Thanks for the references Stalker. Will look into them when grandkids are in bed tonite.

Dan i stumbled onto the K88 manual
http://www.electronics123.net/amazon/datasheet/k88.pdf

looks like it comes with a heatsink.

It is possible to deform a speaker frame by overtightening the mounting screws if there's any misalignment. I trust they were a good fit. Also as Stalker mentioned if there's a gasket you should tighten just enough to start squeezing it uniformly, you don't want to bend the stamped steel frame by horsing down on the screws.

For that enclosure volume test - i'd start with a gallon jug of water, maybe two if they'll go.

a.

Well I took the bass boost off and I tried it with the amps bass turned on. It has to reach a fairly loud volume but certainly not the loud that would be going at a party or something. To seal the speakers I used some epoxy around the edges and tightened the screws. I didn't tighten them a whole hell of a lot though, certainly not enough to deform anything. The ipod has a headphone jack out that I have hooked up to the amps aux in with a cable that turns the headphone to RCA left and right cables. I used foam to seal the top and I would think it was a fairly good seal. I'm eventually planning on building a sub enclosure and sending all the low frequencies to that leaving the mids and highs to these speakers, since they seem to do find with everything except very low bass.

thanks dan.

Do not despair.
Your speakers will be quite capable of good sound at reasonable volume though they're not going to compete with huge disco earth moving equipment.

Read this article on IPOD earphone output:
http://members.chello.nl/~m.heijligers/ipod/Performance/measurements.html

those folks preferred the IPOD's line output to its earphone jack. Note their remarks on distortion.

For a sanity check I went to a different speaker design site. You ought to try it out, here's the link.

http://www.mhsoft.nl/spk_calc.asp#sealed

and a writeup on enclosure design.
http://diyaudiocorner.tripod.com/dilemma.htm

It lets you plot frequency response. Type in the numbers for your speaker. First time it tells you to build a HUGE enclosure, like hundreds of liters.
That's for theoretically perfect damping of 0.707 . So type in Qtc of 1.3 and it gives the number we used for target volume.
I experimented with Qtc's until it produced your as-built volume of about 35 liters then hit 'show frequency response'. Qtc around 1.2 is what we appear to have. Volume appears not overly sensitive to Q, meaning we're not teetering on the cusp of some design criterion..

Plugging in the numbers from your speaker and tweaking Q to make program produce your as-built volume I get a Q of about 1.2125 This gives a slight (3db) peak in response at around 70 to 150 hz. That's going to sound pretty "bass-ey_". True hifi purists would call it 'boomy'. That's why i suggested it for your first project, it's what we like in our youth - i know I did and it's how i still listen to old r&r!

Now a Q greater than 0.71 means the enclosure has a resonant frequency around which the cone travel will be more than you'd expect. We have used this phenomenon to exaggerate the bass response of your speakers in anticipation of a low powered amplifier. A high powered one might overdrive them in the 70 hz range. That could be what's going on if Dad's amp is high powered , and judging by your description of his speakers I'd guess he has really good stuff..

When troubleshooting one always tries to split the system in half isolating the trouble.
Our first split is: source (amplifier, ipod) or speakers?
So first thing i'd try is swapping to line output of that Ipod. Might take a different plug.

Watch cones - can you see them moving much?

If it's resonance the problem should go away with a smaller amplifier.

Strictly speaking the amplifier output characteristics should go into the enclosure design but that's a refinement that is seldom aplied. It is conceivable (but unlikely) that dad's amplifier does not expect underdamped speaker system. If you can find some telephone wire, that small #22 solid stuff, put a few yards in series with the speakers. That'll make them look more resistive which increases damping and decreases Q. From the speaker's point of view it makes the amplifier's output impedance look a bit higher.

If it is resonance and it doesn't go away there's other things to try. I was going to suggest venting it but the calculator programs are giving far out results. Might be worth an experiment though anyway. Do you have enough material to make another top for experimenting? If so make one with a hole in it to fit an inch & a half sink tailpiece (plastic, about $2 at hardware store) and see what that does.

