Hi all DIY gurus

[cmsajith]

Only the amp and sub are finalised, not the design.. I am looking for the best design for this combo..

Attached the sample plan of the room :
http://www.hometheatershack.com/gallery/file.php?n=2868 (Full Size)

 

[doors666]

try this one out. I used the box size from the sealed design. 5.937 cubic feet. so when you plug the port, you get a qtc of 0.703. used 250w for simulation as your cone excursion and air speed needs to be checked at this wattage.
tuned to 18hz, 4" port length 14.77". highpass at 18 hz.
with 120w, it gives u about 102db at 20 and a max of 109 db. -6db at 20hz and 23.6 hz is -3db.

 

[doors666]

my friend has ordered a hpsa500 amp for me.. finally all components are decided and ordered.

I would probably also need an SPL meter. any idea which are the good ones. I have a yamaha microphone that came with the 663, can I plug it in to the laptop's line in and record the spl levels? Will that give me accurate (or close enough) results.

edit: oops, i put it in the wrong thread.

 

[cmsajith]

I tried removing the hipass filter for both the subs, still it shows higher (till i changed the tuning to 23HZ) donno why..
Also i tried to change the tuning around 21 - 22. Now the Transfer Function Magnitude graph shows a bump in the 25 to 40Hz range. So i think for me its better i stick to 20Hz, or a 21\22 is better?

Also one more thing i noticed is that the max power requirement seems to be less than 3/4 of the amp power. So i just tried changing the power input to 300w (in my graph), even then the max power requirement is 200w. So i am confused about the extra headroom for the high power requirement. Whether this difference is enough before the amp starts clipping (almost all plate amps will have soft clipping also)? Please somebody clarify.. may be i am wrong

Sorry for hijacking your thread.

yeah the curves are crossing at around 15 hz.
the bump is becuase for that size, the frequency is too high, so it gives more power in the lowest range its able to do. you can increase it further, the bump size will increase further. if you want to tune to 23hz, you'll have to reduce the size to get rid of the bump. for 7ft box, you need to tune lower or the bump will be there.

the max power varies inversely of the impedence. the amount of power withdrawn will depend upon the impedence the driver presents to the amp at a given frequency.

i think its a good thing to have a bump less than 15Hz (since this freq area will be of sound feeling) and also this will be enhanced a ~6db further with the room gain. My current plan is to stick to the 7cuft box since it gives a Qtc of .607 when it is sealed with an effective tuning ~29Hz.

Group Delay: Which is the best or ideal group delay range for music?

Transfer Function Magnitude: What does this mean? In this graph the -3db point comes at 21.85Hz. Also when i was tuning for 18Hz, the graph is having a small db gain less than 10Hz. So I tried tuning to 20Hz, this gives a db gain of frequencies from 25Hz to 60Hz and the graph is smooth by retaining the db gain ~10Hz. But at 21Hz it shows a small hump (is this good?). How this graph should be?

I have attached a picture of this graph:

FullSize:
http://img2.imageshack.us/img2/2558/20hz.jpg
http://img2.imageshack.us/img2/8665/21hz.jpg

 

[doors666]

i think its a good thing to have a bump less than 15Hz (since this freq area will be of sound feeling) and also this will be enhanced a ~6db further with the room gain. My current plan is to stick to the 7cuft box since it gives a Qtc of .607 when it is sealed with an effective tuning ~29Hz.

its a question of preference. you have to decide which frequency zone you want more prominent. you can tune to get more even more gain in 10-20 range by sacrificing some of the performance in the 20-40hz range.

Group Delay: Which is the best or ideal group delay range for music?

my understanding is its the time delay in the signal while it gets processed by the entire system. dont worry too much about the absolute values, usually these will be fine. it should be reducing overall, except for the tuning frequency, where it will be higher. gurus can correct me if I am wrong on this and I could very well be.

Transfer Function Magnitude: What does this mean? In this graph the -3db point comes at 21.85Hz. Also when i was tuning for 18Hz, the graph is having a small db gain less than 10Hz. So I tried tuning to 20Hz, this gives a db gain of frequencies from 25Hz to 60Hz and the graph is smooth by retaining the db gain ~10Hz. But at 21Hz it shows a small hump (is this good?). How this graph should be?

