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ompdiburi
01-24-2007, 12:37 PM
Hi guys.
I built a tower cabinet for my LE8T-H following the JBL PROFESSIONAL ENCLOSURE GUIDE:
Enclosure net volume is 3.4 cubic feet, (260x360x1150mm.), vent area is 12.6 square inches and 6.8 inches length. Inside I use different absorber materials like felt and foam-rubber.
According pipe is on the back side at 300 mm. from the floor. According to Jbl specs tuned frequency is 32 HZ, my dubt is that the low extension seems to be not so good as indicated.
May be the drivers are new and need time to match a good performance in the low end region…
Does somebody have any experience regarding a similar project?
One more question: I cut a baffle to house a 240x hf driver, at the moment I am using a 077 tw but I have also a 2402 H and waiting for 2403 horns, any suggestion about the best solution and filter network?
Thanks to all will help me.
Giuliano

GordonW
01-25-2007, 05:24 PM
What amp are you using? Paradoxically enough (or so it would seem at first glance), a tube amp may help bass extension, in an enclosure that big with a LE8T. The reduced damping factor of a tube amp, might allow the speaker driver to move "freer" in the bottom octave.

With solid-state amps, I've found that 2 to 2.5 cubic foot enclosures, tuned to around 30-35 Hz or so, seem to give good results. It may be that the 3.2 cubic foot enclosure is just asking too much of the driver (trying to force it to go low, at the expense of bass "weight" or "power"). You might want to try blocking off maybe .5 to .75 cubic feet inside the enclosure... solid objects like bricks or blocks of wood, can make good temporary "volume reducers" inside the box... just set them in the bottom of the box, and try listening again...

Regards,
Gordon.

ompdiburi
01-26-2007, 01:03 PM
Hi and thanks for your opinion.
Regarding the amplifier I am using to drive the speakers, it is a hybrid equipped with a vacuum tube input stage and a single ended class A power output stage using a parallel of three BDX53C transistors. This amplifier works very well driving a small TQWT speaker system using a 130 mm. driver 4 ohm impedance.
I agree with you that amplifier may be the problem and I am sure that more power is needed to drive the LE8T-H system, I will try to use different amplifiers and let you know as soon as I check.
Thanks
Giuliano

Flodstroem
02-18-2007, 07:39 PM
Hi and thanks for your opinion.
Regarding the amplifier I am using to drive the speakers, it is a hybrid equipped with a vacuum tube input stage and a single ended class A power output stage using a parallel of three BDX53C transistors. This amplifier works very well driving a small TQWT speaker system using a 130 mm. driver 4 ohm impedance.
I agree with you that amplifier may be the problem and I am sure that more power is needed to drive the LE8T-H system, I will try to use different amplifiers and let you know as soon as I check.
Thanks
Giuliano

Why didnt you built an ML-TQWT for your LE8T-H ? They are very/extremely good in application of this type of speakers. I have tried that (with less suitable 2115A) and it sounds very good down to ca 30-35Hz (tuned to half octave under fs). Also I have added a baffle steep correction filter to damp some higher frequencies which is a very useful filter for compensate purposes and for to "tune" in the speaker for the baffle, for your ears, room acoustics etc. Also, this type of application is absolutely worth to consider if you are going to drive the speaker with tube amps.
Regards

ompdiburi
02-22-2007, 10:11 AM
What do you mean for "ML-TQWT ?
In every case what I know is that the LE8 is not suitable for TQWT loading, maybe I am wrong...
I am not driving the speaker whit a tube amp, (only the input stage is by vacuum tube), the output stage is solid state.
Now I am using another amp with tube input stage and transistor AB class output stage, it delivers around 25 w, seems to be much better, also maybe the speaker is starting to work better...
thanks for yr opinion
Bye

