The AM Forum

I replaced the cracked Jensen 10 in my R46B with a new Jensen MOD speaker. They cost about $35.  The sound was great but the high end of the new speaker was way up there.. After a few days the high end Hiss really bothered me.

We played with different caps across the speaker terminals.  A 10 to 12 UF cap takes the hiss right out. A 22 makes it sound nice and mellow. almost no anoying his.. I dont hear much if any loss of fidelity while listening to BC stations or ham stations. Its now warm and smooth.

C

Not sure what a Jensen MOD speaker is... but...

Assuming it is a single driver:

I'd do two things before I put a cap across the speaker terminals.
A cap across the speaker terminals looks like a dead short at some high frequency, maybe within the audio band.
Not good for the amp that feeds it.

An inductor in series will only raise the impedance... not much of a problem.
A resistor in series with a shunting cap will limit the rolloff and shelve it (usually good enough) and still prevent
the impedance from getting too low.

An inductor in series and a cap shunting will give you a 12dB/oct rolloff - but again you can put a resistor in series with the cap and across the inductor to moderate that rolloff if you wanted to.

There are various "crossover simulators" and calculators online now that you can plug values into and see what the electrical part of the crossover will do - it won't show the combined acoustic + electrical response though. You'll have to use ur ears, or else measure that.

But, the easiest and safest way to go is the venerable acoustic roll off method.
Sounds good when you say it that way.
That means that you put a bit of material of the proper thickness and type (cotton, felt, wool, etc) between the speaker and you. Usually behind the grille cloth! Thicker & denser material will roll off lower in frequency. Quite nicely. A bit of experimenting will get it just right... try draping a bath towel over it for starters...  ;D

In the recording biz, the technique often involves scotch tape and some tissues. Thus the "one, two or three tissue tweeter".
Of course with the tissues the idea is to get a rising response above ~10khz to be relatively flat...

IF it is a two or three way (two or three driver) speaker then the methods to use are similar but a bit different - you can simply pad down the tweeter and/or alter some values in the crossover to suit... or at least to start.

                      _-_-bear

Hmm. Never thought of the cap loading down the audio amp. This is how the filters in most ham speakers are made. Just a cap across the terminals inside.  The Hallicrafters used caps in some of the big speakers. I studied some schematics.  It sounds just wonderfull.  All the very high end hiss is gone. But none of the Freqs in a persons voice is reduced at 22 UF. 

The Jensen MOD is a replacement speaker.  visit Jensentone.com  They sell different speakers marketed towards guitarists. The original was a jensen Alnico.  They make that same speaker but its $90.  I decided the $30 MOD would be fine and it is.. It really sounds fantastic.  Lots of low end. My factory speaker had a tear in it from coil to mount.

C

Antique Electronics Supply has the Mod 10 for $35.00.

During my TV servicing days that was common to see that done to alter the response of audio for whatever characteristics the manufacturer was trying to achieve.

Fred

Many receivers in the past put a cap across the primary side of the outpoot transformer to accomplish the same effect. Usually somewhere between .001 and .01. Also sometimes seriesing a pot with the cap for a somewhat rudimentary "tone" control. This was very common in "antique" radios.

so putting a larger cap scross the speaker would give the same effect. the larger cap is necessary due to the much lower impedance of the outpoot side of the transformer.

                                                    the Slab Bacon

The Hallicrafters R-42 speaker has a front Hi-Fi/Communications switch with just a capacitor and it does an excellent job here knocking down hiss and static. The later R-48 & R48A speakers also have the switch. For a steeper rolloff a simple LPF can be built using one of the on line calculators.

Carl
KM1H

My Multi-Elmac PMR-7 receiver had a cap across the primary.    I clipped it and AM sounds much better on the speaker I am using.

Yeah.. The cap wont hurt or load anything.  We just tore down some Famous model huge klipsh speakers that had Caps right on the Crossover board.  The JBLs I worked on also had big paper caps in the network.

