Another plan for open baffles

yup,ur right suri.once u've listened to good,no excellent(read urs,sg's) TL applications,just cant think of wanting anything else ;)!!!

am for sure hooked,'T-Lined' and sunk :p.cheers
 
I think the members are reasonably happy to get their SQ at a given budget without indulging in the complexities of cabinet making

but looking for the pot of gold at the end of one's rainbow? -

well, with this vitriolic - i hope i can dissuade some of the reading public from -

abusing (family) finances on ill-advised ventures.
 
hmmm,

Suri, Sorry to hear that your open baffles sucked. I should count myself lucky that mine did not. In fact they were pleasant not only to me but to all(not even a single one disliked the sound) the guests who visited me.I didn't ask anyone if they liked the speakers. It was always a spontaneus response that the speakers are sounding good. I admit that they were not all audiophiles but one of them was.

I have never heard TLs but i have heard some good speakers(including Quad floor standers with Denon 710, PSb towers with NAD, JBL E seriestowers with HK3490, Denon with jamo C series, Wharf towers with NAD and CA 650). All these speakers are considered good by many people. I liked OBs after hearing those.So come what may, I can't get OBs out of my head. After all perception of sound is personal.:)
 
I used a pc based active xover setup using my Creative Audigy Value 5.1 sound card. Used foobar with foo_dsp_xover plugin. The sound card outputs were directly connected to the amplifiers via RCA connectors.

Dainty is a cheap Taiwan make speaker. It should be easily available with the local speaker dealers. I bought it from Globe in SP road Bangalore, forgot what price i bought it - might be around 300 rupees. The model no of dainty is PF0820B(8Ohms 50W). I can post the measured TS parameters if you need it.

Hi antony, i just picked up the dainty PF0820B from sp road..it would be a great help if you could post the ts parameters. thanks!!!
 
Hi Karthik,

Here are the measured t/s params of my dainty PF0820B.

Fs = 45.06 Hz
Re = 7.50 ohms[dc]
Le = 1525.41 uH
L2 = 592.00 uH
R2 = 1.25 ohms
Qt = 1.07
Qes = 1.53
Qms = 3.54
Mms = 19.57 grams
Rms = 1.563969 kg/s
Cms = 0.000637 m/N
Vas = 51.79 liters
Sd = 240.53 cm^2
Bl = 5.212395 Tm

I haven't measured the xmax - my guess is it will be <= 4mm.

Are you planning to use it in an OB arrangement?

Regds...
 
Thanks a lot antony. i am not planning to use it in an OB environment but planing to construct a sealed enclosure. I am using winisd with these parameters and the enclosure volume seems to be too high and in the range of 9.35 cubic feet. am i doing something wrong here??? i was thinking about a enclosure volume of around 0.5 cubic feet. please let me know if i have missed something here
 
Thanks a lot antony. i am not planning to use it in an OB environment but planing to construct a sealed enclosure. I am using winisd with these parameters and the enclosure volume seems to be too high and in the range of 9.35 cubic feet. am i doing something wrong here??? i was thinking about a enclosure volume of around 0.5 cubic feet. please let me know if i have missed something here

The high Qts of this driver will raise the QTC(Overall Q) to about 1, which cold translate to boomy bass in a cabinet of modest dimensions. WinISD is trying to attain flattest response, that could be the reason for the high volume of enclosure.

You will not get tight bass from this loudspeaker in a home environment. However in a car the cabin gain could compensate for the lower end removing some of the boominess.

If you are willing to experiment, you need to have a good equalizer at your disposal.

Regds...
 
Thanks antony. yeah as you mentioned this is slightly on the boomy side, but i have controlled it to some extent with the equilizer settings initially and inside a car environment. hopefully i must be able to reduce that some more.
 
hmmm,

Suri, Sorry to hear that your open baffles sucked. I should count myself lucky that mine did not. In fact they were pleasant not only to me but to all(not even a single one disliked the sound) the guests who visited me.I didn't ask anyone if they liked the speakers. It was always a spontaneus response that the speakers are sounding good. I admit that they were not all audiophiles but one of them was.