Why didnt you built an ML-TQWT for your LE8T-H ? They are very/extremely good in application of this type of speakers. I have tried that (with less suitable 2115A) and it sounds very good down to ca 30-35Hz (tuned to half octave under fs). Also I have added a baffle steep correction filter to damp some higher frequencies which is a very useful filter for compensate purposes and for to "tune" in the speaker for the baffle, for your ears, room acoustics etc. Also, this type of application is absolutely worth to consider if you are going to drive the speaker with tube amps.
Regards

Flodstroem
02-22-2007, 11:01 AM
What do you mean for "ML-TQWT ?
In every case what I know is that the LE8 is not suitable for TQWT loading, maybe I am wrong...
I am not driving the speaker whit a tube amp, (only the input stage is by vacuum tube), the output stage is solid state.
Now I am using another amp with tube input stage and transistor AB class output stage, it delivers around 25 w, seems to be much better, also maybe the speaker is starting to work better...
thanks for yr opinion
Bye

ML-TQWT = Mass Loaded Tapered Quarter Wavelength Tube. This is a Martin J. King -design and you could read of it here:
www.quarter-wave.com

Also you could read of Transmission Line speaker here: (many pictures)
http://www.t-linespeakers.org/
(there is a lot of design suggestions for this ML-TQWT design)

When driving this speaker full-range you will also need a Baffle Steep Correction filter (Zobel) for your baffle. This filter will give you the opportunity to correct the frequency response and get more bass.
(you will find the filter design at M.J. King´s site)

ML-TQWT´s is the most suited TL-design for JBL speakers I have found out, but the LE8, LE8T, LE8T-2, LE8T-H, 2115 (A/B) are extremely well suited for a TL design and not only for the ML-TQWT due to their relative high Qts value. :D
Regards

ompdiburi
02-23-2007, 10:55 AM
Thanks, very interesting site, I like the TQWT sound, but the reason because I did not build a TQWT enclosure is because I read that speakers with a Qts parameter around 0,5 are not suitable for this application, so I decide for a reflex project.
One more question, are you using any HF speaker to help the JBl in the HI region?


ML-TQWT = Mass Loaded Tapered Quarter Wavelength Tube. This is a Martin J. King -design and you could read of it here:
www.quarter-wave.com (http://www.quarter-wave.com)

Also you could read of Transmission Line speaker here: (many pictures)
http://www.t-linespeakers.org/
(there is a lot of design suggestions for this ML-TQWT design)

When driving this speaker full-range you will also need a Baffle Steep Correction filter (Zobel) for your baffle. This filter will give you the opportunity to correct the frequency response and get more bass.
(you will find the filter design at M.J. King´s site)

ML-TQWT´s is the most suited TL-design for JBL speakers I have found out, but the LE8, LE8T, LE8T-2, LE8T-H, 2115 (A/B) are extremely well suited for a TL design and not only for the ML-TQWT due to their relative high Qts value. :D
Regards

Flodstroem
02-23-2007, 03:15 PM
Thanks, very interesting site, I like the TQWT sound, but the reason because I did not build a TQWT enclosure is because I read that speakers with a Qts parameter around 0,5 are not suitable for this application, so I decide for a reflex project.
One more question, are you using any HF speaker to help the JBl in the HI region?

Wander where you read about the 0.5 Qts not suitable for TL!!??
Especially, ML-TQWT´s are extremely well suited for JBL´s Qts values between 0.35-0.55
The type LE8T speaker is a full range speaker, but if not using a properly designed BSC filter its frequency response could be dominating in the mid freq. region and thats why you must use the BSC filter for to correct for speaker frequency response, baffles, and for room acoustics

If need be (your choice) you could use a small JBL "ti" dome tweeter for the UHF (crossed at > 12 kHz ca).