I spent a few hours listening.  Don and some other guys where comming in BIG late last night.  On Don,the 22 cap has little effect on his tone. The HiSS is GONE.  The tone is mellow.  One of the guys he was talking to was hifi and had a wide range of audio.  The 22 did knock down his high end quite a bit.  A 10, 12, or 14 UF is what you are looking for to knock JUST the hiss and noise out but still have full hifi audio.

Without the cap, I get listening fatigue and just want to turn the damn thing off after an hour.. ITs playing some freq that just bothers me. With the cap, I can listen for a long time without being bothered.


C

yeah, caps on the xover board - but in what position??

In a SERIES xover the cap appears across the woofer, but in series with the tweeter, and the inductor appears
across the tweeter but in series with the tweeter.

In a PARALLEL xover there would be a cap in series with the tweeter and an inductor in series with the woofer.

That would be for a first order filter.

If you take the PARALLEL xover configuration and add a cap across the woofer, and after the inductor, not before(!)[/i] then the woofer now has a 2nd order or 12dB/octave slope.

The reason that the cap is not before the inductor is not because that changes the filter's frequency response (much), but because it dramatically changes the impedance the amplifier looks at.

The fact that it is a quick and dirty solution and has been used by various manufacturers to roll of woofers, doesn't make it good practice, or a good solution.  I suppose with flea power amps its not much of a big problem, but some solid state amps will become rather unstable when faced with a mostly capacitive load...

                            _-_-

Klipsch and JBL disagree.  Both of them have caps right across the midrange.   So does the Icom and yaesu speakers with filters built in. There are probably 10 ways to do this :)

C

Sounds like either there is an acoustical resonance in the speaker at the nuisance frequency, or a spurious peak in the response of the audio amp. If you have a smooth, wide frequency response, you should not have this problem.  From my experience, putting caps across something to limit high frequency response also kills the sibilance response and results in loss of voice articulation frequencies and thus loss of intelligibility. My outboard receiver audio amp (a 50's vintage 10w monaural "hi-fi" amplifier) has bass and treble controls.  I keep the bass control at flat, but adjust the treble from time to time for the best compromise. The Sherwood synch detector has a 3-position treble boost/flat/cut control.

For sure Don. If the IF bandwidth of the RX is correct, any sort of lowpass filtering in the audio chain is useless or will only further reduce the high frequency response. Most ham radios use such techniques because either the last IF is very noisy or the audio amplifier is very noisy.

Yes, All my receivers are broken and or of poor quality.

R390
R390a
SP600 JX14
Sp600 JX21
SX62
RME 6100
SX100
SX101
SX110
RME42
75A1
75A2
74A4


I better sell them off or just throw them out and get something else.. They all hear band noise and hiss!

Clark

Only because the IF bandwidth is too wide. It's receiver agnostic. Drama not needed.

I can adjust the bandwidth.. Come on..   The 10UF cap kills the hiss.  Does not effect anything in the human voice as recieved.

C

Having somewhere around 15 receivers in my stable (give or take a few) I guess it's time for me to chime in again.

I have to agree with Clark on this one. Sometimes the high frequency band "hiss" and ambient QRN / QRM can be a bit fatiguing on the ears. On many occasions I run the '390A in the 4kc bandwidth to eliminate some of the background noise.

But this brings one particular receiver that I have to mind. It is an old WW2 military RBS receiver. It has very interesting audio filtering / shaping that eliminates much if not all of the high frequency component from the audio outpoot. This makes it very quiet between tuned signals as you hear no "front end noise" at all, or at least very little. So little that you sometimes wonder whether or not it crapped out. Yet it has little effect on the audio in the normal voice range and does not sound at all "muddy". If anything it actually improves the percieved signal to noise ratio. It is a very pleasant radio to listen to and "easy on the ears", especially on a noisy night. It also creates a very "quieting" effect even from the weaker signals that wouldnt normally quiet out the receiver. Everyone that has heard it comments on how nice it is to listen to.

