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Exhaust Resonators : What are they and do I need one?

What is a resonator?

Resonators are basically mufflers that fit underneath the car. They are typically round-bodied and longer than a normal muffler, but are really just smaller skinnier mufflers.

The reason resonators exist is to help alleviate "drone" or cabin resonation that can occur in aftermarket performance exhaust systems. This sound can range from being mild to being unbearable when driving a car. It typically will occur at lower engine speeds at higher loads (2-3000 rpm, with a little throttle applied). Vehicles with automatic transmissions, convertibles, and trucks can have especially hard times with drone.

Because of their placement under the vehicle, resonators are usually effective at helping keep sound from coming up through the floor and into the cabin where it bounces around, and can hit a resonant frequency that can get very booming.

Styles of resonators

There are different kinds of resonators. Some are actually constructed like mufflers, with endcaps either crimped or welded on. Many times these resonators have perforated-tube cores which offer great performance and have more space for sound deadening material.

Other resonators are "glass pack" style resonators, which have more of a bottle shape formed at the ends. These resonators are usually smaller which provide more ground clearance under the vehicle, but also have less sound deadening material making them less effective at doing what they are supposed to do.

The core is the internal tube that the exhaust gases actually flow through. The core of a resonator can be resigned a few different ways, but the most popular cores are either perforated or louvered.

A perforated core is great for performance because they flow almost like a bare tube does. However without a good packing material inside they won't do much to reduce drone without a more substantial body design. So many times one will find resonators with perforated cores will be larger and sometimes difficult to fit under the car.

Louvered cores feature scallops or fins on the inside of the car that intrude into the core. These louvers will effectively "catch" more exhaust waves and be effective at quieting a system down with a smaller body, but do so at the expense of exhaust flow. Louvered cores are not preferred but are sometimes the only option in tight-fitting applications.

Do I need one?

While resonators will not usually impact the tailpipe sound of a system, they can to varying degrees change the interior sound. How "bad" an exhaust resonates can be very subjective. People will make claims about resonation, being either good or bad, and it is hard to translate that into what another person finds reasonable. The best means that Heeltoe has found in helping customers make this choice has been by asking them how quiet they want the system to be.

If a customer wants the car barely louder than stock, we recommend keeping the system stock and then changing out the rear muffler boxes only.

If a customer is only looking for a slight increase in sound, but for the most part want the sound intrusion at a minimum, then a resonator is recommended to be fit to the aftermarket system.

If a customer really wants to hear the exhaust, we suggest the do not install resonators to get the most sound from the system. This does not mean that without a resonator a system will be obnoxious (people like to avoid rasp or buzzing sounds, associated with 4-cylinder Hondas...this is more a byproduct of poor exhaust design than resonators and their placement).

Final note...

Keep in mind though, that in any aftermarket upgrade, the results can be unpredictable. This is especially try of concerns about "fitment" and sound of exhaust. Mixing and matching aftermarket components will cause individual results to vary (do you have headers, or cat deletes on the vehicle?). And one man's "loud-as-heck" is another man's "bad-ass-that's-just-right!"

Since resonators are just welded-in mufflers available as aftermarket universal parts, they can be added and deleted by qualified fabricators. Just keep in mind that resonation is oftentimes a function of thee vehicle's engine and wheelbase design...the original maker of the vehicle tends to put resonators in the most effective areas, so if you are installing one custom try to put yours in the same general place.


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