SpeakerHobby

Passive Radiators

As you can probably tell by my main speaker and subwoofer designs, is that I am a huge fan of the use of the passive radiator in loudspeaker building. Many people who are purchasing speakers for their home theater, or are new to the DIY speaker building have never heard of passive radiators. I have auditioned my system to many people, and I would say 95% of these folks have never heard of a passive radiator.

I have a total of 16 - 15" passive radiators in my front speakers and subwoofers, and have incorporated their use in the Olufsen Redline 60 side surrounds speakers that I have re-designed for a total of 20 passive radiators in my home theater.

Passive radiators have a unique and deep, rich bass quality that is unsurpassed by a typical sealed or ported design, based on what I have heard in the retail and high end audio stores and the speakers I've owned and built in the past.

Their are many other types of loudspeaker subwoofers that incorporate push-pull speaker configurations, isobaric speakers, infinite baffel designs, a line transmission type box design, and many others that do sound good, but I haven't listened to them all or know much more about them other than what I've read, so I'll concentrate on the passive radiator for this topic's sake and provide you with some links and comments and reviews by other audiophiles about the use of the passive radiator for your DIY speaker hobby.

Here is a link to Dan Marx's site that has some very good information about the different box designs I've just described. His website can also be found on my "Resources" page and if you need his help or want to purchase one of his designs, send him an email. http://www.danmarx.org/audioinnovation/theories.html I've known Dan for several years through the internet and have consulted with him several times and find him to be quite helpful and knowledgeable.

The sealed design speaker requires much more power to reach the low bass extensions that the passive radiators can give you. The ported speaker has to be tuned just to the right specs to reduce and or eliminate port huffing, chuffing, and resonant noises. As Vance Dickason puts it, a poorly placed or designed ported system can amplify unwanted port noises or resonance by at least ten times if not built correctly. At a 100 dB output, that equates to a lot of distorted sounding bass! I have utilized their use on my mains, my subs, and the Bang & Olufsen Redline 60 modification.

Pros: You can build a smaller box and have better bass than a sealed or ported speaker. Passive radiators have a fine unique bass quality of their own. The bass extension is usually lower than the cabinet's tuning frequency. At the tuning frequency of the box, the drivers are hardly moving at all and the passives are working at their hardest.

Cons: Passive radiator systems cost more money to build and many DIY speaker enthusiasts are on a budget. In competition and very high output subwoofers, you can probably achieve a higher SPL with the ported system. Passive radiators tend to roll off faster below their tuning frequency than ported or sealed speakers, so build your passive radiator with a low box tuning frequency because the human ear can't hear much below 18 to 19 hz. My subwoofers model out to 13 hz at 1000 watts. This is a bass that is felt and not heard which is ideal for movie reproduction.

When building your passive radiator speaker, you want to use passive radiators that have at least twice as much surface area as the main drivers to perform to their best. Many designers for example, will use two 18" passive radiators with a 15" driver. To lower your box tuning frequency, you need to add mass or weight to the passive radiator to achieve the box tuning frequency you desire. A free modeling program called WinIsd can be found at www.linearteam.dk/ to help you with your design. www.lalena.com also has a lot of free design material for your use in the design of your subwoofer or loudspeaker. Links for other software and information can be found here.

Watch out for what is known as the "white van speakers". These are the guys that pull up in the parking lot and try to sell you some fine looking speakers that they just happened to have left over from a big purchase or installation. Many of these have several passive radiators that make them look like they have to be a fantastic sounding speaker with that many speakers in them. Most of them are pure junk and the passive radiators are $2.00 foreign made junk drivers stuck in a box with a driver and tweeter and nothing matches as far as the cabinet and speaker design. You will find out you have been had when you hook them up when you get home.

You won't find very many retail speakers in the regular audio stores that utilize the passive radiator design because a $2.00 port is much cheaper than a $75 to $150 passive radiator and the market is saturated with tons of speakers with so many manufacturers fighting for the sales of their speakers, and they are very competitive.

When using passive radiators in your design, your drivers must have a "Q" or "QTS" of .4 or lower. Anything higher than that should be used in a ported or sealed design.

Have fun with your speaker project, and if you are not sure you are capable of designing a speaker, well get your hands on a kit which can be found in many of my links on this site and purchase a ready tested and proven design. You can save a lot of money building your first speaker this way. Only if I knew that. I've got drawers and shelves full of left over parts and drivers I've used and ordered that haven't been used to learn to build my speakers. It can be expensive on an untested design.