However, the audio filter / shaping network is a lot more than just a cap across the outpoot. It is quite involved with a series of caps and chokes before the outpoot tubes.
I had thought about bypassing them out for more HiFi audio (it has P-P 6V6s),
but it would have detracted from the personality and charm of THAT receiver, so I left it stock. I have enough HiFi receivers. It seems to have just the right audio passband for good voice reproduction with minimal / no background noise. It may be a little lacking in syballance (for some) but no one that has heard it has had anything bad to say about it.

I guess they figured that tightening up the audio bandwidth was easier (or cheaper) than tightening up the IF bandwidth when they designed it.

                                                    The Slab Bacon

Oh Yeah, and, err, furthermore....................

The caps that they put across the primaries of the outpoot transformers of some of the "antique" radios did wonders to improve what came out of the speakers.

FB bacon. 

I would like to make a filter box.  With speaker terminals in and out.  This will give me different levels of sound shaping.  It really makes the operating experience much more pleasurable to my ears!  Hearing that hiss and static all night really wears you down.

C

Back in the 60's there was an article about improving voice communications intelligibility and reducing operator fatigue by filtering out high frequency hiss. Now, if I remember this was from NASA, USAF, or a similar organization so I have a tendency to believe them.

I do know that it worked for me on a 75A4 and has been installed in its headphone circuit ever since.

For the TS-940's and TS-830's used with transverters I use headphones with a sharp cutoff.

The article was reprinted in either CQ or HRM (Im somewhat sure  :-\ )if someone has time to do the searching.

Carl
KM1H

What's the difference if the hiss is removed at the IF or AF level? If I have an 8 kHz IF bandwidth, I should not need a 4 kHz lowpass filter in the audio chain. If you do, then the IF or AF amps in your receiver are very noisy.

Good receiver design dictates narrowing the bandwidth as early in the receiver chain as possible. Using audio filters is a band-aid approach for a weak, noisy or too wide IF. This is not something I just made up. The concept has been around for many decades.

So, think what you will, but you aren't arguing with me. You are trying to refute engineering concepts that have been widely known and accepted before we were born.

I am not arguing.  You dont understand what I am talking about.  This cap is not limiting bandwidth at all.  I think you cant get past that. I just played 20 to 20K through the reciever. I can hear clearly 80 to 10K.  Without the cap, 80 to 10K. The cap is removing very high Freq noise and hiss that has NOTHING to do with what is comming out of your transmitter.  There is no bandwidth limiting going on. Just no damn anoying HISS and band noise.

Do you understand now :) 

C

No, I don't understand. Please explain how the cap knows the difference between hiss at some frequency and voice at the same frequency.

Much to my relief the 75A3 isn't in there.  It must be noiseless  ;D ;D

This is a timely topic because I have been searching for a nice big speaker in a box for my recently arrived A3, and having found nothing that appears to be what I had in mind, have begun to seriously contemplate HB.  A friend is a wood worker hobbyist and I'm thinking a dark stained mahogany looking cabinet around 20" high and wide and maybe 12 or 18" deep.  Dark gray grill with silver thread.   Get one of those Jensen speakers, 25 watt 4 ohm 15 inch diam. however I think that might be too much of a load for the little 2 1/2 watt AF output stage in the A3.  Maybe 10 watts is better.  Anyone here ever built their own speaker cabinet?

rob

The 12 or 15 will work great. Look at what QIX uses.. A huge speaker.

I would like an R12 hallicrafters Style speaker with a 12 inch jensen.  We are going to build a panel for the rack that holds a 12.  These speakers are realy effiecient.  Go to jensentone.com and read the charts and specs. Most are 95 to 96 DB for 1 watt input. 2 watts would be loud.