Regarding your amp´s output power capability: I feel the the 25 watts total power is far to small for to receive good, high output in the VLF regions. This speaker can withstand at least 50W of power (25 Watts RMS) and if trying to get high bass output with only 25 Watts at hands you will very soon reach the clipping level in the peaks/dynamics resulting in distorted heights and bass response. :( You could also damage the speaker due to it is not built for clipped/distorted audio signals. :biting: For to receive good sound reproduction from this speaker you will need a one that is capable of at least 50-75watts of clean power outputs for to make this speaker sense and if using a well design BSC filter, some of the power will be lost in this filter resulting in even less power to the speaker than what your amp is pumping out.

Myself uses a bridged NAD for those speaker (@ 90 Watts maximum outputs) and I feel it is amazing how much sound this small speaker is capable to re-create/produce, from 30 Hz to beyond 15 kHz.:p
Regards

ompdiburi
02-24-2007, 01:42 AM
I read that speakers with a Qts bigger than 0,5 are not suitable for TQWT on the italian magazine " Costruire HIFI", was the n. 17 of december 1995.
By the way, I will try to drive the speakers using an old NAD 2150 wich delivers around 75 Watts/ch. and let you know.
Regarding the HF speaker, I am now using a 2402H modified with a 2403 horn drived by a dedicated amplifier, (around 8 watts/ch with single ended vacuum input stage and solid state class A output), I use a 2.2 microFarad capacitor only, as network, (need to be improved).
Using a Biamp system I can balance the output levels of the speakers without lost power in resistance networks.
thanks again and bye
Giuliano


Wander where you read about the 0.5 Qts not suitable for TL!!??
Especially, ML-TQWT´s are extremely well suited for JBL´s Qts values between 0.35-0.55
The type LE8T speaker is a full range speaker, but if not using a properly designed BSC filter its frequency response could be dominating in the mid freq. region and thats why you must use the BSC filter for to correct for speaker frequency response, baffles, and for room acoustics

If need be (your choice) you could use a small JBL "ti" dome tweeter for the UHF (crossed at > 12 kHz ca).

Regarding your amp´s output power capability: I feel the the 25 watts total power is far to small for to receive good, high output in the VLF regions. This speaker can withstand at least 50W of power (25 Watts RMS) and if trying to get high bass output with only 25 Watts at hands you will very soon reach the clipping level in the peaks/dynamics resulting in distorted heights and bass response. :( You could also damage the speaker due to it is not built for clipped/distorted audio signals. :biting: For to receive good sound reproduction from this speaker you will need a one that is capable of at least 50-75watts of clean power outputs for to make this speaker sense and if using a well design BSC filter, some of the power will be lost in this filter resulting in even less power to the speaker than what your amp is pumping out.

Myself uses a bridged NAD for those speaker (@ 90 Watts maximum outputs) and I feel it is amazing how much sound this small speaker is capable to re-create/produce, from 30 Hz to beyond 15 kHz.:p
Regards

Flodstroem
02-24-2007, 04:21 AM
I read that speakers with a Qts bigger than 0,5 are not suitable for TQWT on the italian magazine " Costruire HIFI", was the n. 17 of december 1995.
By the way, I will try to drive the speakers using an old NAD 2150 wich delivers around 75 Watts/ch. and let you know.
Regarding the HF speaker, I am now using a 2402H modified with a 2403 horn drived by a dedicated amplifier, (around 8 watts/ch with single ended vacuum input stage and solid state class A output), I use a 2.2 microFarad capacitor only, as network, (need to be improved).
Using a Biamp system I can balance the output levels of the speakers without lost power in resistance networks.
thanks again and bye
Giuliano

Ok, ML-TQWT was not designed at that time, its a more resent design than the TQWT¨s. ML-TQWT is a TQWT, with the addition of a port, the same as in a base reflex design (ML= Mass Loaded from the mass of air in the port/tube). Thats also the reason for why you could use a wider span of Qts speakers for ML-TQWT´s.

Regarding your NAD ide this will be fine, and driving your HF by a Class-A amp would be the best choice I think. Networks need to be improved, yes and you should study this Forum for x-overs suited for that HF-speaker.

Good luck Giuliano :wave:
Regards