Sooo -to summarize
try LINE out on ipod;
if amp has a button labelled "10 hz" or "low filter" try it;
try it on a FM radio station which won't have sub audible bass in the signal;
try some telephone wire in series;

that should answer "source or speakers ?"

gently push the speaker cone in and out with your fingers listening for sound of something dragging;
try a full gallon jug inside the enclosure;
try a sink tailpiece a foot long in a temporary experimental top.

one must experiment to learn anything.


keep up the good work!

a.

Yea that amp was top of the line 30 years ago my Dad said. Yea I have a lot of material left over. I'm guessing the amp is too powerful for my speakers since his enclosures have 2 woofers a mid and two different tweeters, I think... So I'll just wait and see how my amp performs. I tried the cd player that is hooked up to the amp via RCA cables. I got a slightly deeper bass before It "bottomed out" or whatever it's doing. I looked at the meters on the amp and the speaker would distort when they hit their max at 60 Watts for 8 Ohms. My amp is barely going to make 10 so I doubt that it will muffle, or make a deep bass for that matter, so it should be fine. By the way, there is not really an easy way to access the line out of the ipod. There's a port on the bottom that you connect to the computer to sync it up and it's tied into that port. But any who, what amp should I get? I would like to get the cheaper one that needs less parts since I still haven't gotten my tax returns back and don't have a bunch of spending money yet.

Well that answers a lot.
It's a safe bet the meters are slower to move than the speaker cone so there's no telling how much the instantaneous power was. You should have seen a lot of speaker cone movement. That condition is hard on the voice coil bobbin so avoid it.

I believe the k88 will do for 99% of your listening. it has great sound quality . People will be amazed how small it is yet gives such big sound.
The 3db bass boost from your underdamped speakers will help them sound good at normal background listening level.

Keep your eyes peeled in thrift shops for something like Dad's amp, you might get lucky. Cost of monster amp + miscellaneous parts could buy a secondhand factory stero.

I would say for this project go ahead with the K88. Look for a DC power supply 18 to 24 volts an amp or two.... many hewlett packard printers have a corded one 30 volts at 2 amps, one of those and a 3 terminal regulator would work well.

You said in beginning you wanted to learn to tie things together. This should have been a good intro to speakers and enclosures. I know I learned a lot-



THanks to you both - Dan and Stalker!!!!

ps let us know how it sounds.

a.

Haha yea I certainly learned a lot. Thanks to the both of you as well. I will go with the k88 then. I was at all of the thrift stores around and found nothing. I went to this junk store and they had two but the one was 75 and the other was 90, and I don't have the cash for one of them at the moment. I will definitely let you know how it sounds. I'll probably order the kit this weekend and build it down at college since I go back this monday. I saw a TON of printers at the thrift stores so I'll just go and buy one of them as long as they're not crazy high priced. Thanks a bunch, talk to ya soon!

So is there any way to modify the circuit of the k88 found here: http://www.kitsrus.com/pdf/k88.pdf with a potentiometer for volume control??

Just use a dual 10k audio potentiometer on the input.
Tie one end to ground common, tie your input jack to the other end and take your input signal to the amp off the wipers.

The pot then presents a steady 10k load to the source while allowing the signal strength attenuation into the amp to be fully controlled from 0 to maximum.

Interesting there is no provisions for a volume control on the kit. It looks like the combinations of R1/R2 and R3/R4 set a fixed gain for the amp stage. It might be possible to tinker with those values maybe replacing that divider with a pot, but a pot on the input looks like the best option, it would allow attenuation of input signals strengths that might otherwise overdrive the amp and doesn't alter the original operating parameters or set gain of the amp at all.

Alright! thanks, I may have more questions with the hookup when I get my kit. I believe our lab has some 10k pots too.