C

<snip> Much to my relief the 75A3 isn't in there.  It must be noiseless <snip>

Rob,
      Dont kid yourself, I have an 'A3, it SUCKS compared to some of my other receivers. It has the usual crappy Collins audio, and that noisy assed 6BA7 mixer make it one of my LEAST favorite receivers. The only thing that I like about it is the dial accuracy and stability of the Collins PTO. A slightly warmed over 390A blows it away!! Actually a good working SX-28 is a lot better receiver for AM.

                                                                The Slab Bacon

Geez Clark... calm down!!

A midrange will have a bandpass filter on it, yes?
That would be an inductor in series with cap going to the speaker. (at minimum)
I am quite confident that JBL never ever made a speaker or design where the impedance would drop to nil at some HF, even out of the audio band. So, no single caps to ground without something else in there to limit the impedance drop and limit the reactance.

Rob - the size of a speaker means absolutely nothing WRT the power of an audio amp.
Actually, large old 15" speakers are rather high sensitivity - meaning not much power in gets a pretty good power out.
So, it's fine as long as it has sufficient sensitivity. Typical speakers "back in the day" when it was a big deal to have a "record changer" in a fine "console" had to sound loud because the power available was typically <10watts on a good day going down hill!

Most modern "hi-fi" speakers are much lower in sensitivity - more on the 85db/1w/1m to about 90db/1w/1m and so need more power to reach equivalent loudness. Those older speakers and some newer ones are in the 100db/1w/1m class.

The newer guitar speaker that Clark has may have an aluminum dustcap and be designed to give a rising response or HF boost range, since it is a guitar speaker and not a hi-fi speaker... typically (seat-of-the-pants reckoning now...) a 10 ufd cap on an 8 ohm speaker would start rolling at about 2khz or so... maybe lower... which would mean that if the speaker was rising from around that range at 6dB/oct that this cap will flatten the response out to the point where the rise stops and then the whole thing will roll off neatly at a faster rate...  You can hear 10khz, but that doesn't tell you if the level is up or down, or if the response is or has been flattened.  If you want to try the inductor you need between a 1.0mh and 0.5mh - 0.65 being exactly at 2kHz @ 8ohms. Fwiw.

                    _-_-bear

In decent communications speaker systems, there are at least some L and C components to shape bandwidth.

Take a look at the schematic of the SP-820

http://www.n6wk.com/kenwood/

Just scroll down to the SP-820 pdf file and check out the schematic there. I have changed the 40 F cap to 8 and 20 uFd switchables for better LF rolloff.

Regards,

Phil - AC0OB

Steve, most all radios have audio hiss that starts at the detector. With a detector tube, 1st audio, phase inverter, and PP outputs that is a substantial string of noise generators with lots of gain. Scratch the phase inverter in some sets.

Pull the last IF tube and the noise is quite audible without having to crank up the volume. Especially with headphones.

Carl
KM1H

A hiss reducing or eliminating technique I have used on occasions is simply putting a rag over the speaker. 

Now that I'm old, I don't hear hiss, although, now that I'm old, I'm happy I hear anything.

95 to 96 DB of what? Are you saying you get 95 DB of sound with one watt? I want to see how that's measured.

The standard for loudspeaker (direct radiators, ie. cone speakers) is by the IEC.

For a given size speaker there is a standard size baffle, placed in an anechoic chamber. Then a 1 watt signal (2.83volts into an 8 ohm load - assuming this is an 8 ohm speaker) is fed to the speaker. A calibrated microphone is placed at a distance of ! meter.
The signal is swept sine wave. The resulting mic output is recorded on a log scale: dB vs. Frequency.

After that, it's a bit of a guessing game, and sometimes marketing hype, but for a wide range speaker the reference sensitivity is considered to be the region around 1 kHz.

The result is the "sensitivity" - sometimes called the "efficiency" but that is a misnomer - in dB. More precisely dB/1w/1m.
That is how most drivers are spec'd these days.

