Setting the Internal Crossover for My Hsu VTF-2

[Joel McIntosh]

I'm running my Polk RTi8s (similar to the old RTi70s) L/R fronts directly into the subwoofer and using the subwoofer's (HSU VTF-2) internal crossover (rather than my receiver's crossover -- fronts are set to large in the receiver). The Hsu subwoofer's manual says to set the crossover at approximately the point of the speaker's lowest frequency (-3dB limit). The RTi8 manual says that limit is 40Hz, but this seems too low for the RTi8s (the speakers have 1 tweeter, 2 6.5" drivers, and no woofer). Can anyone with these speakers who is bypassing their receiver's crossover and using the sub's crossover suggest where they set their crossover for the RTi8s?

[Lwang]

You cannot assume your speaker will roll off @ 40hz, since that is pretty room dependent. Get an SPL meter, place it at listening position and measure with narrow band (1/3 oct) pink noise or warble toine and find out where the -3dB is. Then with only the sub playing the same signals, first adjust the level so that it is roughly the same as the main speakers, then adjust the crossover until the -6dB point os at the same freq as the speaker's rolloff point. Then measure again with both speaker and sub playing and see if the transition is seamless and flat. If there is a dip at the crossover freq, change the polarity setting and see if it gets filled out.

[Dudley]

Don't believe the manual. My BP-8's claim to go down to 22 Hz. When I measured them they are flat to 50 Hz and then 20 Db down at 40 Hz. They do maintain that lower level to about 30 Hz.

[Joel McIntosh]

OK, I know you guys are going out of your way to help, and I appreicate it. However, this stuff is a bit above my head. For example, I have a SPL meter, but I don't have the foggiest idea how to "measure with narrow band (1/3 oct) pink noise or warble toine and find out where the -3dB is." I don't even know what "narrow band (1/3 oct)" means, nor do I understand what "where the -3db is" means. Is there a web site that could explain this process in more basic terms for a novice like me?

[BeFree]

Hey, a man with good taste in speakers. I have the Polk RTi70's and they're absolutely awesome.

Why are you hooking up your speakers directly to the Hsu instead of using a subwoofer cable and the receiver's crossover set at 80 Hz? It just makes life simple.

[Retread]

Originally posted by Joel McIntosh
OK, I know you guys are going out of your way to help, and I appreicate it. However, this stuff is a bit above my head. For example, I have a SPL meter, but I don't have the foggiest idea how to "measure with narrow band (1/3 oct) pink noise or warble toine and find out where the -3dB is." I don't even know what "narrow band (1/3 oct)" means, nor do I understand what "where the -3db is" means. Is there a web site that could explain this process in more basic terms for a novice like me?

Looking for the collected works are you? Maybe someone will tell us. There are some things I've gleaned over the years, and recently while trying to set up a home theater.

A dB (deciBel, or hundredth of a Bel) is a measure of relative loudness. Relative, that is, to some other loudness. It takes a 3 dB change in loudness for a human to perceive a change. Decrease the sound pressure by 3 dB, and a human can perceive that a change has occurred. This is why -3 dB is important. If someone says the sound is +/- 1 dB to 100 Hz, rolls off at 12 dB per octave, and is -3 dB at 40 Hz, you know that you can't detect differences in sound level until the frequency drops to 40 Hz or lower, but will be noticably lower at 20 Hz.

An octave is a doubling or halving of frequency. 1/3 oct is one third of an octave. Why octaves? Because there are certain properties that translate well in octaves.

Warble tones are audio signals that randomly jump around within the specified frequency range, e.g., 1/3 oct. Why warble tones? Pure tones tend to excite room responses and upset the results of measurements. Warbling spreads out the signals and produce better measurements.

Pink noise is a particular kind of noise that produces flat responses in sound pressure measurements. If you are using a spectrum analyzer, and the sound system has a flat frequency response, pink noise should produce a flat spectrum on the analyzer. White noise does not.

I imagine you have a Radio Shack SPL, which seems to be the most usually available kind. If you also have the DVD that came with the Hsu subwoofer, then making measurements using warble tones is simple. Put the meter at the listening point. Set the meter for C-weighting and Slow. Set the dB level to the level just above the one where you get readings from room noise. Play the Hsu disk from Track 9 (I think) forward. Play it through once and set the volume on your receiver so you are getting a maximum of +5 dB on the meter. Then play it back through and record the meter reading in each segment. What you get is the sound levels in each of the frequency bands, comprised of both the system response and room effects.

Ideally, you should have equal readings in all bands. You won't. Room effects alone will prevent it. If you move the SPL meter to a different location, you'll get different readings (Also, the SPL meter gives progressively weaker readings below 30 Hz). If you move to a number of locations, make measurements, and then average the results in each band, that will give you a better approximation of the system response. If you plot the result (in dB), and draw a smooth curve through the results, you should be able to spot approximately the point at which the system rolls off more than 3 dB. But don't be surprised at seeing variations a LOT bigger than 3 dB from band to band.

[Joel McIntosh]

Retread: Thanks a million. I understand this issue much better now. I'll follow the directions you gave and see what I come up with. Thanks again for the help.

BeFree: Yes, I really like my RTi8s too. They were a great choice for my HT and budget. I'm having to bypass the receiver's crossover because my Marantz DV-8300 SACD player's one major flaw is it's weak bass management. It only allows me to set my speakers to "Large" when playing SACDs and DVD-As, and I just don't feel that the RTi8 (RTi70s) offer enough bass without the aid of the subwoofer.

[BeFree]

Not enough bass with your Rti8's????

What are you listening to -- organ music??!!