I have never heard TLs but i have heard some good speakers(including Quad floor standers with Denon 710, PSb towers with NAD, JBL E seriestowers with HK3490, Denon with jamo C series, Wharf towers with NAD and CA 650). All these speakers are considered good by many people. I liked OBs after hearing those.So come what may, I can't get OBs out of my head. After all perception of sound is personal.:)

no offense meant, jaudere -

i have followed your posts and as a fellow DIY'er - i posted those comments above -

i have heard (supposedly) high-end OB loudspeakers (commercial as well as DIY - i will not name - do not want to be a magnet for ire) -

and-

none approach the ease and fluidity - and accuracy and wholesomeness - of systems that isolate completely the rear and front compression/rarefaction waves of the component drivers that constitute the loudspeaker in question.

my comments are not directed at anyone (you included) in particular - and is not meant to be a diatribe against OB loudspeakers either.

However, i would urge you to listen to well-implemented (DIY and commercial) box (enclosure) loudspeakers -

you are frittering your life away (subjective, yes - but i wasted a good part of my life, and i feel like Semmelweis).

and to quote -

"Beginning from 1861 Semmelweis (suri) suffered from various nervous complaints. He suffered from severe depression and became excessively absentminded. Paintings from 1857 to 1864 show a progression of aging.[Note 13] He turned every conversation to the topic of childbed fever (transmission line loudspeakers).

After a number of unfavorable foreign reviews of his 1861 book, Semmelweis (suri) lashed out against his critics in series of Open Letters.[Note 14] They were addressed to various prominent European obstetricians (audio-video fora), including Spth, Scanzoni, Siebold, and to "all obstetricians"(DIY'ers). They were full of bitterness, desperation, and fury and were "highly polemical and superlatively offensive"[4]:57 at times denouncing his critics as irresponsible murderers[6]:73 or ignoramuses.[4]:41 He also called upon Siebold to arrange a meeting of German obstetricians somewhere in Germany to provide a forum for discussions on puerperal fever where he would stay "until all have been converted to his theory."[13] The attacks undermined his professional credibility.

In mid-1865, his public behaviour became irritating and embarrassing to his associates. He also began to drink immoderately; he spent progressively more time away from his family, sometimes in the company of a prostitute; and his wife noticed changes in his sexual behavior. On July 13, 1865 the Semmelweis family visited friends, and during the visit Semmelweis's behavior seemed particularly inappropriate.[6]:74

It is impossible to appraise the nature of Semmelweis's disorder. It may have been Alzheimer's disease, a form of senile dementia, which is associated with rapid aging.[18]:270 It may have been third stage of syphilis, a then-common disease of obstetricians who examined thousands of women at gratis institutions.[6] Or it may have been emotional exhaustion from overwork and stress.

In 1865 Jnos Balassa wrote a document referring Semmelweis to a mental institution. On July 30 Ferdinand von Hebra lured him, under the pretense of visiting one of Hebra's "new Institutes", to a Viennese insane asylum located in Lazarettgasse (Landes-Irren-Anstalt in der Lazarettgasse).[5]:293 Semmelweis surmised what was happening and tried to leave. He was severely beaten by several guards, secured in a straitjacket and confined to a darkened cell. Apart from the straitjacket, treatments at the mental institution included dousing with cold water and administering castor oil, a laxative. He died after two weeks, on August 13, 1865, aged 47, from a gangrenous wound, possibly caused by the beating. The autopsy revealed extensive internal injuries, the cause of death pyemiablood poisoning.[6]:7678

Semmelweis was buried in Vienna on August 15, 1865. Only a few people attended the service.[6]:78 Brief announcements of his death appeared in a few medical periodicals in Vienna and Budapest. Although the rules of the Hungarian Association of Physicians and Natural Scientists specified that a commemorative address be delivered in honor of a member who had died in the preceding year, there was no address for Semmelweis; his death was never even mentioned.[6]:79

Jnos Diescher was appointed Semmelweis's successor at the Pest University maternity clinic. Immediately mortality rates jumped sixfold to six percent. But the physicians of Budapest said nothing; there were no inquiries and no protests. Almost no one either in Vienna or in Budapest seems to have been willing to acknowledge Semmelweis's life and work.[6]:79

His remains were transferred to Budapest in 1891. On October 11, 1964 they were transferred once more to the house in which he was born. The house is now a historical museum and library, honoring Ignaz Semmelweis.[4]:58

well - hehehe!!

regds suri
 
hi,
Semmelweis is highly regarded for improving obstetric care by incorporating aseptic techniques.We know him as a part of curriculum in microbiology. I never knew his last days were so horrible.:sad:

Ok. I accept that it may be a waste of time going open baffle way. but please answer my basic questions:

1)2 drivers of 4 ohm each connected in series thus making impedance of 8 ohm Vs one driver of 8 ohm (both cases having 8 " drivers of same sensitivity , only the impedance is different), when driven by the same amp with volume knob at same level,which one will play louder?

