double bass provides better FR???

[samnor]

Hi,
I thought I'd post this question to you audiophiles (I'm not one... more of an enthusiast) on the impact of "double bass" and low frequency extension/output. Before I get any flames, I am well aware that many think "double bass" settings on AVRs are a gimmick to satisfy those who want their floorstanders to run full range and are upset when audyssey labels them as small.. anyways...

I have a non hsu sub that is rated to go down to 30hz , a pair of wharfedale diamonds that are rated to go down to 32hz (-6db) and I have an onkyo (very basic receiver) with only 65wpc... I took out my spl meter to do some calibration and experienced something that I cannot explain...

When I have the crossover set to 80hz, all speakers small, I get 71db (70db being my ref level) at 25hz (using a 25hz test tone from the binks audio test cd) so the sub placement is getting me a better than rated extension... All frequencies above 25hz are getting more than 80db with 31.5 hz getting 86db...

however, if i turn on double bass with my fronts set to large (supposedly some amount of bass (not sure if its everything below my 80hz crossover) is going to both sub and full range is going to fronts), I get a 70db reading at 16Hz, 75db at 20hz, 86db at 25hz and 90db at 31.5hz...

Whats puzzling me is when I listen to regular music, I feel tighter bass with the double bass on vs higher bass output with the double bass off even though the spl's above indicate I should be getting more output(more extension appears to be a given) with double bass.

probably, there are other room notch effects in the mid bass frequencies that appear to convey more bass output with double bass off whereas the frequency response with the double bass may be smoother since the sub may not be hitting that "room-notch" frequency at all......

sorry for the length of the thread but I'd appreciate y'all putting in your 2cents and whether you've experienced stuff like this...

Thanks,
Sam

[Pete_Hsu]

Hi Sam,

Do you have any measurements above 31.5Hz to share with us (ie 40/50/63/80/100Hz)? What crossover frequency are you using when everything is set to "Small", and do you have the ability to adjust the crossover frequency on the receiver?

Based on your current measurements, we can see that the system is actually already starting to roll off below 30Hz, as expected.

Setting all speakers to "Small" will give you wider dynamic range by taking strain off the main speakers from having to reproduce lower frequencies. That said, with a single subwoofer placed in a corner and using an 80Hz crossover, you may be getting more mid-bass response anomalies too.

Sincerely,

[samnor]

Hi Pete,
My crossover is 80hz with or without the double bass setting. I am also wondering as you pointed out whether I get a room notch effect with the mid bass range over 40hz-80hz which artifically boosts the bass so that the sound without the double bass option appears louder. Since onkyo receivers seem to change the crossover with the double bass on, it might be that I bypass the notch range of the sub and that smooths out the FR. On the flip side it might be that I may have a "suck-out" and a drop in the 40hz-80hz with the double bass on due to the standing wave cancellation between the fronts and the sub (since the fronts run full range with double bass and dont have a crossover limit). I need to verify that the spl doesnt drop in that mid bass area with double bass on vs whether I get a boost from the sub when double bass is on...

My ulterior motive here is to also determine whether another sub such as the stf-2 or the vtf-1 which has a 25hz tuning will help to work in a stereo sub setup. My budget and room size (16x13x8) suggests the above will be most suitable. at the same time, I dont want to throw away my current sub which does seem to extend nicely enough to 25hz. I know its not recommended to have two subs of different brands but if they extend to a similar frequency, that might not be a bad thing, right... my current sub is a wharfedale with 250watt rms, 10" downfiring sealed driver.

Thanks,
Sam

[Pete_Hsu]

Hi Sam,

I'd say that it would be worthwhile to add the VTF-1 to your system to see if it can help to smooth out the response. Included with the VTF sub is a test tone CD that has 1/3 octave-spaced test tones from 16-200Hz, which will help immensely to understand the differences noted above.

Even though mixing and matching different subs can give unpredictable results, it can certainly be a notable improvement vs just one subwoofer. We recently had a customer who had a Klipsch 10" subwoofer up front, and added a VTF-3 MK3 12" subwoofer in back, with reportedly very good results.

Sincerely,

[samnor]

Hi Pete,
I did a broader sweep going up from 31.5hz, 40,50,60,63, 70 and 80 hz... what I found was interesting. Running the fronts at full range with double bass on does create a "suck-out" in the mid bass range.. After hitting 90db and 88db at 31.5hz and 40hz, the rest of the frequencies drop off down to around 80db... whereas the version without double bass and crossover set to 80hz with fronts running small actually has consistent 88-90+db throughout the above range.. that explains why the bass seems to have more output with the sub handling the entire spectrum below 80hz..
One analog of this would be a vtf-1 running in the Max Output mode vs the double bass gives the max extension mode... I would probably be very interested in getting a vtf-1 to pair along with my wharfedale sw250. Another question I do have is that the wattage of vtf-1 is about 50watts lower rms, so I guess thats about a 1/2 db drop off.. that shouldnt cause any blending issues, right... how do we go about hooking both up if I have them... use the y-adaptor or do you recommend daisy chaining...
Thanks,
Sam

[Pete_Hsu]

Hi Sam,

Looks like the double bass option results in some cancellation, leading to a dip in the response in the 40-80Hz region. So it is interesting that you prefer music with the double bass option enabled! Could you describe the subjective differences in more detail when comparing double bass enabled to disabled?

The VTF-1 actually uses a 250w amp, just underrated at 200w. To connect two subwoofers, simply split the signal at the subwoofer pre-out on the receiver using a y-splitter, and feed one low level rca input on each subwoofer.

Sincerely,

[samnor]

Hi Pete,
Actually I prefer the version with NO double bass (basically sub takes all frequencies below x-over of 80hz) since it seems to correspond better with the "max output" mode but it does seem to bottom out at 25hz. Granted I havent raised the volume level on the AVR nor have I raised the gain on the sub in order to see if I can hear even lower frequencies below 25hz. I didnt want to raise it further since I am already at a master volume which is quite high.

whereas the bass is tighter but weaker (for the same reference volume) with double bass on... So I certainly like more output but I was pointing out that I seem to get better extension with the double bass on for lower frequencies below 25hz and am hearing more detail but less oomph with it...

I am wondering if two subs will raise the db level so that I can run it in the "no double bass" mode and actually hear frequencies below 25hz without having to raise the volume/gain.
Thanks and appreciate all your input...
Sam

[Pete_Hsu]

Hi Sam,

I do think that adding a second true subwoofer will work wonders for your system, I highly recommend that you try it out!

With the double bass option enabled, you mains seem to be positively contributing to the subwoofer at relatively low frequencies (25-35Hz region), but with cancellation in the mid-bass frequencies. The bad thing about double bass is that you really don't have flexiblity to move your main left/right speakers for better deep bass response, so you need to keep them in their current location for best midrange/high frequency performance. Having two separate subwoofers will give much more flexibility in terms of adjusting placement of the low frequency transducers to give a flatter deep bass and mid-bass response.

Sincerely,