                    _-_-bear

Thanks Bear, That's interesting stuff. I'm having a hard time figuring out how, even at one meter, one watt of power can produce 95 DB at 1KHz. 95 DB is an awesome amount of sound. Exposure to 85 dB (sound pressure level - SPL) or higher can cause hearing loss over time. Maybe I'm missing something here.

It just seems to me that a 25 w. speaker would be taxing a little 2.5 w. audio amp and the amp would be struggling to make any noise at all with such a speaker.  There's a lot about audio amps and speakers and power I don't know.  my 12 w. p.p. tube amps can almost blow out my Polk CS1 speaker (120 watts).  I guess an amp can drive a x 10 power limit speaker okay.

Slabola -- I have been only running the A3 on 160 past night or two and condx have not been so good.  I don't use the stock 3 khz mech. filter -- I'm using a simple (and fairly wide) RC filter in the 455 KHz IF with the xtal filter out.   I'm contemplating a detector tap out to an external amp but wanted to hear the A3 direct to a decent speaker first.   Yeah, while I miss the big flywheel feel with a variable cap weighted shaft that you get with a NC300, I do like the accuracy and stability of the PTO.

Rob

Bear, looks like the 4 ohm jensen Mod 8-20 is the ticket:

http://jensentone.com/mod8-20.php

The way to understand this is that it is not a linear relationship 1 + 1 not= 2 in dB.

The "25 watt speaker" is a reference to the maximum power that the speaker can handle - usually this is a thermal limit, sometimes also the excursion limit at LF. There is no "taxing" at all... as long as you don't clip the amp, and don't exceed the thermal and excursion limits of a speaker, anything inside that range is ok fine!

You have to understand that most speakers are less than 1% efficient in terms of turning electricity into sound!! It is mostly turned into heat.

The 1 watt SPL rating is the key to understanding this. At one watt of input power most speakers will produce an adequate and "normal level" sound output. It takes DOUBLE the power to increase the percieved output by "two just noticeable differences" that is 3dB. So if the speaker is typical and produces 90dB/1w/1m it will take 8 watts to get to 99dB. But sound falls off with distance... so unless you are sitting nearfield, you will be getting less and less SPL the farther away you are... (a big problem with PA/SR systems).

Actually this is a partial truth - otherwise we'd all be stone deaf long ago... maybe government OSHA stuff?

Long exposures at highish levels can cause long term damage
SHORT exposures at VERY HIGH levels will cause damage.

95dB at your ears is a somewhat loud sound - far far less than you hear in a typical concert. That's about the level that you'd listen to Led Zep if you like it just slightly loudish... not crushing...

                   _-_-bear

Yup. But that ain't band noise. It's crappy design. Either way, a lowpass filter to remove the hiss will also lowpass filter the desired audio too. As you know TANSTAAFL.

Well actually a LPF set between 5-7kHz ought to be quite ok... especially since most transmitted bandwidth falls within that range. Most, not all. Most of the hiss is heard as HF noise, so that ought to reduce a lot of it. If you still have noise after that, then I'd be looking into the receiver a bit more, or doing something to get more signal into the front end??

                       _-_-bear

I'd not get a 4 ohm speaker to use with boatanchor gear. 8 ohms or higher is better.

The speaker you mention here is an 8" driver.
For me that is smallish.
However, I do use a JBL D-208 (iirc the number)in a sealed cabinet with my TS 440. It has wonderful sound.
That is an 8" driver. Vintage.
Look it up.

In the 15" size the JBL D-120 or K-140 is worthy too...

I looked at the Jensen guitar speakers, I'd not want to use any of them for listening to AM.
Well, maybe if I could have one of each and try them all??

One might consider other drivers. Parts Express sells a ton of drivers as does MCM. There are other places too.
Eminence has a wide range of stuff that is high sensitivity too.

