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audiophile.1963
02-04-2010, 02:16 PM
Hi,
years ago (1994) I assembled a cabinet like L250 (same form) but using different woofer and tweeter. This four way system uses a woofer 2231h, mid bass 2118h, mid high 2105h and 2403h tweeter. I don't know the crossover's cuts but I woud like to know the right volume for the 2231h because for me the guy which calculated the volume, made a terrible mistake calculating a volume very very less than the right for this woofer.
Thanks
Giuseppe

Ruediger
02-05-2010, 06:46 AM
Several combinations of box volume and port dimensions are possible.

Please do tell me the box volume and the number and dimensions of ports.

If possible find out the DC resistance of the series coil (bass coil) in the crossover as well.

Ruediger

Mr. Widget
02-05-2010, 09:12 AM
years ago (1994) I assembled a cabinet like L250 (same form) but using different woofer and tweeter. Very interesting project!

In answer to your question, you will get the most linear performance from that woofer with a 5 cu ft box (~142 liters) with a port or pair of ports tuned to 30Hz.


Widget

Robh3606
02-05-2010, 09:13 AM
Download some box software and try yourself. It's easy. It thats a correct size L250 box it's about 4 cubic ft for the woofer. The sub enclosures for the 2118 and 2105 should be the same as 108H and 104H

WinIsd

http://www.linearteam.dk/default.aspx?pageid=winisd

Rob:)

audiophile.1963
02-05-2010, 09:19 AM
Thank you very much for your reply Ruediger.
Today I have measured the box inside.
The volumes of the three loudspeakers:
2231h 78784 cm3 = 79 litres
2118h 10120 cm3 = 10 litres
2105h 225 cm3 = 2,2 litres
The woofer has four reflex tubes deep 30,5 cm with a diameter of 7,5 cm and there are 13 cm between the centre of every hole. The volumes of the cabinets were calculated in 1993 by a guy with a mic and a software (I don't know what software) but I fear that the volume should be less than the right because with a 15" woofer I would listen a bass more low (It should be my impression, because I listen these loudspeaker from a lot of year). Now they are in the laboratory of my woodworker for a restyling: I could increase the volume with other 11 litres, more litres it should be a great problem. I don't know the crossover's cuts but I think very very low for the woofer, aroud 150hz. Please let me know your impression, thank you
Giuseppe

Ruediger
02-05-2010, 11:20 AM
Thank you very much for your reply Ruediger.
Today I have measured the box inside.
The volumes of the three loudspeakers:
2231h 78784 cm3 = 79 litres
2118h 10120 cm3 = 10 litres
2105h 225 cm3 = 2,2 litres
The woofer has four reflex tubes deep 30,5 cm with a diameter of 7,5 cm and there are 13 cm between the centre of every hole. The volumes of the cabinets were calculated in 1993 by a guy with a mic and a software (I don't know what software) but I fear that the volume should be less than the right because with a 15" woofer I would listen a bass more low (It should be my impression, because I listen these loudspeaker from a lot of year). Now they are in the laboratory of my woodworker for a restyling: I could increase the volume with other 11 litres, more litres it should be a great problem. I don't know the crossover's cuts but I think very very low for the woofer, aroud 150hz. Please let me know your impression, thank you
Giuseppe
1st the usual disclaimer: I may have made an error in my calculations.

The relevant Thiele Small parameters for the 2231H are:

fs = 16 Hz, Vas = 736 liter
Qt = 0.21, Qm = 5.5, Qe = 0.22, Re = 6.3 Ohms

Only one alignment from Thiele's tables fits: Alignment #2, QB3 (Quasi Butterworth 3rd Order)

f3 / fs = 2.28
f3 / fb = 1.32
Vas/Vab = 7.48
Qt = 0.209

Calculate the values for the 2231H:

f3 = fs * 2.28 = 36.5 Hz
fb = f3 / 1.32 = 27.6 Hz
Vab = Vas / 7.48 = 98.4 liter

I calculated the box resonant frequency for the current volume which is 79 liters. The result is 4 Hz. This is definitely wrong and reason #1 why the bass is so weak.

The f3 (36.5 Hz) is great for such a small cabinet! The 4430 monitor is not any better.

For a proper alignment we would need 98.4 liter. 79 liter plus 11 liter is a bit short but it would work.

The current volume (79 liters) is reason #2 for the weak bass.

Question: did You already subtract the volume occupied by the pipes from the box volume?

