Need Advice With Drivers And Crossovers

[Ak Canuck]

I'm installing new woofers, mids, tweeters, and passive 3-way crossover panels in a pair of old MTX speaker boxes.

Each speaker box should be getting somewhere in the neighborhood of 625 watts RMS. The crossovers are each rated for 500 watts RMS, 1200 watts max. I have some new drivers but before installing anything, I need to understand how the crossovers split up the wattage that goes to each driver.

In other words, if 625 watts of power is coming from the amp to the crossover input, how many watts will be going to the woofer, midrange, and tweeter? Is it still 625 to each driver, or is there a certain percentage of the power going to each?

Thanks

 

[roadrune]

Why is this interresting?

What you should worry about, except the obvious fact that you need drivers with parameters which actually fit the box, is sensitivity.

They should be really close, if not a l-pad can be used to atenuate the driver(s) with higher sensitivity.

When they are all matched you can calculate the theoretical spl the speaker can produce from the power you give them.

If you double the power, you double the spl.

E.g: your speaker have a sensitivity of 90db with 1w/8ohm then it will produce:
93db with 2w
96db with 4w
99db with 8w
102db with 16w
105 with 32w
108 with 64w
111 with 128w
114 with 256w
And 117db with 512w which is LOUD.

In other words: power is not really interresting unless you have really low sensitivity speakers.

Also if you just throw in some drivers with a random crossover you will be really lucky if you get a useful result.

 

[j_garcia]

The x-over does not split up the power. The drivers use what they need.

Random x-over with randomly chosen drivers fed with a lot of power sounds like a recipe for poor sound. There's a lot more to getting a functional speaker than what you propose and actually getting good results takes a bit of knowledge.

 

[MrBoat]

I recall a time when component audio systems for cars started becoming popular. Those of us on a budget opted for coaxial speakers that didn't need a crossover, and those that did, typically had them included. To get the full benefit of a component system, it would not only have to be designed for the drivers, but the car as well.

With that said, I have had some pretty amazing car audio systems based on coaxial speakers. I can only imagine they have gotten better since. With the addition of dedicated subwoofers, surely there is available DSP options to make this work even better?

 

[j_garcia]

My last car had an Alpine with Audessey in it. I didn't have the mic though

 

[BoredSysAdmin]

I'm installing new woofers, mids, tweeters, and passive 3-way crossover panels in a pair of old MTX speaker boxes.

Each speaker box should be getting somewhere in the neighborhood of 625 watts RMS. The crossovers are each rated for 500 watts RMS, 1200 watts max. I have some new drivers but before installing anything, I need to understand how the crossovers split up the wattage that goes to each driver.

In other words, if 625 watts of power is coming from the amp to the crossover input, how many watts will be going to the woofer, midrange, and tweeter? Is it still 625 to each driver, or is there a certain percentage of the power going to each?

Thanks

Your question reminds of this recent thread:
http://forums.audioholics.com/forums/threads/would-wiring-4-super-tweeters-per-speaker-box-increase-life-of-tweeters.106754/

 

[Ak Canuck]

All right, let me try this a different way, and I'm going to use a random wattage here, since it seems like the impression is that I'm doing everything at random.

Let's say an amp is putting out 100 W to a speaker. Speaking strictly in terms of power, not sensitivity or whatever, does each driver in the box need to be able to handle 100 W? Or should some drivers be rated to handle the majority of that power, or only a tiny fraction of that power?

Someone gave me what looks to be some sort of rule of thumb for illustrating Db per watt, and that's fine. Maybe somebody can chime in and give me a rule of thumb for choosing the wattage rating of each driver in a speaker based on the amount of power that may be going to it.

 

[roadrune]

Choose a powerrating based on the sensitivity and how loud you are going to play.

It is no problem finding sub-drivers capable of handling 3000w, but most people would not like to be in the same room when its actually fed 3000w....

Think of it as a car. Even if you have 500hp, for the most of the time you will only be using 100 of them.

As long as the driver can take the wattage needed to play as loud as you want, you are ok.

Edit: it did seem from your initial post that you where doing things randomly without any knowledge, if thats wrong, i appologize.

 

[TLS Guy]

All right, let me try this a different way, and I'm going to use a random wattage here, since it seems like the impression is that I'm doing everything at random.

Let's say an amp is putting out 100 W to a speaker. Speaking strictly in terms of power, not sensitivity or whatever, does each driver in the box need to be able to handle 100 W? Or should some drivers be rated to handle the majority of that power, or only a tiny fraction of that power?

Someone gave me what looks to be some sort of rule of thumb for illustrating Db per watt, and that's fine. Maybe somebody can chime in and give me a rule of thumb for choosing the wattage rating of each driver in a speaker based on the amount of power that may be going to it.

The question is not answerable. First you need to pick a bass driver that has the correct T/S parameters for the box. That is tough and it is usually easier to make a new box. Then you need to design and build (not purchase) a crossover that is designed to give a flat response taking account of the acoustic responses and sensitivities of the drivers. The power splits all depend on overall design and driver selection.

Matching the drivers are the start of the design and an essential component of the design. If you choose drivers are random, the chances a far greater then not that it will be impossible to design and build a crossover to make a speaker worth listening to.

 

[MrBoat]

There used to be some kind of average (IIRC) along the lines of, the wattage of the lowest value driver, times the amount of drivers in the box. In other words, if the tweeter was 20 watts, and there was a midrange that had 50 watts and a woofer that handled 100 watts, you would likely be safe rating the whole speaker at 60 watts.

