Effect of multiple drivers on ideal box volume - diyAudio
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Old 31st July 2001, 06:07 AM   #1
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I was wondering what effect putting multiple drivers in different enclosures would have on ideal box volumes and the calculations for the bass cutoff freq. and tuned port freq. The situations I am wondering about are 2 drivers in a closed box, 2 drivers in a vented box, 4 drivers in a closed box, 4 drivers in a vented box, and any other situation you might want to tell me about.

Thanks.
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Old 31st July 2001, 02:53 PM   #2
Eric is offline Eric  United States
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Will: Typically, each time you add another sub/woof/mid driver to an enclosure, you need to increase the volume of the enclosure. For example, if a particluar mid-woof needs a 50 liter volume, putting 2 of this same driver in the enclosure increases the volume to 100 liters. 4 drivers will require 200 liters. This is true for both sealed and vented enclosures. However, for vented enclosures, each time you increase the radiating surface of the drivers (by adding more drivers) you also need to change the port dimensions. This typically means adding more and/or larger diameter ports. Do a web search on WinISD and download it. You'll need the Thiell/Small parameters for the driver, but it will give you a rough approximation of the relationship between drivers and closed/vented cabinets.
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Old 31st July 2001, 03:54 PM   #3
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Eric, I have a question.

Say you are using 3 of the same mid/bass driver in a single enclosure. How much does matching of drivers come into play? Does the +/- 10% for enclosure size tolerance, within T/S parameters, forgive differences in woofer specs? Or could mis-matched woofers complicate things even more?

Vince
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Old 31st July 2001, 04:07 PM   #4
Eric is offline Eric  United States
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Vince: Hmmm... I'll give you my impression with the hope that others will join in here also. Matching drivers, depending upon who you talk to, plays a more or less significant role. I read somewhere that NHT matches drivers in their 3.3 line to within 1.5 db of one another. I have a set of Atlantic Technology speakers. When I was talking with the tech folks there, the fellow mentioned that each speaker must perform within 3db of the final prototype or they don't pass THX certification. Northcreek kits match drivers to within 0.5% and crossover components to 1%. BESL kits do the same matching by tweaking crossover components.

Drawing out the common points from above, it appears that as the speakers become more expensive in price, the drivers are matched to increasingly tighter tolerances. The matching is easier if you purchase from places the sell kits because they have lots of stock to choose from and matching is easy. For folks like us, matching can become very difficult (and expensive) to perform.

So, to get back to your question, I'd say that +/- 10% in cabinet volume might just outweigh and cover over the differences in matching drivers. These differences can be manipulated pretty easily by adding/removing stuffing to your box, chaning the port lenght slighly, adding a flare to the port (if ported), etc. I know many people who spend a good deal of time tweaking the box stuffing and porting once they have finished a speaker.
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Old 31st July 2001, 04:24 PM   #5
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Closely matched drivers sound like a good foundation. Using the anology of a straight line, if you are off by a degree early on, it's not easy to detect, but as the line moves on, the deviation begins to show. Like you said and I agree, it's difficult and expensive for the average guy, but close matching is something to strive for, if it's a serious project. Some sets of tweeters are match and are only sold that way, like Dynaudio (who are not selling raw drivers anymore) and Morel. Some pairs starting at $200.

thanks for the input,

Vince
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Old 31st July 2001, 06:25 PM   #6
Helix is offline Helix  United Kingdom
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Thumbs up driver set up

I have found this software called winISD, it is useful for the beginner and advanced alike.

It would allow you to compare dirrent speaker/box setups and tuning all on the same graph so you can very easy compare. It plots freq responce, phase plot, SPL and group delay. The inbuilt speaker library is VERY comprehensive.

It has wizards so it's mega easy to get started, also it is only a 800K or so download.

try
http://www.linearteam.dk/winisd.html
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Old 1st August 2001, 02:26 PM   #7
Eric is offline Eric  United States
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Helix: Thanks for posting the URL for WinISD, I was just too lazy to include it in my post...
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