2)in commercially available crossovers/filters, some wattage is written. what does thta mean? e.g. low pass filter 250Hz , 200Watts,8 ohm. If i use this filter with a 50 watt RMS speaker, what would happen?

Regards,
 
1)2 drivers of 4 ohm each connected in series thus making impedance of 8 ohm Vs one driver of 8 ohm (both cases having 8 " drivers of same sensitivity , only the impedance is different), when driven by the same amp with volume knob at same level,which one will play louder?

Since Power=Voltage*Current & Current=Voltage/Resistance

At a given setting assuming amplifier output voltage = 8v

1) Two 4ohms in series will see 2amps each and power of 16w each
2) Single 8ohms will see 1amp and a power of 8w

In the first case since power is doubled there is a gain of 3db each. So two 4ohms in series will be 6db louder than a single 8ohm speaker.

e.g. low pass filter 250Hz , 200Watts,8 ohm. If i use this filter with a 50 watt RMS speaker, what would happen?
The components in the crossover are designed to operate up to 200w. So you can safely connect a 50w rms @ 8ohms amp which is well within this limits.

Regds...
 
Hi Antony.

You are my saviour

Today it so happened that i visited chiplun, which is the nearest town to me,
I was roaming in the market while my car was getting serviced. i suddenly bumped into a shop which has some ahuja compoenents. There i found this

Ahuja Sound Solutions

There was no taker for it for 1 year in that shop. got it for 1K.
At home, i tried it on open baffle with 12" full ranger(wanted to use it as woofer because that was lying idle), sounded so so. Then i suddenly remembered that i have a 12" woofer lying idle in my cupboard. Got it on the open baffle and yes, I got what i was looking for.so philips is playing as full range , augmented by this woofer below 250Hz.going by baffle size, 20" baffle has natural roll off at around 250 Hz , so this design should work well.

Th sound is so pleasing( feels more full bodied) that I will soon get another low pass filter and another woofer, its a local company, Dolbycon. TS parameters are not available but i guess that Qt must be near 1 because it is working nicely on open baffle.

The real task now lies ahead.I have another question, will simple open baffle be better for woofer or you suggest H frame?, if yes, can you suggest that dimensions of that H frame for 12" woofer?

regards,

thanks for that explanation of 2 speakers vs 1 speaker, i had (or should i say "have")forgotten my maths and electronics since the time i joined MBBS course.:)
 
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Hi Jaudere

Thank you and good to know that you could get a matching driver with the Philips. IMO for a passive approach OBs(AKA I frames) are much easier to build and tweak than an H frame setup. Balancing the roll off of the H baffle with that of Philips (possibly fitted in a narrow OB) passively could pose a few more design challenges. Martin J Kings studies show higher SPLs for OBs compared to H frames

Philips has a sensitivity of 92db, the local woofers might be in the 70-80db range, Its a good idea to have two (or 3) drivers per channel in your OB.

However using H frames will reduce the visual footprint of the system with the benefit of bass extension. If you wish to make them, MJK has a H Frame Two Way Worksheet with Passive Crossover.I havent used them, but they are highly regarded. Another place to look for information is Linkwitz site

I haven't come across a formula to calculate the resonant frequency of the H baffle. However, there is another approach due to the fact that the resonant freq is lower than the quarter wave frequency (given by the length and effective radius) of the H frame. This approach to calculate the f/4 is mentioned at Martin J King's site.

f1/4 = c / (4 x L-effective) & L-effective = Frame depth + (0.6 x r-effective).

According to MJK, the H baffle's f/4 freq needs to be higher than the low pass frequency of your crossover. Its a good idea as it reduces the peaks that happen at f/4.

