Hello everyone! Ready to give me your input?

[REDLINE]

Wait, i'm confused, you mean the impedence of my sub is not equal to the impedence of my driver? Now i'm really confused. All the commercial subs I have ever looked at are 8 Ohms for a single, and 4 Ohms for a double. I don't want to build a sub that's going to have some weird impedence.

[Bill Fitzmaurice]

. All the commercial subs I have ever looked at are 8 Ohms for a single, and 4 Ohms for a double.

Horn loaded subs add to the impedance load. It's how they have higher sensitivity.

I don't want to build a sub that's going to have some weird impedence.

If it works better what's the difference? Anyway, your amps will be a lot happier. Higher impedance plus higher sensitivity equals less work and higher output.

[Sydney]

All the commercial subs I have ever looked at are 8 Ohms for a single, and 4 Ohms for a double.

That is a what is called a nominal value at a particular frequency.
I guarantee you that it is not 8 or 4 ohms across all of it's frequency range.

[REDLINE]

If the impedence isn't 4 or 8 Ohms, then how am I going to calculate what wattage my amp will provide to the sub? All the values are always given for 2, 4 and 8 Ohms. Also, how will I calculate this nominal value for my Titan 39.

[Sydney]

See:
http://billfitzmaurice.com/phpBB2/viewtopic.php?t=3933
And forum members have/will post appropriate values for model/driver combos

[REDLINE]

I'm still really confused. I thought the only thing being wired is the driver. There is no other resistive component in the sub, correct? So if the sub is rated at 4 Ohms, shouldn't I look at how much power the amp outputs at 4 Ohms per channel? I don't see how the horn is affecting the electrical components, it's just making the driver do less work because it sounds better. There must be something i'm not understanding properly.

[Sydney]

For a T48
Impedance, 24.5 inch wide 3015LF loaded:

24.5inch wide HL10c loaded:

Same cab different driver.
The air in front and behind the speaker in combination with the speakers electrical AND Physical properties combine to shape the system response - Both electrically (impedance) and acoustically ( loudness and extension).
Take either driver into free air and you get a different sum and curve.
Put either driver into a different cab and you get a different sum and curve.
In the same way that horsepower in an engine is assigned a value based upon it's load and power curve - amps are given power ratings for nominal ( common) impedance values

A horn is an air transformer - coupling the motion of the speaker to the outside air

[Bill Fitzmaurice]

There must be something i'm not understanding properly.

Yes, impedance, but outside of the engineering community very few do understand it. Fear not, all is explained in the plans.

[Ron K]

The driver is coupled to the air through the horn.Horns convert large pressure differences that have a small displacement into a low pressure differences with a large displacement.

This adds impedance and makes the driver/system more efficient. Like Bill said. Why worry about it when its a plus on all sides.

Any loudspeaker system is not impedance flat across the entire frequency range. As soon as you get toward the resonance frequency of any given driver the impedance begins to rise and it rises as you move lower or higher above the high frequency cutoff as well. It also changes at the port tuning frequency in reflex enclosures.

In short impedance changes with frequency and enclosures can and do change impedance. Nominal basically means average but be assured no system is impedance flat from it's lowest usable frequency to its highest and amplifier output will change with impedance!!

[Mikey]

If the impedence isn't 4 or 8 Ohms, then how am I going to calculate what wattage my amp will provide to the sub? All the values are always given for 2, 4 and 8 Ohms. Also, how will I calculate this nominal value for my Titan 39.

Impedence is a constantly fluctuating phenomenon. Nominal impedence (like an "8 ohm" driver) is simply a "rough guideline" to allow users to do VERY BASIC amp/speaker matching.

As far as how many watts an amp will feed your drivers, again, that's a fluctuating figure, and besides that, an exact figure wouldn't be necessary. As long as you're "in the ball park", you're fine. Example ... if an amp is rated at 500w into 4 ohms ... a 5 ohm speaker load will get a little less than 500w, and a 3.5 ohm load will get a little more than 500w. As long as you're in the general range of power that you want to make available to your drivers, that's close enough. BELIEVE ME, it is!

