bk12m fe126en speakers question

[soundnovice]

hi
i have built bk12m speakers using fostex fe126en drivers. the Fs of these drivers is 83hz. since i dont have proper measuring setup, can anybody who have tried it (or measured it), tell me upto what freq. these speakers go down? i am interested in augmenting the lows with a dedicated woofer/subwoofer. also i need help in selecting a low cost woofer/sub for these drivers.

[tbirdron]

The best moderately priced sub would be the REL 5 at about $600.if your
funds are limited ( who in diy audio aren't?) a great place to look at powered subs is a company called deep discount on ebay.I am currently
using their 8" 300watt sub.My room is small.they have 10",12",and 15"
models, all under $300.

[chris661]

I've found the higher you can cross over these speakers, the better. IMHO, crossing them at ~80Hz (subwoofer area) doesn't take away enough strain to let them produce a truly dynamic performance.
I'm using them crossed over at 500Hz, and they do rather well as a mid-tweeter.

[Scottmoose]

Which totally negates the point of having the BK-12m Chris. If the gentleman wishes to follow your advice (which is reasonable in the abstract -I also like a ~500Hz XO frequency to dedicated bass units per channel if outright dynamic range is the priority) then he might as well junk the enclosures and stuff his 126s into sealed boxes. Which would be a bit of a waste of his time, effort and money thus far. The BK-12m is a decent little performer for what it is (I know, because I designed it), and should give solid performance for most reqirements if crossed to a quality sub. around 70Hz or so.

If you can run two subs., so much the better of course. You don't necessarily need / want to place them per channel though as you would with woofers covering a wider BW -I would follow Harman's approach on this score.

The Fs of the driver is largely immaterial as far as the lower cutoff frequency (F0) of a horn is concerned, since this is essentially a function of the flarepath length & profile. F0 on the BK-12m is 70Hz.

[chrisb]

FWIW, in this or any moderate sized BLH, to fully relieve the FE126 of the grunt work, and allow it to excel, I'd go dual small (6-8" mid-bass drivers as opposed to a single 15" HT flatulateur) and XO the FE126 in the region of 100-120Hz

[soundnovice]

if i xover at 100-120 hz as per chrib's suggestion, bass SPL will be increased in the 80-120hz region (as both woofers and fe126 will cover this region). will this be ok? i dont want to put any passive xover component for fostex driver.

[chris661]

With lower frequency crossovers, you're much better off going for line-level crossovers rather than speaker-level.

The impedance peaks caused by the cabinet loading will interact with the crossover, creating a peaky response around the impedance peaks.
The required parts will also be very large in value, and will therefore be rather expensive.

Line level crossovers are great if you have another amplifier lying around (or if the sub has one built in), as they use much smaller-value components (= far cheaper), without having to worry about the speaker impedance throughout the XO region. There's some good articles on active crossovers (and other stuff) here

(Again, IMHO) Steeper crossovers can be beneficial in bringing out the dynamics in a speaker, as the greater rate of attenuation means less low bass reaching the FR driver (so there's less stress on the driver). However, higher order crossovers have greater phase shifts and component counts than the lower order ones, so a compromise is to be found.


Page 3 of this PDF is useful - the bass is flat to ~75Hz, -6dB @ ~65Hz.

Chris

[soundnovice]

Originally Posted by Scottmoose

Which totally negates the point of having the BK-12m Chris. If the gentleman wishes to follow your advice (which is reasonable in the abstract -I also like a ~500Hz XO frequency to dedicated bass units per channel if outright dynamic range is the priority) then he might as well junk the enclosures and stuff his 126s into sealed boxes. Which would be a bit of a waste of his time, effort and money thus far. The BK-12m is a decent little performer for what it is (I know, because I designed it), and should give solid performance for most reqirements if crossed to a quality sub. around 70Hz or so.

If you can run two subs., so much the better of course. You don't necessarily need / want to place them per channel though as you would with woofers covering a wider BW -I would follow Harman's approach on this score.

The Fs of the driver is largely immaterial as far as the lower cutoff frequency (F0) of a horn is concerned, since this is essentially a function of the flarepath length & profile. F0 on the BK-12m is 70Hz.

thats true! no point in crossing high. i like these small wonders, just because these speakers can produce vocals so well. totally non-ear-fatiguing. can go for listening to them for hours. thats why i am careful in chosing sub/woofer for these. addition of woofer/sub should not disturb the natural sound these fostex are producing already.
one more thing i am worried is, will any sub that i will add, can match the dynamics of the fostex drivers? i mean the FE126 are quite fast. how about a single eminence beta 12 in closed/ported box?

[soundnovice]

Originally Posted by chris661

With lower frequency crossovers, you're much better off going for line-level crossovers rather than speaker-level.

The impedance peaks caused by the cabinet loading will interact with the crossover, creating a peaky response around the impedance peaks.
The required parts will also be very large in value, and will therefore be rather expensive.

Line level crossovers are great if you have another amplifier lying around (or if the sub has one built in), as they use much smaller-value components (= far cheaper), without having to worry about the speaker impedance throughout the XO region. There's some good articles on active crossovers (and other stuff) here

(Again, IMHO) Steeper crossovers can be beneficial in bringing out the dynamics in a speaker, as the greater rate of attenuation means less low bass reaching the FR driver (so there's less stress on the driver). However, higher order crossovers have greater phase shifts and component counts than the lower order ones, so a compromise is to be found.


Page 3 of this PDF is useful - the bass is flat to ~75Hz, -6dB @ ~65Hz.

Chris

essentially what you are suggesting is nothing but bi-amping. can give a try. now i want to know one last thing, whether to go for single sub/woofer or one per channel, considering the xover point as 70hz. if going for single, then powered sub makes sense, right?

[Scottmoose]

Single is OK at that frequency, although twin usually have the edge. An active sub. with its own amp & onboard XO is the way to go, or you're going to find the parts required get very large, very expensive, and have very considerable insertion losses.

Bass by definition is slow. Providing you don't run a bass driver up higher than it is capable of going, and use steep XO slopes to ensure it is quickly attenuated you shouldn't have too many problems.