I dont care about noise I wear hearing protectors. Having a decent sized machine cuts down on noise by itself just from the mass. For straight knives sometimes an extra bevel on the knife (not the back flat) can cut cleaner than fresh razor sharp high speed steel. It cuts more like a wedge, learned this from a moulding company owner and results backed it up. Really important is feed rate, I only have one on the old SCM so I kick it in and out of gear and it never reaches full speed. Until I find time to put a gear motor on like the little Woodmaster has but it will be a bit complicated.
I have no complaints with the performance of my Parks 97 with straight knives. It does 'siren' quite loudly with dust collection though. Before I retired, I had the sound engineer at work analyze it and found the primary frequency to be a multiple of a 3 knife head running at speed. Each knife "wolfs" as it cuts the air drawn between the head and chip breaker or pressure bar. At his suggestion, I've tried varying the DC pipe lengths. Even borrowed a friends portable DC to no avail. She's a screamer.
Has anybody experienced significant noise reduction after installing a helix head in a planer that sirens with straight knives?
I have to agree with several posts that yes, straight knives that are sharp and good quality and set up properly with a dial bore gauge to within .001" will definitely plane or join extremely very smooth. The problem is that they just wont stay that way for long enough. We have a lot of minerals in the wood here, especially black walnut and it is hard on even the best high speed steel.
Not all spiral cutter heads are created equal. Many machines that have "spiral cutter heads" or "insert type" heads use Byrd brand cutter heads. Jet and some of the newer Powermatic jointers use proprietary Asian made cutter heads. They are spiral, but the cutting edge of the insert is still straight to the wood being cut, so for tear out you don't get the added advantage of having the insert slice into the face of the wood. Carbide inserts have a sharper cutting angle and this alone may help some with tear out. The new Grizzly machines I have seen have a very radical, much more curved spiral on their cutter heads. Wish I had one to compare to the performance of a Byrd.
As far as the noise, yeah, they are a little quieter, but comparing machines like a DW735 to a 20" Powermatic is probably not too fair...the DW735 has a chip blower that is noisy enough. Take straight knives out of the 20" Powermatic and install a Byrd and the difference is definitely not a reason or factor to spend the money.