 

[Ak Canuck]

There used to be some kind of average (IIRC) along the lines of, the wattage of the lowest value driver, times the amount of drivers in the box. In other words, if the tweeter was 20 watts, and there was a midrange that had 50 watts and a woofer that handled 100 watts, you would likely be safe rating the whole speaker at 60 watts.

That's the most useful and concise information so far, thank you. Is that fairly accurate, as far as you can remember?

 

[Ak Canuck]

My next question is this: How close should the drivers be in their sensitivity? Someone in the first reply said they should be "really close", which doesn't exactly tell me much. And also that some drivers can be "attenuated" with an iPad? I'd like to hear more of this.

My woofers are 15" with a sensitivity of 88.5 db with a frequency response of 20-125 hz.

 

[lovinthehd]

That's the most useful and concise information so far, thank you. Is that fairly accurate, as far as you can remember?

Actually this is least accurate info so far..altho with the hack job you envision you might think otherwise. Putting different drivers in boxes designed for others with generic crossovers is just not a very good approach.

 

[Ak Canuck]

Actually this is least accurate info so far..altho with the hack job you envision you might think otherwise. Putting different drivers in boxes designed for others with generic crossovers is just not a very good approach.

Well I don't have the time or interest to make an entire fucking hobby out of this. I'm just looking to upgrade the speakers in the welding shop I work in. So my fellow basic welders and I can listen to some music.

So, really, regardless of your opinion of my approach, like I said, I'm not looking to turn this into a hobby or become a self-educated sound engineer.

 

[rojo]

Well I don't have the time or interest to make an entire fucking hobby out of this. I'm just looking to upgrade the speakers in the welding shop I work in. So my fellow basic welders and I can listen to some music.

So, really, regardless of your opinion of my approach, like I said, I'm not looking to turn this into a hobby or become a self-educated sound engineer.

Do you think it's possible that maybe you don't know how much you don't know about what you're asking? Is it likewise possible that removing drivers and crossover tuned for a specific box and replacing with off-the-shelf components with no regard to driver behavior, enclosure volume, vent tuning, baffle width, the different sensitivity levels of your drivers, or any of the other considerations the OEM designers probably employed, is actually a downgrade rather than an upgrade?

All this absolutely matters, regardless of your time and interest. If you are unwilling to learn, then don't ask for DIY advice. Just buy new completed speakers and be done. There's no shame in that.

OK, all that aside, it seems like you're asking whether you're about to fry your new components in spectacular fashion. The answer is, it depends on how loudly you listen, what type of music, and whether your crossover will successfully filter the frequencies that are out of your tweeters' range. Just trust us that you're most likely not going to be drawing the full rated power of your amp. And the wattage you draw depends not only on your source volume and amp gain, but also on the impedance of the drivers, which varies significantly along the drivers' ranges. Short answer: assuming you cross over your tweeters high enough, you're probably not going to fry anything, but there are no guarantees.

Enjoy your project.

P.S. That you haven't received the answer you are looking for is not from any sort of audiophile snobbery, but just from experience. You wouldn't ask on a mechanics forum whether the carburetor you bought from the junk yard from a random make and model car will work in your 66 Mustang, then say you don't have the time or interest to learn about auto repair, would you? Be nice.

 

[MrBoat]

Actually this is least accurate info so far..altho with the hack job you envision you might think otherwise. Putting different drivers in boxes designed for others with generic crossovers is just not a very good approach.

Wasn't meant to be accurate, or even right. A loose calculation around a collection of unknowns, that usually would be on the safe side and hopefully underpowered based on the weakest speaker in the box. After that, you just don't push it to the point of distortion. From the days of ghetto rigs that used to employ wonky gear out of old car or TV speakers and such. At this point, what's the worst that can happen? Blow a driver? Such is the sacrifice with the approach taken by the OP.

People blow up perfectly good speakers all the time and they are gonna do what they are gonna to do.

 

[rojo]

Wasn't meant to be accurate, or even right. A loose calculation around a collection of unknowns, that usually would be on the safe side and hopefully underpowered based on the weakest speaker in the box. After that, you just don't push it to the point of distortion. From the days of ghetto rigs that used to employ wonky gear out of old car or TV speakers and such. At this point, what's the worst that can happen? Blow a driver? Such is the sacrifice with the approach taken by the OP.

People blow up perfectly good speakers all the time and they are gonna do what they are gonna to do.

Shame that he's unwilling to try some proven DIY designs or to take a chance on the hobby he's dismissing as a waste of time. I know of one welder with some rather impressive speaker builds.

 

[MrBoat]

I bought a $150 RCA bookshelf system for our welding shop that holds 5 CDs, Bluetooth capable etc with two detachable 3 way speakers that is over 200 watts RMS that kicks butt for what it is and sounds way better than I thought it would. It's been in there since 2006 and still works fine.

I'd buy something like that again before I'd take a chance on cobbled together speakers.

 

[MrBoat]

Top left corner of the photo you can just make out the bookshelf speakers being held up on the purlin with a wire across the front of them. When I show up at the shop, I can often hear this thing bumping out in the parking lot and have to turn it down when I get to my bench. They hook up their cell phones to it and play stuff that I would not torture an enemy with.

 

[BoredSysAdmin]

There used to be some kind of average (IIRC) along the lines of, the wattage of the lowest value driver, times the amount of drivers in the box. In other words, if the tweeter was 20 watts, and there was a midrange that had 50 watts and a woofer that handled 100 watts, you would likely be safe rating the whole speaker at 60 watts.

I think you're referring to Ohms law described here:
https://www.swtc.edu/Ag_Power/electrical/lecture/parallel_circuits.htm
Specifically point 3

The problem is that Ohm's laws don't apply to speakers they don't have static resistance, but a dynamic impedance. Ie depends on frequency impedance changes