But one of the best solutions is to find a local flea market or craiglist listing for old console "hifi" and "borrow" the whole inside baffle, drivers and all for the job! Some are quite nice, with a decent paper cone midrange and tweeter. Usually the tweeter can be dispensed with or padded down, but those old paper cone woofers and midranges sound great on voices.

                    _-_-bear

Aint nothing wrong with the design, just components available at the time.  Im sure that replacing all audio stage resistors with metal film and adapting the lowest noise tubes that were available much later would help a lot.

However a simple LPF is a lot less work.

In the 80's a bunch of us in the YCCC and other contest clubs bought a special design Beyer headphone built for communications audio. Its fantastic for no fatigue long operating sessions.  Heil had their own flyweight version that is OK but the Beyer is mo betta. A lot pricer also at $250 back then.

Carl

Thanks Bear; lots of options.  We had an old console hifi that belonged to my parents.  It was a big piece of furniture with a tube amp, AM/FM stereo tuner, and Girard turntable.  One of those wide low cabinet things with a lid that lifted up in the middle for the turntable and tuner.  Speakers on each end.   I sure wish I had that now but we let it go a couple of years ago with some other things. 

Some years ago I had a couple of  18" metal folded horn PA speakers using a compression driver. Awful, restricted, lumpy  frequency response , but because of the horn loading, super efficient at the frequencies it actually worked at.  A pocket transistor radio producing maybe 100mW of audio, was mind numbingly loud thru that speaker, especially when you compared it against the pitiful internal 1 1/2" thing.  One Watt of audio coupled to the air at 100% efficiency would be astonishingly loud.

Also too , don't forget that when we listen to a audio amp, were normally listening to music or talk. The peak to average ratio is quite high, so your 100W amp might be putting out an average of 1 watt possibly less , even thought the peaks are close to 100.


And back to the topic, almost, Arn't the caps across the primaries of output transformers there to form a "build out" network with the leakage inductance of the transformer that extends the frequency response  at expense of an ultimately faster roll off  past the cutoff point, or am I confused, or just deaf - again.
                                                                                    Ian VK3KRI

Yep. 1 watt 1 meter.  96 is pretty good. But not loud by any means.  Years ago, I competed in IASCA car audio competitions. My car was built for sound quality. But it would still produce 129 DB.

I have now toggled the cap in an out 100 times. Listening to Don last night.  It has no effect on dons audio. NONE at 10 UF.  Just the hiss of the SP600 is gone. What a treat the cap is. I just love it. 

The SX28 does not need the cap. It has a built in tone control. Hmm. I wonder how that works?

The rating of the speaker is the MAX power that is supported.  Its really just a general rating. Everyone knows that the Box the speaker is in has more impact on the power handling then anything else. The Xmax is very important :)

A Lower power rated speaker does not play louder then a higher power rating one most of the time. Unless, its motor assembly has been made very stiff for very high power or LOW Freq use. Then, You will have a lower SPL rating.

I have the 8 ohm model 10-30 MOD. Its just great considering its just $34.  I would like the original style Alnico which is still made. But its around $100. Its just not worth the extra money to me for ham radio reciever.

Today, I installed a rack shelf and hooked a $2000 dollar monitor speaker up to the SX28.  Why?  Cause I got both the monitors cheap for resale. Then realised, One had a blown tweeter and the other had a blown woofer. So I made one good speaker out of the set. I cant sell it. Nobody wants one speaker.. LOL.  The SX 28 sounds like FM. Maybe better playing oldies in the shack.  Just shocked out how good this thing sounds! Its up there with the SX62 which is clearly the king of the HiFi receivers...



C

I heard somewhere that the SX25 is a sleeper and sounds pretty good too, something supposedly that is not well known.

Okay 8 ohms it is.  As is often the case, the audio xformers in my two amps have taps for 4, 8 and 16 ohms.  The speakers I use are 8 ohms and the 4 ohm tap sounded the best. 

SX62 guys--go for it:  http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300402979156

The SX-16, 17 and 25 all use PP 6F6's which arent the best of tubes in pentode mode but they sound OK on the ham bands. I have all 3 here.