I will check if we can steal a bit volume from the 2118H, if it can live with less. If that was possible, could You do that? Make the chamber for the 2118H smaller?

==> BUT <== here comes the other side of the coin: the DC resistance of the series coil in a passive xover will make Qt larger, which is bad for us. A tube amplifier with output transformers will do the same.

Measure the DC resistance of that coil and tell me the inductance (milliHenry). Then I can check for a coil with a core and a low DC resistance.

In the worst case You must go "active".

Ruediger

JoMoCo
02-05-2010, 11:47 AM
Here is one simple, very practical, and really rather elegant way of increasing box volume through adding a stand courtesy of Zilchlabs...:hmm:

http://www.audioheritage.org/vbulletin/showthread.php?t=21007

audiophile.1963
02-05-2010, 03:38 PM
Thanks Ruediger,
... I forgot the volume of woofer and tweeter... what can I do to increase with no modifie the cabinet? ...and about the tubes, four tubes 30,5x7,5 cm, is it correct for you? I will can send you better informations next week: I have sent the crossovers to a serious laboratory and I will have real knowledge about cuts and the components only next week.
Ciao Giuseppe

Ruediger
02-05-2010, 11:17 PM
You told me the volume for the bass was 79 liter. Is the space for the 4 tubes included in this? If the 4 tubes were removed, how big would be the volume for the bass?

Ruediger

audiophile.1963
02-06-2010, 01:31 AM
An other thing that I had not thought… the tubes have a volume to embezzle ulteriorly!

audiophile.1963
02-06-2010, 02:28 AM
An Idea should be change the woofer with another JBL 15" (BUT WHAT?) but in this case I must change the crossovers too and I'm not very able to do this... considering that I don't know how much the filters are correct!

Ruediger
02-06-2010, 03:26 AM
An Idea should be change the woofer with another JBL 15" (BUT WHAT?) but in this case I must change the crossovers too and I'm not very able to do this... considering that I don't know how much the filters are correct!

The bass is okay, keep it.

Some "action items" for You.

1.) Get a circuit diagram of the crossover. Include all information which You have (DC resistance of inductors etc.).

2.) Calculate the volume of the bass cabinet when the bass speaker and the tubes are removed.

3.) See if it is possible to remove the internal box for the 2118 and replace it with a smaller one.

Take it easy! Ruediger

audiophile.1963
02-06-2010, 05:04 AM
Thank you very much for all information Ruediger. Next week I will send the crossovers to a real technicist who lives in Tuscany and I have just asked him a plan of the crossover, so I will have a real knowledge of the situation. I will inform you about all news. Thank you too, you are very kind
Have you a nice weekend.
Best regards, ciao
Giuseppe

audiophile.1963
02-08-2010, 10:16 AM
Hi Ruediger,

1.) Get a circuit diagram of the crossover. Include all information which You have (DC resistance of inductors etc.).
I have sent to the laboratory a picture and they said me that it will be very very difficult "to translate" te filter (see the picture)

2.) Calculate the volume of the bass cabinet when the bass speaker and the tubes are removed.
The five tubes are 5 liters + 2 liters speakers

3.) See if it is possible to remove the internal box for the 2118 and replace it with a smaller one.
The volume for the 2118H is correct and I can't touch.

A solution should be to copy the original filter of L250 (the first) modifing only the bass (2231H) and the high (2403H) part of the filter because the other components (mid bass/high) are the same. The cuts are OK for the loudspeakers. But I don't know if it is possible and is yes, how. About the volume I will take a solution.

Ciao
Giuseppe

Ruediger
02-08-2010, 11:21 AM
Hi Giuseppe,

That network looks like a plate of spaghetti :)

I do not want to modify the crossover. I wanted to see if there were resistors in series with the drivers, and what their values are.

If possible, I would like to know the resistance of the 7.4 mH bass coil. To measure that a "Milliohmmeter" would be good. A general purpose multimeter will not do unless the person who does the measurement really knows what he's doing. He might also build a Wheatstone bridge with a couple of resistors. To access the bass coil use the "+" input to the crossover and the "+" wire to the bass.

I do not understand Your remark about the 2403 tweeter. I did not want to change that.

If I got You right
1.) the volume of the bass cabinet is 79 liter
2.) plus another 11 liter available somehow(?)
3.) plus 5 liter occupied by the tubes
for a total of (79 + 11 + 5) liter = 95 liter? Is that true?

As soon as I have Your answer I will calculate and make a suggestion.

