I had measured the distance between the speaker frame and the dust cap of the woofer and off-set the tweeter by that difference. I assumed that the tweeter is reasonably flat vis-a-vis the baffle. I found the difference to be around 1" between the speaker frame and the dust cap. You can use the below method:
1. Keep a steel foot ruler across the speaker frame along the diameter of the woofer.
2. Use one more steel foot rule to measure the difference in mm from the dust cap to the ruler in the point 1. This is the difference in the acoustic center which you will need to align w.r.t the tweeter.
Once you have arrived at this distance you can offset the drivers by either using a sloping baffel (more difficult) or use the method in my design to offset it.
As per my research in the web, the offset will be useful only if you are using a 1st order filter as the 1st order filter has zero phase shift and you will require your acoustic wavefrount to also be with zero phase shift. For higher order filters there is already a phase shift introduced by the cross-over hence the time-alignment will anyway not help.
Also there is a overlap of frequency between the woofer and tweeter due to the gradual roll-off due to the 1st order filter. This would cause cancellation of certian overlap frequncies if they are not aligned in time and the sound stage will lose detail. Hence all 1st order filter design will have to use somekind of time-alignment for allowing coherent sound stage. This will enable both acoustical coherence and zero phase shift due to 1st order filter. Also the drivers need to be wide-bandwidth type to have atleast response of 3 octaves on either side of the cross-over frequency to prevent any resonance effect in the overall speaker system
Hello All,
Photographs of my first Transmission Line speaker system some details below,
Woofer - 6.5" Peerless Kevelar cone for tight bass and smoother mid-range (wide range drivers). Has a reasonable flat response till 5KHz after which roll-off begins. There is a small un-even response between 180Hz to 500Hz (+/-2dB) and between 1KHz to 2.8KHz(+/-4dB). Used some response shaping circuits for these driver anomolies.
Tweeter - 1" Low Fs Peerless Aluminium Dome for smooth and mellow highs (wide range drivers). Has a rising response from 2KHz till 20KHz (+/-3dB). Used some response shaping circuits for these drivers from 3KHz till 20KHz.
Enclosure Type - Transmission Line with traingular wave guides, Time aligned enclosure (coherent sound stage) and diffraction corrected.
Tuning frequency - 34Hz (Quarter wave length)
Frequency Response (-6dB) - 19Hz to 22KHz
Sensitivity - 91dB/w/m
Cross-over - 1st order zero phase shift Butterworth cross-over network, zobel correction, L-pad, parallel and series notch, contour circuits and Baffel step compensators.
Nominal Power - 150 Watts
Nominal Impedance - 6 ohms
Cross-over frequency - 3000Hz (1st Order)
Features:
- Guided wave Transmission Line enclsoure ensure no boomy bass stimulating atmosphere of live performance and extended dynamics
-Wide range drivers ensure optimum performance in the enitre frequency band-width of the speaker system
-1st order filter, time alignment and diffraction compensation on the baffel ensures Excellent on & off- axis response
-Harmonics balanced to ensure real life performance of music and vocals
-Zero phase-shift 1st order Butterworth filter ensures excellent transient response without ringing/ ripple effect and faster settling times for the filter due to fewer passive components
- Cross-over of 3000Hz is more than 3 octaves above the resonating frequency of the tweeter (672Hz). Lower cross-over design helps in preventing cone break-up for tweeters at higher volumes. Also wide frequency response of the woofer allows cross-over at 3KHz there by preventing inter-modutlation distortion. Transmission line design helps in very smooth and balanced mid-range allowing flat impedance range for the entire operating range of the woofer. This allows in better power transfer between amplifier and speaker allowing low vibration of the woofer cone improving sonic performance. There are a total of 15 passive components in the cross-over including 2 actual cross-over filter components.
Photographs of the back of the speaker
Hello Hari,
Your speakers look very nice,
I Accidently happened to find this forum, and am mightily impressed by members work and enthusiasm here.
This is my first venture into Diy, I have no knowledge about making speakers , I read through many threads in this forum before posting this.
I found Address of varsha Electronics, for peerless India Drivers which have been given good reviews in some threads, and you are also using Driver from same brand in your Transmission line Speaker System.
may I request your guidance in making DIY Speakers.
Spirivous is also attempting a DIY bookshelf since quite some time.
Doc,
Remember to carry your surgical blade .... to cut open the TL BS ..
Expect to find 'hollow wilderness' packed with cotton-like fibres (acrylon) only :indifferent14: which gives out audiophile grade SQ
Hey Ashish,like the vivid description
my OB diy thread has the pictures of work in progress... (http://www.hifivision.com/diy/26099-diy-open-baffle-experiment.html). I am getting a few modifications to the baffle by removing the top horizontal strip and reducing the side supports from full length to 12" from bottom. In the meantime I am finding out where to source the inductor and resistor that you mentioned. importing from parts-express is turning to be expensive!
the 3" peerless project is on hold because I was waiting for you to give me the TL design and dimensions. recall our last PM conversation... . I though I won't bother you too much during your vacation.