You'll quickly learn that this isn't your standard internet forum. For the most part, it's a teaching/learning forum. It's productive, and people treat each other with the utmost respect. Once you start reading through a lot of the posts here, you'll find that a lot of the stuff that you thought you knew about pro audio was terribly over-simplified, and often just plain wrong. Most of us went through the same shock when we arrived, not that we still don't occasionally.

I strongly urge you to get yourself a "free" education here. Read as many posts as you can, ASK QUESTIONS if you need clarification, and don't believe everything that you've previously learned. If you approach this forum like a sponge, you'll absorb a lot. There are a lot of very intelligent, well-educated, highly experienced people here who share their knowledge freely.

[Tim A]

I'm still really confused. I thought the only thing being wired is the driver. There is no other resistive component in the sub, correct?

Incorrect. The air pressure inside the cabinet is resistive and adds 2 ohms of acoustic impedance. The amp doesn't care where the impedance comes from, it just knows there's 10ohms at the other end.

If the impedence isn't 4 or 8 Ohms, then how am I going to calculate what wattage my amp will provide to the sub?

You won't. Here's something else to shock your system: Speakers aren't wattage based, they're voltage based. Watts is an easy way to get things across to the unwashed masses. If you poke around in here and stick long enough, you'll learn how to calculate voltage and set your limiters so you won't have to worry about frying a speaker.

Like Mikey said, this was all new to many of us when we first came here. I still get things wrong and learn something new every day on this forum. I'm a wood guy by nature, not an electronics guy. As such I depend on the folks in here to lead me in the right direction. In turn, I try to help when I can.

Most people when first arriving tend to overbuild, simply because they don't understand exactly what these cabs are capable of. If you had told me prior to hearing with my own ears that a 10" sub could keep up with intense volumes in live sound, I would've laughed at you. Now I just laugh at the guys carrying dual 18 cabs around.....

[davygrvy]

Here's something else to shock your system: Speakers aren't wattage based, they're voltage based.

Well said Tim. These days, I ignore watts altogether. Last week I called a rental place asking for amps to do 45 volt RMS and safe into 1.4 Ohms minimum including phase shift. The guy was tweaked and said he only thinks watts

To me, an amplifier outputs voltage and supplies whatever current is required by the load to give it that voltage. The amp does put out watts, but that's wasted as heat.. watts are dissipated at the load. Personally, I think amplifiers should be rated like transformers for a volt*amp (VA) rating.

Vload = sqrt(Zload * Wload)
or
Wload = Vload^2/Zload

So if you have a driver rated at 300W continuous, but know that power compression kicks in at 400W and the driver is 4Ohm, solve for volts:

Code: Select all

V = sqrt(4 * 400)
V= sqrt(1600)
V=40Vrms

For that driver, the proper amplifier needs to output at least 40Vrms for whatever system headroom you choose for your soft-knee and limiter points.

[REDLINE]

Wow this is crazy stuff, I feel like my whole world has been flipped upside down. I will definitely start reading up on all of this tonight. Anyway, getting back to the sub I want to build. I think the Titan 39 is definitely my choice. I will probably either do the 14", 18", or 20" versions, but that doesn't really matter right now. As far as the driver, i've been recommended a few things. The HL10C appeared to be a great option that was suggested. I also like the S2010, Delta 12LF, and 4012 (if I decide to blow my money away for no reason). Once I get the plans I just ordered, I will see what other drivers are recommended, and then make a decision.

[DJPhatman]

The newest plans don't include the HL10C as a driver anymore. That driver is no longer in production. There are still a lot of them left, as it wasn't a fast-selling driver, that's why Eminence no longer produces it. Great driver, especially for a couple different sub designs of Bill's. But, alas, economics wins another casualty! I have 2 dual HL10C loaded T39s 22" internal. They are not that heavy. Quite easy to move around with the bolted on wheels. I have 2 more in the works. I believe 24" is as wide as I can go with these drivers.

[REDLINE]

Ok after reading the plans and speaking with my father, I have a few more questions. First off, my father knows everything about wood and recommended using MDO board. Would this MDO board be a good choice? Also, I noticed you showed a diagram for wiring a passive crossover, but what if I want these subs to be wired just like normal ones? Do I just connect the speakon straight to the driver, and then wire a second speakon in parallel?