Ruediger

audiophile.1963
02-08-2010, 01:47 PM
Hi Ruediger,

The network is a plate of spaghetti, but a bad a plate of spaghetti!:)

I do not want this crossover:blink:. I want build a new crossover, like the original, as the plan that I sent you. The photograph is the crossover of my L250 clone but the plan is of the first original crossover of L250. My question is: considering that the cuts are the same but that I have a different woofer (a 2231H not a LE14H) and a different tweeter (a 2403H not a 044-1) may I use this plan of crossover, modifing only, if it is necessary, the part regarding woofer and tweeter? For the woofer we can use the T&S Parameters. Now the 2231s are to the "doctor" for reconing:(

Yes: 79 + 11 + 5 liters = 95 liters. It Is true, a tube is 1,25 liter.
Let me know

Thank you very much, you are very kind:)

Ciao
Giuseppe

Ruediger
02-14-2010, 09:59 AM
Hi Giuseppe,

Here comes the data.

I had made a mistake in my calculations. In the current configuration the box resonates at 43.3 Hz, and not at 3 to 4 Hz. But still the 43.3 Hz is wrong.

I take Your speaker's Qt as the start parameter and see what the box volume, the box resonant frequency and the -3dB frequency will be.

The value for Qt depends on the resistance which is in series with the speaker. There is the amplifier output resistance, the resistance of the loudspeaker cables, and the resistance of the bass coil in the crossover. I call that resistance Rser.

The following table shows some possible alignments.

#1 Rser=0.0 -> Qt=0.212 -> Vb=087.4, fb=31.0, f3=40.9
#2 Rser=0.1 -> Qt=0.215 -> Vb=091.9, fb=30.5, f3=40.0
#3 Rser=0.2 -> Qt=0.218 -> Vb=096.5, fb=30.0, f3=39.1
#4 Rser=0.3 -> Qt=0.221 -> Vb=101.3, fb=29.6, f3=38.3
#5 Rser=0.4 -> Qt=0.224 -> Vb=106.3, fb=29.2, f3=37.5

The available box volume is 79 + 11 + 5 liter (roughly). The tubes will require some volume.

Alignment #2 would require a bass coil with 0.05 Ohm resistance, that would cost a fortune. No way. But if the loudspeaker was connected directly to the amplifier (using an active crossover) alignment #2 would fit. The required volume is 92 liters, quite exactly what we have.

Alignment #3 would require a bass coil with 0.15 Ohm resistance, that would still be quite expensive. The required volume would be 96.5 liters, a bit more than we can offer, but not really a problem.

Alignment #4 would require more than 100 liters, which we do not have.

Only alignment #2 will be a perfect one. All other alignments will suffer from imperfections, even if You spend lots of money on very good bass coils. These alignments will not have the perfectly flat frequency response.

I still do not know the DC resistance of the bass coils in the current crossovers.

Lets assume that You design the box for alignment #2. This means 92 liters net volume, box resonant frequency of 30.5 Hz, and a -3dB frequency of 40 Hz.

Let us reuse Your tubes of 7.5 cm diameter. The end correction is 5.5 cm, that means the effective length of such a tube is 5.5 cm longer than the physical length.

The assumption is that one end is flanged and the other end is not. Is that true?

Also both ends of the tubes must be unobstructed. Is that true?

If we use two tubes and block the other ones then the effective tube length must be 31.1 cm, which is 25.6 cm physical length plus 5.5 cm end correction.

If we use three tubes the length must be 46.7 cm which is 41.2 cm + 5.5 cm.

If we use four tubes the length must be 62.3 cm which is 56.8 cm + 5.5 cm.

So using two tubes and closing the unused ones seems to be the best way.

If You know the DC resistance of the current bass coils and if You want to keep them then I can optimize the design for best flatness. That would result in a slightly different length for the tubes.

Tell me what You are going to do.

Ruediger

audiophile.1963
02-15-2010, 09:37 AM
Hi Ruediger,
wow! That job! Thank you very much!:)
I have translated in italian and now I will make a test closing and modifing the tubes with the "spaghetti crossover". I understand that It should be correct to measure the values in laboratory directly is for the volume that for the crossover. For this last one, as you will have seen, it had been advised the crossover to me of the JBL 4315H, the 3114h even if my first chosen it is that one to work on the crossover originates them of the L250. What do you think about?

Hello and thank you very much, too!
Have you a good week

Giuseppe