The plots show the influence of diffraction at baffle edges. The are irrelevant in the low bass range.Originally Posted by more10
Ruediger
The plots show the influence of diffraction at baffle edges. The are irrelevant in the low bass range.
Ruediger
See post 83.
You could use for example 2220 in your current boxes, and use E-145 in a huge MLTL or Tapped Horn.My idea would be, to reduce the internal volume from 8ft³ to 5-6ft³ and change the ports from 38hz tuning to aprox. 50hz. This smaller enclosure should gain 2-3db between 50-100hz and give me the punch I´m looking for.
Below 50hz I would use a dedicated sub.
The plot shows box modes. You are using it for midrange as well.
In case you are curious about your box mode frequencies: http://www.mh-audio.nl/standingwaveinbox/calculator.asp
Wow, thanks for the great response!!
@berga:
I will definitely use a highpass at 40-50hz after tuning the enclosure higher.
@mortan:
I will use subs below the E-145, there is no alternative! (btw. most of you guys have told me that before, shame on me... )
A 2220 should provide similar or even worse response than the E-145 in this enclosure. I think the 2220 should rather be used in a horn...
The box will definitely have some nasty boxmodes, that is why I´ve put a lot of acoustic damping in the rear of the box. Still kept a reasonable path between cone and ports free.
@grumpy:
I should get styrofoam from "DOW" here, that would be the easiest way to test a smaller enclosure. Sandbags would be nice for the sound, but if one of them gets damaged it would become a big mess...
@Rüdiger:
Could you please post the documents again, I can´t find them anymore.
2220 has an amazing midrange!A 2220 should provide similar or even worse response than the E-145 in this enclosure. I think the 2220 should rather be used in a horn...
"General Audio Discussion" -> "Technical References" Thread -> "Thiele Paper"
Below is a worked example. It does not fix the problem completely but it can shift parameters in the right direction. It also helps in making educated guesses.
E145 data:
fs = 35 Hz
Qt = 0.25
Qm = 6
Qe = 0.26
Qa is the same as Qm
Vas = 275 ltr
Re = 5.7 Ohm
Re is the DC resistance of the voice coil
Rg is the "Generator resistance". It consists of the amplifier's output impedance, the cables' resistance and the DC resistance of all bass coils in the xover which are in series with the loudspeaker.
The "damping factor" for a certain load is the ratio between load and the amp's output impedance. A damping factor of 200 at 8 Ohm means that the amp's output impedance is 8 / 200 Ohm = 0.04 Ohm.
The specific resistance of copper is 0.015 Ohm * mm**2 / m. Lets assume a cross section of 2.5 mm**2 and a length of 5 m (times 2, back and forth).
Rcable = 0.015 Ohm * mm**2 / m * 10 m / 2.5 mm**2 = 0.015 * 10 / 2.5 Ohm = 0.06 Ohm.
A typical bass coil (inductor) for an 8 Ohm / 1 kHz crossover 2nd order has an inductance of 1.8 mH and a DC resistance of 0.5 Ohm.
Our "Generator resistance" is 0.04 Ohm (amplifier) + 0.06 Ohm (cables) + 0.5 Ohm (crossover) = 0.6 Ohm. You can try 3rd order crossovers as they need more and larger coils.
We put this into equation 70 of the Thiele paper and get a new Qt of 0.274. With this value we can interpolate between alignments 3 and 4.
For a spot landing at a Qt of 0.383 we would need a generator resistance of 3.27 Ohms. A tube amplifier with output transformers may also help you.
You can experiment with large ceramics resistors at your speakers input terminals to get a clue what the impact would be.
Ruediger
You can have room standing Waves issue. Have you some room correction absorber/diffuser?
I believe the published E145 Vas value is grossly inaccurate... closer to 427, IIRC.
Worth validating.
Beautiful work. Holz was the name given to me in my German language class back in high school. It was the closest the instructor could get to Woody.
@Rüdiger:
I had a look through the mentioned thread but couln´t find the Data.
The series coil in the crossover for the E-145 has 1,5mh and 0,08ohms, so even less then your calculations.
I was told, the smaller the impedance of this coil (and cables etc.) the better the damping factor of the ampflifier and this resulting in a more controlled sound.
Putting big resistors in series would ruin this advantage, but Im no expert on crossovers and open to your ideas.
@berga:
I definitely have standing waves issues, who hasn`t
So far there are no absorbers or electronic corrections, but I have moved the speakers to different spots and have listened to them in two different rooms so far.
There are the usual peaks and dips in my rooms, but these aren´t responsible for my major issues. In these huge enclosure they reach very low (for this speaker), but loose efficiency below 100hz.
The complete lowend below 100hz is weak, not just several frequencies...
@grumpy:
I was told the same and always simulated with VAS=427....
@Woody a.k.a. Holzy:
Thanks, I really cherish your competent feedback!
Dr.db, I really admire your skill to make such a beautiful enclosure!
Supporting E145, JBL did E145 with 2215H "staggered" for UREI 813C. They didn't cut the low end of E145.
801C is a coax unit made with E145+2425H.
http://www.jblproservice.com/pdf/URE...s/813C-L,R.pdf
1.) General Audio Discussion, 3rd entry: Technical References, 11th entry therein.
2.) I did some example calculations with "typical" values, to show the principle.
3.) Yes and no.
A speaker with a Qt of 0.7 or more is crap, cause you can't find reasonable alignments for such speakers.
A proper amp should have a damping factor of 200 or better (my personal opinion),
but cables and series coils allow you to adjust a speaker's Qt and thus meet the requirements of a certain alignment.
Less is not always better.
You can experiment with big resistors in series, so you see what you have to expect. When your done with your experiment hide the resistors
4.) Is there nobody in Northern GY who can measure TSPs?
Ruediger
I looked around for a hopefully understandable article about how to measure TSPs. This is what I found and recommend: http://sound.whsites.net/tsp.htm.
If you just want to know Vas you don't need to measure all the other parameters, just Fs and Fb, and Vb of course.
Ruediger
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
