Researching DIY sound, have basic question. - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th February 2012, 03:12 AM   #1
Genem is offline Genem  United States
diyAudio Member
 
Join Date: Feb 2012
Default Researching DIY sound, have basic question.

I been researching diy sound for several weeks now and have learned a lot, but there are still a few things I'm trying to figure out, even if they happen to be very basic.

Say I picked out some drivers to build a loudspeaker (to be used with a PA):
Two 8" 200 RMS drivers and one 80 RMS compression driver. The finished loudspeaker will be 2-way with the 8" drivers wired in parallel.

Will the completed loudspeaker be 400 RMS or 480 RMS?

Also, same thing but for a 3-way loudspeaker:
One 8" 200 RMS woofer, one 8" 200 RMS mid, and one 80 RMS compression driver.

Will the result be a 400 RMS or 480 RMS loudspeaker?
  Reply With Quote
Old 18th February 2012, 04:22 AM   #2
diyAudio Member
 
Join Date: Sep 2010
Quote:
Two 8" 200 RMS drivers and one 80 RMS compression driver. The finished loudspeaker will be 2-way with the 8" drivers wired in parallel.

Will the completed loudspeaker be 400 RMS or 480 RMS?
Watts are just power handling. Use it only to keep yourself from detroying your speaker. It's overall meaningless. You need to look at the sensitivity, impedance curve, and necessary SPL for the application.
  Reply With Quote
Old 18th February 2012, 04:37 AM   #3
Genem is offline Genem  United States
diyAudio Member
 
Join Date: Feb 2012
Yes, I understand that; but I still want to know which it will be just for the sake of knowing.
  Reply With Quote
Old 18th February 2012, 05:53 AM   #4
bwaslo is offline bwaslo  United States
diyAudio Member
 
bwaslo's Avatar
 
Join Date: May 2006
Location: Cinciinati, OH
400. But as mentioned, it is actually rather meaningless. If you hooked it to a 400W amplifier and drove it continuously with a sinewave at full power it would still burn up in a short time. Power handling is a guarantee of nothing much at all. And remember that a decent amplifier will usually deliver about twice the power into 4 ohms as it will into 8 ohms.

Trying to avoid speaker damage by limiting power amplifiers size is like trying to limit the speed of your car by using low-octane gas. Doesn't quite work that way.

As a general rule, whatever power amp size you use, if it starts to sound bad, TURN IT DOWN.
  Reply With Quote
Old 18th February 2012, 06:04 AM   #5
Genem is offline Genem  United States
diyAudio Member
 
Join Date: Feb 2012
Thank you for clearing that up. I run my amps at such a setting that the volume in the room will be comfortable, and that just happens to be nowhere near clipping.
  Reply With Quote
Old 18th February 2012, 11:35 AM   #6
diyAudio Member
 
Join Date: Nov 2009
Location: Birmingham, UK
You should be fine then but there is a general rule-of-thumb in PA sound: The amp should be rated at twice the power of the connected speaker as it is a LOT easier to fry tweeters with a clipping amp than it is to melt woofers with too much clean power (assuming a passive xover and depending on genre of music, some modern dance-type genres are fond of adding lo freq sinewave to the mix which can melt woofer VCs in the long term).

But bear in mind it is just a rough&ready approximation.
  Reply With Quote
Old 18th February 2012, 06:57 PM   #7
Genem is offline Genem  United States
diyAudio Member
 
Join Date: Feb 2012
I started reading articles and hanging out on the forums of prosoundweb sometime last year, so I've been learning a lot there as well and have read about the rule of thumb for picking amps for speakers.

I am also planning on building some subwoofers, but do they need some sort of crossover/circuits inside? Or no?
  Reply With Quote
Old 18th February 2012, 07:55 PM   #8
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by bwaslo View Post
400. But as mentioned, it is actually rather meaningless. If you hooked it to a 400W amplifier and drove it continuously with a sinewave at full power it would still burn up in a short time.
This just isn't really true.

If the sinewave was below the crossover frequency all of it would go to the woofers, if above, it would destroy the compression driver in short order.

If you fed the composite loudspeaker with 480 watts of music, with the crossover frequency chosen so that 80 watts of music power went to the compression driver then 400 watts would go to the woofers, all other things being equal, and you could say that the power handling was 480 watts.

The problem really is that the question you have asked is simplistic. The situation is more complicated than you think.

Beside the issue of impedances hinted at, there's a question of efficiency. If the compression driver were efficient (loud for the power) and the woofers inefficient (quiet for the power), then despite the unequal power split the bass could still be too quiet compared to the treble.

Lest you think that now you know enough, there are other issues as well.

Don't be discouraged though, we've all had this experience.

Get hold of a good book on loudspeaker design, and one on general audio, keep reading the forums and in time you'll know enough to ask a sensible question.
  Reply With Quote
Old 18th February 2012, 08:35 PM   #9
mdocod is offline mdocod  United States
diyAudio Member
 
Join Date: Dec 2011
Location: Black Forest, CO
Send a message via AIM to mdocod
Hi Genem,

The power handling given for a driver has, roughly to do with the voice coils ability to dissipate heat and different companies may opt to use different methods of determining this number. Depending on testing methods, there can be huge differences in the actual power handling. Some companies give "RMS" as "AES" or vice versa, where as other companies might have their own way of determining RMS values. The problem is that, while many of the testing methods that can be used are valid in their own way, at the end of the day, one realizes that if different testing results in different power handling ratings, then power handling is not something that can be nailed down to a single number so accurately anyways. Power handling varies with frequency. Also, most power handling ratings will not take into account mechanical limitations of the driver when used to produce low bass frequency.

Consider the following:

Company A chooses to test based on continuous voltage across a band pass of expected driver frequency range, with the voltage selected corresponding to the nominal impedance rating to achieve a "theoretical" wattage.

Company B chooses to test based on continuous voltage across a band pass of expected driver frequency range, with the voltage selected corresponding to the minimum impedance rating to achieve a "theoretical" wattage.

A and B are gain based ratings, and are valid if you know the parameters of the test. However they may result in different ratings.

Company C chooses to test based on actual measured wattage into the load presented.

C is a very real thermal energy rating and would result in a lower rating than A or B.

Then there is method D: Pull a number out of thin air

So, is your speaker 200W, 400W or 480W capable?

The answer is, depending on conditions, all of the above and many others.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
a basic diy question for my chip amp then_dude Chip Amps 12 13th October 2007 11:05 AM
basic question about sound. Theli Everything Else 12 2nd December 2006 08:22 PM
researching patents? cowanrg Everything Else 12 24th June 2003 06:17 PM
researching diy speaker shapes? Austin Multi-Way 6 9th July 2002 03:06 PM


New To Site? Need Help?

All times are GMT. The time now is 12:26 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2