This shows the variations in the sound as compared to the reference. if a sound drops below -8-10db, it will become pretty much inaudible. the -3db point is where half the power is lost (double the amp power, you gain 3db).

I have attached a picture of this graph:

FullSize:
http://img2.imageshack.us/img2/2558/20hz.jpg
http://img2.imageshack.us/img2/8665/21hz.jpg

 

[cmsajith]

its a question of preference. you have to decide which frequency zone you want more prominent. you can tune to get more even more gain in 10-20 range by sacrificing some of the performance in the 20-40hz range.

I am not aiming below 20Hz, thats why i tried the box tuning in 20, 21Hz range to enhance the 20-60Hz range. With that tuning, if it gives a small gain less than 15Hz, thats good right? With 21Hz, the curve is not smooth, it shows a bump in b/n 20-40Hz range. That why i asked what should be the ideal graph either a smooth curve or a bump (which i had attached in the prev post). I dont want to tune beyond 21Hz, it will decrease the db around the 20Hz range and the bump in the 20-40Hz is increasing.

 

[doors666]

I am not aiming below 20Hz, thats why i tried the box tuning in 20, 21Hz range to enhance the 20-60Hz range. With that tuning, if it gives a small gain less than 15Hz, thats good right? With 21Hz, the curve is not smooth, it shows a bump in b/n 20-40Hz range. That why i asked what should be the ideal graph either a smooth curve or a bump (which i had attached in the prev post). I dont want to tune beyond 21Hz, it will decrease the db around the 20Hz range and the bump in the 20-40Hz is increasing.

hi matthew,

the bump does not look like a good thing. check out this article. I was also aiming for a flattest response, which it seems is a cause for boominess in the ported designs as the room gain is more in lower frequencies, if you design for flat response, the lower end will sound very boomy. I am also planning to tune lower to get not so flat response. I cant go for LLT (large, low tuned) due to WAF, but I can tune lower, with as large size as I can afford.

LLT Explained - Home Theater Systems - Electronics and Forum - HomeTheaterShack

 

[cmsajith]

Hurray, my 15" monster sub and amp have reached me (reached last week). Adil himself came for the delivery and its at 1:30AM !!!, because i had to start a long holiday from Sunday morning. The sub reached the customs 3weeks back and took literally 2 weeks (because of public holidays) to reach me. They had issues in clearing because of the wrong info put by DHL (same From and To address). Anyways it reached me safe (worried because of the heavy rains during that time). The packing was excellent and was really heavy (sub itself ~14kg and amp ~6kg). To be honest, my jaws got dropped on seeing the size of the sub. Its with a sexy black color aluminium cone and dust cap (on knocking the cap, sounded like an aluminium pot:lol. I will post the pics by tomorrow. Now i need to procure some power tools to start with and will take some time to start the build (very busy with the office work and the business).

 

[doors666]

Hurray, my 15" monster sub and amp have reached me (reached last week). Adil himself came for the delivery and its at 1:30AM !!!, because i had to start a long holiday from Sunday morning. The sub reached the customs 3weeks back and took literally 2 weeks (because of public holidays) to reach me. They had issues in clearing because of the wrong info put by DHL (same From and To address). Anyways it reached me safe (worried because of the heavy rains during that time). The packing was excellent and was really heavy (sub itself ~14kg and amp ~6kg). To be honest, my jaws got dropped on seeing the size of the sub. Its with a sexy black color aluminium cone and dust cap (on knocking the cap, sounded like an aluminium pot:lol. I will post the pics by tomorrow. Now i need to procure some power tools to start with and will take some time to start the build (very busy with the office work and the business).

congrats man...
what power tools are u planning to get and from where.
design finalized?

 

[cmsajith]

congrats man...
what power tools are u planning to get and from where.
design finalized?

Initially planning for wood cutter and a good drilling m/c (current one went kaput). Routers seems to be expensive. I think SP road is better. I got a quotation for an Electrex cutter (marble cutter, can be used for cutting wood and metal with different blades) w/ one good quality blade for 1600/-.