band pass, Horn, Reflex, and/or Sealed. There are no exceptions to the rule. However, you need the tools to determine what it is.

What ever program you used to build that design should offer the tools to help you determine the end result in terms of performance; Impedance, Maximum Acoustic, Maximum Electrical, Phase, Group Delay, and, Cone Displacement.

Those that are familiar with enclosure design create their own and, base it on their requirements. Those that copy designs from manufactures cannot expect the same results, when they are using substitute parts from the original. One shouldn’t use the technical specs of the manufacture as a guideline because they are using a replication of the original.  Can you guarantee the woofer you are using in your D&B B2 Replica is the same woofer housed in the D&B B2 in terms of TS Parameters?

If you are familiar with EBP, and, impedance curves, I don't see why you would build a replica when you seem capable of building your own design. That’s how you learn the fundamentals of cabinet design.

Best Regards,
Title: Re: Sub impedance
Post by: Dave Rickard on June 08, 2008, 04:35:19 pm
Aaron Kovacik wrote on Fri, 06 June 2008 20:35

I understand that, but since it is a copy of the D&B B2 subwoofer,

This *could be* similar to the idea that an mp3 file is a "copy" of a 24 bit, 96 kHz, high resolution recording.

I'm just sayin'...