unconventional case modification

[Matchampion]

hello, I was wondering if smoeone would provide an explenation for a modification i made. I have two home built subs at working from 100 hz down, and a pair of tannoy f1 s which i have build cases for. None of the cases are ported they are all sealed. the tannoy crossovers are origonal not modified. the tannoys were just sitting on top of the subs. but i put a plywood box inbetween the sub and the speaker on top of it. as i thought the pahsing was a bit out. this did notthing much, a bit. Then one day i was bored so i modified the boxes inbetween just on a wim working to no plans. I realy thought it made a diffrence. the bass drums seemed to make more of a tthump rather than a boom, the mids seemed cleaner. and the highs seemed to have more definition. i will attach some pictures and also put a link hear to the pictures Flickr: Matchampion's Photostream

please tell me if this modification/extra part dose anything or am i just imangining it ( i dont think i am)

any thoughts would be most helpfull
matthew

[AllenB]

No, you'll definitely make a difference. It may not be conventional to tune this way but in your case you may for example be creating a fortunate combination with another peak or cancellation in your room. You may be able to further tune it by stuffing the cavity.

[dave_gerecke]

Changing the orientation of the spacer box may also have an affect(effect?) upon the sound, good or bad. Which way the concavity faces may change things. Don't know really, until you try!

Peace,

Dave

[Matchampion]

hey thanks for the replys i have tried many many diffrent positioning of the speakers, i even put the tannoys on shelves it seems the higher i put them the more trebble they give out so i found the best hight and position the room has a few annoying spaces in it wich dont help. they seem to do the best in the corners but not shoved right in. thanks for you explanation allenB.
Thanks Dave-gerecke i have tried all sorts of positioning of the spacers and they seem to work best central also i have filled the concave section but to me it sounded worse i even drinking stuck glasses in there to see whay would do (notthing much) i will however at some point make a convex version thankyou for that idear.

also im wondering i just spent some time changing the tweeter depth in the case and found that they sounded alot nicer to me when they were sunk into the case so that they were relitive in depth to the mid point of the depth and extrusion of the bass driver. is this also a coincidence or is there a best depth relitive the the bass driver.
thanks again for you replies im new hear this post dissapeared yesterday but its back now. sorry if this was a problem.

peace

matthew

[AllenB]

Yes, that was unusual.

I think with your tweeter you should put some felt or other soft, breathable material around it and see what you can achieve. Just tack it to the baffle, build it up a bit.

About the woofer, it would be good if you could measure with and without the cavity. The main effect was probably one region somewhere in the lower midrange. Maybe find where the room is creating problems and deal with them elsewhere.

[Matchampion]

Right im not too aqainted with accepted mesuring methods so i did a sweep from left to right of in thwe middle of my room with a high(ish) quality condencer mic whilst my speakers were producing moderatly loud white noise at all frequencies. also i mesured front to back of the room. i used a spectogram display to see the results, Frequency is up axis time (ie Left of my room is left centre is centre right is right side of my room) is bottom axi,s same with the front back arangment. color is aplitude black=0 throught blue and yellow to red.

hear is a pic of the results

also just incase a link as well mesurements | Flickr - Photo Sharing!

From this i sort of think there is loads of peaks and cancelations in my room oh dear oh well. there is a definate big cancelation in the middle. my speakers are all prperly phased i promise. the main diffrence between haveing no spacer and a spacer is that (its very notcible in the top left and right of the top pictures) with the spacers in there seems to be more peaks and cancelations occoring. to be honest im not sure exectly what im doing hear but it was fun. there is a noticable diffrence between the extream left side and the extream right side this is beacouse there is a big stone fireplace on the left side i can't get rid of.
the vertical ish cancelation and peaks also seem to be closer togeather on with the spacer in. but this may have to do with the speed the mic moved i was quite accurate about the speed it moved across the room but theres always human error.

also i did that felt around the tweeter. i think it improved the lower end of the high frequencies my stereo efect is a better as well i think. thanks

P1020118 | Flickr - Photo Sharing!

i think they sound better with the spacers as im probably hearing a few more frequencies than before. maybe.
Matthew

ps im thinking of a new topic i saw a tv program where they were desining the prabola for a satelite and they used a bit of software to put dents and ridges in the prabobla so the signal was focoust better over continents rather than the see. i wonder if there is anything similar for speaker cone desing. What do you think i should call that topic as i cant think of any grabbing titles.

[Matchampion]

ok so i found a bit of software that mesures it so i put a mic in the middle of my room and ran a audio frequency sweep through my speakers and it spat out graphs i dont realy understand them. but i did with and without the splitter box things the pictures are on this link Flickr: Matchampion's Photostream
i dont know if this is any help or not.

matthew