why do my polk sda 1 monitors subdue male vocals?

the equipment i run them with the polks is an adcom 545mk2 amp,a 555mk2 preamp,an audio source equalizer,and a denon 1500mk2 cd player. i listen mostly to classic rock and oldies. it seems male vocals are muddied. any idea on why would be greatly appreciated. speakers were checked by a highly respected audio repair shop here in northwest indiana, he claims they are functioning properly. polk claims they have not heard of this problem with these speakers. other than this i like the sound of the polks. each cabinet contains four 6.5inch midbass drivers and two sl 1000 tweeters and a passive 12 inch bass driver.
Do you have the SDA interconnect cable? Is your amp common ground?
Four mid range drivers. The lower mid is confused by comb filtering. Male vocals are around 300 Hz. But vocals consist of lots of partial harmonics at 600, 900 and 1200 Hz etc. At 600 Hz you have a wavelength of roughly two feet. At 1200 Hz you have a wavelength of roughly a foot.

These distances are roughly what you have between each mid range driver and therefore you will get cancellations (as peak cancels trough) and peaks (as peak matches peak) across a broad range of frequencies in the lower mid range. This is called a "comb filter" as it looks just like a comb when you plot amplitude reposne against frequency.

This means your lower mid range frequencies (male vocals)will have a small strong sweetspot directly in front of the speaker and a very narrow dispersion pattern in this frequency range (in an anechoic environment).

When you add the room's side walls, floor and ceiling then the reverberant energy arriving at the listener is likely to be "comb filtered".....some frequencies will suck out completely and others will reinforce and be quite strong.

You ears/brain can normally compensate for some of this and you can actually hear and make sense of reverberant sound, as your ears are about 6 inches apart and get different signals. In fact reverbant sound provides not just SPL energy but also cues as to stereo image and position of instruments in a stereo sound stage.

In your case the reverberant field may be confusing due to all these drivers producing the same frequencies. The fact that you are positioned in front of the speakers does not help the reverberant field.

Try to imagine each of your side walls as a mirror. Then imagine the position of the virtual speaker that you would see in the mirror. The farthest mid range drivers of the virtual speaker will likely be 6 inches to a foot farther from your ear than the nearest ones. Also try to imagine what happens off the floor and ceilings.

Solution => thick carpet floor treatment and very generous speaker toe-in may help (beam the speakers at your listening position from the room corners if necessary). Acoustic treatment of the side wall and ceiling first reflections may also be needed
i checked and all my cables and sda interconnect is attached. i am not sure if an adcom 545mk2 power amp is a common ground amp? how can i tell?
thanks shadorne, i will try some of your suggestions.

With respect, the SDA speakers do not function as most other speakers do. For example, they are never to be toed in. Two of the four mid drivers are used in a cross cancellation signal at a reduced volume level and limited to certain frequencies. Combing should not be the issue here.


Contact Adcom about that. If you don't have the owners manual for your Polk's, call them and they will send you one for free. It explains proper set up.
because they have a flat response. most pop/rock music is mixed that way. if john mellencamp sounds as if he's substantially out in front of the band, somethings wrong.
merganser thank you for your input. you seem to know alot about sda1 monitors.
Does male vocal clarity change when you hit the EQ/Bypass on the EQ100?
When Racerx322 described four mid range drivers and a male vocal problem, I immediately jumped to what may be the wrong conclusion. I'll do more homework next time. Sorry Racer, for giving what may well be incorrect advice even it was well intended! Do let us know how you solve it.

Thx Merganser for pointing out my wrong assumption.
jameswei, the vocals are very slightly improved with the eq on. could there have been a possible problem with the eq?
jaybo, my klipsch speakers did not have the same effect on vocals when hooked up with the same equipment. could it just be the nature of the sda1.
It sounds like you've narrowed it down to the speakers, especially after noting that male vocals were fine with the Klipsch's. I had thought that it might have been something with the equalizer settings, but apparently not. It could be that the Klipsch's mated particularly well with your other components in reproducing male vocals.

I'd suggest you get that owners manual and ask them for the SDA trouble shooting guide. I know you had them checked out, but it sure seems as though they have a problem. Of course, it could be, as Jameswei pointed out, that the Klipsch simply mate better. Let us know the outcome.

Another thought, try taking the EQ out of the system entirely.
as an example, if you are talking about klipsch heresys, or other hybrids they have a forward midrange character...they also don't have the top end and low end the polk's have. balance is king and the sda's are classics.
thanks i will try removing the eq. frank