Considering a frame of size 12x12inches(internal) and baffle depth of 8inch

L-effective = (8 + 0.6 x 6)x.0254 = 0.295m

f1/4 =345/(4 x 0.295) = 345/1.18 = 292hz

You may choose different dimensions but keep in mind that the frame needs to be a square and the f/4 needs to be higher than your crossover frequency.

Regds
 
hi,

making some slow progress. Bought 2 XO circuits.
Ahuja Sound Solutions
cross over at 4KHz, eactly where I need. again 300W RMS. but nothing better is available locally which gives all specifications. got it for 490 each.
Oddly the site says that it is a one way crossover(???). However on the packaging they mention is rightly as 2 way XO.

Also bought another low pass filter of 250Hz.

Now In my speakers, frequencies below 250 will be played by 2 speakers(full range and woofer while above 250 will be played by single speaker( 250 to 4KHz by full range and by tweeter above 4KHz).

Incidentally , i checxked availability of full rangers , philips is now selling by the name of "PULSE" with the same Philips dealer. Exactly same packaging and specifications. He told me that the brand name has changed but the product and cost is same.
 
Since you are having a full range driver, i will suggest you should design a transmissiion line enclousre which behaves as an open baffle if you do not mass load the terminus. More over the vices of cross-overs can be completely avoided if you use a single driver. More over the load presented to the amplifier will be more stable without any impedance peak (You will have to use zobel network and baffle-step for the full-range driver). Single driver will help you achive the following,

1. Coherent sound stage and no cancellation of sound waves due to multiple drivers. Driver placment in the baffle becomes important to avoid cancellation of sound when using multiple drivers.

2. complete avoidance of a cross-over which would be a necessary evil if multiple drivers are used.

3. Easy adjustment of the baffle-step attenuation as you have to consider only a single driver for adjustments.

Go for a straight line TL design as you need to approximate it to a open baffle. You need to have a varying density damping depending upon the speaker resonating frequency and the enclosure tuning frequency. the speaker system (driver + box) will detrmine the density of the damping material. Allow the area of the TL to be atleast 1Sd or 2Sd of the area of the full range driver. Damp the all the odd harmonics of the TL line with dacron and do not over damp the 1st harmonic of the TL line. You will have to play with the damping to achive the overall low frequency you require. Also mass loading the terminsus to around 50% will help to increase low frequency by around -3dB.

Success with your design. Regards, Hari.



Hi Arun,
That is a good suggestion.
The problem is that i don't know TS parameters of full rangers> so box dimensions are difficult to calculate. I want to avoid sonic mistmatch as far as possible. Thats why i am planning to use the full ranger across all the frquencies upto 4.5KHz.
 
philips8.jpg


Woah this driver looks so much like the 8" 8ohm driver I have inside my philips hi-fi international speaker from late 70's.

The ones here are all 4ohm
Drivers, HQ48001 HQ Series, HQ48002 HQ Series, HQ48413 HQ Series, HQ48414 HQ Series

But the one I have is 8ohm.

It's used as a full range speaker inside a sealed enclosure.

ewdxv.jpg
 
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Woah this driver looks so much like the 8" 8ohm driver I have inside my philips hi-fi international speaker from late 70's.

The ones here are all 4ohm
Drivers, HQ48001 HQ Series, HQ48002 HQ Series, HQ48413 HQ Series, HQ48414 HQ Series

But the one I have is 8ohm.

It's used as a full range speaker inside a sealed enclosure.

ewdxv.jpg
In this Philips Hi Q International speaker, how to identify the polarity of the terminals on the driver? Any marking on that? In the 2 pin DIN, which one is + ? Though it's a full range , Can we add a tweeter with a filter capacitor? Can the front baffle be taken out to make hole for tweeter? or it's sealed one? Thanks.
 
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How low can a FR driver go with OB if it resonance is around say 47Hz? Do we need to use a woofer along with the FR driver in an OB? My concern of going 2 way is the crossover required. If FR can't do justice to low end in an OB, then i will rather prefer TL as i don't have to worry about crossovers.
 
Agreed Yogibear. Hari you will need a woofer with the FRD in an open baffle.
 
A beautiful, well-constructed speaker with class-leading soundstage, imaging and bass that is fast, deep, and precise.
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