The SX-42 and the various SX-62's all share the same audio section. Hallicrafters claims its "flat" out to 15 kc.

I have a pair of SX-62A's all rebuilt. One drives a R-42 bass reflex speaker and sits in the bedroom. The other has the audio section disabled (called pull the tubes) and the phono-in is now audio out. That drives a mid 50's 4 speaker (2 each 12" and 4") RCA AM/FM/Phono console audio deck which has much better control (more knobs to twist) of the audio response. That is in the LR and can rattle the windows. That and the Scott 800B (in the DR) mentioned below get the most comment here at family gatherings

The next on the rebuild list is a SP-400. I had a BC-779 in the 60's and the triode connected 6F6's plus the triode strapped 6F6 driver sounded super into an old 15" coaxial Jensen which probably came from a scrapped Scott 800B. (Anyway its identical to the one in the 800B I have now) The problem with the 779 is that it never stopped drifting.

Carl
KM1H

OK guys, you got me to try this. I took my Icom R75 SWL receiver and tried 10uf, then 20 uf across the speaker. NO CHANGE! The R-75 on AM with a 6 Khz IF filter also has a 3 Khz multi-pole audio LPF with op-amps.

So thinking, the solid state audio probably had a very low source impedance, much different than a Beam Power tube amp without NFB. So I added a 10 ohm resistor in series with the receiver so that the cap works against a series resistor. Had to crank the audio gain a bit, but the headroom was there. Thinking that a 10uf non polar cap has about 10 ohms Xc at 1600 Hz, I thought that would be too much. Adding the cap makes a difference, but barely to my ears. That is until I tune off away from signals in the presence of impulse type QRN. HUGE CHANGE! Now that background is not nearly as irritating.

I will have to play with this idea for a while.

Jim
WD5JKO

Hang on a second!

What sort of speaker are we talking about??

... a few points, the cap's effect is WRT the impedance of the speaker - it has little to do with the output impedance of the power amplifier, tube or solid state.

If the output of the receiver already has a 3kHz LPF engaged, the addition of a cap of the value used would have little effect.

If the series resistor and the impedance of the cap are identical, then you've got a 6dB pad (at that frequency)... and with the series resistor a pad made with the impedance of the speaker itself - same idea if it was a 10 ohm resistor and 10 ohm speaker you'd again have a 6dB drop in level...

Again, I would strongly suggest the use of a small inductor over a cap in parallel. If you need more rapid roll off, then add a cap in parallel to the speaker to get a 12db/oct rolloff rate... you can shelve the rolloff with a resistor or two (depending on if you use one component or two).

Just do a quick search online for "crossover calculator" and you'll find any number of sites that allow you to plunk in various compenents and impedances and get back the nominal turnover frequency. A search for "crossover simulator" might bring up some freeware and online utilities that include graphics as well. LTspice will do this as well, but it is more complex to learn how to run...

                _-_-bear

   Bear, The speaker is a RS 8" in a wooden sealed box with foam. I just looked at similar RS speakers on their web page:

http://support.radioshack.com/support_audio/doc15/15880.htm

    I'm not sure if mine is the same, but it is similar. The VC inductance around 1mh caught my eye. The parallel L-C resonant frequency with a 10uf cap is also 1600 hz!

    I repeated my test with and without the 10 ohm series 'R', and the 10uf across the speaker ONLY makes a difference with the resistor in place. Sorry, but the amplifier Rs does matter.

    Sooo, take a amplifier with a zero ohm Rs, put 10 ohms in series with it to the speaker, and shunt the speaker with 10uf. The R-C by itself form a 6db attenuator at 1600HZ, and the VC inductance with the 10uf have a parallel resonant point at 1600 Hz.

    All of a sudden this is not so simple.... >:(

Jim
WD5JKO

sure it is simple, use an inductor! :D

                _-_-bear