need help tuning TL sub

[zobsky]

built a rather large TL sub a month ago (with generous help from members of this forum)

i stuffed at about 0.8 lb polyfill per cu. ft (IIRC)

i borrowed a radioshack digital SPL meter this week so i set out to benchmark it in room. i'm not sure of the correction factors for the digital model, .. so i assumed the correction factors available on the internet for the old meter were valid

my current mains in this room (sold the maggies) are a pair of paradigm 11se rear ported boxes which i've had for a long time.

in the experiment, .. the SPL meter was mounted at ear level equidistant from the mains at about 2.5 m and all lowpass / eq. etc on the yamaha c-70 preamp / behringer x-over have been defeated.

the sub and the mains have been tested seperately

on plotting the results, .. the 12 ft TL intially tuned for 22Hz as per MLK mathcad model and GM's spreadsheet still doesn't hit the low bass very well (in fact i cannot hear or feel any bass till around 35Hz,

.. likewise for the mains (the paradigms with a spec'd -3db of 35Hz can easily shake the walls in other rooms but sound anaemic in this room).



any suggestions specifically for sub tuning / troubleshooting , ..

the driver is an adire shiva 12" DVc wired in 4ohm. the sub has been dressed up somewhat since the last thread

[zobsky]

the graphs (first one is for the sub, 2nd is for the mains, .. haven't bothered with combined response at this point)

the correction factors i used are also included

[johninCR]

Did you try different locations in the room for measuring? It may be your room that needs tuning first, or sub location, or both before tuning your line. Measure from the listening position first. It may be that you were in a null to measure.

[1audio]

What are you expecting to hear? A good subwoofer needs to be very very loud to hear anything below 35 Hz if it isn't distorting. First look at a Fletcher Munson curve to see how loud it must be to be comparable to a 70 dB 1 KHz tone.
( http://www.allchurchsound.com/ACS/edart/fmelc.html )
At 20 Hz it needs to be 105 dB. The RS meter uses the C curve - almost the reciprocal of this curve so it will also read very low.

Many woofers impress with their low bass output, but on close inspection its the 2nd, 3rd and 4th harmonic people are hearing. Low distortion bass is rare in consumer products. unfortuntely its also harder to sell because it doesn't sound as loud. Listen to music for a while before you judge the performance.

Room effects will also be very significant in the woofers perceived performance. If the woofer or the listening position is in a bass hole you will never hear bass. There is lots of discussion of this on the web.
-Demian

[BillFitzmaurice]

Measuring SPL will tell you what is happening but it won't tell you why. You have to run an impedance sweep to find the actual Fc of the line.

As far as measuring low frequency SPL is concerned you can't get accurate results in room other than when measuring close-field as the room response modes will dominate.

[zobsky]

Originally posted by BillFitzmaurice
Measuring SPL will tell you what is happening but it won't tell you why. You have to run an impedance sweep to find the actual Fc of the line.

As far as measuring low frequency SPL is concerned you can't get accurate results in room other than when measuring close-field as the room response modes will dominate.

thanks all !

okay,. i'll rig up an impedance jig, retest with these tones and respond back

regarding the low bass (20 - 25 Hz), tried different locations .. i can see the cone moving but cannot sense (hear / feel ) anything even nearfield.

[ashok]

regarding the low bass (20 - 25 Hz), tried different locations .. i can see the cone moving but cannot sense (hear / feel ) anything even nearfield.

If you did , you'd be a very special person compared to most of us ! Pump it up to 200 or 500 watts and it might be a different ballgame !
Careful , high spl's can kill your hearing. It's worth saving till you are about 80 or so .
Cheers.

[GM]

I don't remember, please post the details of the design.

GM

[BillFitzmaurice]

regarding the low bass (20 - 25 Hz), tried different locations .. i can see the cone moving but cannot sense (hear / feel ) anything even nearfield

If the speaker's passband doesn't extend that low the movement of the cone will not transform into sound; even if it does at 20 Hz the average ear will not hear it except at high dB levels. See:Fletcher-Munson curves. For that matter at 20 Hz a RS meter is not going to register accurately.

[zobsky]

Originally posted by GM
I don't remember, please post the details of the design.

GM

you asked for it looking for BIG sonotube transmission line advice

basically, a downfiring adire shiva in 4 ohm config. in a 12 ft open sonotube made up of 3 sections of 4 ft. sonotube spliced together with a sleeve re-inforced with liquid nails

stuffed with polyfill at about 0.6 - 0.8 lb per cubic ft (around 0.5 lb per linear ft)

Originally posted by BillFitzmaurice


If the speaker's passband doesn't extend that low the movement of the cone will not transform into sound; even if it does at 20 Hz the average ear will not hear it except at high dB levels. See:Fletcher-Munson curves. For that matter at 20 Hz a RS meter is not going to register accurately.

yes, i know the RS meter isn't to be trusted at the low end. i was looking to the SPL curves to troubleshoot for potential issues. my ears still feel there is something wrong with the very low bass (eg. on electronic music, sometimes low synth bass notes just fall off a cliff)

definately, .. the impedance curves would be better, .. can anyone suggest a simple fairly accurate proven way of doing this (far too many ways of doing this on the web?)